Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a meth...Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a method to construct superior Fe-Beta catalysts based on Al-rich zeolites.This strategy successfully promotes the formation of NH3-SCR-active isolated Fe^(3+)species,thus effectively improving the low-temperature activity of the Fe-Beta catalysts.Thanks to the abundant Brønsted acid sites of the Al-rich zeolite,the Fe_(2)O_(3) particles are redispersed and anchored as isolated Fe^(3+)during hydrothermal aging.This dynamic evolution of Fe species makes up for the adverse effect of dealumination of the Al-rich zeolite framework and achieves high stability for the Al-rich Fe-Beta catalyst.This study may promote the understanding of highly efficient and stable catalyst design using Al-rich zeolites.展开更多
Three new carbonaceous chondrites (GRV 020025,021579 and 022459) collected from the Grove Mountains (GRV), Antarctica, have been classified as the CM2, CO3 and CV3 chondrites, respectively. A total of 27 Ca- and Al-ri...Three new carbonaceous chondrites (GRV 020025,021579 and 022459) collected from the Grove Mountains (GRV), Antarctica, have been classified as the CM2, CO3 and CV3 chondrites, respectively. A total of 27 Ca- and Al-rich inclusions have been found in the three meteorites, which are the earliest assemblages formed in the solar nebula. Most of the inclusions are intensively altered, with abundant phyllosilicates in the inclusions from GRV 020025 and FeO enrichment of spinel in those from GRV 022459. Except for one spinel-spherule in each of GRV 020025 and 021579, all the inclusions can be classified as Type A-like or spinel-pyroxene-rich inclusions, and they probably represent the continuum of solar nebular condensation. In addition, most of the inclusions in these meteorites share much similarity in both petrography and mineral chemistry, suggesting a similar origin of Ca-Al-rich inclusions in various chondrites.展开更多
Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions...Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions in garnet and prismatic sillimanite in the Ai-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich （Xzn=0.33-0.40. Xzn=Zn/Zn＋Mg＋Fe＊） （Fe＊=FeZ＋＋Fe3＋） and Fe3＋ rich （up to 0.31 p.f.u.）. The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path.展开更多
The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wav...The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wavelength of 275 nm,there is still a huge gap in comparison with GaN-based visible light-emitting diodes(LEDs),mainly attributed to the inefficient doping of AlGaN with increase of the Al composition.First,p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency.Although p-GaN cladding layers are widely adopted as a compromise,the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected.While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%,resulting in a low electrical efficiency in sub-250 nm UV-LEDs.This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN,meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.展开更多
We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plag...We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plagioclase,spinel and olivine),C#1 is also surrounded by a pyroxene rim(64 vol%Ca-rich and 36 vol%Ca-poor pyroxenes).On a three-isotope oxygen diagram,δ^(17)O vs.δ^(18)O,the compositions of individual minerals analyzed in C#1 fall along the carbonaceous chondrite anhydrous mineral line(CCAM),and oxygen isotopic compositions in C#1 show significant variability in δ^(18)O and δ^(17)O.The oxygen isotopic compositions of the pyroxene rim minerals are similar to those of the other host minerals,which suggests that the rim likely formed from the same melting process as the host.The rim is considered to have formed as a result of interaction between an ^(16)O-poor gas and a melt.Some spinel grains are typically ^(16)O-rich and likely of relict origin,which is similar to ^(16)O-rich Ca-,Al-rich inclusions,which are probably a precursor of C#1.The inclusion then likely melted in an ^(16)O-poor region where chondrules form,accompanied by oxygen isotope exchange with an ^(16)O-poor gas.Some anorthite,pyroxene and spinel might have undergone fluid-assisted thermal metamorphism on the Ningqiang chondrite parent body.The oxygen isotope data and evolution of the C#1 plagioclase-olivine inclusion are similar with those of Al-chondrules in chondrites.展开更多
