A two-band Hamiltonian for β-graphyne is derived by the k·p method.The energy dispersions around the Dirac points are analytically obtained depending on the relative amplitude of the hopping terms t_(1)/t_(2),an...A two-band Hamiltonian for β-graphyne is derived by the k·p method.The energy dispersions around the Dirac points are analytically obtained depending on the relative amplitude of the hopping terms t_(1)/t_(2),and the Dirac cones are elliptical when -2t_(1)/t_(2)j.This interesting feature is useful for direction-dependent wave filter devices.展开更多
Red-emitting at about 640nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy are demonstrated.A doublepeak structure of photoluminescence(PL)spectra from q...Red-emitting at about 640nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy are demonstrated.A doublepeak structure of photoluminescence(PL)spectra from quantum dots was observed,and a bimodal distribution of dot sizes was also confirmed by an atomic force micrograph(AFM)image for uncapped sample.From the temperature and excitation intensity dependence of PL spectra,it is found that the double-peak structure of PL spectra from quantum dots is strongly correlated to the two predominant quantum dot families.Taking into account the quantum-size effect on the peak energy,it is proposed that the high(low)energy peak results from a smaller(larger)dot family,and this result is identical to the statistical distribution of dot lateral size from the AFM image.展开更多
As an important functional material,Bi_(2)O_(3)is found in seven polymorphs.We systematically analyze the transformation fromα-,β-andε-toδ-Bi_(2)O_(3)by using crystallographic group theory and structural simulatio...As an important functional material,Bi_(2)O_(3)is found in seven polymorphs.We systematically analyze the transformation fromα-,β-andε-toδ-Bi_(2)O_(3)by using crystallographic group theory and structural simulations.A transition phase is proved to exist in the transformation from theα-,β-andε-Bi_(2)O_(3)toδ-Bi2 Os.The transition phase is supposed to be tetragonal phase Bi_(2)O_(2.7)(Z=2)with the 139th I 4/m 2/m 2/m space group.展开更多
Self-assembled In_(x)Ga_(l-x)As quantum dots(QDs)on(311)and(100)GaAs surfaces have been grown by conventional solid source molecular beam epitaxy.Spontaneously ordering alignment of In_(x)Ga_(l-x)As QDs with lower In ...Self-assembled In_(x)Ga_(l-x)As quantum dots(QDs)on(311)and(100)GaAs surfaces have been grown by conventional solid source molecular beam epitaxy.Spontaneously ordering alignment of In_(x)Ga_(l-x)As QDs with lower In content around 0.3 has been observed on As-terminated(B type)surfaces.The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the(311)B surface,and is strongly dependent upon the In content x.The ordering alignment becomes significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on(100)and(311)Ga-terminated(A type)substrates.展开更多
基金Supported by State Key Laboratory of Software Development Environment under Grant Nos SKLSDE-2013ZX-28 and SKLSDE-2013ZX-21the National Natural Science Foundation of China under Grant Nos 10974011 and 11174022the Innovation Foundation of BUAA for PhD Graduates under Grant No 30-2194.
文摘A two-band Hamiltonian for β-graphyne is derived by the k·p method.The energy dispersions around the Dirac points are analytically obtained depending on the relative amplitude of the hopping terms t_(1)/t_(2),and the Dirac cones are elliptical when -2t_(1)/t_(2)j.This interesting feature is useful for direction-dependent wave filter devices.
基金Supported by the National Natural Science Foundation of China under Grant No.69736010the National Advanced Materials Committee of China(715-014-0040).
文摘Red-emitting at about 640nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy are demonstrated.A doublepeak structure of photoluminescence(PL)spectra from quantum dots was observed,and a bimodal distribution of dot sizes was also confirmed by an atomic force micrograph(AFM)image for uncapped sample.From the temperature and excitation intensity dependence of PL spectra,it is found that the double-peak structure of PL spectra from quantum dots is strongly correlated to the two predominant quantum dot families.Taking into account the quantum-size effect on the peak energy,it is proposed that the high(low)energy peak results from a smaller(larger)dot family,and this result is identical to the statistical distribution of dot lateral size from the AFM image.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51072012 and 60776067。
文摘As an important functional material,Bi_(2)O_(3)is found in seven polymorphs.We systematically analyze the transformation fromα-,β-andε-toδ-Bi_(2)O_(3)by using crystallographic group theory and structural simulations.A transition phase is proved to exist in the transformation from theα-,β-andε-Bi_(2)O_(3)toδ-Bi2 Os.The transition phase is supposed to be tetragonal phase Bi_(2)O_(2.7)(Z=2)with the 139th I 4/m 2/m 2/m space group.
基金Supported by the National Natural Science Foundation of China under Grant No.69736010the National Advanced Materials Committee of China under Grant No.715-014-0040.
文摘Self-assembled In_(x)Ga_(l-x)As quantum dots(QDs)on(311)and(100)GaAs surfaces have been grown by conventional solid source molecular beam epitaxy.Spontaneously ordering alignment of In_(x)Ga_(l-x)As QDs with lower In content around 0.3 has been observed on As-terminated(B type)surfaces.The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the(311)B surface,and is strongly dependent upon the In content x.The ordering alignment becomes significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on(100)and(311)Ga-terminated(A type)substrates.
