All-in-One van der Waals Material for Light Detection, Guiding and Modulation

All-in-One van der Waals Material for Light Detection, Guiding and Modulation | 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 Article All-in-One van der Waals Material for Light Detection, Guiding and Modulation Valentyn Volkov, Aleksandr Slavich, Georgy Ermolaev, Nikolay Pak, and 23 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6156048/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Modern optoelectronic devices demand materials that can perform multiple, often conflicting functions, such as acting as metals for interconnects, dielectrics for waveguides, and semiconductors for light emission and detection. The integration of these materials is challenging, slowing industry progress and increasing costs. It inspired an intensive search for a universal optoelectronic response within a single material. Here, we reveal that palladium diselenide (PdSe 2 ) provides an answer to this quest owing to its unique bandstructure. It exhibits a semimetallic band structure with an unusually large bandgap for interband transitions responsible for semiconductor-metallic nature. This duality enables PdSe 2 to function as both a photodetector and a waveguide, integrating two traditionally incompatible responses. As a result, our findings provide a full picture of PdSe 2 optoelectronic properties, paving the way for its use in multifunctional optoelectronic applications in one material. Physical sciences/Materials science/Condensed-matter physics/Electronic properties and materials Physical sciences/Optics and photonics/Optical techniques/Optical spectroscopy palladium diselenide high refractive index in-plane anisotropy optical constants integrated photonics infrared conventional semimetal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Materials properties are crucial for every technology, defining the capabilities and limitations of various devices and techniques 1 , 2 . In electronics, high conductivity and carrier mobility are in strong demand 3 , 4 , while in photonics, critical parameters are the high refractive index and low optical losses 5 , 6 . As a result, numerous groups are constantly searching for artificial and natural materials with record characteristics 7 – 10 . However, the greater challenge is finding a material platform with high performance in several fields simultaneously, such as optoelectronics and photonics 4 . Indeed, optoelectronics requires metals 11 – 13 , which are undesired in photonics because of their high optical losses in the telecommunication range 14 , 15 . In contrast, photonics needs high-refractive-index materials with negligible losses, which traditionally include dielectrics 16 – 18 not suitable for electronics applications. As a result, a material which combines optoelectronic and photonic utility seems like imaginable but unattainable in reality. In this regard, van der Waals (vdW) crystals have emerged as a prospective class of materials with graphene 11 , 19 , black phosphorus 20 , 21 , PtSe 2 22,23 , and WTe 2 24,25 demonstrating promising metallic response for optoelectronics, whereas MoS 2 10,26 , WS 2 5,27 , hBN 17 , GeS 2 28 , SnS 2 29 , ReS 2 30 , and As 2 S 3 31 are semiconductors suitable for modern all-dielectric photonics. However, in practice, it is often required that both properties coexist in a single material. Ideally, it would behave as a metal at giga- and terahertz frequencies for on-chip interconnects, serve as a dielectric for infrared telecom waveguiding, and switch to semiconducting behavior for other applications (like sensing or biomedical). In light of this, palladium diselenide (PdSe 2 ) stands out with ever-growing interest in its diverse applications, such as photodetection 32 , 33 , polarization optics 34 , 35 , modulation 36 , 37 , and biosensing 38 , 39 , to name a few. However, despite these striking achievements, the broadband optical properties of PdSe 2 are not fully understood 34 , 38 , 40 – 42 . Recent research 40 , 41 reveals its semiconducting response, while other works 34 , 38 , 42 report its metallic behavior, which is confusing and hides a horizon of PdSe 2 applications from a clear view. At the same time, the reported controversy of semiconducting and metallic properties positions PdSe 2 as a potential universal platform for both electronics and photonics. In this work, we present PdSe 2 as a material capable of fulfilling all these functionalities within a single platform. For this purpose, we performed far- and near-infrared PdSe 2 characterization to resolve its ultrabroadband (250–17000 nm) optical properties. The results reveal the all-in-one nature of PdSe 2 manifested in three spectral regions. In the first region, from ultraviolet to therapeutic wavelengths, PdSe 2 has a high absorption, which is ideal for photothermal biomedicine. PdSe 2 demonstrates a lossless high refractive index, a perfect combination for light guiding and resonators in the second interval from near-infrared to mid-infrared frequencies. At the same time, from mid-infrared wavelengths, PdSe 2 exhibits a metallic response that is desirable for photodetection. Our first-principle calculations unveil the underlying physics by showing that this material is a semimetal whose conduction and valence bands extrema are shifted in the momentum space thereby prohibiting direct optical transitions. Finally, we experimentally demonstrate PdSe 2 ’s functionality as a waveguide for integrated photonics, a mid-infrared photodetector, and a photothermal converter, underscoring its significant potential as a universal platform for both nanophotonics and optoelectronic applications. Results Crystal structure and stoichiometry characterization of PdSe 2 flakes Palladium diselenide is a layered crystal with an orthorhombic lattice that belongs to the space group Pbca 43 . The lattice parameters of PdSe 2 crystal are a = 5.73562(30) Å, b = 5.8622(3) Å, c = 7.7098(7) Å, α = β = γ = 90° 44 . The unit cell consists of two inverted layers stacked along the c -axis held by weak vdW forces. As demonstrated in Fig. 1 a, each Pd atom within the layer is surrounded by four Se atoms, forming an arrangement of square-planar-like PdSe 4 units linked by a shared selenium atom and two connected selenium atoms from different squares 45 . The resulting pattern represents periodic counter-directional atomic chains aligned along the a -axis. The weak vdW forces facilitates exfoliation into thin flakes (see Methods and the inset in Fig. 1 b). To verify the crystal quality of PdSe₂ flakes we exfoliated and transferred them onto a porous SiNₓ membrane and characterized their structure using scanning transmission electron microscopy (STEM) methods. Figure 1 c shows high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field (HAADF) images. These images correspond well with the [001] crystallographic facet of the PdSe₂ crystal, depicted in Fig. 1 a. Schematic Pd and Se atoms of the palladium diselenide crystal are overlaid on the HAADF image with gray and green dots, respectively. As a result, the observed lattice spacings correspond to the known crystallographic planes, confirming that the exfoliated flakes retain the bulk crystal structure. The homogeneous quality of the PdSe₂ flakes is evidenced by the selected area electron diffraction (SAED) pattern obtained from the same flake (see Fig. 1 d and Supplementary Note 1 ). We also validated the chemical composition of PdSe 2 flakes via scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). Figure 1 e represents SEM image of thick PdSe 2 flake transferred onto Si substrate and corresponding EDX maps of Pd, Se and Si elements confirming the uniform distribution of Pd and Se atoms in the flake. The Pd:Se atomic ratio matched well with the stoichiometry of PdSe 2 , as shown in Fig. 1 f. All-in-one optical properties of PdSe The dielectric permittivity tensor of the crystals with an orthorhombic lattice is defined by three complex refractive indices n j + ik j , j = a , b , c associated with respective crystallographic axes a , b and c . To obtain these complex refractive indices, we identify the principal optical axes of PdSe 2 flakes via polarized Raman and micro-reflectance spectroscopies ( Supplementary Note 2,3 ). Next, we measured ellipsometry and micro-reflectance along optical axes to determine the anisotropic optical properties of PdSe 2 over an ultra-wide spectral range from 250 to 17000 nm (see Methods ). The resulting refractive indices and extinction coefficients are collected in Figs. 2 a-b (for details of spectra fitting see Supplementary Note 4 ). Interestingly, for wavelengths above 1500 nm, optical losses of PdSe 2 remain low, whereas, above 8000 nm, losses increase following the Drude behavior (see inset in Fig. 2 b). These findings indicate a transition in the optical