Layer Systems on the Base of Nitrogen-Doped Tantalum and Niobium with Enhanced Stability

There are presented the results of the investigation of tantalum- and niobium-based metal-oxide bilayers degration in dependence on chemical composition of base metal. Nitrogen dissolved in metal increases stability of chemical composition and electrical properties of oxide films grown on the metal surface by anodic oxidation. This improves reliability and life time of electronic devices containing tantalum- or niobium-based layer systems. The best positive effect of doping tantalum and niobium by nitrogen was achieved after preliminary refining of these metals from oxygen. When nitrogen concentration in the base metal essentialy exceeds its solubility limit at room temperature and nitride phases are formed the dielectrical properties of oxide film get worsen.     

Vibrational studies of metal cation reduction at oxide glass surfaces

Reduction of metal oxide metaphosphate glasses (M₂O · P₂O₅, or MO · P₂O₅, where M is a metal cation) is observed above ca. 100°C when the glass is treated with one several gaseous reducing agents such as H₂, atomic hydrogen, Hg or K. Such amorphous systems are characterized by rapid cation diffusion, with cation reduction occurring principally at the glass surface, which leads to metal cluster formation and eventual continuous metal film growth. Structural changes induced in the glass by cation migration and subsequent reduction are studied by transmission infrared spectroscopy on thin-film samples during the reaction. Scanning electron microscopy and Raman spectroscopy are also employed to study and characterize the glass surfaces. The effect of water vapor on increasing the reaction rate for the mercuric metaphosphate/hydrogen reaction is demonstrated by continuous measurements of vibrational intensity changes. Surface-adsorbed water is seen to reduce the reaction induction period with little effect on the subsequent reaction rate. These results suggest that the rate-determining step of metal ion reduction at glass surface is a diffusion-limited process.     

直接碳燃料电池燃料的研究进展

直接碳燃料电池(DCFC)是一种清洁高效利用碳资源发电的装置。其因能量转换率高,对环境污染小,燃料选择范围广等优点获得了越来越多的关注。DCFC的性能与使用的燃料密切相关,为了探究燃料对DCFC的影响,本文分别阐述了石墨、炭黑、中密度纤维板、生物质、煤、活性炭的特性及改性方法,分析讨论了燃料表面含氧官能团以及燃料中的金属催化剂对阳极电化学反应的促进作用,发现燃料表面化学性质要比比表面积更加重要。同时,本文也提出了对生物质这一优良的可再生资源的期待,为未来DCFC燃料的发展提供参考。     

6H-SiC衬底片的表面处理

相比于蓝宝石,6H-SiC是制作GaN高功率器件更有前途的衬底.本文研究了表面处理如研磨、化学机械抛光对6H-SiC衬底表面特性的影响.用显微镜、原子力显微镜、拉曼光谱、卢瑟福背散射谱表征了衬底表面.结果表明经过两步化学机械抛光后提高了表面质量.经第二步化学机械抛光后的衬底具有优异的表面形貌、高透射率和极小的损伤层,其表面粗糙度RMS是0.12nm.在该衬底上用MOCVD方法长出了高质量的GaN外延膜.     

Nanostructured materials obtained under conditions of hierarchical self-assembly and modified by derivative forms of fullerenes

Gas-sensitive nanocomposites, based on silicon dioxide–metal oxide systems, were obtained via self-assembly using the sol–gel method. Surface morphology diagnostics of nanomaterials, synthesized from sol solutions in a precursor medium based on tetraethoxysilane, were made using atomic force microscopy. The main evolution stages of nanocomposites based on two-component systems were determined. Specific surface area measurements of nanocomposites were made using a Sorbi analytical instrument by the thermal desorption method. A method for increasing the specific surface area and gas-sensitivity of nanomaterials by modifying them using fullerenols is suggested.     

Phenylacetylene half-hydrogenation with Pd supported on vitreous materials having different chemical compositions

Pd metal has been supported on vitreous materials prepared by the gel route. Three supports with different chemical compositions of the SiO₂, Al₂O₃ and Na₂O systems were prepared; the corresponding catalysts, performed with very similar degrees of metal dispersion and Pd loading, have been used in the half-hydrogenation of phenylacetylene at different H₂ pressures. The results display an analogous behaviour with modest changes of the catalytic properties on changing the chemical composition of the support. The relatively better catalytic activity of the catalyst with smaller alkaline content is discussed in terms of the possible electronic shift from the metal to the support.     

Atomic layer deposition of high-k dielectrics on III–V semiconductor surfaces

The goal of this article is to provide an overview of the state of knowledge regarding the Atomic Layer Deposition (ALD) of metal oxides on III–V semiconductor surfaces. An introduction to ALD, the band structure, various defects present on the III–V surface and how they relate to Fermi level pinning are discussed. Surface passivation approaches are examined in detail in conjunction with experimental and computational results. The “interface clean-up” reaction that leads to the formation of a sharp gate oxide/semiconductor interface is related to the surface chemistry and the transport of the surface oxides through the growing dielectric film. Finally, the deposition of metal oxides on semiconductors is discussed in the context of interface quality and some examples of devices using III–V channels and ALD metal oxides are given.     

