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 si...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.展开更多
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...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.展开更多
Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,howeve...Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,however,require the use of materials such as narrow bandgap semiconductors,which are sensitive to thermal noise and often require cryogenic cooling.We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas,using a nonlinear wave-mixing process.We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation.In this process,an infrared image of a target is mixed inside the metasurface with a strong pump beam,translating the image from the infrared to the visible in a nanoscale ultrathin imaging device.Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.展开更多
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 ...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.展开更多
In this study, leaf-like one-dimensional InAs nanostructures were grown by the metal-organic chemical vapor deposition method. Detailed structural charac- terization suggests that the nanoleaves contain relatively low...In this study, leaf-like one-dimensional InAs nanostructures were grown by the metal-organic chemical vapor deposition method. Detailed structural charac- terization suggests that the nanoleaves contain relatively low-energy {122} or {133} mirror twins acting as their midribs and narrow sections connecting the nanoleaves and their underlying bases as petioles. Importantly, the mirror twins lead to identical lateral growth of the twinned structures in terms of crystallography and polarity, which is essential for the formation of lateral symmetrical nanoleaves. It has been found that the formation of nanoleaves is driven by catalyst energy minimization. This study provides a biomimic of leaf found in nature by fabricating a semiconductor nanoleaf.展开更多
Semiconductor nanowires(NWs)could simultaneously provide gain medium and optical cavity for performing nanoscale lasers with easy integration,ultracompact footprint,and low energy consumption.Here,we report Ⅲ-Ⅴsemic...Semiconductor nanowires(NWs)could simultaneously provide gain medium and optical cavity for performing nanoscale lasers with easy integration,ultracompact footprint,and low energy consumption.Here,we report Ⅲ-Ⅴsemiconductor NW lasers can also be used for self-frequency conversion to extend their output wavelengths,as a result of their non-centrosymmetric crystal structure and strongly localized optical field in the NWs.From a GaAs/In0.16Ga0.84As core/shell NW lasing at 1016 nm,an extra visible laser output at 508 nm is obtained via the process of second-harmonic generation,as confirmed by the far-field polarization dependence measurements and numerical modeling.From another NW laser with a larger diameter which supports multiple fundamental lasing wavelengths,multiple self-frequency-conversion lasing modes are observed due to second-harmonic generation and sum-frequency generation.The demonstrated self-frequency conversion of NW lasers opens an avenue for extending the working wavelengths of nanoscale lasers,even to the deep ultraviolet and THz range.展开更多
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 ...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.展开更多
In the last decades,metasurfaces have attracted much attention because of their extraordinary light-scattering properties.However,their inherently static geometry is an obstacle to many applications where dynamic tuna...In the last decades,metasurfaces have attracted much attention because of their extraordinary light-scattering properties.However,their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required.Currently,there is a quest to enable dynamic tuning of metasurface properties,particularly with fast tuning rate,large modulation by small electrical signals,solid state and programmable across multiple pixels.Here,we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon.We show a 9-fold change in transmission by<5 V biasing voltage and the modulation rise-time of<625µs.Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater.It allows for video frame rate optical switching over multiple pixels that can be electrically programmed.Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region,large modulation depth,working at transmission regime,exhibiting low optical loss,low input voltage requirement,and operating with higher than video-rate switching speed.The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays,virtual reality holography and light detection and ranging,where fast,solid-state and transparent optical switches are required.展开更多
Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the tele...Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the telecom band.Here,we report on-substrate vertical emitting lasing from ordered InGaAs/InP multi-quantum well core–shell nanowire array epitaxially grown on InP substrate by selective area epitaxy.To reduce optical loss and tailor the cavity mode,a new nanowire facet engineering approach has been developed to achieve controlled quantum well nanowire dimensions with uniform morphology and high crystal quality.Owing to the strong quantum confinement effect of InGaAs quantum wells and the successful formation of a vertical Fabry–Pérot cavity between the top nanowire facet and bottom nanowire/SiO_(2) mask interface,stimulated emissions of the EH11a/b mode from single vertical nanowires from an on-substrate nanowire array have been demonstrated with a lasing threshold of~28.2μJ cm^(−2) per pulse and a high characteristic temperature of~128 K.By fine-tuning the In composition of the quantum wells,room temperature,single-mode lasing is achieved in the vertical direction across a broad near-infrared spectral range,spanning from 940 nm to the telecommunication O and C bands.Our research indicates that through a carefully designed facet engineering strategy,highly ordered,uniform nanowire arrays with precise dimension control can be achieved to simultaneously deliver thousands of nanolasers with multiple wavelengths on the same substrate,paving a promising and scalable pathway towards future advanced optoelectronic and photonic systems.展开更多
