Study on microstructural, chemical and electrical properties of tantalum nitride thin films deposited by reactive direct current magnetron sputtering

The properties of tantalum nitride (TaN_x) thin films on silicon and low temperature co-fired ceramics based substrates were investigated with respect to their potential use for sensor elements operated under harsh environmental conditions. For deposition reactive direct current magnetron sputtering was applied at constant back pressure (=0.9 Pa) and plasma power (=1,000 W). In all experiments, the substrates were nominally unheated. The films were investigated electrically by four point probing. For morphological and chemical analyses, a large variety of techniques such as focussed ion beam, scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and glow discharge optical emission spectroscopy were used. Only by combining all these techniques for analysing TaN_x films synthesised with varying nitrogen content in the deposition chamber can a proper evaluation of the microstructure and the chemical composition be done. Both the microstructure and the chemical composition are influenced strongly with a resulting effect on the electrical film properties.     

Characterization of aluminium nitride and aluminium oxide thin films sputter-deposited on organic substrates

In microsystems technology, passivation layers are generally required to protect micro devices and functional elements against environmental impact, particularly against corrosion, thus increasing reliability and lifetime to acceptable values. In this work, the use of sputter-deposited aluminium oxide and aluminium nitride thin films on flexible polyimide foils was investigated, aiming at the protection of flow sensitive elements. Due to a high defect density located at the interface between the passivation layer and the organic substrate, the adhesion of pure aluminium oxide thin films was found to be poor when applying a combination of mechanical stress (e.g. bombardment with water droplets) and thermal cycling as an accelerated ageing procedure. A bi-layer consisting of aluminium nitride and aluminium oxide, however, shows a defect-free interface to the organic substrate resulting in an enhanced adhesion. In addition, no structural failure can be detected after applying the aging procedure, making this bi-layer approach well suited for the targeted application.     

Effect of aluminium doping on structural and gas sensing properties of zinc oxide thin films deposited by spray pyrolysis

A facile spray pyrolysis route is used to deposit aluminium doped ZnO (AZO) thin films on to the glass substrates. It is observed that on aluminium doping the particle size of ZnO reduces significantly; moreover, uniformity of particle also gets enhanced. Their XRD study reveals that intensity ratio of crystal planes depend on the aluminium doping concentration. The gas response studies of; ∼800 nm thick Al-doped ZnO films at different operating temperatures show that 5 at% Al-doped ZnO thin film exhibits highest response towards H₂S gas at 200 °C. The results suggest that the gas response strongly depends on the particle size and aluminium doping in the ZnO.     

磁控溅射功率对掺Al氧化锌薄膜特性的影响

利用射频磁控溅射技术在石英玻璃衬底上制备掺Al氧化锌(AZO)薄膜,研究了不同溅射功率(75,120,160,200W)对AZO薄膜的结构、光学和电学特性的影响.结果表明:所制备的AZO薄膜具有良好的c轴择优取向,且随着溅射功率的增加,薄膜的表面颗粒尺寸逐渐增加;薄膜在可见光范围具有较高的透射率,吸收边在350～400...     

纳米材料SnO2的室温固相合成及其气敏特性

以无机物SnCl4.5H2O、Na2CO3（摩尔比1：2）为原料,室温下研磨,使其发生固相化学反应,制得SnO2,采用X－射线衍射技术（XRD）和透射电子显微镜（TEM）等测试手段对材料的物相和微观结构进行了分析,结果表明,所得产物为理论产物,该材料制成的烧结型元件对可燃性气体有很高的灵敏度,通过控制工作温度可提高元件的选择性。     

纳米材料SnO_2的室温固相合成及其气敏特性

以无机物SnCl4 ·5H2 O、Na2 CO3 (摩尔比 1:2 )为原料 ,室温下研磨 ,使其发生固相化学反应 ,制得SnO2 ,采用X -射线衍射技术 (XRD)和透射电子显微镜 (TEM)等测试手段对材料的物相和微观结构进行了分析 ,结果表明 ,所得产物为理论产物 ,且平均粒径约为 2 5nm ;采用HWC - 30A汉威气敏元件测试系统对材料的气敏性能进行了测试 ,结果表明 ,该材料制成的烧结型元件对可燃性气体有很高的灵敏度 ,通过控制工作温度可提高元件的选择性     

Design and control of pressure-swing distillation for azeotropes with different types of boiling behavior at different pressures

The mixture of n-heptane and isobutanol presents minimum- and maximum-boiling azeotropes as the pressure changes. Two different pressure-swing distillation (PSD) processes are available for this mixture if the pressure of the low-pressure column is set as atmospheric. The steady states of the two available PSDs are optimized by minimizing the total annual cost (TAC) following a sequential iterative optimization procedure. On the basis of the steady-state results, the dynamic control of the two available PSDs and a comparison between them are presented. The conventional PSD (CPSD) is more economical but less controllable than the unusual PSD (UPSD), which has seldom been studied in the published literature. These two different PSD processes should be considered for the separation of this type of mixture according to their advantages.     

