Giant photorefractive and photoexpansion effects in a van der Waals semiconductor

Giant photorefractive and photoexpansion effects in a van der Waals semiconductor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Giant photorefractive and photoexpansion effects in a van der Waals semiconductor Anton A. Minnekhanov, Georgy A. Ermolaev, Alexey P. Tsapenko, and 14 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6463506/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Mar, 2026 Read the published version in Proceedings of the National Academy of Sciences → Version 1 posted You are reading this latest preprint version Abstract Nanophotonics relies on precise nanoscale structuring, yet conventional fabrication techniques remain complex and costly. Layered van der Waals (vdW) materials, with their intrinsic anisotropy and high refractive indices, offer a promising route toward simplified nanostructuring and tunable optical functionality. However, no vdW material has previously been shown to exhibit a strong photorefractive effect—a key requirement for light-based modulation. Here we report a giant photorefractive response (Δ n ≈ 0.1) in crystalline arsenic trisulfide (As 2 S 3 ), observed even under low-intensity illumination. In addition to refractive index modulation, light exposure enables controlled thickness tuning of As 2 S 3 . The material exhibits a giant photoexpansion of up to 5%, depending on the illumination intensity. Building on this photoexpansion effect, we introduce a maskless, low-cost nanopatterning technique based on continuous-wave laser writing, achieving resolutions up to 50,000 dots per inch without the need for ultrafast lasers. The combination of high photosensitivity, optical anisotropy, and transparency positions As 2 S 3 as a versatile platform for integrated photonics, adaptive optics, data storage, biomedical imaging, and nanoscale sensing. Optical Materials and Devices Optics/Lasers Photonics/optics van der Waals materials nanostructuring As2S3 2D materials photorefractive effect Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Precise nanostructuring is pivotal for enabling advanced functionalities in photonics and related fields. 1 – 3 . As a result, nanopatterning techniques have evolved from standard photo and electron beam lithography 4 – 6 to self-assembled 7 – 9 and direct writing 10 – 12 techniques. Among them, laser nanostructuring continues to gain popularity due to its high-throughput and cost-efficient technology. 13 – 15 However, traditionally, this method utilizes pulsed irradiation for efficient light-matter interaction, 15 – 17 which requires sophisticated expertise and equipment. In contrast, the use of continuous-wave lasers or even incoherent light sources could greatly simplify the process. Yet, direct writing under continuous illumination remains challenging due to thermal diffusion, which limits spatial resolution. 18 , 19 In this regard, two-dimensional (2D) and van der Waals (vdW) materials serve as excellent platforms for light-driven nanostructuring thanks to their giant anisotropy of thermal, 20 mechanical, 21 and optical 22 properties, arising from their layered crystal structure. This anisotropy, in particular, enables controlled laser thinning from bulk crystals down to atomically thin layers. 23 , 24 Although this approach affords atomic-layer control of vdW materials thickness, its lateral resolution is constrained by the high powers needed for material ablation. An alternative, non‑ablative route is to pattern matter through light‑induced refractive‑index modulation; hence vdW compounds that exhibit a giant photorefractive response (Δ n ) are critically sought for high‑resolution, low‑power optical nanostructuring. A key challenge is the absence of photorefractive materials among the broad family of vdW compounds, which now includes over 1,000 reported structures. 25 , 26 This motivates the search for vdW analogues of traditional photorefractive materials. One promising candidate is recently emerging vdW As 2 S 3 , 21 , 27 also known as orpiment, whose amorphous form is a well-established photorefractive medium. 28 – 30 The photorefractive effect in amorphous As 2 S 3 results in the rapid recording of Bragg gratings, waveguides, and other photonic structures. 28 , 31 – 34 By analogy, we expect similar high-photorefractive properties from vdW As 2 S 3 . Combined with its high refractive index n , exceeding 3, and the record-high in-plane optical anisotropy of around 0.4, 27 , 35 , 36 the photorefractive effect opens the unexplored potential of As 2 S 3 for lithography-free optical nanostructures. This work reveals a pronounced photorefractive response in vdW As 2 S 3 and establishes its broadband photosensitivity from the ultraviolet (UV) to near-infrared (NIR). We also show that even using incoherent illumination induces a photorefractive effect in As 2 S 3 , eliminating the need for lasers in structural nanopatterning. In addition, we show that this response is accompanied by controllable thickness changes with atomic-layer resolution typical for vdW materials. The material’s high photosensitivity further enables submicron-resolution photonic nanopatterning using continuous-wave laser irradiation. Thus, we present vdW As 2 S 3 as a promising platform for next-generation vdW nanophotonics engineering. Results We begin the study of the photorefraction effect in crystalline As 2 S 3 by investigating its anisotropic optical constants before and after 1-hour UV illumination, using a 408 nm light-emitting diode (LED), as pictured in Fig. 1 a (see Methods for details). For this purpose, we recorded the ellipsometry spectra of As 2 S 3 before and after the LED exposure. The resulting spectra demonstrate a dramatic change, which translates into a noticeable photorefraction effect in the anisotropic refractive index (Fig. 1 b) and extinction coefficient (Fig. 1 c) of As 2 S 3 (see Supplementary Note 1 for the ellipsometry data fitting details). Interestingly, before the UV exposure, we observed the distinct peaks at 395 nm (for the a -axis) and 430 nm (for the c -axis) in extinction coefficient (Fig. 1 b) most likely originating from excitons — a common signature of vdW materials 37 . Its excitonic origin is further confirmed by the Bethe–Salpeter equation (BSE) ab initio calculations (see Methods ), shown in Figs. 1 b–c. Hence, the anisotropic photorefractive change (Figs. 1 d–f) results from excitonic quenching (Fig. 1 c) under UV light exposure. Of immediate interest is also the high magnitude of the photorefractive effect Δ n in vdW As 2 S 3 , particularly its anisotropic character, as shown in Fig. 1 g. Along the crystallographic a -axis, Δ n a surpasses values reported for conventional photorefractive materials such as BaTiO 3 , LiNbO 3 , and ZnTe:V. 38 Along the c -axis, Δ n c is comparable to Δ n of photopolymer films. 39 Most notably, along the b -axis, the photorefractive change Δ n b reaches a giant value of about 0.1, comparable to that observed in amorphous As 2 S 3 (Fig. 1 g), 40 and stands among the highest reported for any known photorefractive material. In addition, the crystalline structure of vdW As 2 S 3 maintains after the exposure without any signs of amorphization, as verified by Raman spectroscopy (Fig. 1 c, the inset). At the same time, the color of the flake strongly modifies after the exposure (Figs. 1 h,i). Given the unchanged crystalline structure, this color change indicates the change in thickness. Moreover, amorphous As 2 S 3 also exhibits a thickness modification under light exposure. 41 , 42 Therefore, we expect a similar phenomenon for vdW As 2 S 3 . As a result, we performed a detailed study of vdW As 2 S 3 thickness dependence on illumination conditions using atomic force microscopy (AFM). First, we illuminate several As 2 S 3 flakes with different thicknesses under the same conditions as for the flake, shown in Fig. 1 . In all cases (Fig. 2 a), the thickness of the flakes decreased by 3–4 nm, independent of the original thickness. It also leads to the corresponding color change, as seen in Fig. 2 a. Thus, by adjusting illumination conditions we can manipulate vdW As 2 S 3 thickness with nanometric precision. The next question is how thin As 2 S 3 can become under such UV exposure. It turns out thinning is possible down to a 2D case of just a few layers of vdW As 2 S 3 , as shown in Figs. 2 b–c. In this experiment, the flakes were sequentially irradiated and analyzed by AFM at 1-hour intervals over a 10-hour period (see Figure S2 for details). During this time, a noticeable decrease in thickness was observed, with one of the thinnest flakes reducing in thickness from ~ 12 nm to ~ 2 nm. Additionally, a decline in the thinning rate was observed for this flake, eventually reaching a plateau. The first reason for this saturation effect is that the absorption of vdW As 2 S 3 tends to decrease when exposed to UV (Fig. 1 c). Secondly, the decrease in thickness modifies the band structure of vdW materials increasing their bandgap. 43 Finally, As 2 S 3 thinning is driven by layer-by-layer sublimation of the material: this mechanism was described for MoS 2 , but with much higher illumination intensities I ( I MoS2 / I As2S3 ~ 10 4 ). 23 Due to the weak vdW interaction between layers, heat generated by illumination is poorly distributed, potentially leading to slow localized evaporation. In contrast, the bottom layer is in closer contact with the substrate, facilitating efficient heat dissipation and limiting further sublimation. Noteworthy, the thickness of vdW As 2 S 3 changes after near-infrared (NIR) irradiation too (see Figure S3 ). However, the required irradiation dose is nearly 10 6 times higher, reaching values of ~ 1 J/µm 2 . This significant increase in power is attributed to the large detuning of the 785 nm laser energy from the absorption peaks (Fig. 1 c). Consequently, we can achieve a fine-tuning of vdW As 2 S 3 geometry by varying the incident wavelength and power. Considering the pronounced changes observed at low illumination intensities, the further natural step is exploring high-power radiation effects on the structure of vdW As 2 S 3 to unlock additional control knobs. For this purpose, we utilize a standard continuous-wave (CW) 532 nm laser integrated into a Raman microscope. This simple setup allows us to successfully pattern a grating with a 600 nm period and approximately 100 µm lateral size on the surface of a vdW As 2 S 3 flake. The fabrication process is schematically illustrated in Fig. 3 a, with additional details provided in the Methods section and Supplementary Note 2 . The resulting grating is clearly visible under optical microscopy and AFM, with a height modulation exceeding 40 nm (Figs. 3 b–d). Moreover, transmittance spectra indicate the presence of waveguide modes in the grating, confirming its optical functionality (see Figs. 3 e–g and Supplementary Note 3 for calculation details). Additionally, illuminating the grating with a laser at a wavelength of 785 nm, which exceeds the grating period, resulted in edge emission, further validating grating-assisted coupling into waveguide modes ( Figure S4 ). In contrast to low-power illumination, this intense irradiation induces significant structural transformations in the vdW As 2 S 3 flake. Indeed, Raman spectroscopy ( Figure S5 ) reveals a crystalline-to-amorphous transition on the grating, evidenced by a reduction in the sharp Raman peaks characteristic of vdW As 2 S 3 and a simultaneous increase in broad Raman band near 340 cm − 1 , typically associated with vibrations of AsS 3 pyramids in the amorphous state. 44 This transformation is likely attributed to the high density of structural defects inherent to mechanically sensitive As 2 S 3 crystal. 