Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium

Events at bone-implant interfaces are influenced by implant surface properties. Our previous work has revealed that osteogenic activity is enhanced by a nanotextured Ti surface, obtained by controlled chemical oxidation using a H₂SO₄/H₂O₂ mixture. To better understand the origin of this biological effect, we have carried out a characterization of the modified surface at the nanoscale. In particular, the morphology, structure, and chemical composition of the Ti surface were examined thoroughly. X-ray photoelectron spectroscopy (XPS), combined with grazing-angle Fourier-transform infrared (FTIR) spectroscopy, revealed that the oxidized Ti surface consists of almost pure TiO₂ with Ti:O ratio ranging between 1:2.02 and 1:2.08. Raman spectroscopy and X-ray diffraction (XRD) indicated that the chemically treated Ti surface is mainly composed of amorphous titania. Scanning electron microscopy (SEM) clearly showed that the treated Ti substrate becomes highly porous and has a surface consisting of nano-sized pits, which have average diameters and fractal dimensions ranging between 20-22 nm and 1.11-1.17, respectively. Atomic force microscopy (AFM) revealed a three-fold increase in surface roughness. The thickness of the oxide layer on the treated Ti surface is estimated to be ∼32-40 nm. Together, these observations provide a detailed characterization of chemically oxidized Ti surfaces at the nanoscale and offer new prospects for understanding and controlling the relationship between the properties of materials and their interactions with cells. Our work brings us closer to the creation of “intelligent” implant surfaces, capable of selectively influencing cell behavior.     

Surface microstructures and antimicrobial properties of copper plasma alloyed stainless steel

Bacterial adhesion to stainless steel surfaces is one of the major reason causing the cross-contamination and infection in many practical applications. An approach to solve this problem is to enhance the antibacterial properties on the surface of stainless steel. In this paper, novel antibacterial stainless steel surfaces with different copper content have been prepared by a plasma surface alloying technique at various gas pressures. The microstructure of the alloyed surfaces was investigated using glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM). The viability of bacteria attached to the antibacterial surfaces was tested using the spread plate method. The antibacterial mechanism of the alloyed surfaces was studied by X-ray photoelectron spectroscopy (XPS). The results indicate that gas pressure has a great influence on the surface elements concentration and the depth of the alloyed layer. The maximum copper concentration in the alloyed surface obtained at the gas pressure of 60 Pa is about 7.1 wt.%. This alloyed surface exhibited very strong antibacterial ability, and an effective reduction of 98% of Escherichia coli (E. coli) within 1 h was achieved by contact with the alloyed surface. The maximum thickness of the copper alloyed layer obtained at 45 Pa is about 6.5 μm. Although the rate of reduction for E. coli of this alloyed surface was slower than that of the alloyed surface with the copper content about 7.1 wt.% over the first 3 h, few were able to survive more than 12 h and the reduction reached over 99.9%. The XPS analysis results indicated that the copper ions were released when the copper alloyed stainless steel in contact with bacterial solution, which is an important factor for killing bacteria. Based on an overall consideration of bacterial killing rate and durability, the alloyed surface with the copper content of 2.5 wt.% and the thickness of about 6.5 μm obtained at the gas pressure of 45 Pa is expected to be useful as antimicrobial materials that may have a promising future in antimicrobial applications.     

Characterization of mesoporous VOx/MCM-41 composite materials obtained via post-synthesis impregnation

Spherical-particle MCM-41 was synthesized at room temperature, and, then, impregnated with aqueous solutions of NH₄VO₃ to produce variously loaded VO_x/MCM-41 composite materials. Bulk and surface properties of the materials thus produced were characterized by means of X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), N₂ sorptiometry and X-ray photoelectron spectroscopy (XPS). Results obtained indicated that subsequent calcination at 550 °C (for 2 h) of the blank and impregnated MCM-41 particles, results in materials assuming the same bulk structure of MCM-41, and exposing uniformly mesporous, high area surfaces (P_w = 2.0-2.3 nm; 974-829 m²/g), except for the material obtained at 20 wt%-V₂O₅ that was shown to suffer a considerable loss on surface area (down to 503 m²/g). XPS results implied that the immobilization of the VO_x species occurs via interaction with surface OH/H₂O groups of MCM-41, leading to the formation of vanadate (VO₃⁻) surface species, as well as minor V-O-Si and V₂O₅-like species. However, in all cases, the vanadium sites remained pentavalent and exposed on the surface.     

