Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response, one has a gradient-doping structure and the other has a uniform-dopi...Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response, one has a gradient-doping structure and the other has a uniform-doping structure. The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one. As a result of the downward graded band-bending structure, the cathode performance parameters, such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves, are greater for the gradient-doping photocathode. The electron diffusion length is within a range of from 2.0 to 5.4μm for doping concentration varying from 10^19 to 10^18 cm^-3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2 μm.展开更多
Gradient-doped laser ceramics fabricated via 3D printing have great potential for high-power laser applications.However,it is challenging to produce such types of gain media because it is inconvenient to fabricate dif...Gradient-doped laser ceramics fabricated via 3D printing have great potential for high-power laser applications.However,it is challenging to produce such types of gain media because it is inconvenient to fabricate different component slurries prepared offline using traditional methods precisely.To address these issues,a facile approach for the additive manufacturing of high-power laser ceramics is proposed for gradient structure fabrication.First,a material-extrusion-based 3D printing device with a homemade active mixing module is developed to fabricate gradient-doped Yb:YAG(Y3 Al5 O12)laser ceramics using two slurries with different doping concentrations.Sub-sequently,the active mixing module is systematically investigated to obtain different Yb-doped concentrations of printing slurries with a uniform element distribution.By measuring the switching delay volume between dif-ferent components,a proper volume adjustment enables the Yb concentration distribution of the green bodies to be consistent with the designed profile in the 3D process.Finally,multi-component(0-5-10-5-0 at%Yb:YAG)green bodies are printed,and experimental tests are conducted to evaluate the performance of these gradient-doped laser ceramics.The results show that the gradient-doped ceramic obtained 82.1%in-line transmittance at 1100 nm(4.6 mm thickness,along with the doping concentration gradient)and the average Yb ions diffusion distance across the interface fitted in the 20-30𝜇m range.Furthermore,a 1030 nm laser output with an output power of 4.5 W with a slope efficiency of 41.3%is achieved when pumped with a 940 nm laser diode.This study provides useful insights for developing various gradient rare-earth-doped laser ceramics for high-power laser applications.展开更多
As an effective means to improve charge carrier separation efficiency and directional transport,the gradient doping of foreign elements to build multi-homojunction structures inside catalysts has received wide attenti...As an effective means to improve charge carrier separation efficiency and directional transport,the gradient doping of foreign elements to build multi-homojunction structures inside catalysts has received wide attentions.Herein,we reported a simple and robust method to construct multi-homojunctions in black TiO_(2) nanotubes by the gradient doping of Ni species through the diffusion of deposited Ni element on the top of black TiO2 nanotubes driven by a high temperature annealing process.The gradient Ni distribution created parts of different Fermi energy levels and energy band structures within the same black TiO_(2) nanotube,which subsequently formed two series of multi-homojunctions within it.This special multi-homojunction structure largely enhanced the charge carrier separation and transportation,while the low concentration of defect states near the surface layer further inhibited carrier recombination and facilitated the surface reaction.Thus,the B-TNT-2Ni sample with the optimized Ni doping concentration exhibited an enhanced hydrogen evolution rate of~1.84 mmol·g^(−1)·h^(−1)under visible light irradiation without the assistance of noble-metal cocatalysts,~four times higher than that of the pristine black TiO_(2)nanotube array.With the capability to create multi-homojunction structures,this approach could be readily applied to various dopant systems and catalyst materials for a broad range of technical applications.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.60801036 and 61067001)the Key Science and Technology Project of Henan Province of China(Grant No.112102210202)the Research and Innovation Plan for Graduate Students of Jiangsu Higher Education Institutions of China(Grant No.CX09B_096Z)
文摘Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response, one has a gradient-doping structure and the other has a uniform-doping structure. The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one. As a result of the downward graded band-bending structure, the cathode performance parameters, such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves, are greater for the gradient-doping photocathode. The electron diffusion length is within a range of from 2.0 to 5.4μm for doping concentration varying from 10^19 to 10^18 cm^-3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2 μm.
基金supported by National Key Research and Develop-ment Program of China(Grant No.2023YFB3812000)Jiangsu Provin-cial Key Research and Development Program(Grant No.BE2022069-2),National Natural Science Foundation of China(Grant No.52130207)+1 种基金National Basic Science Research Program of China(Grant No.JCKY2021203B032)the Unveiling and Hanging Project of Nantong(Grant No.JB2022001).
文摘Gradient-doped laser ceramics fabricated via 3D printing have great potential for high-power laser applications.However,it is challenging to produce such types of gain media because it is inconvenient to fabricate different component slurries prepared offline using traditional methods precisely.To address these issues,a facile approach for the additive manufacturing of high-power laser ceramics is proposed for gradient structure fabrication.First,a material-extrusion-based 3D printing device with a homemade active mixing module is developed to fabricate gradient-doped Yb:YAG(Y3 Al5 O12)laser ceramics using two slurries with different doping concentrations.Sub-sequently,the active mixing module is systematically investigated to obtain different Yb-doped concentrations of printing slurries with a uniform element distribution.By measuring the switching delay volume between dif-ferent components,a proper volume adjustment enables the Yb concentration distribution of the green bodies to be consistent with the designed profile in the 3D process.Finally,multi-component(0-5-10-5-0 at%Yb:YAG)green bodies are printed,and experimental tests are conducted to evaluate the performance of these gradient-doped laser ceramics.The results show that the gradient-doped ceramic obtained 82.1%in-line transmittance at 1100 nm(4.6 mm thickness,along with the doping concentration gradient)and the average Yb ions diffusion distance across the interface fitted in the 20-30𝜇m range.Furthermore,a 1030 nm laser output with an output power of 4.5 W with a slope efficiency of 41.3%is achieved when pumped with a 940 nm laser diode.This study provides useful insights for developing various gradient rare-earth-doped laser ceramics for high-power laser applications.
基金support is gratefully acknowledged from the National Natural Science Foundation of China(NSFC)(Nos.62004137,21878257,and 21978196)the Natural Science Foundation(NSF)of Shanxi Province(No.20210302123102)+4 种基金the Key Research and Development Program of Shanxi Province(No.201803D421079)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(No.2019L0156)the Research Project Supported by Shanxi Scholarship Council of China(No.2020-050)the Fundamental Research Funds for the Central Universities(No.2682021CX116)Sichuan Science and Technology Program(No.2020YJ0259).
文摘As an effective means to improve charge carrier separation efficiency and directional transport,the gradient doping of foreign elements to build multi-homojunction structures inside catalysts has received wide attentions.Herein,we reported a simple and robust method to construct multi-homojunctions in black TiO_(2) nanotubes by the gradient doping of Ni species through the diffusion of deposited Ni element on the top of black TiO2 nanotubes driven by a high temperature annealing process.The gradient Ni distribution created parts of different Fermi energy levels and energy band structures within the same black TiO_(2) nanotube,which subsequently formed two series of multi-homojunctions within it.This special multi-homojunction structure largely enhanced the charge carrier separation and transportation,while the low concentration of defect states near the surface layer further inhibited carrier recombination and facilitated the surface reaction.Thus,the B-TNT-2Ni sample with the optimized Ni doping concentration exhibited an enhanced hydrogen evolution rate of~1.84 mmol·g^(−1)·h^(−1)under visible light irradiation without the assistance of noble-metal cocatalysts,~four times higher than that of the pristine black TiO_(2)nanotube array.With the capability to create multi-homojunction structures,this approach could be readily applied to various dopant systems and catalyst materials for a broad range of technical applications.
