Thickness Of TiO2 Layer Research Articles

ＴｉＡｌの酸化特性に及ぼす窒素イオン注入の影響

TiAl was implanted with nitrogen and its effect on cyclic oxidation behavior of TiAl has been investigated in purified oxygen at 1200 K and in static air at 1100 K. The nitrogen implantation was carried out at room temperature, 973 K or 1173 K. The acceleration voltage was 50 kV and the ion dose was 1020 m-2 or 1021 m-2. For the specimen implanted with nitrogen at room temperature with a dose of 1021 m-2, the nitrogen distributed into the depth of about 200 nm with a maximum concentration at about 120 nm, and the concentration changed gradually in the penetration depth. The implantation of nitrogen resulted in the formation of Ti2AlN. The amount of the nitride was larger for the implantation carried out at room temperature than that at 973 K or 1173 K because of the nitrogen diffusion into the matrix during high temperature implantation. The nitrogen implantation deteriorates the oxidation behavior of TiAl in oxygen due to enhanced scale spallation, while the cyclic oxidation behavior of the nitrogen-implanted specimen in air was comparable to that of TiAl without implantation. From the specimen oxidized in oxygen for a very short period, small amount of Ti2N was detected along with TiO2 by X-ray diffraction, indicating that the nitride formed by implantation is not stable during oxidation. The scale formed on the specimen oxidized in oxygen had thick outer layer of TiO2 and stratified inner layer with micro pores. This scale structure seems to be responsible for the lower scale strength. The present results suggest that nitride layer formed by implantation is not continuous thus ineffective for improvement of the oxidation resistance of TiAl.

Nanoscale Imaging of the Electronic Conductivity of the Native Oxide Film on Titanium Using Conducting Atomic Force Microscopy

Conducting atomic force microscopy (C-AFM) is used to visualize the heterogeneous electronic conductivity of the native oxide film (nominally a 2.9 nm thick TiO2 layer) on polycrystalline Ti electrodes (hereafter referred to as Ti/TiO2 electrodes). Ex situ C-AFM images of Ti/TiO2 electrodes recorded in air demonstrate that the electronic conductivity of the oxide film in contact with the underlying Ti grain boundaries is at least 200× higher than the conductivity of the oxide film on grain faces. The width of the conductive zone in the oxide film over grain boundaries is estimated to be less than 50 nm (resolution limited by the C-AFM tip size). Small islands of oxide exhibiting high electronic conductivity are also observed on topographically featureless regions of grain faces. The observed spatial variations in conductivity are tentatively attributed to the presence of defects (e.g., Ti3+ sites) and lower valence oxides (e.g., Ti2O3) in the native oxide film.

Contactless Determination of the Photoconductivity Action Spectrum, Exciton Diffusion Length, and Charge Separation Efficiency in Polythiophene-Sensitized TiO2 Bilayers

The flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study photoinduced charge separation in bilayers consisting of a smooth, transparent, 80 nm thick layer of anatase TiO2 onto which poly(3-hexylthiophene) (P3HT) sensitizer layers have been spin-coated. Interfacial charge separation, resulting from excitation of the polymer in the visible, is found to persist well into the millisecond time domain. Photoconductivity action spectra have been measured between 420 and 700 nm for P3HT layer thicknesses, L, from ∼2 to 200 nm. Using this electrodeless technique, the bilayers could be irradiated from either the polymer (“front”) or semiconductor (“back”) side. On front-side irradiation at 540 nm (close to the absorption maximum of the polymer), the efficiency of charge separation per incident photon (IPCSE) initially increased to a maximum value of 0.8% for L ≈ 10 nm. For thicker layers the IPCSE gradually decreased, eventually to 0.1% for L ≈ 170 nm. On back-side irradi...