Sol → gel → glass: I. Gelation and gel structure

The mechanisms of gel formation in silicate systems derived from metal alkoxides were reviewed. There is compelling experimental evidence proving, that under many conditions employed in silica gel preparation, the resulting polysilicate species formed prior to gelation is not a dense colloidal particle of anhydrous silica but instead a solvated polymeric chain or cluster. The skeletal gel phase which results during desiccation is, therefore, expected to be less highly crosslinked than the corresponding melted glass, and perhaps to contain additional excess free volume. It is proposed that, during gel densification, the desiccated gel will change to become more highly crosslinked while reducing its surface area and free volume. Thus, it is necessary to consider both the macroscopic physical structure and the local chemical structure of gels in order to explain the gel to glass conversion.     

Recent developments and progress on electrical contacts to CdTe, CdS and ZnSe with special reference to BARRIER contacts to CdTe

A summary of experimental work on electrical contacts to CdTe, CdS and ZnSe is presented and recent progress of research on electrical contacts to these materials is reviewed in this paper. The surface preparation and surface characterisation prior to metallisation, interactions at the interface during contact fabrication, Schottky barrier characterisation and subsequent aging effects are considered. XPS, AES, SIMS and PL are used for surface characterisation; XPS and soft-XPS are used for interface interaction studies; I-V, C-V, DLTS and BEEM are used for Schottky barrier characterisation; and AES, GDOES and EDX profiling are used to study aging effects. The surfaces of all three materials behave in a similar way when etched in wet chemical etchants. The semiconductor cation is preferentially etched by acidic solutions and the semiconductor anion is preferentially removed by alkaline solutions. It has also been shown that the surface stoichiometry affects the Fermi level pinning position at metal/semiconductor interfaces. Furthermore, the observed Schottky barrier heights with all three materials demonstrate a multi-level pinning behaviour producing different barrier heights depending on the history of the materials used and the fabrication procedure followed. Barrier heights observed are independent of the metal work function, and their stability depends mainly on interactions occurring at the metal/semiconductor interface and are strongly related to the native defect levels within the bulk material.     

Three-dimensionality of space in the structure of the periodic table of chemical elements

The effect of the dimension of the 3D homogeneous and isotropic Euclidean space, and the electron spin on the self-organization of the electron systems of atoms of chemical elements is considered. It is shown that the finite dimension of space creates the possibility of periodicity in the structure of an electron cloud, while the value of the dimension determines the number of stable systems of electrons at different levels of the periodic table of chemical elements and some characteristics of the systems. The conditions for the stability of systems of electrons and the electron system of an atom as a whole are considered. On the basis of the results obtained, comparison with other hierarchical systems (nanostructures and biological structures) is performed.     

Rutherford backscattering investigation of the corrosion of borosilicate nuclear waste glass

The corrosion properties of several borosilicate nuclear waste glasses exposed to aqueous environments have been investigated using a combination of Rutherford backscattering (RBS) depth profiling and solution analysis. Using the technique of RBS, the concentration of individual elements in the glass can be quantitatively profiled within a 1–2 μm surface layer. All of the glass surfaces were corroded in distilled water at 90°C for times ranging from 0–28 days. The evolution and composition of the altered layer that formed on the glass surface was of particular interest, since this layer can be crucial in determining whether or not the remainder of the glass undergoes further rapid corrosion. Within the altered surface layer produced by the corrosion process, there was an enhancement in the concentrations of U, Ti, Sr, Nd, Gd, and Ca and a depletion of Na, Si, Cs, (and probably B) relative to the concentrations present in the bulk glass. The U concentration, for example, was often 3–4 times greater in the altered surface layer than in the bulk. The layer apparently forms due to a local reaction that results in the formation of insoluble complexes on the glass surface. A simple model of the corrosion process has been used to identify the most likely insoluble metal complex for each metal present in excess in the alteration layer. The mechanical and chemical stability of this layer are also discussed.     

Material characteristics of metalorganic chemical vapor deposition of Bi2Te3 films on GaAs substrates

Metal organic chemical vapor deposition has been investigated for growth of Bi₂Te₃ films on (0 0 1) GaAs substrates using trimethylbismuth and diisopropyltelluride as metal organic sources. The results of surface morphology, electrical and thermoelectric properties as a function of growth parameters are given. The surface morphologies of Bi₂Te₃ films were strongly dependent on the deposition temperatures. Surface morphologies varied from step-flow growth mode to island coalescence structures depending on deposition temperature. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's ratio of VI/V and deposition temperature. By optimizing growth parameters, we could clearly observe an electrically intrinsic region of the carrier concentration at the temperature higher than 240 K. The high Seebeck coefficient (of −160 μVK⁻¹) and good surface morphology of this material is promising for Bi₂Te₃-based thermoelectric thin film and two-dimensional supperlattice device applications.     

