Pb(111)film is a special system that exhibits strong quantum size effects in many electronic properties.The collective excitations,i.e.,plasmons,in Pb(111)films are also expected to show signatures of the quantum size...Pb(111)film is a special system that exhibits strong quantum size effects in many electronic properties.The collective excitations,i.e.,plasmons,in Pb(111)films are also expected to show signatures of the quantum size effect.Here,using high-resolution electron energy loss spectroscopy,we measured the plasmons on the surface of Pb(111)films with different film thicknesses and analyzed the plasmon dispersions.One surface plasmon branch exhibits prominent damping in the small momentum range,which can be attributed to the interaction between the top and bottom interfaces of the Pb(111)films.With the film thickness increasing,the critical momentum characterizing the damping in Pb(111)films decays not only much slower in Pb(111)films than in other metal films,and even in films with the thickness up to 40 monolayers the damping still exists.The slow decay of the surface plasmon damping,manifesting the strong quantum size effect in Pb(111)films,might be related to the strong nesting of the Fermi surface along the(111)direction.展开更多
The energies and the magnetization of an electron in a piece of metal in the structure of Metal/Insulator/Metal/Insulator…(M/I/M/I…), in a magne tic field, at high temperature, and in range of quantum size thickness...The energies and the magnetization of an electron in a piece of metal in the structure of Metal/Insulator/Metal/Insulator…(M/I/M/I…), in a magne tic field, at high temperature, and in range of quantum size thickness of the pi ece of metal layer have been obtained. The results show that when the thickness of the metal layer becomes smaller, the orbital magnetism of the charged particl es which collide with the wall of the metal layer is to vary from diamagnetism t o paramagnetism. The smaller the thickness of the metal layer becomes, the more particles will collide with the boundary of the metal layer, and then the parama gnetism becomes stronger. Finally, when the thickness of the metal layer becomes very small (<100 nm), all of the orbital diamagnetism will reverse to paramagn etism, and then the paramagnetization will be almost a maximum constant.展开更多
There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite wi...There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite width, the edge states on the two sides can couple together to produce a gap in the spectrum. The phenomenon is called the finite size effect in quantum spin Hall systems. In this paper, we investigate the effects of the spin–orbit coupling due to bulk- and structure-inversion asymmetries on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. When the bulk-inversion asymmetry is taken into account, it is shown that the energy gap Eg of the edge states due to the finite size effect features an oscillating exponential decay as a function of the strip width of the HgTe quantum well. The origin of this oscillatory pattern on the exponential decay is explained. Furthermore, if the bulk- and structure-inversion asymmetries are considered simultaneously, the structure-inversion asymmetry will induce a shift of the energy gap Eg closing point.Finally, based on the roles of the bulk- and structure-inversion asymmetries on the finite size effects, a way to realize the quantum spin Hall field effect transistor is proposed.展开更多
Nano material is one of the low-dimensional materials. It is a hot point and the frontiers in materials research, and absorbs much interest because of the high nonlinear optical effect. In 1983, Jain and Lind first fo...Nano material is one of the low-dimensional materials. It is a hot point and the frontiers in materials research, and absorbs much interest because of the high nonlinear optical effect. In 1983, Jain and Lind first found that glass containing CdS<sub>x</sub>Se<sub>1-x</sub> microcrystallite exhibited high resonant nonlinear optical snsceptibility of 10<sup>-9</sup>—10<sup>-8</sup> esu with fast response time, and the size of the Cd<sub>x</sub>Se<sub>1-x</sub> microcrystallite was estimated to be about 10—100nm. Since then, more people have worked on the research of semiconductor-doped glass. In Japan, Masayuki Nagomi and the staff researched the quantum size effect and adsorption spectra of CdS, PbS, CuCl, CdTe-doped silica gel glass. Much work has been done on the semiconductor-doped glass in the Electronic Materials Research Laboratory, Xi’an Jiaotong University. A series of semiconductor microcrystallite-doped silica gel glass was prepared and the structure and properties were researched.展开更多
With the development of advanced new technologies, optoelectronics has anincreasing need of nonlinear optical materials. Research into nanometer materials hasbeen very active since the Japanese physicist R. Kubo first...With the development of advanced new technologies, optoelectronics has anincreasing need of nonlinear optical materials. Research into nanometer materials hasbeen very active since the Japanese physicist R. Kubo first proposed the so-called'Kubo effect' in metallic nanometer particles. The research of nano-materials hasextended to metal oxides, polar compounds, semiconductors, etc.展开更多
The finite size effect in a two-dimensional topological insulator can induce an energy gap Eg in the spectrum of helical edge states for a strip of finite width.In a recent work,it has been found that when the spin–o...The finite size effect in a two-dimensional topological insulator can induce an energy gap Eg in the spectrum of helical edge states for a strip of finite width.In a recent work,it has been found that when the spin–orbit coupling due to bulk-inversion asymmetry is taken into account,the energy gap Eg of the edge states features an oscillating exponential decay as a function of the strip width of the inverted Hg Te quantum well.In this paper,we investigate the effects of the interface between a topological insulator and a normal insulator on the finite size effect in the Hg Te quantum well by means of the numerical diagonalization method.Two different types of boundary conditions,i.e.,the symmetric and asymmetric geometries,are considered.It is found that due to the existence of the interface between topological insulator and normal insulator this oscillatory pattern on the exponential decay induced by bulk-inversion asymmetry is modulated by the width of normal insulator regions.With the variation of the width of normal insulator regions,the shift of the Dirac point of the edge states in the spectrum and the energy gap Eg closing point in the oscillatory pattern can occur.Additionally,the effect of the spin–orbit coupling due to structure-inversion asymmetry on the finite size effects is also investigated.展开更多
