The energy band structure with type-I alignment at the PbTe/CdTe（111） heterojunction interface is determined by the ultraviolet photoelectron spectrum using synchrotron radiation. The valence band and conduction ban...The energy band structure with type-I alignment at the PbTe/CdTe（111） heterojunction interface is determined by the ultraviolet photoelectron spectrum using synchrotron radiation. The valence band and conduction band offsets are obtained to be 0.09±0.12 and 1.19±0.12 eV, respectively. These results are in agreement with theoretically predicted ones. The accurate determination of the valence band and conduction band offsets is useful for the fundamental understanding of the mid-infrared light emission from the PbTe/CdTe heterostructures and its application in devices.展开更多
A study of the atmospheric photochemical reaction of CF3 radical with CO and O2 was performed by using a homemade ultraviolet photoelectron spectrometer-photoionization mass spectrometer (PES- PIMS). The electronic st...A study of the atmospheric photochemical reaction of CF3 radical with CO and O2 was performed by using a homemade ultraviolet photoelectron spectrometer-photoionization mass spectrometer (PES- PIMS). The electronic structures and mechanism of ionization and dissociation of CF3OC(O)OOC(O)- OCF3 were investigated. It was indicated that the two bands on the photoelectron spectrum of CF3OC(O)OOC(O)OCF3 are the result of ionization of an electron from a lone pair of oxygen and a fluo- rine lone pair of CF3 group. The outermost electrons reside in the oxygen lone pair. The experimental and theoretical first vertical ionization energy is 13.21 and 13.178 eV, respectively, with the PES and OVGF method. They are in good agreement. The photo ionization and dissociation processes were discussed with the help of theoretical calculations and PES-PIMS experiment. After ionization, the parent ions prefer the dissociation of the C-O bond and giving the fragments CF3OCO+ and CF3+. It demonstrated that the ultraviolet photoelectron and photoionization mass spectrometer could be ap- plied widely in the study of atmospheric photochemical reaction.展开更多
Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the vale...Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO2, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO2（110） surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO2 substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytie process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.展开更多
La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 ...La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 generation. However,the hygroscopic nature of La2O3 hampers its application as dielectrics in electron devices. To cope with this challenge,ultraviolet（UV） ozone post treatment is proposed to suppress the moisture absorption in the H2O-based atomic layer deposition（ALD） La2O3/Al2O3 nanolaminates which is related to the residual hydroxyl/hydrogen groups after annealing.The x-ray photoelectron spectroscopy（XPS） and conductive atomic force microscopy（AFM） results indicate that the moisture absorption of the H2O-based ALD La2O3/Al2O3 nanolaminates is efficiently suppressed after 600？C annealing,and the electrical characteristics are greatly improved.展开更多
Microscopes in vacuum ultraviolet and soft X-ray regions using a normal incidence type of Schwarzschild objective are reviewed. The objective consists of a concave mirror and a convex mirror coated with a high reflect...Microscopes in vacuum ultraviolet and soft X-ray regions using a normal incidence type of Schwarzschild objective are reviewed. The objective consists of a concave mirror and a convex mirror coated with a high reflectance multilayer,having a large numerical aperture comparing with other objectives. The microscopes have been used to diagnose inertia-confinement-fusion plasmas,and to investigate small samples or microstructures of in- organic and organic materials by imaging them using laboratory light sources. Synchrotron radiation has been also used to obtain a microbeam for a photoelectron scanning microscope with a spatial resolution of 0.1 μm. The struc- ture and performance of two laboratory microscopes developed at Tohoku University are demonstrated. One of them is a soft X-ray emission imaging microscope. An image of an artificial pattern made of W and SiO2 on Si wafer by focusing Si L emission was presented. The other is an ultraviolet photoelectron scanning microscope using a He (he- lium) gas discharge lamp. The valence band spectra of a microcrystal of FeWO4 were presented. Furthermore other applications such as demagnifying optics for lithography and optics to gather fluorescence for emission spectroscopy are introduced.展开更多
Semiconductors are a major category of functional materials essential to various applications to sustain the modern society.Most applied materials or devices utilizing semiconductors are enabled by interfaces or junct...Semiconductors are a major category of functional materials essential to various applications to sustain the modern society.Most applied materials or devices utilizing semiconductors are enabled by interfaces or junctions,such as solar cells,electronic/photonic devices,environmental sensors,and redox hetero-catalysts.Herein,the author provides a critical commentary on photoemission measurement of the work function and,more importantly,the electron affinity of semiconductors essential for energy band diagram of heterojunctions.Particular effort is made towards addressing complications associated with Fermi level pinning due to surficial states of doped semiconductors.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10974174 and 60676003)
文摘The energy band structure with type-I alignment at the PbTe/CdTe（111） heterojunction interface is determined by the ultraviolet photoelectron spectrum using synchrotron radiation. The valence band and conduction band offsets are obtained to be 0.09±0.12 and 1.19±0.12 eV, respectively. These results are in agreement with theoretically predicted ones. The accurate determination of the valence band and conduction band offsets is useful for the fundamental understanding of the mid-infrared light emission from the PbTe/CdTe heterostructures and its application in devices.
