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Quasi-two-dimensional organic–inorganic hybrid halide perovskite materials have attracted extensive attention in the field of optoelectronic devices owing to their unique photoelectric properties. However, lead toxicity greatly hinders their practical applications. Using environmentally friendly elements to substitute lead is an effective solution, but even worse stability and photoelectric performance pose a great challenge for further device fabrication. Here, high-performance lead-free photodetectors (PDs) are developed based on a BA2FAn-1SnnI3n+1 (n = 1, 2) film via a one-step spin coating method. The films could be stable for two to three hours in ambient conditions. The devices show the dark current of 2.1 × 10−9 (n = 1) and 2.6 × 10−9 A (n = 2), the on/off ratio of 458 (n = 1) and 1108 (n = 2), and the detectivity of 1.46 × 1013 (n = 1) and 6.23 × 1012 Jones (n = 2), which were outstanding in the reported Sn-based PDs. The excellent performance is attributed to the low Sn4+ self-doping realized by adding Sn powder and SnF2 in a precursor solution in the synthesis process and the high-performance optoelectronic properties of FA-based perovskite. This study demonstrates that BA2FAn-1SnnI3n+1 is a promising material for photovoltaic devices.

Organic–inorganic hybrid perovskites have exhibited unprecedented advantages for x-ray photon detection due to their exotic properties. Their high-crystalline quality has a great impact for high-detection sensitivity under a low electric field, especially related to the synthesis method. In this work, we analyze the capability of CH3NH3PbI3 (MAPbI3) perovskites as an x-ray detection material and propose to control the temperature gradient (TG) during the synthesis of MAPbI3 single crystal perovskites for device fabrication. Our results show that the decreasing TG can effectively reduce the trap density and improve the crystal quality, which could lead to a boosted sensitivity of 1471.7 μC/Gyair/cm2 under a low electric field of 3.3 V/mm. In addition, a higher detection sensitivity can be achieved by increasing the electric field. Our work presents a strategy to construct high-performance direct x-ray detectors.

Topological insulators possess unique surface states, which can be very useful for low power electronics. Most research on topological insulators focuses on their fundamental physical properties, and until now, there has been little work on their practical applications. Here, we extend the application of topological insulators to the field of acoustics. We show that topological insulators can be used for sound source applications using a large area of Bi2Se3. The sound pressure level (SPL) can reach up to 30 dB with an 85 mW input at a measured 1 cm distance at room temperature. More interestingly, an anomalous valley with a sound pressure level (SPL) drop of ∼9 dB occurs at 21.5 kHz in a Bi2Se3 topological insulator, which is not observed in monolayer graphene. This anomalous phenomenon is related to the unique surface and bulk states of Bi2Se3. A theoretical equivalent circuit model is built for a topological insulator and compared with that of graphene. Based on the equivalent circuit model combined with thermoacoustic sound-generation theory, such an anomalous thermoacoustic effect with an SPL valley at around 21.5 kHz can be simulated. Our work shows that topological insulators have potential as powerful sound sources, such as earphones and loudspeakers, and that the unique surface states are highly conducive to frequency-selected sound emission.

TiS2 has been intensively studied as an electrode material and a thermoelectric material for energy storage and conversion applications due to its high electrical conductivity. Understanding the influence of defects on electrical transport is of importance not only to resolve the long-standing question concerning the nature of TiS2, but also for the rational design of TiS2 based devices for energy scavenging applications. In this study, we integrate photoemission spectroscopy, Raman spectroscopy, and electrical transport measurements to determine the chemical compositions dominated by defects and their influence on the doping and electrical properties. Our results demonstrate that TiS2 is a heavily self-doped semiconductor with the Fermi level close to the conduction band, which serves as the conclusive experimental evidence regarding the semiconducting nature of TiS2. The doping effect is sensitive to the (subtle) changes in the chemical composition. The electron donation from the Ti interstitials (Tii) to the TiS2 host explains the high carrier concentration. The Ti Frenkel pair (TiF) acting as the acceptor is responsible for the decrease in the electron carrier concentration and electrical conductivity. High conductivity maintains upon partial oxidization, indicating the oxidization-tolerance in terms of the electronic structure. Our results provide valuable insight into the evolution of electronic properties modulated by defects that reveal unambiguously the self-doped semiconducting nature of TiS2 and chemical- and environment-tolerance of TiS2 as an advanced energy scavenging material.