The microstructural evolution characteristics of thermo-mechanically affected zone were investigated during friction stir processing (FSP) of the thixoformed AZ91D alloy. Simultaneously, an Al-rich surface layer was p...The microstructural evolution characteristics of thermo-mechanically affected zone were investigated during friction stir processing (FSP) of the thixoformed AZ91D alloy. Simultaneously, an Al-rich surface layer was prepared by combination of Al powder using FSP method. The results indicate that the dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are the main mechanisms of grain refinement. For the thixoformed alloy, the operation efficiency of these mechanisms is less than that of the permanent mould casting AZ91D alloy, thus its microstructural evolution is relatively slow and the resulting grain size is relatively large. These are attributed to the differences in their original microstructures. The Al-rich surface layer can obviously improve the corrosion resistance in NaCl aqueous solution. A proper solution heat treatment (at 415 ℃ for 1 h) can further increase the corrosion resistance. In order to improve corrosion resistance, increasing the amount and improving the distribution uniformity of the Al-rich phase are more effective than increasing the Al solubility in the matrix.展开更多
Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/bi...Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/binuclear Fe3+in zeolites is challenging,and the reaction mechanism of low-temperature alkane oxidation remains unclear.Different from previous impregnation and ion-exchange methods generating clusters/nanoparticles,here we developed an efficient amino acid-assisted one-pot hydrothermal synthesis strategy for in situ incorporation of mono-/binuclear Fe^(3+)species into framework Al-rich ZSM-5 zeolites.The high framework Al content(Si/Al=9)provided sufficient negatively charged sites to anchor mono-/binuclear Fe^(3+)Fe loading=0.44∼0.90 wt%).The as-prepared 0.44Fe@Z-L_(0.3)H_(6)-9 catalyst exhibited superior catalytic properties for selective oxidation of both methane and ethane in the H_(2)O_(2)solution at 50℃,presenting a toplevel catalytic performance among various heterogeneous/homogeneous catalysts.Combining advanced characterizations and density functional theory calculations,the complex reaction networks for methane and ethane conversions into C1/C2 oxygenates over mononuclear and binuclear Fe^(3+)were mapped out for the first time.The mononuclear Fe^(3+)was more active than the binuclear Fe^(3+)for both methane and ethane conversions.This work not only provides a whole picture on low-temperature alkane oxidation mechanisms,but it also guides the rational design of high-performance catalysts for C-H bond activation and beyond.展开更多
The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca....The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca. 0.36 mm in diame ter. There is only one light red euhedral spinel crystal, ca. 34％ in volume of this chondrule, while prismatic fassaite crystals occupy ca. 29％ and only one small crystal of olivine and light brown intergranular glass of the above minerals, ca. 37％ （Fig. 1）.展开更多
长兴陨石于1964年10月17日降落在上海市长兴岛。本文利用上海天文馆馆藏的第一手样品,在重新界定其分类的基础上,研究了长兴陨石经历的热变质和流体交代作用,并探讨了其中富铝球粒(简称ARC)的成因。长兴陨石是一块H5型普通球粒陨石,金...长兴陨石于1964年10月17日降落在上海市长兴岛。本文利用上海天文馆馆藏的第一手样品,在重新界定其分类的基础上,研究了长兴陨石经历的热变质和流体交代作用,并探讨了其中富铝球粒(简称ARC)的成因。长兴陨石是一块H5型普通球粒陨石,金属相丰度高达15.1vol%,橄榄石和辉石的成分均一(Fa_(17.9±0.6),Fs_(16.1±0.8),相对平均偏差PMD<5%),基质经历了明显重结晶。长兴陨石的热变质过程伴随着流体交代作用,导致了斜长石的钠长石化、球粒中微孔结构和氧化物微晶的形成、以及氯磷灰石的形成等。与前人的报道不同,长兴陨石中斜长石的成分并不均一(An_(72-9)),说明H群母体上流体交代反应的条件很可能与L和LL群母体并无显著差异。长兴陨石中共发现12个富铝球粒,平均全岩Al_(2)O_(3)含量为14.8%,平均直径(0.30±0.17mm)与富镁铁质球粒(简称FMC,0.41±0.16mm)接近;全岩SiO_(2)、FeO和CaO含量与普通球粒陨石的II型FMC相似,Ca/Al质量比(0.18~0.58)低于宇宙值(1.10;Ahrens and Von Michaelis,1968)。ARC中橄榄石、辉石的TiO_(2)和Al_(2)O_(3)含量以及斜长石的An指数均明显高于FMC。岩相学、矿物学和全岩化学结果表明长兴陨石中的ARC形成于与FMC相似的高温过程,同一类型球粒陨石中的ARC和FMC很可能形成于原行星盘中的相同或相近区域。ARC的前体物质相对于FMC富集Al、Ti等难熔元素可能是太阳星云中气-固交换反应的结果。展开更多
AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-ele...AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-electrode and Alrich n-AlGaN,adversely impeding electron injection and resulting in considerable heat generation.Here,we fabricate V-based electrodes of V/Al/Ti/Au on n-AlGaN with Al content over 80%and investigate the relationship between the metal diffusion and contact properties during the high-temperature annealing process.Experiments reveal that decreasing V thickness in the electrode promotes the diffusion of Al towards the surface of n-AlGaN,which facilitates the formation of VN and thus the increase of local electron concentration,resulting in lower specific contact resistivity.Then,increasing the Al thickness inhibits the diffusion of Au to the n-AlGaN surface,suppressing the rise of Schottky barrier.Experimentally,an optimized n-electrode of V(10 nm)/Al(240 nm)/Ti(40 nm)/Au(50 nm)on n-Al_(0.81)Ga_(0.19)N is obtained,realizing an optimal specific contact resistivity of 7.30×10^(−4)Ω·cm^(2).Based on the optimal n-electrode preparation scheme for Al-rich n-AlGaN,the work voltage of a far-UVC LED with peak wavelength of 233.5 nm is effectively reduced.展开更多
基金supported by the National Key R&D Program of China(No.2023YFC3707200)the National Natural Science Foundation of China(Nos.22306191 and 52270112).
文摘Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a method to construct superior Fe-Beta catalysts based on Al-rich zeolites.This strategy successfully promotes the formation of NH3-SCR-active isolated Fe^(3+)species,thus effectively improving the low-temperature activity of the Fe-Beta catalysts.Thanks to the abundant Brønsted acid sites of the Al-rich zeolite,the Fe_(2)O_(3) particles are redispersed and anchored as isolated Fe^(3+)during hydrothermal aging.This dynamic evolution of Fe species makes up for the adverse effect of dealumination of the Al-rich zeolite framework and achieves high stability for the Al-rich Fe-Beta catalyst.This study may promote the understanding of highly efficient and stable catalyst design using Al-rich zeolites.
基金This work was supported by the pilot project of knowledge-innovation of Chinese Academy of Sciences(Grant No:KZCX3-SW-123)the National Natural Science Foundation of China(Grant No.40025311).
文摘Three new carbonaceous chondrites (GRV 020025,021579 and 022459) collected from the Grove Mountains (GRV), Antarctica, have been classified as the CM2, CO3 and CV3 chondrites, respectively. A total of 27 Ca- and Al-rich inclusions have been found in the three meteorites, which are the earliest assemblages formed in the solar nebula. Most of the inclusions are intensively altered, with abundant phyllosilicates in the inclusions from GRV 020025 and FeO enrichment of spinel in those from GRV 022459. Except for one spinel-spherule in each of GRV 020025 and 021579, all the inclusions can be classified as Type A-like or spinel-pyroxene-rich inclusions, and they probably represent the continuum of solar nebular condensation. In addition, most of the inclusions in these meteorites share much similarity in both petrography and mineral chemistry, suggesting a similar origin of Ca-Al-rich inclusions in various chondrites.
基金supported by a JSPS Grant-in-Aid for Scientific Research (No. 17340149) to Akira Takasuby the NSFS of China (No. 40739905) to Yongjiang Liu+1 种基金by the 973 project of the Ministry of Science and Technology of China (No. 2013CB429802)by the National Natural Science Foundation for the Youth of China (No. 41302175) to Weimin Liu
文摘Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions in garnet and prismatic sillimanite in the Ai-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich （Xzn=0.33-0.40. Xzn=Zn/Zn＋Mg＋Fe＊） （Fe＊=FeZ＋＋Fe3＋） and Fe3＋ rich （up to 0.31 p.f.u.）. The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path.
基金This work was supported by the National Key Research and Development Program of China(No.2022YFB3605100)the National Natural Science Foundation of China(Nos.62234001,61927806,61974002,62135013,and 62075081)+1 种基金the Key-Area Research and Development Program of Guangdong Province(No.2020B010172001)the Major Scientific and Technological Innovation Project(MSTIP)of Shandong Province(No.2019JZZY010209).
