气相传输平衡技术制备LiGaO2薄膜

为获得与GaN薄膜晶格失配小的衬底材料,报道了利用气相传输平衡技术(VTE)在(100)-βGa2O3单晶衬底上制备高度[001]取向LiGaO2薄膜的方法。经过X射线衍射分析表明得到的薄膜是由单相LiGaO2组成。利用扫描电镜(SEM)观察表面形貌,发现经气相传输平衡技术处理得到的薄膜表面形貌主要受温度的影响,表面晶粒尺寸随温度上升而增大。而X射线衍射测试表明随着温度上升,所得到的薄膜也从多晶向单晶化转变。在经过退火处理后,通过观察吸收谱发现LiGaO2薄膜中产生色心,并且色心的种类与温度有关。表明可以通过气相传输平衡技术技术,在远低于LiGaO2熔点的温度制备外延GaN用(001)LiGaO2∥(100)β-Ga2O3复合衬底。     

ZnS衬底上GeC/GaP增透保护膜系的制备及红外光学性质

把GeC/GaP双层膜用作ZnS衬底的长波红外(8~11.5μm波段)增透保护膜系。采用射频磁控溅射法,以高纯Ar为工作气体、单晶GaP圆片为靶制备了GaP薄膜;用射频磁控反应溅射法在高纯Ar和CH4的混合气体中,以单晶Ge圆片为靶制备了GeC薄膜。分别用柯西(Cauchy)公式和乌尔巴赫(Urbach)公式表示折射率和吸收系数,对薄膜的红外透射率曲线进行最小二乘法拟合,得到了它们的厚度及折射率、吸收系数等光学常数。GaP膜的折射率与块体材料的相近,在波长10μm处约为2.9;GeC膜的折射率较小,在波长10μm处约为1.78。用所得到的薄膜折射率,通过计算机膜系自动设计软件在ZnS衬底上设计并制备出了GeC/GaP双层增透保护膜系,当GaP膜厚较大时,由于吸收增大膜系增透效果较差;当GaP膜厚较小时,膜系有较好的增透效果。     

Investigation of the intrinsic absorption edge in nanostructured polycrystalline zinc oxide thin films

We have studied the temperature variation of the intrinsic absorption edge of thin polycrystalline films of zinc oxide, obtained by high-frequency magnetron reactive sputtering. We ha ve observed that the intrinsic absorption edge in such films is described by a modified Urbach’s rule. We have calculated the effective frequency of phonons taking part in formation of the absorption edge. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 200–203, March–April, 2006.     

Thin-Film Flow Influenced by Thermal Noise

We study the influence of thermal fluctuations on the dewetting dynamics of thin liquid films. Starting from the incompressible Navier-Stokes equations with thermal noise, we derive a fourth-order degenerate parabolic stochastic partial differential equation which includes a conservative, multiplicative noise term—the stochastic thin-film equation. Technically, we rely on a long-wave-approximation and Fokker–Planck-type arguments. We formulate a discretization method and give first numerical evidence for our conjecture that thermal fluctuations are capable of accelerating film rupture and that discrepancies with respect to time-scales between physical experiments and deterministic numerical simulations can be resolved by taking noise effects into account.     

Optical properties of amorphous films

We have analyzed the optical properties of a-Ge_30-xSb_xS₇₀ chalcogenide glass films (x=0,10,20 and 30 at%); the chalcogenide films were prepared by vacuum thermal evaporation. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the optical band gap, E_opt, decreases from 2.04±0.01 to 1.74±0.01 eV, whereas the refractive index increases with increasing Sb content. Data are analyzed by the Wemple equation, which is based on the single-oscillator model.     

