Rutile Surface Research Articles

Organic-Inorganic Nanohybrid Materials for Photovoltaic Applications

Thin film morphology is a key factor determining the performance of bulk heterojunction organic solar cells through its influence on charge separation, charge transport and recombination losses in donor-acceptor blends. With this respect, both descriptive and predictive modeling of structural properties of blends of PCBM or organic-inorganic hybrid perovskites of the type CH3NH3PbX3 (X=Cl, Br, I) with P3HT, P3BT or some squaraine SQ2 dye sensitizer, including adsorption on TiO2 clusters having rutile (110) surface, is presented with the use of a methodology that allows computing the microscopic structure of blends on the nanometer scale and getting insight on miscibility of its components at various thermodynamic conditions. The methodology is based on the integral equation theory of molecular liquids in the reference interaction site representation/model (RISM) and uses the universal force field. It is statistical mechanical theory to describe the equilibrium structure of molecular liquids in terms of the site-site pair correlation functions, from which all the thermodynamic quantities can be derived. It provides a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. Input parameters for RISM, such as optimized molecular geometries and charge distribution of interaction sites, are derived with the use of the density functional theory (DFT) methods. In particular, the environment effects were taken into account by Conductor-like Screening Model (COSMO) while the charges were obtained by fitting them to reproduce the molecular electrostatic potential (ESP). To compare the diffusivity of the PCBM in binary blends with P3HT and P3BT, respectively, the study is complemented with MD simulation. In addition, the analysis of MD trajectories allows us to better choose the initial positions of molecules in the follow-up DFT analysis which is focused on the study of electronic properties on the border of the perovskite-polymer or perovskite-macromolecule system. These properties define charge transfer processes from donor to acceptor and are utilized in development of new generation organic solar cells. For better understanding, the DFT analysis is also run to study the electronic structure of perovskite surfaces cleaved by (001) and (110) planes. To explore the dependence from the layer thickness we use slabs of different width formed by clusters of unit cells in a slab plain, while to characterize the dependence of electronic structure from layer width we refer to induced partial charges of surface sites (lead and halogens) as well as their electrophilic and nucleophilic Fukui indexes (local softness and hardness), which could be used as quantitative indications for chemical reactivity. As the result of this multiscale modeling approach that includes DFT, RISM, and MD, a remarkably good agreement with available experimental data and results of alternative modeling/simulation is observed for PCBM in P3HT system. We interpret this as a step in validation of the use of our approach for organic photovoltaics and support of its results for new systems that do not have reference data for comparison or calibration. In particular, for the less studied P3BT our results show that expectations about its performance in binary blends with PCBM may be overestimated, as it does not demonstrate the required level of miscibility and short-range structural organization. The RISM model is very sensitive to the blend composition, which happens to be in very good agreement with experimental observations. The inability to find physically meaningful solutions to RISM equations at certain solute concentrations is interpreted as an indicator of the existence of an unstable region on the composition-temperature phase diagram. In case of PCBM in P3BT, the physically meaningful solutions to RISM equations were found for the infinite dilution only, which suggests a much stronger tendency toward phase segregation in PCBM-P3BT blends. This suggestion was confirmed once again in MD simulations that we run (also with the universal force fields) to quickly estimate the diffusion coefficients of PCBM solute in P3HT or P3BT solvents at infinite dilution. Quantitatively, the diffusion coefficients of PCBM in P3HT fall into the range of the ones that are typical for high polymers, while the diffusion coefficients of PCBM in P3BT are closer to the ones that are found for diffusion in fluids. The performance of P3BT with perovskites, however, seems as expected. The calculated nanoscale morphologies of blends of P3HT, P3BT or SQ2 with perovskites, including adsorption on TiO2, are all new and serve as an instrument in rational design of organic/hybrid photovoltaics. They are used in collaboration with experts who actually make prototypes or devices for practical applications.

