Realizing High Thermoelectric Performance in n-Type Se-Free Bi_(2)Te_(3)Materials by Spontaneous Incorporation of FeTe_(2)Nanoinclusions

Bi_(2)Te_(3)-based materials have drawn much attention from the thermoelectric community due to their excellent thermoelectric performance near room temperature.However,the stability of existing n-type Bi_(2)(Te,Se)_(3)materials is still low due to the evaporation energy of Se(37.70 kJ mol^(-1))being much lower than that of Te(52.55 kJ mol^(-1)).The evaporated Se from the material causes problems in interconnects of the module while degrading the efficiency.Here,we have developed a new approach for the high-performance and stable n-type Se-free Bi_(2)Te_(3)-based materials bymaximizing the electronic transport while suppressing the phonon transport,at the same time.Spontaneously generated FeTe_(2)nanoinclusions within the matrix during the melt-spinning and subsequent spark plasma sintering is the key to simultaneous engineering of the power factor and lattice thermal conductivity.The nanoinclusions change the fermi level of the matrix while intensifying the phonon scattering via nanoparticles.With a fine-tuning of the fermi level with Cu doping in the n-type Bi_(2)Te_(3)-0.02FeTe_(2),a high power factor of∼41×10^(-4)Wm^(-1)K^(-2)with an average zT of 1.01 at the temperature range 300-470 K are achieved,which are comparable to those obtained in n-type Bi_(2)(Te,Se)_(3)materials.The proposed approach enables the fabrication of high-performance n-type Bi_(2)Te_(3)-based materials without having to include volatile Se element,which guarantees the stability of the material.Consequently,widespread application of thermoelectric devices utilizing the n-type Bi_(2)Te_(3)-based materials will become possible.

Wearable Triboelectric Nanogenerators Based on Printed Polyvinylidene Fluoride Films Incorporated with Cobalt-Based Metal-Organic Framework for Self-Powered Mobile Electronics

In this study,wearable triboelectric nanogenerators comprising bar-printed polyvinylidene fluoride(PVDF)films incorporated with cobalt-based metal-organic framework(Co-MOF)were developed.The enhanced output performance of the TENGs was attributed to the phase transition of PVDF from a-crystals toβ-crystals,as facilitated by the incorporation of the MOF.The synthesis conditions,including metal ion,concentration,and particle size of the MOF,were optimized to increase open-circuit voltage(VOC)and open-circuit current(I_(SC))of PVDF-based TENGs.In addition to high operational stability,mechanical robustness,and long-term reliability,the developed TENG consisting of PVDF incorporated with Co-MOF(Co-MOF@PVDF)achieved a VOC of 194 V and an I_(SC)of 18.8μA.Furthermore,the feasibility of self-powered mobile electronics was demonstrated by integrating the developed wearable TENG with rectifier and control units to power a global positioning system(GPS)device.The local position of the user in real-time through GPS was displayed on a mobile interface,powered by the battery charged through friction-induced electricity generation.

Fabrication of ultrafine Nd-Fe-B powder by a modified reduction-diffusion process

In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.

Micro-Photoluminescence Confocal Mapping of Single V-Grooved GaAs Quantum Wire

We perform the micro-photoluminescence measurement at low temperatures and a scanning optical mapping with high spatial resolution of a single V-grooved GaAs quantum wire modified by the selective ion-implantation and rapid thermally annealing. While the mapping shows the luminescences respectively from the quantum wires and from quantum well areas between quantum wires in general, the micro-photoluminescence at liquid He temperatures reveals a plenty of spectral structures of the PL band for a single quantum wire. The spectral structures are attributed to the inhomogeneity and non-uniformity of both the space structure and compositions of real wires as well as the defects nearby the interface between quantum wire and surrounding quantum well structures. All these make the excitons farther localized in quasi-zero-dimensional quantum potential boxes related to these non-uniformity and/or defects. The results also demonstrate the ability of micro-photoluminescence measurement and mapping for the characterization of both opto-electronic and structural properties of real quantum wires.

