Materials physics and mechanics

RAR RUS 61-66 Naval Research Laboratory Rath B.B.

USA

Naval Research Laboratory Imam M.A.

USA

Naval Research Laboratory Pande C.S.

USA

Nucleation and Growth of Twin Interfaces in FCC Metals and Alloys Presence of coherent interfaces within crystallites, referred to as «annealing twins,» has many effects on the properties of several fcc metals and alloys. The mechanism of the formation of these twins have been subject of numerous studies over fifty years. Although much progress has been made in recent years, a universally accepted view on the formation of these twins has not yet emerged. This brief review will describe recent studies at Naval Research Laboratory to understand several aspects of the annealing twins including nature of these twins, the mechanism of their formation, and the compositional parameters which affect their densities. These studies have established a relation between twin density and grain size, temperature and material properties. A model of the mechanism of their formation based on the emergence of Shockley partial loops on consecutive {111} planes during grain migration has also been developed. It is argued that various experimental and theoretical results obtained over the years can be consistently and satisfactorily explained by this model. This study has analyzed two aspects of annealing twins in details viz, a) role of boron additions in reducing twin density in nickel and b) the effect of annealing twins in HallPetch relation. Twin Interfaces; FCC Metals and Alloys https://mpm.spbstu.ru/article/2000.2.1/ 2000_1_2_p1.pdf

RAR RUS 67-65 National University of Singapore Chow G.M.

Singapore

National University of Singapore Kent Ridge Li Y.Y.

Singapore

Institute of Physics, Academia Sinica Hwu Y.K.

Taiwan

Mechanical and Magnetic Properties of Polyol Electrodeposited NiCo Films The effects of applied voltage on the magnetic and mechanical properties of polyol electrodeposited NiCo films were studied and reported. Both electroless and electrolytic processes competed with each other during deposition. There existed a clear influence of voltage on the composition and magnetic properties of deposited films. However, a simple, systematic correlation of these properties with the structure, composition and microstructure could not be made. This lack of correlation was attributed to the complex variation of deposition chemistry with deposition time and voltage. It is conceivable that thick films deposited using long reaction time may have through-thickness inhomogeneity, thus obscuring the correlation of properties with the volume-averaged film characteristics. Polyol Electrodeposited NiCo Films; Mechanical Properties; Magnetic Properties https://mpm.spbstu.ru/article/2000.2.2/ 2000_1_2_p2.pdf

RAR RUS 73-82 Utrecht University Schropp R.E.I.

Utrecht, The Netherlands

Utrecht University Stannowski B.

Utrecht, The Netherlands

Utrecht University Brockhoff A.M.

Utrecht, The Netherlands

Utrecht University van Veenendaal P.A.T.T.

Utrecht, The Netherlands

Utrecht University Rath J.K.

Utrecht, The Netherlands

Hot Wire CVD of Heterogeneous and Polycrystalline Silicon Semiconducting Thin Films for Applications in Thin Film Transistors and Solar Cells Using Hot Wire Chemical Vapor Deposition (HWCVD), also known as thermocatalytic decomposition, heterogeneous silicon thin films can be obtained with a widely varying degree of order and crystallinity. Specific parameter regimes have been identified which allow the deposition of films with a structure ranging from purely amorphous to fully polycrystalline. In polycrystalline Si, all hydrogen appears in isolated, compact monohydride bonds. A comparison of XTEM and Raman studies confirmed that the 2000 cm-1 infrared mode indeed originates from a completely crystalline region and that there is no amorphous tissue in these films. The 2000 cm-1 vibration is due to Si-H bonds at completely coalescent crystal faces (between adjacent crystals). In films with this type of crystallinity, oxygen incorporation is greatly reduced, both during growth and after completion. The heterogeneous growth has been utilized in two types of devices, thin film transistors (TFTs) and thin film solar cells. TFTs have been made exhibiting excellent stability. The field-effect channel of these transistors consists of amorphous silicon hosting nanocrystalline domains which yields TFTs with a high mobility of 1.5 cm2 V-1s-1, virtually without the usual threshold voltage instabilities. Solar cells with an intrinsic poly-Si absorber layer have also been further optimized by deliberately profiling the active layer. A stepwise profiling sequence has been developed, starting from immediate-nucleation growth of small random crystallites to continued singly oriented growth of columnar polycrystalline material at a deposition rate of 5 Å/s. These n-i-p solar cells on stainless steel substrates presently have 4.41 % conversion efficiency. The short circuit current density is as high as 19.95 mA/cm2 while the light absorbing i-layer is only 1.2 µm thick and no enhanced back reflector is used. CVD; Silicon Semiconducting Thin Films; Thin Film Transistors; Solar Cells https://mpm.spbstu.ru/article/2000.2.3/ 2000_1_2_p3.pdf

RAR RUS 83-97 Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FO.R.T.H.) Kiriakidis G.

