Ultrasensitive piezoelectric sensor based on two-dimensional Na2Cl crystals with periodic atom vacancies

Ultrasensitive piezoelectric sensor based on two-dimensional Na2Cl crystals with periodic atom vacancies | 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 Physical Sciences - Article Ultrasensitive piezoelectric sensor based on two-dimensional Na 2 Cl crystals with periodic atom vacancies Liang Chen, Tao Wang, Yan Fan, Jie Jiang, Yangyang Zhang, Yingying Huang, and 12 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4170610/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Pursuing ultrasensitivity in pressure sensors that offer precise mechano-electric transduction of tiny mechanical stimuli under complex ambient conditions, is of great importance and has been a long-standing goal 1-10 . The introduction of microstructures at micro- and nano-scale, can effectively improve the sensitivity, detection limit, and pressure-response range due to their structural asymmetries and compressibility 5,6,11-19 . However, numerous atom vacancies anticipated in sensors that are expected to exhibit giant asymmetries may make it difficult to maintain stability under ambient conditions. Here, we report a piezoelectric sensor that exhibits supreme pressure-sensing performance, including a peak sensitivity up to 3.5×10 6 kPa −1 in the pressure range of 1-100 mPa and a detection limit of less than 1 mPa, superior to the current state-of-the-art pressure sensors. These properties are attributed to the high percentage of periodic atom vacancies in the two-dimensional Na 2 Cl crystals formed within multilayered graphene oxide membrane in the sensor, which provides giant polarization with high stability. The sensor can even clearly detect the airflow fluctuations surrounding a flapping butterfly, which have long been the elusive tiny signals mentioned in the famous “butterfly effect”. The finding represents a step towards next-generation pressure sensors for various precision applications. Physical sciences/Nanoscience and technology/Nanoscale materials/Two-dimensional materials Physical sciences/Nanoscience and technology/Nanoscale devices/Sensors Figures Figure 1 Figure 2 Figure 3 Figure 4 Full Text Microstructures at the micro- or nano-scale, introduced in pressure sensors, exhibit an inextricable link with the promotion of sensitivity and detection limit for pressure sensors due to their asymmetries and compressibility 5,6,11-19 . The microstructures at the micro-scale with high asymmetry can effectively improve sensitivity, including micro-pyramid arrays 5,6,20-22 , wrinkles 23 , micro-domes 24,25 , micro-pillar arrays 11 , and micro-protrusions 26 , as well as other assembly patterns 12-15,27-29 . More precisely, asymmetrical nano-structures and heterogeneities 16-18,30-33 are recognized to play a key role in significantly promoting the mechano-electric transduction of various stimuli. At the smallest atom-scale, the microstructures, with atom vacancies induced by a strong electric field 19 , have exhibited very large piezoelectric sensitivities. Despite extensive exploration and advances, it remains difficult to achieve expected atom vacancies exhibiting large structural asymmetry while maintaining structural compressibility and stability under ambient conditions. This is the limitation and challenge of pressure sensors for achieving more excellent pressure-sensing performance. Here, we present a piezoelectric sensor with supreme pressure-sensing performance in the sensitivity and detection limit, based on a high percentage of atom vacancies in the unique two-dimensional (2D) Na 2 Cl crystals within multilayered graphene oxide (GO) membrane. Different from the ordinary NaCl crystal, the 2D Na 2 Cl crystal has a Na:Cl atom ratio of 2:1 and contains atom vacancies where Cl atoms should be located. The atom vacancies result in a very high piezoelectric coefficient of the membrane. The periodic arrangement of these atom vacancies ensures the structural stability. Remarkably, the sensor is capable of detecting signals as low as 1 mPa (corresponding to a 25 nanonewton force), together with excellent mechanical stability. The small size, fast response, and self-powered capability of the sensor make it particularly suitable for use in biological systems and complex environments. In addition, the application scope of the sensor can be greatly extended to encompass the detection of other tiny signals including electrical, magnetic, optical, and thermal signals, by converting these signals into mechanical forces. The membranes of piezoelectric sensors were prepared from a graphene oxide (GO) suspension and dilute NaCl solution via the spray-coating method (see Methods). Explicitly, the GO suspension (20 μL, 5 mg/mL) was sprayed on a polyethylene glycol terephthalate (PET) substrate, followed by drying at 60°C for 6 hours. The prepared GO membrane was then drop-cast with dilute NaCl solution (0.01 mol/L) and exposed to the air for 2 hours. Next, the GO suspension was sprayed on the membrane again and dried at 60°C for another 6 hours, to form multilayered GO membrane containing sodium and chloride ions, which are denoted as Na–Cl@GO membrane. Different from GO membranes directly immersed in NaCl solutions in our previous work 34 , this spay-coating method creates up-down asymmetry in the distribution of Na and Cl ions in the membrane. These membranes, having a thickness of ~5 μm, were removed from the substrate and cut into ~5 × 5 mm 2 sections. Then, they were made into sensor devices with a platinum (Pt) film coating to serve as conductive electrode and encapsulated with insulation PI film (Fig. 1a). The sensor exhibits supreme sensitivity for pressure sensing in the low-pressure range of 1-100 mPa. An acoustic pressure below 100 mPa was generated with the acoustic excitation of a tuning fork with a frequency of ~260 Hz. The acoustic pressure ( P ) of the acoustic excitation was monitored using an acoustic tester (UMM-6, Dayton Audio). The voltage response of the sensor ( U ) to changes in the acoustic pressure was simultaneously monitored by a digital lock-in amplifier (HF2LI, Zurich Instruments) with a sampling frequency of 10 kHz (Fig. 1c). A good correlation between the voltage output of the sensor and the acoustic pressure is shown. The sensitivity S of the piezoelectric sensor is typically defined as S = δ(( U - U 0 )/ U 0 )/δ p 35 , where U 0 = 0.1 mV is the initial voltage of the sensor without pressure, and U is the voltage response under the applied pressure p . The peak sensitivity reaches 3.5×10 6 kPa -1 (Fig. 1e), which is approximately one order of magnitude larger than the highest sensitivity of 3.8×10 5 kPa -1 36 obtained from the current state-of-the-art pressure sensors. Importantly, at pressure of 1 mPa or even lower, the sensor still exhibits a clear decay in the voltage response, indicating that the sensor can effectively detect pressure variations of 1 mPa or less (Fig. 1d). This value is lower than the lowest pressure detection limit of recently reported pressure sensors, 2 mPa 3 . The sensor thereby demonstrates supreme pressure-sensing performance in terms of sensitivity and pressure detection limit, superior to the state-of-the-art pressure sensors reported so far (Fig. 1b). Moreover, based on the pressure detection limit of 1 mPa and the sensor size of ~5 × 5 mm 2 , the sensor is capable of detecting tiny force as low as 25 nanonewtons. We attribute the observed piezoelectric behaviors to the 2D Na 2 Cl crystals within GO membrane in the sensor. This Na 2 Cl crystal was discovered in our previous work 34 , originating from the ion–π interactions 37 between the ions and the π-conjugated system in the graphitic surface 38-40 . Different from the ordinary NaCl crystal, the 2D Na 2 Cl crystal has a Na:Cl atom ratio of 2:1 and contains atom vacancies where Cl atoms should be located (Fig. 2c); here, we refer to these anion vacancies as “ghost atoms”. These Cl atom vacancies in the crystal lead to very high asymmetry, while their periodic arrangement in the crystal ensures the structural stability. The existence of 2D Na 2 Cl crystals in the sensor was confirmed by transmission electron microscopy (TEM) experiments. The high-resolution TEM image shows a square structure with a lattice spacing of 3.96 ± 0.03 Å (Fig. 2a). The enlarged image overlays well with the Na 2 Cl structure in our previous work 34 , as shown by the inset in Fig. 2a, in which the Na and Cl atoms are shown as blue and green spheres, respectively. The dark-field TEM images demonstrate that the Na:Cl ratio is approximately 2:1 (Fig. 2b and Supplementary Fig. 4). We then performed density functional theory (DFT) computations to illustrate the underlying physics. The structure of the 2D Na 2 Cl crystal based on the graphene surface (Na 2 Cl@graphene) is shown in Fig. 2c and 2d. Here, the graphene surface is considered as