behavior of PdSe 2 with the increase in wavelength. The low losses for the near-infrared wavelengths are a sign of dielectric response. In contrast, the onset of significant losses around 8000 nm implies a metallic behavior and reflects the increased free-carrier contributions in optical absorption. In general, we can highlight three regions of PdSe 2 optical response: (i) from 250 to around 1500 nm, it behaves as a strongly absorbing semiconductor with a high extinction coefficient (high- k ); (ii) from 1500 to around 8000 nm it complements the family of high refractive index materials (high- n ), as illustrated in Fig. 2 b; (iii) at long wavelengths above 8000 nm it shows metallic optical response (see inset in Fig. 2 b). Ab initio calculations explain the physics behind these unique optical properties of PdSe 2 . From the bandstructure in Figs. 2 c-d, one can notice that this material is a conventional semimetal. As a result, in PdSe 2 , unlike Weyl, Dirac, and nodal line semimetals often met among vdW materials, the momentum selection rule prohibits direct optical transitions between the conduction and valence bands. Hence, the optical absorption above 8000 nm originates from free carriers, whose density is about 5⋅10 19 cm − 3 at room temperature ( Supplementary Note 5 ). This value translates into the plasma frequency of 0.43 eV which is close to experimental Drude oscillator fit of 0.37 eV from optical constants in Figs. 2 a-b (see Supplementary Note 4 for details). Alternatively, PdSe 2 film can be synthesized in a chemically doped state with a much more pronounced Drude response (Figs. 2 a-b). According to our calculations, if the Fermi level is shifted (as, for instance, by gating) by 0.1 eV – it may result in an order of magnitude increase in a free carrier density. From an application standpoint, gate-tunable properties show great promise for light modulation in integrated photonics and imaging beyond the already demonstrated photodetection. Furthermore, a well-defined transparency region of PdSe 2 (Fig. 2 a-b) separating free carriers and interband absorption bands makes it suitable for lossless integrated nanophotonics, which was previously considered impossible for metals and semimetals. Light detection based on metallic optical response of PdSe In order to confirm our conclusions from Figs. 2 a-b, we demonstrate applications for all three regions. We commence from mid-infrared wavelengths above 8000 nm, where PdSe 2 optical response is determined by free carrier absorption as in metals. This behavior allows for the detection of mid-infrared radiation. To this end, we fabricated a PdSe 2 -based photodetector, presented in Fig. 3 a, to study PdSe 2 detection capabilities. In our device, extra control over the optical and electronic properties of PdSe 2 is achieved via electrostatic gating. The silicon substrate acts as a global back gate, tuning the overall carrier density in the sample via the back gate voltage V bg . Additionally, we placed a transparent top gate made of 4-layer graphite atop the channel. The graphite layer was split into two sections by a 200 nm gap. As a result, independent gate biases V TG1 and V TG2 were applied to the split sections, enabling an all-electric induction of p-n junctions. Interestingly, we have not observed any significant zero-bias photocurrent upon application of opposite voltages to the split top gate, corresponding to the p-n junction formation (Supplementary Fig. 12). At the same time, even for a small source-drain bias V SD = 100 mV, the device demonstrates a significant photocurrent of up to 450 pA, as seen in Fig. 3 b. Further recording of the photocurrent upon scanning the top gate voltages reveals an intriguing pattern, shown in Fig. 3 c. Indeed, the current has maximum values for the overall n-doping of the sample and demonstrates small values in all other cases corresponding to the formation of p-n, n-p, and p-p junctions along the PdSe 2 channel. The minimum is observed at the neutrality point of the sections under either of the gates, corresponding to the white cross in the photocurrent map. Moreover, the photocurrent magnitude grows when an overall positive voltage V BG = 15 V is applied to the back gate and enhances the n-doping (Fig. 3 d). The observed dependences are in stark contrast to the photocurrent observed in two-dimensional (2D) photodetectors exploiting the photo-thermoelectric and interband photovoltaic effects, where a clear zero-bias current is maximized for the opposite doping of two channel sections 46 , 47 . We suggest that it is the bolometric effect, which most likely governs the detection physics in the present case, i.e., the change in PdSe 2 bulk resistance upon intraband radiation absorption and subsequent heating. In order to demonstrate this, we assume that the device resistance R is composed of junctions ( R J ) and bulk ( R B ) connected in series. The former depends on the relative polarity of doping, R J ( V TG1 , V TG2 ), and is maximized for the opposite polarity. The latter depends on the temperature as in conventional metals R B = R B0 (1 + αT ). Denoting the radiation-induced heating as ΔT ph , we arrive at the photocurrent I ph = R B0 αΔT ph V sd /( R J + R B ) 2 . The latter explains the enhancement of photocurrent with overall uniform doping that leads to reduced total resistance (see Supplementary Note 6 for resistance maps corresponding to the doping conditions of Figs. 3 c-d). Finally, the weak sensitivity of radiation-induced heating Δ T ph to the doping is characteristic of the intraband metallic absorption, not the interband electron-hole generation. In detail, the energy balance between radiation absorption and carrier cooling due to substrate coupling reads as σ ’ E 2 = C e Δ T ph / τ E , where σ ’ is the real part of material conductivity at the infrared wavelength, E is the strength of incident electric field, C e is the heat capacitance of charge carriers per unit volume, and τ E is the energy relaxation time (characteristic time of substrate phonon emission). C e is proportional to the density of charge carriers, and so is σ’ in the case of metallic Drude absorption. As a result, photo-induced heating in the metallic case depends very weakly on gate-controlled carrier density. Therefore, our detected photoresponse in Fig. 3 c-d unambiguously validates the metallic optical response of PdSe 2 , shown in Fig. 2 a-b. Light guiding based on high refractive index of PdSe Lossless high- n optical properties of PdSe 2 within a broad spectral range of around 1500–8000 nm make it attractive for photonic applications. This characteristic enables efficient light confinement, an excellent property for light guiding. To this end we performed near-field measurements of PdSe 2 for the long-wavelength border of the high- n spectral range (Fig. 2 a). Figures 4 a-b show the measured near-field amplitude of a 1.12-µm-thick PdSe 2 flake excited at 5219 nm and 7824 nm wavelengths. From them, we found the effective index of fundamental transverse magnetic (TM 0 ) mode (Fig. 4 c), which perfectly matches the transfer matrix method (TMM) calculations (Fig. 4 d) based on optical constants in Figs. 2 a-b. Then, we focus on the short-wavelength border of Fig. 2 a, which includes the telecommunication band. For this, we conduct near-field measurements of planar, 255-nm-thick PdSe 2 waveguides in the near-infrared wavelength region (1500–1600 nm). Despite the appearance of absorption due to interband optical transitions of PdSe 2 , which limit the propagation distance to around 40 µm in this wavelength region, the waveguide mode is visible (Figs. 4 e-f) and shows the perfect agreement with the mode dispersion calculated by TMM (Fig. 4 g). For more details on the s-SNOM data processing see Supplementary Note 7,8 . Notably, the optical losses diminish significantly with the wavelength increase. At 2000 nm, the waveguide mode propagation distance reaches more than 1 mm length, sufficient for use in photonic integrated circuits. With this application in mind, we estimate the integration density of the ultrathin PdSe 2 waveguide with SiO 2 cladding for 2000 nm wavelength (the inset in Fig. 4 g). Our calculations show that PdSe 2 allows a 25% higher integration density than similar Si waveguides for a target crosstalk length of around 1 mm. These findings underscore PdSe 2 potential for waveguide applications that enhance optical communication systems. Light absorption based on high extinction of PdSe Above the optical bandgap in the high- k region of Figs. 2 a-b, PdSe 2 strongly absorbs light. In combination with the high refractive index, it is advantageous for photothermal applications since the conversion of absorbed light into heat is greatly improved thanks to photonic resonances, such as Mie resonances in nanospheres. To demonstrate this application, we adopted