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We investigated the crystallinity, orientation, and stability of hydroxyapatite (HAp) thin films on structural materials including SiO 2 and metals (Ru, Ti, and Pt). The HAp films were deposited by electron cyclotron resonance (ECR) plasma sputtering with an Xe sputtering gas under simultaneous flow of H 2 O vapor. The HAp films as-crystallized during deposition and solid-phase crystallized by post annealing were analyzed with X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman scattering. The lowest solid-phase crystallization temperatures were 350 °C on Ru, 300 °C on Ti, and 300 °C on Pt. These crystallization temperatures are much lower than those on silicon and SiO 2 substrates (550 °C). For HAp films as-crystallized at temperatures above 400 °C, the elements out diffused and reacted with substrates. Precipitation of CaO was observed for HAp films deposited on SiO 2 and Ru substrates. Diffusion of PO 4 3 − into SiO 2 and Ru-catalyzed decomposition of HAp crystals are suggested for the mechanism. When deposited on Pt substrates, CaPt 2 O 4 alloy byproducts were created for solid-phase crystallized films and CaPt 2 alloy byproducts were created for as-crystallized films, indicating reaction of Ca atoms with Pt substrates. [ABSTRACT FROM AUTHOR]

Abstract: Li2O–Nb2O5 ternary compound thin films were deposited by dual sputtering from LiNbO3 and Li2O targets to cover a wide range of Li/Nb molar ratios. When all parts of the films were crystallized during sputtering at elevated temperatures, pyrochlore phase crystallites of Li3NbO4, LiNbO3, and LiNb3O8 were preferentially oriented toward their respective (222), (006), and ( ) directions. These closely packed crystallographic planes having the lowest surface free energies were initially created under exposure to the plasma and the crystallization that followed proceeded exclusively on these seed planes. The volume fraction of each crystalline component as a function of the Li/Nb molar ratio obeyed the established phase diagram. In contrast, solid-phase crystallization of pre-deposited amorphous films through post annealing exhibited a non-equilibrium nature, and the volume fraction of each crystalline component depended on the crystallization rate rather than the Li/Nb molar ratio. Solid-phase crystallization decelerated when excess Li2O was contained in the film. Specifically, LiNbO3 crystallites with near-stoichiometric compositions were randomly oriented without the operating mechanism of preferential orientation toward c-planes. In certain situations, crystalline domains were spatially of inhomogeneous composition, resulting in the simultaneous coexistence of Li3NbO4, LiNbO3, and LiNb3O8. [Copyright &y& Elsevier]

Abstract: Adding N2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO1−x N x having a face-centered cubic (fcc) structure to TiO2−x N x having an anatase structure. Titanium oxynitride films deposited on an Al2O3(0001) substrate were epitaxial with major orientations toward the (111) and (200) directions for fcc-TiO1−x N x and (112) for anatase-TiO2−x N x . Intermediately oxidized films between TiO1−x N x and TiO2−x N x were amorphous on the glass substrate but crystallized into a Magneli phase, Ti n O(N)2n−1, on the Al2O3(0001) substrate. Partially substituting oxygen in TiO2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO2−x N x films on Al2O3(0001) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiO x N y films vary continuously with changing N2 flow rate, their transparent conductive properties can be controlled more easily than TiO x . Nb5+ ions could be doped as donors in TiO2−x N x anatase crystals. [Copyright &y& Elsevier]

Abstract: Pt films directly deposited on SiO2 by electron-cyclotron-resonance (ECR) plasma sputtering and DC-magnetron sputtering have been compared in terms of their performance as electrodes. The DC-magnetron sputtered Pt film consisted of sharply (111) oriented crystallites, which was reflected in hexagonal crystallites observed in atomic force microscopy images. While ECR-sputtered Pt film was also (111) oriented, the X-ray diffraction rocking curve of the (111) peak was broader than that of the DC-magnetron sputtered film. The surface image revealed fine grains, thus having a flatter surface. A scratch test revealed that ECR-sputtered films had an adhesive strength about twice that of DC-magnetron-sputtered films, which was consistent with our tape-test results. Possible reasons for the different adhesion characteristics are discussed. [Copyright &y& Elsevier]