44 These defects may arise during exfoliation, and subsequent irradiation could provide enough energy to overcome a relatively low energy barrier, promoting a transition into a more stable amorphous phase. Moreover, different from the thinning at low irradiation doses, high-power irradiation leads to local expansion of approximately 3%, numerically consistent with previous observations in amorphous As 2 S 3 . 45 , 46 This expansion depends on the power of the illumination or, more universally, on the incident (absorbed) energy, i.e., the dosage. The grating in Fig. 3 is fabricated with a radiant exposure of about 0.83 mJ/µm 2 , which is three orders of magnitude higher than the low-intensity conditions employed for flake thinning with an LED source (Figs. 1 – 2 ). The correlation between structural transformations and illumination intensity naturally raises an important question: what is the threshold energy at which bulges erupt and become holes, and does such a threshold exist at all? In other words, at what point does photoexpansion shift toward rapid evaporation? To address this, we irradiate vdW As 2 S 3 using laser beams of varying powers, resulting in the formation of diverse point-like structures, ranging from small bumps to deep crater-shaped holes (Figs. 4 a,b, S6). The transition from expansion to rapid evaporation occurred at a radiant exposure of ~ 3 mJ/µm 2 . Meanwhile, irradiation below ~ 0.9 mW/µm 2 does not produce noticeable changes on the flake surface, therefore we consider this value as a threshold between layer-by-layer sublimation. Further increasing the laser power led to a rapid growth in the size and depth of the holes, eventually penetrating the flakes (see Figure S7 ). Importantly, the dimensions of the individual bumps or holes can be precisely controlled by adjusting either the laser power or irradiation time. Similar patterns have recently been demonstrated in amorphous As 2 S 3 films; 46 however, those experiments employed femtosecond pulsed lasers. Notably, the highest observed bumps reached approximately 200 nm in height, corresponding to a giant photoexpansion of about 6–7%. Similarly, giant expansion values have previously been reported in amorphous As 2 S 3 glasses. 45 The observed photoexpansion effect may originate from light-induced charge redistribution on sulfur atoms, which increases electrical repulsion between them, causing cluster expansion through network reconfiguration without breaking bonds. 42 This discovery enables direct fabrication of arbitrary patterns on the surface of As 2 S 3 flakes using a standard Raman microscope equipped with a motorized stage. A laser power of 0.3–0.4 mW was found to be optimal based on the dimensions of the resulting surface features (Fig. 4 a,b). We determined the minimal separation distance between two distinct points to be approximately 500 nm, corresponding to a dot density equivalent to ~ 50,000 dots per inch (DPI). As a result, we imprint a variety structures ranging from periodic arrays to arbitrary monochromatic images (Fig. 4 c–f; see also Figure S8a–c for AFM maps). The QR-code shown in Fig. 4 f was patterned on the surface of an As 2 S 3 flake previously transferred onto a flexible PDMS substrate, demonstrating a proof of concept for potential information encoding in this transparent material, assuming appropriate encapsulation of As 2 S 3 . This facile nanopatterning approach holds promise for a wide range of applications, as discussed below. Outlook vdW materials exhibit exceptional optical, electronic, and magnetic properties, primarily enabled by their weak interlayer bonding, which facilitates isolation into atomically thin layers. However, practical methods for actively controlling these properties remain limited, posing a significant barrier to their broader technological adoption. Furthermore, nanophotonic applications inherently demand efficient and precise nanostructuring – a task that is particularly challenging for such layered materials. In this context, light sculpting techniques have emerged as powerful and versatile methods to achieve controlled nanostructuring, potentially addressing the specific fabrication challenges posed by vdW materials. Here, we demonstrate that illumination not only enables precise structural patterning of crystalline As 2 S 3 but also actively modulates its optical properties, significantly broadening its applicability in advanced nanophotonics. Figure 5 schematically illustrates the remarkable multifunctionality of this material under light exposure. We now discuss the broader implications and potential applications of these effects. First, the discovery of a giant photorefractive effect in crystalline As 2 S 3 , reaching values as high as Δ n = 0.1, significantly expands the scope of photonic modulation achievable in anisotropic vdW crystals. Such optically-induced changes in refractive index surpass those typically observed in conventional photorefractive materials, positioning crystalline As 2 S 3 as a powerful platform for next-generation adaptive photonic elements. The combination of strong anisotropy and this unusually large refractive index modulation makes As 2 S 3 ideal for dynamic waveguiding, optically reconfigurable integrated photonic circuits, and high-sensitivity optical sensors. 47 – 49 Moreover, this substantial photorefractive response may enable advanced holographic storage solutions, adaptive microlenses, and tunable polarization optics, 9 , 50 , 51 highlighting the broad technological potential of crystalline As 2 S 3 in future optical systems. Second, it was surprising to discover that the thickness of crystalline As 2 S 3 flakes can be precisely controlled by illumination, even without using laser irradiation: we observed a gradual, slow evaporation and refractive index modification at low illumination intensities. This behavior then transitioned to photoexpansion with increased intensity, and ultimately to rapid evaporation at even higher intensities. Such intensity-dependent control over anisotropic As 2 S 3 properties provides diverse operational modalities: atomic-level thickness modulation, photorefractive effects for tailored light propagation and absorption, structural and geometric patterning by imprinting features such as gratings or bumps, and even rapid material ablation for laser cutting and drilling. Remarkably, we demonstrate precise nanostructuring of crystalline As 2 S 3 using only a simple CW laser. Such extensive control through a single parameter - illumination intensity - opens exciting and far-reaching possibilities for advanced applications. Third, we demonstrated the information-recording capabilities of vdW As 2 S 3 . Arbitrary patterns can be efficiently fabricated on crystalline As 2 S 3 flakes using a low-power CW laser integrated into a Raman microscope. This method achieves an impressive resolution reaching 50,000 DPI, corresponding to a dot pitch of ~ 500 nm, currently limited by the diffraction limit but with potential for further optimization. Importantly, the pattern formation is based not on destructive laser ablation but rather on the intrinsic photoexpansion effect in vdW As 2 S 3 . The formed nanostructures offer versatile opportunities across multiple domains. Periodic patterns created by this method can be directly applied in optics, 52 biomedicine, 52 , 53 tribology, 52 , 54 sensing, 55 , 56 and color encryption. 57 Furthermore, even individual photoinduced bumps can serve as microlenses, making them attractive components for integrated 2D optoelectronic circuits. 58 Patterned images can encode valuable information for diverse applications, such as QR-coding ( Figure S8d ) or user-defined tags. Additionally, the inherent optical transparency of crystalline vdW As 2 S 3 ensures that these nanostructures remain visible under transmitted illumination ( Figure S9 ), further expanding their functional potential. This accessible and straightforward nanostructuring approach effectively circumvents the complexity and cost of traditional femtosecond laser techniques. Coupled with its demonstrated photorefractive properties, pronounced optical anisotropy, and high refractive index, crystalline As 2 S 3 thus emerges as a highly promising platform for future advances in nanophotonics and related emerging technologies. Declarations Author Contributions A.A.M. and G.A.E. contributed equally to this work. A.A.M., G.A.E., G.I.T., I.P.R., A.V.A., K.S.N., and V.S.V. suggested and directed the project. A.A.M., G.A.E., A.P.T., I.M.F., A.N.T., A.S.S., and S.A.I. performed the measurements and analyzed the data. I.M.F., A.B.M., S.A.S., N.D.O., I.A.K., and A.A.V. provided theoretical support. A.A.M. and G.A.E. wrote the original manuscript. All authors reviewed and edited the paper. All authors contributed to the discussions and commented on the paper. Competing Interests The authors declare no competing interests. Acknowledgments The authors thank Dr. V. Solovey for his help in creating the illustrations. The authors acknowledge S. Dyakov and N. Gippius for providing the code of Fourier Modal Method for optical calculations. Data Availability The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request. Methods Sample Preparation Bulk As 2 S 3 crystals were purchased from 2D Semiconductors (Scottsdale, USA) and exfoliated onto the desired substrates. Adhesive tape from Nitto Denko Corporation (Osaka, Japan) carrying the As 2 S 3 crystal was brought into contact with the substrates. The flakes were then transferred onto silicon substrates or Schott glass. Subsequently, the tape was removed, completing the exfoliation procedure. The choice of substrate was based on the intended characterization and use of the samples. An optical microscope (Nikon ECLIPSE LV150NA, 100× objective, Nikon CFI TU Plan Fluor BD) was employed to visually identify exfoliated flakes of suitable size. To place flakes onto a flexible substrate, a PDMS-based pick-up technique was used. Flakes were first mechanically exfoliated onto PDMS, 35 and the exfoliated flakes were then transferred onto a flexible PDMS substrate at room temperature using a manual transfer system (HQ2D MAN). UV and NIR Exposure As 2 S 3 flakes on substrates were exposed to UV light for 66 min (that equals to ~1 hour, which was used in the article text) using an Omicron_LedHUB (408.4 nm, Power 100%) light source of Accurion Nanofilm EP4 Imaging Ellipsometer (the corresponding parameters of polarizer, compensator, and analyzer were set to 50°, 45°, and 30°), utilized in reflection mode. The angle of incidence and angle of view of the ellipsometer were set to an equal angle of 50°. For the described ellipsometer configuration, the light source power on the surface of the substrates (265 µW) was estimated using Power Meter Detector “ThorLabs TH-084 (CAL 05-09-2023) S120VC 200-1100nm 50mW”. The spot size on the surface of the substrate had an elliptical shape with a semi-major axis and a semi-minor axis of ~750 µm and ~500 µm, respectively. The corresponding power density on the surface of the substrate was ~2.25×10 −10 W/µm 2 . For NIR exposure, a 785 nm laser was employed in continuous Raman Area Scan mode using an alpha300 RA confocal Raman-AFM microscope (WITec, Ulm, Germany). The 4×4 µm areas were exposed with laser power increasing from 0 to 80 mW with the total exposure time per area of 400 s (resulting in a radiant exposure from 0 to 2 J/µm 2 ). Ellipsometry To analyze the anisotropic optical constants of As 2 S 3 before and after UV irradiation, we implement the Accurion EP4 imaging spectroscopic ellipsometer in the rotating compensator mode. Two measurements were performed with the plane of incidence aligned with the crystallographic a -axis and c -axis, respectively, which allows for quasi-isotropic optical recording of Ψ and Δ instead of Mueller matrix measurements. Ellipsometry spectra of Ψ and Δ were recorded in the spectral range from 360 to 950 nm for two incident angles 45° and 50°. Laser Nanostructuring of As 2 S 3 Flakes All precise surface