Showing papers on "Titanium published in 1992"

Ti8C12+-Metallo-Carbohedrenes: A New Class of Molecular Clusters?

Abstract: During the course of studying the dehydrogenation reactions of hydrocarbons by titanium atoms, ions, and clusters, an exceptionally stable and abundant cluster which contains 8 titaniums and 12 carbons was discovered "Titration" reactions with ND3 reveal the uptake of eight molecules, pointing to the fact that the titanium atoms are at exposed positions of similar coordination A dodecahedral structure of Th point group symmetry is proposed to account for the unusual stability of this molecular cluster The Ti8C12+ dodecahedron has 12 pentagonal rings and each of the rings is formed by two titanium and three carbon atoms, where each titanium is bound to three carbons Based on the model, it is expected that neutral Ti8C12 would be a stable metallo-carbododecahedral molecule and may comprise one member of a new class of molecules, namely metallo-carbohedrenes

In Situ Raman Spectroscopy of Alumina-Supported Metal Oxide Catalysts

Abstract: The molecular structures of the surface overlayerers of rhenium(VII) oxide, molybdenum(VI) oxide, tungsten(VI) oxide, chromium(VI) oxide, vanadium(V) oxide, niobium(V) oxide, and titanium(IV) oxide on γ-alumina were determined by in situ Raman spectroscopy under dehydrated conditions. It was found that the dehydrated surface metal oxide structures of all the systems under study, except for supported titanium oxide, are different from those under ambient condition where moisture is present on the surface

Method of selectively etching titanium-containing materials on a semiconductor wafer using remote plasma generation

Abstract: A method of selectively etching titanium-containing materials without attacking aluminum or silicon dioxide is describe, wherein an atomic chlorine etching environment is generated using downstream techniques. Atomic chlorine in the absence of ion bombardment (as provided by downstream etching) etches titanium-containing materials such as titanium nitride without attacking silicon dioxide. In one embodiment of the invention, atomic chlorine is generated by the discharge of energy into molecular chlorine. In another embodiment of the invention, discharge of energy into a fluorine-containing gas causes the generation of atomic fluorine. Molecular chlorine is then added, creating a fluorine-chlorine exchange reaction which produces atomic chlorine. The presence of fluorine inhibits etching of aluminum, but does not impede the etching of titanium-containing materials.

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

Abstract: This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10−3 to 10.4× 10−3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10−3 to 11.6 × 10−3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. ...

Effect of surface processing on the attachment, orientation, and proliferation of human gingival fibroblasts on titanium.

Abstract: The adhesion, orientation, and proliferation of human gingival fibroblasts was studied on electropolished (elpTi), etched (etchTi), and sandblasted (sblTi) titanium surfaces. The texture, chemical state, and composition of the titanium surfaces were analyzed using a surface tracing instrument and electron spectroscopy for chemical analysis. Considerable differences were evident in the surface texture and chemical composition of the differently treated titanium plates. Electropolishing produced the smoothest and cleanest surface. Human gingival fibroblasts attached, spread, and proliferated on all titanium surfaces. However, cells on elpTi exhibited an extremely flat morphology and seemed to form cellular bridges with adjacent cells, whereas the etchTi and sblTi surfaces harbored both round and flat cells with many long processes. Cells on elpTi appeared to grow in thick layers with no specific orientation, whereas on etchTi surfaces they were migrating along the parallel, irregular minor grooves caused by mechanical polishing, and on sblTi surfaces they seemed to grow in clusters. Stress-fiber type actin bundles and vinculin-containing focal adhesions were present in cells spreading on elpTi and etchTi surfaces but not in cells spreading on sblTi surfaces. Cell shape, orientation, and proliferation appear to depend on the texture of the titanium surface and probably also on the properties of the oxide layer and adjacent bulk material. Our findings suggest that smooth or finely grooved titanium surfaces could be optimal in implants adjacent to soft tissues as they support the attachment and growth of human gingival fibroblasts.

Enhanced extracellular matrix production and mineralization by osteoblasts cultured on titanium surfaces in vitro.

Abstract: Long-term stability of orthopaedic and dental implants depends on the integration of the artificial material into the surrounding bone tissue. The physical and chemical properties of implants, including those made of metals such as titanium, are thought to influence osseointegration. Despite the known importance of this interface, little is known about the factors that promote its formation. In this study, chick embryonic calvarial osteoblasts were cultured in vitro on smooth, rough-textured and porous-coated titanium surfaces and examined for morphology, biosynthesis of extracellular matrix and mineralization as a function of culture time. Scanning electron microscopy revealed that osteoblasts adhered securely to the titanium surface and frequently bridged the uneven surface by means of cellular processes. The osteoblast phenotype was retained in the cell cultures on titanium. In addition, the synthesis of extracellular matrix and subsequent mineralization were both substantially enhanced in the cultures on rough-textured and porous-coated titanium. These results strongly suggest that porous or rough titanium implant surfaces may act like "natural" substrata to permit microscopic tissue/cell ingrowth to improve clinical implant fixation.