Monitoring dynamics of different processes on rutile TiO2(110) surface by following work function change

Time evolution of the work function (WF) change of TiO2 (110) rutile surface due to the oxygen adsorption and electron bombardment has been investigated. Oxygen adsorption has been performed on surfaces prepared in different ways (annealing temperature, in UHV or in oxygen atmosphere) which have different amounts of bridging oxygen vacancies (BOVs). The surfaces having low amount of BOVs were used in electron bombardment experiments. WF increases due to the O2 adsorption, and the overall change increases with the amount of BOVs. The result is consistent with the BOV healing by O2 adsorption. Oxygen adsorption results can be correlated with the shape of the Ti 2p photoelectron line: there is a linear dependence between the total WF change and the relative amount of the Ti3+ contribution in the Ti 2p3/2 line up to 0.2 eV when WF change reaches the saturation. Electron bombardment reduces WF due to the well known process of electron stimulated desorption of oxygen from bridging oxygen sites. The total change reaches about 0.5 eV, when the saturation is reached. It was shown that the efficiency for creating BOVs by electron bombardment increases with the electron energy.

THE STUDY OF NANOSTRUCTURED ANATASE COATINGS ON THE SURFACE OF RUTILE

Nanosized titanium dioxide allows solving complex engineering problems. One of such tasks is the creation of materials and coatings that reduce the likelihood of nosocomial infections on the surface of orthopedic structures including implant systems. The paper presents the results of the Raman spectroscopy, X-ray diffraction analysis and scanning electron microscopy of anatase ceramic coatings deposited by sol-gel technology on a sintered material based on a nanosized titanium dioxide powder (rutile modification). The resulting coating has a complex layered structure, which is almost completely represented by titanium dioxide in the anatase phase according to the Raman spectroscopy data. The simultaneous existence of both phases in the coating was recorded. The identification of rutile on diffractograms seems to be due to the fact that modified peak intensity rutile is mainly formed during the first stages of coating application on the polycrystalline rutile surface. The fact that non-stoichiometric phases also present in the diffractograms suggests that coating phase composition is not the same in thickness and is represented by a gradual layerwise transition from rutile to anatase. The coating thickness is 60 ± 15 μm. The coating is represented by lamellar blocks of various sizes. The thickness of a single plate in the coating is 60–80 nm. The developed technique makes it possible to apply the anatase coating not only on samples of titanium dioxide ceramics but also on the surface of titanium implants with the preliminary formation of a titanium dioxide layer in the form of rutile on the metal surface. Experiments on the study of antibacterial properties and morphological characteristics of bone tissue in contact with the implant were carried out at the Department of Prosthetic Dentistry at the PSMU.

Adhesion between a rutile surface and a polyimide: a coarse grained molecular dynamics study

Titanium, due to its high strength to weight ratio and polyimides, due to their excellent thermal stability are being increasingly used in aerospace applications. We investigate the bonding between a (110) rutile substrate and a popular commercial polyimide, PMR-15, starting from the known atomic structure of the rutile substrate and the architecture of the polymer. First, the long PMR-15 molecule is divided into four fragments and an all-atom non-bonded forcefield governing the interaction between PMR-15 and a rutile substrate is developed. To this end, parameters of Buckingham potential for interaction between each atom in the fragments and the rutile surface are fitted, so as to ensure that the sum of non-bonded and electrostatic interaction energy between the substrate and a large number of configurations of each fragment, calculated by the quantum mechanical route and obtained from the fitted potential, is closely matched. Further, two coarse grained models of PMR-15 are developed—one for interaction between two coarse grained PMR-15 molecules and another for that between a coarse grained PMR-15 and the rutile substrate. Molecular dynamics simulations with the coarse grained models yields a traction separation law—a very useful tool for conducting continuum level finite element simulations of rutile-PMR-15 joints—governing the normal separation of a PMR-15 block from a flat rutile substrate. Moreover, detailed information about the affinity of various fragments to the substrate are also obtained. In fact, though the separation energy between rutile and PMR-15 turns out to be rather low, our analysis—with merely the molecular architecture of the polyimide as the starting point—provides a scheme for in-silico prediction of adhesion energies for new polyimide formulations.

