Junction Piezotronic Transistor Arrays Based on Patterned ZnO Nanowires for High-Resolution Tactile and Photo Mapping.

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel's center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human-computer interaction, and electronic skin.

Single-mode lasing of CsPbBr3 perovskite NWs enabled by the Vernier effect.

Inorganic lead halide perovskite (CsPbX3, X = Cl, Br, I) NWs (NWs) have been employed in lasers due to their intriguing attributes of tunable wavelength, low threshold, superior stability, and easy preparation. However, current CsPbX3 NW lasers usually work in a multi-mode modal, impeding their practical applications in optical communication due to the associated false signaling. In this work, high-performance single-mode lasing has been demonstrated by designing and fabricating coupled cavities in the high-quality single-crystal CsPbBr3 NWs via the focused ion beam (FIB) milling approach. The single-mode laser shows a threshold of 20.1 µJ cm-2 and a high quality factor of ∼2800 profiting from the Vernier effect, as demonstrated by the experiments and finite-different time-domain (FDTD) simulations. These results demonstrate the promising potentials of the CsPbX3 NW lasers in optical communication and integrated optoelectronic devices.

Strain-modulated high-quality ZnO cavity modes on different crystal orientations.

Dynamically regulated coherent light emission offers a significant impact on improving white light generation, optical communication, on-chip photonic integration, and sensing. Here, we have demonstrated two mechanisms of strain-induced dynamic regulation of ZnO lasing modes through an individual ZnO microbelt and microrod prepared by vapor-phase transport method. We systematically explained the dependence on externally applied strain and crystal orientation. Compared with the reduced size of resonant cavity played a major role in the microbelt, the resonant wavelength variation of the microrod under tensile stress is affected by the change in both the cavity size and the refractive index, which tends to antagonize in the direction of movement. It shows that the refractive index can be effectively regulated only when the stress is in the same direction along the c-axis. The results on the linear relationship between the resonance wavelength variation and applied strain imply the capacity of the devices to detect tiny stresses due to the ultra-narrow line width of the cavity mode with a high-quality factor of âˆ¼104. It not only has a positive influence in the field of the modulated coherent light source, but also provides a feasible strategy for implementing color-resolved non-contact strain sensors.

Piezoelectricity in Multilayer Black Phosphorus for Piezotronics and Nanogenerators.

Recently, piezoelectric characteristics have been a research focus for 2D materials because of their broad potential applications. Black phosphorus (BP) is a monoelemental 2D material predicted to be piezoelectric because of its highly directional properties and non-centrosymmetric lattice structure. However, piezoelectricity is hardly reported in monoelemental materials owing to their lack of ionic polarization, but piezoelectric generation is consistent with the non-centrosymmetric structure of BP. Theoretical calculations of phosphorene have explained the origin of piezoelectric polarization among P atoms. However, the disappearance of piezoelectricity in multilayer 2D material generally arises from the opposite orientations of adjacent atomic layers, whereas this effect is limited in BP lattices due to their spring-shaped space structure. Here, the existence of in-plane piezoelectricity is experimentally reported for multilayer BP along the armchair direction. Current-voltage measurements demonstrate a piezotronic effect in this orientation, and cyclic compression and release of BP flakes show an intrinsic current output as large as 4 pA under a compressive strain of -0.72%. The discovery of piezoelectricity in multilayer BP can lead to further understanding of this mechanism in monoelemental materials.

Two Photon-Pumped Whispering-Gallery Mode Lasing and Dynamic Regulation.

Realizing the dynamic regulation of nonlinear optical signals has a great scientific significance for the development of new-type nonlinear optoelectronic devices and expands its application in the field of laser technology, spectroscopy, material structure analysis, etc. Here, two photon absorption-induced whispering-gallery mode lasing from a single ZnO microresonator with a relatively low lasing threshold (15 µW) and high quality factor (Q ≈ 3200) under ambient conditions is demonstrated. Furthermore, success is achieved in obtaining the dynamic regulation of two photon-pumped lasing mode in the UV gain region. The corresponding resonant wavelength can be tuned dynamically from 388.99 and 391.12 to 390.01 and 392.12 nm for TE33 and TE32 modes, respectively. This work provides a new strategy for building high-performance mode-adjustable frequency upconversion lasers.

Crystal-Orientation-Related Dynamic Tuning of the Lasing Spectra of CdS Nanobelts by Piezoelectric Polarization.

