Synthesis and Diameter-dependent Thermal Conductivity of InAs Nanowires

In this work, we synthesized high-quality In As nanowires by a convenient chemical vapor deposition method,and developed a simple laser heating method to measure the thermal conductivity of a single In As nanowire in air. During the measurement, a focused laser was used to heat one end of a freely suspended nanowire, with its other end embedded into a carbon conductive adhesive. In order to obtain the thermal conductivity of In As nanowires, the heat loss in the heat transfer process was estimated, which includes the heat loss through air conduction, the heat convection, and the radiation loss. The absorption ratio of the laser power in the In As nanowire was calculated. The result shows that the thermal conductivity of In As nanowires monotonically increases from 6.4 W m-1K-1to 10.5 W m-1K-1with diameters increasing from 100 nm to 190 nm, which is ascribed to the enhanced phonon-boundary scattering.

Highly stable lead-free Cs3Bi2I9 perovskite nanoplates for photodetection applications

Lead halide perovskites have received tremendous attentions recently for their excellent properties such as high light absorption coefficient and long charge carrier diffusion length. However, the stability issues and the existence of toxic lead cations have largely limited their applications in optoelectronic area. Herein, we report the synthesis and investigation of highly stable and lead-free Cs3Bi2I9 perovskite nanoplates for visible light photodetection applications. The Cs3Bi2I9 nanoplates were synthesized through a facile solution-processed method, which is also applicable to various substrates. The achieved nanoplates present very good crystal quality and exhibit excellent long-term stability even exposed in moist air for several months. Photodetectors were constructed based on these high-quality perovskite nanoplates for the first time, and display a maximum photoresponsivity of 33.1 mA/W under the illumination of 450 nm laser, which is six times higher than the solution-synthesized CH3NH3PbI3 nanowire photodetectors. The specific detectivity of these devices can reach up to 10^10 Jones. Additionally, the devices exhibit fast rise and decay time of 10.2 and 37.2 ms, respectively, and highly stable photoswitching behavior with their photoresponse well retaining under alternating light and darkness. This work opens up a new opportunity for stable and low-toxic perovskite-based optoelectronic applications.

Vapor growth of WSe2/WS2 heterostructures with stacking dependent optical properties

Two-dimensional(2D)vertically stacked heterostructures based on layered transition-metal dichalcogenides(MDCs)have remarkablepote ntial in future applications due to their rich in terlayer related properties,such as in terlayer excitons,tun able interlayer band alignments.However,the controlled growth of TMDC bilayer heterostructures with preferred stacking structure remains challenging.Here,we report atwo-step van der Waals epitaxial vapor growth of WSe2/WS2 vertically stacked bilayer heterostructures with controllable commensurate crystallographic alignments(so called AA and AB stacki ng),by controlling the deposition temperature.Moire patter ns were obtai ned in bothAA and AB stacked WSe2/WS2 heterostructures.The stacking configuration of the vertical heterostructures was verified by the secondharmonic generation signals.Photoluminescenee and Raman spectroscopy studies further confirm that the heterostructures with differentstacking configuration have obviously different optical properties,which is ascribed to the distinct in terlayer coupling and resonance excitation between the distinguishing AA and AB stacked heterostructures.The controlled growth of AA and AB stacked heterostructures could provide an importa nee platform not only for fun dame ntal researches but also for functional electronic and optoelectronic deviceapplications.

Van der Waals epitaxial growth and optoelectronics of a vertical MoS_(2)/WSe_(2)p-n junction

Two-dimensional(2D)transition metal dichalcogenides(TMDs)have attracted extensive attention due to their unique electronic and optical properties.In particular,TMDs can be fexibly combined to form diverse vertical van der Waals(vdWs)heterostructures without the limitation of lattice matching,which creates vast opportunities for fundamental investigation of novel optoelectronic applications.Here,we report an atomically thin vertical p-n junction WSe_(2)/MoS_(2)produced by a chemical vapor deposition method.Transmission electron microscopy and steady-state photoluminescence experiments reveal its high quality and excellent optical properties.Back gate feld efect transistor(FET)constructed using this p-n junction exhibits bipolar behaviors and a mobility of 9 cm^(2)/(V·s).In addition,the photodetector based on MoS_(2)/WSe_(2)heterostructures displays outstanding optoelectronic properties(R=8 A/W,D^(*)=2.93×10^(11)Jones,on/of ratio of 10^(4)),which benefted from the built-in electric feld across the interface.The direct growth of TMDs p-n vertical heterostructures may ofer a novel platform for future optoelectronic applications.