the part of GO membrane without functional groups. The electric polarization direction from Na 2 Cl layer to graphene layer is shown in the line profile of the interfacial differential charge densities (DCD, a measure of charge variation at the interface)) in the out-of-plane direction (Fig. 2e). By analyzing the Bader charges of the atoms, a very large spontaneous out-of-plane polarization (P 0 ), serving as one of crucial parameters for piezoelectric materials 17,41 , was obtained for the Na 2 Cl@graphene, namely, P 0 = 39.0 pC/m (see Supplementary Note 2). This value is nearly two orders of magnitude larger than the out-of-plane polarization of 0.6 pC/m for MoS 2 /WS 2 18 . The induced mechanical deformation of Na 2 Cl@graphene under external pressure was then investigated by varying the distance between the Na atom in the upper layer of the Na 2 Cl crystal and the graphene surface using DFT simulations. Fig. 2f clearly shows that in the out-of-plane direction, the average displacement ( h 1 ) between the Na atom in the upper layer of the Na 2 Cl crystal and the atom vacancy in the bottom layer of the Na 2 Cl crystal is much larger than the average displacement ( h 2 ) between the Cl atom in the upper layer of the Na 2 Cl crystal and the Na atom in the bottom layer of the Na 2 Cl crystal under stress. In contrast, along the in-plane direction, the distances between adjacent atoms ( d x and d y ) in each layer remain approximately constant. These results indicate that the atom vacancies make the Na 2 Cl crystal susceptible to deformation along the direction of applied stress, while maintaining structural stability. The very large intrinsic polarization suggests an extraordinarily large piezoelectric coefficient in the sensor 42 . According to the stress-output charge relation from the acoustic excitation of the tuning fork (Fig. 2g), we experimentally obtained a piezoelectric coefficient ( d 33 ) up to 6.8×10 5 pC/N in the range of 0.025–2 μN (corresponding to the pressure range of 1–80 mPa). This value is larger than the d 33 of ~2×10 5 pC/N in cubic fluorite gadolinium-doped CeO 2-x films obtained by rearranging oxygen vacancies under very large electric fields at millihertz frequencies 19 . The famous butterfly effect, a metaphor for chaos theory that posits “Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?” 43 , reflects sensitive dependence on an initial condition, with extremely small signals leading to extraordinarily large responses. To our knowledge, the airflow variation caused by a flapping butterfly has not been well measured because the variation is quite small 44 . Using the presented sensor, the open-circuit voltage response to the airflow variation at a 5 cm distance from a flapping butterfly was obtained, and the movement of the butterfly and the real-time motoring of voltage response were shown in the movies (Supplementary Video 1). The corresponding pressure variations above, on the side of, and below the butterfly were ~3.9 mPa, ~6.8 mPa, and ~14.7 mPa, respectively (Fig. 3b and Supplementary Fig. 12b), calculated by the conversion relation between the pressure and voltage response (Supplementary Note 9). The pressure variations of 2 mPa or even lower can be clearly distinguished by the sensor (Fig. 3b). These variations in the airflow pressures are extremely small, only approximately one millionth of the airflow pressure caused by a tornado. A wing-beat frequency of ~5 Hz was obtained (Supplementary Fig. 12c), which is consistent with the results from other studies on flapping frequency 44 . The sensor also exhibits a very high sensitivity in the high-pressure range. We used a force gauge (Mark-10, FS05) to produce a series of mechanical loads in the pressure range of 0.1 to 100 kPa. The voltage response of the sensor was measured using an electrochemical workstation (CHI760E) (Supplementary Fig. 6a). The output voltage shows a cyclic and step-like response, which increases from ~0.06 V to ~0.80 V and is well correlated with the applied mechanical load (Supplementary Fig. 6a). The sensitivity of the sensor was then calculated. The sensitivity decreases from 2.0×10 4 kPa -1 to 1.2×10 2 kPa -1 when the applied pressure is varied in the range of 0.1–100 kPa (Supplementary Fig. 6b). In addition, the sensor has excellent mechanical stability and a fast response. The peak voltage due to a mechanical pressure of 80 kPa decreases by less than 3% when the sensor is subjected to over 10000 cycles of loading and unloading (Fig. 4a). A response time ( τ r ) of 1 μs and recovery time ( τ d ) of 238 ms were obtained using an oscilloscope (Tektronix, MSO44 4-BW-200) (Fig. 4b). The detected response time of 1 μs is actually the limit of our measurement set-up instead of the intrinsic limit of the sensor. The excellent mechanical stability and fast response ensure its application in the area of sensitive pressure sensing. In summary, we developed an ultrasensitive piezoelectric sensor made of multilayered Na 2 Cl@GO membrane prepared by spray-coating method. The sensor exhibits excellent pressure-sensing performance, including ultrahigh sensitivity and an extremely low detection pressure limit under ambient conditions. DFT computations reveal that the ultrasensitive piezoelectric response of the sensor can be attributed to the unique atom vacancies of the Cl atoms ("ghost atoms") in Na 2 Cl crystals. The high percentage of atom vacancies induces a very large intrinsic polarization and the spray-coating method further enhances up-down asymmetry in the distribution of Na and Cl ions in the membrane. Consequently, the sensor exhibits an extraordinarily large piezoelectric constant and sensitive response to mechanical pressure, while the periodic arrangement of the atom vacancies ensures the structural stability. Notably, the sensor can detect nanonewton forces as low as 25 nanonewtons, based on its low pressure detection limit of ~1 mPa and device size of ~5 × 5 mm 2 . The extremely small airflow fluctuations at a 5 cm distance from a flapping butterfly can be clearly detected, which have long been the elusive tiny signals in the famous “butterfly effect”. Moreover, the sensitivity and the pressure detection limit can be further optimized by increasing the content of the Na 2 Cl crystals within GO membrane. Similarly, the size of the sensor can be even smaller while keeping the excellent pressure-sensing performance by further increasing the crystal content. Considering its excellent mechanical stability, fast response and self-powered capability, the sensor shows great potential in applications that require the high sensitivity to external mechanical stimuli and the detection of the tiny forces with only several nanonewtons, even for monitoring the very fast changed signals of systems in very small spaces such as the brain and other organs. Finally, the presented sensor can serve as a seminal sensor to detect other tiny signals, including electrical, magnetic, optical, and thermal signals, by converting these signals into mechanical forces, and thus the applications can be further greatly extended; for example, combined with a magnet, the sensor can measure the very small magnetic fields by detecting the tiny force acting on the magnet. Declarations Data and materials availability: All data supporting the findings of this study are available within the article and its Extended Data and Supplementary Information. Acknowledgments: This work was supported by the National Natural Science Foundation of China (12074341, 12004109, and 11974366), the Fundamental Research Funds for the Central Universities of East China University of Science. Author contributions: L. C. and H. F. designed the work. T. W., Y. F., J. J., Y. Z., C. Z., B. P., Z. G., Q. P., J. W., J. C., P. L., and L. Z. performed experiments and analysis. Y. H., L. Z., and H. Z. conducted theoretical calculations. H. F., L. C., C. L., Y. H., and T. W. wrote the manuscript. All authors discussed the results and commented on the manuscript. All authors discussed the results and commented on the manuscript. Competing interests: The authors declare that they have no competing interests. References Wu, W. et al. 