Combined effect of inherent residual chloride and bound water content and surface morphology on the intrinsic electron-transfer activity of ruthenium oxide

RuO2 is an unparalleled electrode with wider applications. Chloride, bound water, and surface stoichiometry are the inherent residues of RuO2 left upon the high-temperature pyrolysis of a RuCl3⋅xH2O precursor. Although the electrocatalytic properties of RuO2 for specific applications have been studied extensively, there is a paucity of studies linking the intrinsic electron-transfer (ET) activity of RuO2 with the oxide preparation temperature-dependent inherent residual parameters. This paper presents the intrinsic ET activity-oxide residue correlations for RuO2 electrodes. The ET kinetic parameters were estimated using a surface oxide-sensitive Fe3+/Fe2+ redox probe by rotating disc electrode voltammetry. Oxide powder-based electrodes (RuO2 powder-PVC/Pt-modified electrodes), which were fabricated conveniently at room temperature even with high-temperature oxides, were used instead of the traditional thermally prepared electrodes to circumvent the primary problems at the coating|support interface and inefficient chloride removal. RuO2 powders prepared at five temperatures (Tprep), i.e., 300, 400, 500, 600, and 700 °C, were used for electrode fabrication. The results showed that the electron exchange rate was highest for the 400 °C RuO2 electrode, and it was independent of the Tprep in the range 500 to 700 °C. The oxide powders were characterized using a range of techniques. The measured intrinsic ET activity and the associated structural correlation over the Tprep range 300–700 °C suggest that the best activity of the 400 °C electrode can be attributed to the optimal chloride and bound water contents in a completely formed rutile surface layer containing the catalyst sites of a particular nature with the highest electroactivity.

Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO2(110)

Photocatalytic nitrogen fixation provides a promising route to produce reactive nitrogen compounds at benign conditions. Titania has been reported as an active photocatalyst for reduction of dinitrogen to ammonia; however there is little fundamental understanding of how this process occurs. In this work the rutile (110) model surface is hypothesized to be the active site, and a computational model based on the Bayesian error estimation functional (BEEF-vdW) and computational hydrogen electrode is applied in order to analyze the expected dinitrogen coverage at the surface as well as the overpotentials for electrochemical reduction and oxidation. This is the first application of computational techniques to photocatalytic nitrogen fixation, and the results indicate that the thermodynamic limiting potential for nitrogen reduction on rutile (110) is considerably higher than the conduction band edge of rutile TiO2, even at oxygen vacancies and iron substitutions. This work provides strong evidence against the m...

Stability and charge separation of different CH3NH3SnI3/TiO2 interface: A first-principles study

Interface has an important effect on charge separation of perovskite solar cells. Using first-principles calculations, we studied several different interfaces between CH3NH3SnI3 and TiO2. The interfacial structure and electronic structure of these interfaces are thoroughly explored. We found that the SnI2/anatase (SnI2/A) system is more stable than the other three systems, because an anatase surface can make SnI bond faster restore to the pristine value than a rutile surface, and SnI2/A system has a smaller standard deviation. The calculated plane-averaged electrostatic potential and the density of states suggest that SnI2/anatase interface has a better separation of photo-generated electron-hole pairs.