Growth-controlled cubic zirconia microstructure in zirconia–titania nanolaminates

Zirconia microstructure selection (phase and crystallographic orientation) was studied in sputter-deposited multilayer films consisting of nanocrystalline ZrO2 and amorphous TiO2. The goal was to understand the mechanism for ZrO2 microstructure selection as a function of nanolaminate architecture (number of interfaces and ZrO2 and TiO2 layer thickness) in a growth regime of limited surface diffusion. The results show that there are two competing paths that ZrO2 microstructure can follow in a ZrO2–TiO2 nanolaminate. One path depends upon geometric shadowing resulting in the formation of a columnar morphology within a ZrO2 layer. This path leads to cubic (220) growth as an intermediate microstructure, and ultimately to the formation of cubic (200) crystallites spanning several bilayers. In this case, ZrO2 renucleation within a layer is suppressed. The second path depends upon renucleation within a ZrO2 layer, involving first tetragonal (111) formation, and then the transformation of tetragonal (111) to monoclinic(11-1)-(111), consistent with a finite crystal size effect. The establishment and maintenance of a columnar morphology (and hence, the suppression of renucleation events), ultimately leads to cubic (200) growth, and is consistent with a growth-controlled microstructure selection mechanism. This mechanism appears to strongly depend upon the existence and planar quality of the TiO2 growth–restart surfaces.

Three-Dimensional Surface Pattern and Chemical Composition of Mucosal Titanium Implant Compartments

Surface topography and chemical composition of mucosal-implant interfaces is thougt to be critical to their clinical success. The aim of our study was to investigate the topography and chemical composition of titanium mucosal-implant interfaces using surface analytical techniques. The mucosal surface compartments of 10 different implant systems were utilized as a test area. The ultramorphological analysis were carried out using Confocal Laser Scanning Microscopy (CLSM), X-ray photoelectron spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES), Scanning Electron Microscopy (SEM) and Scanning Force Microscopy (SFM). The surfaces of samples showed different fracturing of metal chips and pitting attack. From the CLSM- and SEM analysis in comparison to the Developed Surface Area (DSA) as ratio of microroughnesses it appears that the diameter of the pits varied in the range of 0,1 to 10 \\micron. MIES showed the presence of Ti, O and C . Several peaks pertaining to titanium and oxygen can be found. The Ti-surface is covered by a 3–5 nm thick TiO2 layer. Only titanium in the oxidic, not in the metallic state is found within the observation depth of 1 nm. We find clear evidence from MIES that saturated hydrocarbon chains form the outermost molecular layer. Virtually no signal from TiO2 is found at the very surface. The results suggest a two-layer structure for the passive film formed on titanium after exposition to the sulcus crevicular fluid. The inner layer has a structure close to TiO2, while the outlayer is dominated by CH2-groups with a few –C=O groups inside the hydrocarbon overlayer. The granular structure observed on mucosal-implant surfaces seems to indicate that the dissolution occurs at localized defects in the passive film influencing the barrier function of implanto-gingival tissues. This was confirmed by the DSA as a hybrid parameter including both spatial and amplitude aspects of the surfaces.

Dry etching of platinum films with TiN masks in an Ar/O2 helicon wave plasma

Platinum thin films have been successfully patterned without fence residues using an Ar/O2 helicon wave plasma. Photoresist and silicon oxide masks were also studied for comparison. The etch rate of the TiN mask decreases, but the etch slope increases with an increase of the oxygen concentration in the Ar/O2 gas mixture. An etch rate of about 670 Å/min was obtained by operating at 4 mTorr with an Ar/O2 flow rate of 32/8 sccm. The etch selectivity is enhanced with the addition of oxygen to Ar, and a high Pt-to-TiN selectivity of above 14 could be obtained. X-ray photoelectron spectroscopy and Auger electron spectroscopy indicated that a thick TiO2 layer could be formed on the TiN mask in the Ar/O2 plasma. The high etch selectivity of platinum to TiN may be attributed to the presence of a TiO2 layer of ∼60 Å thickness on the TiN surface. A high etch selectivity and fence-free Pt etching with sidewall angles of ∼70° could be achieved using a thin TiN hard mask without a postwet cleaning.

Electrophoretic Deposition To Control Artificial Opal Growth

In this work we propose and demonstrate a solution to the problems which arise when SiO2 monodisperse nanospheres of diameters under 300 nm or over 550 nm are used to obtain opal-based photonic crystals. If the nanospheres are too small, the sedimentation rate is very slow or even may not occur; if they are large enough, no significant order can be achieved because the velocity is too high. This method, based on the electrophoretic phenomenon, allows us to control the sedimentation velocity. Furthermore, other species of importance in this field, such as SiO2 spheres covered with a thick layer of TiO2, do profit from this method.