The mechanisms of passive dissolution of titanium in a model physiological environment

Abstract: The surface chemistry, oxidation, and disolution kinetics of titanium were measured to establish the mechanisms of passive dissolution in physiological environments. Titanium thin films were immersed in 8.0 mM ethylenediamine-tetraacetic acid in simulated interstitial electrolyte (EDTA/SIE) and maintained at 37 degrees C, 10% O2, 5% CO2 and 7.2 pH for periods of time up to 3200 h (133 days). Two immersion schemes were employed: the integral sequentially determined the titanium released into a solution of accumulated dissolution products; and the differential continuously replenished the test solution. The solutions were analyzed for titanium by electrothermal atomic absorption spectrometry (EAAS), and the sample surfaces were analyzed by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) to determine oxide composition, stoichiometry, and thickness. Prior to immersion two types of hydroxyl (OH) groups were distinguished on the TiO2 surface. Upon immersion, the chemistry of the surface changed as a function of immersion: the presence of OH groups increased and P (nonelemental) was detected at the surface. The dissolution kinetics obeyed a two-phase logarithmic model, where the transition between phases occurred simultaneously with the adsorption of the P-containing species. The dissolution kinetics depended on surface reactions, electric field strength, and molecular diffusion. These mechanisms explain the observed dependence of dissolution kinetics on the properties of the surface oxide and solution ligands.

Microstructural characterization of hydroxyapatite coating on titanium

Abstract: The microstructure of hydroxyapatite plasma sprayed onto titanium alloy has been studied by using transmission electron microscopy. It has been shown that while substantial portions of the coating are crystalline hydroxyapatite, regions of amorphous calcium phosphate with Ca/P ratios of 0.6–1.0 are also present, both in the coatings and at the metal-ceramic interface. The microstructures observed have also been found to be consistent with devitrification of the amorphous calcium phosphates producing regions of very fine grained hydroxyapatite. A calcium titanate phase has also been detected at the metal-ceramic interface produced by the chemical reaction of hydroxyapatite to titanium.

Light and Transmission Electron Microscopy of the Intact Interfaces Between Non-submerged Titanium-coated Epoxy Resin Implants and Bone or Gingiva

Abstract: This experiment was aimed at studying the intact tissue/implant interface of non-submerged dental implants with a titanium surface. Epoxy-resin replicas were fabricated from 3.05 x 8 mm cylindrical titanium implants with a plasma-sprayed apical portion and a smooth coronal collar. The replicas were coated with a 90-120-nm-thick layer of pure titanium and autoclaved. The coated replicas were inserted as non-submerged endosseous implants in the edentulous premolar region of dog mandibles and allowed to heal for three months. Jaw sections containing the implants were processed for light and electron microscopic study of the intact tissue/implant interface with and without prior demineralization. Gingival connective tissue fibers were closely adapted to the titanium layer, in an orientation more or less parallel to the implant surface. There was no evidence of any fiber insertions into the surface irregularities of the smooth or rough titanium surface. Undemineralized bone was intimately adapted to the titanium surface without any intervening space. In demineralized sections, the collagen fibers of the bone matrix tended to be somewhat thinner and occasionally less densely packed in the vicinity of the implant surface. However, they extended all the way to the titanium surface, without any intervening fibril-free layer.

Synthesis of titanium-containing ZSM-48

Abstract: Titanium-containing ZSM-48 is synthesized with silicon to titanium ratios of 26 or larger; changes in unit cell volume and IR data show that titanium is incorporated into framework positions.

Correlation of the electrical properties of metal contacts on diamond films with the chemical nature of the metal-diamond interface. I. Gold contacts: A non-carbide-forming metal.

Abstract: The I-V characteristics of titanium contacts on polycrystalline diamond have been correlated with x-ray-photoelectron-spectroscopy (XPS) and Auger-electron-spectroscopy (AES) characterizations of the interface. As-deposited titanium contacts were rectifying in nature because of minimal interaction between as-deposited titanium and diamond as confirmed via XPS and AES. Once annealed, however, these contacts became Ohmic. The change was related to the formation of a carbide at the interface as observed by XPS. The Schottky-barrier height of the titanium contacts, which was determined by valence-band XPS, decreased from 1.3 to 0.8 eV as a result of the postdeposition annealing. It is believed that the carbide formation at the interface creates a diamond surface layer rich in electrically active defects which lower the barrier height of the metal and increase the leakage current. The interface between titanium and an argon-sputtered diamond surface was also characterized. Titanium formed as-deposited Ohmic contacts on the sputtered surface. A high density of ion-radiation-induced defects and a formation of a carbide during deposition both contributed to the Ohmic-contact formation. These contacts remained Ohmic after postdeposition annealing despite the fact that the annealing did not increase the carbide formed at the interface. It is believed that the carbide formed by the deposition of titanium behaved as a diffusion barrier to prevent the damaged layer from being annealed out into the titanium overlayer. It is concluded that most materials will yield rectifying contacts on a clean diamond surface. Ohmic contacts can be obtained by modifying the interface in some way (i.e., carbide formation, sputtering, etc.).

