[en] A simple model is presented that predicts the kinetics of tensile stress evolution during the deposition of thin films that grow by the Volmer--Weber mechanism. The generation of a tensile stress was attributed to the impingement and coalescence of growing islands, while concurrent stress relaxation was assumed to occur via a microstructure-dependent diffusive mechanism. To model the process of island coalescence, finite element methods were employed and yielded average tensile stresses more consistent with experimental observations than those predicted using previously reported analytical models. A computer simulation was developed that models the process of film growth as the continuous nucleation of isolated islands, which grow at a constant rate to impinge and coalesce to form a continuous polycrystalline film. By incorporating the finite element results for stress generation and a microstructure-dependent stress relaxation model, the simulation qualitatively reproduced the complex temperature-dependent trends observed from in situ measurements of stress evolution during the deposition of Ag thin films. The agreement includes simulation of the decreasing stress relaxation rate observed during deposition at increasing temperatures

[en] We report the first experimental observation of nonclassical morphological equilibration of a corrugated crystalline surface. Periodic rippled structures with wavelengths of 290-550 nm were made on Si(001) by sputter rippling and then annealed at 650-750 degree sign C . In contrast to the classical exponential decay with time, the ripple amplitude A_λ(t) followed an inverse linear decay, A_λ(t)=A_λ( 0)/(1+k_λt) , agreeing with a prediction of Ozdemir and Zangwill. We measure the activation energy for surface relaxation to be 1.6±0.2 eV , consistent with the fundamental energies of creation and migration on Si(001). (c) 2000 The American Physical Society

[en] We report the first experimental observation of non-classical morphological equilibration of a corrugated crystalline surface. Periodic rippled structures with wavelengths of 290-550 nm were made on Si(OO1) by sputter rippling and then annealed at 650 - 750 ampersand deg;C. In contrast to the classical exponential decay with time, the ripple amplitude, A_λ(t), followed an inverse linear decay, A_λ(t)= A_λ(0)/(1 +k_λt), agreeing with a prediction of Ozdemir and Zangwill. We measure the activation energy for surface relaxation to be 1.6 ampersand plusmn;0.2 eV, consistent with an interpretation that dimers mediate transport

[en] This document summarizes research of reactively deposited metal hydride thin films and their properties. Reactive deposition processes are of interest, because desired stoichiometric phases are created in a one-step process. In general, this allows for better control of film stress compared with two-step processes that react hydrogen with pre-deposited metal films. Films grown by reactive methods potentially have improved mechanical integrity, performance and aging characteristics. The two reactive deposition techniques described in this report are reactive sputter deposition and reactive deposition involving electron-beam evaporation. Erbium hydride thin films are the main focus of this work. ErH_x films are grown by ion beam sputtering erbium in the presence of hydrogen. Substrates include a Al₂O₃ {0001}, a Al₂O₃ {1120}, Si{001} having a native oxide, and polycrystalline molybdenum substrates. Scandium dideuteride films are also studied. ScD_x is grown by evaporating scandium in the presence of molecular deuterium. Substrates used for scandium deuteride growth include single crystal sapphire and molybdenum-alumina cermet. Ultra-high vacuum methods are employed in all experiments to ensure the growth of high purity films, because both erbium and scandium have a strong affinity for oxygen. Film microstructure, phase, composition and stress are evaluated using a number of thin film and surface analytical techniques. In particular, we present evidence for a new erbium hydride phase, cubic erbium trihydride. This phase develops in films having a large in-plane compressive stress independent of substrate material. Erbium hydride thin films form with a strong <111> out-of-plane texture on all substrate materials. A moderate in-plane texture is also found; this crystallographic alignment forms as a result of the substrate/target geometry and not epitaxy. Multi-beam optical sensors (MOSS) are used for in-situ analysis of erbium hydride and scandium hydride film stress. These instruments probe the evolution of film stress during all stages of deposition and cooldown. Erbium hydride thin film stress is investigated for different growth conditions including temperature and sputter gas, and properties such as thermal expansion coefficient are measured. The in-situ stress measurement technique is further developed to make it suitable for manufacturing systems. New features added to this technique include the ability to monitor multiple substrates during a single deposition and a rapidly switched, tiltable mirror that accounts for small differences in sample alignment on a platen

[en] The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the 〈110〉 direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.