Growth of Al2O3 thin films on NiAl(1 0 0) by gas-phase oxidation and electro-oxidation

The growth and structures of aluminum oxides on NiAl(1 0 0) have been investigated by RHEED (reflection high energy electron diffraction), complemented by LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and STM (scanning tunneling microscopy). Crystalline θ-Al₂O₃ phase grows through gas-phase oxidation on the NiAl(1 0 0) substrate with its a and b-axes parallel to [0 −1 0] and [0 0 1] direction of the substrate, respectively, forming a (2 × 1) unit cell. Whilst, three-dimensional nano-sized NiAl(1 0 0) protrusions and Al₂O₃, NiAl(0 1 1) clusters were found to co-exit at the surface, evidenced by extraordinary transmission spots superposed to the substrate reflection rods in the RHEED patterns. Particularly, the NiAl(0 1 1) clusters develop with their (0 1 1) plane parallel to the NiAl(1 0 0) surface, and [1 0 0] axis parallel to the [0 −1 1] direction of the substrate surface. STM observation combined with information from AES and TPD (temperature programmed desorption) suggest the formation of these 3D structures is closely associated with partial decomposition of the crystalline oxides during annealing. On the other hand, smoother (2 × 1) oxide islands with thickness close to a complete monolayer of θ-Al₂O₃ can be formed on NiAl(1 0 0) by electro-oxidation, in contrast with the large crystalline films formed by gas-oxidation.     

Active role of buried ultrathin oxide layers in adsorption of O2 on Au films

Ultrathin oxide layers can exhibit special behavior by enabling the coupling of structural distortions and charge transfer beyond that allowed in the bulk. In this work, we show from first-principles calculations that ultrathin layers of titania, a prototypical oxide, are active in stabilizing adsorption of O₂ on Au overlayers. The adsorbed O₂ molecules induce charge redistribution in Au that penetrates to the Au-titania interface, which responds through structural distortions that lower the total energy of the system. We suggest that this effect may be of more general nature and useful in catalysis.     

相变域硅薄膜材料的光稳定性

采用RF-PECVD技术，通过改变反应气体的硅烷浓度制备了一系列不同晶化率不掺杂的硅薄膜材料，研究了工艺变化对材料结构的影响及材料光电特性同微结构的关系.随后进行了光衰退试验，在分析光照前后光电特性变化规律的基础上，认为材料中的非晶成分是导致材料光电特性衰退的主要原因.在靠近过渡区非晶一侧的硅材料比普通非晶硅稳定，衰退率较少；高晶化率微晶硅材料性能稳定，基本不存在光衰退；在靠近过渡区微晶一侧的硅材料虽然不是完全不衰退，但相比高晶化率硅材料来说更适合制备高效微晶硅电池. 关键词： 射频等离子体增强化学气相沉积 硅薄膜 Staebler-Wronski(SW)效应 稳定性     

波纹壳的格林函数方法

应用轴对称旋转扁壳的基本方程,研究了在任意载荷作用下具有型面锥度的浅波纹壳的非线性弯曲问题·　采用格林函数方法,将扁壳的非线性微分方程组化为非线性积分方程组·　再使用展开法求出格林函数,即将格林函数展成特征函数的级数形式,积分方程就成为具有退化核的形式,从而容易得到非线性代数方程组·　应用牛顿法求解非线性代数方程组时,为了保证迭代的收敛性,选取位移作为控制参数,逐步增加位移,求得相应的载荷·　在算例中,研究了具有球面度的浅波纹壳的弹性特征·　结果表明,由于型面锥度的引入,特征曲线发生显著变化,随着荷载的增加,将出现类似扁球壳的总体失稳现象·　本文的解答符合实验结果·     

Semiconductor Nanoparticles

Semiconductor nanoparticles exhibit size dependent properties, when their size is comparable to the size of Bohr diameter for exciton. This can be exploited to increase fluorescence efficiency or increase the internal magnetic field strength in doped semiconductors. Nanoparticles are usually unstable and can aggregate. It is therefore necessary to protect them. Surface passivation using capping molecules or by making core–shell particles are some useful ways. Here synthesis and results on doped and un-doped nanoparticles of ZnS, CdS and ZnO will be discussed. We shall present results on core–shell particles using some of these nanoparticles and also discuss briefly the effect of Mn doping on hyperfine interactions in case of CdS nanoparticles.