To explore the effect of the ZrO2 content on the switching speed of ferroelectric HfO2-ZrO2 (FE-HZO), we demonstrate 10 nm FE-HZO capacitors fabricated with 5:5, 6:4, and 7:3 HfO2 and ZrO2 atomic-layer-deposition-cycling ratios. The FE-HZO devices show high remanent polarization (Pr) of 26, 20, and 11 μC/cm2 for the 5:5, 6:4, and 7:3 samples, respectively. The FE-HZO capacitors with lower ZrO2 contents show increasing coercive fields, which intuitively seem to increase switching difficulty. However, the FE-HZO devices with 50 mol. %, 40 mol. %, and 30 mol. % ZrO2 contents show decreasing switching times for 80% polarization, namely, 1.2, 0.9, and 0.7 μs, respectively. Because of the polycrystalline nature of FE-HZO, the distribution of local fields in the film is analyzed based on the inhomogeneous field mechanism model. The results show that the FE-HZO devices with lower ZrO2 contents have higher active fields and less uniform distribution of local fields. However, time constants for the 5:5, 6:4, and 7:3 samples decrease dramatically, being 137, 98, and 14 ps, respectively. These results unveil the distribution of the local fields in FE-HZO with varying ZrO2 contents and are helpful for understanding and optimizing the switching dynamics of FE-HZO for non-volatile memory applications.

Vacuum pressure sensors play a significant role in industry and scientific research. However, there are still many challenges for further application of vacuum pressure sensors due to their complex fabrication and high cost. In this work, we have fabricated a graphene vacuum pressure sensor by one-step laser scribing within 25 min. The resistance of the sensor decreases with declining vacuum pressure. Four linear segments are obtained in the relationship between the resistance response and the vacuum pressure ranging from 7.5 × 10−4 Torr to 2.35 Torr at room temperature. Besides, the graphene sensor exhibits a high sensitivity of 1.2 × 10−2 Torr−1 and a rapid response time of 9 s, which are superior to previously reported sensors. The sensing mechanism of the graphene vacuum pressure sensor is investigated. Under the influence of van der Waals interactions between the stacked graphene multilayers, the void space among the neighboring graphene layers reduces with decreasing vacuum pressure, resulting in a decrease of the sheet resistance. The designed graphene vacuum pressure sensor with the distinguished features of high performance, small size, low cost, and simple fabrication shows great feasibility and tremendous potential for vacuum measurement applications.

The discovery of HfO2-based ferroelectric (FE) films gives FE memory devices great potential for the next-generation memory technology. In this letter, TiNx with varying nitrogen atomic contents was demonstrated as electrodes of FE Hf0.5Zr0.5O2 memory devices on quartz substrates for transparent memory applications. The transmittance and reflectance from 350 nm to 2500 nm of the TiNx/Hf0.5Zr0.5O2/TiNx structures generally increased and decreased, respectively. Selectivity between the visible and infrared light altered as the N content is increased. When the N2 ratio increases from 0% to 30%, the transmittance selectivity between 1064 nm (infrared) and 532 nm (green) lights increases from 79.6% to 105.3%, while the reflectance selectivity decreases from 107.9% to 48.9%. The polarization cycling performance of FE TiNx/Hf0.5Zr0.5O2/TiNx was explored up to 107 times. The devices with N-rich TiNx electrodes showed suppression of the wake-up effect during cycling. The transient current loops and atomic-fraction depth profiles of capacitors were inspected as well. The results indicated that there were fewer oxygen-vacancy defects in the as-grown N-rich devices and no influential redistribution of oxygen-vacancy defects during the cycling.