nanostructuring of crystalline As 2 S 3 flakes described in this work was conducted using a 532 nm continuous wave laser and the alpha300 RA confocal Raman-AFM microscope. Parameter control was managed via WITec Control SIX software. A 100× objective (Zeiss EC Epiplan-Neofluar, NA 0.9 DIC) with a spot diameter of approximately 0.3 µm for the 532 nm laser was employed for focusing. Sample positioning was achieved using a motorized stage with a step precision of 25 nm. Raman and Atomic Force Microscopy (AFM) Analysis Raman analysis was performed using the WITec alpha300 RA confocal Raman-AFM microscope. Spectral processing was executed with WITec Project SIX software. Raman spectra were acquired with the Zeiss 100× objective, producing a spot diameter of approximately 0.45 µm for the used 785 nm laser (2 mW, equivalent to a laser density of ~12 mW/µm 2 ). A 1200 lines/mm grating was utilized, and the backscattered light was detected with a back-illuminated deep depletion CCD detector cooled to −60°C, achieving a spectral resolution of ~0.5 cm⁻ 1 . Each spectrum acquisition lasted 10 seconds and was repeated 10 times. AFM imaging was conducted in tapping mode using the WITec alpha300 RA microscope equipped with a NanoWorld ARROW-FMR probe (75 kHz, 2.8 N/m). The scanning speed, scan size, and resolution were tailored to each study area to ensure optimal visualization quality. Surface morphology and thickness of the As 2 S 3 flakes (Figures 2, S2) were estimated via Cypher S microscope (Oxford Instruments) operated in tapping mode, using AC160TSA-R3 tip type. AFM image processing was conducted using Gwyddion software. First principles calculations The optical response of bulk vdW As 2 S 3 ( a = 4.255 Å, b = 9.578 Å, c = 11.415 Å, α = 90°, β = 90.44°, γ = 90°) was computed using the BSE@GW approach as implemented in the VASP package. 59 Single-particle ground-state wavefunctions were first obtained from a self-consistent density functional theory (DFT) calculation. These were then used to initialize the GW step and compute the screened Coulomb interaction kernels. The resulting quasiparticle energies served as input for a Bethe–Salpeter Equation (BSE) calculation to evaluate the frequency-dependent dielectric function including electron–hole interactions. A plane-wave cutoff energy of 400 eV and 512 bands were used. The exchange correlation effects in the DFT run were described with the generalized gradient approximation (Perdew-Burke-Ernzerhof functional). 60 The behavior of the core electrons and their interaction with the valence electrons was described using the projector augmented wave pseudopotentials. 61 The BSE step included 24 valence and 24 conduction bands. References Shcherbakov MR et al (2023) Nanoscale reshaping of resonant dielectric microstructures by light-driven explosions. Nat Commun 14:6688 Koenderink AF, Alù A, Polman A, Nanophotonics (2015) Shrinking light-based technology. Science 348:516–521 Öktem B et al (2013) Nonlinear laser lithography for indefinitely large-area nanostructuring with femtosecond pulses. Nat Photonics 7:897–901 Tselikov GI et al (2023) Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Ultrahigh Sensitivity. ACS Nano 17:19338–19348 Munkhbat B et al (2020) Transition metal dichalcogenide metamaterials with atomic precision. Nat Commun 11:4604 Cho SR et al (2021) Universal Patterning for 2D Van der Waals Materials via Direct Optical Lithography. Adv Funct Mater 31:2105302 Rossi-Gendron C et al (2023) Isothermal self-assembly of multicomponent and evolutive DNA nanostructures. Nat Nanotechnol 18:1311–1318 Tselikov GI et al (2022) Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics. Proc. Natl. Acad. Sci. 119, e2208830119 Statsenko TG et al (2025) Bio-Inspired Giant Refractive Index Gradient Lenses Based on Ionic Polymers. Adv Opt Mater 13:2402488 Xu X et al (2022) Femtosecond laser writing of lithium niobate ferroelectric nanodomains. Nature 609:496–501 Lapidas V et al (2024) Surface Coloring and Plasmonic Information Encryption at 50000 dpi Enabled by Direct Femtosecond Laser Printing. Nano Lett 24:12590–12596 Liu D et al (2022) Direct optical patterning of perovskite nanocrystals with ligand cross-linkers. Sci Adv 8:eabm8433 Lin H et al (2020) Diffraction-limited imaging with monolayer 2D material-based ultrathin flat lenses. Light Sci Appl 9:137 Ródenas A et al (2019) Three-dimensional femtosecond laser nanolithography of crystals. Nat Photonics 13:105–109 Makarov SV et al (2017) Light-Induced Tuning and Reconfiguration of Nanophotonic Structures. Laser Photonics Rev 11:1700108 Huang X et al (2020) Reversible 3D laser printing of perovskite quantum dots inside a transparent medium. Nat Photonics 14:82–88 Geng J, Xu L, Yan W, Shi L, Qiu M (2023) High-speed laser writing of structural colors for full-color inkless printing. Nat Commun 14:565 Sedghamiz E, Liu M, Wenzel W (2022) Challenges and limits of mechanical stability in 3D direct laser writing. Nat Commun 13:2115 Lin L et al (2018) Optothermoplasmonic Nanolithography for On-Demand Patterning of 2D Materials. Adv Funct Mater 28:1803990 Kim SE et al (2021) Extremely anisotropic van der Waals thermal conductors. Nature 597:660–665 Šiškins M et al (2019) Highly Anisotropic Mechanical and Optical Properties of 2D Layered As 2 S 3 Membranes. ACS Nano 13:10845–10851 Ermolaev GA et al (2021) Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics. Nat Commun 12:854 Castellanos-Gomez A et al (2012) Laser-Thinning of MoS 2: On Demand Generation of a Single-Layer Semiconductor. Nano Lett 12:3187–3192 Ghoshal D et al (2025) Spatially Precise Light-Activated Dedoping in Wafer‐Scale MoS 2 Films. Adv Mater 37:2409825 Bereznikova LA et al (2025) Artificial intelligence guided search for van der Waals materials with high optical anisotropy. Mater Horiz. 10.1039.D4MH01332H Mounet N et al (2018) Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds. Nat Nanotechnol 13:246–252 Slavich AS et al (2024) Exploring van der Waals materials with high anisotropy: geometrical and optical approaches. Light Sci Appl 13:68 Ozols A, Saharovs D, Reinfelde M (2006) Holographic recording in amorphous As2S3 films at 633nm. J Non-Cryst Solids 352:2652–2656 Tanaka K, Saitoh A (2022) Pulsed light effects in amorphous As2S3: review. J Mater Sci Mater Electron 33:22029–22052 Hisakuni H, Tanaka K (1995) Optical Microfabrication of Chalcogenide Glasses. Science 270:974–975 Gao W et al (2011) Visible Light Generation and Its Influence on Supercontinuum in Chalcogenide As $ _{2} $ S $ _{3} $ Microstructured Optical Fiber. Appl Phys Express 4:102601 Zoubir A et al (2004) Direct femtosecond laser writing of waveguides in As_2S_3 thin films. Opt Lett 29:748 Meneghini C, Villeneuve A (1998) As_2S_3 photosensitivity by two-photon absorption: holographic gratings and self-written channel waveguides. J Opt Soc Am B 15:2946 Wong S et al (2006) Direct Laser Writing of Three- Dimensional Photonic Crystals with a Complete Photonic Bandgap in Chalcogenide Glasses. Adv Mater 18:265–269 Voronin KV et al (2024) Chiral Photonic Super-Crystals Based on Helical van der Waals Homostructures. Laser Photonics Rev 18:2301113 Dyakov SA et al (2024) Chiral Light in Twisted Fabry–Pérot Cavities. Adv Opt Mater 12:2302502 Ermolaev GA et al (2020) Broadband optical properties of monolayer and bulk MoS2. Npj 2D Mater Appl 4:21 Springer Handbook of Glass . (Springer International Publishing, Cham, (2019) 10.1007/978-3-319-93728-1 Zanutta A, Orselli E, Fäcke T, Bianco A (2016) Photopolymeric films with highly tunable refractive index modulation for high precision diffractive optics. Opt Mater Express 6:252 Bhardwaj P, Shishodia PK, Mehra RM (2003) Photo-induced changes in optical properties of As2S3 and As2Se3 films deposited at normal and oblique incidence. J Mater Sci 38:937–940 Azhniuk Y et al (2022) Mass transport in amorphous As2S3 films due to directional light scattering under illumination by an oblique tightly focused beam. J Non-Cryst Solids 576:121269 Lőrinczi A, Sava F, Simandan I-D, Velea A, Popescu M (2016) Photoexpansion in amorphous As2S3: A new explanation. J Non-Cryst Solids 447:123–125 Tongay S et al (2014) Monolayer behaviour in bulk ReS2 due to electronic and vibrational decoupling. Nat Commun 5:3252 Frumar M, Firth AP, Owen AE (1995) Optically induced crystal-to-amorphous-state transition in As2S3. J Non-Cryst Solids 192–193:447–450 Hisakuni H, Tanaka K (1994) Giant photoexpansion in As2S3 glass. Appl Phys Lett 65:2925–2927 Mihai C et al (2024) Fs Laser Patterning of Amorphous As2S3 Thin Films. Materials 17:798 Ling H, Li R, Davoyan AR (2021) All van der Waals Integrated Nanophotonics with Bulk Transition Metal Dichalcogenides. ACS Photonics 8:721–730 Zhou Y et al (2024) A solution-processable natural crystal with giant optical anisotropy for efficient manipulation of light polarization. Nat Photonics 18:922–927 Kravets VG et al (2013) Singular phase nano-optics in plasmonic metamaterials for label-free single-molecule detection. Nat Mater 12:304–309 Rubin NA, Zaidi A, Dorrah AH, Shi Z, Capasso F (2021) Jones matrix holography with metasurfaces. Sci Adv 7:eabg7488 Biswas S, Grajower MY, Watanabe K, Taniguchi T, Atwater HA (2021) Broadband electro-optic polarization conversion with atomically thin black phosphorus. Science 374:448–453 Wang H, Deng D, Zhai Z, Yao Y (2024) Laser-processed functional surface structures for multi-functional applications-a review. J Manuf Process 116:247–283 Zheng H, Liu J, Qiu Y (2024) The Design and Analysis of the Fabrication of Micro- and Nanoscale Surface Structures and Their Performance Applications from a Bionic Perspective. Materials 17:4014 Bonse J, Kirner SV, Krüger J (2020) Laser-Induced Periodic Surface Structures (LIPSS). in Handbook of Laser Micro- and Nano-Engineering (ed. Sugioka, K.) 1–59Springer International Publishing, Cham. 10.1007/978-3-319-69537-2_17-1 Vaghasiya H, Miclea P-T (2023) Investigating Laser-Induced Periodic Surface Structures (LIPSS) Formation in Silicon and Their Impact on Surface-Enhanced Raman Spectroscopy (SERS). Optics 4:538–550 Vo TS et al (2024) A comprehensive review of laser processing-assisted 2D functional materials and their specific applications. Mater Today Phys 47:101536 Shvedov VG, Izdebskaya YV, Shadrivov IV (2024) Control of Orientation and Periodicity of Laser-Induced Surface Structures on Metals. Adv Mater Interfaces 2400589. 