For a two-dimensional Lieb lattice,that is,a line-centered square lattice,the inclusion of the intrinsic spin–orbit(ISO)coupling opens a topologically nontrivial gap,and gives rise to the quantum spin Hall(QSH) effec...For a two-dimensional Lieb lattice,that is,a line-centered square lattice,the inclusion of the intrinsic spin–orbit(ISO)coupling opens a topologically nontrivial gap,and gives rise to the quantum spin Hall(QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap.Generally,due to the finite size effect in QSH systems,the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum.In this paper,we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions,i.e.,the straight,bearded and asymmetry edges.The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice.For a strip Lieb lattice with two straight edges,the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum.Moreover,it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice,and no gap is opened in the edge band.It is concluded that the finite size effect of QSH states is absent in the case with the straight edges.However,in the other two cases with the bearded and asymmetry edges,the energy gap induced by the finite size effect is still opened with decreasing the width of the strip.It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms.展开更多
Exciton energies as a function of radii of quantum dots in the range of 5-35 A are calculated based on effective mass approximation model with the B-spline technique and compared with experimental and other theoretica...Exciton energies as a function of radii of quantum dots in the range of 5-35 A are calculated based on effective mass approximation model with the B-spline technique and compared with experimental and other theoretical data for the CdS dots. This method leads to accurate and fast convergent exciton energy, which are in good agreement with experimental data in the whole confinement regime. The effect of penetration of wave function from the inside to the outside of the dots and the effect of dielectric constants are taken into account. The magnitudes of dynamical parameters are discussed. It is found that the different materials surrounding the CdS quantum dot affect not only the potential energy and Coulomb interaction energy of the system, but also the effective masses. The comparison shows that the effective mass approximation model can describe very well the quantum size effects observed experimentally on the exciton ground state energy.展开更多
Optoelectronic nanocomposites are a new class of materials,which exhibit very interesting and particular properties and attract a growing attention due to their potential applications in information storage and op- to...Optoelectronic nanocomposites are a new class of materials,which exhibit very interesting and particular properties and attract a growing attention due to their potential applications in information storage and op- toelectronic devices.Zinc oxide,ZnO,is one of the most interesting binary semiconductor(3.37 eV)with very important optical properties,which can be used in the fields such as short wavelength lasers,blue light emitting diodes,UV detectors,gas sensors,etc.This paper reviews the very recent progress in the prepa- ration of silica-based ZnO nanocomposites.After an introduction reviewing the theoretical background,the article will begin with a survey of the optical properties and the quantum size effect(QSE)of ZnO/SiO_2 nanocomposites prepared by the inclusion of ZnO nanoclusters inside silica mesoporous materials.The sec- ond part will focus on one of the most interesting properties of ZnO/SiO_2 nanocomposites,which is the random lasing effect after one-and two-photon excitation.The final part will deal with the introduction of ZnO nanoparticles inside microporous zeolites and the observation of QSE.For comparison,the photoluminescence (PL)and QSE properties of ZnS nanopartictes occluded in mesoporous media are also described.New potential applications will be discussed since short-wavelength devices are required by industry to design,for instance, new information storage supports and biolabelling devices.展开更多
Taking into account the quantum size effects and considering three types of scattering from bulk impurities,rough surface and rough interfaces, we use quantum-statistical Green's function approach and Kubo theory ...Taking into account the quantum size effects and considering three types of scattering from bulk impurities,rough surface and rough interfaces, we use quantum-statistical Green's function approach and Kubo theory to calculate the electronic conductivity and the giant magnetoresistance in magnetic multilayered cylindrical systems. It is found that in the limit of weakly scattering from impurities surface and interfaces, the total conductivity is given by a sum of conductivities of all the subbands and two spin-channels. For each subband and each spin-channel the scattering rate due to the impurities, surface and interfaces is added up.展开更多
基金the National Natural Science Foundation of China(Grant Nos.11874404 and 11634016)the National Key Research and Development Program of China(Grant Nos.2016YFA0302400,2016YFA0202300,and 2017YFA0303600)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33000000)supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences。
文摘Pb(111)film is a special system that exhibits strong quantum size effects in many electronic properties.The collective excitations,i.e.,plasmons,in Pb(111)films are also expected to show signatures of the quantum size effect.Here,using high-resolution electron energy loss spectroscopy,we measured the plasmons on the surface of Pb(111)films with different film thicknesses and analyzed the plasmon dispersions.One surface plasmon branch exhibits prominent damping in the small momentum range,which can be attributed to the interaction between the top and bottom interfaces of the Pb(111)films.With the film thickness increasing,the critical momentum characterizing the damping in Pb(111)films decays not only much slower in Pb(111)films than in other metal films,and even in films with the thickness up to 40 monolayers the damping still exists.The slow decay of the surface plasmon damping,manifesting the strong quantum size effect in Pb(111)films,might be related to the strong nesting of the Fermi surface along the(111)direction.