文摘The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wavelength of 275 nm,there is still a huge gap in comparison with GaN-based visible light-emitting diodes(LEDs),mainly attributed to the inefficient doping of AlGaN with increase of the Al composition.First,p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency.Although p-GaN cladding layers are widely adopted as a compromise,the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected.While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%,resulting in a low electrical efficiency in sub-250 nm UV-LEDs.This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN,meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.
基金supported by the Natural Science Foundation of China(Grant Nos.41673070,41103032,41503062)the Hunan Provincial Natural Science Foundation of China(Grant No.2021JJ30242)the Scientific Research Fund of Hunan Provincial Education Department(Grant No.18A204)。
文摘We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plagioclase,spinel and olivine),C#1 is also surrounded by a pyroxene rim(64 vol%Ca-rich and 36 vol%Ca-poor pyroxenes).On a three-isotope oxygen diagram,δ^(17)O vs.δ^(18)O,the compositions of individual minerals analyzed in C#1 fall along the carbonaceous chondrite anhydrous mineral line(CCAM),and oxygen isotopic compositions in C#1 show significant variability in δ^(18)O and δ^(17)O.The oxygen isotopic compositions of the pyroxene rim minerals are similar to those of the other host minerals,which suggests that the rim likely formed from the same melting process as the host.The rim is considered to have formed as a result of interaction between an ^(16)O-poor gas and a melt.Some spinel grains are typically ^(16)O-rich and likely of relict origin,which is similar to ^(16)O-rich Ca-,Al-rich inclusions,which are probably a precursor of C#1.The inclusion then likely melted in an ^(16)O-poor region where chondrules form,accompanied by oxygen isotope exchange with an ^(16)O-poor gas.Some anorthite,pyroxene and spinel might have undergone fluid-assisted thermal metamorphism on the Ningqiang chondrite parent body.The oxygen isotope data and evolution of the C#1 plagioclase-olivine inclusion are similar with those of Al-chondrules in chondrites.
基金Project(2007CB613706) supported by the National Basic Research Program of ChinaProject(3ZS042-B25-003) supported by the Natural Science Foundation of Gansu Province, ChinaProject(SKL03004) supported by the Development Program for Outstanding Young Teachers in Lanzhou University of Technology, China
文摘The microstructural evolution characteristics of thermo-mechanically affected zone were investigated during friction stir processing (FSP) of the thixoformed AZ91D alloy. Simultaneously, an Al-rich surface layer was prepared by combination of Al powder using FSP method. The results indicate that the dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are the main mechanisms of grain refinement. For the thixoformed alloy, the operation efficiency of these mechanisms is less than that of the permanent mould casting AZ91D alloy, thus its microstructural evolution is relatively slow and the resulting grain size is relatively large. These are attributed to the differences in their original microstructures. The Al-rich surface layer can obviously improve the corrosion resistance in NaCl aqueous solution. A proper solution heat treatment (at 415 ℃ for 1 h) can further increase the corrosion resistance. In order to improve corrosion resistance, increasing the amount and improving the distribution uniformity of the Al-rich phase are more effective than increasing the Al solubility in the matrix.
基金support of the National Natural Science Foundation of China(grant nos.22288101,21920102005,91961119,and 22101098)the National Key Research and Development Program of China(grant nos.2021YFA1501202 and 2022YFA1503600)the 111 Project(B17020).
文摘Zeolite-encapsulated extraframework mono-/binuclear Fe3+species exhibit higher catalytic activity compared to clusters and nanoparticles for direct low-temperature alkane oxidation.However,the fine control of mono-/binuclear Fe3+in zeolites is challenging,and the reaction mechanism of low-temperature alkane oxidation remains unclear.Different from previous impregnation and ion-exchange methods generating clusters/nanoparticles,here we developed an efficient amino acid-assisted one-pot hydrothermal synthesis strategy for in situ incorporation of mono-/binuclear Fe^(3+)species into framework Al-rich ZSM-5 zeolites.The high framework Al content(Si/Al=9)provided sufficient negatively charged sites to anchor mono-/binuclear Fe^(3+)Fe loading=0.44∼0.90 wt%).The as-prepared 0.44Fe@Z-L_(0.3)H_(6)-9 catalyst exhibited superior catalytic properties for selective oxidation of both methane and ethane in the H_(2)O_(2)solution at 50℃,presenting a toplevel catalytic performance among various heterogeneous/homogeneous catalysts.Combining advanced characterizations and density functional theory calculations,the complex reaction networks for methane and ethane conversions into C1/C2 oxygenates over mononuclear and binuclear Fe^(3+)were mapped out for the first time.The mononuclear Fe^(3+)was more active than the binuclear Fe^(3+)for both methane and ethane conversions.This work not only provides a whole picture on low-temperature alkane oxidation mechanisms,but it also guides the rational design of high-performance catalysts for C-H bond activation and beyond.