Adsorption behavior and mechanism of Bi(III) ions on rutile–water interface in the presence of nonyl hydroxamic acid

Abstract The adsorption behavior and mechanism of Bi(III) ions on the rutile–water interface were investigated through micro-flotation, Zeta potential measurement, adsorption amount measurement and X-ray photoelectron spectroscopy (XPS). According to the results of micro-flotation, Bi(III) ions could largely improve the rutile flotation recovery (from 62% to 91%), and they could increase the activating sites and reduce the competitive adsorption between nonyl hydroxamic acid negative ions and OH− ions, which determined that Bi(III) ions were capable of activating rutile flotation. The adsorption of Bi(III) ions onto the rutile surface led to the shift of Zeta potential into the positive direction, which was good for the adsorption of nonyl hydroxamic acid anions. In addition, the results of XPS indicated that the chemical environment around Ti atom had not changed before and after the adsorption of Bi(III) ions. Based on the adsorption mechanism of Bi(III) ions, it was deduced that firstly Bi(III) ions occupied the vacancies of the original Ca2+, Mg2+ and Fe2+ ions on the rutile surface; secondly Bi(III) ions covered on the rutile surface in the form of hydroxides.

Mechanistic insights into water adsorption and dissociation on amorphous TiO2-based catalysts

Despite having defects, amorphous titanium dioxide () have attracted significant scientific attention recently. Pristine, as well as various doped catalysts, have been proposed as the potential photocatalysts for hydrogen production. Taking one step further, in this work, the author investigated the molecular and dissociative adsorption of water on the surfaces of pristine and doped catalysts by using density functional theory with Hubbard energy correction (DFT+U). The adsorption energy calculations indicate that even though there is a relatively higher spatial distance between the adsorbed water molecule and the surface, pristine surface is capable of anchoring molecule more strongly than the doped as well as the rutile (1 1 0) surface. Further, it was found that unlike water dissociation on crystalline surfaces, water on pristine catalyst experience the dissociation barrier. However, this barrier reduces significantly when is doped with , providing an alternative route for the development of an inexpensive and more abundant catalyst for water splitting.

The role of EDTA on rutile flotation using Al3+ ions as an activator.

Rutile is a relatively stable mineral, due to its weakly specific adsorption to collectors. The development and application of a high efficiency and low-toxicity activator is the main challenge in rutile flotation. In this study, Al3+ ions and EDTA (ethylene diamine tetraacetic acid) as mixed activators were investigated using micro-flotation tests. The results of the micro-flotation tests showed that the flotation recovery was slightly increased (from 65.8% to 69.7%) using single Al3+ ions as the activator and surprisingly, the activating effect was sharply improved (from 69.7% to 80.6%) after adding EDTA. The activating mechanism of Al3+ ions and EDTA was revealed by adsorption capacity measurements, zeta potential measurements, FT-IR spectroscopy analysis and XPS analysis. Al3+ ions were adsorbed on the rutile surface in the form of Al(OH)n3−n (n = 0, 1, 2), which increased the zeta potential and the activating sites for anionic collector adsorption. The addition of EDTA removed the surplus Al3+ ions, and prevented the generation of hydrophilic colloidal Al(OH)3 over the pH range of optimum flotation.

Direct observation of atomic step edges on the rutile TiO2(110)-(1 × 1) surface using atomic force microscopy.

Clarifying the atomic configuration of step edges on a rutile TiO2 surface is crucial for understanding its fundamental reactivity, and the direct observation of atomic step edges is still a challenge. AFM is a powerful tool for investigating surface structures with true atomic resolution, and it provides the opportunity to resolve the real structure of step edges with improved techniques. In this work, we successfully imaged the atomic configuration of 001 and 1-11 step edges on the surface of rutile TiO2(110)-(1 × 1), and we present the direct observation of oxygen vacancies along the 1-11 step edges, indicating that one 1-11 step edge site corresponds to one oxygen vacancy using AFM. We also made use of the simultaneous AFM/STM measurements to explore the electronic structure of step edges, which enhanced the evidence of oxygen vacancies existing along the 1-11 step edges and further demonstrated that the 001 step edge was terminated by an O row. The effect of the reduced 1-11 step edges was explored by probing the O2 adsorption and the nucleation behavior of gold clusters. It was found that oxygen vacancies along the 1-11 step edges could contribute to O2 dissociative adsorption and there was no obvious difference compared with the oxygen vacancies on the flat terrace. The reduced step edge and terrace likewise acted as nucleation and growth sites for gold atoms/nanoparticles, in line with previous reports. The present study provides a complete characterization of the atomic configuration of the step edges on the TiO2(110) surface and plays an important role in investigating the surface chemistry of metal oxides.

