Electronic structure of amorphous semiconductors

The effect of light soaking and thermal quenching on the electronic structure of hydrogenated amorphous silicon (a-Si:H) and chalcogenide glasses was studied. It was found that lithium dopeda-Si:H shows both light and thermal induced changes in electronic transport properties. In contrast, chalcogenides do not show any effect of thermal quenching, although they exhibit changes upon light soaking. By analysing the conductivity and thermopower data we have concluded that the light soaking increases the potential fluctuations present in lithium dopeda-Si:H, whereas quenching does not change them. A model qualitatively explaining these effects is presented.     

Ag掺杂非晶碳膜结构、力学与电学行为研究

采用反应磁控溅射技术, 通过改变溅射靶电流实现了不同Ag掺杂含量0.7at%~41.4at%非晶碳膜(a-C:Ag)的可控制备, 并系统研究了Ag含量对薄膜组分、结构、机械特性的影响规律, 以及薄膜的电学特性。结果表明: 当Ag含量在0.7at%~1.2at%时, Ag原子固溶于非晶碳基质; 当Ag含量在13.0at%~41.4at%范围, 薄膜中出现尺寸约为6 nm的Ag纳米晶。随着Ag含量增加, 碳网络结构的sp ²团簇尺寸增大, 结构无序度降低。应力测试表明, 在低Ag含量范围, Ag原子固溶于碳膜网络结构中, 起到枢纽作用, 促进碳网络结构键长、键角畸变弛豫, 从而降低薄膜应力。随着Ag含量增加, 部分Ag原子将形成Ag纳米晶粒, 薄膜通过Ag纳米晶与非晶碳界面处的滑移以及扩散作用释放过高的畸变能降低应力。Ag含量为37.8at%时, 在11.6 K附近, 薄膜出现金属-半导体特性转变。而Ag含量为41.4at%的薄膜, 在2~400 K测试温度范围内, 均表现为半导体特性, 其中在164~400 K范围内, 薄膜表现出典型的热激活导电机制。     

一种新型含三苯胺二苯乙烯衍生物的合成及性能研究

合成了一种新型的空穴传输材料三苯胺二苯乙烯衍生物DPAVBi,并通过一系列手段对其进行了表征。DPAVBi具有较好的无定形成膜性及较高的热稳定性。以DPAVBi为电荷传输层,TiOPc为光生层制备的双层光电导体,其光敏性在762nm处达到1.67cm2·μJ-1,是一种优良的空穴传输材料。     

Electronic band-edge properties of rock salt PbY and SnY (Y= S, Se, and Te)

The electronic band-edges of lead chalcogenides PbY and tin chalcogenides SnY (where Y = S, Se, and Te) are investigated by the means of a full-potential linearized augmented plane wave (FPLAPW) method and the local density approximation (LDA). All six chalcogenide binaries have similar electronic structures and density-of-states, but there are differences in the symmetry of the band-edge states at and near the Brillouin zone L-point. These differences give the characteristic composition, pressure, and temperature dependences of the energy gap in Pb_1−xSn_xY alloys.We find that: (1) SnY are zero-gap semiconductors E_g = 0 if the spin–orbit (SO) interaction is excluded. The reason for this is that the conduction band (CB) and the valence band (VB) cross along the Q ≡ LW line. (2) Including the SO interaction splits this crossing and creates a direct gap along the Q-line, thus away from the L symmetry point. Hence, the fundamental band gap E_g in SnY is induced by the SO interaction and the energy gap is rather small E_g ≈ 0.2–0.3 eV. At the L-point, the CB state has symmetric and the VB state is antisymmetric thereby the L-point pressure coefficient ∂E_g(L)/∂p is a positive quantity. (3) PbY have a direct band gap at the L-point both when SO coupling is excluded and included. In contrast to SnY, the SO interaction decreases the gap energy in PbY. (4) Including the SO interaction, the LDA yields incorrect symmetries of the band-edge states at the L-point; the CB state has and the VB state has symmetry. However, a small increase of the cell volume corrects this LDA failure, producing an antisymmetric CB state and a symmetric VB state, and thereby also yields the characteristic negative pressure coefficient ∂E_g(L)/∂p in agreement with experimental findings. (5) Although PbY and SnY have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. (6) Finally, in the discussion of the symmetry of the band edges, it is important to clearly state the chosen unit cell origin; a shift by (a/2,0,0) changes the labeling of the irreducible representations.     

非晶半导体的研究与应用

1968年Ovshinsky在多元硫系薄膜中观察到电的开关与存贮效应以来,特别是1975年氢化非晶Si的p型与n型掺杂控制的实现,非晶半导体作为一个重要的电子材料,在过去的30多年中吸引了大量的基础研究并得到了广泛的应用。本文综述了至今为止非晶半导体重要的研究与应用进展,并探讨非晶半导体今后主要的发展趋势。     

热喷涂亚稳态复合涂层研究进展

热喷涂亚稳态复合涂层能克服许多亚稳材料不易直接成形的不足,有效发挥非晶、纳米晶和准晶材料的特殊功效.等离子喷涂和高速火焰喷涂亚稳态铁基、镍基、陶瓷粉末制备的涂层质量优异,在热障、耐磨、防腐等领域应用前景广阔,但尚需拓展涂层功能,降低成本.电弧喷涂粉芯丝材制备亚稳态涂层具有成本低、效率高、成分易调节等优势,在大规模高效制备耐磨、防腐、防高温腐蚀与冲蚀涂层方面优势明显,但尚需提高涂层稳定性,开发更多涂层材料体系.目前,我国需要从自动化热喷涂设备开发和新型亚稳态材料体系研究两方面展开深入研究,提高亚稳态喷涂层的组织结构稳定性和性能质量可靠性,使该技术走出实验室面向工业应用,更好地为国家循环经济建设服务.     

Effect of sonication time on the synthesis of the CdS nanoparticle based multiwall carbon nanotube – maleic anhydride – 1-octene nanocomposites

Effect of sonication time on the synthesis of the CdS nanoparticles within the matrix obtained through the covalent functionalization of multiwall carbon nanotube (MWCNT) with maleic anhydride (MA) – 1-octene copolymer was investigated. Cadmium chloride and thiourea were used as the raw materials. MWCNTs used for the matrix were synthesized by Catalytic Chemical Vapor Deposition using Fe-Co/Al₂O₃ as the catalyst. The obtained nanostructures were characterized by FTIR, XRD, Raman spectroscopy, TEM, SEM, TG and UV-Vis spectroscopy. Electrophysical properties of the polymer nanocomposites obtained using different periods of time for sonication were comparably investigated. The average CdS particle diameter was between 3.9–7.9 nm as confirmed independently by TEM and XRD. UV-Vis spectroscopy revealed that the obtained nanostructures are appropriate base materials for making optical devices.