XPS study of the a-C:H/Ti and a-C:H/a-Si interfaces

In this study ultrathin hydrogenated amorphous carbon (a-C:H) films have been grown onto the titanium and amorphous silicon (a-Si) overlayers by direct ion beam deposition using acetylene gas as a hydrocarbon source. X-ray photoelectron spectroscopy (XPS) was used for study of the DLC-Ti and DLC-Si interfaces. It was revealed that a-Si is a good interlayer for improvement of adhesion in the case of diamond-like carbon film deposition onto the steel substrate at room temperature. a-C:H film growth without substantial intermixing occurred on the a-Si. On the other hand, adhesion between the Ti interlayer and the diamond like carbon film was very sensitive to the deposition conditions (presence of the pump oil) as well as structure and stress level of the Ti film. It was explained by strong intermixing between the growing carbon film and Ti. Bad adhesion between the growing DLC film and Ti interlayer was observed despite formation of the TiC. At the same time, formation of the TiO_x was not an obstacle for good adhesion. It is shown that composition of the used hydrocarbon gas, structure of the Ti thin film and mechanical stress in it had greater influence on adhesion with a-C:H film than elemental composition of the Ti interlayer surface.     

Transmission electron microscopy study of the initial growth stage of GaSb grown on Si (001) substrate by molecular beam epitaxy method

The microstructural properties at the initial growth stage of the GaSb heteroepitaxial growth on a silicon (Si) substrate were investigated using transmission electron microscopy. Well-separated and tall GaSb islands were observed when GaSb was directly grown on a Si substrate (sample A). On the other hand, GaSb was grown to the coalesced and flat islands when a low-temperature AlSb buffer (sample B) was introduced. The different morphologies of the GaSb islands were related to the microstructural properties of the interface between the GaSb and the Si substrate. The GaSb/Si interface was rough, and disordered atomic arrangements were observed at the interface in sample A. On the other hand, the GaSb/Si interface was flat, and well-ordered atomic arrangements appeared at the interface in sample B. Entirely different mechanisms for the relaxation of a misfit strain were demonstrated from a microstructural viewpoint.     

A role of parameters in RF PA CVD technology of a-C:N:H layers

Results concerning influence of radio-frequency plasma-assisted chemical vapor deposition (RF PA CVD; 13.56 MHz) processing parameters on a-C:N:H layer deposition are presented in this work. The following parameters have been taken into consideration: substrate temperature, plasma RF generator power, composition of reactive gas mixture, gas pressure and time of deposition. A special interest has been focused on the deposition rate as well as on the structure and chemical composition of layers. The layer thicknesses have been measured and deposition rates evaluated. Structure analysis has been performed with application of FT-IR spectroscopy. The obtained results may serve as a basis in the design of the technology of a-C:N:H layers for various applications.     

Microstructural evolution of reinforcements in the remelting in situ TiC/Al-12Si composites treated by ultrasonic vibration

Clusters of reinforced particles and long rod-like Al₃Ti particles are usually present in the matrix of in situ TiC/Al alloy composites fabricated via SHS reaction of the Al-Ti-C system in the molten aluminum alloys. In order to improve the properties of the composites, the above issues should be solved effectively. In our research, high-intensity ultrasonic vibration was introduced into the remelting TiC/Al-12Si composites containing clusters of TiC particles and long rod-like Al₃Ti phase to optimize the microstructure of the composites. The results of SEM showed that long rod-like Al₃Ti particles were turned into small blocky ones and large clusters were broken up into small ones. In the meantime, individual TiC particles could be peeled off from the clusters and distributed uniformly in the matrix. An in situ TiC/Al-12Si composite with a homogeneous microstructure was attained successfully. The evolution of the morphology of Al₃Ti phase and the clusters in the ultrasonic field was also discussed.     