Influence of sputtering power on properties of ZnO thin films fabricated by RF sputtering in room temperature

High mobility and c-axis orientated ZnO thin films were deposited on glass substrates using RF sputtering method at room temperature.Structural properties of ZnO thin films were investigated by X-ray diffraction (XRD).Surface morphology and roughness were studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM).Electrical properties were measured at room temperature using a Hall effect measurement system.The influence of sputtering power on characteristics of ZnO thin films is studied.The results indicate that the sputtering powers have great influence on the crystal quality and mobility of ZnO thin films.By using optimized sputtering conditions,high crystal quality ZnO thin films with Hall mobility of 34 cm 2 /V·s at room temperature were obtained.     

磁控溅射SiC薄膜及其电学特性研究

用磁控溅射法(RMS)制备了SiC微晶薄膜,并对其进行了退火处理.用AFM观察了薄膜的表面形貌,测量了薄膜的厚度、方块电阻和电阻-温度曲线.结果表明:薄膜表面平整光滑;退火处理前后薄膜样品的lnR随1/kT的变化曲线均满足表达式,电子激活能的变化范围为0.0142 eV～0.0185 eV,且随退火温度的升高而增大;分析确定其导电机理为定域态间近程跳跃电导.退火前后薄膜电阻率的范围为2.4×10-3～4.4×10-Ω·cm,且随退火温度的升高而增大,与电子激活能的变化趋势一致,这进一步验证了本文提出的薄膜导电机理和激活能随退火温度的变化趋势.     

Synthesis and optical properties of iron doped gallium nitride nanostructures by sol gel method

Recently, wide band-gap III-Nirtride (III-N) materials and its alloys have attracted much research due to its unique properties and diverse field of applications. In the present study, GaN with various concentration of iron (Fe) in the range 0–5 at% nanostructures were prepared by facile solution process using (Ga(NO₃)₃·9H₂O), iron (III) chloride hexahydrate (FeCl₃·6H₂O) at mild temperature for the first time. The microstructure was analyzed by means of X-ray diffraction and atomic force microscopy. The detailed studies demonstrate that the as-synthesized nanoparticles are well crystallined GaN with a hexagonal wurtzite structure and having the average size of 31 nm in diameter. The optical properties of as the prepared GaN are investigated for Fe doping concentrations ranging from 0.1 to 5 at%. The optical band gap value increases with increasing Fe concentration. These results suggest that the Fe doped-GaN is a promising candidate for optoelectronics and spintronics devices.     

Etching behaviour of sputter-deposited aluminium nitride thin films in H3PO4 and KOH solutions

Aluminium nitride (AlN) reactively sputter deposited from an aluminium target is an interesting compound material due to its CMOS compatible fabrication process and its piezoelectric properties. For the implementation in micromachined sensors and actuators an appropriate patterning technique is needed to form elements made of AlN. Therefore, the influence of different sputtering conditions on the vertical etch rate of AlN thin films with a typical thickness of 600 nm is investigated in an etch mixture based on phosphoric acid. Under comparable conditions, such as temperature and concentration of the etchant, thin films with a high c-axis orientation are etched substantially slower compared to films with a low degree of (002) orientation. When a high c-axis orientation is present detailed analyses of the etched topographies reveal surface characteristics with a low porosity and hence, low roughness values. From temperature dependant etching experiments an activation energy of 800(± 30) meV is determined showing a reaction-controlled etching regime independent of sputter deposition conditions. For comparison, AlN films synthesized under the same conditions were etched in potassium hydroxide (KOH) at room temperature revealing comparable etching characteristics as a function of deposition parameters. Depending on the degree of (002) orientation the topography of the etched samples show a strong increase in surface roughness with time due to a selective etching behaviour between (002) and residual crystallographic planes.     

Gas sensing properties of CuO nanorods synthesized by a microwave-assisted hydrothermal method

P-type CuO nanorods with the breadth of 15-20 nm and the length of 60-80 nm, have been synthesized using a microwave-assisted hydrothermal (MH) method. The band gap of CuO nanorods was calculated to be 2.75 eV based on the UV-vis absorption spectrum of the product. The gas sensing property of the CuO nanorods to several organic vapors was tested in temperatures ranging from 160 °C to 300 °C. The response of the CuO sensor to ethanol (1000 ppm) was 9.8 at the working temperature of 210 °C. The response time and the recovery time were within the range of 13-42 s and 17-51 s, respectively. Further measurements exhibited stronger response to ethanol than to other target gases. The enhanced gas sensing performance of the sensor to ethanol may be attributed to the small size of the CuO particles.     

The combination of different type elements using a Lagrangian multiplier technique for static and dynamic structural analysis

This paper extends the previous applications of the combination technique of axisymmetric solid and solid elements for three dimensional stress analysis to several other types of element combinations, such as, plate-solid, axisymmetric plate-axisymmetric solid and beam-plane stress elements. Without using the multipoint constraint equations or transition elements, this technique is also intended to deal with eigenvalue and transient analysis of compound realistic structures. At each instant, the displacement compatibility conditions at the interface between two adjacent, different type elements are still achieved through the use of the Lagrangian multiplier technique. Several numerical examples are presented to demonstrate the validity and efficiency of the technique developed. Comparisons of calculated results and the referenced solutions also show the high accuracy and advantages of this technique.     