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The GO suspension was dialyzed with a dialysis bag (MD 77 mm and MW 14000) for 7 days to remove the absorbed impurity ions. Fabrication of pressure sensor To fabricate pressure sensors with the specific sizes, the prepared multilayered GO membrane containing sodium and chloride ions (Na–Cl@GO membrane) was placed inside cutting molds with different areas and cut using a scalpel. The Na–Cl@GO membrane was cut into sections with an area of ~5 mm × 5 mm and a thickness of ~5 μm. They were coated with platinum layers as positive and negative electrodes and encapsulated with PI films. Then, the device was edge-packaged using 3M Kapton tape. Eventually, a soft, flexible, and robust mechanical sensor was fabricated. Weight experiments To test the sensitivity and the response and recovery times, the sensor was placed on the flat test platform. Weights of different masses from 0.25 g to 250 g were placed on the position close to the top surface of the sensor and then approached the sensor slowly. After the weights and sensor were in contact for 5 seconds, the weights were removed, producing a series of mechanical pressures of 0.1-98 kPa. Measurements of response and recovery times of the sensor The open-circuit voltage signals were recorded in real time during the loading and unloading processes by an electrochemical workstation (CHI 760e, Shanghai Chen Hua) at the testing frequency of 1 kHz. The response time and the recovery time were measured, and they were both 1 ms. These measured times reach the temporal resolution of electrochemical workstation, indicating that the real response and recovery speeds should be faster. To further test the real response and recovery times, the sensor was placed on a custom tension machine test platform. The mechanical pressure was applied to the sensor by an indenter comparable to the sensor size, and a force of ~98 kPa was loaded. An oscilloscope (Tektronix, MSO44 4-BW-200) was used to record the open-circuit voltage signals at 1 MHz. Characterization method for crystal structure within Na–Cl@GO membrane High-resolution TEM micrographs were acquired at room temperature by FEI F200C transmission electron microscope (TEM) operating at 200 kV. Selected-area electron diffraction (SAED) images were taken with a ~350 nm diameter selected-area aperture. The exposure time was varied between 0.2 s and 1 s. Characterization method for the ratio of Na to Cl High-angle annular dark field scanning TEM (HADDF-STEM) and energy-dispersive X-ray spectroscopy (EDS) were performed at room temperature using a JEOL JEM-F200 (HR) TEM operating at 200-kV with a JEOL 4k × 4k CMOS camera. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were conducted at room temperature using a HITACHI SU8000 Cold Field Emission Scanning Electron Microscopy operating at 15.0 kV. Selected areas of EDS were randomly chosen from different samples. This operation was repeated 12 times to obtain the statistical results for the atomic fraction. Analysis of capacitance frequency The capacitance frequency curve was acquired using an impedance analyzer (Hioki IM 3570, Japan) with a sweep point (frequency range) from 4 Hz to 500 Hz. Firstly, the piezoelectric sensor was connected to the test fixture of the impedance analyzer, ensuring a stable connection. Secondly, suitable test parameters were established based on the properties of the test sample. In this case, the operating mode was set to constant current, with a value of 0.2 mA, and the frequency range was set from 4 Hz to 500 Hz. Finally, the impedance analyzer was initiated to begin the test and then capacitance values of the test sample were recorded. Experimental setup for indentation test and calculation method for modulus The effective modulus of the Na-Cl@GO membrane was measured through a nanoindentation test using a Berkovich indenter (Agilent Nano Indenter G200, USA) at ambient temperature. Twenty-five tests were conducted with a 5×5 testing array selected on the membrane. The indentation velocity was set as 10 nm/s with a maximum indentation depth of about 230 nm. To determine the effective modulus of the piezoelectric material, an indentation test was carried out with a low-force electronic universal testing machine (Instron 5943, USA), equipped with a load cell with a range of 2 N and a rigid cylindrical flat pressure head with a diameter of 8 mm. Firstly, the sample was prepared with suitable shape and size, and the smoothness of the surface of the sample was checked. Secondly, the indenter was positioned on the sample surface, and a load was applied using a testing machine. The load was applied slowly and steadily to avoid any sudden impacts. Thirdly, the load was held for a specific period and then removed, and the size and shape of the resulting indentation were measured using a microscope. Finally, the effective modulus was obtained. Experimental setup for mechanical pressures of triangular and square waves The mechanical pressure test system consists of a digital force gauge (Mark-10, FS05, ~50.0 N), a motorized test stand (Mark-10, F505H), and an electrochemical workstation (CHI, 760E). Our piezoelectric sensor was fixed on the sample stage (diameter of round compression plate: 0.8 cm) and linked with an electrochemical workstation. Set points of pressure were controlled by IntelliMESUR software. Density functional theory (DFT) calculations Our DFT calculations were performed using the generalized gradient approximation (GGA) 45 within the Perdew−Burke−Ernzerhof (PBE) formulation 46 for the exchange-correlation potential, the projector augmented-wave (PAW) method 47,48 and a plane-wave basis set as implemented in the Vienna ab-initio simulation package (VASP) 49 . The van der Waals interactions were introduced in the calculations, and they were described by a correction through Grimme’s zero-damping D-3 method 50 . The single electron wave functions are expanded in plane waves with kinetic energy cutoff of 700 eV. A vacuum thickness of 30 Å was used to decouple the periodic images along the thickness or the z direction. The Brillouin zones were sampled with 3 × 1 × 1 and 7 × 2 × 1 Γ-centered k -mesh for geometric relaxations and electric polarization calculations, respectively. In structural relaxations, all ionic positions and the shape and volume were allowed to relax until the residual force on each atom was less than 0.0001 eV/Å. The electric charge of each atom was obtained by Bader charge analysis. 45. Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77 , 3865–3868 (1996). 46. Ernzerhof, M. & Scuseria, G. E. Assessment of the Perdew–Burke–Ernzerhof exchange-correlation functional. J. Chem. Phys. 110 , 5029–5036 (1999). 47. Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59 , 1758–1775 (1999). 48. Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50 , 17953–17979 (1994). 49. Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54 , 11169–11186 (1996). 50. Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132 , 154104 (2010). Additional Declarations There is NO Competing Interest. Supplementary Files ado2017SupplementaryMoviemov1seq1v11.mp4 SUPPLEMENTARY VIDEO1 ChenLUltraPiezoelectricSIhyy20240326.docx SUPPLEMENTARY INFORMATION Cite Share Download PDF Status: Posted 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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Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYBACPmYwdYCBgb2BgaECysYL2OBaeID4DFFaGGBaJBKI1cLO/Ozhl5o7cuaSzx9+ONjGIMd3I4HxcwFeh7GZG8sce2ZsOTshWQKoxVjyRgKz9Az8fjGTlmw4nLjhdsIB6Y9tDIkbbiSwMfPg1cL+DaSlfsPNg80/gLbUE6GFx0zyY8PhBIMbzGwghwEZhLWUSTMcO2y44Uwam8WBcxKGM888bJbGp4Wf//g2yR81h+UNjh9/fONAmY083/Hkg5/xaQEBZGdIADFjAwENQCU/CCoZBaNgFIyCEQ0A9LBM58SfD7wAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0006-3361-2953","institution":"Ningbo university","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Chen","suffix":""},{"id":284427714,"identity":"c82aa2c9-3575-4ecb-a7b7-ef432e07122c","order_by":1,"name":"Tao Wang","email":"","orcid":"","institution":"Ningbo University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Wang","suffix":""},{"id":284427715,"identity":"3f3a495a-cbe7-4c85-a60e-38d88dc7e032","order_by":2,"name":"Yan Fan","email":"","orcid":"","institution":"Zhejiang A\u0026F University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Fan","suffix":""},{"id":284427716,"identity":"b8d7ed4c-337e-4488-9789-aae89f3f734c","order_by":3,"name":"Jie Jiang","email":"","orcid":"","institution":"Ningbo University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jie","middleName":"","lastName":"Jiang","suffix":""},{"id":284427717,"identity":"3eed82a1-8dc7-483a-913e-6f3a626c4ad4","order_by":4,"name":"Yangyang Zhang","email":"","orcid":"","institution":"Ningbo 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University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Haifei","middleName":"","lastName":"Zhan","suffix":""},{"id":284427721,"identity":"a4aabb7e-5e17-4767-9f24-b4a942bf2df0","order_by":8,"name":"Chunli Zhang","email":"","orcid":"https://orcid.org/0000-0002-6688-2785","institution":"Zhejiang University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chunli","middleName":"","lastName":"Zhang","suffix":""},{"id":284427722,"identity":"f3ff24a2-22fb-4463-afc2-bd7771479fc0","order_by":9,"name":"Bingquan Peng","email":"","orcid":"","institution":"Wenzhou Institute, University of Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Bingquan","middleName":"","lastName":"Peng","suffix":""},{"id":284427723,"identity":"01e55f67-7b65-4dd3-8bf2-0ce004d163bf","order_by":10,"name":"Zhen Gu","email":"","orcid":"","institution":"East