Multilayer amorphous hydrogenated carbon (a-C:H) and SiOx doped a-C:H films for optical applications

In this study SiO_x doped amorphous hydrogenated carbon (a-C:H) films were formed from hexamethyldisiloxane (with hydrogen transport gas) by closed drift ion beam deposition applying variable ion beam energy (300-800 eV). The band gap dependence on the deposition energy was determined and used in production of SiO_x doped a-C:H and a-C:H (formed from acetylene gas) multilayer (two and four layers) stack. Optical properties of the multilayer structures as well as individual layers were analysed in the UV-VIS-NIR range (200-1000 nm). It was shown that employing double or four layer systems, the reflectivity of the multilayer structure-crystalline silicon can be tuned to almost 0% at specific wavelength range (550-950 nm), important in solar cell applications.     

Investigation of space charge at pentacene/Au interface with UV/ozone treatment by a near-field microwave microprobe

The near-field microwave microprobe (NFMM) and Kelvin-probe measurements were performed to evaluate the conductivity in terms of surface potential of pentacene films on Au electrode. The UV/ozone treated and untreated Au electrodes were prepared to reveal the relationship between the electrical conductivity and interfacial electrostatic charging phenomena. For the pentacene film deposited on the Au electrode with UV/ozone treatment, holes were displaced from Au electrode to pentacene film, resulting the accumulation of apparent positive charges in the interfacial region of pentacene film around Au electrode. The NFMM measurement revealed that the reflection coefficient of microwave, S₁₁ increased with UV/ozone treatment, indicating the resistance decrease of the surface. Accumulation of positive charge in the interfacial region of Au electrode/pentacene film is one of the essential reasons for the increase of the conductivity of pentacene film.     

Thermal stability of nanocomposite CrC/a-C:H thin films

The thermal stability of low-friction Me-C/a-C:H coatings is important for their potential applications in the tool and automotive industry. Recently we showed that CrC_x/a-C:H coatings prepared by unbalanced magnetron sputtering of a Cr target in Ar + CH₄ glow discharges exhibit a nanocomposite structure where metastable fcc CrC nanocrystals are encapsulated by an a-C:H phase. Here, we present the structural evolution of these nanocomposite CrC/a-C:H coatings during annealing. High-temperature X-ray diffraction in vacuum and differential scanning calorimetry (DSC) combined with thermo-gravimetric analysis in Ar atmosphere indicate decomposition of the formed metastable fcc CrC phase and subsequent formation of Cr₃C₂ and Cr₇C₃ and structural transformation of the a-C:H matrix phase towards higher sp² bonding contents at temperatures above 450 °C. Combined DSC and mass spectrometer analysis as well as elemental profiling after annealing in vacuum by elastic recoil detection analysis relate this transformation to the loss of bonded hydrogen at temperatures above 200 °C.Due to these structural changes the coefficient of friction depends on the annealing temperature of the nanocomposite a-C:H coatings and shows a minimum of ∼ 0.13 for T = 200 °C. The more complex tribochemical reactions, influenced by the hydrogen loss from the coating during in-situ high temperatures ball-on disc tests, result in coefficient of friction values below 0.05 for T < 120 °C.     

Diffusion barrier performances of thin Mo, Mo-N and Mo/Mo-N films between Cu and Si

In this work, we have studied the diffusion barrier performances of Mo, Mo-N and Mo/Mo-N metallization layers deposited by sputtering Mo in Ar/N₂ atmospheres, respectively. Samples were subsequently annealed at different temperatures ranging from 400 to 800 °C in vacuum condition. The film properties and their suitability as diffusion barriers and protective coatings in silicon devices were characterized using four-point probe measurement, X-ray diffractometry, scanning electron microscopy, Auger electron spectroscopy and transmission electron microscopy analyses. Experimental results revealed that the Mo (20 nm)/Mo-N (30 nm) layer was able to prevent the diffusion reaction between Cu and Si substrate after being annealed at 600 °C for 30 min. The adhesion between layers and the content of N atoms are the key parameters to improve the properties of Mo-based barrier materials. The Mo layer interposed between Cu and Mo-N diluted the high nitrogen concentration of the barrier and so enhanced the barrier performances.     