Realizing dynamic wavelength tunability could bring about tremendous impacts in laser technology, pressure nanosensing, and lab-on-a-chip devices. Here, we demonstrate an original strategy to operate the lasing mode shift through reversible length changes of a CdS nanobelt, which is determined by the direction of piezoelectric polarization. The relationships between the direction of applied strain, the lasing mode shift, and the tunable effective refractive index are elaborated in detail. The correlation between the piezoelectric polarization-induced lasing mode red shift and the blue shift in the wavelength of the lasing mode output caused by the Poisson effect is discussed in depth, as well. Our study comprehensively considers the influence of both the cavity size variations and refractive index changes on the control of the lasing mode and provides a deeper understanding of the strain-induced lasing mode shift.

Enhanced Electrochemical Properties of Li3 VO4 with Controlled Oxygen Vacancies as Li-Ion Battery Anode.

Li3 VO4 , as a promising intercalation-type anode material for lithium-ion batteries, features a desired discharge potential (ca. 0.5-1.0 V vs. Li/Li+ ) and a good theoretical storage capacity (590 mAh g-1 with three Li+ inserted). However, the poor electrical conductivity of Li3 VO4 hinders its practical application. In the present work, various amounts of oxygen vacancies were introduced in Li3 VO4 through annealing in hydrogen to improve its conductivity. To elucidate the influence of oxygen vacancies on the electrochemical performances of Li3 VO4 , the surface energy of the resulting material was measured with an inverse gas chromatography method. It was found that Li3 VO4 annealed in pure hydrogen at 400 °C for 15 min exhibited a much higher surface energy (60.7 mJ m-2 ) than pristine Li3 VO4 (50.6 mJ m-2 ). The increased surface energy would lower the activation energy of phase transformation during the charge-discharge process, leading to improved electrochemical properties. As a result, the oxygen-deficient Li3 VO4 achieved a significantly improved specific capacity of 495 mAh g-1 at 0.1 Ag-1 (381 mAh g-1 for pristine Li3 VO4 ) and retains 165 mAh g-1 when the current density increases to 8 Ag-1 .

Effects of Preinserted Na Ions on Li-Ion Electrochemical Intercalation Properties of V2O5.

Na-preinserted V2O5 samples of NaxV2O5 (x = 0.00, 0.005, 0.01, or 0.02) were synthesized through sol-gel and freeze-drying routes and subsequent calcination. X-ray diffraction (XRD) results showed that all of the synthesized materials have typical orthorhombic structures without impurity phases. The lattice parameters were refined via the Rietveld refinement method, and the results suggested that the lattice parameters of preinserted samples increased in comparison with pristine V2O5. X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the V(4+) concentration in the Na-preinserted V2O5 samples gradually increased as amount of sodium increased. Results from both XRD and XPS strongly suggested that Na ions indeed enter the interlamination position in the V2O5 crystal to expand the channels for Li-ion migration. NaxV2O5 samples exhibited improved electrochemical properties compared with those of pristine V2O5. Among all of the samples, Na0.01V2O5 delivered the highest reversible specific capacity, best cycling stability, and excellent rate capability. The analysis and discussion on ion diffusion revealed that the preinserted Na ions benefited the mobility of Li ions to improve the rate capabilities of electrodes.

Impacts of Surface Energy on Lithium Ion Intercalation Properties of V2O5.

Oxygen vacancies have demonstrated to be one of the most effective ways to alter electrochemical performance of electrodes for lithium ion batteries, though there is little information how oxygen vacancies affect the electrochemical properties. Vanadium pentoxide (V2O5) cathode has been investigated to explore the relationship among oxygen vacancies, surface energy, and electrochemical properties. The hydrogen-treated V2O5 (H-V2O5) sample synthesized via thermal treatment under H2 atmosphere possesses a high surface energy (63 mJ m(-2)) as compared to that of pristine V2O5 (40 mJ m(-2)) and delivers a high reversible capacity of 273.4 mAh g(-1) at a current density of 50 mA g(-1), retaining 189.0 mAh g(-1) when the current density increases to 2 A g(-1). It also displays a capacity retention of 92% after 100 cycles at 150 mA g(-1). The presence of surface oxygen vacancies increases surface energy and possibly serves as a nucleation center to facilitate phase transition during lithium ion intercalation and deintercalation processes.