China University of Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhen","middleName":"","lastName":"Gu","suffix":""},{"id":284427724,"identity":"84798bc0-42cb-4e82-b595-0e05bf8ea4af","order_by":11,"name":"Qiubo Pan","email":"","orcid":"","institution":"East China University of Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Qiubo","middleName":"","lastName":"Pan","suffix":""},{"id":284427725,"identity":"a32589dd-ccad-4c7c-a9ec-6930f7031fb1","order_by":12,"name":"Junjie Wu","email":"","orcid":"","institution":"Zhejiang University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Junjie","middleName":"","lastName":"Wu","suffix":""},{"id":284427726,"identity":"4a606a8b-f336-4605-90b6-7753efa7bc39","order_by":13,"name":"Junlang Chen","email":"","orcid":"","institution":"Zhejiang A\u0026F University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Junlang","middleName":"","lastName":"Chen","suffix":""},{"id":284427727,"identity":"5187615f-a498-4d44-af2b-da4b2d3ae41b","order_by":14,"name":"Pei Li","email":"","orcid":"","institution":"Ningbo University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Pei","middleName":"","lastName":"Li","suffix":""},{"id":284427728,"identity":"21d49f0c-0d01-43a9-99d5-fd6e7290b292","order_by":15,"name":"Lei Zhang","email":"","orcid":"","institution":"Xi'an Jiaotong University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Zhang","suffix":""},{"id":284427729,"identity":"bd63732c-75db-43d0-a5a0-c4f57b3d6b52","order_by":16,"name":"Chaofeng Lü","email":"","orcid":"","institution":"ningbo university","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chaofeng","middleName":"","lastName":"Lü","suffix":""},{"id":284427730,"identity":"2f5982fb-85ad-427e-8ee6-6ef0a03583c0","order_by":17,"name":"Haiping Fang","email":"","orcid":"https://orcid.org/0000-0002-3496-9923","institution":"East China University of Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Haiping","middleName":"","lastName":"Fang","suffix":""}],"badges":[],"createdAt":"2024-03-26 14:33:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4170610/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4170610/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54679058,"identity":"b7bef8ae-43a7-4fcd-bb0d-1e10336280f3","added_by":"auto","created_at":"2024-04-15 07:24:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":397713,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePiezoelectric sensor with supreme pressure-sensing performance. a\u003c/strong\u003e, Schematic of a flexible piezoelectric sensor based on Na\u003csub\u003e2\u003c/sub\u003eCl crystal/GO membrane between conductive Pt/polyimide (PI) films. The enlarged views depict the microstructure of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal/GO membrane and show a cross-section of an atom-thick slice, as well as mechanical deformation under external pressure. \u003cstrong\u003eb\u003c/strong\u003e, Comparison of sensitivity and the pressure detection limit of the proposed sensor and other high-performance pressure sensors (for details, see Supplementary Table 1). \u003cstrong\u003ec\u003c/strong\u003e, Decay process of the acoustic excitation with ~100 mPa and ~260 Hz in a tuning fork test. A bandpass filter ranging from 250 to 270 Hz was applied to the output voltage to remove background signals, as well as 50 Hz alternating current (AC) signal and its harmonics. \u003cstrong\u003ed\u003c/strong\u003e, An enlarged view of the voltage response of the sensor. \u003cstrong\u003ee\u003c/strong\u003e, Normalized relative change in voltage ((\u003cem\u003eU\u003c/em\u003e-\u003cem\u003eU\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e)/\u003cem\u003eU\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e) as a function of acoustic pressure below 100 mPa. \u003cem\u003eU\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e = 0.1 mV is the initial voltage of the sensor without pressure, and \u003cem\u003eU\u003c/em\u003e is the voltage under the applied pressure \u003cem\u003ep\u003c/em\u003e. The dashed red and black lines in the figure are the tangent lines on the curve, and their slopes are the values of sensitivity \u003cem\u003eS\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/ead08445c627a72d80adef25.png"},{"id":54679060,"identity":"1a1a11ce-38af-4fae-be16-f14a39f22786","added_by":"auto","created_at":"2024-04-15 07:24:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2896358,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanism of the piezoelectric sensor with Na\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eCl crystals. a, \u003c/strong\u003eHigh-resolution transmission electron microscopy (TEM) image of Na\u003csub\u003e2\u003c/sub\u003eCl crystals observed in the GO membrane. The inset shows a zoomed-in area of the high-resolution image and the Na\u003csub\u003e2\u003c/sub\u003eCl model, in which the Na and Cl atoms are shown as blue and green spheres respectively. \u003cstrong\u003eb, \u003c/strong\u003eNa:Cl ratio for the Na-Cl@GO membrane (from 20 different regions in the dark-field TEM images). Side view (\u003cstrong\u003ec\u003c/strong\u003e) and top view (\u003cstrong\u003ed\u003c/strong\u003e) of the 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystal structure on the graphene base (Na\u003csub\u003e2\u003c/sub\u003eCl@graphene). Here, the graphene base represents the part of GO without functional groups. \u003cem\u003eh\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e is the average displacement between the Na atom in the upper layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal and the atom vacancies in the bottom layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal; \u003cem\u003eh\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e is the average displacement between the Cl atom in the upper layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal and the Na atom in the bottom layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal; \u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003ey\u003c/sub\u003e are the distances between adjacent atoms in each layer in x and y direction. \u003cstrong\u003ee,\u003c/strong\u003e Differential charge densities (DCD) of Na\u003csub\u003e2\u003c/sub\u003eCl@graphene. \u003cstrong\u003ef,\u003c/strong\u003e Relative changes in different distances (induced strain) as a function of applied strain. \u003cstrong\u003eg,\u003c/strong\u003e Piezoelectric constant obtained from the decay process of the acoustic pressure. The dashed blue line is the tangent line on the curve in the figure and the slope of tangent line represents the piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/4e762757788e7e14cbb60920.png"},{"id":54679061,"identity":"aba26232-1d80-404f-a07a-1a139e55ef3c","added_by":"auto","created_at":"2024-04-15 07:24:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":686438,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePiezoelectric sensor for detection of tiny airflow fluctuations surrounding a flapping butterfly. a, \u003c/strong\u003eA schematic of the real-time monitoring of airflow pressure surrounding a flapping butterfly. Three piezoelectric sensors are at a 5 cm distance from a flapping butterfly. \u003cstrong\u003eb\u003c/strong\u003e, Air pressure variations in real time. The top picture depicts air pressure variations obtained using the sensor above a flapping butterfly, and the bottom picture is a partially enlarged view of the top picture.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/31c107d43fe2e96f6d45f98f.png"},{"id":54679524,"identity":"51acac22-9d9e-4283-95b4-77ae74fb1c43","added_by":"auto","created_at":"2024-04-15 07:32:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":86958,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanical stability and response time of the piezoelectric sensor. a\u003c/strong\u003e, Relative change in voltage (\u003cem\u003eU/U\u003c/em\u003e\u003csub\u003eload\u003c/sub\u003e) during cyclic loading/unloading experiments under the loaded pressure of 80 kPa. \u003cem\u003eU\u003c/em\u003e\u003csub\u003eload\u003c/sub\u003e = 0.431 V is the average voltage when the sensor is loaded at the initial stage. The inserts are two partially enlarged views. \u003cstrong\u003eb\u003c/strong\u003e, Response and recovery times of the sensor under loaded pressure of 98 kPa measured by oscilloscope with a time step of 1 μs. The light red-shaded and light blue-shaded areas show the response and recovery processes of the sensor. The inset is a partially enlarged view.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/a5fbd7037e20f6f538b11de6.png"},{"id":56815676,"identity":"286665b0-8898-43db-bd4c-69e0aa52648c","added_by":"auto","created_at":"2024-05-20 21:13:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5829852,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/5ea02f14-3134-4df2-a870-7571647ce273.pdf"},{"id":54679059,"identity":"0f5f0e36-9450-4252-85b5-b81d3e925dbe","added_by":"auto","created_at":"2024-04-15 07:24:56","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":596753,"visible":true,"origin":"","legend":"SUPPLEMENTARY VIDEO1","description":"","filename":"ado2017SupplementaryMoviemov1seq1v11.