Investigation of surface treatment effect of catalyst on the lifetime for Cat-CVD method

In case of amorphous silicon (a-Si) film deposition by catalytic chemical vapor deposition (Cat-CVD) method, a metal catalyzing wire is converted to silicide and this silicidation causes shortening lifetime of the catalyzing wire. In the present work, the effect of surface carbonization of catalyzing wire against silicide formation is investigated to obtain long-life catalyzer. Characteristics of a-Si film deposited by carbonized tungsten (W) catalyzer are also investigated. Silicide layer thickness formed on carbonized catalyzing wires after 60 min a-Si film deposition decreases to half of that on uncarbonized wires. Device quality a-Si films having defect density less than 4 × 10¹⁵ cm^?3 are obtained by using carbonized W, indicating that surface carbonization of W catalyzer is effective process for industrial application of Cat-CVD method.     

InGaN/GaN微米阵列结构的生长及发光性能研究

采用金属有机化学气相外延技术,在图形化蓝宝石衬底上通过选区外延可控生长了三种不同形貌的InGaN/GaN微米阵列结构,阵列尺寸均为6μm.其中,六方片状阵列结构以(0001)c面为主,高度为0.6μm;六棱台状阵列结构包括一个(0001)c面和六个等效的(10-11)半极性面,高度为1.2μm;六棱锥状阵列结构以(10...     

离子轰击增强金刚石膜与Si衬底结合力的进一步研究

由于金刚石与Si有较大的表面能差,利用化学气相沉积(CVD)制备金刚石膜时,金刚石在镜面光滑的Si表面上成核困难,而负衬底偏压能够增强金刚石在镜面光滑Si表面上的成核,表明金刚石核与Si表面的结合力也得到增强.本文分析衬底负偏压引起的离子轰击对Si表面产生的影响之后,基于离子轰击使得Si衬底表面产生了微缺陷(凹坑)增大了金刚石膜与Si衬底结合的面积,理论研究了离子轰击对金刚石膜与Si衬底结合力的影响.     

化学气相沉积法制备CNOs及其磁选纯化研究

以金属镍铁为催化剂,通过化学气相沉积法高选择性地制备了纳米洋葱碳( CNOs)。所制备的CNOs为内嵌金属核心与中空CNOs的混合物,常规的酸洗-煅烧纯化工艺往往会造成外层碳壳的破坏,形成无定型碳。通过对CNOs的铁磁性分析,提出了磁选分离工艺,可以有效地将内嵌金属的CNOs与空心CNOs分离,分离后空心CNOs纯度在95;以上。     

Compaction of adsorbed alkali metal submonolayers on the {111} and {0001} surfaces of metal crystals

The structural mechanism has been suggested of formation of the ordered surface hexagonal structures with an increase of the coverage during adsorption of alkali metal atoms on the {111} surfaces of face-centered cubic and {0001} surfaces of a hexagonal metal crystal. The coverage θ_s providing the formation of close-packed hexagonal adsorbed layers in adsorption systems is determined for alkali metals. The theoretically calculated and the experimentally obtained θ_s values are in good agreement.     

Nanostructure formation on metal-chalcogenide surface using electron beam irradiation

In this letter, we demonstrate a method to form a nano-structured pattern on metal-chalcogenide sandwich like structures, using electron beam (EB) irradiation. After pointing EB at surface, we observed nano-dots and nano-lines formation on metal-chalcogenide (AgS, AgSe, CuS, CuSe) surface, considerably made of Ag or Cu, depending on metal in compound (Ag or Cu). This technique is based on the solid-state electrochemical reaction between EB and surface. Our results demonstrate repeatable metal structures with dimension of nanometers. As this process is carried out with scanning electron microscope (SEM) and does not require wet chemicals, it has potential for use as a simple metal patterning technique to fabricate functional structures and devices.     

Studies of vapour transport reactions for III–V compounds

Although the III-V compounds and their alloys are increasingly important in the ever widening range of electronic and electro- optic devices, fundamental thermodynamic and chemical kinetic data for the chemical transport reactions used for their preparation is sparse, with few exceptions. The modified entrainment method developed by Faktor, Garrett and co-workers can be used to study chemical transport reactions and to obtain thermodynamic and chemical kinetic data. The direct analogy between the results of these experiments and corresponding crystal growth experiments is emphasised. Results from the systems GaAs-HCl, GaAs-HBr, AlAs-HBr, InSb-HCl, GaP-HBr, and InAs-HCl are discussed and used to illustrate the effects of competing transport reactions and the interplay between gas transport and surface reaction kinetics. Some of the pitfalls in simplistic calculations relating crystal growth rates to thermodynamic data are pointed out.     

Chemical Principles of Designing Organometallic Ferromagnets

The idea of designing ferromagnets chemically boils down to uniting paramagnetic atoms by means of a chemical reaction and “turning on” positive exchange interaction between them, which aligns the atoms'electron spins into ferromagnetic order. This general idea can be tested using organometallic polymers with metal paramagnetic atoms in the polymer chain. The metal atoms are isolated by organic fragments and are not bound by exchange interaction. Two ways can be used to turn on the exchange. The first is to remove the isolating fragments between the metal atoms or to replace them by electron-conductive fragments which allow the exchange interaction. The second is to build new molecular bridges able to turn it on.