Ultrasensitive Indium Phosphide Nanomembrane Wearable Gas Sensors

Air quality is deteriorating due to continuing urbanization and industrialization.In particular,nitrogen dioxide(NO_(2))is a biologically and environmentally hazardous byproduct from fuel combustion that is ubiquitous in urban life.To address this issue,we report a high-performance flexible indium phosphide nanomembrane NO_(2)sensor for real-time air quality monitoring.An ultralow limit of detection of~200 ppt and a fast response have been achieved with this device by optimizing the film thickness and doping concentration during indium phosphide epitaxy.By varying the film thickness,a dynamic range of values for NO_(2)detection from parts per trillion(ppt)to parts per million(ppm)level have also been demonstrated under low bias voltage and at room temperature without additional light activation.Flexibility measurements show an adequately stable response after repeated bending.On-site testing of the sensor in a residential kitchen shows that NO_(2)concentration from the gas stove emission could exceed the NO_(2)Time Weighted Average limit,i.e.,200 ppb,highlighting the significance of real-time monitoring.Critically,the indium phosphide nanomembrane sensor element cost is estimated at<0.1 US$due to the miniatured size,nanoscale thickness,and ease of fabrication.With these superior performance characteristics,low cost,and real-world applicability,our indium phosphide nanomembrane sensors offer a promising solution for a variety of air quality monitoring applications.

质子注入和快速退火对GaAs/AlGaAs量子阱红外探测器的影响

利用质子注入和快速退火技术改变GaAs/AlGaAs量子阱能级分布,使量子阱红外探测器的光电特性发生变化,在较大地移动了探测波长的同时,探测器的响应率、探测率以及暗电流特性也发生相应变化.在质子注入剂量为2.5×1015cm-2、快速退火条件为950℃、30s时,峰值探测波长移动2μm.

质子注入和快速退火对GaAs/AlGaAs量子阱能级结构的调整

本文介绍利用界面混合技术对ＧａＡｓ／ＡｌＧａＡｓ量子阱结构进行微调，通过荧光光谱和光响应电流谱给出了质子注入和快速返火对禁带宽度及导带内子带位置的影响，荧光光谱峰位随注入剂量（５ｘ１０４～５ｘ１０１５ｃｍ２）的增加从７６６ｕｍ持续蓝移至７５３ｕｍ，光响应峰值波长从８．２ｕｍ移至１０．３ｕｍ．

Real-time monitoring of polarization state deviations with dielectric metasurfaces

We propose and experimentally demonstrate a dielectric metasurface that allows monitoring of polarization deviations from an arbitrary elliptical input anchor state simply by tracking in real-time the output ratio between the powers of horizontal and vertical components after the metasurface.Importantly,this ratio can be enhanced corresponding to increased responsivity.Such nontrivial functionality is achieved by designing binary metasurfaces that realize tailored nonunitary and chiral polarization transformation.We experimentally demonstrate the operation at telecommunication wavelengths with enhanced responsivity up to 25 for various anchor states,including the strongly elliptical and circular.We also achieve the uncertainty of deviation measurement that is significantly better than the fundamental limit for nonchiral metasurfaces.

Large area van der Waals epitaxy of II-VI CdSe thin films for flexible optoelectronics and full-color imaging

The demand for future semiconductor devices with enhanced performance and lower cost has driven the development of epitaxial growth of high quality,free-standing semiconductor thin film materials without the requirement of lattice matching to the substrate,as well as their transfer to other substrates and associated device processing technology.This work presents a study on the van der Waals epitaxy based molecular beam epitaxy of CdSe thin films on two-dimensional layered mica substrates,as well as related etch-free layer transfer technology of large area,free-standing layers and their application in flexible photodetectors for full-color imaging.The photoconductor detectors based on these flexible CdSe thin films demonstrate excellent device performance at room temperature in terms of responsivity(0.2 A·W^(-1))and detectivity(1.5×10^(12)Jones),leading to excellent full-color imaging quality in the visible spectral range.An etch-free and damage-free layer transfer method has been developed for transferring these CdSe thin films from mica to other substrate for further device processing and integration.These results demonstrate the feasibility of van der Waals epitaxy method for growing high quality,large area,and free-standing epitaxial layers without the requirement for lattice matching to substrate for applications in low-cost flexible and/or monolithic integrated optoelectronic devices.