10.1002/admi.202400589 Popescu M, Velea A, Miclos S, Savastru D (2013) Optics of microlenses created by irradiation of As 2 S 3 amorphous chalcogenide films with femtosecond laser pulses. Philos Mag Lett 93:213–220 Kresse G, Furthmüller J (1996) Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys Rev B 54:11169–11186 Perdew JP, Burke K, Ernzerhof M (1996) Generalized Gradient Approximation Made Simple. Phys Rev Lett 77:3865–3868 Kresse G, Joubert D (1999) From ultrasoft pseudopotentials to the projector augmented-wave method. Phys Rev B 59:1758–1775 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Published Journal Publication published 26 Mar, 2026 Read the published version in Proceedings of the National Academy of Sciences → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6463506","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":443836140,"identity":"95037473-8e1a-410c-8271-2888ae28dce4","order_by":0,"name":"Anton A. Minnekhanov","email":"","orcid":"https://orcid.org/0000-0002-7685-8463","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Anton","middleName":"A.","lastName":"Minnekhanov","suffix":""},{"id":443836141,"identity":"ad4537e1-7b49-4376-ab1a-f7b063eb2f04","order_by":1,"name":"Georgy A. Ermolaev","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Georgy","middleName":"A.","lastName":"Ermolaev","suffix":""},{"id":443840452,"identity":"5a00092b-a56e-40d1-bba3-f47b458bea06","order_by":2,"name":"Alexey P. Tsapenko","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Alexey","middleName":"P.","lastName":"Tsapenko","suffix":""},{"id":443840454,"identity":"472ea165-b436-4f5d-b25b-08486f021bbf","order_by":3,"name":"Ilia M. Fradkin","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Ilia","middleName":"M.","lastName":"Fradkin","suffix":""},{"id":443840457,"identity":"59f4487c-4003-4e92-b690-65f56cb56e4e","order_by":4,"name":"Gleb I. Tselikov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Gleb","middleName":"I.","lastName":"Tselikov","suffix":""},{"id":443840458,"identity":"4e46720e-48b6-4f52-933d-c22c1c2bafb2","order_by":5,"name":"Adilet N. Toksumakov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Adilet","middleName":"N.","lastName":"Toksumakov","suffix":""},{"id":443840459,"identity":"79ba0600-2b80-46a7-aac2-c3a680d14ca0","order_by":6,"name":"Aleksandr S. Slavich","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Aleksandr","middleName":"S.","lastName":"Slavich","suffix":""},{"id":443840460,"identity":"d97ca836-eda2-4fca-aea6-b558540ca634","order_by":7,"name":"Arslan B. Mazitov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Arslan","middleName":"B.","lastName":"Mazitov","suffix":""},{"id":443840461,"identity":"a4a00004-623a-42b4-a30b-8569814187e5","order_by":8,"name":"Sergey A. Smirnov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Sergey","middleName":"A.","lastName":"Smirnov","suffix":""},{"id":443840462,"identity":"13006e69-5164-4a94-9881-8834b1df5284","order_by":9,"name":"Nikita D. Orekhov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Nikita","middleName":"D.","lastName":"Orekhov","suffix":""},{"id":443840463,"identity":"5eb792fd-b88b-4047-a51d-21217bf8610b","order_by":10,"name":"Ivan A. Kruglov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"A.","lastName":"Kruglov","suffix":""},{"id":443840464,"identity":"b1b3d370-9c8a-45c2-9949-2219e7a2110c","order_by":11,"name":"Sergei A. Ivanov","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Sergei","middleName":"A.","lastName":"Ivanov","suffix":""},{"id":443840465,"identity":"318ca2fc-e00b-48de-af8f-59a42765a382","order_by":12,"name":"Ilya P. Radko","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Ilya","middleName":"P.","lastName":"Radko","suffix":""},{"id":443840466,"identity":"a4c6ec71-ccca-48d2-9d27-eadbfcc73269","order_by":13,"name":"Andrey A. Vyshnevyy","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Andrey","middleName":"A.","lastName":"Vyshnevyy","suffix":""},{"id":443840467,"identity":"dc3846e8-1ea1-4d8d-8a46-4d3ad0f4aa30","order_by":14,"name":"Aleksey V. Arsenin","email":"","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Aleksey","middleName":"V.","lastName":"Arsenin","suffix":""},{"id":443840468,"identity":"477366ee-ba5a-45f8-ae6b-edd735f588a0","order_by":15,"name":"Kostya S. Novoselov","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2klEQVRIiWNgGAWjYBACCQhlA6F4iNTC2MDAkEa6lsMkaJFsb3/+mKfmfJ7B+QOMD962MdjLOxDQIs1zxrCZ59jtYoMbCcyGc9sYEjceIKBFTiKHsZmH7XbihhsMbNK8bQwJhg0EtaQ/bOb5dy5xw/kD7L+BWuwJapGWSDBs5m07kLjhQAIbM1AL43wCOhgke84Yzpzbl5w480Zis+SccxKJGwhpkTje/uDDm292iX3nDx/88KbMxl6ekMNAgAkSHaD4AcaTwQEitDD+QOYRZcsoGAWjYBSMKAAA4SxBt9U0ebMAAAAASUVORK5CYII=","orcid":"","institution":"Department of Materials Science and Engineering, National University of Singapore","correspondingAuthor":true,"prefix":"","firstName":"Kostya","middleName":"S.","lastName":"Novoselov","suffix":""},{"id":443840469,"identity":"6a92f05d-50d3-4d24-99a5-1df59c2642a6","order_by":16,"name":"Valentyn S. Volkov","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAq0lEQVRIiWNgGAWjYHACxgcka2E2IFkLmwRp6g3OnzGr5t1hl8ff3nyA4UfFNiK03MgxuznzTHKxxJljCYw9Z24T1iI5gy3txsc25sQNEjkGzIxtxGjpP5ZWkNhWn7hB/g2RWvgZko8xfGw7DLSFh1gtEsmHJWeeOZ4440xawkGi/MLGf7DxM++O6sT+9sMHH/yoIEILGDA2QOgDRKpH0jIKRsEoGAWjACsAAKz6Os7VKtKRAAAAAElFTkSuQmCC","orcid":"","institution":"Emerging Technologies Research Center, XPANCEO","correspondingAuthor":true,"prefix":"","firstName":"Valentyn","middleName":"S.","lastName":"Volkov","suffix":""}],"badges":[],"createdAt":"2025-04-16 12:26:35","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6463506/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6463506/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1073/pnas.2531552123","type":"published","date":"2026-03-27T00:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81028732,"identity":"064f42e5-2a4b-4637-a15c-80afa94f8796","added_by":"auto","created_at":"2025-04-21 11:07:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2061815,"visible":true,"origin":"","legend":"\u003cp\u003ePhotorefractive effect in vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. (a) Schematic of the UV exposure process. (b)\u0026nbsp;Anisotropic refractive index \u003cem\u003en\u003c/em\u003e before and after 1 hour UV exposure. (c) Anisotropic extinction coefficient \u003cem\u003ek\u003c/em\u003e before and after 1 hour UV exposure. The inset shows the Raman spectra, demonstrating their stability before and after UV exposure. (d-f) Photorefractive effect after 1 hour UV exposure on refractive index along crystallographic (d) \u003cem\u003ea\u003c/em\u003e-axis, (e) \u003cem\u003eb\u003c/em\u003e-axis, and (f) \u003cem\u003ec\u003c/em\u003e-axis. The insets provide a magnified view of the 550-950 nm region. (g) Comparison of the photorefractive effect in As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (solid lines) with other materials.\u003csup\u003e38–40\u003c/sup\u003e (h-i) Optical microscopy images of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (h) before and (i) after 1 hour UV exposure.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/e102b00ff9d82d855422b4fb.png"},{"id":81031394,"identity":"80e68d3f-1550-4363-b744-d0189d5d6684","added_by":"auto","created_at":"2025-04-21 11:23:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":4337044,"visible":true,"origin":"","legend":"\u003cp\u003eIrradiation-controlled thinning of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e layered flakes. (a) Optical microscopy images of five As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes before and after UV exposure (for 1 hour, corresponding to 0.81 µJ/µm\u003csup\u003e2\u003c/sup\u003e radiant exposure), showing color changes corresponding to decreasing thickness (thickness values obtained from AFM are indicated). (b) AFM topography scans illustrating the gradual thinning of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes under 408 nm UV light, with irradiation times specified in each panel. (c) Flake thickness dependence on the radiant exposure for the flakes (flake 1, flake 2, flake 3) shown in (b).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/c8a03f8a574e9850cd19e31e.png"},{"id":81028748,"identity":"56e3538a-56a3-46a1-8b07-6f57a7d18905","added_by":"auto","created_at":"2025-04-21 11:07:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3317060,"visible":true,"origin":"","legend":"\u003cp\u003eCW-laser-written grating on the surface of an As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flake. (a) Schematic illustrating the writing process: the laser of the Raman microscope performs an area scan (line by line) of the As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flake, resulting in grating formation. (b) Optical image of the flake with the grating in its bottom-right corner. (c) AFM topography image of the area indicated by a yellow square in (b). The inset shows a Fourier-transformed image with distinct peaks corresponding to the grating. (d)\u0026nbsp;AFM topography image of the small area indicated by a red square in (c). The inset shows the profile across the dashed line. (e,f) Transmission spectra recorded from two different points: (e) outside the grating area, and (f) on the grating. (g) Calculated transmission curves. Peaks corresponding to waveguide modes are marked with vertical gray lines on (f) and (g).\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/3ecac840c341f5520bd8e5c7.png"},{"id":81030376,"identity":"d05f9f8b-bec2-4af0-97da-73b13e5c1a11","added_by":"auto","created_at":"2025-04-21 11:15:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":3751805,"visible":true,"origin":"","legend":"\u003cp\u003eLaser nanopatterning of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes. All the patterns were obtained using the Sample Raster point-by-point scan mode of the Raman microscope with a CW 532 nm laser. (a, b) Effect of laser power on bump size or hole depth, shown via AFM topography: (a) a 3D reconstruction of (b) AFM topography mapping. A Z-axis scale on (a) is enhanced for improved visualization. (c–f) Laser-written arbitrary patterns, optical microscope photographs: (c) a 700 nm period 25×25 bump array, (d) the diamond pattern, created with 500 nm spacing between points, (e) a portrait imprinted on the flake surface with a 700 nm point spacing, (f) a QR code with a point spacing of 600 nm encoding the phrase “Let’s connect”.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/f1c585143dc9a07c4507f2d8.png"},{"id":81028735,"identity":"4d4f280d-66ed-48aa-880f-d1e82522b893","added_by":"auto","created_at":"2025-04-21 11:07:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1803933,"visible":true,"origin":"","legend":"\u003cp\u003eLight-driven multifunctionality of crystalline vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. The combination of a high refractive index, strong anisotropy, and extreme light sensitivity enables unprecedented optical control in As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. The material exhibits tunable excitonic properties (top left), structural transformations (top right), and dynamic thickness modulation (center right) upon illumination. Its high refractive index and strong anisotropy position it among the most optically responsive materials (center left). Light-induced refractive index tuning allows for controlled patterning of optical properties (bottom left), while direct CW laser writing enables high-resolution nanopatterning with feature sizes down to 0.5 µm, even when the material is placed onto a flexible substrate (bottom right).\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/c8b1d5ed30d999ad1db6f626.png"},{"id":105767027,"identity":"da05a604-b08f-4f5b-8b49-419aadb9cf9a","added_by":"auto","created_at":"2026-03-30 20:59:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":14798076,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6463506/v1/db854671-0c40-4e1b-91bf-6a571d4d27c1.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eGiant photorefractive and photoexpansion effects in a van der Waals semiconductor\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePrecise nanostructuring is pivotal for enabling advanced functionalities in photonics and related fields.\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. As a result, nanopatterning techniques have evolved from standard photo and electron beam lithography\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e to self-assembled\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e and direct writing\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e techniques. Among them, laser nanostructuring continues to gain popularity due to its high-throughput and cost-efficient technology.\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e However, traditionally, this method utilizes pulsed irradiation for efficient light-matter interaction,\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e which requires sophisticated expertise and equipment. In contrast, the use of continuous-wave lasers or even incoherent light sources could greatly simplify the process. Yet, direct writing under continuous illumination remains challenging due to thermal diffusion, which limits spatial resolution.