Nonpolar m-plane AlGaN offers the advantage of polarization-free multiple quantum wells(MQWs)for ultraviolet(UV)emission and can be achieved on the sidewalls of selective area grown GaN nanowires.We reveal that the gr...Nonpolar m-plane AlGaN offers the advantage of polarization-free multiple quantum wells(MQWs)for ultraviolet(UV)emission and can be achieved on the sidewalls of selective area grown GaN nanowires.We reveal that the growth of AlGaN on GaN nanowires by metal organic chemical vapor deposition(MOCVD)is driven by vapor-phase diffusion,and consequently puts a limit on the pitch of nanowire array due to shadowing effect.An insight into the difficulty of achieving metal-polar AlGaN nanowire by selective area growth(SAG)in MOCVD is also provided and can be attributed to the strong tendency to form pyramidal structure due to a very small growth rate of{1011}semipolar planes compared to(0001)c-plane.The nonpolar m-plane sidewalls of GaN nanowires obtained via SAG provides an excellent platform for growth of nonpolar AlGaN MQWs.UV emission from mplane Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N MQWs grown on sidewalls of dislocation-free GaN nanowire is demonstrated in the wavelength range of 318–343 nm.展开更多
Catalyst-free InGaAs nanowires grown by selective area epitaxy are promising building blocks for future optoelectronic devices in the infrared spectral region.Despite progress,the role of pattern geometry and growth p...Catalyst-free InGaAs nanowires grown by selective area epitaxy are promising building blocks for future optoelectronic devices in the infrared spectral region.Despite progress,the role of pattern geometry and growth parameters on the composition,microstructure,and optical properties of InGaAs nanowires is still unresolved.Here,we present an optimised growth parameter window to achieve highly uniform In1-xGaxAs nanowire arrays on GaAs(111)B substrate over an extensive range of Ga concentrations,from 0.1 to 0.91,by selective-area metal-organic vapor-phase epitaxy.We observe that the Ga content always increases with decreasing In/(Ga+In)precursor ratio and group V flow rate and increasing growth temperature.The increase in Ga content is supported by a blue shift in the photoluminescence peak emission.The geometry of the nanowire arrays also plays an important role in the resulting composition.Notably,increasing the nanowire pitch size from 0.6 to 2μm in a patterned array shifts the photoluminescence peak emission by up to 120 meV.Irrespective of these growth and geometry parameters,the Ga content determines the crystal structure,resulting in a predominantly wurtzite structure for xGa≤0.3 and a predominantly zinc blende phase for xGa≥0.65.These insights on the factors controlling the composition of InGaAs nanowires grown by a scalable catalyst-free approach provide directions for engineering nanowires as functional components of future optoelectronic devices.展开更多
Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition.A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed,where its origin is helpful to deepen the u...Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition.A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed,where its origin is helpful to deepen the understanding of GaN nanorod growth.The pattern forms at the very early stages of nanorod growth,which consists of yellow luminescence at the edges and the non-luminous region at six vertices of the hexagon.To clarify its origin,we carried out detailed cathodoluminescence studies,electron microscopy studies and nanoscale secondary ion mass spectrometry at both the nanorod surface and cross-section.We found the pattern is not related to optical resonance modes or polarity inversion,which are commonly reported in GaN nanostructures.After chemical composition and strain analysis,we found higher carbon and nitrogen cluster concentration and large compressive strain at the pattern area.The pattern formation may relate to facet preferential distribution of non-radiative recombination centers related to excess carbon/nitrogen.This work provides an insight into strain distribution and defect-related emission in GaN nanorod,which is critical for future optoelectronic applications.展开更多
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 co...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.展开更多
The quest for net-zero emissions highlights the signifi-cance of hydrogen as a clean energy carrier,necessitating efficient production methods.Electrochemical water splitting emerges as a crucial method for hydrogen g...The quest for net-zero emissions highlights the signifi-cance of hydrogen as a clean energy carrier,necessitating efficient production methods.Electrochemical water splitting emerges as a crucial method for hydrogen generation,with its further advancement hinging on the development of effective bifunctional catalysts that are efficient in both oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).In this study,we develop the bifunctional electrocatalyst NiFe(OH)x/Fe/graphene through a simple solution-corrosion approach.The overpotentials required for OER and HER to achieve a current density of 10 mA cm^(−2) are 237 and 42 mV,respectively,while the overall water splitting occurs at a low cell voltage of 1.51 V for the same current density.Remarkably,the catalyst displays robust stability exceeding 70 h at 20 mA cm^(−2) in 1 M KOH.When scaled to 10×10 cm^(2),its performance is comparable to that of a smaller size 0.5×0.5 cm^(2) electrode,indicating the scalability of our method and potential for industrial-scale hydrogen production.Trace incorporation of iron and the facilitation by graphene modify the electronic structures and coordination environment in the amorphous NiFe(OH)x/Fe/graphene composite.This alteration enhances the distribution of active sites and reduces kinetic barriers for both HER and OER,thereby increasing its bifunctional catalytic activity.This study not only introduces a novel catalyst design that incorporates in-situ Fe metal powder within OER-active catalysts to generate HER active sites for enabling bifunctionality,but also offers a pathway to manufacture high performance electrocatalysts for industrial applications.展开更多
文摘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.