Probing the interaction between 2,2'-bithiophene-5-carboxylic acid and TiO2 by photoelectron spectroscopy: A joint experimental and theoretical study.

The interaction between 2,2'-bithiophene-5-carboxylic acid (PT2) sublimed under ultra-high vacuum conditions and anatase (101) and rutile (110) TiO2 single crystal surfaces is investigated by studying the electronic spectral density near the Fermi level with synchrotron-based spectroscopy. The experimental results are compared to density functional theory calculations of the isolated PT2 molecule and of the molecule adsorbed on an anatase TiO2 (101) cluster. The relative concentrations of Ti, C, and S atoms indicate that the adsorbed molecule remains intact upon deposition, which is typical of a Stranski-Krastanov growth mode. The analysis of the O1s spectrum suggests a predominant bidentate geometry of the adsorption with both rutile and anatase surfaces, as supported by previous theoretical simulations. It is also theoretically and experimentally demonstrated that the PT2 adsorption causes the appearance of new electronic states in the gap near the TiO2 valence band. A pinning effect of the LUMO level of the dye is also theoretically predicted.

Surface oxidation of NiTi during thermal exposure in flowing argon environment

Surface oxidation at elevated temperatures has been a phenomenon of interest for NiTi alloys. On one hand it has been deliberately used to provide a surface protective layer to prevent Ni release for biomedical applications, and on the other it is to be minimised in metal processing and production. This study investigated the use of flowing argon as a protective gas for heat treating NiTi at elevated temperatures. It was found that under flowing argon protection, complex oxidation reactions still take place within the surface layers of NiTi. This includes the formation of transient oxides of Ni2Ti4O and TiO at lower temperatures, followed by formation of TiNi3 underneath the oxide layers, and conversion of TiO to TiO2 at higher temperatures. The final product contained a rutile TiO2 outer surface, a composite middle layer consisting of Ni(Ti)+TiO2, a TiNi3 inner layer and a Ti-depleted zone within the body of the alloy. For heating at 1223K for 24h, the surface layers have a combined thickness of ~15μm and a Ti-depleted zone of ~400μm within the body of the alloy. The Ti-depleted zone appeared to play a major role in affecting the transformation and mechanical properties of the alloy.

Surface Modification of Perfect and Hydroxylated TiO2 Rutile (110) and Anatase (101) with Chromium Oxide Nanoclusters.

We use first-principles density functional theory calculations to analyze the effect of chromia nanocluster modification on TiO2 rutile (110) and anatase (101) surfaces, in which both dry/perfect and wet/hydroxylated TiO2 surfaces are considered. We show that the adsorption of chromia nanoclusters on both surfaces is favorable and results in a reduction of the energy gap due to a valence band upshift. A simple model of the photoexcited state confirms this red shift and shows that photoexcited electrons and holes will localize on the chromia nanocluster. The oxidation states of the cations show that Ti3+, Cr4+, and Cr2+ (with no Cr6+) can be present. To probe potential reactivity, the energy of oxygen vacancy formation is shown to be significantly reduced compared to that of pure TiO2 and chromia. Finally, we show that inclusion of water on the TiO2 surface, to begin inclusion of environment effects, has no notable effect on the energy gap or oxygen vacancy formation. These results help us to understand earlier experimental work on chromia-modified anatase TiO2 and demonstrate that chromia-modified TiO2 presents an interesting composite system for photocatalysis.