In this paper, low-voltage, large-strain flexible electrothermal actuators (ETAs) based on laser-reduced graphene oxide (LRGO)/Ag particle composites were fabricated in a simple and cost-efficient process. By adding Ag particles to the LRGO, the sheet resistance decreased effectively. Under a driving voltage of 28 V, the actuator obtained a bending angle of 192° within 6 s. Besides, the bending deformation could be precisely controlled by the driving voltage ranging from 10° to 192°. Finally, a gripper composed of two actuators was demonstrated to manipulate a piece of polydimethylsiloxane block. With the advantages of low-voltage, fast-response, and easy-to-manufacture, the graphene based ETAs have a promising application in soft robotics and soft machines.

In this paper, we have developed a high-performance graphene electrothermal actuator (ETA). The fabrication method is easy, fast, environmentally friendly, and suitable for preparing both large-size and miniature graphene ETAs. When applied with the driving voltage of 65 V, the graphene ETA achieves a large bending angle of 270° with a fast response of 8 s and the recovery process costs 19 s. The large bending deformation is reversible and can be precisely controlled by the driving voltage. A simple robotic hand prepared by using a single graphene ETA can hold the object, which is more than ten times the weight of itself. By virtue of its large-strain, fast response, and easy-to-manufacture, we believe that the graphene ETA has tremendous potential in extensive applications involving biomimetic robotics, artificial muscles, switches, and microsensors in both macroscopic and microscopic fields.

Existing thermoacoustic devices are based on a complicated fabrication process, which extremely limits their practical applications. In this paper, we realize a flexible graphene sound device based on laser reduced graphene. The graphene oxide is converted into graphene by a 450 nm laser with a one-step process. The performance of the graphene sound device is affected by the laser power, the scanning speed, and the substrate thickness. The experimental results match well with the theoretical results. Besides, the sound device has the advantages of excellent flexibility, broad frequency spectrum (0–40 kHz), fast fabrication process, and low cost, which will become a promising alternative in the flexible electronic systems in the future.

In this paper, a flexible, wearable, and functional graphene-textile composite is demonstrated. Laser scribing technology is applied to fabricate a graphene film. The thin layer of polydimethylsiloxane is covered on the surface of the graphene-textile film evenly, which would improve the abrasive resistance of the film, enhance the ability to adapt to environmental changes, and extend the service life, while maintaining the device's excellent flexibility and comfort. The graphene-textile composite can achieve constant temperature heating by controlling the input voltage, detect the human movement, and perceive the human pulse signal. The composite presents great commercial prospects and a large value in the medical, daily wear, and other areas that are closely related to human lives.

This letter investigates repeated uniaxial mechanical stress-induced degradation behavior in flexible amorphous In-Ga-Zn-O thin-film transistors (TFTs) of different geometric structures. Two types of via-contact structure TFTs are investigated: symmetrical and UI structure (TFTs with I- and U-shaped asymmetric electrodes). After repeated mechanical stress, I-V curves for the symmetrical structure show a significant negative threshold voltage (VT) shift, due to mechanical stress-induced oxygen vacancy generation. However, degradation in the UI structure TFTs after stress is a negative VT shift along with the parasitic transistor characteristic in the forward-operation mode, with this hump not evident in the reverse-operation mode. This asymmetrical degradation is clarified by the mechanical strain simulation of the UI TFTs.

In this letter, the effects of hot carriers on amorphous In-Ga-Zn-O thin film transistors (TFTs) of different geometric structures were investigated. Three types of via-contact structure TFTs are used in this experiment, defined as source-drain large (SD large), source-drain normal (SD normal), and fork-shaped. After hot-carrier stress, the I-V curves of both SD normal and fork-shaped TFTs with U-shaped drains show a threshold voltage shift along with the parasitic transistor characteristic in the reverse-operation mode. Asymmetrical degradation is exhibited in an ISE-TCAD simulation of the electric field, which shows the distribution of hot electrons injected into the etch-stop layer below the redundant drain electrode.

In this paper, a flexible, simple-preparation, and low-cost graphene-silk pressure sensor based on soft silk substrate through thermal reduction was demonstrated. Taking silk as the support body, the device had formed a three-dimensional structure with ordered multi-layer structure. Through a simple and low-cost process technology, graphene-silk pressure sensor can achieve the sensitivity value of 0.4 kPa − 1, and the measurement range can be as high as 140 kPa. Besides, pressure sensor can have a good combination with knitted clothing and textile product. The signal had good reproducibility in response to different pressures. Furthermore, graphene-silk pressure sensor can not only detect pressure higher than 100 kPa, but also can measure weak body signals. The characteristics of high-sensitivity, good repeatability, flexibility, and comfort for skin provide the high possibility to fit on various wearable electronics.