基金Supported by the National Natural Science Foundation of China(5 96 0 2 0 0 4)
文摘The energies and the magnetization of an electron in a piece of metal in the structure of Metal/Insulator/Metal/Insulator…(M/I/M/I…), in a magne tic field, at high temperature, and in range of quantum size thickness of the pi ece of metal layer have been obtained. The results show that when the thickness of the metal layer becomes smaller, the orbital magnetism of the charged particl es which collide with the wall of the metal layer is to vary from diamagnetism t o paramagnetism. The smaller the thickness of the metal layer becomes, the more particles will collide with the boundary of the metal layer, and then the parama gnetism becomes stronger. Finally, when the thickness of the metal layer becomes very small (<100 nm), all of the orbital diamagnetism will reverse to paramagn etism, and then the paramagnetization will be almost a maximum constant.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274102)the Program for New Century Excellent Talents in Universities,China(Grant No.NCET-11-0960)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20134208110001)
文摘There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite width, the edge states on the two sides can couple together to produce a gap in the spectrum. The phenomenon is called the finite size effect in quantum spin Hall systems. In this paper, we investigate the effects of the spin–orbit coupling due to bulk- and structure-inversion asymmetries on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. When the bulk-inversion asymmetry is taken into account, it is shown that the energy gap Eg of the edge states due to the finite size effect features an oscillating exponential decay as a function of the strip width of the HgTe quantum well. The origin of this oscillatory pattern on the exponential decay is explained. Furthermore, if the bulk- and structure-inversion asymmetries are considered simultaneously, the structure-inversion asymmetry will induce a shift of the energy gap Eg closing point.Finally, based on the roles of the bulk- and structure-inversion asymmetries on the finite size effects, a way to realize the quantum spin Hall field effect transistor is proposed.
基金Project supported by the National Advanced Materials Research Project.
文摘Nano material is one of the low-dimensional materials. It is a hot point and the frontiers in materials research, and absorbs much interest because of the high nonlinear optical effect. In 1983, Jain and Lind first found that glass containing CdS<sub>x</sub>Se<sub>1-x</sub> microcrystallite exhibited high resonant nonlinear optical snsceptibility of 10<sup>-9</sup>—10<sup>-8</sup> esu with fast response time, and the size of the Cd<sub>x</sub>Se<sub>1-x</sub> microcrystallite was estimated to be about 10—100nm. Since then, more people have worked on the research of semiconductor-doped glass. In Japan, Masayuki Nagomi and the staff researched the quantum size effect and adsorption spectra of CdS, PbS, CuCl, CdTe-doped silica gel glass. Much work has been done on the semiconductor-doped glass in the Electronic Materials Research Laboratory, Xi’an Jiaotong University. A series of semiconductor microcrystallite-doped silica gel glass was prepared and the structure and properties were researched.