Heraklion, Greece

Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FO.R.T.H.) Katsarakis N.

Heraklion, Greece

IESL/FORTH Bender M.

Greece

IESL/FORTH Gagaoudakis E.

Greece

IESL/FORTH Cimalla V.

Greece

InOx Thin Films, Candidates for Novel Chemical and Optoelectronic Applications The potentials of InOx microcrystalline thin films for novel chemical and optoelectronic applications are investigated. In particular, these films are candidates for gas sensor applications due to their sensitivity to reactive gas environments such as ozone. This sensitivity is recorded as the result of the variation of the film conductivity level up to six orders of magnitude, which is attributed to the formation of oxygen vacancies. The microcrystalline nature of the films is investigated by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) while film surface characteristics are revealed by Atomic Force Microscopy (AFM). Depth profiling is examined by Auger Electron Spectroscopy (AES) while the stoichiometry of the films is determined by Energy Dispersive X-Ray analysis (EDX). Finally, the photorefractive properties of InOx films as well as their potential for the fabrication of optical gratings for novel telecom and waveguide applications are discussed. InOx Thin Films; Gas Sensor; Optoelectronic Devices https://mpm.spbstu.ru/article/2000.2.4/ 2000_1_2_p4.pdf

RAR RUS 98-102 Ufa State Aviation Technical University Zhilyaev Alexandr P.

Ufa, Russia

Superplasticity and microstructure evolution in nanonickel Although superplasticity has been studied for decades, few observations of this behavior have been reported for pure metals. A problem generally attributed to the difficulty of maintaining a grain size small enough for superplastic flow at the temperatures required for superplasticity. With the produce of nanocrystalline (NC) materials it has been hoped that superplasticity could be obtained in a number of pure metals due to the large volume fraction of grain boundaries in nanocrystalline material should enhance the tendency for superplastic behavior. Two methods of nanocrystalline materials producing (severe plastic deformation and elctrodeposition) allow making fully dense samples available for testing. In this paper, superplasticity was obtained from electrodeposited nickel with initially nanocrystalline structure at the lowest normalized superplastic temperature reported for any crystalline material. A maximum elongation of 895% was obtained at 0.4·TM. Although a mean grain size of ultrafine-grained (UFG) microstructure obtained by severe plastic deformation is comparable with grain size of NC nickel at the beginning of tensile test (about 0.5 µm), no superplastic behavior of UFG samples was detected. This controversy is discussed from viewpoint of non-homogeneity of microstructure in UFG pure nickel. Superplasticity;Nanonickel; Nanocrystalline Materials https://mpm.spbstu.ru/article/2000.2.5/ 2000_1_2_p5.pdf

RAR RUS 103-101 Institute of Problems of Mechanical Engineering RAS I.A. Ovid’ko И.А.

St.Petersburg, Russia

Institute of Problems of Mechanical Engineering, Russian Academy of Sciences Reizis A.B.

St.Petersburg, Russia

Naval Research Laboratory Masumura R.A.

USA

Effects of Transformations of Grain Boundary Defects on Diffusion in Nanocrystalline Materials The specific features of diffusion processes in nanocrystalline materials are discussed. Theoretical models are suggested that describe the effects of transformations (climbing, splitting) of grain boundary dislocations and disclinations on self-diffusion in nanocrystalline materials. It is shown that climbing of grain boundary dislocations strongly enhances diffusion processes in nanocrystalline materials, causing the self diffusion coefficient to be increased by several orders. Grain Boundary Defects; Nanocrystalline Materials https://mpm.spbstu.ru/article/2000.2.6/ 2000_1_2_p6.pdf

RAR RUS 111-118 P-4505-2016 7006034020 0000-0002-2973-8645 Institute of Problems of Mechanical Engineering RAS Kukushkin S.A. sergey,a.kukushkin@gmail.com

St.Petersburg, Russia

Institute of Problems of Mechanical Engineering RAS Grigoriev D.A.