基金A.T.gratefully acknowledges the support of the Australian Research Council for a Future Fellowship(FT200100939)Discovery grant DP190101864+1 种基金A.T.also acknowledges financial support from the North Atlantic Treaty Organization Science for Peace and Security Programme project AMOXES(#G5634)ARC-NISDRG-NS210100083.
文摘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.
基金The authors acknowledge the use of the Australian National Fabrication Facility(ANFF),ACT Node.Rocio CamachoMorales acknowledges a grant from the Consejo Nacional de Ciencia y Tecnología(CONACYT),MexicoNikolay Dimitrov and Lyubomir Stoyanov acknowledge a grant from the EU Marie-Curie RISE program NOCTURNO+1 种基金Mohsen Rahmani acknowledges support from the UK Research and Innovation Future Leaders Fellowship(MR/T040513/1)Dragomir N.Neshev acknowledges a grant from the Australian Research Council(CE20010001,DP190101559).
文摘Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,however,require the use of materials such as narrow bandgap semiconductors,which are sensitive to thermal noise and often require cryogenic cooling.We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas,using a nonlinear wave-mixing process.We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation.In this process,an infrared image of a target is mixed inside the metasurface with a strong pump beam,translating the image from the infrared to the visible in a nanoscale ultrathin imaging device.Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.
文摘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.
文摘In this study, leaf-like one-dimensional InAs nanostructures were grown by the metal-organic chemical vapor deposition method. Detailed structural charac- terization suggests that the nanoleaves contain relatively low-energy {122} or {133} mirror twins acting as their midribs and narrow sections connecting the nanoleaves and their underlying bases as petioles. Importantly, the mirror twins lead to identical lateral growth of the twinned structures in terms of crystallography and polarity, which is essential for the formation of lateral symmetrical nanoleaves. It has been found that the formation of nanoleaves is driven by catalyst energy minimization. This study provides a biomimic of leaf found in nature by fabricating a semiconductor nanoleaf.
基金This work is supported by the National Key R&D Program of China(Grant Nos.2018YFA0307200 and 2017YFA0303800)the National Natural Science Foundation of China(Grant Nos.61775183,11634010,61905196,and 62005222)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.3102017jc01001,3102019JC008,and 3102019110x032)the Natural Science Basic Research Program of Shaanxi Province(2020JQ 222).
文摘Semiconductor nanowires(NWs)could simultaneously provide gain medium and optical cavity for performing nanoscale lasers with easy integration,ultracompact footprint,and low energy consumption.Here,we report Ⅲ-Ⅴsemiconductor NW lasers can also be used for self-frequency conversion to extend their output wavelengths,as a result of their non-centrosymmetric crystal structure and strongly localized optical field in the NWs.From a GaAs/In0.16Ga0.84As core/shell NW lasing at 1016 nm,an extra visible laser output at 508 nm is obtained via the process of second-harmonic generation,as confirmed by the far-field polarization dependence measurements and numerical modeling.From another NW laser with a larger diameter which supports multiple fundamental lasing wavelengths,multiple self-frequency-conversion lasing modes are observed due to second-harmonic generation and sum-frequency generation.The demonstrated self-frequency conversion of NW lasers opens an avenue for extending the working wavelengths of nanoscale lasers,even to the deep ultraviolet and THz range.
