Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investig...Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.展开更多
High quality chromium （Cr） doped three-dimensional topological insulator （TI） Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 （111） substrates. We report that the Dirac surfac...High quality chromium （Cr） doped three-dimensional topological insulator （TI） Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 （111） substrates. We report that the Dirac surface states are insensitive to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled in epitaxial Sb2 xCrxTe3 films. The anomalous Hall effect is modulated by applying a bottom gate, contrary to the ferromagnetism in conventional diluted magnetic semiconductors （DMSs）, here the coercivity field is not significantly changed with decreasing cartier density. Carrier-independent ferromag- netism heralds Sbz_xCrxTe3 films as the base candidate TI material to realize the quantum anomalous Hall （QAH） effect. These results also indicate the potential of controlling anomalous Hall voltage in future TI-based magneto-electronics and spintronics.展开更多
GaNs grown by hydride vapor phase epitaxy(HVPE) were irradiated by protons with different fluences.The changes of surface topography of as-grown and irradiated samples were characterized by atomic force microscopy(AFM...GaNs grown by hydride vapor phase epitaxy(HVPE) were irradiated by protons with different fluences.The changes of surface topography of as-grown and irradiated samples were characterized by atomic force microscopy(AFM).The crystal quality and optical properties of GaN films were examined by the variations of the micro-Raman and photoluminescence(PL) spectra with proton fluence.It was observed that the surface became a little more rough after irradiation.The Raman spectra indicated that the strain of materials and carrier concentration were not affected by the proton injection.The full-width at half-maximum(FWHM) of E 2 high phonon mode narrowed,which was consistent with the FWHM of PL near-band-edge emission(BE).The spectra of yellow luminescence and blue luminescence normalized to the intensity of BE demonstrated a little increase of Ga vacancy and a large decrease of O N,which may be the main reason for the change of optical properties.展开更多
In this paper,we introduce different forms of mobility into a quantitative phase-field model to produce arbitrary Ehrlich-Schwoebel(ES)effects.Convergence studies were carried out in the one-side step-flow model,which...In this paper,we introduce different forms of mobility into a quantitative phase-field model to produce arbitrary Ehrlich-Schwoebel(ES)effects.Convergence studies were carried out in the one-side step-flow model,which showed that the original mobility not only induces the ES effect,but also leads to larger numerical instability with increase of the step width.Thus,another modified form of the ES barrier is proposed,and is found to be more suitable for large-scale simulations.Model applications were performed on the wedding-cake structure,coarsening and coalescence of islands and spiral growth.The results show that the ES barrier exhibits more significant kinetic effects at the larger deposition rates by limiting motions of atoms on upper steps,leading to aggregation on the top layers,as well as the roughening of growing surfaces.展开更多
基金Project(51201187)supported by the National Natural Science Foundation of China
文摘Vanadium carbide/titanium carbide （VC/TiC） superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.
基金the National Natural Science Foundation of China(Grant No.11174343)the Ministry of Science and Technology of Chinathe Chinese Academy of Sciences
文摘High quality chromium （Cr） doped three-dimensional topological insulator （TI） Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 （111） substrates. We report that the Dirac surface states are insensitive to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled in epitaxial Sb2 xCrxTe3 films. The anomalous Hall effect is modulated by applying a bottom gate, contrary to the ferromagnetism in conventional diluted magnetic semiconductors （DMSs）, here the coercivity field is not significantly changed with decreasing cartier density. Carrier-independent ferromag- netism heralds Sbz_xCrxTe3 films as the base candidate TI material to realize the quantum anomalous Hall （QAH） effect. These results also indicate the potential of controlling anomalous Hall voltage in future TI-based magneto-electronics and spintronics.
基金supported by the National Natural Science Foundation of China (Grant No. 61106106)the Fundamental Research Funds for the Central Universities (Grant No. K50510250006)
文摘GaNs grown by hydride vapor phase epitaxy(HVPE) were irradiated by protons with different fluences.The changes of surface topography of as-grown and irradiated samples were characterized by atomic force microscopy(AFM).The crystal quality and optical properties of GaN films were examined by the variations of the micro-Raman and photoluminescence(PL) spectra with proton fluence.It was observed that the surface became a little more rough after irradiation.The Raman spectra indicated that the strain of materials and carrier concentration were not affected by the proton injection.The full-width at half-maximum(FWHM) of E 2 high phonon mode narrowed,which was consistent with the FWHM of PL near-band-edge emission(BE).The spectra of yellow luminescence and blue luminescence normalized to the intensity of BE demonstrated a little increase of Ga vacancy and a large decrease of O N,which may be the main reason for the change of optical properties.
基金The National Natural Science Foundation of China(Grant Nos.61078057,61471301,51172183,51402240 and 51471134)The NPU Foundation for Fundamental Research(Grant No.JC20120246)+2 种基金The National Science Foundation of Shaanxi Province,China(Grant No.2012JQ8013)The Doctorate Foundation of Northwestern Polytechnical University(Grant No.CX201325)The Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20126102110045)
文摘In this paper,we introduce different forms of mobility into a quantitative phase-field model to produce arbitrary Ehrlich-Schwoebel(ES)effects.Convergence studies were carried out in the one-side step-flow model,which showed that the original mobility not only induces the ES effect,but also leads to larger numerical instability with increase of the step width.Thus,another modified form of the ES barrier is proposed,and is found to be more suitable for large-scale simulations.Model applications were performed on the wedding-cake structure,coarsening and coalescence of islands and spiral growth.The results show that the ES barrier exhibits more significant kinetic effects at the larger deposition rates by limiting motions of atoms on upper steps,leading to aggregation on the top layers,as well as the roughening of growing surfaces.