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Surface chemical composition of human maxillary first premolar as assessed by X-ray photoelectron spectroscopy (XPS)

The surface chemical composition of dental enamel has been postulated as a contributing factor in the variation of bond strength of brackets bonded to teeth, and hence, the probability of bracket failure during orthodontic treatment. This study systematically investigated the chemical composition of 98 bonding surfaces of human maxillary premolars using X-ray photoelectron spectroscopy (XPS) to ascertain compositional differences between right and left first premolars. The major elements detected in all samples were calcium, phosphorus, oxygen, nitrogen and carbon. Surface compositions were highly variable between samples and several elements were found to be highly correlated. No statistical significant difference in the chemical composition of the maxillary right and left first premolars was found (p > 0.05). Knowledge of the chemical composition of enamel surfaces will facilitate future studies that relate this information to the variations in dental enamel bond strength.     

Surface structure of sphalerite studied by medium energy ion scattering and XPS

The reactivity of high-Fe containing sphalerite (Zn_1−xFe_xS), the major source of Zn, is of great interest for industrial applications. Since the initial reactivity depends on the physical and chemical properties of the surface, it is important to understand the structure of cleaved and fractured surfaces. Zn_1−xFe_xS zincblende (1 1 0) oriented samples cleaved in air and in vacuum were studied with medium energy ion scattering (MEIS) in order to study surface relaxation and reconstruction associated with the possible formation of S dimers. The experimental results are presented together with ion scattering Monte Carlo simulations that have been performed using the different models of the surface structure. The MEIS blocking patterns are different for the air- and vacuum-cleaved specimens. Models for the air-cleaved samples found S atoms in the first layer that are relaxed outwards by 0.08 Å and Zn(Fe) atoms relaxed inwards by 0.51 Å, with some lateral translation of both species. Results for the vacuum-cleaved sample indicate S atoms have been displaced laterally by 0.5 Å at the surface. X-ray photoelectron spectroscopic (XPS) measurements provide evidence for a high binding energy species indicative of S-S bonds in the near-surface region that are consistent with the ion scattering structural data for both cleaving protocols.     

Morphological, structural and adsorption features of oxide composites with silica and titania matrices

Morphological, structural, electronic, and adsorption characteristics of complex oxides such as fumed silica/alumina and silica/titania, fumed silica with deposited oxides of Mg, Ti, Mn, Ni, Cu, Zn and Zr, silica gel with grafted ZrO₂, sol-gel titania doped by 3d-metals (Cr, Fe, Mn, V) were compared using adsorption, TEM, AFM, XRD, XPS, Mössbauer and Raman spectroscopy data. It was shown that surface, volume, and phase compositions of oxides, particle size distributions (5 nm-3 μm), specific surface area (S_BET ∼ 50-500 m²/g), and porosity (V_P ∼ 0.1-2 cm³/g) affected by synthesis technique and subsequent treatment determine electronic structure (bandgap, valence band and core levels structure) of the materials, adsorption of molecules and metal ions as well as other characteristics.     

Ab-initio pseudopotential study of electronic structure and chemisorption of oxygen on aluminium surface

Chemisorption of oxygen atom on aluminium (1 1 1), (1 1 0) and (1 0 0) surfaces is studied using ab-initio plane wave pseudopotential method based on density functional theory (DFT). Oxygen atom chemisorbed on three different high symmetry sites; top, short-bridge and hollow sites on the aluminium surfaces are examined. It has been found that the O-adatom adsorbed at the hollow site on aluminium (1 1 1), (1 1 0) and (1 0 0) plane yield energetically most stable structure. Calculation of chemisorption energies of O-adatom on aluminium surfaces shows that oxygen is most strongly bound to aluminium atoms on Al(1 1 1) plane and the calculated value of the chemisorption energy of O-adatom at the hollow site on Al(1 1 1) surface is 4.8 eV. In this work, the chemisorption energies calculated for O-adatom on Al(1 1 0) and Al(1 0 0) surfaces are reported for the first time. The electronic structures and the electronic charge density distributions of the oxygen chemisorbed aluminium surfaces are also investigated. Calculations show that for aluminium, p orbitals also contribute significantly along with the s orbitals during the bond formation with oxygen atom. Therefore, the possibilities of hybridizations lead to the strong bonding configurations.     