ＴｉＯ２（Ｔｉ）粉およびＴｉ粉添加（Ｂａ，Ｓｒ）ＴｉＯ３真空焼結体のＰＴＣＲ特性に及ぼすＴｉＯ２（Ｔｉ）粉中ＴｉＯ２量およびＴｉ粉粒度の影響

The effects of TiO2 contents (or thickness of TiO2 surface layer) in TiO2(Ti) powder and the grain size of Ti powder (or interparticle spacing of Ti particles) on the PTCR characteristic of the (Ba, Sr)TiO3 compact added with TiO2(Ti) or Ti, which were sintered in vacuum at 1623K for 3.6ks, were investigated.The results obtained were as follows; (1)With increasing TiO2 content of the TiO2(Ti) from 12.5mass% to 25 and 37.5mass%, the range of metallic Ti content in TiO2(Ti) needed for the development of PTCR characteristic became 1.7 times larger at maximum. (2)For the sintered compact added with 2μm Ti powder, the range of Ti content needed for the development of PTCR characteristic was larger than that of the compact with 18μm Ti powder. (3)The above phenomena seemed to be due to the homogenization of oxygen ion concentration in (Ba, Sr)TiO3 particles which are caused by increasing thickness of TiO2 layer or decreasing interparticle spacing of Ti particles.

Experimental approach to a biological characterization of materials

Titanium oxide surfaces with thin (4 to 5 nm) or thick (30–40 nm) TiO2 layers and rough (Rrms 1.9 μm) or smooth (Rrms 0.45 μm) surface structure were exposed to capillary blood for 5 s through 64 min. The adsorption of main plasma proteins (albumin, IgG, fibrinogen), binding of cascade enzymes (serine proteases) and adhesion and activation of blood cells was measured with immunofluorescence techniques using specific antibodies, the binding of which was quantitated by computer-aided image analysis. The activation of cascade enzymes was detected with antibodies against prothrombin/thrombin (terminal step in the coagulation cascade), C1q and C3c (initial complement activation), terminal complement complex (TCC), and plasmin (terminal step in fibrinolysis). The activation of cells was measured by expression of selectin (platelet CD62), expression of integrins (neutrophil CD11b), or respiratory burst (NBT test) of peritoneal leucocytes adhering to the surfaces after in vivo exposure. The results show different profiles of protein adsorption at the four surfaces. Fibrinogen was the dominating protein on all surfaces, significant amounts of IgG was found on the rough surfaces only. Prothrombin/thrombin and C1q were found initially on the thick-rough surface only. No TCC or plasmin levels were detected during the exposure time studied. Platelets and neutrophils were activated to a significantly higher degree on rough surfaces than on smooth, and neutrophils more on the rough surface with a thin oxide layer than on the thick one. The ensemble of antigens and enzyme activity detected shows a fingerprint which is unique for each material investigated.

Corrosion of Ti99.8-Pd Under Gamma Irradiation in MgC12-Rich Brine

ABSTRACTThe combined influence of gamma radiation (10 Gy/h) and high temperature (150 °C) on the corrosion of the promising HLW container material Ti99.8-Pd was investigated in an MgCl2-rich brine, and the corrosion surface films formed were characterized by XPS. For comparison, specimens without irradiation were also examined.Under the test conditions used, the alloy Ti99.8-Pd is resistant to local corrosion and its general corrosion is negligible low. The thin corrosion films formed on the surface of unirradiated specimens and in the crevices of specimens exposed to radiation consist of TiO2. However, outside the crevices of irradiated specimens, a surface layer consisting of Mg (main component of the brine) and Si (impurity in the brine) oxide is built up over the TiO2 layer. Comparable TiO2 layer thicknesses (30 - 65 nm, depending on the experimental conditions) are found for unirradiated and irradiated laboratory specimens. The TiO2 layer formed on the in-situ corrosion specimens (33 nm / 5.3 years) is thinner than that of the laboratory specimens (58 nm / 191 days) indicating less aggressive conditions in the field experiments. In view of these results, the alloy Ti99.8-Pd continues to be considered as a strong candidate container material and will be further investigated.