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/36b19c6f13cb60a8635e5044.mp4"},{"id":54679064,"identity":"a0c37af7-8ab6-453a-bb24-d9c66703cc9f","added_by":"auto","created_at":"2024-04-15 07:24:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3037965,"visible":true,"origin":"","legend":"SUPPLEMENTARY INFORMATION","description":"","filename":"ChenLUltraPiezoelectricSIhyy20240326.docx","url":"https://assets-eu.researchsquare.com/files/rs-4170610/v1/b4df129bf7ae2af20462e79f.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eUltrasensitive piezoelectric sensor based on two-dimensional Na\u003csub\u003e2\u003c/sub\u003eCl crystals with periodic atom vacancies\u003c/p\u003e","fulltext":[{"header":"Full Text","content":"\u003cp\u003eMicrostructures at the micro- or nano-scale, introduced in pressure sensors, exhibit an inextricable link with the promotion of sensitivity and detection limit for pressure sensors due to their asymmetries and compressibility\u003csup\u003e5,6,11-19\u003c/sup\u003e. The microstructures at the micro-scale with high asymmetry can effectively improve sensitivity, including micro-pyramid arrays\u003csup\u003e5,6,20-22\u003c/sup\u003e, wrinkles\u003csup\u003e23\u003c/sup\u003e, micro-domes\u003csup\u003e24,25\u003c/sup\u003e, micro-pillar arrays\u003csup\u003e11\u003c/sup\u003e, and micro-protrusions\u003csup\u003e26\u003c/sup\u003e, as well as other assembly patterns\u003csup\u003e12-15,27-29\u003c/sup\u003e. More precisely, asymmetrical nano-structures and heterogeneities\u003csup\u003e16-18,30-33\u003c/sup\u003e are recognized to play a key role in significantly promoting the mechano-electric transduction of various stimuli. At the smallest atom-scale, the microstructures, with atom vacancies induced by a strong electric field\u003csup\u003e19\u003c/sup\u003e, have exhibited very large piezoelectric sensitivities. Despite extensive exploration and advances, it remains difficult to achieve expected atom vacancies exhibiting large structural asymmetry while maintaining structural compressibility and stability under ambient conditions. This is the limitation and challenge of pressure sensors for achieving more excellent pressure-sensing performance.\u003c/p\u003e\n\u003cp\u003eHere, we present a piezoelectric sensor with supreme pressure-sensing performance in the sensitivity and detection limit, based on a high percentage of atom vacancies in the unique two-dimensional (2D) Na\u003csub\u003e2\u003c/sub\u003eCl crystals within multilayered graphene oxide (GO) membrane. Different from the ordinary NaCl crystal, the 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystal has a Na:Cl atom ratio of 2:1 and contains atom vacancies where Cl atoms should be located. The atom vacancies result in a very high piezoelectric coefficient of the membrane. The periodic arrangement of these atom vacancies ensures the structural stability. Remarkably, the sensor is capable of detecting signals as low as 1 mPa (corresponding to a 25 nanonewton force), together with excellent mechanical stability. The small size, fast response, and self-powered capability of the sensor make it particularly suitable for use in biological systems and complex environments. In addition, the application scope of the sensor can be greatly extended to encompass the detection of other tiny signals including electrical, magnetic, optical, and thermal signals, by converting these signals into mechanical forces.\u003c/p\u003e\n\u003cp\u003eThe membranes of piezoelectric sensors were prepared from a graphene oxide (GO) suspension and dilute NaCl solution via the spray-coating method (see Methods). Explicitly, the GO suspension (20 \u0026mu;L, 5 mg/mL) was sprayed on a polyethylene glycol terephthalate (PET) substrate, followed by drying at 60\u0026deg;C for 6 hours. The prepared GO membrane was then drop-cast with dilute NaCl solution (0.01 mol/L) and exposed to the air for 2 hours. Next, the GO suspension was sprayed on the membrane again and dried at 60\u0026deg;C for another 6 hours, to form multilayered GO membrane containing sodium and chloride ions, which are denoted as Na\u0026ndash;Cl@GO membrane. Different from GO membranes directly immersed in NaCl solutions in our previous work\u003csup\u003e34\u003c/sup\u003e, this spay-coating method creates up-down asymmetry in the distribution of Na and Cl ions in the membrane. These membranes, having a thickness of ~5 \u0026mu;m, were removed from the substrate and cut into ~5 \u0026times; 5 mm\u003csup\u003e2\u003c/sup\u003e sections. Then, they were made into sensor devices with a platinum (Pt) film coating to serve as conductive electrode and encapsulated with insulation PI film (Fig. 1a).\u003c/p\u003e\n\u003cp\u003eThe sensor exhibits supreme sensitivity for pressure sensing in the low-pressure range of 1-100 mPa. An acoustic pressure below 100 mPa was generated with the acoustic excitation of a tuning fork with a frequency of ~260 Hz. The acoustic pressure (\u003cem\u003eP\u003c/em\u003e) of the acoustic excitation was monitored using an acoustic tester (UMM-6, Dayton Audio). The voltage response of the sensor (\u003cem\u003eU\u003c/em\u003e) to changes in the acoustic pressure was simultaneously monitored by a digital lock-in amplifier (HF2LI, Zurich Instruments) with a sampling frequency of 10 kHz (Fig. 1c). A good correlation between the voltage output of the sensor and the acoustic pressure is shown. The sensitivity \u003cem\u003eS\u003c/em\u003e of the piezoelectric sensor is typically defined as \u003cem\u003eS\u003c/em\u003e = \u0026delta;((\u003cem\u003eU\u003c/em\u003e-\u003cem\u003eU\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e)/\u003cem\u003eU\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e)/\u0026delta;\u003cem\u003ep\u003c/em\u003e\u003csup\u003e35\u003c/sup\u003e, where\u003cem\u003e U\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e = 0.1 mV is the initial voltage of the sensor without pressure, and\u003cem\u003e U\u003c/em\u003e is the voltage response under the applied pressure \u003cem\u003ep\u003c/em\u003e. The peak sensitivity reaches 3.5\u0026times;10\u003csup\u003e6\u003c/sup\u003e kPa\u003csup\u003e-1\u003c/sup\u003e (Fig. 1e), which is approximately one order of magnitude larger than the highest sensitivity of 3.8\u0026times;10\u003csup\u003e5\u003c/sup\u003e kPa\u003csup\u003e-1 \u003c/sup\u003e\u003csup\u003e36\u003c/sup\u003e obtained from the current state-of-the-art pressure sensors.\u003c/p\u003e\n\u003cp\u003eImportantly, at pressure of 1 mPa or even lower, the sensor still exhibits a clear decay in the voltage response, indicating that the sensor can effectively detect pressure variations of 1 mPa or less (Fig. 1d). This value is lower than the lowest pressure detection limit of recently reported pressure sensors, 2 mPa\u003csup\u003e3\u003c/sup\u003e. The sensor thereby demonstrates supreme pressure-sensing performance in terms of sensitivity and pressure detection limit, superior to the state-of-the-art pressure sensors reported so far (Fig. 1b). Moreover, based on the pressure detection limit of 1 mPa and the sensor size of ~5 \u0026times; 5 mm\u003csup\u003e2\u003c/sup\u003e, the sensor is capable of detecting tiny force as low as 25 nanonewtons.\u003c/p\u003e\n\u003cp\u003eWe attribute the observed piezoelectric behaviors to the 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystals within GO membrane in the sensor. This Na\u003csub\u003e2\u003c/sub\u003eCl crystal was discovered in our previous work\u003csup\u003e34\u003c/sup\u003e, originating from the ion\u0026ndash;\u0026pi; interactions\u003csup\u003e37\u003c/sup\u003e between the ions and the \u0026pi;-conjugated system in the graphitic surface\u003csup\u003e38-40\u003c/sup\u003e. Different from the ordinary NaCl crystal, the 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystal has a Na:Cl atom ratio of 2:1 and contains atom vacancies where Cl atoms should be located (Fig. 2c); here, we refer to these anion vacancies as \u0026ldquo;ghost atoms\u0026rdquo;. These Cl atom vacancies in the crystal lead to very high asymmetry, while their periodic arrangement in the crystal ensures the structural stability.\u003c/p\u003e\n\u003cp\u003eThe existence of 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystals in the sensor was confirmed by transmission electron microscopy (TEM) experiments. The high-resolution TEM image shows a square structure with a lattice spacing of 3.96 \u0026plusmn; 0.03 \u0026Aring; (Fig. 2a). The enlarged image overlays well with the Na\u003csub\u003e2\u003c/sub\u003eCl structure in our previous work \u003csup\u003e34\u003c/sup\u003e, as shown by the inset in Fig. 2a, in which the Na and Cl atoms are shown as blue and green spheres, respectively. The dark-field TEM images demonstrate that the Na:Cl ratio is approximately 2:1 (Fig. 2b and Supplementary Fig. 4).