基金supported by the National Natural Science Foundation of China(51402078,21702041,and 11674354)the National Basic Research Program of China(2014CB660815)the Fundamental Research Funds for the Central Universities(JZ2016HGTB0711,JZ2016HGTB0719,and JZ2017HGPA0167)
文摘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.
基金The Royal Society and the Wolfson Foundation(RSWF\FT\191022)as well as the Australian Research Council through TMOS Centre of Excellence(CE20010001)and Discovery Project(DP200101353).
文摘In the last decades,metasurfaces have attracted much attention because of their extraordinary light-scattering properties.However,their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required.Currently,there is a quest to enable dynamic tuning of metasurface properties,particularly with fast tuning rate,large modulation by small electrical signals,solid state and programmable across multiple pixels.Here,we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon.We show a 9-fold change in transmission by<5 V biasing voltage and the modulation rise-time of<625µs.Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater.It allows for video frame rate optical switching over multiple pixels that can be electrically programmed.Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region,large modulation depth,working at transmission regime,exhibiting low optical loss,low input voltage requirement,and operating with higher than video-rate switching speed.The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays,virtual reality holography and light detection and ranging,where fast,solid-state and transparent optical switches are required.
基金supported by the Key Research and Development Program(2022YFA1404800)the National Natural Science Foundation of China(62375226,62375225,12374359,62105267)+1 种基金the Fundamental Research Funds for the Central Universities(23GH02023)the Analytical&Testing Center of Northwestern Polytechnical University and the Australian Research Council.The Australian National Fabrication Facility ACT Node is acknowledged for access to the epitaxial growth facilities.
文摘Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies,which require compact,multiwavelength laser sources at the telecom band.Here,we report on-substrate vertical emitting lasing from ordered InGaAs/InP multi-quantum well core–shell nanowire array epitaxially grown on InP substrate by selective area epitaxy.To reduce optical loss and tailor the cavity mode,a new nanowire facet engineering approach has been developed to achieve controlled quantum well nanowire dimensions with uniform morphology and high crystal quality.Owing to the strong quantum confinement effect of InGaAs quantum wells and the successful formation of a vertical Fabry–Pérot cavity between the top nanowire facet and bottom nanowire/SiO_(2) mask interface,stimulated emissions of the EH11a/b mode from single vertical nanowires from an on-substrate nanowire array have been demonstrated with a lasing threshold of~28.2μJ cm^(−2) per pulse and a high characteristic temperature of~128 K.By fine-tuning the In composition of the quantum wells,room temperature,single-mode lasing is achieved in the vertical direction across a broad near-infrared spectral range,spanning from 940 nm to the telecommunication O and C bands.Our research indicates that through a carefully designed facet engineering strategy,highly ordered,uniform nanowire arrays with precise dimension control can be achieved to simultaneously deliver thousands of nanolasers with multiple wavelengths on the same substrate,paving a promising and scalable pathway towards future advanced optoelectronic and photonic systems.
基金the ACT node of the NCRIS-enabled Australian National Fabrication Facility(ANFF-ACT).
文摘Nonpolar m-plane AlGaN offers the advantage of polarization-free multiple quantum wells(MQWs)for ultraviolet(UV)emission and can be achieved on the sidewalls of selective area grown GaN nanowires.We reveal that the growth of AlGaN on GaN nanowires by metal organic chemical vapor deposition(MOCVD)is driven by vapor-phase diffusion,and consequently puts a limit on the pitch of nanowire array due to shadowing effect.An insight into the difficulty of achieving metal-polar AlGaN nanowire by selective area growth(SAG)in MOCVD is also provided and can be attributed to the strong tendency to form pyramidal structure due to a very small growth rate of{1011}semipolar planes compared to(0001)c-plane.The nonpolar m-plane sidewalls of GaN nanowires obtained via SAG provides an excellent platform for growth of nonpolar AlGaN MQWs.UV emission from mplane Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N MQWs grown on sidewalls of dislocation-free GaN nanowire is demonstrated in the wavelength range of 318–343 nm.
