Combining a progressive tandem junction design with a unique Si nanowire(SiNW)framework paves the way for the development of high‐onset‐potential photocathodes and enhancement of solar hydrogen production.Herein,a r...Combining a progressive tandem junction design with a unique Si nanowire(SiNW)framework paves the way for the development of high‐onset‐potential photocathodes and enhancement of solar hydrogen production.Herein,a radial tandem junction(RTJ)thin film water‐splitting photo‐cathode has been demonstrated experimentally for the first time.The photocathode is directly fab‐ricated on vapor‐liquid‐solid‐grown SiNWs and consists of two radially stacked p‐i‐n junctions,featuring hydrogenated amorphous silicon(a‐Si:H)as the outer absorber layer,which absorbs short wavelengths,and hydrogenated amorphous silicon germanium(a‐SiGe:H)as the inner layer,which absorbs long wavelengths.The randomly distributed SiNW framework enables highly efficient light‐trapping,which facilitates the use of very thin absorber layers of a‐Si:H(~50 nm)and a‐SiGe:H(~40 nm).In a neutral electrolyte(pH=7),the three‐dimensional(3D)RTJ photocathode delivers a high photocurrent onset of 1.15 V vs.the reversible hydrogen electrode(RHE),accompanied by a photocurrent of 2.98 mA/cm^(2) at 0 V vs.RHE,and an overall applied‐bias photon‐to‐current effi‐ciency of 1.72%.These results emphasize the promising role of 3D radial tandem technology in developing a new generation of durable,low‐cost,high‐onset‐potential photocathodes capable of large‐scale implementation。展开更多
An a-SiNx/nanocrystalline silicon [（nc-Si）/a-SiNx] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition （PECVD） system at low temperature （250℃）. The nc-Si layer is fabricated from...An a-SiNx/nanocrystalline silicon [（nc-Si）/a-SiNx] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition （PECVD） system at low temperature （250℃）. The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2 ×10^11 cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiNs insulator layer are obtained. The density of interface state at the midgap is calculated to be 1 ×10^10 cm^-2eV^-1 from the quasistatic and high frequency C - V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage （C- V） measurement at room temperature. An ultra-large hysteresis is observed in the C - V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiNx/Si substrate.展开更多
The a-SiNx/nanocrystalline silicon （nc-Si）/a-SiNx sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition （PECVD） system on p-type Si substrates. The nc-...The a-SiNx/nanocrystalline silicon （nc-Si）/a-SiNx sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition （PECVD） system on p-type Si substrates. The nc-Si layer in thickness 5nm is fabricated from a hydrogen-diluted silane gas by the layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layers are 3nm and 20nm, respectively. Frequency-dependent capacitance spectroscopy is used to study the electron tunnelling and the storage in the sandwiched structures. Distinct frequency-dependent capacitance peaks due to electrons tunnelling into the nc-Si dots and capacitance-voltage （C - V） hysteresis characteristic due to electrons storage in the nc-Si dots are observed with the same sample. Moreover, conductance peaks have also been observed at the same voltage region by conductance-voltage （G - V） measurements. The experimental results demonstrate that electrons can be loaded onto nc-Si dots via resonant tunnelling and can be stored in our a-SiNx/nc-Si/a-SiNx structures.展开更多
Self-oscillation is an intriguing and omnipresent phenomenon that governs a broad range of growth dynamics and formation of nanoscale periodic and delicate heterostructures.A self-oscillating growth phenomenon of cata...Self-oscillation is an intriguing and omnipresent phenomenon that governs a broad range of growth dynamics and formation of nanoscale periodic and delicate heterostructures.A self-oscillating growth phenomenon of catalyst droplets,consuming surface-coating a-Si/a-Ge bilayer,is exploited to accomplish a high-frequency alternating growth of ultrathin crystalline Si and Ge(c-Si/c-Ge)nano-slates,with Ge-rich layer thickness of 14–19 nm,embedded within a superlattice nanowire structure,with pre-known