Electrochemical and surface behavior of hydyroxyapatite/Ti film on nanotubular Ti-35Nb-xZr alloys

In this paper, we investigated the electrochemical and surface behavior of hydroxyapatite (HA)/Ti films on the nanotubular Ti-35Nb-xZr alloy. The Ti-35Nb-xZr ternary alloys with 3-10 wt.% Zr content were made by an arc melting method. The nanotubular oxide layers were developed on the Ti-35Nb-xZr alloys by an anodic oxidation method in 1 M H₃PO₄ electrolyte containing 0.8 wt% NaF at room temperature. The HA/Ti composite films on the nanotubular oxide surfaces were deposited by a magnetron sputtering method. Their surface characteristics were analyzed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and an X-ray diffractometer (XRD). The corrosion behavior of the specimens was examined through potentiodynamic and AC impedance tests in 0.9% NaCl solution. From the results, the Ti-35Nb-xZr alloys showed a solely β phase microstructure that resulted from the addition of Zr. The nanotubular structure formed with a diameter of about 200 nm, and the HA/Ti thin film was deposited on the nanotubular structure. The HA/Ti thin film-coated nanotubular Ti-35Nb-xZr alloys showed good corrosion resistance in 0.9% NaCl solution.     

The structure of ordered Au films on TiOx

The growth of Au on an ultra-thin, ordered Mo(1 1 2)-(8 × 2)-TiO_x, was investigated using scanning tunneling microscopy (STM), low energy ion scattering spectroscopy (LEISS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Wetting of the TiO_x surface by Au was observed with STM and LEISS, and the ordering of the Au films was atomically resolved with STM. TPD showed that Au binds more strongly to the reduced TiO_x film than to bulk TiO₂, but more weakly than to the Mo substrate. The Au-TiO_x binding energy is greater than Au-Au in bulk Au. The oxidation state of Ti in the TiO_x film was deduced by XPS and from the Ti-O phonon shifts relative to bulk TiO₂. The TiO_x/Mo(1 1 2) film structure and those for the (1 × 1)- and (1 × 3)-Au/TiO_x/Mo(1 1 2) surfaces are discussed.     

XPS study of porous dental implants fabricated by electro-discharge-sintering of spherical Ti-6Al-4V powders in a vacuum atmosphere

A single electro-discharge-sintering (EDS) pulse (0.7-2.0 kJ/0.7 g), from a 300 μF capacitor, was applied to atomized spherical Ti-6Al-4V powder in a vacuum to produce a porous-surfaced implant compact. A solid core surrounded by a porous layer was formed by a discharge in the middle of the compact. X-ray photoelectron spectroscopy was used to study the surface characteristics of the implant material. C, O, and Ti were the main constituents, with smaller amounts of Al, V, and N. The implant surface was lightly oxidized and was primarily in the form of TiO₂ with a small amount of metallic Ti. A lightly etched EDS implant sample showed the surface form of metallic Ti, indicating that EDS breaks down the oxide film of the as-received Ti-6Al-4V powder during the discharge process. The EDS Ti-6Al-4V implant surface also contained small amounts of aluminum oxide in addition to TiO₂. However, V detected in the EDS Ti-6Al-4V implant surface did not contribute to the formation of the oxide film. The small amount of N in the implant surface resulted from nitride material that was also found in the as-received Ti-6Al-4V powders.     

Fluorination of polymethylmethaacrylate with tetrafluoroethane using DC glow discharge plasma

Fluorination of polymer surfaces has technological applications in various fields such as microelectronics, biomaterials, textile, packing, etc. In this study PMMA surfaces were fluorinated using DC glow discharge plasma. Tetrafluoroethane was used as the fluorinating agent. On the fluorinated PMMA surface, static water contact angle, surface energy, optical transmittance (UV-vis), XPS and AFM analyses were carried out. After the fluorination PMMA surface becomes hydrophobic with water contact angle of 107° without losing optical transparency. Surface energy of fluorine plasma-treated PMMA decreased from 35 mJ/cm² to 21.2 mJ/cm². RMS roughness of the fluorinated surface was 4.01 nm and XPS studies revealed the formation of C-CF_x and CF₃ groups on the PMMA surface.     

Surface modification of silica-coated zirconia by chemical treatments

Zirconia surface modification by various chemical treatments after silica coating by sandblasting was investigated in this study. The surface of silica-coated dental zirconia was hydroxylated by treatment with different acids at room temperature for 4 h, rinsed with deionized water and air-dried. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Shifts in binding energies for Zr 3d_5/2 and Si 2p peaks were observed after treatment with acids, thereby showing a change in the chemical states of zirconium and silicon on the surface layer of silica-coated zirconia. The XPS analysis revealed that the silica-coated zirconia (SiO₂-ZrO₂) surfaces had changed to hydrous silica-coated zirconia (SiO₂-ZrO₂·nH₂O). One-way ANOVA analysis revealed there was significant difference in both surface roughness parameters of silica-coated zirconia after chemical treatments and the surface topography varied depending on the acid treatment.     