文摘With the development of advanced new technologies, optoelectronics has anincreasing need of nonlinear optical materials. Research into nanometer materials hasbeen very active since the Japanese physicist R. Kubo first proposed the so-called'Kubo effect' in metallic nanometer particles. The research of nano-materials hasextended to metal oxides, polar compounds, semiconductors, etc.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274102)the Program for New Century Excellent Talents in University of the Ministry of Education of China(Grant No.NCET-11-0960)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20134208110001)
文摘The finite size effect in a two-dimensional topological insulator can induce an energy gap Eg in the spectrum of helical edge states for a strip of finite width.In a recent work,it has been found that when the spin–orbit coupling due to bulk-inversion asymmetry is taken into account,the energy gap Eg of the edge states features an oscillating exponential decay as a function of the strip width of the inverted Hg Te quantum well.In this paper,we investigate the effects of the interface between a topological insulator and a normal insulator on the finite size effect in the Hg Te quantum well by means of the numerical diagonalization method.Two different types of boundary conditions,i.e.,the symmetric and asymmetric geometries,are considered.It is found that due to the existence of the interface between topological insulator and normal insulator this oscillatory pattern on the exponential decay induced by bulk-inversion asymmetry is modulated by the width of normal insulator regions.With the variation of the width of normal insulator regions,the shift of the Dirac point of the edge states in the spectrum and the energy gap Eg closing point in the oscillatory pattern can occur.Additionally,the effect of the spin–orbit coupling due to structure-inversion asymmetry on the finite size effects is also investigated.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274102)the Program for New Century Excellent Talents in University of the Ministry of Education of China(Grant No.NCET-11-0960)the Specialized Research Fund for the Doctoral Program of the Higher Education of China(Grant No.20134208110001)
文摘For a two-dimensional Lieb lattice,that is,a line-centered square lattice,the inclusion of the intrinsic spin–orbit(ISO)coupling opens a topologically nontrivial gap,and gives rise to the quantum spin Hall(QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap.Generally,due to the finite size effect in QSH systems,the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum.In this paper,we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions,i.e.,the straight,bearded and asymmetry edges.The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice.For a strip Lieb lattice with two straight edges,the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum.Moreover,it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice,and no gap is opened in the edge band.It is concluded that the finite size effect of QSH states is absent in the case with the straight edges.However,in the other two cases with the bearded and asymmetry edges,the energy gap induced by the finite size effect is still opened with decreasing the width of the strip.It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms.
文摘Exciton energies as a function of radii of quantum dots in the range of 5-35 A are calculated based on effective mass approximation model with the B-spline technique and compared with experimental and other theoretical data for the CdS dots. This method leads to accurate and fast convergent exciton energy, which are in good agreement with experimental data in the whole confinement regime. The effect of penetration of wave function from the inside to the outside of the dots and the effect of dielectric constants are taken into account. The magnitudes of dynamical parameters are discussed. It is found that the different materials surrounding the CdS quantum dot affect not only the potential energy and Coulomb interaction energy of the system, but also the effective masses. The comparison shows that the effective mass approximation model can describe very well the quantum size effects observed experimentally on the exciton ground state energy.
基金the FNRS(Fonds National de la Recherche Scientifique,Belgium)for a FRIA doctoral fellowship and then a"Chargéde Recherches"fellowshipThis work was realised in the frame of the Belgian Federal Government PAI-IUAP program(INANOMAT P6/17)The financial support from the University of Namur(FUNDP),"Aide institutionnelle aux collaborations internationales"is also acknowledged.
文摘Optoelectronic nanocomposites are a new class of materials,which exhibit very interesting and particular properties and attract a growing attention due to their potential applications in information storage and op- toelectronic devices.Zinc oxide,ZnO,is one of the most interesting binary semiconductor(3.37 eV)with very important optical properties,which can be used in the fields such as short wavelength lasers,blue light emitting diodes,UV detectors,gas sensors,etc.This paper reviews the very recent progress in the prepa- ration of silica-based ZnO nanocomposites.After an introduction reviewing the theoretical background,the article will begin with a survey of the optical properties and the quantum size effect(QSE)of ZnO/SiO_2 nanocomposites prepared by the inclusion of ZnO nanoclusters inside silica mesoporous materials.The sec- ond part will focus on one of the most interesting properties of ZnO/SiO_2 nanocomposites,which is the random lasing effect after one-and two-photon excitation.The final part will deal with the introduction of ZnO nanoparticles inside microporous zeolites and the observation of QSE.For comparison,the photoluminescence (PL)and QSE properties of ZnS nanopartictes occluded in mesoporous media are also described.New potential applications will be discussed since short-wavelength devices are required by industry to design,for instance, new information storage supports and biolabelling devices.
基金Supported by the National Natural Science Foundation of China under Grant No.60940020the Natural Foundation of Hebei Province under Grant No.E2008000619
文摘Taking into account the quantum size effects and considering three types of scattering from bulk impurities,rough surface and rough interfaces, we use quantum-statistical Green's function approach and Kubo theory to calculate the electronic conductivity and the giant magnetoresistance in magnetic multilayered cylindrical systems. It is found that in the limit of weakly scattering from impurities surface and interfaces, the total conductivity is given by a sum of conductivities of all the subbands and two spin-channels. For each subband and each spin-channel the scattering rate due to the impurities, surface and interfaces is added up.