position and uniform channel diameter.A subsequent selective etching of the Ge-rich segments leaves a chain of ultrafine standing c-Si nanosheets down to~6 nm thick,without the use of any expensive high-resolution lithography and growth modulation control.A ternary-phase-competition model has been established to explain the underlying formation mechanism of this nanoscale self-oscillating growth dynamics.It is also suggested that these ultrathin nanosheets could help to produce ultrathin fin-channels for advanced electronics,or provide size-specified trapping sites to capture and position hetero nanoparticle for high-precision labelling or light emission.展开更多
Enhanced crystallization of Si nanocrystals(Si NCs)has been achieved in an Al_(2)O_(3):Er/Si:Er multilayer structure,which is fabricated by pulsed laser deposition and subsequent rapid thermal annealing.The Er atoms i...Enhanced crystallization of Si nanocrystals(Si NCs)has been achieved in an Al_(2)O_(3):Er/Si:Er multilayer structure,which is fabricated by pulsed laser deposition and subsequent rapid thermal annealing.The Er atoms introduce strains in the initial amorphous Si layers and serve as nucleation centers that enhance the crystallization of Si NCs at low annealing temperatures.The average size of Si NCs is well controlled by adjusting the Si layer thickness.Thanks to the formation of Si NCs and the favored chemical environment of Er3+after annealing around 600–700℃,optimized photoluminescence peaked at 1.54μm has been obtained.The present results stress the importance of controlling the formation of Si NCs to improve the performance of Er3+luminescence.展开更多
We demonstrate a simple while very effective approach to tune the photoluminescence （PL） performance of monolayer MoS2 by dipping into the H2O2 aqueous solution, which is a strong oxidizer that extracts electrons fr...We demonstrate a simple while very effective approach to tune the photoluminescence （PL） performance of monolayer MoS2 by dipping into the H2O2 aqueous solution, which is a strong oxidizer that extracts electrons from the MoS2 sheet within several seconds without damaging the crystal structure. During this process, the trion （electron-coupled exciton, X-） is transformed into an exciton （X°）, and thus achieves a greatly enhanced PL performance. These results indicate a convenient way to tune and to control the PL luminescence from monolayer MoS2 and thus lay a basis for the MoS2-based optoelectronic application.展开更多
基金国家重点基础研究发展规划(批准号:2001CB610503)和国家自然科学基金(批准号:90101020,90301009,10174035)资助项目 Project supported by the State Key Development Program for Basic Research of China(No. 2001CB610503) and the National Natural Science Foundation of China(Nos.90101020,90301009,10174035)
文摘Combining a progressive tandem junction design with a unique Si nanowire(SiNW)framework paves the way for the development of high‐onset‐potential photocathodes and enhancement of solar hydrogen production.Herein,a radial tandem junction(RTJ)thin film water‐splitting photo‐cathode has been demonstrated experimentally for the first time.The photocathode is directly fab‐ricated on vapor‐liquid‐solid‐grown SiNWs and consists of two radially stacked p‐i‐n junctions,featuring hydrogenated amorphous silicon(a‐Si:H)as the outer absorber layer,which absorbs short wavelengths,and hydrogenated amorphous silicon germanium(a‐SiGe:H)as the inner layer,which absorbs long wavelengths.The randomly distributed SiNW framework enables highly efficient light‐trapping,which facilitates the use of very thin absorber layers of a‐Si:H(~50 nm)and a‐SiGe:H(~40 nm).In a neutral electrolyte(pH=7),the three‐dimensional(3D)RTJ photocathode delivers a high photocurrent onset of 1.15 V vs.the reversible hydrogen electrode(RHE),accompanied by a photocurrent of 2.98 mA/cm^(2) at 0 V vs.RHE,and an overall applied‐bias photon‐to‐current effi‐ciency of 1.72%.These results emphasize the promising role of 3D radial tandem technology in developing a new generation of durable,low‐cost,high‐onset‐potential photocathodes capable of large‐scale implementation。
基金Supported by the National Basic Research Programme of China under Grant No 2006CB932202, and the National Natural Science Foundation of China under Grant Nos 60571008 and 60471021.
