Tantalum Layer Research Articles

Electrolytic stent in the normal bile duct. An experimental study.

To evaluate and compare changes in the bile-duct wall after the insertion of electrolytic and nonelectrolytic stents. The electrolytic stents were composed of 3 different layers (iron, isolating polyethylene and tantalum) and were implanted surgically in the bile duct of 8 healthy pigs. The nonelectrolytic stents were also composed of 3 layers (2 layers of tantalum and an isolating layer of polyethylene) and were implanted surgically in the bile ducts of 9 healthy pigs. After an observation time of 8 weeks, the pigs were killed and the bile ducts were excised and sent for histopathological examination. One pig was killed after the procedure owing to postoperative complications; all the other pigs survived without complications. Migration of the stent to the bowel occurred in 4 pigs. A slight inflammatory reaction was seen at histopathological examination in 6 pigs with the electrolytic stent and in 6 pigs with the nonelectrolytic stent. There was no difference in the specimens from pigs with electrolytic and nonelectrolytic stents. The electrolytic stents did not cause more changes in the normal bile-duct wall than the nonelectrolytic stents.

Preparation of oxygen evolving electrodes with long service life under extreme conditions

Among the numerous base metals tested for DSA® type electrodes (e.g., titanium and its alloys, zirconium, niobium etc.), tantalum is a potentially excellent substrate owing to its good electrical conductivity and corrosion resistance, and the favourable dielectric properties of its oxide. Nevertheless, a DSA® type electrode fabricated on a tantalum substrate would be very expensive due to the high cost of the metal. To prepare an anode combining the excellent properties of tantalum at reasonable price, a new material has been developed in our laboratory. This consists of a common base metal (e.g., Cu) covered with a thin tantalum coating. This tantalum layer was obtained by molten salt electroplating in a LiF–NaF–K2TaF7 melt at 800°C. Thus, an anode of the type Metal/Ta/Ta2O5–IrO2 with a surface load of 22gm-2 IrO2, submitted to the severe test conditions used in this work, exhibits a standardized lifetime tenfold greater than one made with ASTM grade 4 titanium base metal. Thus, this type of electrode might be advantageously employed as an oxygen evolution anode in acidic solutions.

Solitons on vortex filaments generated by ns laser pulse on metal surface

Laser-induced vaporization in the nonstationary (oscillatory) regime, on the ns time scale, that generates the nonlinear dynamics of the molten surface layer of tantalum, was studied. Microscale vortex filaments with the cascade of splittings raise up the bushlike structure. The cascade of vortex filament angle-locking splittings was shown to represent the period doubling bifurcation to chaos. Torsion of the filaments generates two-dimensional solitons in the side zones of the bush and three-dimensional solitons in the central zone. Two-dimensional solitons are obtained from a modified Korteweg–de Vries equation, while three-dimensional ones are obtained from nonlinear Schrödinger equation. The surface dynamics associated with metal vaporization appears to be more complex than usually assumed.

Dominant diffusing species during cobalt silicide formation

The dominant moving species during cobalt monosilicide and cobalt disilicide formation has been examined using a thin tantalum layer as a metal marker. The marker data obtained following the formation of CoSi from Co2Si showed that monosilicide growth was essentially due Si diffusion only. When used to study CoSi2 formation, the data indicated that silicon was also the dominant moving species during disilicide formation, although a noninsignificant amount of cobalt diffusion was also observed to take place.

Technique for the growth of metal coatings by ion implantation

Abstract Ion implantation of metals and non-metals is a recognized method for creating surface alloys and buried layers with unique and desirable properties. However, surface sputtering during implantation limits the maximum achievable atomic concentration to the point at which implanted atoms are sputtered away at the same rate as those being added. Since surface properties are often concentration dependent, the restriction of the maximum to less than the few tens of atomic per cent usually observed is a major constraint. A simple technique is described to produce an effective sputtering rate approaching zero by codepositing a sacrificial coating at a rate that just equals sputtering losses. This permits arbitrary surface alloy concentrations, allowing new uses for the existing base of ion implantation technology. A specific demonstration of the procedure has been made for ion implantation of tantalum into both M50 bearing steel and D2 tool steel. A buried layer of tantalum with a peak concentration between 50 and 60 at.% was achieved.

On-line monitoring of monoclonal antibody production with regenerable flow-injection immuno systems

In this paper two systems for the observation of the production of mouse-IgG during the cultivation of hybridoma cells in a perfusion reactor are presented. The direct immunosystem is based on the detection of changes in capacitance of a dielectric layer (tantalum oxide) on a metal surface (tantalum) when antibodies bind to immobilized anti-antibodies. The sensor consisted of a 25 nm tantalum oxide layer, electrochemically grown onto a laser patternized 1 μm thick tantalum layer. The indirect system is based on an automated fluorimetric sandwich ELISA system with β-galactosidase conjugated secondary antibodies. Two cultivations of mouse hybridoma cells in a 2-1 perfusion reactor were performed. The first cultivation was monitored with the capacitance system, the second cultivation was monitored with the fluorimetric system.