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl₂ group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.     

Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.     

Characterization and human gingival fibroblasts biocompatibility of hydroxyapatite/PMMA nanocomposites for provisional dental implant restoration

The aim of this study was to determine nHA/PMMA composites (H/P) in an optimal ratio with improved cytocompatibility as well as valid physical properties for provisional dental implant restoration. 20 wt.%, 30 wt.%, 40 wt.% and 50 wt.% H/P were developed and characterized using XPS, bending strength test and SEM. Human gingival fibroblasts cultured in extracts or directly on sample discs were investigated by fluorescent staining and MTT assay. Chemical integration in nHA/PMMA interface was indicated by XPS. Typical fusiform cells with adhesion spots were detected on H/P discs. MTT results also indicated higher cell viability in 30 wt.% and 40 wt.% H/P discs (P < 0.05). We conclude that nHA addition to PMMA enhances cytocompatibility and the optimal nHA/PMMA ratio for provisional fixed crowns (PFC) is 0.4:1.     

SEM and XPS studies of nanohole arrays on InP(1 0 0) surfaces created by coupling AAO templates and low energy Ar ion sputtering

The aim of the present study is to demonstrate the feasibility to form well-ordered nanoholes on InP(1 0 0) surfaces by low Ar⁺ ion sputtering process in UHV conditions from anodized aluminum oxide (AAO) templates. This process is a promising approach in creating ordered arrays of surface nanostructures with controllable size and morphology. To follow the Ar⁺ ion sputtering effects on the AAO/InP surfaces, X-ray photoelectron spectroscopy (XPS) was used to determine the different surface species. In_4d and P_2p core level spectra were recorded on different InP(1 0 0) surfaces after ions bombardment. XPS results showed the presence of metallic indium on both smooth InP(1 0 0) and AAO/InP(1 0 0) surfaces. Finally, we showed that this experiment led to the formation of metallic In dropplets about 10 nm in diameter on nanoholes patterned InP surface while the as-received InP(1 0 0) surface generated metallic In about 60 nm in diameter.     

The growth and structure of titanium dioxide films on a Re(1 0 −1 0) surface: Rutile(0 1 1)-(2 × 1)

Titanium dioxide films were grown on Re(1 0 −1 0) by Ti vapor deposition in oxygen at T = 830 K and studied by means of low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS) and X-ray diffraction (XRD). The Ti oxide stoichiometry was determined by XPS as Ti:O = 1:2, with the Ti oxidation state (4+). The TiO₂ growth was monitored by means of LEED as a function of film thickness. Extending the coverage from the submonolayer into the multilayer regime gives rise to a p(2 × 2) pattern, a (poorly ordered) (1 × 1), and, finally, a stable (2 × 2) structure, the latter being associated with a homogeneous TiO₂ phase. For normal electron incidence, the (2 × 2) LEED pattern exhibits systematically extinguished beams at (n ± 1/2, 0) positions, indicating a glide mirror plane. The pg(2 × 2) structure could be explained by both a rutile(0 1 1)-(2 × 1) reconstructed surface and a bulk truncated brookite(0 0 1) surface. Faceting phenomena, i.e. running LEED spots, observed with thin TiO₂ films point to the formation of a rutile(0 1 1)-(2 × 1) surface with two domains and {0 1 1}-(2 × 1) facets and rule out the brookite alternative. Confirmation of this assignment was obtained by an XRD analysis performed at the Berlin synchrotron facility BESSY.     

Dependence of the strain energies on grain orientations in HCP metal films

A thin polycrystalline film bonded tightly to a thick substrate of different thermal expansion coefficients will experience thermal strain when the temperature is changed. Calculations of the strain energies for grains having various crystallographic orientations (h k l) relative to the film surface were made for a polycrystalline film composed of the close-packed hexagonal (HCP) metal Be, Cd, Co, Hf, Mg, Re, Ru, Sc, Ti, Y, Zr and Zn, respectively. From strain energy minimization, the (0 0 1), (0 1 3), (0 4 5), (1 2 3), (2 5 8), (0 5 7), (0 3 5), (0 5 7), (0 1 0), (5 5 8), (1 4 7) and (0 0 1) textures should be favorable in Be, Cd, Co, Hf, Mg, Re, Ru, Sc, Ti, Y, Zr and Zn film, respectively.