文摘An a-SiNx/nanocrystalline silicon [（nc-Si）/a-SiNx] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition （PECVD） system at low temperature （250℃）. The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2 ×10^11 cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiNs insulator layer are obtained. The density of interface state at the midgap is calculated to be 1 ×10^10 cm^-2eV^-1 from the quasistatic and high frequency C - V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage （C- V） measurement at room temperature. An ultra-large hysteresis is observed in the C - V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiNx/Si substrate.
基金Supported by the National Basic Research Programme of China under Grant No 2006CB932202, and the National Natural Science Foundation of China under Grant Nos 60571008 and 60471021.
文摘The a-SiNx/nanocrystalline silicon （nc-Si）/a-SiNx sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition （PECVD） system on p-type Si substrates. The nc-Si layer in thickness 5nm is fabricated from a hydrogen-diluted silane gas by the layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layers are 3nm and 20nm, respectively. Frequency-dependent capacitance spectroscopy is used to study the electron tunnelling and the storage in the sandwiched structures. Distinct frequency-dependent capacitance peaks due to electrons tunnelling into the nc-Si dots and capacitance-voltage （C - V） hysteresis characteristic due to electrons storage in the nc-Si dots are observed with the same sample. Moreover, conductance peaks have also been observed at the same voltage region by conductance-voltage （G - V） measurements. The experimental results demonstrate that electrons can be loaded onto nc-Si dots via resonant tunnelling and can be stored in our a-SiNx/nc-Si/a-SiNx structures.
基金the National Natural Science Foundation of China(Grant Nos.92164201,61921005,61974064,61934004,and 11874198)。
文摘Self-oscillation is an intriguing and omnipresent phenomenon that governs a broad range of growth dynamics and formation of nanoscale periodic and delicate heterostructures.A self-oscillating growth phenomenon of catalyst droplets,consuming surface-coating a-Si/a-Ge bilayer,is exploited to accomplish a high-frequency alternating growth of ultrathin crystalline Si and Ge(c-Si/c-Ge)nano-slates,with Ge-rich layer thickness of 14–19 nm,embedded within a superlattice nanowire structure,with pre-known position and uniform channel diameter.A subsequent selective etching of the Ge-rich segments leaves a chain of ultrafine standing c-Si nanosheets down to~6 nm thick,without the use of any expensive high-resolution lithography and growth modulation control.A ternary-phase-competition model has been established to explain the underlying formation mechanism of this nanoscale self-oscillating growth dynamics.It is also suggested that these ultrathin nanosheets could help to produce ultrathin fin-channels for advanced electronics,or provide size-specified trapping sites to capture and position hetero nanoparticle for high-precision labelling or light emission.
基金Supported by the National Natural Science Foundation of China under Grant No 6061204050the Jiangsu Provincial Fund under Grant No BK2011435.
文摘Enhanced crystallization of Si nanocrystals(Si NCs)has been achieved in an Al_(2)O_(3):Er/Si:Er multilayer structure,which is fabricated by pulsed laser deposition and subsequent rapid thermal annealing.The Er atoms introduce strains in the initial amorphous Si layers and serve as nucleation centers that enhance the crystallization of Si NCs at low annealing temperatures.The average size of Si NCs is well controlled by adjusting the Si layer thickness.Thanks to the formation of Si NCs and the favored chemical environment of Er3+after annealing around 600–700℃,optimized photoluminescence peaked at 1.54μm has been obtained.The present results stress the importance of controlling the formation of Si NCs to improve the performance of Er3+luminescence.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB932900 and 2013CBA01600the National Natural Science Foundation of China under Grant Nos 61204050 and 60990314
文摘We demonstrate a simple while very effective approach to tune the photoluminescence （PL） performance of monolayer MoS2 by dipping into the H2O2 aqueous solution, which is a strong oxidizer that extracts electrons from the MoS2 sheet within several seconds without damaging the crystal structure. During this process, the trion （electron-coupled exciton, X-） is transformed into an exciton （X°）, and thus achieves a greatly enhanced PL performance. These results indicate a convenient way to tune and to control the PL luminescence from monolayer MoS2 and thus lay a basis for the MoS2-based optoelectronic application.