Production of hybrid macro/micro/nano surface structures on Ti6Al4V surfaces by picosecond laser surface texturing and their antifouling characteristics

The development of surfaces which reduce biofouling has attracted much interest in practical applications. Three picosecond laser generated surface topographies (Ti1, Ti2, Ti3) on titanium were produced, treated with fluoroalkylsilane (FAS), then characterised using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy, Fourier Transform Infra-Red (FTIR) spectroscopy, contact angle measurements and white light interference microscopy. The surfaces had a range of different macro/micro/nano topographies. Ti2 had a unique, surface topography with large blunt conical peaks and was predominantly a rutile surface with closely packed, self-assembled FAS; this was the most hydrophobic sample (water contact angle 160°; ΔGiwi was −135.29mJm−2). Bacterial attachment, adhesion and retention to the surfaces demonstrated that all the laser generated surfaces retained less bacteria than the control surface. This also occurred following the adhesion and retention assays when the bacteria were either not rinsed from the surfaces or were retained in static conditions for one hour. This work demonstrated that picosecond laser generated surfaces may be used to produce antiadhesive surfaces that significantly reduced surface fouling. It was determined that a tri-modally dimensioned surface roughness, with a blunt conical macro-topography, combined with a close-packed fluoroalkyl monolayer was required for an optimised superhydrophobic surface. These surfaces were effective even following surface immersion and static conditions for one hour, and thus may have applications in a number of food or medical industries.

Crystal Orientation and Electrical Properties of Tin Oxide Transparent Conducting Films Deposited on Rutile Surface

Thin films of tin oxide (SnO2) without doping are attractive transparent conducting film since environmentally unfavorable elements of antimony or fluorine are eliminated. Tin oxide films without doping were fabricated very cheaply on (001) and (100) planes of single crystal of rutile (TiO2) by spray chemical vapor deposition (mist CVD). The film deposited on rutile (001) surface was poorly epitaxial (double domain) but with higher mobility (24 cm2 V-1 s-1) and lower resistivity (1.6×10-3 Ω cm) than that deposited on glass substrate (16 cm2 V-1 s-1 and 2.4×10-3 Ω cm) for reference. Deposition on rutile (100) surface resulted in better epitaxial growth (single domain). The mobility (39 cm2 V-1 s-1) and the carrier electron density (2.7×1020 cm-3) were much higher. The resistivity (6.2×10-4 Ω cm) was compatible with those doped with antimony or fluorine and will be the lowest among tin oxide films without doping.

Study of the modes of adsorption and electronic structure of hydrogen peroxide and ethanol over TiO2 rutile (110) surface within the context of water splitting

While photocatalytic water splitting over many materials is favourable thermodynamically the kinetic of the reaction is very slow. One of the proposed reasons linked to the slow oxidation reaction rate is H2O2 formation as a reaction intermediate. Using Density Functional Theory (DFT) H2O2 is investigated on TiO2 rutile (110) surface to determine its most stable adsorption modes: molecular, (H)O(H)O − (a), partially dissociated, (H)OO − (a), and fully dissociated (a) − OO − (a). We then compare H2O2 interaction to that of a fast hole scavenger molecule, ethanol. Geometry, electronic structure, charge density difference and work function determination of both adsorbates are presented and compared using DFT with different functionals (PBE, PBE-D, PBE-U, and HSE + D). H2O2 is found to be strongly adsorbed on TiO2 rutile (110) surface with adsorption energies reaching 0.95 eV, comparable to that of ethanol (0.89 eV); using GGA PBE. The negative changes in the work function upon adsorption were found to be highest for molecular adsorption ( − 1.23 eV) and lowest for the fully dissociated mode ( − 0.54 eV) of H2O2. This may indicate that electrons flow from the surface to the adsorbate in order to make O(s)-H partially offset the overall magnitude of the oxygen lone pair interaction (of H2O2) with Ti4+ cations. Examination of the electronic structure through density of states (DOS) at the PBE level of computation, indicates that the H2O2 highest occupied molecular orbital (HOMO) level is not overlapping with oxygen atoms of TiO2 surface at any of its adsorption modes and at any of the computation methods. Some overlap is seen using the HSE + D computational method. On the other hand the dissociated mode of ethanol (ethoxides) does overlap with all computational methods used. The high adsorption energy and the absence of overlapping of the HOMO level of H2O2 with TiO2 rutile (110) surface may explain why water splitting is slow.