High-speed multiwavelength InGaAs/InP quantum well nanowire array micro-LEDs for next generation optical communications

Miniaturized light sources at telecommunication wavelengths are essential components for on-chip optical communication systems.Here,we report the growth and fabrication of highly uniform p-i-n core-shell InGaAs/InP single quantum well(QW)nanowire array light emitting diodes(LEDs)with multi-wavelength and high-speed operations.Two-dimensional cathodoluminescence mapping reveals that axial and radial QWs in the nanowire structure contribute to strong emission at the wavelength of~1.35 and~1.55μm,respectively,ideal for low-loss optical communications.As a result of simultaneous contributions from both axial and radial QWs,broadband electroluminescence emission with a linewidth of 286 nm is achieved with a peak power of~17μW.A large spectral blueshift is observed with the increase of applied bias,which is ascribed to the band-filling effect based on device simulation,and enables voltage tunable multi-wavelength operation at the telecommunication wavelength range.Multi-wavelength operation is also achieved by fabricating nanowire array LEDs with different pitch sizes on the same substrate,leading to QW formation with different emission wavelengths.Furthermore,high-speed GHz-level modulation and small pixel size LED are demonstrated,showing the promise for ultrafast operation and ultracompact integration.The voltage and pitch size controlled multi-wavelength highspeed nanowire array LED presents a compact and efficient scheme for developing high-performance nanoscale light sources for future optical communication applications.

Polarization-dependent optical engineering of ferroelectric domains

Ferroelectric domain engineering with infrared femtosecond laser pulses has been a powerful technique to achieve a spatially modulated second-order nonlinear coefficient in three dimensions.However,studies regarding the in-fluence of laser writing conditions on the light-induced ferroelectric domain inversion remain limited.Herein,an experimental study to reveal the role of laser polarization in light-induced domain inversions is discussed.The dependence of the optical threshold and maximal writing depth of inverted domains on light polarization is ex-perimentally investigated.The results are explained by considering the second-order nonlinear optical properties and birefringence-induced focus splitting in the crystal.These findings are useful in fabricating high-quality and large-scale ferroelectric domain structures for applications in optics,electronics,and quantum technologies.

Ballistic transport and quantum interference in InSb nanowire devices

An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron＇s wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.

Optical tuning of exciton and trion emissions in monolayer phosphorene

Monolayer phosphorene provides a unique two-dimensional(2D)platform to investigate the fundamental dynamics of excitons and trions(charged excitons)in reduced dimensions.However,owing to its high instability,unambiguous identification of monolayer phosphorene has been elusive.Consequently,many important fundamental properties,such as exciton dynamics,remain underexplored.We report a rapid,noninvasive,and highly accurate approach based on optical interferometry to determine the layer number of phosphorene,and confirm the results with reliable photoluminescence measurements.Furthermore,we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range.Based on our measured optical gap and the previously measured electronic energy gap,we determined the exciton binding energy to be~0.3 eV for the monolayer phosphorene on SiO_(2)/Si substrate,which agrees well with theoretical predictions.A huge trion binding energy of~100 meV was first observed in monolayer phosphorene,which is around five times higher than that in transition metal dichalcogenide(TMD)monolayer semiconductor,such as MoS_(2).The carrier lifetime of exciton emission in monolayer phosphorene was measured to be,220 ps,which is comparable to those in other 2D TMD semiconductors.Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.

Two-dimensional materials for light emitting applications:Achievement,challenge and future perspectives

The two-dimensional(2D)materials have been widely developed recently in material characteristics with advanced optical and electrical properties,and they have been extensively studied as candidates for the next generation of optoelectronic devices.This review will mainly focus on the preparation methods and the light emitting applications of 2D transition metal dichalcogenides(TMDs),2D black phosphorene(BP)and 2D perovskites.The review will first introduce the preparation methods for TMDs and BP.Due to the variations of band structure,exciton binding energies and light-matter interaction in TMDs and BP,the different light emitting devices(LEDs)designs based on TMDs and BP will be discussed and summarized.Then the review will turn the focus to 2D perovskites,starting with a description of the preparation methods for the different structural perovskites.In order to review and summarize the achievements of 2D perovskites-based LEDs,the high efficiency perovskites LEDs are discussed.Finally,the review will present challenges,opportunities,and outlook for the future development of 2D materials-based light emitting applications.

Growth and optical properties of InxGa1-xP nanowires synthesized by selective-area epitaxy

Ternary III-V nanowires （NWs） cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1-xP NW arrays using metal-organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. Transmission electron microscopy and energy dispersive X-ray measurements performed on cross- section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis.

Tunnel junctions in a III-V nanowire by surface engineering

We demonstrate a simple way of fabricating high performance tunnel devices from p-doped InAs nanowires by tailoring the n-doped surface accumulation layer inherent to InAs surfaces. By using appropriate ammonium sulfide based surface passivation before metallization without any further thermal treatment, we demonstrate characteristics of tunnel p-n junctions, namely Esaki and backward diodes, with figures of merit better than previously published for InAs homojunctions. The further optimization of both the surface doping, in a quantitative way, and the device geometry allows us to demonstrate that these nanowire-based technologically-simple diodes have promising direct current characteristics for integrated high frequency detection or generation.