\u003c/p\u003e\n\u003cp\u003eWe then performed density functional theory (DFT) computations to illustrate the underlying physics. The structure of the 2D Na\u003csub\u003e2\u003c/sub\u003eCl crystal based on the graphene surface (Na\u003csub\u003e2\u003c/sub\u003eCl@graphene) is shown in Fig. 2c and 2d. Here, the graphene surface is considered as the part of GO membrane without functional groups. The electric polarization direction from Na\u003csub\u003e2\u003c/sub\u003eCl layer to graphene layer is shown in the line profile of the interfacial differential charge densities (DCD, a measure of charge variation at the interface)) in the out-of-plane direction (Fig. 2e). By analyzing the Bader charges of the atoms, a very large spontaneous out-of-plane polarization \u003cem\u003e(P\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e), serving as one of crucial parameters for piezoelectric materials\u003csup\u003e17,41\u003c/sup\u003e, was obtained for the Na\u003csub\u003e2\u003c/sub\u003eCl@graphene, namely, \u003cem\u003eP\u003c/em\u003e\u003csub\u003e0 \u003c/sub\u003e= 39.0 pC/m (see Supplementary Note 2). This value is nearly two orders of magnitude larger than the out-of-plane polarization of 0.6 pC/m for MoS\u003csub\u003e2\u003c/sub\u003e/WS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e18\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe induced mechanical deformation of Na\u003csub\u003e2\u003c/sub\u003eCl@graphene under external pressure was then investigated by varying the distance between the Na atom in the upper layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal and the graphene surface using DFT simulations. Fig. 2f clearly shows that in the out-of-plane direction, the average displacement (\u003cem\u003eh\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) between the Na atom in the upper layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal and the atom vacancy in the bottom layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal is much larger than the average displacement (\u003cem\u003eh\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e) between the Cl atom in the upper layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal and the Na atom in the bottom layer of the Na\u003csub\u003e2\u003c/sub\u003eCl crystal under stress. In contrast, along the in-plane direction, the distances between adjacent atoms (\u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003ey\u003c/sub\u003e) in each layer remain approximately constant. These results indicate that the atom vacancies make the Na\u003csub\u003e2\u003c/sub\u003eCl crystal susceptible to deformation along the direction of applied stress, while maintaining structural stability.\u003c/p\u003e\n\u003cp\u003eThe very large intrinsic polarization suggests an extraordinarily large piezoelectric coefficient in the sensor\u003csup\u003e42\u003c/sup\u003e. According to the stress-output charge relation from the acoustic excitation of the tuning fork (Fig. 2g), we experimentally obtained a piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e) up to 6.8\u0026times;10\u003csup\u003e5\u003c/sup\u003e pC/N in the range of 0.025\u0026ndash;2 \u0026mu;N (corresponding to the pressure range of 1\u0026ndash;80 mPa). This value is larger than the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of ~2\u0026times;10\u003csup\u003e5\u003c/sup\u003e pC/N in cubic fluorite gadolinium-doped CeO\u003csub\u003e2-x\u003c/sub\u003e films obtained by rearranging oxygen vacancies under very large electric fields at millihertz frequencies\u003csup\u003e19\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe famous butterfly effect, a metaphor for chaos theory that posits \u0026ldquo;Does the flap of a butterfly\u0026rsquo;s wings in Brazil set off a tornado in Texas?\u0026rdquo;\u003csup\u003e43\u003c/sup\u003e, reflects sensitive dependence on an initial condition, with extremely small signals leading to extraordinarily large responses. To our knowledge, the airflow variation caused by a flapping butterfly has not been well measured because the variation is quite small\u003csup\u003e44\u003c/sup\u003e. Using the presented sensor, the open-circuit voltage response to the airflow variation at a 5 cm distance from a flapping butterfly was obtained, and the movement of the butterfly and the real-time motoring of voltage response were shown in the movies (Supplementary Video 1). The corresponding pressure variations above, on the side of, and below the butterfly were ~3.9 mPa, ~6.8 mPa, and ~14.7 mPa, respectively (Fig. 3b and Supplementary Fig. 12b), calculated by the conversion relation between the pressure and voltage response (Supplementary Note 9). The pressure variations of 2 mPa or even lower can be clearly distinguished by the sensor (Fig. 3b). These variations in the airflow pressures are extremely small, only approximately one millionth of the airflow pressure caused by a tornado. A wing-beat frequency of ~5 Hz was obtained (Supplementary Fig. 12c), which is consistent with the results from other studies on flapping frequency\u003csup\u003e44\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe sensor also exhibits a very high sensitivity in the high-pressure range. We used a force gauge (Mark-10, FS05) to produce a series of mechanical loads in the pressure range of 0.1 to 100 kPa. The voltage response of the sensor was measured using an electrochemical workstation (CHI760E) (Supplementary Fig. 6a). The output voltage shows a cyclic and step-like response, which increases from ~0.06 V to ~0.80 V and is well correlated with the applied mechanical load (Supplementary Fig. 6a). The sensitivity of the sensor was then calculated. The sensitivity decreases from 2.0\u0026times;10\u003csup\u003e4\u003c/sup\u003e kPa\u003csup\u003e-1\u003c/sup\u003e to 1.2\u0026times;10\u003csup\u003e2\u003c/sup\u003e kPa\u003csup\u003e-1\u003c/sup\u003e when the applied pressure is varied in the range of 0.1\u0026ndash;100 kPa (Supplementary Fig. 6b).\u003c/p\u003e\n\u003cp\u003eIn addition, the sensor has excellent mechanical stability and a fast response. The peak voltage due to a mechanical pressure of 80 kPa decreases by less than 3% when the sensor is subjected to over 10000 cycles of loading and unloading (Fig. 4a). A response time (\u003cem\u003e\u0026tau;\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) of 1 \u0026mu;s and recovery time (\u003cem\u003e\u0026tau;\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e) of 238 ms were obtained using an oscilloscope (Tektronix, MSO44 4-BW-200) (Fig. 4b). The detected response time of 1 \u0026mu;s is actually the limit of our measurement set-up instead of the intrinsic limit of the sensor. The excellent mechanical stability and fast response ensure its application in the area of sensitive pressure sensing.\u003c/p\u003e\n\u003cp\u003eIn summary, we developed an ultrasensitive piezoelectric sensor made of multilayered Na\u003csub\u003e2\u003c/sub\u003eCl@GO membrane prepared by spray-coating method. The sensor exhibits excellent pressure-sensing performance, including ultrahigh sensitivity and an extremely low detection pressure limit under ambient conditions. DFT computations reveal that the ultrasensitive piezoelectric response of the sensor can be attributed to the unique atom vacancies of the Cl atoms (\"ghost atoms\") in Na\u003csub\u003e2\u003c/sub\u003eCl crystals. The high percentage of atom vacancies induces a very large intrinsic polarization and the spray-coating method further enhances up-down asymmetry in the distribution of Na and Cl ions in the membrane. Consequently, the sensor exhibits an extraordinarily large piezoelectric constant and sensitive response to mechanical pressure, while the periodic arrangement of the atom vacancies ensures the structural stability.\u003c/p\u003e\n\u003cp\u003eNotably, the sensor can detect nanonewton forces as low as 25 nanonewtons, based on its low pressure detection limit of ~1 mPa and device size of ~5 \u0026times; 5 mm\u003csup\u003e2\u003c/sup\u003e. The extremely small airflow fluctuations at a 5 cm distance from a flapping butterfly can be clearly detected, which have long been the elusive tiny signals in the famous \u0026ldquo;butterfly effect\u0026rdquo;. Moreover, the sensitivity and the pressure detection limit can be further optimized by increasing the content of the Na\u003csub\u003e2\u003c/sub\u003eCl crystals within GO membrane. Similarly, the size of the sensor can be even smaller while keeping the excellent pressure-sensing performance by further increasing the crystal content. Considering its excellent mechanical stability, fast response and self-powered capability, the sensor shows great potential in applications that require the high sensitivity to external mechanical stimuli and the detection of the tiny forces with only several nanonewtons, even for monitoring the very fast changed signals of systems in very small spaces such as the brain and other organs. Finally, the presented sensor can serve as a seminal sensor to detect other tiny signals, including electrical, magnetic, optical, and thermal signals, by converting these signals into mechanical forces, and thus the applications can be further greatly extended; for example, combined with a magnet, the sensor can measure the very small magnetic fields by detecting the tiny force acting on the magnet.