Journal of Physics-Condensed Matter
Crystalline C, Si and Ge in a lonsdaleite (hexagonal diamond) structure are studied by plane-wave pseudopotential calculations in the scheme of density-functional theory and the local density approximation. The same calculations with generalized gradient corrections and also for the cubic diamond phases of these elements are also performed for comparison. Our results show that the bulk moduli are quite similar between the diamond and lonsdaleite polytypes of these elements. The theoretical bulk modulus of lonsdaleite C is 0.2-0.3% higher than diamond. It is expected to replace diamond as the hardest material in the world. The LDA result shows lonsdaleite Ge as a semimetal for its zero band gap at its Gamma point. Considering the exchange-correlation energy correction, it is estimated that lonsdaleite Ge is a semiconductor with a small direct band gap.
关键词:
diamond hexagonal silicon;total-energy calculations;plane-wave;electronic-structure;pseudopotentials;semiconductors;germanium;pressure;microscopy;defects
李伟文
,
赵新兵
,
邬震泰
,
曹高劭
功能材料
对掺C和Ge的Fe-Su-Si-Mn基热电材料的电学性能研究表明,相对于未掺的Fe-Si-Mn基热电材料,掺C样品的电阻率降低,但热电动势率增加.掺Ge样品的电阻率有所升高,但热电动势率增加更快,因此掺C、Ge样品有较高的功率因子,比未掺样品提高近1倍.
关键词:
热电材料
,
FeSi2
,
电学性能
,
掺杂
沈海军
,
付光俊
,
陈裕
功能材料与器件学报
doi:10.3969/j.issn.1007-4252.2006.06.018
采用扩展的Hückel方法与格林函数方法,分析了双Au电极作用下,C60、Si@C60以及Ge@C60富勒烯分子的电子结构与导电性,并对三种富勒烯分子的电子结构与电子输运特性进行了对比.研究结果表明,C60、Si@C60或Ge@C60分子与Au电极"接触"后,其最高占据分子轨道与最低未占据分子轨道间的能隙减小,它们与Au电极之间的结合既有共价键的成分,又有离子键的成分;三种富勒烯分子的电子输运性能依次具有Ge@C60＞Si@C60＞C60的顺序.
关键词:
C60富勒烯分子
,
Hückel方法
,
格林函数
,
电子结构
,
电子传输
刘鹏强
,
王茺
,
周曦
,
杨杰
,
杨宇
功能材料
doi:10.3969/j.issn.1001-9731.2014.05.012
采用离子束溅射技术,通过改变诱导量子点形成的C层生长温度,在n型Si(100)衬底上自组装生长了一系列Ge量子点。利用 AFM和 Raman光谱对样品的表面形貌和结构进行了表征。实验结果表明,当C层的温度从600℃升高到700℃时,Ge 量子点的密度逐渐降低,且结晶性变差；此时,量子点中的 Si 组分升高。当C层的生长温度从700℃升高到800℃过程中,Ge量子点的密度逐渐增大,结晶性也有所改善；此时,量子点中的Si含量降低。
关键词:
离子束溅射
,
Ge量子点
,
扩散
,
C诱导
沈海军
功能材料
采用基于Tersoff势的分子动力学方法,模拟了温度T=300、700和1100K下C60、M@C60(M=Si,Ge)富勒烯分子的对径压缩过程.根据模拟结果,讨论了温度T对3种富勒烯分子压缩力学特性的影响以及它们压缩力学特性的差异.研究表明,在300～1100K范围内,温度T对C60、M@C60(M=Si,Ge)分子压缩力学特性无显著影响;当压缩应变至8%～16%左右,各富勒烯分子在加载点处开始"塌陷",当压缩应变至28%～32%左右,各富勒烯达到承载极限;C60、Si@C60、Ge@C60分子依次具有由低到高的承载能力.
关键词:
富勒烯
,
分子动力学
,
力学特性
,
内嵌M@C60富勒烯
Physical Chemistry Chemical Physics
Information on orbital hybridization is very important to understand the structural, physical, and chemical properties of a material. Results of a comparative first-principles study on the behaviours of orbital hybridization in the two-dimensional single-element phases by carbon, silicon, and germanium are presented. From the well-known three-dimensional hexagonal lonsdaleite structure, in which the atoms are in ideal sp(3)-bonding, the layer spacing along c-axis is gradually stretched to simulate the evolutions of structural and electronic properties from three-dimensional to two-dimensional lattice configurations in the three materials. A turning point of the total system energy due to the sp(3) to sp(2) transition is observed during this process in carbon. In contrast, no such phenomenon is found in silicon and germanium. The differences in electronic structure and bonding behaviour are further examined through comparative investigation of atomic angular-momentum projected density of states and electronic energy band spectrums of these materials. We demonstrate that the valence electronic orbital in the two-dimensional hexagonal crystals of Si and Ge shows sp(3)-like behaviour for the partial hybridization of s and p(z), which leads to their different lattice configurations to graphene. The role of pi-bonds in stabilizing the flat configuration of graphene is also discussed.
关键词:
lonsdaleite phases;elastic-constants;silicon nanotubes;graphite;carbon;graphene
Journal of Alloys and Compounds
Crystal structures of compounds at ambient temperature in the pseudobinary system Gd5Ge4-La5Ge4 were studied by X-ray powder diffraction (XRD). There exist three single-phase regions in this system. The crystal structure of Gd5Ge4, La5Ge4 and Gd3La2Ge4, which are prototype compounds in three phase regions, respectively, were reported. The Gd5Ge4 and La5Ge4 crystallize in the orthorhombic Sm5Ge4-type structure with space group Pnma. The ternary intermediate compound Gd3La2Ge4, which is determined for the first time, crystallizes in the monoclinic Gd5Si2Ge2-type structure with space group P112(1)/a. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structure. The lattice parameters, atomic occupations, interatomic distances of the Gd5Ge4, La5Ge4 and Gd3La2Ge4 compounds were derived. (C) 2003 Elsevier B.V. All rights reserved.
关键词:
rare earth compounds;crystal structure;X-ray diffraction;phase-relationships;gd-5(si2ge2);transition;silicon
Applied Physics Letters
Uniform Ge-nanocrystals (Ge-ncs) embedded in amorphous SiO(2) film were formed by using (74)Ge(+) ion implantation and neutron transmutation doping (NTD) method. Both experimental and theoretical results indicate that the existence of As dopants transmuted from (74)Ge by NTD tunes the already stabilized (crystallized) system back to a metastable state and then activates the mass transfer processes during the transition form this metastable state back to the stable (crystallized) state, and hence the nanocrystal size uniformity and higher volume density of Ge-ncs. This method has the potential to open a route in the three-dimensional nanofabrication. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553770]
关键词:
transmutation-doped gaas;electrical-properties;misfit dislocations;lasers go;silicon;films