the femtosecond laser ablation 48 – 50 (Fig. 5 a) to synthesize PdSe 2 nanospheres (Fig. 5 b) with a broad diameter distribution (Fig. 5 c). For photothermal therapy, smaller nanoparticles are preferred because they are safer for biological systems since reaching target organs and leaving the organism after the therapy is easier for smaller nanostructures. Accordingly, we calculated the extinction (Fig. 5 d), scattering (Fig. 5 e), and absorption (Fig. 5 f) spectra of PdSe 2 nanoparticles with 80 nm diameter (which were indeed successfully fabricated in abundance in our experiments, see Fig. 5 c and the inset in Fig. 5 d). For fabrication and calculation details see Supplementary Note 9 . Surprisingly, PdSe 2 has the best photothermal conversion efficiency compared to traditionally used gold 51 , silicon 52 , and MoS 2 53 within the NIR-I (700–980 nm) therapeutic window, as seen in Fig. 5 f. Hence, PdSe 2 optical properties in the high- k spectral range in Figs. 2 a-b are promising for photothermal medicine. Conclusion Current multifunctional devices are based on several materials platforms, which always pose a complex integration task. In this regard, PdSe 2 offers a universal solution with semiconducting, dielectric, and metallic properties depending on the spectral range. In particular, PdSe 2 exhibits a strong excitonic absorption at short wavelengths, switches to high refractive index dielectric as wavelength grows, and finally transforms to metal with free carrier absorption. This all-in-one nature of PdSe 2 makes it suitable for seemingly contradictory applications in optoelectronics and nanophotonics. Thus, we have demonstrated the multifaceted functionality of PdSe 2 as a waveguide for integrated photonics, a mid-infrared photodetector, and a photothermal converter for biomedical theranostics. In addition, we note the high tunability of bulk PdSe 2 optoelectronic properties by gating, which unlocks yet unexplored applications of PdSe 2 for light modulation. Our findings establish a paradigm shift by introducing a universal material, which challenges photonic and optoelectronic device design fundamentals. Methods Sample preparation. PdSe 2 crystal was purchased from 2D Semiconductors (Scottsdale, USA). Thin flakes were mechanically exfoliated via scotch-tapes from Nitto Denko Corporation (Osaka, Japan) and then were transferred on top of Si, Si/SiO 2 , CaF 2 substrates. The substrates were sequentially sonicated in acetone, isopropanol and deionized water and treated in air plasma to remove natural absorbents. Next, tape with crystals was glued to the substrate and heated up to 100°C. Then the tape was removed, leaving microcrystals on the surface. The thicknesses of the PdSe 2 flakes were accurately measured by an atomic-force microscope (NT-MDT Ntegra II) in contact mode at ambient conditions. Silicon tips (ETALON HA_FM TipsNano) with a tip curvature radius of < 10 nm, a force constant of 6 N⋅m − 1 , and a resonant frequency of 114 kHz were used during all measurements. Angle-resolved micro-reflectance. Polarization-resolved reflectance map was measured in the 550–900 nm range on a trinocular microscope RX50M modified by a polarizer and an analyzer 54 . One of the oculars was adapted to a splitted system of a camera (SIMAGIS TC-3CU) and a spectrometer (Optosky ATP5020P) which was connected by fiber (Thorlabs M92L02) with core diameter 200 µm. The reflected light was collected from a spot of < 20 µm using an objective with ×50 magnification and numerical aperture N.A. = 0.8 (SOPTOP MPlanFL). For polarization-resolved infrared spectroscopy, a Fourier transform infrared spectrometer (Bruker Vertex 80v) equipped with a Hyperion 2000 microscope was employed. Normal incidence reflection measurements on the face of the flakes were performed using a standard 15× reflective objective (NA = 0.4). The setup for near infrared frequency range (NIR, 900–1400 nm) included a halogen lamp as a source, CaF 2 beamsplitter, and an MCT detector. To extend the range into the middle infrared wavelength range (MIR 1400–17000 nm) Globar source and KBr beam splitter were used. Polarization of the incident light was controlled by a film polarizer, with experiments conducted at room temperature. Scattering-type scanning near-field optical microscopy Near-field measurements for mid-infrared wavelengths were performed using a NT-MDT NTEGRA nanoIR (NT-MDT, Russia) scanning near-field optical microscope. To excite the modes in that region we used QD5250C2 and QD7500M1 (Thorlabs) quantum cascade lasers operating at 5219 nm and 7824 nm wavelengths, respectively. We used Pt-coated silicon tip oscillating at the resonance frequency of Ω ≈ 185 kHz with an amplitude of \(\:\sim\) 155 nm (NSG10/Pt). For the near-infrared wavelength near-field measurements we used a NeaSNOM (Neaspec GmbH, Germany) s-SNOM. As a source for that wavelength region, a continuous wave Agilent 81600B tunable laser with a tunability range of 1500–1600 nm was used. We also used different Pt/Ir-coated silicon tips oscillating at the resonance frequency of Ω ≈ 280 kHz with an amplitude of ~ 145 nm (ARROW-NCPt-50). For both wavelength regions, microscopes operated in the reflection mode, utilizing the same parabolic mirror for excitation and collection of near-field signals. To enhance the visibility of the near-field images, we minimized the optical background by demodulating the received signal at a high-order harmonic frequency nΩ (where n can be 2, 3, or 4), using an interferometric pseudoheterodyne approach with a reference beam modulated by an oscillating mirror 55 . Here, n = 3 was sufficient to suppress the background. Spectroscopic ellipsometry Ellipsometric measurements were performed via Accurion EP4 (Accurion GmbH) imaging spectral ellipsometer. The samples of PdSe 2 were aligned along their crystalline axes (as determined by Raman and micro-reflectance measurements) in order to eliminate intermixing of s- and p- polarizations, which with an arbitrary sample orientation requires more complex Mueller-matrix analysis. With aligning PdSe 2 flakes along their axes we managed to measure in-plane optical constants along a- and b- axes separately from each other. All of the measurements were carried in a 250–1700 nm wavelength range with 2 nm step in 250–950 nm region and 5 nm step in 950–1700 nm region. Transmission electron microscopy The samples of PdSe 2 in the form of the flake were characterized using a Titan Themis Z transmission electron microscope (ThermoFisherScientific, The Netherlands) allowing us to study the fine structure of samples. 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J Phys D Appl Phys 50:074002 Ocelic N, Huber A, Hillenbrand R (2006) Pseudoheterodyne detection for background-free near-field spectroscopy. Appl Phys Lett 89:101124 Additional Declarations There is NO Competing Interest. Supplementary Files PdSe2SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Nature Communications → 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. 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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-6156048","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":426844148,"identity":"33b63950-7210-4f82-b3e1-c1932128db82","order_by":0,"name":"Valentyn 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Studies","correspondingAuthor":false,"prefix":"","firstName":"Sergey","middleName":"","lastName":"Novikov","suffix":""},{"id":426844172,"identity":"97df3ffa-da49-4d17-a7c6-6f497dad6600","order_by":24,"name":"Andrey Vyshnevyy","email":"","orcid":"","institution":"XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Andrey","middleName":"","lastName":"Vyshnevyy","suffix":""},{"id":426844173,"identity":"9cdcfb94-127b-40f7-abdf-29f45c634799","order_by":25,"name":"Aleksey Arsenin","email":"","orcid":"https://orcid.org/0000-0002-7506-4389","institution":"XPANCEO","correspondingAuthor":false,"prefix":"","firstName":"Aleksey","middleName":"","lastName":"Arsenin","suffix":""},{"id":426844174,"identity":"dcfbe083-c204-4143-8ee5-0d7d46b80076","order_by":26,"name":"Kostya S. Novoselov","email":"","orcid":"https://orcid.org/0000-0003-4972-5371","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Kostya","middleName":"S.","lastName":"Novoselov","suffix":""}],"badges":[],"createdAt":"2025-03-04 16:40:49","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6156048/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6156048/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-64247-8","type":"published","date":"2025-10-16T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":78324582,"identity":"7eb599a2-0059-43cb-9095-780a0afb5cad","added_by":"auto","created_at":"2025-03-12 06:04:37","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":237851,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePdSe\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e