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn this regard, two-dimensional (2D) and van der Waals (vdW) materials serve as excellent platforms for light-driven nanostructuring thanks to their giant anisotropy of thermal,\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e mechanical,\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e and optical\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e properties, arising from their layered crystal structure. This anisotropy, in particular, enables controlled laser thinning from bulk crystals down to atomically thin layers.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e Although this approach affords atomic-layer control of vdW materials thickness, its lateral resolution is constrained by the high powers needed for material ablation. An alternative, non‑ablative route is to pattern matter through light‑induced refractive‑index modulation; hence vdW compounds that exhibit a giant photorefractive response (Δ\u003cem\u003en\u003c/em\u003e) are critically sought for high‑resolution, low‑power optical nanostructuring.\u003c/p\u003e \u003cp\u003eA key challenge is the absence of photorefractive materials among the broad family of vdW compounds, which now includes over 1,000 reported structures.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e This motivates the search for vdW analogues of traditional photorefractive materials. One promising candidate is recently emerging vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e,\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e also known as orpiment, whose amorphous form is a well-established photorefractive medium.\u003csup\u003e\u003cspan additionalcitationids=\"CR29\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e The photorefractive effect in amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e results in the rapid recording of Bragg gratings, waveguides, and other photonic structures.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e By analogy, we expect similar high-photorefractive properties from vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. Combined with its high refractive index \u003cem\u003en\u003c/em\u003e, exceeding 3, and the record-high in-plane optical anisotropy of around 0.4,\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e the photorefractive effect opens the unexplored potential of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e for lithography-free optical nanostructures.\u003c/p\u003e \u003cp\u003eThis work reveals a pronounced photorefractive response in vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e and establishes its broadband photosensitivity from the ultraviolet (UV) to near-infrared (NIR). We also show that even using incoherent illumination induces a photorefractive effect in As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e, eliminating the need for lasers in structural nanopatterning. In addition, we show that this response is accompanied by controllable thickness changes with atomic-layer resolution typical for vdW materials. The material\u0026rsquo;s high photosensitivity further enables submicron-resolution photonic nanopatterning using continuous-wave laser irradiation. Thus, we present vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e as a promising platform for next-generation vdW nanophotonics engineering.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eWe begin the study of the photorefraction effect in crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e by investigating its anisotropic optical constants before and after 1-hour UV illumination, using a 408 nm light-emitting diode (LED), as pictured in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea (see \u003cem\u003eMethods\u003c/em\u003e for details). For this purpose, we recorded the ellipsometry spectra of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e before and after the LED exposure. The resulting spectra demonstrate a dramatic change, which translates into a noticeable photorefraction effect in the anisotropic refractive index (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and extinction coefficient (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (see \u003cb\u003eSupplementary Note 1\u003c/b\u003e for the ellipsometry data fitting details). Interestingly, before the UV exposure, we observed the distinct peaks at 395 nm (for the \u003cem\u003ea\u003c/em\u003e-axis) and 430 nm (for the \u003cem\u003ec\u003c/em\u003e-axis) in extinction coefficient (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) most likely originating from excitons \u0026mdash; a common signature of vdW materials\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Its excitonic origin is further confirmed by the Bethe\u0026ndash;Salpeter equation (BSE) \u003cem\u003eab initio\u003c/em\u003e calculations (see \u003cem\u003eMethods\u003c/em\u003e), shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb\u0026ndash;c. Hence, the anisotropic photorefractive change (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed\u0026ndash;f) results from excitonic quenching (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) under UV light exposure.\u003c/p\u003e \u003cp\u003eOf immediate interest is also the high magnitude of the photorefractive effect Δ\u003cem\u003en\u003c/em\u003e in vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e, particularly its anisotropic character, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg. Along the crystallographic \u003cem\u003ea\u003c/em\u003e-axis, Δ\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sub\u003e surpasses values reported for conventional photorefractive materials such as BaTiO\u003csub\u003e3\u003c/sub\u003e, LiNbO\u003csub\u003e3\u003c/sub\u003e, and ZnTe:V.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e Along the \u003cem\u003ec\u003c/em\u003e-axis, Δ\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e is comparable to Δ\u003cem\u003en\u003c/em\u003e of photopolymer films.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e Most notably, along the \u003cem\u003eb\u003c/em\u003e-axis, the photorefractive change Δ\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e reaches a giant value of about 0.1, comparable to that observed in amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg),\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e and stands among the highest reported for any known photorefractive material.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, the crystalline structure of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e maintains after the exposure without any signs of amorphization, as verified by Raman spectroscopy (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, the inset). At the same time, the color of the flake strongly modifies after the exposure (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh,i). Given the unchanged crystalline structure, this color change indicates the change in thickness. Moreover, amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e also exhibits a thickness modification under light exposure.\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e Therefore, we expect a similar phenomenon for vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eAs a result, we performed a detailed study of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e thickness dependence on illumination conditions using atomic force microscopy (AFM). First, we illuminate several As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes with different thicknesses under the same conditions as for the flake, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In all cases (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), the thickness of the flakes decreased by 3\u0026ndash;4 nm, independent of the original thickness. It also leads to the corresponding color change, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. Thus, by adjusting illumination conditions we can manipulate vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e thickness with nanometric precision.\u003c/p\u003e \u003cp\u003eThe next question is how thin As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e can become under such UV exposure. It turns out thinning is possible down to a 2D case of just a few layers of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb\u0026ndash;c. In this experiment, the flakes were sequentially irradiated and analyzed by AFM at 1-hour intervals over a 10-hour period (see \u003cb\u003eFigure S2\u003c/b\u003e for details). During this time, a noticeable decrease in thickness was observed, with one of the thinnest flakes reducing in thickness from ~\u0026thinsp;12 nm to ~\u0026thinsp;2 nm. Additionally, a decline in the thinning rate was observed for this flake, eventually reaching a plateau. The first reason for this saturation effect is that the absorption of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e tends to decrease when exposed to UV (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Secondly, the decrease in thickness modifies the band structure of vdW materials increasing their bandgap.\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e Finally, As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e thinning is driven by layer-by-layer sublimation of the material: this mechanism was described for MoS\u003csub\u003e2\u003c/sub\u003e, but with much higher illumination intensities \u003cem\u003eI\u003c/em\u003e (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eMoS2\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eAs2S3\u003c/sub\u003e ~ 10\u003csup\u003e4\u003c/sup\u003e).\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e Due to the weak vdW interaction between layers, heat generated by illumination is poorly distributed, potentially leading to slow localized evaporation. In contrast, the bottom layer is in closer contact with the substrate, facilitating efficient heat dissipation and limiting further sublimation.\u003c/p\u003e \u003cp\u003eNoteworthy, the thickness of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e changes after near-infrared (NIR) irradiation too (see \u003cb\u003eFigure S3\u003c/b\u003e). However, the required irradiation dose is nearly 10\u003csup\u003e6\u003c/sup\u003e times higher, reaching values of ~\u0026thinsp;1 J/\u0026micro;m\u003csup\u003e2\u003c/sup\u003e. This significant increase in power is attributed to the large detuning of the 785 nm laser energy from the absorption peaks (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Consequently, we can achieve a fine-tuning of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e geometry by varying the incident wavelength and power.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eConsidering the pronounced changes observed at low illumination intensities, the further natural step is exploring high-power radiation effects on the structure of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e to unlock additional control knobs. For this purpose, we utilize a standard continuous-wave (CW) 532 nm laser integrated into a Raman microscope. This simple setup allows us to successfully pattern a grating with a 600 nm period and approximately 100 \u0026micro;m lateral size on the surface of a vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flake. The fabrication process is schematically illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, with additional details provided in the \u003cem\u003eMethods\u003c/em\u003e section and \u003cb\u003eSupplementary Note 2\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eThe resulting grating is clearly visible under optical microscopy and AFM, with a height modulation exceeding 40 nm (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb\u0026ndash;d). Moreover, transmittance spectra indicate the presence of waveguide modes in the grating, confirming its optical functionality (see Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee\u0026ndash;g and \u003cb\u003eSupplementary Note 3\u003c/b\u003e for calculation details). Additionally, illuminating the grating with a laser at a wavelength of 785 nm, which exceeds the grating period, resulted in edge emission, further validating grating-assisted coupling into waveguide modes (\u003cb\u003eFigure S4\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast to low-power illumination, this intense irradiation induces significant structural transformations in the vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flake. Indeed, Raman spectroscopy (\u003cb\u003eFigure S5\u003c/b\u003e) reveals a crystalline-to-amorphous transition on the grating, evidenced by a reduction in the sharp Raman peaks characteristic of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e and a simultaneous increase in broad Raman band near 340 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, typically associated with vibrations of AsS\u003csub\u003e3\u003c/sub\u003e pyramids in the amorphous state.