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData and materials availability:\u0026nbsp;\u003c/strong\u003eAll data supporting the findings of this study are available within the article and its Extended Data and Supplementary Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u0026nbsp;\u003c/strong\u003eThis work was supported by the National Natural Science Foundation of China (12074341, 12004109, and 11974366), the Fundamental Research Funds for the Central Universities of East China University of Science.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u0026nbsp;\u003c/strong\u003eL. C. and H. F. designed the work. T. W., Y. F., J. J., Y. Z., C. Z., B. P., Z. G., Q. P., J. W., J. C., P. L., and L. Z. performed experiments and analysis. Y. H., L. Z., and H. Z. conducted theoretical calculations. H. F., L. C., C. L., Y. H., and T. W. wrote the manuscript. All authors discussed the results and commented on the manuscript. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWu, W.\u003cem\u003e et al.\u003c/em\u003e Piezoelectricity of single-atomic-layer MoS\u003csub\u003e2\u003c/sub\u003e for energy conversion and piezotronics. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e514\u003c/strong\u003e, 470\u0026ndash;474 (2014).\u003c/li\u003e\n\u003cli\u003eLee, S.\u003cem\u003e et al.\u003c/em\u003e Nanomesh pressure sensor for monitoring finger manipulation without sensory interference. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e370\u003c/strong\u003e, 966\u0026ndash;970 (2020).\u003c/li\u003e\n\u003cli\u003eYan, W.\u003cem\u003e et al.\u003c/em\u003e Single fibre enables acoustic fabrics via nanometre-scale vibrations. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e603\u003c/strong\u003e, 616\u0026ndash;623 (2022).\u003c/li\u003e\n\u003cli\u003eDobashi, Y.\u003cem\u003e et al.\u003c/em\u003e Piezoionic mechanoreceptors: force-induced current generation in hydrogels. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e376\u003c/strong\u003e, 502\u0026ndash;507 (2022).\u003c/li\u003e\n\u003cli\u003eHuang, Y.-C.\u003cem\u003e et al.\u003c/em\u003e Sensitive pressure sensors based on conductive microstructured air-gap gates and two-dimensional semiconductor transistors. \u003cem\u003eNat. 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Rev.\u003c/em\u003e \u003cstrong\u003e113\u003c/strong\u003e, 2100\u0026ndash;2138 (2013).\u003c/li\u003e\n\u003cli\u003eGeim, A. K. \u0026amp; Novoselov, K. S. The rise of graphene. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 183\u0026ndash;191 (2007).\u003c/li\u003e\n\u003cli\u003eDikin, D. A.\u003cem\u003e et al.\u003c/em\u003e Preparation and characterization of graphene oxide paper. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e448\u003c/strong\u003e, 457\u0026ndash;460 (2007).\u003c/li\u003e\n\u003cli\u003eJoshi, R. K.\u003cem\u003e et al.\u003c/em\u003e Precise and ultrafast molecular sieving through graphene oxide membranes. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e343\u003c/strong\u003e, 752\u0026ndash;754 (2014).\u003c/li\u003e\n\u003cli\u003eLi, F.\u003cem\u003e et al.\u003c/em\u003e Giant piezoelectricity of Sm-doped Pb(Mg\u003csub\u003e1/3\u003c/sub\u003eNb\u003csub\u003e2/3\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e-PbTiO\u003csub\u003e3\u003c/sub\u003e single crystals. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e364\u003c/strong\u003e, 264\u0026ndash;268 (2019).\u003c/li\u003e\n\u003cli\u003eHuang, Y.\u003cem\u003e et al.\u003c/em\u003e Enhanced piezoelectricity from highly polarizable oriented amorphous fractions in biaxially oriented poly (vinylidene fluoride) with pure beta crystals. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 675 (2021).\u003c/li\u003e\n\u003cli\u003eLorenz, E. The butterfly effect. \u003cem\u003eWorld Scientific Series on Nonlinear Science Series A\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, 91\u0026ndash;94 (2000).\u003c/li\u003e\n\u003cli\u003eTakahashi, H. MEMS-based micro sensors for measuring the tiny forces acting on insects. \u003cem\u003eSensors\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 8018 (2022).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003ePreparation of graphene oxide (GO) suspension\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGraphite powders were placed into a solution of concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e, and P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eand continuously stirred for several hours. The mixture was then diluted with deionized water (DI), centrifuged and washed with DI water. After drying, the pre-oxidized graphite was obtained. The pre-oxidized graphite was further oxidized in concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and KMnO\u003csub\u003e4\u003c/sub\u003e, diluted with DI water, and then oxidized again with 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The product was centrifuged and washed using a 1:10 HCl aqueous solution and DI water sequentially to remove ions. Finally, a few-layer graphene oxide was separated by centrifugation at 4000 rpm. The concentration of the as-prepared GO suspension was approximately 5 mg/mL. The GO suspension was dialyzed with a dialysis bag (MD 77 mm and MW 14000) for 7 days to remove the absorbed impurity ions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of pressure sensor\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo fabricate pressure sensors with the specific sizes, the prepared multilayered GO membrane containing sodium and chloride ions (Na\u0026ndash;Cl@GO membrane) was placed inside cutting molds with different areas and cut using a scalpel.\u003c/p\u003e\n\u003cp\u003eThe Na\u0026ndash;Cl@GO membrane was cut into sections with an area of ~5 mm \u0026times; 5 mm and a thickness of ~5 \u0026mu;m. They were coated with platinum layers as positive and negative electrodes and encapsulated with PI films. Then, the device was edge-packaged using 3M Kapton tape. Eventually, a soft, flexible, and robust mechanical sensor was fabricated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWeight experiments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo test the sensitivity and the response and recovery times, the sensor was placed on the flat test platform. Weights of different masses from 0.25 g to 250 g were placed on the position close to the top surface of the sensor and then approached the sensor slowly. After the weights and sensor were in contact for 5 seconds, the weights were removed, producing a series of mechanical pressures of 0.1-98 kPa.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMeasurements of response and recovery times of the sensor\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe open-circuit voltage signals were recorded in real time during the loading and unloading processes by an electrochemical workstation (CHI 760e, Shanghai Chen Hua) at the testing frequency of 1 kHz. The response time and the recovery time were measured, and they were both 1 ms. These measured times reach the temporal resolution of electrochemical workstation, indicating that the real response and recovery speeds should be faster.\u003c/p\u003e\n\u003cp\u003eTo further test the real response and recovery times, the sensor was placed on a custom tension machine test platform. The mechanical pressure was applied to the sensor by an indenter comparable to the sensor size, and a force of ~98 kPa was loaded. An oscilloscope (Tektronix, MSO44 4-BW-200) was used to record the open-circuit voltage signals at 1 MHz.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization method for crystal structure within Na\u0026ndash;Cl@GO membrane\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHigh-resolution TEM micrographs were acquired at room temperature by FEI F200C transmission electron microscope (TEM) operating at 200 kV. Selected-area electron diffraction (SAED) images were taken with a ~350 nm diameter selected-area aperture. The exposure time was varied between 0.2 s and 1 s.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization method for the ratio of Na to Cl\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHigh-angle annular dark field scanning TEM (HADDF-STEM) and energy-dispersive X-ray spectroscopy (EDS) were performed at room temperature using a JEOL JEM-F200 (HR) TEM operating at 200-kV with a JEOL 4k \u0026times; 4k CMOS camera.