anisotropic crystalline structure exploration. a\u003c/strong\u003e, Crystal structure of PdSe\u003csub\u003e2\u003c/sub\u003e along the crystallographic \u003cem\u003ec\u003c/em\u003e-axis (top) and \u003cem\u003ea\u003c/em\u003e-axis (bottom). \u003cstrong\u003eb\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eOptical image of a thin PdSe\u003csub\u003e2\u003c/sub\u003e flake (scale bar, 40 μm). \u003cstrong\u003ec\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eHRTEM image of PdSe\u003csub\u003e2 \u003c/sub\u003eflake. Inset: HAADF image with atomic models within the unit cell (red dashed rectangle). \u003cstrong\u003ed\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eSAED pattern. \u003cstrong\u003ee\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eSEM image of PdSe\u003csub\u003e2\u003c/sub\u003e flake on Si substrate along with EDX mapping of Pd (green), Se (red) and Si (blue) elements. \u003cstrong\u003ef\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eEDX spectrum taken from the area on the flake shown in \u003cstrong\u003ee\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/edaa1da06c780729a43713b4.jpeg"},{"id":78322402,"identity":"d15b6f9c-b1cc-4b39-981e-5fc38007b138","added_by":"auto","created_at":"2025-03-12 05:32:37","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":337837,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOptical properties of PdSe\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. a\u003c/strong\u003e,\u003cstrong\u003eb \u003c/strong\u003eComplex refractive index \u003cem\u003en\u003c/em\u003e+i\u003cem\u003ek\u003c/em\u003e of PdSe\u003csub\u003e2\u003c/sub\u003e in the broad spectral range from 250 nm to 17 μm. The inset in high-\u003cem\u003en\u003c/em\u003e region shows PdSe\u003csub\u003e2\u003c/sub\u003e position among optical materials based on refractive index in optical bandgap energy. The inset in the metallic region represents a plot that marks the onset of free-carrier absorption.\u003cstrong\u003e c\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eThe First Brillouin zone of orthorhombic PdSe\u003csub\u003e2\u003c/sub\u003e. High-symmetry points are marked with black dots. \u003cstrong\u003ed\u003c/strong\u003e, The electronic bandstructure cuts of PdSe\u003csub\u003e2\u003c/sub\u003e. Tabulated optical constants of PdSe\u003csub\u003e2\u003c/sub\u003e are presented in \u003cstrong\u003eSupplementary Note 10,11\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/d0caddda9a5bcbeb41fa3ccc.jpeg"},{"id":78323327,"identity":"8e89378b-e645-40a2-b500-b3a1659bdd51","added_by":"auto","created_at":"2025-03-12 05:40:37","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":308786,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePdSe\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-based mid infrared photodetection. a\u003c/strong\u003e, Optical image and schematic side view (inset) of PdSe\u003csub\u003e2\u003c/sub\u003e photodetector. \u003cstrong\u003eb\u003c/strong\u003e, Spatial mapping of the photocurrent \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e in the biased configuration in the n-n region (\u003cem\u003eV\u003c/em\u003e\u003csub\u003esd\u003c/sub\u003e=100 mV, \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBG\u003c/sub\u003e = 15 V, \u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG1\u003c/sub\u003e = \u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG2\u003c/sub\u003e = 3 V). \u003cstrong\u003ec,d\u003c/strong\u003e, Maps of photocurrent \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e dependence on top gate voltages \u003cem\u003eV\u003c/em\u003e\u003csub\u003etg1\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003etg2\u003c/sub\u003e at source-drain bias voltage \u003cem\u003eV\u003c/em\u003e\u003csub\u003esd\u003c/sub\u003e = 100 mV and back gate voltage \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e = 0 V (\u003cstrong\u003eb\u003c/strong\u003e) and \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e = 15 V (\u003cstrong\u003ec\u003c/strong\u003e).\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/20a0dfbcc0a39f2a3dc0ddc1.jpeg"},{"id":78322408,"identity":"de95c9d5-5bbb-491b-ac27-d167499e7c6b","added_by":"auto","created_at":"2025-03-12 05:32:37","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1101169,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eZero-order transverse magnetic waveguide mode in PdSe\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e flake. a\u003c/strong\u003e,\u003cstrong\u003eb\u003c/strong\u003e, Near-field amplitude map of a PdSe\u003csub\u003e2\u003c/sub\u003e flake at wavelengths of 5219 nm and 7824 nm, respectively. Green curves represent line scans. \u003cstrong\u003ec\u003c/strong\u003e, Fast Fourier transform of the amplitude signal from panels (a) and (b). Green arrows denote observable effective mode indices: air and TM0. \u003cstrong\u003ed\u003c/strong\u003e, Map of reflection amplitude \u003cem\u003er\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e of p-polarized light calculated by the transfer matrix method (TMM) for the PdSe\u003csub\u003e2\u003c/sub\u003e flake and experimental results (green points). \u003cstrong\u003ee\u003c/strong\u003e, Amplitude (Amp(\u003cem\u003eE\u003c/em\u003e)) and phase (Arg(\u003cem\u003eE\u003c/em\u003e)) maps of near-field interference for PdSe\u003csub\u003e2\u003c/sub\u003e flake acquired at different laser wavelengths. \u003cstrong\u003ef\u003c/strong\u003e, Fourier transform of the complex near-field signal taken from (e). Green arrows denote observable effective modes: air and TM\u003csub\u003e0\u003c/sub\u003e. \u003cstrong\u003eg\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eMap of reflection amplitude \u003cem\u003er\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e of p-polarized light calculated by TMM for 255-nm-thick PdSe\u003csub\u003e2\u003c/sub\u003e flake. Green dots show data extracted from the near-field experiments. Inset presents the crosstalk length as a function of the distance between Si(red) and PdSe\u003csub\u003e2\u003c/sub\u003e (green) waveguide cores at a wavelength of 2000 nm.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/e8fa95899231fb88b7b8348a.jpeg"},{"id":78322405,"identity":"5dd616c2-221c-4f84-b95c-1b9e70d3b2ed","added_by":"auto","created_at":"2025-03-12 05:32:37","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":336677,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOptical properties of PdSe\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e nanoparticles. a\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eSchematic representation of femtosecond pulsed laser ablation setup used for the fabrication of PdSe\u003csub\u003e2\u003c/sub\u003e nanoparticles. \u003cstrong\u003eb\u003c/strong\u003e,\u003cstrong\u003ec\u003c/strong\u003e, SEM image of laser-ablated PdSe\u003csub\u003e2 \u003c/sub\u003enanoparticles and their size distribution \u003cstrong\u003ed-f\u003c/strong\u003e, extinction, scattering and absorption spectra of nanoparticles made of PdSe\u003csub\u003e2\u003c/sub\u003e and other popular photonics materials in water, respectively. The inset in panel (d) shows TEM image of the PdSe\u003csub\u003e2\u003c/sub\u003e nanoparticle with \u003cem\u003ed\u003c/em\u003e = 80 nm. The scale bar corresponds to 30 nm. The gray area in panels (a-c) marks NIR-I therapeutic window.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/1015b9e5c3e5b6bf517cf987.jpeg"},{"id":93748192,"identity":"63eb813f-3907-4eb8-bf47-baed982c36ce","added_by":"auto","created_at":"2025-10-17 07:10:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3396741,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/3cbc72a1-b956-479f-9009-7ee6133a03cd.pdf"},{"id":78323329,"identity":"2f29f705-6c37-4747-b8ce-7da0eb7d1f0d","added_by":"auto","created_at":"2025-03-12 05:40:37","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":6494823,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"PdSe2SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6156048/v1/b354944d654cef6843f9af3f.