Young's Modulus and Density of thin TiO2 Films Produced by Different Methods

AbstractThe Young's modulus and density are analyzed for 280 and 500 nm thick TiO2 layers deposited by reactive evaporation (RE) and ion plating (IP) by means of surface acoustic wave spectroscopy (SAWS) and grazing incidence X-ray reflection spectroscopy (GIXR). The layers are amorphous or polycrystalline, and have densities between 2.9 g/cm3 and 3.8 g/cm3, depending on the deposition conditions. The measured Young's moduli vary between 65 GPa for RE films and 147 GPa for IP layers. They are independent of film thickness, but correlate with the density. A change of the Young's modulus due to the phase transition from amorphous to anatase is described, which occurs at temperatures above 210°C.

Electrochemical and thermal oxidation of TiN coatings studied by XPS

AbstractX‐ray photoelectron spectroscopy (XPS) has been used to investigate the electrochemical and thermal oxidation of titanium nitride (TiN) coatings prepared by physical vapour deposition (PVD) at 200°C. Electrochemical oxidation of TiN was carried out at various potentials in phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide species in the layer formed by anodic oxidation. The electrochemical oxidation of TiN to TiO2 proceeds through the formation of a mixed oxynitride/oxide layer, which transforms into oxide (TiO2) at sufficiently positive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO2 is accompanied by the formation of molecular nitrogen (N2). The thickness of the oxide layer reaches ∼7 nm after oxidation at the highest potential (1.9 V). A complete coverage of the TiN surface by TiO2 leads to an anodic peak in the polarization curve. On the basis of angle‐resolved XPS measurements, two types of oxynitride species are identified, which are distributed differently throughout the oxidized layer.X‐ray photoelectron spectroscopy depth profiles of TiN oxidized at 450°C and 600°C in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO2 layer appears on top of TiN at the higher temperature. The interface between the nitride and oxide phases is relatively sharp. It is suggested that the mechanism of TiN oxidation proceeds by a progressive replacement of nitrogen by oxygen. The TiN coatings can be used up to 600°C as a protective coating in an oxygen atmosphere.Valance band spectra of TiN, as well as of electrochemically and thermally oxidized TiN, are presented and discussed.

Titanium-Porcelain System Part I: Oxidation Kinetics of Nitrided Pure Titanium, Simulated to Porcelain Firing Process

The bonding strength of porcelains to metals depends on the oxide layer between the porcelain and the metal. Oxidation of a metal surface increases the bonding strength, whereas excessive oxidation decreases it. Titanium and its alloys are gaining acceptance for dental use since they exhibit excellent biocompatibility, corrosion resistance, low specific gravity, good mechanical properties, and low cost. However, titanium suffers from its violent reactivity with oxygen at high temperatures that yields an excessive thick layer of TiO2, and this presents difficulties with porcelain bonding. The present study deals with the oxidation kinetics of titanium simulated to porcelain firing and evaluating surface nitridation of titanium as a process of controlling the oxidation behavior of titanium. Nitrided samples with the Arc Ion Plating PVD process and un-nitrided control commercially pure titanium (CPT, Grade 1) were subjected to oxidation simulating firing of Procera porcelain with 550 degrees, 700 degrees, and 800 degrees C firing temperatures for 10 min in both 1 and 0.1 atmospheric air. Weight difference before and after oxidation was calculated and the parabolic rate constant, Kp (mg2/cm4/s), was plotted against inverse absolute temperature. Surface layers of the samples were subjected to x-ray and electron diffraction techniques for phase identifications. Results revealed that both nitrided and un-nitrided samples obey a parabolic rate law with activation energy of 50 kcal/mol. In addition this study shows that nitrided CPT had a Kp about 5 times lower than the un-nitrided CPT and hence the former needs about 2.24 times longer oxidation time to show the same degree of oxidation. Phase identification resulted in confirming the presence of TiO2 as the oxide film in both groups but with 1-2 microns thickness for the un-nitrided CPT and 0.3-0.5 micron thickness for the nitrided samples. Therefore it can be concluded that nitridation of titanium surface can be effective in controlling the surface oxide thickness that might ensure satisfactory bonding with porcelain.

