The surface science of titanium dioxide

Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This article reviews the various surface modification technologies pertaining to titanium and titanium alloys including mechanical treatment, thermal spraying, sol–gel, chemical and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively using the appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. The proper surface treatment expands the use of titanium and titanium alloys in the biomedical fields. Some of the recent applications are also discussed in this paper.

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Surface modification of titanium, titanium alloys, and related materials for biomedical applications

During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science—promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008

Ab-initio simulations of materials using VASP: Density-functional theory and beyond.

Journal of Physics Condensed Matter: Preface

The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts.

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Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals

By means of a density functional theory approach, materials properties of $\mathrm{V}\mathrm{N}[001](100)\ensuremath{\parallel}\mathrm{Ti}\mathrm{N}[001](100)$ multilayers are studied focusing on the elastic and mechanical properties of the interface For the isolated bulk phases of TiN and VN, elastic constants and moduli are derived in order to analyze the matching conditions at the interface Modeling of the mechanical properties was done in terms of brittle cleavage by calculating cleavage energies and critical stresses for the bulk phases as well as for the multilayer system The interface energy of $\ensuremath{-}0054\phantom{\rule{03em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ was derived for the lateral lattice parameter of MgO(100) according to the multilayer growth on this substrate For this case, also atomic interlayer distances and critical stresses are determined and a Poisson ratio of the VN[001] and TiN[001] was evaluated The values of $\ensuremath{\nu}=0279$ and $\ensuremath{\nu}=0235$, respectively, agree very well with the available experimental data The strain energy and the interfacial cleavage properties of the multilayer are calculated as a function of the lateral lattice parameter illustrating growth conditions on different substrates The cleavage energy at the interface considerably changes with respect to the lateral lattice parameter, but the critical stress of $\ensuremath{\approx}27\phantom{\rule{03em}{0ex}}\mathrm{GPa}$ remains rather unchanged The relaxation of atoms following an epitaxial strain of VN layers transforms VN into the structure with tetragonal-like stacking This fact is an indication that stoichiometric VN is metastable against tetragonal distortion

Density functional theory applied to VN∕TiN multilayers

Vacancy induced changes in the electronic structure of titanium carbide—I. Band structure and density of states

Starting from KKR-CPA and KKR-GF densities of states and cross-sections within the single-scatterer final-state approximation, X-ray photoemission intensities were calculated for a series of stoichiometric and substoichiometric transition metal carbides and nitrides. For all compounds nonmetal vacancies give rise to an additional peak in the XPS spectra. The theoretical results are compared to several experimental XPS measurements. In most cases very good agreement is found. The discrepancies between theory and experiment are discussed in detail.

Vacancy-induced changes in the electronic structure of transition metal carbides and nitrides: Calculation of X-ray photoemission intensities

We investigate the effect of transition metal (TM) substitution in cuprous oxide ${\mathrm{Cu}}_{2}\mathrm{O}$ on the basis of ab initio calculations employing density-functional theory $(\mathrm{GGA}+\mathrm{U})$. By using the supercell approach, we study the effect of substituting Cu by Mn, Fe, Co, and Ni, assuming both low TM concentrations (3.2%) in a cubic geometry and higher TM concentrations (9.1%) in a trigonal setup. For the elements Mn and Co, magnetic exchange constants up to the fifth nearest neighbor are calculated, assuming both cases, perfect $\mathrm{Mn}∕\mathrm{Co}:{\mathrm{Cu}}_{2}\mathrm{O}$ as well as defects in the host such as single copper and oxygen vacancies. Our results clearly show the importance of defects in these materials and thus offer an explanation for various, seemingly opposed, experimental results.

Electronic and magnetic structure of cuprous oxide Cu 2 O doped with Mn, Fe, Co, and Ni: A density-functional theory study

Scanning tunneling spectroscopy permits real-space observation of one-dimensional electronic states on a Fe(100) surface alloyed with Si. These states are localized along chains of Fe atoms in domain boundaries of the Fe(100) cs2 3 2dSi surface alloy, as confirmed by first-principles spinpolarized calculations. The calculated charge densities illustrate the d-like orbital character of the one-dimensional state and show its relationship to a two-dimensional state existing on the pure Fe(100) surface. [S0031-9007(96)00335-3]

J. Redinger

Papers

Density functional theory applied to VN∕TiN multilayers

Vacancy induced changes in the electronic structure of titanium carbide—I. Band structure and density of states

Vacancy-induced changes in the electronic structure of transition metal carbides and nitrides: Calculation of X-ray photoemission intensities

Electronic and magnetic structure of cuprous oxide Cu 2 O doped with Mn, Fe, Co, and Ni: A density-functional theory study

Scanning tunneling spectroscopy of one-dimensional surface states on a metal surface.