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"All-in-One van der Waals Material for Light Detection, Guiding and Modulation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMaterials properties are crucial for every technology, defining the capabilities and limitations of various devices and techniques\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. In electronics, high conductivity and carrier mobility are in strong demand\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, while in photonics, critical parameters are the high refractive index and low optical losses\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. As a result, numerous groups are constantly searching for artificial and natural materials with record characteristics\u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. However, the greater challenge is finding a material platform with high performance in several fields simultaneously, such as optoelectronics and photonics\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Indeed, optoelectronics requires metals\u003csup\u003e\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, which are undesired in photonics because of their high optical losses in the telecommunication range\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. In contrast, photonics needs high-refractive-index materials with negligible losses, which traditionally include dielectrics\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e not suitable for electronics applications. As a result, a material which combines optoelectronic and photonic utility seems like imaginable but unattainable in reality.\u003c/p\u003e \u003cp\u003eIn this regard, van der Waals (vdW) crystals have emerged as a prospective class of materials with graphene\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, black phosphorus\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, PtSe\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e22,23\u003c/sup\u003e, and WTe\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e24,25\u003c/sup\u003e demonstrating promising metallic response for optoelectronics, whereas MoS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e10,26\u003c/sup\u003e, WS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e5,27\u003c/sup\u003e, hBN\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, GeS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e28\u003c/sup\u003e, SnS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e29\u003c/sup\u003e, ReS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e30\u003c/sup\u003e, and As\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e31\u003c/sup\u003e are semiconductors suitable for modern all-dielectric photonics. However, in practice, it is often required that both properties coexist in a single material. Ideally, it would behave as a metal at giga- and terahertz frequencies for on-chip interconnects, serve as a dielectric for infrared telecom waveguiding, and switch to semiconducting behavior for other applications (like sensing or biomedical). In light of this, palladium diselenide (PdSe\u003csub\u003e2\u003c/sub\u003e) stands out with ever-growing interest in its diverse applications, such as photodetection\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, polarization optics\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, modulation\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e, and biosensing\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, to name a few. However, despite these striking achievements, the broadband optical properties of PdSe\u003csub\u003e2\u003c/sub\u003e are not fully understood\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. Recent research\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e reveals its semiconducting response, while other works\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e report its metallic behavior, which is confusing and hides a horizon of PdSe\u003csub\u003e2\u003c/sub\u003e applications from a clear view. At the same time, the reported controversy of semiconducting and metallic properties positions PdSe\u003csub\u003e2\u003c/sub\u003e as a potential universal platform for both electronics and photonics.\u003c/p\u003e \u003cp\u003eIn this work, we present PdSe\u003csub\u003e2\u003c/sub\u003e as a material capable of fulfilling all these functionalities within a single platform. For this purpose, we performed far- and near-infrared PdSe\u003csub\u003e2\u003c/sub\u003e characterization to resolve its ultrabroadband (250\u0026ndash;17000 nm) optical properties. The results reveal the all-in-one nature of PdSe\u003csub\u003e2\u003c/sub\u003e manifested in three spectral regions. In the first region, from ultraviolet to therapeutic wavelengths, PdSe\u003csub\u003e2\u003c/sub\u003e has a high absorption, which is ideal for photothermal biomedicine. PdSe\u003csub\u003e2\u003c/sub\u003e demonstrates a lossless high refractive index, a perfect combination for light guiding and resonators in the second interval from near-infrared to mid-infrared frequencies. At the same time, from mid-infrared wavelengths, PdSe\u003csub\u003e2\u003c/sub\u003e exhibits a metallic response that is desirable for photodetection. Our first-principle calculations unveil the underlying physics by showing that this material is a semimetal whose conduction and valence bands extrema are shifted in the momentum space thereby prohibiting direct optical transitions. Finally, we experimentally demonstrate PdSe\u003csub\u003e2\u003c/sub\u003e\u0026rsquo;s functionality as a waveguide for integrated photonics, a mid-infrared photodetector, and a photothermal converter, underscoring its significant potential as a universal platform for both nanophotonics and optoelectronic applications.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eCrystal structure and stoichiometry characterization of PdSe\u003csub\u003e2\u003c/sub\u003e flakes\u003c/h2\u003e \u003cp\u003ePalladium diselenide is a layered crystal with an orthorhombic lattice that belongs to the space group Pbca\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. The lattice parameters of PdSe\u003csub\u003e2\u003c/sub\u003e crystal are \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5.73562(30) \u0026Aring;, \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5.8622(3) \u0026Aring;, \u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7.7098(7) \u0026Aring;, \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eβ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eγ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;90\u0026deg;\u003csup\u003e44\u003c/sup\u003e. The unit cell consists of two inverted layers stacked along the \u003cem\u003ec\u003c/em\u003e-axis held by weak vdW forces. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, each Pd atom within the layer is surrounded by four Se atoms, forming an arrangement of square-planar-like PdSe\u003csub\u003e4\u003c/sub\u003e units linked by a shared selenium atom and two connected selenium atoms from different squares\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. The resulting pattern represents periodic counter-directional atomic chains aligned along the \u003cem\u003ea\u003c/em\u003e-axis.\u003c/p\u003e \u003cp\u003eThe weak vdW forces facilitates exfoliation into thin flakes (see Methods and the inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). To verify the crystal quality of PdSe₂ flakes we exfoliated and transferred them onto a porous SiNₓ membrane and characterized their structure using scanning transmission electron microscopy (STEM) methods. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec shows high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field (HAADF) images. These images correspond well with the [001] crystallographic facet of the PdSe₂ crystal, depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. Schematic Pd and Se atoms of the palladium diselenide crystal are overlaid on the HAADF image with gray and green dots, respectively. As a result, the observed lattice spacings correspond to the known crystallographic planes, confirming that the exfoliated flakes retain the bulk crystal structure. The homogeneous quality of the PdSe₂ flakes is evidenced by the selected area electron diffraction (SAED) pattern obtained from the same flake (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and \u003cb\u003eSupplementary Note 1\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eWe also validated the chemical composition of PdSe\u003csub\u003e2\u003c/sub\u003e flakes via scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee represents SEM image of thick PdSe\u003csub\u003e2\u003c/sub\u003e flake transferred onto Si substrate and corresponding EDX maps of Pd, Se and Si elements confirming the uniform distribution of Pd and Se atoms in the flake. The Pd:Se atomic ratio matched well with the stoichiometry of PdSe\u003csub\u003e2\u003c/sub\u003e, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eAll-in-one optical properties of PdSe\u003c/h3\u003e\n\u003cp\u003eThe dielectric permittivity tensor of the crystals with an orthorhombic lattice is defined by three complex refractive indices \u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e\u003c/sub\u003e + \u003cem\u003eik\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003ej\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003ea\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e, \u003cem\u003ec\u003c/em\u003e associated with respective crystallographic axes \u003cem\u003ea\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e