St.Petersburg, Russia

On the Theory of Island Films Growth from Eutectic Melt at the Late Evolution Stage The theory of late-stage evolution of island films from the eutectic composition binary melt is developed. The complete system of equations describing the island film evolution on the substrate surface at the stage of Ostwald ripening is suggested. The asymptotic solution of that system of equations reveals a strong correlation in the evolution of the islands of different compositions at the Ostwald ripening stage which is associated with some specific features of eutectic systems. All main characteristics of island films at the late evolution stage such as islands size distribution function, critical sizes and density of the islands have been obtained. Relations between the individual agents constants causing predisposition of the eutectic system to one of the specific mechanisms of heat mass transfer have been found. The processes accompanying growth of the films from the eutectic composition melts in the presence of heat sink are discussed. Island Films Growth; The theory of late-stage evolution https://mpm.spbstu.ru/article/2000.2.7/ 2000_1_2_p7.pdf

RAR RUS 119-126 Institute of Electron Technology Misiuk Andrzej

Warsaw, Poland

High Pressure; High Temperature Treatment to Create Oxygen Nano-Clusters and Defects in Single Crystalline Silicon Effect of enhanced hydrostatic pressure (HP) on oxygen clustering in as-grown Czochralski silicon (Cz-Si) treated at up to 1000K – 1.6 GPa as well as on creation of defects in Cz-Si with SiOx precipitates, HP treated at 295K – 2 GPa and at 1580K – 1 GPa, has been investigated by infrared spectroscopy, electrical, photoluminescence and related structure – sensitive methods. Treatment of Cz-Si at 720–1000K resulted in enhanced generation of oxygen – containing nano-clusters exhibiting thermal donor activity while the HP treatment at 295K and 1580K – in creation of some additional defects (nonradiative recombination centres). Above effects are related to HP – induced creation of nucleation centres for oxygen clustering in initially “defect free” Cz-Si at 720–1000K and to generation of nano-defects at the SiOx /Si boundary in Cz-Si containing oxygen precipitates. Single Crystalline Silicon; Silicon https://mpm.spbstu.ru/article/2000.2.8/ 2000_1_2_p8.pdf

RAR RUS 127-132 Himeji Institute of Technology Yamasaki T.

Hyogo, Japan

High-Strength Nanocrystalline Ni-Alloys Produced by Electrodeposition Nanocrystalline Ni-W alloys having both high ductility and high strength were produced by electrodeoisition. The plating bath for the electrodeposition contained nickel sulfate, citric acid, sodium tungstate and ammonium chloride, and was operated at various bath concentrations and conditions of electrolysis. The ductility and tensile strength of the deposited alloys are strongly influenced by inclusion of codeposited hydrogen during deposition process. After degassing the hydrogen, the high-strength nanocrystalline Ni-W alloy containing about 20.7 at. % W with an average grain size of about 3 nm has been obtained: the tensile strength attained to about 2300 MPa. The high ductility of this alloy was also observed: bending through an angle of 180 degree was possible without breaking Nanocrystalline alloys; Ni-W Alloys; Electrodeposition https://mpm.spbstu.ru/article/2000.2.9/ 2000_1_2_p9.pdf

RAR RUS 133-139 Freiberg University of Mining and Technology Seefeldt M.

Freiberg, Germany

Catholic University of Leuven Van Houtte

Heverlee, Belgium

A Disclination-based Model for Anisotropic Substructure Development and its Impact on the Critical Resolved Shear Stresses The anisotropic mechanical response of f.c.c. metals deformed up to large strains at low homologous temperatures is controlled by interfaces, namely by fragment and grain boundaries. The proposed model starts from initial grain orientations and the corresponding slip rates as predicted by a full constraints (FC) Taylor code. It describes the cell structure development on the microscopic scale and the fragment structure development on the mesoscopic scale in terms of evolution equations for dislocation densities in the twelve f.c.c. slip systems and for disclination densities in six fragment boundary families, respectively. The redundant dislocation densities (or: the cell walls) and the immobile disclination densities and strengths (or: the fragment boundary triple junctions) are connected to critical resolved shear stress (CRSS) contributions. Thus, substructure and texture evolution as well as the resulting macroscopic mechanical behaviour are coupled to each other. Results for several initial grain orientations are presented and compared to experimental observations. Disclination; Critical Resolved Shear Stresses; FCC metals https://mpm.spbstu.ru/article/2000.2.10/ 2000_1_2_p10.pdf