文摘The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca. 0.36 mm in diame ter. There is only one light red euhedral spinel crystal, ca. 34％ in volume of this chondrule, while prismatic fassaite crystals occupy ca. 29％ and only one small crystal of olivine and light brown intergranular glass of the above minerals, ca. 37％ （Fig. 1）.
文摘长兴陨石于1964年10月17日降落在上海市长兴岛。本文利用上海天文馆馆藏的第一手样品,在重新界定其分类的基础上,研究了长兴陨石经历的热变质和流体交代作用,并探讨了其中富铝球粒(简称ARC)的成因。长兴陨石是一块H5型普通球粒陨石,金属相丰度高达15.1vol%,橄榄石和辉石的成分均一(Fa_(17.9±0.6),Fs_(16.1±0.8),相对平均偏差PMD<5%),基质经历了明显重结晶。长兴陨石的热变质过程伴随着流体交代作用,导致了斜长石的钠长石化、球粒中微孔结构和氧化物微晶的形成、以及氯磷灰石的形成等。与前人的报道不同,长兴陨石中斜长石的成分并不均一(An_(72-9)),说明H群母体上流体交代反应的条件很可能与L和LL群母体并无显著差异。长兴陨石中共发现12个富铝球粒,平均全岩Al_(2)O_(3)含量为14.8%,平均直径(0.30±0.17mm)与富镁铁质球粒(简称FMC,0.41±0.16mm)接近;全岩SiO_(2)、FeO和CaO含量与普通球粒陨石的II型FMC相似,Ca/Al质量比(0.18~0.58)低于宇宙值(1.10;Ahrens and Von Michaelis,1968)。ARC中橄榄石、辉石的TiO_(2)和Al_(2)O_(3)含量以及斜长石的An指数均明显高于FMC。岩相学、矿物学和全岩化学结果表明长兴陨石中的ARC形成于与FMC相似的高温过程,同一类型球粒陨石中的ARC和FMC很可能形成于原行星盘中的相同或相近区域。ARC的前体物质相对于FMC富集Al、Ti等难熔元素可能是太阳星云中气-固交换反应的结果。
基金supported by National Key R&D Program of China(2022YFB3605103)National Natural Science Foundation of China(62425408,62121005,U22A2084,12234018)+2 种基金Youth Innovation Promotion Association of the Chinese Academy of Sciences(2023223)Natural Science Foundation of Jilin Province(20230101345JC,20230101360JC,SKL202302026)Young Elite Scientist Sponsorship Program by CAST(YESS20200182).
文摘AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-electrode and Alrich n-AlGaN,adversely impeding electron injection and resulting in considerable heat generation.Here,we fabricate V-based electrodes of V/Al/Ti/Au on n-AlGaN with Al content over 80%and investigate the relationship between the metal diffusion and contact properties during the high-temperature annealing process.Experiments reveal that decreasing V thickness in the electrode promotes the diffusion of Al towards the surface of n-AlGaN,which facilitates the formation of VN and thus the increase of local electron concentration,resulting in lower specific contact resistivity.Then,increasing the Al thickness inhibits the diffusion of Au to the n-AlGaN surface,suppressing the rise of Schottky barrier.Experimentally,an optimized n-electrode of V(10 nm)/Al(240 nm)/Ti(40 nm)/Au(50 nm)on n-Al_(0.81)Ga_(0.19)N is obtained,realizing an optimal specific contact resistivity of 7.30×10^(−4)Ω·cm^(2).Based on the optimal n-electrode preparation scheme for Al-rich n-AlGaN,the work voltage of a far-UVC LED with peak wavelength of 233.5 nm is effectively reduced.