\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e This transformation is likely attributed to the high density of structural defects inherent to mechanically sensitive As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e crystal.\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e These defects may arise during exfoliation, and subsequent irradiation could provide enough energy to overcome a relatively low energy barrier, promoting a transition into a more stable amorphous phase. Moreover, different from the thinning at low irradiation doses, high-power irradiation leads to local expansion of approximately 3%, numerically consistent with previous observations in amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e This expansion depends on the power of the illumination or, more universally, on the incident (absorbed) energy, i.e., the dosage. The grating in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e is fabricated with a radiant exposure of about 0.83 mJ/\u0026micro;m\u003csup\u003e2\u003c/sup\u003e, which is three orders of magnitude higher than the low-intensity conditions employed for flake thinning with an LED source (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe correlation between structural transformations and illumination intensity naturally raises an important question: what is the threshold energy at which bulges erupt and become holes, and does such a threshold exist at all? In other words, at what point does photoexpansion shift toward rapid evaporation? To address this, we irradiate vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e using laser beams of varying powers, resulting in the formation of diverse point-like structures, ranging from small bumps to deep crater-shaped holes (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea,b, S6). The transition from expansion to rapid evaporation occurred at a radiant exposure of ~\u0026thinsp;3 mJ/\u0026micro;m\u003csup\u003e2\u003c/sup\u003e. Meanwhile, irradiation below ~\u0026thinsp;0.9 mW/\u0026micro;m\u003csup\u003e2\u003c/sup\u003e does not produce noticeable changes on the flake surface, therefore we consider this value as a threshold between layer-by-layer sublimation. Further increasing the laser power led to a rapid growth in the size and depth of the holes, eventually penetrating the flakes (see \u003cb\u003eFigure S7\u003c/b\u003e). Importantly, the dimensions of the individual bumps or holes can be precisely controlled by adjusting either the laser power or irradiation time. Similar patterns have recently been demonstrated in amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e films;\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e however, those experiments employed femtosecond pulsed lasers.\u003c/p\u003e \u003cp\u003eNotably, the highest observed bumps reached approximately 200 nm in height, corresponding to a giant photoexpansion of about 6\u0026ndash;7%. Similarly, giant expansion values have previously been reported in amorphous As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e glasses.\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e The observed photoexpansion effect may originate from light-induced charge redistribution on sulfur atoms, which increases electrical repulsion between them, causing cluster expansion through network reconfiguration without breaking bonds.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThis discovery enables direct fabrication of arbitrary patterns on the surface of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes using a standard Raman microscope equipped with a motorized stage. A laser power of 0.3\u0026ndash;0.4 mW was found to be optimal based on the dimensions of the resulting surface features (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea,b). We determined the minimal separation distance between two distinct points to be approximately 500 nm, corresponding to a dot density equivalent to ~\u0026thinsp;50,000 dots per inch (DPI). As a result, we imprint a variety structures ranging from periodic arrays to arbitrary monochromatic images (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec\u0026ndash;f; see also \u003cb\u003eFigure S8a\u0026ndash;c\u003c/b\u003e for AFM maps). The QR-code shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef was patterned on the surface of an As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flake previously transferred onto a flexible PDMS substrate, demonstrating a proof of concept for potential information encoding in this transparent material, assuming appropriate encapsulation of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. This facile nanopatterning approach holds promise for a wide range of applications, as discussed below.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eOutlook\u003c/h2\u003e \u003cp\u003evdW materials exhibit exceptional optical, electronic, and magnetic properties, primarily enabled by their weak interlayer bonding, which facilitates isolation into atomically thin layers. However, practical methods for actively controlling these properties remain limited, posing a significant barrier to their broader technological adoption. Furthermore, nanophotonic applications inherently demand efficient and precise nanostructuring \u0026ndash; a task that is particularly challenging for such layered materials. In this context, light sculpting techniques have emerged as powerful and versatile methods to achieve controlled nanostructuring, potentially addressing the specific fabrication challenges posed by vdW materials. Here, we demonstrate that illumination not only enables precise structural patterning of crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e but also actively modulates its optical properties, significantly broadening its applicability in advanced nanophotonics. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e schematically illustrates the remarkable multifunctionality of this material under light exposure. We now discuss the broader implications and potential applications of these effects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFirst, the discovery of a giant photorefractive effect in crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e, reaching values as high as Δ\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.1, significantly expands the scope of photonic modulation achievable in anisotropic vdW crystals. Such optically-induced changes in refractive index surpass those typically observed in conventional photorefractive materials, positioning crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e as a powerful platform for next-generation adaptive photonic elements. The combination of strong anisotropy and this unusually large refractive index modulation makes As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e ideal for dynamic waveguiding, optically reconfigurable integrated photonic circuits, and high-sensitivity optical sensors.\u003csup\u003e\u003cspan additionalcitationids=\"CR48\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e Moreover, this substantial photorefractive response may enable advanced holographic storage solutions, adaptive microlenses, and tunable polarization optics,\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e highlighting the broad technological potential of crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e in future optical systems.\u003c/p\u003e \u003cp\u003eSecond, it was surprising to discover that the thickness of crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes can be precisely controlled by illumination, even without using laser irradiation: we observed a gradual, slow evaporation and refractive index modification at low illumination intensities. This behavior then transitioned to photoexpansion with increased intensity, and ultimately to rapid evaporation at even higher intensities. Such intensity-dependent control over anisotropic As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e properties provides diverse operational modalities: atomic-level thickness modulation, photorefractive effects for tailored light propagation and absorption, structural and geometric patterning by imprinting features such as gratings or bumps, and even rapid material ablation for laser cutting and drilling. Remarkably, we demonstrate precise nanostructuring of crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e using only a simple CW laser. Such extensive control through a single parameter - illumination intensity - opens exciting and far-reaching possibilities for advanced applications.\u003c/p\u003e \u003cp\u003eThird, we demonstrated the information-recording capabilities of vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. Arbitrary patterns can be efficiently fabricated on crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes using a low-power CW laser integrated into a Raman microscope. This method achieves an impressive resolution reaching 50,000 DPI, corresponding to a dot pitch of ~\u0026thinsp;500 nm, currently limited by the diffraction limit but with potential for further optimization. Importantly, the pattern formation is based not on destructive laser ablation but rather on the intrinsic photoexpansion effect in vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe formed nanostructures offer versatile opportunities across multiple domains. Periodic patterns created by this method can be directly applied in optics,\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e biomedicine,\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e,\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e tribology,\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e,\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e sensing,\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e,\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e and color encryption.\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e Furthermore, even individual photoinduced bumps can serve as microlenses, making them attractive components for integrated 2D optoelectronic circuits.\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e Patterned images can encode valuable information for diverse applications, such as QR-coding (\u003cb\u003eFigure S8d\u003c/b\u003e) or user-defined tags. Additionally, the inherent optical transparency of crystalline vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e ensures that these nanostructures remain visible under transmitted illumination (\u003cb\u003eFigure S9\u003c/b\u003e), further expanding their functional potential.\u003c/p\u003e \u003cp\u003eThis accessible and straightforward nanostructuring approach effectively circumvents the complexity and cost of traditional femtosecond laser techniques. Coupled with its demonstrated photorefractive properties, pronounced optical anisotropy, and high refractive index, crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e thus emerges as a highly promising platform for future advances in nanophotonics and related emerging technologies.