Electronic structure and magnetic properties of two-dimensional nonstoichiometric rutile

The coherent potential approximation is applied to study the influence of vacancies in the oxygen lattice on the electronic structure and magnetic properties of the TiO1.99 rutile (110) surface. Stoichiometric two-dimensional rutile is found to be a nonmagnetic semiconductor. Vacancies in the oxygen positions on the surface lead to the metallic type of the electronic spectrum. Additionally, they result in the appearance of spin magnetic moments on titanium atoms surrounded by only five oxygen atoms due to the surface formation. The vacancies in all the other oxygen positions except of the surface cause a nonmagnetic semiconducting character of the energy spectrum of two-dimensional TiO1.99. A mechanism that underlies the formation of spin magnetic moments of the titanium atoms, namely Stoner ferromagnetism of a defect related impurity band, is discussed.

Adsorption and photolysis of trimethyl acetate on TiO2(B)(001) studied with synchrotron radiation core level photoelectron spectroscopy

We present a synchrotron radiation photoelectron spectroscopy study of the adsorption and photooxidation of trimethyl acetate (TMA) on TiO2(B)(001). The TiO2(B)(001) substrate was realized in the form of 2 nm thick film on Au(111). The TMA species adopt the bidentate bonding configuration, as expected for carboxylic acids on TiO2, but cannot coordinate to all surface Ti ions due to steric hindrance. The proposed arrangement of the TMA species thus allows for the formation of an overlayer with a (2 × 1) periodicity. The thermal stability is found to be comparable to that on rutile (110) although the results indicate differences in the threshold for the TMA + H→TMAA reaction. Photolysis using both ultraviolet (UV) light and soft x-ray synchrotron radiation (SR) was studied and compared to the reaction on the reduced rutile (110) surface. A kinetic analysis suggests that the photoreaction rate for TMA on the TiO2(B) thin film is initially two times faster than that on the reduced rutile TiO2(110) surface. The higher activity of the TiO2(B) film is assigned to a reduced influence from surplus electrons associated with reduced Ti species, thereby decreasing the probability for hole-annihilation at high TMA coverage.

The Effect of Surface Electronic Structure on the Bioactivity of Neutral Dopant Si, Ge, and Sn on TiO2 (110): A DFT Study

In this paper, first principles calculations based on density functional theory were used to study the electronic properties and adsorption behavior of modified rutile surfaces with neutral element dopants (Si, Ge, Sn). The results showed that Sn doped surface has the smallest work function (7.07 eV) and Ge doped surface has the lowest conduction band edge (1.28 eV). Furthermore, the adsorption behavior of H2O and Arg‐Gly‐Asp (RGD) molecules on modified rutile surfaces was calculated to estimate the biocompatibility of modified dental implant surfaces. For the purpose of simulating the real solution environment, the free energy of solvation for adsorbates, calculated by Gaussian 09 program code, was taken into account. The results of the adsorption calculations of H2O indicate that Sn doped surface has a more negative adsorption energy (−3.15 eV) and a higher charge transfer (−0.1) than any other modified surface, which is consistent with its low work function. The results of the adsorption calculations of Arg‐Gly‐Asp demonstrate that Ge doped surface also has a shorter distance (1.95 Å) between Ti atom and O atom in RGD, which is similar with the partial density of states results. All of the results show that the electronic structure of an implant surface has a significant influence on its bioactivity and is also useful for the design of modification methods on dental implant surfaces.