[en] Depending on kinetic and thermodynamic factors, numerous interesting structures can be created starting from epitaxially grown Si Ge:Si(001). In a regime of relatively low growth temperatures (about 550 degree C), a cooperative nucleation process takes place: pyramidal pits are formed preferentially, followed by the nucleation of {105} elongated islands, leading to Quantum Dot Molecules (QDMs), where the islands can interact electronically with each other. A thorough understanding of the formation of these structures requires knowledge of their strain and compositional fields. Recently, Grazing Incidence Anomalous X ray Diffraction (GIXRD) has been used to understand these issues. The purpose of the measurements taken on the XD1 beam line of the LNLS was to investigate compositional inhomogeneities in QDMs, which helped to elucidate their mechanisms of formation. (author)

[en] In this paper, we report Lorentz Transmission Electron Microscopy (LTEM) observations of magnetic domain structures in a near-eutectoid ${\mathrm{Co}}_{40}{\mathrm{Pt}}_{60}$ alloy. The crystallographic microstructure is characterized using conventional bright field/dark field TEM imaging. The magnetic induction orientation inside magnetic domains is extracted from Fresnel through-focus images by reconstructing the phase of electron wave using the transport-of-intensity equation. The alloy shows a nano-chessboard pattern composed of the L1₀ tetragonal and L1₂ cubic phases. The magnetization distribution in four neighboring L1₀ tiles in the nano-chessboard structure is found to follow a vortex/anti-vortex configuration to reduce the magnetostatic and magneto-crystalline anisotropy energies. An unconventional domain wall referred to as an inter phase magnetic domain wall (IPMDW) is observed at the inter-phase boundaries of L1₀ and L1₂ phases. Magnetic domain walls in other microstructures (tweed microstructure, macro-twinned structure, coarsened L1₀ plates) are also documented.

[en] The time evolution of the amplitude of periodic nanoscale ripple patterns formed on Ar⁺ sputtered Si(001) surfaces was examined using a recently developed in situ spectroscopic technique. At sufficiently long times, we find that the amplitude does not continue to grow exponentially as predicted by the standard Bradley-Harper sputter rippling model. In accounting for this discrepancy, we rule out effects related to the concentration of mobile species, high surface curvature, surface energy anisotropy, and ion-surface interactions. We observe that for all wavelengths the amplitude ceases to grow when the width of the topmost terrace of the ripples is reduced to approximately 25 nm. This observation suggests that a short circuit relaxation mechanism limits amplitude growth. A strategy for influencing the ultimate ripple amplitude is discussed. (c) 2000 American Vacuum Society

[en] Amorphous Ge_1-xMn_x thin films have been prepared by co-depositing Ge and Mn on SiO₂/Si using an ultrahigh vacuum molecular beam epitaxy system. Across a range of growth temperatures and Mn concentrations (2.8 at. %, 10.9 at. %, and 21.3 at. %), we achieved enhanced magnetic and electrical properties with non-magnetic codopants dispersed in the films. Self-assembled Mn-rich amorphous nanostructures were observed in the amorphous Ge matrix, either as isolated nanoclusters or as nanocolumns, depending on Mn concentration. The ferromagnetic saturation moments were found to increase with Mn concentration and reached a maximum of 0.7 μ_B/Mn in the as-grown samples. Two magnetic transition temperatures around 15 K and 200 K were observed in these amorphous MBE-grown samples. Coercivity is considered within the context of local magnetic anisotropy. The anomalous Hall effect confirmed a strong correlation between the magnetization and transport properties, indicating that global ferromagnetic coupling was carrier-mediated rather than through direct exchange. In addition, negative magnetoresistance was detected from 5 K to room temperature.

[en] Highlights: • Eutectic/Eutectoid processing strategy to produce novel hierarchical microstructure. • Thermal conductivity of β-FeSi₂+Si nanocomposite can be reduced with a few at% Ge. • Local Ge incorporation into Si_1-xGe_x nanoinclusions can be controlled via processing. • Ge incorporation can reduce the β/Si_1-xGe_x thermal boundary conductance by 91%. • Local composition can supersede lengthscales, and may enhance thermal stability.