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contributions\u003c/h2\u003e\n\u003cp\u003eA.A.M. and G.A.E. contributed equally to this work. A.A.M., G.A.E., G.I.T., I.P.R., A.V.A., K.S.N., and V.S.V. suggested and directed the project. A.A.M., G.A.E., A.P.T., I.M.F., A.N.T., A.S.S., and S.A.I. performed the measurements and analyzed the data. I.M.F., A.B.M., S.A.S., N.D.O., I.A.K., and A.A.V. provided theoretical support. A.A.M. and G.A.E. wrote the original manuscript. All authors reviewed and edited the paper. All authors contributed to the discussions and commented on the paper.\u003c/p\u003e\n\u003ch2\u003eCompeting Interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eThe authors thank Dr. V. Solovey for his help in creating the illustrations.\u0026nbsp;The authors acknowledge S. Dyakov and N. Gippius for providing the code of Fourier Modal Method for optical calculations.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003eSample Preparation\u003c/h2\u003e\n\u003cp\u003eBulk As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e crystals were purchased from 2D Semiconductors (Scottsdale, USA) and exfoliated onto the desired substrates. Adhesive tape from Nitto Denko Corporation (Osaka, Japan) carrying the As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e crystal was brought into contact with the substrates. The flakes were then transferred onto silicon substrates or Schott glass. Subsequently, the tape was removed, completing the exfoliation procedure. The choice of substrate was based on the intended characterization and use of the samples. An optical microscope (Nikon ECLIPSE LV150NA, 100× objective, Nikon CFI TU Plan Fluor BD) was employed to visually identify exfoliated flakes of suitable size.\u003c/p\u003e\n\u003cp\u003eTo place flakes onto a flexible substrate, a PDMS-based pick-up technique was used. Flakes were first mechanically exfoliated onto PDMS,\u003csup\u003e35\u003c/sup\u003e and the exfoliated flakes were then transferred onto a flexible PDMS substrate at room temperature using a manual transfer system (HQ2D MAN).\u003c/p\u003e\n\u003ch2\u003eUV and NIR Exposure\u003c/h2\u003e\n\u003cp\u003eAs\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes on substrates were exposed to UV light for 66 min (that equals to ~1 hour, which was used in the article text) using an Omicron_LedHUB (408.4 nm, Power 100%) light source of Accurion Nanofilm EP4 Imaging Ellipsometer (the corresponding parameters of polarizer, compensator, and analyzer were set to 50°, 45°, and 30°), utilized in reflection mode. The angle of incidence and angle of view of the ellipsometer were set to an equal angle of 50°. For the described ellipsometer configuration, the light source power on the surface of the substrates (265 µW) was estimated using Power Meter Detector\u0026nbsp;“ThorLabs TH-084 (CAL 05-09-2023) S120VC 200-1100nm 50mW”. The spot size on the surface of the substrate had an elliptical shape with a semi-major axis and a semi-minor axis of ~750 µm and ~500 µm, respectively. The corresponding power density on the surface of the substrate was ~2.25×10\u003csup\u003e−10\u003c/sup\u003e W/µm\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFor NIR exposure, a 785 nm laser was employed in continuous Raman Area Scan mode using an alpha300 RA confocal Raman-AFM microscope (WITec, Ulm, Germany). The 4×4 µm areas were exposed with laser power increasing from 0 to 80 mW\u0026nbsp;with the total exposure time per area of 400 s (resulting in a radiant exposure from 0 to 2\u0026nbsp;J/µm\u003csup\u003e2\u003c/sup\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEllipsometry\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo analyze the anisotropic optical constants of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e before and after UV irradiation, we implement the Accurion EP4 imaging spectroscopic ellipsometer in the rotating compensator mode. Two measurements were performed with the plane of incidence aligned with the crystallographic \u003cem\u003ea\u003c/em\u003e-axis and \u003cem\u003ec\u003c/em\u003e-axis, respectively, which allows for quasi-isotropic optical recording of \u003cem\u003eΨ\u003c/em\u003e and \u003cem\u003eΔ\u003c/em\u003e instead of Mueller matrix measurements. Ellipsometry spectra of \u003cem\u003eΨ\u003c/em\u003e and \u003cem\u003eΔ\u003c/em\u003e were recorded in the spectral range from 360 to 950 nm for two incident angles 45° and 50°.\u003c/p\u003e\n\u003ch2\u003eLaser Nanostructuring of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e Flakes\u003c/h2\u003e\n\u003cp\u003eAll precise surface nanostructuring of crystalline As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes described in this work was conducted using a 532 nm continuous wave laser and the alpha300 RA confocal Raman-AFM microscope. Parameter control was managed via WITec Control SIX software. A 100× objective (Zeiss EC Epiplan-Neofluar, NA 0.9 DIC) with a spot diameter of approximately 0.3 µm for the 532 nm laser was employed for focusing. Sample positioning was achieved using a motorized stage with a step precision of 25 nm.\u003c/p\u003e\n\u003ch2\u003eRaman and Atomic Force Microscopy (AFM) Analysis\u003c/h2\u003e\n\u003cp\u003eRaman analysis was performed using the\u0026nbsp;WITec alpha300 RA confocal Raman-AFM microscope. Spectral processing\u0026nbsp;was executed with WITec Project SIX software. Raman spectra\u0026nbsp;were acquired with the Zeiss 100× objective, producing a spot diameter of approximately 0.45 µm for the used 785 nm laser (2 mW, equivalent to a laser density of ~12 mW/µm\u003csup\u003e2\u003c/sup\u003e). A 1200 lines/mm grating was utilized, and the backscattered light was detected with a back-illuminated deep depletion CCD detector cooled to −60°C, achieving a spectral resolution of ~0.5 cm⁻\u003csup\u003e1\u003c/sup\u003e. Each spectrum acquisition lasted 10 seconds and was repeated 10 times.\u003c/p\u003e\n\u003cp\u003eAFM imaging was conducted in tapping mode using the WITec alpha300 RA microscope equipped with a NanoWorld ARROW-FMR probe (75 kHz, 2.8 N/m). The scanning speed, scan size, and resolution were tailored to each study area to ensure optimal visualization quality. Surface morphology and thickness of the As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e flakes (Figures 2, S2) were estimated via Cypher S microscope (Oxford Instruments) operated in tapping mode, using AC160TSA-R3 tip type. AFM image processing was conducted using Gwyddion software.\u003c/p\u003e\n\u003ch2\u003eFirst principles calculations\u003c/h2\u003e\n\u003cp\u003eThe optical response of bulk\u0026nbsp;vdW As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (\u003cem\u003ea\u0026nbsp;\u003c/em\u003e= 4.255 Å, \u003cem\u003eb\u0026nbsp;\u003c/em\u003e= 9.578 Å, \u003cem\u003ec\u0026nbsp;\u003c/em\u003e= 11.415 Å,\u0026nbsp;\u003cem\u003eα\u003c/em\u003e = 90°,\u0026nbsp;\u003cem\u003eβ\u003c/em\u003e = 90.44°,\u0026nbsp;\u003cem\u003eγ\u003c/em\u003e = 90°) was computed using the BSE@GW approach as implemented in the VASP package.\u003csup\u003e59\u003c/sup\u003e Single-particle ground-state wavefunctions were first obtained from a self-consistent density functional theory (DFT) calculation. These were then used to initialize the GW step and compute the screened Coulomb interaction kernels. The resulting quasiparticle energies served as input for a Bethe–Salpeter Equation (BSE) calculation to evaluate the frequency-dependent dielectric function including electron–hole interactions. A plane-wave cutoff energy of 400 eV and 512 bands were used.\u0026nbsp;The exchange correlation effects in the DFT run were described with the generalized gradient approximation (Perdew-Burke-Ernzerhof functional).\u003csup\u003e60\u003c/sup\u003e The behavior of the core electrons and their interaction with the valence electrons was described using the projector augmented wave pseudopotentials.\u003csup\u003e61\u003c/sup\u003e The BSE step included 24 valence and 24 conduction bands.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eShcherbakov MR et al (2023) Nanoscale reshaping of resonant dielectric microstructures by light-driven explosions. Nat Commun 14:6688\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoenderink AF, Al\u0026ugrave; A, Polman A, Nanophotonics (2015) Shrinking light-based technology. Science 348:516\u0026ndash;521\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u0026Ouml;ktem B et al (2013) Nonlinear laser lithography for indefinitely large-area nanostructuring with femtosecond pulses. Nat Photonics 7:897\u0026ndash;901\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTselikov GI et al (2023) Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Ultrahigh Sensitivity. ACS Nano 17:19338\u0026ndash;19348\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMunkhbat B et al (2020) Transition metal dichalcogenide metamaterials with atomic precision. Nat Commun 11:4604\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCho SR et al (2021) Universal Patterning for 2D Van der Waals Materials via Direct Optical Lithography. Adv Funct Mater 31:2105302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRossi-Gendron C et al (2023) Isothermal self-assembly of multicomponent and evolutive DNA nanostructures. Nat Nanotechnol 18:1311\u0026ndash;1318\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTselikov GI et al (2022) Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics. \u003cem\u003eProc. Natl. Acad. Sci.\u003c/em\u003e 119, e2208830119\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStatsenko TG et al (2025) Bio-Inspired Giant Refractive Index Gradient Lenses Based on Ionic Polymers. Adv Opt Mater 13:2402488\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu X et al (2022) Femtosecond laser writing of lithium niobate ferroelectric nanodomains. Nature 609:496\u0026ndash;501\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLapidas V et al (2024) Surface Coloring and Plasmonic Information Encryption at 50000 dpi Enabled by Direct Femtosecond Laser Printing. Nano Lett 24:12590\u0026ndash;12596\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu D et al (2022) Direct optical patterning of perovskite nanocrystals with ligand cross-linkers. Sci Adv 8:eabm8433\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLin H et al (2020) Diffraction-limited imaging with monolayer 2D material-based ultrathin flat lenses. Light Sci Appl 9:137\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eR\u0026oacute;denas A et al (2019) Three-dimensional femtosecond laser nanolithography of crystals. Nat Photonics 13:105\u0026ndash;109\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMakarov SV et al (2017) Light-Induced Tuning and Reconfiguration of Nanophotonic Structures. Laser Photonics Rev 11:1700108\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang X et al (2020) Reversible 3D laser printing of perovskite quantum dots inside a transparent medium. Nat Photonics 14:82\u0026ndash;88\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGeng J, Xu L, Yan W, Shi L, Qiu M (2023) High-speed laser writing of structural colors for full-color inkless printing. Nat Commun 14:565\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSedghamiz E, Liu M, Wenzel W (2022) Challenges and limits of mechanical stability in 3D direct laser writing. Nat Commun 13:2115\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLin L et al (2018) Optothermoplasmonic Nanolithography for On-Demand Patterning of 2D Materials. Adv Funct Mater 28:1803990\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim SE et al (2021) Extremely anisotropic van der Waals thermal conductors. Nature 597:660\u0026ndash;665\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eŠiškins M et al (2019) Highly Anisotropic Mechanical and Optical Properties of 2D Layered As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e Membranes. ACS Nano 13:10845\u0026ndash;10851\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErmolaev GA et al (2021) Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics. Nat Commun 12:854\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCastellanos-Gomez A et al (2012) Laser-Thinning of MoS 2: On Demand Generation of a Single-Layer Semiconductor. Nano Lett 12:3187\u0026ndash;3192\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhoshal D et al (2025) Spatially Precise Light-Activated Dedoping in Wafer‐Scale MoS\u003csub\u003e2\u003c/sub\u003e Films. Adv Mater 37:2409825\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBereznikova LA et al (2025) Artificial intelligence guided search for van der Waals materials with high optical anisotropy. Mater Horiz. 