and \u003cem\u003ec\u003c/em\u003e. To obtain these complex refractive indices, we identify the principal optical axes of PdSe\u003csub\u003e2\u003c/sub\u003e flakes via polarized Raman and micro-reflectance spectroscopies (\u003cb\u003eSupplementary Note 2,3\u003c/b\u003e). Next, we measured ellipsometry and micro-reflectance along optical axes to determine the anisotropic optical properties of PdSe\u003csub\u003e2\u003c/sub\u003e over an ultra-wide spectral range from 250 to 17000 nm (see \u003cb\u003eMethods\u003c/b\u003e). The resulting refractive indices and extinction coefficients are collected in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b (for details of spectra fitting see \u003cb\u003eSupplementary Note 4\u003c/b\u003e). Interestingly, for wavelengths above 1500 nm, optical losses of PdSe\u003csub\u003e2\u003c/sub\u003e remain low, whereas, above 8000 nm, losses increase following the Drude behavior (see inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). These findings indicate a transition in the optical behavior of PdSe\u003csub\u003e2\u003c/sub\u003e with the increase in wavelength. The low losses for the near-infrared wavelengths are a sign of dielectric response. In contrast, the onset of significant losses around 8000 nm implies a metallic behavior and reflects the increased free-carrier contributions in optical absorption.\u003c/p\u003e \u003cp\u003eIn general, we can highlight three regions of PdSe\u003csub\u003e2\u003c/sub\u003e optical response: (i) from 250 to around 1500 nm, it behaves as a strongly absorbing semiconductor with a high extinction coefficient (high-\u003cem\u003ek\u003c/em\u003e); (ii) from 1500 to around 8000 nm it complements the family of high refractive index materials (high-\u003cem\u003en\u003c/em\u003e), as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb; (iii) at long wavelengths above 8000 nm it shows metallic optical response (see inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eAb initio calculations explain the physics behind these unique optical properties of PdSe\u003csub\u003e2\u003c/sub\u003e. From the bandstructure in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec-d, one can notice that this material is a conventional semimetal. As a result, in PdSe\u003csub\u003e2\u003c/sub\u003e, unlike Weyl, Dirac, and nodal line semimetals often met among vdW materials, the momentum selection rule prohibits direct optical transitions between the conduction and valence bands. Hence, the optical absorption above 8000 nm originates from free carriers, whose density is about 5\u0026sdot;10\u003csup\u003e19\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e at room temperature (\u003cb\u003eSupplementary Note 5\u003c/b\u003e). This value translates into the plasma frequency of 0.43 eV which is close to experimental Drude oscillator fit of 0.37 eV from optical constants in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b (see \u003cb\u003eSupplementary Note 4\u003c/b\u003e for details). Alternatively, PdSe\u003csub\u003e2\u003c/sub\u003e film can be synthesized in a chemically doped state with a much more pronounced Drude response (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b). According to our calculations, if the Fermi level is shifted (as, for instance, by gating) by 0.1 eV \u0026ndash; it may result in an order of magnitude increase in a free carrier density. From an application standpoint, gate-tunable properties show great promise for light modulation in integrated photonics and imaging beyond the already demonstrated photodetection. Furthermore, a well-defined transparency region of PdSe\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b) separating free carriers and interband absorption bands makes it suitable for lossless integrated nanophotonics, which was previously considered impossible for metals and semimetals.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eLight detection based on metallic optical response of PdSe\u003c/h3\u003e\n\u003cp\u003eIn order to confirm our conclusions from Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b, we demonstrate applications for all three regions. We commence from mid-infrared wavelengths above 8000 nm, where PdSe\u003csub\u003e2\u003c/sub\u003e optical response is determined by free carrier absorption as in metals. This behavior allows for the detection of mid-infrared radiation. To this end, we fabricated a PdSe\u003csub\u003e2\u003c/sub\u003e-based photodetector, presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, to study PdSe\u003csub\u003e2\u003c/sub\u003e detection capabilities. In our device, extra control over the optical and electronic properties of PdSe\u003csub\u003e2\u003c/sub\u003e is achieved via electrostatic gating. The silicon substrate acts as a global back gate, tuning the overall carrier density in the sample via the back gate voltage \u003cem\u003eV\u003c/em\u003e\u003csub\u003ebg\u003c/sub\u003e. Additionally, we placed a transparent top gate made of 4-layer graphite atop the channel. The graphite layer was split into two sections by a 200 nm gap. As a result, independent gate biases \u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG1\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG2\u003c/sub\u003e were applied to the split sections, enabling an all-electric induction of p-n junctions. Interestingly, we have not observed any significant zero-bias photocurrent upon application of opposite voltages to the split top gate, corresponding to the p-n junction formation (Supplementary Fig.\u0026nbsp;12). At the same time, even for a small source-drain bias \u003cem\u003eV\u003c/em\u003e\u003csub\u003eSD\u003c/sub\u003e = 100 mV, the device demonstrates a significant photocurrent of up to 450 pA, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. Further recording of the photocurrent upon scanning the top gate voltages reveals an intriguing pattern, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. Indeed, the current has maximum values for the overall n-doping of the sample and demonstrates small values in all other cases corresponding to the formation of p-n, n-p, and p-p junctions along the PdSe\u003csub\u003e2\u003c/sub\u003e channel. The minimum is observed at the neutrality point of the sections under either of the gates, corresponding to the white cross in the photocurrent map. Moreover, the photocurrent magnitude grows when an overall positive voltage \u003cem\u003eV\u003c/em\u003e\u003csub\u003eBG\u003c/sub\u003e = 15 V is applied to the back gate and enhances the n-doping (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The observed dependences are in stark contrast to the photocurrent observed in two-dimensional (2D) photodetectors exploiting the photo-thermoelectric and interband photovoltaic effects, where a clear zero-bias current is maximized for the opposite doping of two channel sections\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eWe suggest that it is the bolometric effect, which most likely governs the detection physics in the present case, i.e., the change in PdSe\u003csub\u003e2\u003c/sub\u003e bulk resistance upon intraband radiation absorption and subsequent heating. In order to demonstrate this, we assume that the device resistance \u003cem\u003eR\u003c/em\u003e is composed of junctions (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eJ\u003c/sub\u003e) and bulk (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e) connected in series. The former depends on the relative polarity of doping, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eJ\u003c/sub\u003e(\u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG1\u003c/sub\u003e,\u003cem\u003eV\u003c/em\u003e\u003csub\u003eTG2\u003c/sub\u003e), and is maximized for the opposite polarity. The latter depends on the temperature as in conventional metals \u003cem\u003eR\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e = \u003cem\u003eR\u003c/em\u003e\u003csub\u003eB0\u003c/sub\u003e(1\u0026thinsp;+\u0026thinsp;\u003cem\u003eαT\u003c/em\u003e). Denoting the radiation-induced heating as \u003cem\u003eΔT\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e, we arrive at the photocurrent \u003cem\u003eI\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e = \u003cem\u003eR\u003c/em\u003e\u003csub\u003eB0\u003c/sub\u003e\u003cem\u003eαΔT\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e\u003cem\u003eV\u003c/em\u003e\u003csub\u003esd\u003c/sub\u003e/(\u003cem\u003eR\u003c/em\u003e\u003csub\u003eJ\u003c/sub\u003e+\u003cem\u003eR\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e)\u003csup\u003e2\u003c/sup\u003e. The latter explains the enhancement of photocurrent with overall uniform doping that leads to reduced total resistance (see \u003cb\u003eSupplementary Note 6\u003c/b\u003e for resistance maps corresponding to the doping conditions of Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec-d). Finally, the weak sensitivity of radiation-induced heating Δ\u003cem\u003eT\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e to the doping is characteristic of the intraband metallic absorption, not the interband electron-hole generation. In detail, the energy balance between radiation absorption and carrier cooling due to substrate coupling reads as \u003cem\u003eσ\u003c/em\u003e\u0026rsquo;\u003cem\u003eE\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003eΔ\u003cem\u003eT\u003c/em\u003e\u003csub\u003eph\u003c/sub\u003e/\u003cem\u003eτ\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e, where \u003cem\u003eσ\u003c/em\u003e\u0026rsquo; is the real part of material conductivity at the infrared wavelength, \u003cem\u003eE\u003c/em\u003e is the strength of incident electric field, \u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e is the heat capacitance of charge carriers per unit volume, and \u003cem\u003eτ\u003c/em\u003e\u003csub\u003eE\u003c/sub\u003e is the energy relaxation time (characteristic time of substrate phonon emission). \u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e is proportional to the density of charge carriers, and so is σ\u0026rsquo; in the case of metallic Drude absorption. As a result, photo-induced heating in the metallic case depends very weakly on gate-controlled carrier density. Therefore, our detected photoresponse in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec-d unambiguously validates the metallic optical response of PdSe\u003csub\u003e2\u003c/sub\u003e, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eLight guiding based on high refractive index of PdSe\u003c/h3\u003e\n\u003cp\u003eLossless high-\u003cem\u003en\u003c/em\u003e optical properties of PdSe\u003csub\u003e2\u003c/sub\u003e within a broad spectral range of around 1500\u0026ndash;8000 nm make it attractive for photonic applications. This characteristic enables efficient light confinement, an excellent property for light guiding. To this end we performed near-field measurements of PdSe\u003csub\u003e2\u003c/sub\u003e for the long-wavelength border of the high-\u003cem\u003en\u003c/em\u003e spectral range (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Figures\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-b show the measured near-field amplitude of a 1.12-\u0026micro;m-thick PdSe\u003csub\u003e2\u003c/sub\u003e flake excited at 5219 nm and 7824 nm wavelengths. From them, we found the effective index of fundamental transverse magnetic (TM\u003csub\u003e0\u003c/sub\u003e) mode (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), which perfectly matches the transfer matrix method (TMM) calculations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) based on optical constants in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b.\u003c/p\u003e \u003cp\u003eThen, we focus on the short-wavelength border of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, which includes the telecommunication band. For this, we conduct near-field measurements of planar, 255-nm-thick PdSe\u003csub\u003e2\u003c/sub\u003e waveguides in the near-infrared wavelength region (1500\u0026ndash;1600 nm). Despite the appearance of absorption due to interband optical transitions of PdSe\u003csub\u003e2\u003c/sub\u003e, which limit the propagation distance to around 40 \u0026micro;m in this wavelength region, the waveguide mode is visible (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee-f) and shows the perfect agreement with the mode dispersion calculated by TMM (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). For more details on the s-SNOM data processing see \u003cb\u003eSupplementary Note 7,8\u003c/b\u003e. Notably, the optical losses diminish significantly with the wavelength increase. At 2000 nm, the waveguide mode propagation distance reaches more than 1 mm length, sufficient for use in photonic integrated circuits. With this application in mind, we estimate the integration density of the ultrathin PdSe\u003csub\u003e2\u003c/sub\u003e waveguide with SiO\u003csub\u003e2\u003c/sub\u003e cladding for 2000 nm wavelength (the inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). Our calculations show that PdSe\u003csub\u003e2\u003c/sub\u003e allows a 25% higher integration density than similar Si waveguides for a target crosstalk length of around 1 mm. These findings underscore PdSe\u003csub\u003e2\u003c/sub\u003e potential for waveguide applications that enhance optical communication systems.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eLight absorption based on high extinction of PdSe\u003c/h3\u003e\n\u003cp\u003eAbove the optical bandgap in the high-\u003cem\u003ek\u003c/em\u003e region of Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b, PdSe\u003csub\u003e2\u003c/sub\u003e strongly absorbs light. In combination with the high refractive index, it is advantageous for photothermal applications since the conversion of absorbed light into heat is greatly improved thanks to photonic resonances, such as Mie resonances in nanospheres. To demonstrate this application, we adopted the femtosecond laser ablation\u003csup\u003e\u003cspan additionalcitationids=\"CR49\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) to synthesize PdSe\u003csub\u003e2\u003c/sub\u003e nanospheres (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) with a broad diameter distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). For photothermal therapy, smaller nanoparticles are preferred because they are safer for biological systems since reaching target organs and leaving the organism after the therapy is easier for smaller nanostructures. Accordingly, we calculated the extinction (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed), scattering (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee), and absorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef) spectra of PdSe\u003csub\u003e2\u003c/sub\u003e nanoparticles with 80 nm diameter (which were indeed successfully fabricated in abundance in our experiments, see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and the inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). For fabrication and calculation details see \u003cb\u003eSupplementary Note 9\u003c/b\u003e. Surprisingly, PdSe\u003csub\u003e2\u003c/sub\u003e has the best photothermal conversion efficiency compared to traditionally used gold\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e, silicon\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, and MoS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e53\u003c/sup\u003e within the NIR-I (700\u0026ndash;980 nm) therapeutic window, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef. Hence, PdSe\u003csub\u003e2\u003c/sub\u003e optical properties in the high-\u003cem\u003ek\u003c/em\u003e spectral range in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-b are promising for photothermal medicine.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eCurrent multifunctional devices are based on several materials platforms, which always pose a complex integration task. In this regard, PdSe\u003csub\u003e2\u003c/sub\u003e offers a universal solution with semiconducting, dielectric, and metallic properties depending on the spectral range. In particular, PdSe\u003csub\u003e2\u003c/sub\u003e exhibits a strong excitonic absorption at short wavelengths, switches to high refractive index dielectric as wavelength grows, and finally transforms to metal with free carrier absorption. This all-in-one nature of PdSe\u003csub\u003e2\u003c/sub\u003e makes it suitable for seemingly contradictory applications in optoelectronics and nanophotonics. Thus, we have demonstrated the multifaceted functionality of PdSe\u003csub\u003e2\u003c/sub\u003e as a waveguide for integrated photonics, a mid-infrared photodetector, and a photothermal converter for biomedical theranostics. In addition, we note the high tunability of \u003cem\u003ebulk\u003c/em\u003e PdSe\u003csub\u003e2\u003c/sub\u003e optoelectronic properties by gating, which unlocks yet unexplored applications of PdSe\u003csub\u003e2\u003c/sub\u003e for light modulation. Our findings establish a paradigm shift by introducing a universal material, which challenges photonic and optoelectronic device design fundamentals.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eSample preparation.