Abstract: The electrical and optical properties of undoped ZnO films deposited by electron cyclotron resonance (ECR) plasma sputtering at room temperature were characterized. The lowest resistivity we achieved was 2.6×10−3 Ωcm with optical transmittance at visible wavelengths higher than 85%. The X-ray diffraction (002) peak was weak and the rocking curve was asymmetrical, indicating that oxygen vacancies prevented large crystalline domains from forming. At low argon-sputtering-gas pressure, carrier concentration and Hall mobility increased with increasing argon pressure. When the optimum pressure (40 mPa) was exceeded, however, Hall mobility and optical transmittance were severely reduced, which indicated that excess Zn atoms were populated at the interstitials of the network. Admitting only 0.67 mPa of O2 gas during deposition deteriorated resistivity over 1 MΩcm due to high excitation efficiency in the ECR plasma. Deposition under a higher magnetic field produced lower resistivities. [Copyright &y& Elsevier]

Abstract: The crystallinity of LiNbO3 (LN) films sputtered from LN single crystal target was shown to be better than those from sintered target, confirming that the target quality is an important factor. In the particular case, Li2CO3 precipitated and crystallized to form a c-axis oriented overlayer on the surface of amorphous LiNbO3 film below 400 °C at an early stage of using an as-sintered target. This phenomenon reflects highly mobile nature of Li ions, resulting in phase-separation in the Li2O–Nb2O5 system under the plasma irradiation, which behavior represents Li-based electrolyte. [Copyright &y& Elsevier]

The crystallographic orientation of epitaxial LiNbO3 films on the Al2O3(1120) substrate can be controlled either toward the c-axis or a-axis depending on the situation at crystallization. Crystallization during high-rate sputter deposition at elevated temperatures produced c-axis-oriented film with 60°-rotated twin domains. Minimizing the surface energy when the growing surface was exposed to abundant ion flux selected (0001) terminated mosaic crystal. In contrast, solid-phase crystallization or as crystallization during a low-rate sputter deposition yielded a-axis-oriented film coexisting with 180° polarization twin domains. The enhanced migration of atoms in low-density amorphous film as well as pseudomorphic lattice matching growth under thermal equilibrated conditions led to the self-organization of relaxed crystalline domains. [ABSTRACT FROM AUTHOR]

Distinct channels for relaxing strain were identified in epitaxial LiNbO3 thin films depending on whether the film was crystallized during or after sputter-deposition on an Al2O3(0001) substrate. When LiNbO3 continuously crystallizes during deposition, pseudomorphic growth continues with a build up of strain as the thickness increases. The primary process for relieving strain is achieved by dividing the crystal into small mosaic grains. Crystallization by postannealing amorphous films, in contrast, produces nearly dislocation-free, relaxed crystals with a wider domain of 100–200 nm. Introducing lattice disorder at antiphase positions that correspond to matching between 12 lattice units of LiNbO3 and 13 lattice units of Al2O3 in the a-direction limits the chemical interaction with the Al2O3 lattice within a short range and efficiently accommodates misfit strain. This results in atomic-scale grapho-epitaxy sustaining disordered lattice regions at the interface. [ABSTRACT FROM AUTHOR]

Abstract: When the core electronic states of atoms in solids are excited by intense high-energy photons (hν>100 eV), a situation where the excited atoms are at energetically high levels while the surroundings are frozen is realized. Irradiation by a synchrotron radiation beam places a material in such a state, which leads to extensive movement of the constituent atoms. In the first half of this paper, results on how synchrotron radiation illumination causes the modification of several silicon-based materials, i.e., a-SiO2, a-Si3N4, a-SiN x :H, a-Si:H, and a-Si are described. A means for distinction between purely photolytic and thermally assisted mechanisms is presented. Factors affecting the consequence include chemical potentials in the network''s topological structure, ionicity of the chemical bonds, and types and numbers of vacancies contained in the network. In the second half, synchrotron radiation-excited epitaxy of short-period Si/Si1−x Ge x multiple quantum wells and Si n Ge m strained-layer superlattices is demonstrated. The atomically abrupt interfaces, similar to those obtained by solid-source molecular beam epitaxy, and the atomic-scale controllability of thickness are illustrated by real-time characterization of structural parameters through spectroscopic ellipsometry. [Copyright &y& Elsevier]