10.1039.D4MH01332H\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMounet N et al (2018) Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds. Nat Nanotechnol 13:246\u0026ndash;252\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSlavich AS et al (2024) Exploring van der Waals materials with high anisotropy: geometrical and optical approaches. Light Sci Appl 13:68\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOzols A, Saharovs D, Reinfelde M (2006) Holographic recording in amorphous As2S3 films at 633nm. J Non-Cryst Solids 352:2652\u0026ndash;2656\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTanaka K, Saitoh A (2022) Pulsed light effects in amorphous As2S3: review. J Mater Sci Mater Electron 33:22029\u0026ndash;22052\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHisakuni H, Tanaka K (1995) Optical Microfabrication of Chalcogenide Glasses. Science 270:974\u0026ndash;975\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao W et al (2011) Visible Light Generation and Its Influence on Supercontinuum in Chalcogenide As\u003cspan\u003e$\u003c/span\u003e_{2}\u003cspan\u003e$\u003c/span\u003eS\u003cspan\u003e$\u003c/span\u003e_{3}\u003cspan\u003e$\u003c/span\u003e Microstructured Optical Fiber. Appl Phys Express 4:102601\u003c/span\u003e \u003c/li\u003e \u003cli\u003e\u003cspan\u003eZoubir A et al (2004) Direct femtosecond laser writing of waveguides in As_2S_3 thin films. Opt Lett 29:748\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeneghini C, Villeneuve A (1998) As_2S_3 photosensitivity by two-photon absorption: holographic gratings and self-written channel waveguides. J Opt Soc Am B 15:2946\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWong S et al (2006) Direct Laser Writing of Three- Dimensional Photonic Crystals with a Complete Photonic Bandgap in Chalcogenide Glasses. Adv Mater 18:265\u0026ndash;269\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVoronin KV et al (2024) Chiral Photonic Super-Crystals Based on Helical van der Waals Homostructures. Laser Photonics Rev 18:2301113\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDyakov SA et al (2024) Chiral Light in Twisted Fabry\u0026ndash;P\u0026eacute;rot Cavities. Adv Opt Mater 12:2302502\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErmolaev GA et al (2020) Broadband optical properties of monolayer and bulk MoS2. Npj 2D Mater Appl 4:21\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u003cem\u003eSpringer Handbook of Glass\u003c/em\u003e. (Springer International Publishing, Cham, (2019) \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/978-3-319-93728-1\u003c/span\u003e\u003cspan address=\"10.1007/978-3-319-93728-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZanutta A, Orselli E, F\u0026auml;cke T, Bianco A (2016) Photopolymeric films with highly tunable refractive index modulation for high precision diffractive optics. Opt Mater Express 6:252\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBhardwaj P, Shishodia PK, Mehra RM (2003) Photo-induced changes in optical properties of As2S3 and As2Se3 films deposited at normal and oblique incidence. J Mater Sci 38:937\u0026ndash;940\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAzhniuk Y et al (2022) Mass transport in amorphous As2S3 films due to directional light scattering under illumination by an oblique tightly focused beam. J Non-Cryst Solids 576:121269\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLőrinczi A, Sava F, Simandan I-D, Velea A, Popescu M (2016) Photoexpansion in amorphous As2S3: A new explanation. J Non-Cryst Solids 447:123\u0026ndash;125\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTongay S et al (2014) Monolayer behaviour in bulk ReS2 due to electronic and vibrational decoupling. Nat Commun 5:3252\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFrumar M, Firth AP, Owen AE (1995) Optically induced crystal-to-amorphous-state transition in As2S3. J Non-Cryst Solids 192\u0026ndash;193:447\u0026ndash;450\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHisakuni H, Tanaka K (1994) Giant photoexpansion in As2S3 glass. Appl Phys Lett 65:2925\u0026ndash;2927\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMihai C et al (2024) Fs Laser Patterning of Amorphous As2S3 Thin Films. Materials 17:798\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLing H, Li R, Davoyan AR (2021) All van der Waals Integrated Nanophotonics with Bulk Transition Metal Dichalcogenides. ACS Photonics 8:721\u0026ndash;730\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou Y et al (2024) A solution-processable natural crystal with giant optical anisotropy for efficient manipulation of light polarization. Nat Photonics 18:922\u0026ndash;927\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKravets VG et al (2013) Singular phase nano-optics in plasmonic metamaterials for label-free single-molecule detection. Nat Mater 12:304\u0026ndash;309\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRubin NA, Zaidi A, Dorrah AH, Shi Z, Capasso F (2021) Jones matrix holography with metasurfaces. Sci Adv 7:eabg7488\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBiswas S, Grajower MY, Watanabe K, Taniguchi T, Atwater HA (2021) Broadband electro-optic polarization conversion with atomically thin black phosphorus. Science 374:448\u0026ndash;453\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang H, Deng D, Zhai Z, Yao Y (2024) Laser-processed functional surface structures for multi-functional applications-a review. J Manuf Process 116:247\u0026ndash;283\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZheng H, Liu J, Qiu Y (2024) The Design and Analysis of the Fabrication of Micro- and Nanoscale Surface Structures and Their Performance Applications from a Bionic Perspective. Materials 17:4014\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBonse J, Kirner SV, Kr\u0026uuml;ger J (2020) Laser-Induced Periodic Surface Structures (LIPSS). in \u003cem\u003eHandbook of Laser Micro- and Nano-Engineering\u003c/em\u003e (ed. Sugioka, K.) 1\u0026ndash;59Springer International Publishing, Cham. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/978-3-319-69537-2_17-1\u003c/span\u003e\u003cspan address=\"10.1007/978-3-319-69537-2_17-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVaghasiya H, Miclea P-T (2023) Investigating Laser-Induced Periodic Surface Structures (LIPSS) Formation in Silicon and Their Impact on Surface-Enhanced Raman Spectroscopy (SERS). Optics 4:538\u0026ndash;550\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVo TS et al (2024) A comprehensive review of laser processing-assisted 2D functional materials and their specific applications. Mater Today Phys 47:101536\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShvedov VG, Izdebskaya YV, Shadrivov IV (2024) Control of Orientation and Periodicity of Laser-Induced Surface Structures on Metals. Adv Mater Interfaces 2400589. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/admi.202400589\u003c/span\u003e\u003cspan address=\"10.1002/admi.202400589\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePopescu M, Velea A, Miclos S, Savastru D (2013) Optics of microlenses created by irradiation of As\u003csub\u003e2\u003c/sub\u003e S\u003csub\u003e3\u003c/sub\u003e amorphous chalcogenide films with femtosecond laser pulses. Philos Mag Lett 93:213\u0026ndash;220\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKresse G, Furthm\u0026uuml;ller J (1996) Efficient iterative schemes for \u003cem\u003eab initio\u003c/em\u003e total-energy calculations using a plane-wave basis set. Phys Rev B 54:11169\u0026ndash;11186\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePerdew JP, Burke K, Ernzerhof M (1996) Generalized Gradient Approximation Made Simple. Phys Rev Lett 77:3865\u0026ndash;3868\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKresse G, Joubert D (1999) From ultrasoft pseudopotentials to the projector augmented-wave method. Phys Rev B 59:1758\u0026ndash;1775\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"Emerging Technologies Research Center, XPANCEO","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"van der Waals materials, nanostructuring, As2S3, 2D materials, photorefractive effect","lastPublishedDoi":"10.21203/rs.3.rs-6463506/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6463506/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNanophotonics relies on precise nanoscale structuring, yet conventional fabrication techniques remain complex and costly. Layered van der Waals (vdW) materials, with their intrinsic anisotropy and high refractive indices, offer a promising route toward simplified nanostructuring and tunable optical functionality. However, no vdW material has previously been shown to exhibit a strong photorefractive effect\u0026mdash;a key requirement for light-based modulation. Here we report a giant photorefractive response (Δ\u003cem\u003en\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;0.1) in crystalline arsenic trisulfide (As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e), observed even under low-intensity illumination. In addition to refractive index modulation, light exposure enables controlled thickness tuning of As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e. The material exhibits a giant photoexpansion of up to 5%, depending on the illumination intensity. Building on this photoexpansion effect, we introduce a maskless, low-cost nanopatterning technique based on continuous-wave laser writing, achieving resolutions up to 50,000 dots per inch without the need for ultrafast lasers. The combination of high photosensitivity, optical anisotropy, and transparency positions As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e as a versatile platform for integrated photonics, adaptive optics, data storage, biomedical imaging, and nanoscale sensing.\u003c/p\u003e","manuscriptTitle":"Giant photorefractive and photoexpansion effects in a van der Waals semiconductor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-21 11:06:56","doi":"10.21203/rs.3.rs-6463506/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"583e3b0a-901d-4076-bc4f-d3083ed9c063","owner":[],"postedDate":"April 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47303131,"name":"Optical Materials and Devices"},{"id":47303132,"name":"Optics/Lasers"},{"id":47303133,"name":"Photonics/optics"}],"tags":[],"updatedAt":"2026-03-30T20:59:24+00:00","versionOfRecord":{"articleIdentity":"rs-6463506","link":"https://doi.org/10.1073/pnas.2531552123","journal":{"identity":"proceedings-of-the-national-academy-of-sciences","isVorOnly":true,"title":"Proceedings of the National Academy of Sciences"},"publishedOn":"2026-03-27 00:00:00","publishedOnDateReadable":"March 27th, 2026"},"versionCreatedAt":"2025-04-21 11:06:56","video":"","vorDoi":"10.1073/pnas.2531552123","vorDoiUrl":"https://doi.org/10.1073/pnas.2531552123","workflowStages":[]},"version":"v1","identity":"rs-6463506","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6463506","identity":"rs-6463506","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}