The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. ...The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.展开更多
Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite （Ga,Mn）As nanowires （NWs） grown along the [0001] direction were investigated based on density functional theory （DFT）...Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite （Ga,Mn）As nanowires （NWs） grown along the [0001] direction were investigated based on density functional theory （DFT）. We found that （Ga,Mn）As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the N-Ws. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.展开更多
ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO：Cu film can be enhanced by a moderate level ...ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO：Cu film can be enhanced by a moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO：Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of the Burstein–Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples.展开更多
By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal（TM） atoms（from Sc to Zn） adsorbed monolayer Ga As nanosheets...By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal（TM） atoms（from Sc to Zn） adsorbed monolayer Ga As nanosheets（Ga As NSs） are systematically investigated.Upon TM atom adsorption,Ga As NS,which is a nonmagnetic semiconductor,can be tuned into a magnetic semiconductor（Sc,V,and Fe adsorption）,a half-metal（Mn adsorption）,or a metal（Co and Cu adsorption）.Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the Ga As NSs with Sc,V,and Fe adsorption.However,the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit,resulting in a stronger exchange interaction.Our results may be useful for electronic and magnetic applications of Ga As NS-based materials.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11004142the Program for New Century Excellent Talents in University under Grant No 11-035the Project Sponsored by the Scientific Research Foundation for ROCS of the Ministry of Education of China
文摘The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.
基金supported by the National Natural Science Foundation of China(Grant Nos.11004141 and 11174212)the Program for New Century Excellent Talents in University of Ministry of Education of China(Grant No.11-0351)the Scientific Research Starting Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China
文摘Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite （Ga,Mn）As nanowires （NWs） grown along the [0001] direction were investigated based on density functional theory （DFT）. We found that （Ga,Mn）As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the N-Ws. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.
基金Project supported by the Natural Science Foundation of Gansu Province, China (Grant No. 0803RJZA008)the Fundamental Research Funds for the Central Universities, China (Grant No. zyz2012057)+1 种基金the National Natural Science Foundation of China (Grant No. 11004141)the Program for New Century Excellent Talents in University, China (Grant No. 11-0351)
文摘ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO：Cu film can be enhanced by a moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO：Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of the Burstein–Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples.
基金Project supported by the National Natural Science Foundation of China(Grant No.11174212)
文摘By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal（TM） atoms（from Sc to Zn） adsorbed monolayer Ga As nanosheets（Ga As NSs） are systematically investigated.Upon TM atom adsorption,Ga As NS,which is a nonmagnetic semiconductor,can be tuned into a magnetic semiconductor（Sc,V,and Fe adsorption）,a half-metal（Mn adsorption）,or a metal（Co and Cu adsorption）.Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the Ga As NSs with Sc,V,and Fe adsorption.However,the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit,resulting in a stronger exchange interaction.Our results may be useful for electronic and magnetic applications of Ga As NS-based materials.