Oxidation Resistance of Alumina–Titanium Nitride and Alumina–Titanium Carbide Composites

The presence of TiC or TiN paritcles in an Al2O3 matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤T≤ 1100°C. At low temperatures (T < 900°C), the oxidation follows a phase‐boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO2 rutile crystals that subsequently grow and coalesce. When a continuous TiO2 rutile layer is formed (T≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O2 through a thick TiO2 layer is proposed as the governing step.

Oxidation Effects on Porcelain-Titanium Interface Reactions and Bond Strength

Titanium is strong, resists corrosion and has a low density and excellent biocompatibility. Conventional ceramic-metal restorations have been extensively used in dentistry because of their esthetic appearance and good mechanical properties. This study investigates oxidation effects on the porcelain-titanium interface reactions and bond strength. Pure titanium was treated in a porcelain furnace at temperatures of 600 to 1000 degrees C under either vacuum or air. X-ray diffraction analysis of the surface of pure titanium revealed that the relative peak intensity of alpha-Ti decreased and that of TiO2 increased, with increasing firing temperature. The Vickers hardness number of titanium increased with temperature especially over 900 degrees C, and was harder in air than in vacuum. The tension-shear bond strength of the porcelain-titanium system was the highest in the green stage and lowest after 900 degrees C treatment. Metallographic microscopy of the porcelain-titanium interface revealed a thick band-like zone in the sample treated over 900 degrees C. The excess thick layer of TiO2 apparently weakened the bond strength of porcelain-titanium. Unlike the conventional ceramic-gold alloy system the recommended degassing procedure was not suitable for porcelain-pure titanium restoration.

Properties of thin antimultipactor TiN and Cr2O3 coatings for klystron windows

Low secondary electron emission yield (1–1.3), low radio-frequency (rf) loss films are of interest as coatings for alumina ceramic high power klystron windows. Very thin (15–50 Å) Ti and TiN layers have been previously used with success in klystron tubes operating at lower power levels (<35 MW peak power) and short (2.5 μs) pulses but are subject to property changes during air exposure, tube bakeout (550 °C for up to 10 days) and in situ electron bombardment. Higher power tubes (≥50 MW) with longer (5 μs) pulse lengths require coatings that remain stable under these more rigorous conditions in order to avoid multipactoring and window failure due to overheating. Air-oxidized Cr films offer an alternative to TiN. This work shows that they have the required resistivity for low rf loss, combined with stability in the secondary electron emission (SEE) yield under bakeout and electron bombardment. SEE, AES, XPS, ELS, oxidation, bakeout, and electron bombardment results are presented for Cr and TiN layers deposited by sputtering onto high density alumina substrates. The surface of TiN oxidized to a 9 Å thick TiO2 layer which, under bakeout to 550 °C in vacuum, thinned to 6 Å. This extreme layer thinness resulted in a significant drop in the SEE yield which, unfortunately, was reversible upon reoxidation. The oxidized layer on Cr was 17 Å of Cr2O3 which thinned to 13 Å upon bakeout. This thicker oxide layer produced a stable SEE yield which, although not as low as oxidized TiN, is sufficient to prevent electron multipactor. Windows covered by air-oxidized Cr films are at least as good, under tube processing conditions, as the best TiN-coated windows.

AN ATOM-PROBE STUDY OF Fe-Ti ALLOYS

The ToF atom-probe FIM was used to study surface segregation of Fe-Ti alloys. Ti segregates to the surface upon annealing at or above 650°C. The degree of segregation depends on the crystallographic orientation, 100% at the (110) and (111), 70% at the (100) and ≤50% at the (121) plane. It is found that the presence of H2 (D2) during annealing enhances surface segregation of Ti and that oxygen deters Ti segregation. An interesting observation is that when a small amount of oxygen exists during annealing in H2 (~10-4Torr) The thick TiO2 layer (up to a few hundreds layers) is formed on the surface.