Comparative Cell Culture Effects of Shape Memory Metal (Nitinol®), Nickel and Titanium: A Biocompatibility Estimation

Abstract: Nitinol® is an equiatomic alloy of nickel and titanium which has been attracting increasing interest in the field of biomedical engineering. To quantify toxicity as a preliminary evaluation of biocomp

Method for the formation of tin barrier layer with preferential (111) crystallographic orientation

Abstract: A process is described for forming, over a silicon surface, a titanium nitride barrier layer having a surface of (111) crystallographic orientation. The process comprises: depositing a first titanium layer over a silicon surface; sputtering a titanium nitride layer over the titanium layer; depositing a second titanium layer over the sputtered titanium nitride layer; and then annealing the structure in the presence of a nitrogen-bearing gas, and in the absence of an oxygen-bearing gas, to form the desired titanium nitride having a surface of (111) crystallographic orientation and a sufficient thickness to provide protection of the underlying silicon against spiking of the aluminum. When an aluminum layer is subsequently formed over the (111) oriented titanium nitride surface, the aluminum will then assume the same (111) crystallographic orientation, resulting in an aluminum layer having enhanced resistance to electromigration.

A single-source precursor to titanium nitride thin films. Evidence for the intermediacy of imido complexes in the chemical vapor deposition process

Abstract: Monomeric titanium and zirconium complexes with multiple bonds to oxygen, sulfur, and nitrogen have attracted considerable attention due to their novel structural features and interesting reactivity. Recently, we have initiated a research program that is designed to prepare models for complexes involved in chemical vapor deposition (CVD) processes of early transition metal materials. Species containing metal-element multiple bonds have featured prominently in mechanistic conjecture about CVD reactions, although little hard evidence is available to back up such speculation. It was disclosed that excellent-quality thin films of titanium nitride can be prepared by the atmospheric pressure CVD reaction of titanium tetrachloride with alkylamines at temperatures between 350 and 600 {degrees}C. This process appeared ideal for detailed mechanistic scrutiny, since titanium tetrachloride is well-known to be highly reactive toward amines{sup 9} and because titanium should be capable of stabilizing a variety of nitrogen ligand types. In this context, we report the synthesis and characterization of two complexes that are formed in the solution-phase reactions of titanium tetrachloride with tert-butylamine. To the best of our knowledge, the first of these, a chloride-amide-amine complex, comprises the first single-source CVD precursor to high-quality gold-colored films of titanium nitride. Additionally, a monomeric imido complex has beenmore » trapped with triphenyl-phosphine oxide and has been structurally characterized. Evidence is presented from mass spectrometry for the intermediacy of imido complexes in the CVD process. The present results provide partial mechanistic insight into the sequence that leads from titanium tetrachloride and tert-butyl-amine to titanium nitride thin films. The system implies that imido complexes play an important role in other film forming processes.« less

Ti/TiN/Ti contact metallization

Abstract: The present invention concerns a method for contact metallization on a semiconductor where a contact hole is formed in an interlevel dielectric layer down to a doped silicon region on the silicon substrate, and then the wafer is placed into a sputtering chamber where titanium is sputtered onto the wafer. A titanium nitride layer is sputtered on top of the titanium layer in the contact hole. This invention saves time and money, because the titanium nitride layer depositing and titanium layer forming steps can occur in the same chamber without forming the boro-phosphorous silicate glass layer in between. The titanium layer reacts with the silicon to form a silicide layer at the time of the sputtering in a hot deposition or in later steps that supply heat to the wafer for a period of time. Optionally, an additional titanium layer can be formed on top of the titanium nitride layer to clean off the titanium target used to sputter the titanium and titanium nitride layers on the wafer. A metal layer including aluminum is then formed on top of the titanium layer or the titanium nitride layer to form the contact metallization with the doped silicon region in the semiconductor.

Increasing of the corrosion resistance of the Ti6Al4V alloy by high thickness anodic oxidation

Abstract: Oxide films with different thicknesses and electrochemical properties can be anodically formed on titanium and titanium alloys. In this work the resistance, and particularly, the passivity currents of a Ti6Al4V alloy anodized under different conditions were evaluated. The tests were performed in a physiological solution simulating the environment of the human body. A significant reduction in the passivity current and an increase of the range of passive potentials have been observed on anodized specimens. Consequently the anodic oxidation of the Ti6Al4V alloy to obtain an high thickness oxide film can be considered an important improvement in the finishing of prosthetic devices.

Infrared studies of the surface and gas phase reactions leading to the growth of titanium nitride thin films from tetrakis(dimethylamido)titanium and ammonia

Abstract: The reaction of tetrakis(dimethylamido)titanium (Ti(NMe 2 ) 4 ) with ammonia has been studied in the gas phase and on titanium disilicide, aluminum, and copper surfaces using infrared spectroscopy. In the gas phase the main product of this reaction, dimethylamine, forms rapidly even at 300 K, and a fine yellow powder is deposited on the windows of the IR cell. Under ultrahigh vacuum conditions there is no reaction between Ti(NMe 2 ) 4 and NH 3 on any of the three surfaces studied at temperature-between 300 and 650 K