Graphene woven fabrics (GWFs) consisting of a large number of overlapping graphene micro-ribbons were fabricated by chemical vapor deposition. We demonstrated that GWF films can emit sound efficiently once they are actuated by a sound-frequency electric field owing to the thermoacoustic effect. Because of its ultra-low heat capacity per unit area, the GWF shows sound generation performance comparable to single-layer graphene and carbon nanotubes, and would perform better than them when it is suspended on a high porosity substrate. This sound source can be used in a wide variety of applications, taking advantage of its transparency, flexibility, ultrathin nature, absence of moving parts, and biologically compatible characteristics.

A silicon junctionless (JL) trench gate-all-around (GAA) nanowire field-effect transistor with an atomically thin channel thickness of 0.65 nm and a very thin oxide with a thickness of 12.3 nm are demonstrated experimentally. Experimental results indicate that this device with a channel thickness of 0.65 nm achieves a sub-threshold slope (SS) of 43 mV/decade, which is the best yet achieved by any reported JLFET. Owing to the atomically thin channel, this device has an extremely high ION/IOFF current ratio of >108. Furthermore, the atomically thin channel GAA JLFET exhibits a low threshold voltage (VTH) variation and negligible drain-induced barrier lowering (DIBL

Tunneling electroresistance (TER) effect has been observed in high quality ultrathin BiFeO3 thin films. The growth quality of the ultrathin BiFeO3 films was confirmed using the synchrotron high resolution X-ray diffraction techniques as well as high-resolution transmission electron microscopy. Ferroelectric-based resistive switching behavior is observed down to 2 u.c. of BiFeO3 ultrathin film, which is way below the critical thickness of BiFeO3 thin films exhibiting ferroelectricity reported in the previous research works. Upon fitting mathematically using the direct tunneling model, it could be seen that there is an increase in the change in the average potential barrier height when the barrier thickness increases from 2 u.c. to 10 u.c., which also results in an increase in the TER ratio by one order of magnitude. These results are promising and pave the way for developing ultrathin BiFeO3 films to be adopted in the non-volatile memory applications.

The application of epitaxial yttrium iron garnet (YIG) thin film on high frequency on-chip spiral inductors is investigated. The YIG thin film with the thickness of 3.6 μm was grown on GGG(111) substrate using the liquid phase method, which exhibits relatively high saturation magnetization 4πMs of 1615 Oe close to the bulk value of 1750 Oe and low initial coercivity Hc of 0.5 Oe that minimizes the hysteretic losses. Subsequently, the spiral inductors were directly fabricated on the YIG/GGG(111) substrate. The results show substantial improvement in the optimum operating frequency and self-resonance frequency of the on-chip spiral inductor with the YIG thin film with an increase of 50% up to ∼7.5 GHz and 14.2 GHz, respectively, implying that on-chip spiral inductors with the YIG thin film can be applied to much higher frequency RF circuits.

In this paper, a flexible heater based on anisotropic laser-reduced graphene oxide (LRGO) is established. Attributing to precision and shape design of laser processing and excellent adhesion of graphene oxide, the LRGO-based heater can be microminiaturized with custom patterns and integrated on various substrates, which is what the existing film heaters cannot do and can be widely used for wearable heating devices, flexural warming systems in medical science, and light deicing equipment and heaters for aero vehicles. The electrothermal performance of the anisotropic LRGO is investigated systematically through a series of experiments including Raman spectra, SEM, white-light interferograms, IV testing, and infrared thermography. The electrothermal performance of the LRGO with the parallel aligned direction is better than the LRGO with the vertical aligned direction. The electrothermal performance can be improved greatly through radiating repeatedly. The saturated temperature and heating rate of the LRGO ra...