Properties of nitrogen diluted hydrogenated amorphous carbon (n-type a-C:H) films and their realization in n-type a-C:H/p-type crystalline silicon heterojunction diodes

Nitrogen incorporated hydrogenated amorphous carbon (a-C:N:H) films were grown in an asymmetric rf PECVD system using C₂H₂ and N₂ gaseous mixture. Deposition rate, stress, hardness, optical bandgap, refractive index, and electrical characteristics have been studied as a function of self bias. Microstructures of these films were also studied using LASER Raman technique. Finally nitrogen diluted a-C:H films were realized as n-type semiconductor in n-type a-C:H/p-type crystalline silicon hetrojunction diodes. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics have also been studied as a function of self bias on these heterojunction diodes.     

a-C∶H/a-Se复合膜晶化分形凝聚的计算机模拟研究

本文基于红外透射及喇曼谱分析的结果提出了一个 a-C:H/a-Se 复合膜的 a-C∶H 层非平衡晶化凝聚模型,并做了计算机模拟研究。模拟得到的图形是具有良好的无标度性的链环状分形。其分维值为1.37±0.02,此结果得到了实验的肯定。这对非晶膜的结构及晶化机理的研究均富有价值。     

Synthesis reactions for Ti3SiC2 through pulse discharge sintering TiH2/Si/TiC powder mixture

Ternary compound Ti₃SiC₂ was rapidly synthesized by pulse discharge sintering the powder mixture of 1TiH₂/1Si/1.8TiC without preliminary dehydrogenation. Almost single-phase dense Ti₃SiC₂ was synthesized at 1400 °C for 20 min. The grain size of synthesized Ti₃SiC₂ strongly depends on sintering temperature. The synthesis mechanism of Ti₃SiC₂ was revealed to be completed via the reactions among the intermediate phases of Ti₅Si₃, TiSi₂ and the other reactants in the starting powder. The Ti-Si liquid reaction occurring above the Ti-Ti₅Si₃ eutectic temperature at 1330 °C was found to assist the synthesis reaction and densification of Ti₃SiC₂. The dehydrogenation of TiH₂ was accelerated by the synthesis reactions.     

a-C∶H/a-Se 复合膜结构的红外及喇曼谱研究

a-C∶H/a-Se/Al 是一种优良的新型复印感光体。我们在 KCl 和 Si 单晶上制备了 a-C∶H/a-Se 复合膜,以进行红外和喇曼谱分析。结果表明,a-Se 上 a-C∶H 层中 CH_n 键型(n=1～3)的比例为:sp~1∶sp~2∶sp~3=0.10∶0.09∶0.81;而 sp~3键型中各功能团比例为:sp~3CH∶sp~3CH_2∶sp~3CH_3=0.28∶0.38∶0.34。在同样工艺条件下制备的 KCl 上 a-C∶H 中的相应比例则为 sp~1∶sp~2∶sp~3=0∶0∶1;sp~3CH∶sp~3CH_2∶sp~3CH_3=0.45∶0.33∶0.22。二者相比,可认为 a-Se(?)衬底上的 a-C∶H 层中主要由 sp~3CH_2和 sp~2CH 构成的“长链型”近程有序成分大大增加。由此可解释复合膜的性能并寻找改进复合膜的途径。     

Dissolution and reprecipitation of barium at the particulate BaTiO3-aqueous solution interface

The electrokinetic behavior of BaTO₃ particles in an aqueous medium exhibited a hysteresis loop with titration direction. As BaTiO₃ suspension was titrated toward acidic pH, the amount of Ba²⁺ dissolution strongly increased, and in the subsequent titration toward alkaline pH, Ba²⁺ adsorbed and/or reprecipitated on the Ba-depleted BaTiO₃ surface. This dissolution-reprecipitation cycle results in the observed hysteresis behavior. An attempt was made to identify the responsible species of the adsorbed/reprecipitated compound by XPS in conjunction with electrokinetic titrations.     

a-C∶H/a-Se复合膜非平衡晶化分形特征的SEM观测

a-C∶H/a-Se/Al 感光体的 a-C:H 层在能流密度的6.4×10~(14)eV/mm~2·s 的离子流轰击下发生了非平衡晶化凝聚。晶体凝聚物为“链环状分形”。用盒子计数法测得其分数维 D_0=1.35±0.04;用相关函数法测得其关联维为 D_2=1.39±0.03。这与我们用计算机模拟的结果很好地符合。本文同时讨论了这一系列文章([2][3]及本文)对发展一种新的非平衡晶化分析方法的意义。     