文摘Catalyst-free InGaAs nanowires grown by selective area epitaxy are promising building blocks for future optoelectronic devices in the infrared spectral region.Despite progress,the role of pattern geometry and growth parameters on the composition,microstructure,and optical properties of InGaAs nanowires is still unresolved.Here,we present an optimised growth parameter window to achieve highly uniform In1-xGaxAs nanowire arrays on GaAs(111)B substrate over an extensive range of Ga concentrations,from 0.1 to 0.91,by selective-area metal-organic vapor-phase epitaxy.We observe that the Ga content always increases with decreasing In/(Ga+In)precursor ratio and group V flow rate and increasing growth temperature.The increase in Ga content is supported by a blue shift in the photoluminescence peak emission.The geometry of the nanowire arrays also plays an important role in the resulting composition.Notably,increasing the nanowire pitch size from 0.6 to 2μm in a patterned array shifts the photoluminescence peak emission by up to 120 meV.Irrespective of these growth and geometry parameters,the Ga content determines the crystal structure,resulting in a predominantly wurtzite structure for xGa≤0.3 and a predominantly zinc blende phase for xGa≥0.65.These insights on the factors controlling the composition of InGaAs nanowires grown by a scalable catalyst-free approach provide directions for engineering nanowires as functional components of future optoelectronic devices.
基金B.J.Z.would like to thank the China Scholarship Council and the Australia National University for her scholarship supportX.Y.thanks the National Natural Science Foundation of China(Nos.61974166 and 51702368)for financial supportWe would like to thank Dr.Xu Zhang from Zhengzhou University for helpful discussion on some of the strain aspects in this work.
文摘Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition.A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed,where its origin is helpful to deepen the understanding of GaN nanorod growth.The pattern forms at the very early stages of nanorod growth,which consists of yellow luminescence at the edges and the non-luminous region at six vertices of the hexagon.To clarify its origin,we carried out detailed cathodoluminescence studies,electron microscopy studies and nanoscale secondary ion mass spectrometry at both the nanorod surface and cross-section.We found the pattern is not related to optical resonance modes or polarity inversion,which are commonly reported in GaN nanostructures.After chemical composition and strain analysis,we found higher carbon and nitrogen cluster concentration and large compressive strain at the pattern area.The pattern formation may relate to facet preferential distribution of non-radiative recombination centers related to excess carbon/nitrogen.This work provides an insight into strain distribution and defect-related emission in GaN nanorod,which is critical for future optoelectronic applications.
基金We acknowledge the financial support of the NSF through Grants DMR 1507844,DMR 1531373,and ECCS 1509706 and also the financial support of the Australian Research Council and the European Research Council(Grant No.716471,ACrossWire)The Australian National Fabrication Facility(ACT Node)is acknowledged for access to the growth facility used in this workThe Australian Microscopy and Microanalysis Research Facility is acknowledged for access to the electron microscopes used in this work.
文摘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.
基金the funding support from the Australian Research Council(ARC)and the Australian Renewable Energy Agencythe funding support from the Macquarie University Research Fellowships.
文摘The quest for net-zero emissions highlights the signifi-cance of hydrogen as a clean energy carrier,necessitating efficient production methods.Electrochemical water splitting emerges as a crucial method for hydrogen generation,with its further advancement hinging on the development of effective bifunctional catalysts that are efficient in both oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).In this study,we develop the bifunctional electrocatalyst NiFe(OH)x/Fe/graphene through a simple solution-corrosion approach.The overpotentials required for OER and HER to achieve a current density of 10 mA cm^(−2) are 237 and 42 mV,respectively,while the overall water splitting occurs at a low cell voltage of 1.51 V for the same current density.Remarkably,the catalyst displays robust stability exceeding 70 h at 20 mA cm^(−2) in 1 M KOH.When scaled to 10×10 cm^(2),its performance is comparable to that of a smaller size 0.5×0.5 cm^(2) electrode,indicating the scalability of our method and potential for industrial-scale hydrogen production.Trace incorporation of iron and the facilitation by graphene modify the electronic structures and coordination environment in the amorphous NiFe(OH)x/Fe/graphene composite.This alteration enhances the distribution of active sites and reduces kinetic barriers for both HER and OER,thereby increasing its bifunctional catalytic activity.This study not only introduces a novel catalyst design that incorporates in-situ Fe metal powder within OER-active catalysts to generate HER active sites for enabling bifunctionality,but also offers a pathway to manufacture high performance electrocatalysts for industrial applications.