Electrochemical hydrogenation of mixed-phase TiO2 nanotube arrays enables remarkably enhanced photoelectrochemical water splitting performance

We first report that photoelectrochemical （PEC） performance of electrochemically hydrogenated TiO2 nanotube arrays （TNTAs） as high-efficiency photoanodes for solar water splitting could be well tuned by designing and adjusting the phase structure and composition of TNTAs. Among various TNTAs annealed at different temperature ranging from 300 to 700℃, well-crystallized single anatase （A） phase TNTAs-400 photoanode shows the best photoresponse properties and PEC performance due to the favor- able crystallinity, grain size and tubular structures. After electrochemical hydrogenation （EH）. anatase- rutile （A-R） mixed phase EH-TNTAs-600 photoanode exhibits the highest photoactivity and PEC perfor- mance for solar water splitting. Under simulated solar illumination, EH-TNTAs-600 achieves the best photoconversion efficiency of up to 1.52% and maximum H2 generation rate of 40.4 ~mol h i cm-2, our- stripping other EH-TNTAs photoanodes. Systematic studies reveal that the signigicantly enhanced PEC performance for A-R mixed phaes EH-TNTAs-600 photoanode could be attributed to the synergy of A-R mixed phases and intentionally introduced Ti3~ （oxygen vacancies） which enhances the photoactivity over both UV and visible-light regions, and boosts both charge separation and transfer efficiencies. These findings provide new insight and guidelines for the construction of highly efficient TiO2-based devices for the application of solar water splitting.

Observation of polarity-switchable photoconductivity in lInitride/MoS_(x)core-shell nanowires

Ⅱ-Ⅴsemiconductor nanowires are indispensable building blocks for nanoscale electronic and optoelectronic devices.However,solely relying on their intrinsic physical and material properties sometimes limits device functionalities to meet the increasing demands in versatile and complex electronic world.By leveraging the distinctive nature of the one-dimensional geometry and large surface-to-volume ratio of the nanowires,new properties can be attained through monolithic integration of conventional nanowires with other easy-synthesized functional materials.Herein,we combine high-crystal-quality lInitridle nanowires with amorphous molybdenum sulfides(a-MoS)to construct II.nitride/a-MoS_(x) core-shell nanostructures.Upon light ilumination,such nanostructures exhibit striking spectrally distinctive photodetection characteristic in photoelectrochemical environment,demonstrating a negative photoresponsivity of-100.42 mA W^(-1)under 254 nm ilumination,and a positive photoresponsivity of 29.5 mA W^(-1)under 365 nm ilumination.Density functional theory calculations reveal that the successful surface modifcation of the nanowires via a-MoS_(x)decoration accelerates the reaction process at the electrolyte/nanowire interface,leading to the generation of opposite photocurrent signals under different photon ilumination.Most importantly,such polarity-switchable photoconductivity can be further tuned for multiple wavelength bands photodetection by simply adjusting the surrounding environment and/or tailoring the nanowire composition,showing great promise to build light-wavelength controllable sensing devices in the future.

Comprehensive analysis of two-dimensional charge transport mechanism in thin-film transistors based on random networks of single-wall carbon nanotubes using transient measurements

Understanding charge transport mechanisms in thin-film transistors based on random networks of single-wall carbon nanotubes(SWCNT-TFTs)is essential for further advances to improve the potential for various nanoelectronic applications.Herein,a comprehensive investigation of the two-dimensional(2D)charge transport mechanism in SWCNT-TFTs is reported by analyzing the temperature-dependent electrical characteristics determined from the direct-current and non-quasi-static transient measurements at 80-300 K.To elucidate the time-domain charge transport characteristics of the random networks in the SWCNTs,an empirical equation was derived from a theoretical trapping model,and a carrier velocity distribution was determined from the differentiation of the transient response.Furthermore,charge trapping and de-trapping in shallow-and deep-traps in SWCNT-TFTs were analyzed by investigating charge transport based on their trapping/de-trapping rate.The comprehensive analysis of this study provides fundamental insights into the 2D charge transport mechanism in TFTs based on random networks of nanomaterial channels.

Exploring the band structure of Wurtzite InAs nanowires using photocurrent spectroscopy

Nano Research volume We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs.Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory.The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate.From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs.This information is vital to the development of crystal phase engineering of this important III-V semiconductor.