György Radnóczi

Bio: György Radnóczi is an academic researcher from Hungarian Academy of Sciences. The author has contributed to research in topics: Thin film & Amorphous solid. The author has an hindex of 24, co-authored 131 publications receiving 2278 citations.

Al induced crystallization of a‐Si

Abstract: The crystallization of amorphous Si induced by Al during heat treatment has been investigated by cross section and plan view transmission electron microscopy. The lowest temperature of Al induced crystallization of amorphous Si was found to be 440 K. The crystallization temperature, however, depends on the thickness of Al layers in layered structures and on the concentration of Al in co‐deposited layers below 1‐nm‐layer thickness and 15 at.% of Al concentration, respectively. Al‐induced crystallization in layered structures starts at the Al/amorphous Si interfaces and is located close to them. The amount of crystallized Si depends on the quantity of Al and on the temperature and increases with them. The mechanism of crystallization involves intermixing of Al with Si and the formation of an alloy of high metal concentration in the amorphous/crystalline interface. When the formation of this alloy is not assured due to low Al concentration, then crystallization does not start or the process of crystallization stops. In Al induced crystallization the nucleation of polycrystalline Si grains rather than their crystal growth is affected.

Oriented crystal growth model explains the formation of titania nanotubes.

Abstract: We discuss the formation mechanism of titania nanotubes synthesized by the hydrothermal method. On the basis of a comprehensive analysis of TEM, HRTEM, FT-Raman, and N(2) adsorption data, we point out some major shortcomings of the currently accepted trititanate sheet rollup mechanism. We suggest that a novel formation mechanism, oriented nanotube crystal growth from nanoloop seeds, can explain the experimental findings better than the ones proposed so far.

Nickel based ohmic contacts on SiC

Abstract: We have compared the chemical and structural properties of Ni/SiC and Ni2Si/SiC interfaces. In the case of Ni/SiC, the contact formation is initiated by the dissociation of SiC, due to the strong reactivity of nickel at 950 °C. Ni2Si is formed and carbon accumulates, both at the interface and throughout the metal layer. At the interface, many Kirkendall voids are observed by TEM. Despite this poor interface morphology, low contact resistances have been measured. But the presence of carbon in the contact layer and at the interface is a potential source of contact degradation at high temperature. In the case of Ni/Si multilayers evaporated on SiC instead of pure Ni, the contact formation is preceded by Ni and Si mutual diffusion in the deposited layer yielding Ni2Si. Therefore, a smaller amount of carbon is released from SiC. Low carbon segregation, abrupt interface and low contact resistance characterize this contact. The thermal stability of Ni2Si contacts is illustrated with ageing experiments carried out at 500 °C.

Ultra-Thin Aluminium Oxide Films Deposited by Plasma-Enhanced Atomic Layer Deposition for Corrosion Protection

Abstract: We have employed plasma-enhanced and thermal atomic layer deposition (ALD) within the temperature range of 50-150°C for the deposition of ultra-thin (10-50 nm) Al 2 O 3 films on 100Cr6 steel and aluminium Al2024-T3 alloys. [Al(CH 2 ) 3 ] was used as the precursor with either an O 2 plasma or water as co-reactants. Neutral salt spray tests showed that the thicker films offered the best corrosion-resistance. Using cyclic voltametry, the 50 nm films were found to be the least porous (<0.5%). For 10 nm thick films, plasma-enhanced ALD afforded a lower porosity and higher film density than thermal ALD. ToF-SIMS measurements on 100Cr6 showed that the main 'bulk' of the films contained very few impurities, but OH and C were observed at the interfaces. TEM confirmed that the films were conformal on all substrates and the adhesion was excellent for the films deposited by plasma-enhanced ALD but not for thermal ALD, as delamination was observed. On the basis of these and other results, the prospects of the application of ALD films for corrosion protection, and the use of plasma-enhanced ALD to promote their nucleation, is discussed.

Mechanical properties of thin films

Abstract: The mechanical properties of thin films on substrates are described and studied. It is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur. It is argued that the approaches that have proven useful in the study of bulk structural materials can be used to understand the mechanical behavior of thin film materials. Understanding the mechanical properties of thin films on substrates requires an understanding of the stresses in thin film structures as well as a knowledge of the mechanisms by which thin films deform. The fundamentals of these processes are reviewed. For a crystalline film on a nondeformable substrate, a key problem involves the movement of dislocations in the film. An analysis of this problem provides insight into both the formation of misfit dislocations in epitaxial thin films and the high strengths of thin metal films on substrates. It is demonstrated that the kinetics of dislocation motion at high temperatures are expecially important to the understanding of the formation of misfit dislocations in heteroepitaxial structures. The experimental study of mechanical properties of thin films requires the development and use of nontraditional mechanical testing techniques. Some of the techniques that have been developed recently are described. The measurement of substrate curvature by laser scanning is shown to be an effective way of measuring the biaxial stresses in thin films and studying the biaxial deformation properties at elevated temperatures. Submicron indentation testing techniques, which make use of the Nanoindenter, are also reviewed. The mechanical properties that can be studied using this instrument are described, including hardness, elastic modulus, and time-dependent deformation properties. Finally, a new testing technique involving the deflection of microbeam samples of thin film materials made by integrated circuit manufacturing methods is described. It is shown that both elastic and plastic properties of thin film materials can be measured using this technique.

Past achievements and future challenges in the development of optically transparent electrodes

Abstract: Increasing demand for raw materials means that alternatives to indium-tin oxide are desired for optically transparent electrode applications. Carbon nanotube, metal nanowire networks and regular metal grids have been investigated as possible options. In this review, these materials and recently rediscovered graphene are compared with the usual transparent conductive oxides.

Protonated Titanates and TiO2 Nanostructured Materials: Synthesis, Properties, and Applications

Abstract: Tubular and fibrous nanostructures of titanates have recently been synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed. The crystal structures, morphologies, and mechanism of formation of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar-cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.

Microstructural evolution during film growth

Abstract: Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.

Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and Beyond

Abstract: Spinels with the formula of AB2O4 (where A and B are metal ions) and the properties of magnetism, optics, electricity, and catalysis have taken significant roles in applications of data storage, biotechnology, electronics, laser, sensor, conversion reaction, and energy storage/conversion, which largely depend on their precise structures and compositions. In this review, various spinels with controlled preparations and their applications in oxygen reduction/evolution reaction (ORR/OER) and beyond are summarized. First, the composition and structure of spinels are introduced. Then, recent advances in the preparation of spinels with solid-, solution-, and vapor-phase methods are summarized, and new methods are particularly highlighted. The physicochemical characteristics of spinels such as their compositions, structures, morphologies, defects, and substrates have been rationally regulated through various approaches. This regulation can yield spinels with improved ORR/OER catalytic activities, which can furth...