\u003c/b\u003e PdSe\u003csub\u003e2\u003c/sub\u003e crystal was purchased from 2D Semiconductors (Scottsdale, USA). Thin flakes were mechanically exfoliated via scotch-tapes from Nitto Denko Corporation (Osaka, Japan) and then were transferred on top of Si, Si/SiO\u003csub\u003e2\u003c/sub\u003e, CaF\u003csub\u003e2\u003c/sub\u003e substrates. The substrates were sequentially sonicated in acetone, isopropanol and deionized water and treated in air plasma to remove natural absorbents. Next, tape with crystals was glued to the substrate and heated up to 100\u0026deg;C. Then the tape was removed, leaving microcrystals on the surface. The thicknesses of the PdSe\u003csub\u003e2\u003c/sub\u003e flakes were accurately measured by an atomic-force microscope (NT-MDT Ntegra II) in contact mode at ambient conditions. Silicon tips (ETALON HA_FM TipsNano) with a tip curvature radius of \u0026lt;\u0026thinsp;10 nm, a force constant of 6 N\u0026sdot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a resonant frequency of 114 kHz were used during all measurements.\u003c/p\u003e \u003cp\u003e \u003cb\u003eAngle-resolved micro-reflectance.\u003c/b\u003e Polarization-resolved reflectance map was measured in the 550\u0026ndash;900 nm range on a trinocular microscope RX50M modified by a polarizer and an analyzer\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e. One of the oculars was adapted to a splitted system of a camera (SIMAGIS TC-3CU) and a spectrometer (Optosky ATP5020P) which was connected by fiber (Thorlabs M92L02) with core diameter 200 \u0026micro;m. The reflected light was collected from a spot of \u0026lt;\u0026thinsp;20 \u0026micro;m using an objective with \u0026times;50 magnification and numerical aperture N.A. = 0.8 (SOPTOP MPlanFL). For polarization-resolved infrared spectroscopy, a Fourier transform infrared spectrometer (Bruker Vertex 80v) equipped with a Hyperion 2000 microscope was employed. Normal incidence reflection measurements on the face of the flakes were performed using a standard 15\u0026times; reflective objective (NA\u0026thinsp;=\u0026thinsp;0.4). The setup for near infrared frequency range (NIR, 900\u0026ndash;1400 nm) included a halogen lamp as a source, CaF\u003csub\u003e2\u003c/sub\u003e beamsplitter, and an MCT detector. To extend the range into the middle infrared wavelength range (MIR 1400\u0026ndash;17000 nm) Globar source and KBr beam splitter were used. Polarization of the incident light was controlled by a film polarizer, with experiments conducted at room temperature.\u003c/p\u003e\n\u003ch3\u003eScattering-type scanning near-field optical microscopy\u003c/h3\u003e\n\u003cp\u003eNear-field measurements for mid-infrared wavelengths were performed using a NT-MDT NTEGRA nanoIR (NT-MDT, Russia) scanning near-field optical microscope. To excite the modes in that region we used QD5250C2 and QD7500M1 (Thorlabs) quantum cascade lasers operating at 5219 nm and 7824 nm wavelengths, respectively. We used Pt-coated silicon tip oscillating at the resonance frequency of \u003cem\u003eΩ\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;185 kHz with an amplitude of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sim\\)\u003c/span\u003e\u003c/span\u003e155 nm (NSG10/Pt). For the near-infrared wavelength near-field measurements we used a NeaSNOM (Neaspec GmbH, Germany) s-SNOM. As a source for that wavelength region, a continuous wave Agilent 81600B tunable laser with a tunability range of 1500\u0026ndash;1600 nm was used. We also used different Pt/Ir-coated silicon tips oscillating at the resonance frequency of \u003cem\u003eΩ\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;280 kHz with an amplitude of ~\u0026thinsp;145 nm (ARROW-NCPt-50). For both wavelength regions, microscopes operated in the reflection mode, utilizing the same parabolic mirror for excitation and collection of near-field signals. To enhance the visibility of the near-field images, we minimized the optical background by demodulating the received signal at a high-order harmonic frequency nΩ (where n can be 2, 3, or 4), using an interferometric pseudoheterodyne approach with a reference beam modulated by an oscillating mirror\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. Here, n\u0026thinsp;=\u0026thinsp;3 was sufficient to suppress the background.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSpectroscopic ellipsometry\u003c/h2\u003e \u003cp\u003eEllipsometric measurements were performed via Accurion EP4 (Accurion GmbH) imaging spectral ellipsometer. The samples of PdSe\u003csub\u003e2\u003c/sub\u003e were aligned along their crystalline axes (as determined by Raman and micro-reflectance measurements) in order to eliminate intermixing of s- and p- polarizations, which with an arbitrary sample orientation requires more complex Mueller-matrix analysis. With aligning PdSe\u003csub\u003e2\u003c/sub\u003e flakes along their axes we managed to measure in-plane optical constants along a- and b- axes separately from each other. All of the measurements were carried in a 250\u0026ndash;1700 nm wavelength range with 2 nm step in 250\u0026ndash;950 nm region and 5 nm step in 950\u0026ndash;1700 nm region.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eTransmission electron microscopy\u003c/h2\u003e \u003cp\u003eThe samples of PdSe\u003csub\u003e2\u003c/sub\u003e in the form of the flake were characterized using a Titan Themis Z transmission electron microscope (ThermoFisherScientific, The Netherlands) allowing us to study the fine structure of samples. The Titan Themis Z microscope is equipped with a sample corrector to correct spherical aberrations, which significantly improves the resolution of the microscope. The resolution in transmission mode is 120 pm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eEnergy dispersive X-ray spectroscopy analysis\u003c/h2\u003e \u003cp\u003eThe stoichiometry of the PdSe\u003csub\u003e2\u003c/sub\u003e crystal flakes was precisely verified by an energy dispersive X-ray spectroscopy (EDX) using EDX spectrometer (Bruker QUANTAX EDX) integrated with a scanning electron microscope (SEM, JEOL JSM-7001F) working in secondary electron imaging mode.\u003c/p\u003e \u003c/div\u003e "},{"header":"Declarations","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eData Availability\u003c/h2\u003e \u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e \u003c/div\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMerchant A et al (2023) Scaling deep learning for materials discovery. 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Appl Phys Lett 89:101124\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":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"palladium diselenide, high refractive index, in-plane anisotropy, optical constants, integrated photonics, infrared, conventional semimetal","lastPublishedDoi":"10.21203/rs.3.rs-6156048/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6156048/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eModern optoelectronic devices demand materials that can perform multiple, often conflicting functions, such as acting as metals for interconnects, dielectrics for waveguides, and semiconductors for light emission and detection. The integration of these materials is challenging, slowing industry progress and increasing costs. It inspired an intensive search for a universal optoelectronic response within a single material. Here, we reveal that palladium diselenide (PdSe\u003csub\u003e2\u003c/sub\u003e) provides an answer to this quest owing to its unique bandstructure. It exhibits a semimetallic band structure with an unusually large bandgap for interband transitions responsible for semiconductor-metallic nature. This duality enables PdSe\u003csub\u003e2\u003c/sub\u003e to function as both a photodetector and a waveguide, integrating two traditionally incompatible responses. As a result, our findings provide a full picture of PdSe\u003csub\u003e2\u003c/sub\u003e optoelectronic properties, paving the way for its use in multifunctional optoelectronic applications in one material.\u003c/p\u003e","manuscriptTitle":"All-in-One van der Waals Material for Light Detection, Guiding and Modulation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-12 05:32:32","doi":"10.21203/rs.3.rs-6156048/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"db603043-716d-4d9c-8abe-8873f3f3025b","owner":[],"postedDate":"March 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":45480571,"name":"Physical sciences/Materials science/Condensed-matter physics/Electronic properties and materials"},{"id":45480572,"name":"Physical sciences/Optics and photonics/Optical techniques/Optical spectroscopy"}],"tags":[],"updatedAt":"2025-10-17T07:09:59+00:00","versionOfRecord":{"articleIdentity":"rs-6156048","link":"https://doi.org/10.1038/s41467-025-64247-8","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-10-16 04:00:00","publishedOnDateReadable":"October 16th, 2025"},"versionCreatedAt":"2025-03-12 05:32:32","video":"","vorDoi":"10.1038/s41467-025-64247-8","vorDoiUrl":"https://doi.org/10.1038/s41467-025-64247-8","workflowStages":[]},"version":"v1","identity":"rs-6156048","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6156048","identity":"rs-6156048","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}