Molybdenum disulfide is a promising channel material for field effect transistors (FETs). In this paper, monolayer MoS2 grown by chemical vapor deposition (CVD) was used to fabricate top-gate FETs through standard optical lithography. During the fabrication process, charged impurities and interface states are introduced, and the photoresist is not removed cleanly, which both limit the carrier mobility and the source-drain current. We apply a SiO2 protective layer, which is deposited on the surface of MoS2, in order to avoid the MoS2 directly contacting with the photoresist and the ambient environment. Therefore, the contact property between the MoS2 and the electrodes is improved, and the Coulomb scattering caused by the charged impurities and the interface states is reduced. Comparing MoS2 FETs with and without a SiO2 protective layer, the SiO2 protective layer is found to enhance the characteristics of the MoS2 FETs, including transfer and output characteristics. A high mobility of ∼42.3 cm2/V s is achi...

Van der Waals epitaxialgrowth had been thought to have trivial contribution on inducing substantial epitaxial strain in thin films due to its weak nature of van der Waals interfacial energy. Due to this, electrical and optical structure engineering via van der Waals epitaxial strain has been rarely studied. In this report, we show that significant band structure engineering could be achieved in a soft thin film material PbI2 via van der Waals epitaxy. The thickness dependent photoluminescence of single crystal PbI2 flakes was studied and attributed to the substrate-film coupling effect via incommensurate van der Waals epitaxy. It is proposed that the van der Waals strain is resulted from the soft nature of PbI2 and large van der Waals interaction due to the involvement of heavy elements. Such strain plays vital roles in modifying the band gap of PbI2. The deformation potential theory is used to quantitatively unveil the correlation between thickness, strain, and band gap change. Our hypothesis is confirmed by the subsequent mechanical bending test and Raman characterization.

Gallium nitride epitaxial layers were grown on sapphire by molecular-beam epitaxy using nitridated gallium metal films as buffer layers. The mechanical properties of the buffer layers were investigated and correlated with their chemical composition as determined by synchrotron radiation photoelectron spectroscopy. Biaxial tension experiments were performed by bending the substrates in a pressure cell designed for simultaneous photoluminescence measurements. The shift of the excitonic luminescence peak was used to determine the stress induced in the main GaN epilayer. The fraction of stress transferred from substrate to main layer was as low as 27% for samples grown on nitridated metal buffer layers, compared to nearly 100% for samples on conventional low-temperature GaN buffer layers. The efficiency of stress relief increased in proportion to the fraction of metallic Ga in the nitridated metal buffer layers. These findings suggest GaN films containing residual metallic Ga may serve as compliant buffer layers for heteroepitaxy.

The comprehensive parameter space of self-oscillation and its period-doubling route to chaos are shown for bounded beam-plasma systems. In this parametrization, it is helpful to use a potentially universal parameter in close analogy with free-electron-laser chaos. A common parameter, which is related to the velocity slippage and the ratio of bounce to oscillation frequencies, is shown to have similar significance for different physical systems. This single parameter replaces the dependences on many input parameters, thus suitable for a simplifying and diagnostic measure of nonlinear dynamical and chaotic phenomena for various systems of particle-wave interactions. The results of independent kinetic simulations verify those of nonlinear fluid simulations.

For a low dielectric constant intermetal dielectric application, fluorinated silicon oxide (FxSiOy) films were deposited in an electron cyclotron resonance chemical vapor deposition system, with SiH4, O2, and CF4 as the reaction gases. Since the CF4 is an indirect fluorinating precursor, the fluorinating mechanism resembles that of the oxide etching by a fluorocarbon plasma. Thermal stability of the incorporated fluorine (and hence, the dielectric constant) relies heavily on the deposition parameters and technologies. According to experimental results, adding Ar gas during deposition can improve the thermal stability of incorporated fluorine. Such an improvement is due to the fact that Ar sputtering enhances the removal of weakly bonded silicon fluoride on the as-deposited film surface, thereby elevating the mean bonding strength of fluoride remaining in the oxide.