基金Supported by the Knowledge Innovation Program of the Chinese Academy of Sci-ences (Grant No. KZCX2-YW-205)Hundred Talents Fund, 973 Program of Minis-try of Science and Technology of China (Grant No. 2006CB403701)the Na-tional Natural Science Foundation of China (Grant Nos. 20577052, 20673123)
文摘A study of the atmospheric photochemical reaction of CF3 radical with CO and O2 was performed by using a homemade ultraviolet photoelectron spectrometer-photoionization mass spectrometer (PES- PIMS). The electronic structures and mechanism of ionization and dissociation of CF3OC(O)OOC(O)- OCF3 were investigated. It was indicated that the two bands on the photoelectron spectrum of CF3OC(O)OOC(O)OCF3 are the result of ionization of an electron from a lone pair of oxygen and a fluo- rine lone pair of CF3 group. The outermost electrons reside in the oxygen lone pair. The experimental and theoretical first vertical ionization energy is 13.21 and 13.178 eV, respectively, with the PES and OVGF method. They are in good agreement. The photo ionization and dissociation processes were discussed with the help of theoretical calculations and PES-PIMS experiment. After ionization, the parent ions prefer the dissociation of the C-O bond and giving the fragments CF3OCO+ and CF3+. It demonstrated that the ultraviolet photoelectron and photoionization mass spectrometer could be ap- plied widely in the study of atmospheric photochemical reaction.
文摘Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO2, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO2（110） surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO2 substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytie process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61604016 and 51501017)the Fundamental Research Funds for the Central Universities,China(Grant No.310831161003)
文摘La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 generation. However,the hygroscopic nature of La2O3 hampers its application as dielectrics in electron devices. To cope with this challenge,ultraviolet（UV） ozone post treatment is proposed to suppress the moisture absorption in the H2O-based atomic layer deposition（ALD） La2O3/Al2O3 nanolaminates which is related to the residual hydroxyl/hydrogen groups after annealing.The x-ray photoelectron spectroscopy（XPS） and conductive atomic force microscopy（AFM） results indicate that the moisture absorption of the H2O-based ALD La2O3/Al2O3 nanolaminates is efficiently suppressed after 600？C annealing,and the electrical characteristics are greatly improved.
文摘Microscopes in vacuum ultraviolet and soft X-ray regions using a normal incidence type of Schwarzschild objective are reviewed. The objective consists of a concave mirror and a convex mirror coated with a high reflectance multilayer,having a large numerical aperture comparing with other objectives. The microscopes have been used to diagnose inertia-confinement-fusion plasmas,and to investigate small samples or microstructures of in- organic and organic materials by imaging them using laboratory light sources. Synchrotron radiation has been also used to obtain a microbeam for a photoelectron scanning microscope with a spatial resolution of 0.1 μm. The struc- ture and performance of two laboratory microscopes developed at Tohoku University are demonstrated. One of them is a soft X-ray emission imaging microscope. An image of an artificial pattern made of W and SiO2 on Si wafer by focusing Si L emission was presented. The other is an ultraviolet photoelectron scanning microscope using a He (he- lium) gas discharge lamp. The valence band spectra of a microcrystal of FeWO4 were presented. Furthermore other applications such as demagnifying optics for lithography and optics to gather fluorescence for emission spectroscopy are introduced.
文摘Semiconductors are a major category of functional materials essential to various applications to sustain the modern society.Most applied materials or devices utilizing semiconductors are enabled by interfaces or junctions,such as solar cells,electronic/photonic devices,environmental sensors,and redox hetero-catalysts.Herein,the author provides a critical commentary on photoemission measurement of the work function and,more importantly,the electron affinity of semiconductors essential for energy band diagram of heterojunctions.Particular effort is made towards addressing complications associated with Fermi level pinning due to surficial states of doped semiconductors.