Single-molecule biophysics: at the interface of biology, physics and chemistry

Single-molecule methods have matured into powerful and popular tools to probe the complex behaviour of biological molecules, due to their unique abilities to probe molecular structure, dynamics and function, unhindered by the averaging inherent in ensemble experiments. This review presents an overview of the burgeoning field of single-molecule biophysics, discussing key highlights and selected examples from its genesis to our projections for its future. Following brief introductions to a few popular single-molecule fluorescence and manipulation methods, we discuss novel insights gained from single-molecule studies in key biological areas ranging from biological folding to experiments performed in vivo.     

a－C：H膜折射率的变化规律及红外应用

本文对ａ－Ｃ：Ｈ膜的性质如折射率和生长速率的变化规律进行了研究，并且在增透原理的指导下制备了具有高红外透过率的单波段、双波段和宽波段的ａ－Ｃ：Ｈ增透保护膜     

退火温度对a-C:H膜结构及摩擦学性能的影响

为研究环境温度对含氢无定形碳(a-C:H)膜结构和性能的影响,将a-C:H膜在大气环境中进行高温退火处理,并借助红外光谱、拉曼光谱、X射线光电子能谱、3D表面分析仪和球盘摩擦试验机等手段对退火前后a-C:H膜的结构、组成和性能进行了系统地考察.研究发现,在较低的退火温度下(300℃),a-C:H膜结构无明显变化,而其内应力降低,摩擦学性能显著提高;在400℃和500℃下退火,膜结构发生明显变化并伴随严重氧化,同时摩擦学性能降低甚至完全失效.结果表明,退火温度的选择对a-C:H膜的结构、组成及性能具有重要影响.     

Crystallinity and surface roughness dependent photoluminescence of Y1 − xGdxVO4:Eu thin films grown on Si (100) substrate

Gd-substitution dependency on the photoluminescence in YVO₄:Eu³⁺ films grown on Si (100) substrates have been investigated by analyzing the crystalline phase and surface morphology of the films. The substitution of Gd induced not only the change of crystallinity but also the surface roughness of the films. The change of the preferred orientation in the films can be explained on the basis of the lattice mismatch between the film and Si (100) substrate. Also, the surface roughness of the films shows the similar behavior to the grain size as a function of Gd amounts. The photoluminescence (PL) intensity obtained from the Y_1 − xGd_xVO₄:Eu³⁺ films grown under optimized conditions have indicated that the PL intensity is more dependent on the surface roughness than the crystallinity of films. In particular, the incorporation of Gd into the YVO₄ lattice remarkably enhanced the intensity of PL and the highest emission intensity of Y_0.57Gd_0.40Eu_0.03VO₄ film was 3.3 times higher than that of YVO₄:Eu³⁺ film.     

Microstructure and optical properties of chromium containing amorphous hydrogenated carbon thin films (a-C:H/Cr)

Chromium containing amorphous hydrogenated carbon thin films was deposited using a dc sputter deposition technique under various mixtures of methane and Ar. The microstructure, composition, and optical properties of the resulting films were investigated. We show that a-C:H/Cr thin films exhibiting absorptance in certain wavelengths are greater than 95% and the average absorptance was 86% in the 0.3 to 2.5 µm wavelength can be obtained by using appropriate methane/Ar ratios and deposition times.     

Magnetic nanofilms of nickel prepared at the liquid-liquid interface

Thin films of metallic nickel with a thickness of the order of 20 nm have been prepared at the organic-aqueous interface at room temperature by the reaction of nickel cupferronate [Ni(C₆H₅N₂O₂)₂] in toluene medium and sodium borohydride (NaBH₄) in aqueous medium. The films were characterized with transmission electron microscopy, scanning electron microscopy and atomic force microscopy. Thicker Ni films could be prepared by carrying out the reaction at the interface at 60 °C. The Ni nanofilms exhibit superparamagnetic behavior.