ZnS:Cu nanocrystals were synthesized in polymeric networks. X-ray photoemission spectroscopy and atomic absorption data show that the Zn and Cu ion mass contents were about 8.2% and 0.12%, respectively. The particle size of ZnS:Cu nanocrystals was about 3.0 nm, measured by UV-vis spectrum. Due to the quantum size effects, the band gap energy of ZnS nanocrystals was about 4.2 eV. Compared with the photoluminescence of ZnS which peaks at 390 nm, the photoemission of ZnS:Cu/polymer thin films was peaking at 415 nm because of Cu acting as luminescent centers. The ZnS:Cu/polymer was also used to fabricate light-emitting diode (LED), as the emitting layer of LED, the blue light of electroluminescence was observed at room temperature, and its turn-on voltage was less than 4 V.

The hexagonal ZnS nanocrystals were synthesized in polymer matrix. The ZnS polymer composite doped with tetraphenylbenzidine (TPB) as light‐emitting layer was used to fabricate a single layer structure light‐emitting diode which has a low turn on voltage such as 2.5 V. The electroluminescence spectrum was obtained at room temperature. Owing to the effect that TPB interacted with ZnS nanocrystal to form the luminescent center, the emission was peaking at 520 nm which shifts to the lower energy compared with that of ZnS, and the half‐width of the emission was about 20 nm.

We use real time, high sensitivity infrared reflectance spectroscopy to quantitatively study hydrogen incorporation during the growth of hydrogenated amorphous silicon by magnetron sputtering. For the range of deposition conditions studied (substrate temperature between 120 and 270 °C and H2 partial pressure between 0.1 and 1.0 mTorr, which result in film hydrogen content between 10 and 30 at. %), hydrogen incorporation reaches steady state for film thickness, d≳25 A. Deviations from uniform growth for d

In this article, an expression for the surface passivation has been derived in terms of the surface recombination velocity and the field-effect exponential. The analytical solutions provide a comprehensive understanding of the injection dependency of minority charge carrier lifetime as measured by photoconductance decay. The model has been utilized to analyze the field-effect passivation of silicon exerted by the fixed dielectric charge in an overlying dielectric film. Possible limitations and restrictions of the technique are also addressed.

In this work, we fabricate a heterojunction small-signal generator (HSSG) based on a graphene-molybdenum disulfide (MoS2) heterojunction. The HSSG is fundamentally different from any analog device developed previously. The HSSG is composed of two quasi-2D heterojunctions and has three terminals named injector (I), recombinator (R), and generator (G). MoS2 serves as I and G, and graphene works as R in the HSSG. The scale coefficient (β = IG/IR) of the HSSG is 1.14 × 10−4 (VIG, IR = 0.2 V) to 1.95 × 10−4 (VIG, IR = 1 V). The current generated from G could be as low as pA scale, which reveals the good performance of the HSSG.

A compositionally matched superlattice-like (SLL) structure comprised of Ge2Sb2Te5 (GST) and nitrogen-doped GST (N-GST) was developed to achieve both low current and high endurance Phase Change Random Access Memory (PCRAM). N-GST/GST SLL PCRAM devices demonstrated ∼37% current reduction compared to single layered GST PCRAM and significantly higher write/erase endurances of ∼108 compared to ∼106 for GeTe/Sb2Te3 SLL devices. The improvements in endurance are attributed to the compositionally matched N-GST/GST material combination that lowers the diffusion gradient between the layers and the lower crystallization-induced stress in the SLL as revealed by micro-cantilever stress measurements.

Visible-light photoresponse of an AlN-based film bulk acoustic wave resonator (FBAR) is demonstrated. It is found that the FBAR exhibits a resonant frequency downshift under purple light illumination and the magnitude of the frequency downshift increases as the power density increases within the range of 5–40 mW/cm2. A resonant frequency downshift of 1313 KHz is observed under 40 mW/cm2 illumination, corresponding to a minimum detection power of 6.09 nW. A sub-bandgap photoresponse of the AlN thin film is proposed to explain this phenomenon.

We analyze the conversion efficiency of a bilayered thermoelectric composite, and conclude that thermoelectric conversion efficiency of a composite is not bounded by its constituents, and can be higher than all its constituents in the absence of size and interface effects. Conditions on constituent phases for enhanced conversion efficiency are also identified, and the upper bound on their conversion efficiency is established. This points to a new route for high efficiency thermoelectric materials.