\u003c/p\u003e\n\u003cp\u003eScanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were conducted at room temperature using a HITACHI SU8000 Cold Field Emission Scanning Electron Microscopy operating at 15.0 kV. Selected areas of EDS were randomly chosen from different samples. This operation was repeated 12 times to obtain the statistical results for the atomic fraction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis of capacitance frequency\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe capacitance frequency curve was acquired using an impedance analyzer (Hioki IM 3570, Japan) with a sweep point (frequency range) from 4 Hz to 500 Hz. Firstly, the piezoelectric sensor was connected to the test fixture of the impedance analyzer, ensuring a stable connection. Secondly, suitable test parameters were established based on the properties of the test sample. In this case, the operating mode was set to constant current, with a value of 0.2 mA, and the frequency range was set from 4 Hz to 500 Hz. Finally, the impedance analyzer was initiated to begin the test and then capacitance values of the test sample were recorded.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eExperimental setup for indentation test and calculation method for modulus\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe effective modulus of the Na-Cl@GO membrane was measured through a nanoindentation test using a Berkovich indenter (Agilent Nano Indenter G200, USA) at ambient temperature. Twenty-five tests were conducted with a 5\u0026times;5 testing array selected on the membrane. The indentation velocity was set as 10 nm/s with a maximum indentation depth of about 230 nm.\u003c/p\u003e\n\u003cp\u003eTo determine the effective modulus of the piezoelectric material, an indentation test was carried out with a low-force electronic universal testing machine (Instron 5943, USA), equipped with a load cell with a range of 2 N and a rigid cylindrical flat pressure head with a diameter of 8 mm. Firstly, the sample was prepared with suitable shape and size, and the smoothness of the surface of the sample was checked. Secondly, the indenter was positioned on the sample surface, and a load was applied using a testing machine. The load was applied slowly and steadily to avoid any sudden impacts. Thirdly, the load was held for a specific period and then removed, and the size and shape of the resulting indentation were measured using a microscope. Finally, the effective modulus was obtained.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eExperimental setup for mechanical pressures of triangular and square waves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe mechanical pressure test system consists of a digital force gauge (Mark-10, FS05, ~50.0 N), a motorized test stand (Mark-10, F505H), and an electrochemical workstation (CHI, 760E). Our piezoelectric sensor was fixed on the sample stage (diameter of round compression plate: 0.8 cm) and linked with an electrochemical workstation. Set points of pressure were controlled by IntelliMESUR software.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDensity functional theory (DFT) calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOur DFT calculations were performed using the generalized gradient approximation (GGA)\u003csup\u003e45\u003c/sup\u003e within the Perdew\u0026minus;Burke\u0026minus;Ernzerhof (PBE) formulation\u003csup\u003e46\u003c/sup\u003e for the exchange-correlation potential, the projector augmented-wave (PAW) method\u003csup\u003e47,48\u003c/sup\u003e and a plane-wave basis set as implemented in the Vienna ab-initio simulation package (VASP)\u003csup\u003e49\u003c/sup\u003e. The van der Waals interactions were introduced in the calculations, and they were described by a correction through Grimme\u0026rsquo;s zero-damping D-3 method\u003csup\u003e50\u003c/sup\u003e. The single electron wave functions are expanded in plane waves with kinetic energy cutoff of 700 eV. A vacuum thickness of 30 \u0026Aring; was used to decouple the periodic images along the thickness or the z direction. The Brillouin zones were sampled with 3 \u0026times; 1 \u0026times; 1 and 7 \u0026times; 2 \u0026times; 1 \u0026Gamma;-centered \u003cem\u003ek\u003c/em\u003e-mesh for geometric relaxations and electric polarization calculations, respectively. In structural relaxations, all ionic positions and the shape and volume were allowed to relax until the residual force on each atom was less than 0.0001 eV/\u0026Aring;. The electric charge of each atom was obtained by Bader charge analysis.\u003c/p\u003e\n\u003cp\u003e45. Perdew, J. P., Burke, K. \u0026amp; Ernzerhof, M. Generalized gradient approximation made simple. \u003cem\u003ePhys. Rev. Lett.\u003c/em\u003e \u003cstrong\u003e77\u003c/strong\u003e, 3865\u0026ndash;3868 (1996).\u003c/p\u003e\n\u003cp\u003e46. Ernzerhof, M. \u0026amp; Scuseria, G. E. Assessment of the Perdew\u0026ndash;Burke\u0026ndash;Ernzerhof exchange-correlation functional. \u003cem\u003eJ. Chem. Phys.\u003c/em\u003e \u003cstrong\u003e110\u003c/strong\u003e, 5029\u0026ndash;5036 (1999).\u003c/p\u003e\n\u003cp\u003e47. Kresse, G. \u0026amp; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. \u003cem\u003ePhys. Rev. B\u003c/em\u003e \u003cstrong\u003e59\u003c/strong\u003e, 1758\u0026ndash;1775 (1999).\u003c/p\u003e\n\u003cp\u003e48. Bl\u0026ouml;chl, P. E. Projector augmented-wave method. \u003cem\u003ePhys. Rev. B\u003c/em\u003e \u003cstrong\u003e50\u003c/strong\u003e, 17953\u0026ndash;17979 (1994).\u003c/p\u003e\n\u003cp\u003e49. Kresse, G. \u0026amp; Furthm\u0026uuml;ller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. \u003cem\u003ePhys. Rev. B\u003c/em\u003e \u003cstrong\u003e54\u003c/strong\u003e, 11169\u0026ndash;11186 (1996).\u003c/p\u003e\n\u003cp\u003e50. Grimme, S., Antony, J., Ehrlich, S. \u0026amp; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. \u003cem\u003eJ. Chem. Phys.\u003c/em\u003e \u003cstrong\u003e132\u003c/strong\u003e, 154104 (2010).\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":false,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"","lastPublishedDoi":"10.21203/rs.3.rs-4170610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4170610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePursuing ultrasensitivity in pressure sensors that offer precise mechano-electric transduction of tiny mechanical stimuli under complex ambient conditions, is of great importance and has been a long-standing goal\u003csup\u003e1-10\u003c/sup\u003e. The introduction of microstructures at micro- and nano-scale, can effectively improve the sensitivity, detection limit, and pressure-response range due to their structural asymmetries and compressibility\u003csup\u003e5,6,11-19\u003c/sup\u003e. However, numerous atom vacancies anticipated in sensors that are expected to exhibit giant asymmetries may make it difficult to maintain stability under ambient conditions. Here, we report a piezoelectric sensor that exhibits supreme pressure-sensing performance, including a peak sensitivity up to 3.5×10\u003csup\u003e6\u003c/sup\u003e kPa\u003csup\u003e−1\u003c/sup\u003e in the pressure range of 1-100 mPa and a detection limit of less than 1 mPa, superior to the current state-of-the-art pressure sensors. These properties are attributed to the high percentage of periodic atom vacancies in the two-dimensional Na\u003csub\u003e2\u003c/sub\u003eCl crystals formed within multilayered graphene oxide membrane in the sensor, which provides giant polarization with high stability. The sensor can even clearly detect the airflow fluctuations surrounding a flapping butterfly, which have long been the elusive tiny signals mentioned in the famous “butterfly effect”. The finding represents a step towards next-generation pressure sensors for various precision applications.\u003c/p\u003e","manuscriptTitle":"Ultrasensitive piezoelectric sensor based on two-dimensional Na2Cl crystals with periodic atom vacancies","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-15 07:24:51","doi":"10.21203/rs.3.rs-4170610/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":"9dfa86c4-683b-4531-b3a6-1d045cbdab50","owner":[],"postedDate":"April 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":30672218,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Two-dimensional materials"},{"id":30672219,"name":"Physical sciences/Nanoscience and technology/Nanoscale devices/Sensors"}],"tags":[],"updatedAt":"2025-09-16T08:02:08+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-15 07:24:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4170610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4170610","identity":"rs-4170610","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}