Optical properties of composite heterophase objects with liquid crystal material for different display applications

Liquid crystal (LC) director distribution and optical transmission for different types of heterophase systems with different LC boundary conditions is simulated. The first type is a transparent isotropic material with spherical or cylindrical liquid crystalline objects. There are polymer dispersed liquid crystal, LC fiber, lyotropic LC in polarizing films, LC in microgroove and nanogrooves and pores. The second type is an LC layer incorporating an isotropic transparent or non‐transparent object like microparticles and nanoparticles, spacers, protrusions in multi‐domain vertical alignment LC display et al. The system parameters' influence on LC display performances is discussed.     

Representations and structural properties of periodic systems

We consider periodic behavioral systems as introduced in [Kuijper, M., & Willems, J. C. (1997). A behavioral framework for periodically time-varying systems. In Proceedings of the 36th conference on decision & control (Vol. 3, pp. 2013-2016). San Diego, California, USA, 10-12 December 1997] and analyze two main issues: behavioral representation/controllability and autonomy. More concretely, we study the equivalence and the minimality of kernel representations, and introduce latent variable (and, in particular, image) representations. Moreover we relate the controllability of a periodic system with the controllability of an associated time-invariant system known as lifted system, and derive a controllability test. Further, we prove the existence of an autonomous/controllable decomposition similar to the time-invariant case. Finally, we introduce a new concept of free variables and inputs, which can be regarded as a generalization of the one adopted for time-invariant systems, but appears to be more adequate for the periodic case.     

Novel properties of malarial S-adenosylmethionine decarboxylase as revealed by structural modelling

In the malaria parasite, the two main regulatory activities of polyamine biosynthesis, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) occur in a single bifunctional protein. The AdoMetDC domain was modeled using the human and potato X-ray crystal structures as templates. Three parasite-specific inserts and the core active site region was identified using a structure-based alignment approach. The domain was modeled without the two largest inserts, to give a root mean square deviation of 1.85 angstroms from the human template. Contact with the rest of the bifunctional complex is predicted to occur on one face of the Plasmodium falciparum AdoMetDC (PfAdoMetDC) domain. In the active site there are four substitutions compared to the human template. One of these substitutions may be responsible for the lack of inhibition by Tris, compared to mammalian AdoMetDC. The model also provides an explanation for the lack of putrescine stimulation in PfAdoMetDC compared to mammalian AdoMetDC. A network of residues that connects the putrescine-binding site with the active site in human AdoMetDC is conserved in the malarial and plant cognates. Internal basic residues are found to assume the role of putrescine, based on the model and site-directed mutagenesis: Arg11 is absolutely required for normal activity, while disrupting Lys15 and Lys215 each cause 50% inhibition of AdoMetDC activity. These novel features of malarial AdoMetDC suggest possibilities for the discovery of parasite-specific inhibitors.     

Quality assessment of 3D synthesized images based on structural and textural distortion

Depth image based rendering (DIBR) is a popular technique for rendering virtual 3D views in stereoscopic and autostereoscopic displays. The quality of DIBR-synthesized images may decrease due to various factors, e.g., imprecise depth maps, poor rendering techniques, inaccurate camera parameters. The quality of synthesized images is important as it directly affects the overall user experience. Therefore, the need arises for designing algorithms to estimate the quality of the DIBR-synthesized images. The existing 2D image quality assessment metrics are found to be insufficient for 3D view quality estimation because the 3D views not only contain color information but also make use of disparity to achieve the real depth sensation. In this paper, we present a new algorithm for evaluating the quality of DIBR generated images in the absence of the original references. The human visual system is sensitive to structural information; any deg radation in structure or edges affects the visual quality of the image and is easily noticeable for humans. In the proposed metric, we estimate the quality of the synthesized view by capturing the structural and textural distortion in the warped view. The structural and textural information from the input and the synthesized images is estimated and used to calculate the image quality. The performance of the proposed quality metric is evaluated on the IRCCyN IVC DIBR images dataset. Experimental evaluations show that the proposed metric outperforms the existing 2D and 3D image quality metrics by achieving a high correlation with the subjective ratings.

     

Ambiguity and structural properties of basic sequence diagrams

Sequence Diagrams (SDs) are one of the most popular elements of the UML notation to model the dynamics of systems. However, the graphical representation of basic SDs suffers from an inherent ambiguity that has led to different definitions in UML 1.x and in UML 2.0. This ambiguity paves the way for the consideration of several semantics for basic SDs. The paper studies four of these semantics and shows to what extent their differences for a given SD (that is the amount of ambiguity of this diagram) comes from its structural properties (linearity, local control and local causality). The fulfilment of these properties can serve as a measure of the ambiguity of a SD, and thus the attention to be paid at its validation.