Behaviour of adsorbed oxygen during rapid electron-beam heating of Ta/Ti bilayers on single-crystal silicon

Silicidation of thin films of Ta/Ti bilayers on silicon substrates, in the temperature range 750–1000 °C, using rapid electron-beam heating is described. The redistribution of adsorbed oxygen in the metal films and its effect on the formation of the suicide is examined. It was found that the silicidation of the bimetallic films proceeded sequentially. First titanium and then tantalum layers were converted into their respective suicides. During the growth of titanium disilicide, adsorbed oxygen moved to the interface between the unreacted tantalum film and the grown titanium disilicide, where it formed a thin layer of silicon dioxide. The silicon dioxide barrier inhibited silicon diffusion and the tantalum layer only converted to suicide at temperatures higher than 750 °C which were maintained for a few seconds.

A study of transmission of multilayer thin-film X-ray guides

Abstract A study has been made of excitation of X-ray waveguide modes in thin-film X-ray guides. X-ray radiation was excited in a silicon bremsstrahlung target by a beam of 100 keV electrons and directed to an end face of a 250-layer thin-film X-ray guide consisting of alternating layers of tantalum and aluminium. Measurement was made of the angular distribution of photons passed through the X-ray guide.

Tantalum as a diffusion barrier between copper and silicon: Failure mechanism and effect of nitrogen additions

The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross-section transmission electron microscopy. Ta prevents Cu-silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η″-Cu3Si precipitates at the Ta-Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal-TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta-Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen-alloyed Ta is a very similar diffusion barrier to Ta. It was found that Ta2N is a more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 650 °C for 30 min. In this case, local Cu-Si reaction occurs along with the formation of a uniform Ta5Si3 layer at the Ta2N-Si interface.

Investigation of Ti/Al 2O 3 joints with intermediate tantalum and niobium layers

The microstructure of TiTa30 alloys diffusion bonded to a 99.7 wt% AI 2O 3 ceramic was subdivided into a reaction double layer containing the intermetallic phases TiAl and Ti 3AI and the (a + β) Ti microstructure. Excellent fracture toughness data of the TiTa30/AI 2O 3 joints of about 37 J/m 2 were obtained after welding at 1200°C for 1 h. The fracture energies of the joints were strongly dependent on the welding temperature which also influenced the thickness of the reaction double layer. The uptake of aluminium and oxygen into the reaction layer and the metal caused an embrittlement and decreased the yield stress and ductility of the metal. Introducing an Nb or Ta layer between pure Ti and AI 2O 3 before welding resulted in high fracture energies of 40 J/m 2 for the Ti/AI 2O 3 joints. The thermal-induced stresses at the metal-ceramic interface were reduced by the occurrence of an Nb- or Ta-enriched region. The intermediate metal foils also decreased the O and AI uptake of the metal and therefore reduced the brittleness of the reaction zone and the adjacent metal. The thermal-induced stresses at the metal-ceramic interface caused a deflection of the crack into the ceramic during fracture mechanical testing in four-point bending.

Tungsten and tantalum diffusion barriers for metal-in-gap magnetic heads

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Magnetic and structural properties of permalloy-tantalum multilayer thin films

This work describes a detailed investigation into the magnetic and structural properties of permalloy-tantalum multilayered thin films produced by vacuum evaporation. Their microstructure was investigated using high-resolution TEM and the magnetic properties were measured with vibrating-sample and vibrating-reed magnetometers. The results show a reduction in coercivity for the multilayer films which is independent of the number of layers but depends strongly on the magnetic layer thickness. The tantalum layer is shown to be continuous and microcrystalline down to 25-Å thickness, but the interface between the layers is irregular and may give rise to additional magnetostatic coupling as the tantalum layer thickness is reduced.

Quantitative X-ray analysis of interdiffusing Ta/Si multilayer structures

Multilayers of amorphous tantalum and silicon form a synthetic one-dimensional lattice which can be observed by a sequence of intense low angle X-ray diffraction peaks. Annealing a Ta/Si multilayer structure of 20 layer pairs, each layer pair consisting of nominally 4 nm thick tantalum and 7 nm thick silicon layers, leads to rapid diffusion of silicon into the tantalum layers forming a homogeneous TaSi x solution. The thickness of the pure silicon layers decreases linearly with increasing annealing temperature. The width Δ t of the transition layers between the silicon and the TaSi x layers is analysed by comparing the measured absolute reflectivity of the multilayer structure with calculated data up to the 10th diffraction order. The computational approach is based on the Fresnel equations and assumes a linear composition profile at the interface leading to a trapezoidal lattice structure. An upper limit value of 0.7 nm for the interface width is estimated. The interdiffusion is complete at T = 540°C, indicated by the breakdown of the multilayer structure.

Field emission from metal-coated silicon tips

Microfabrication processes previously described by D. Stephani and J. Eibl (1989) were refined and used to fabricate silicon tips coated with layers of titanium, tantalum, or platinum using physical vapor deposition techniques. The emphasis was upon creating tips with a large ratio of length to diameter. The emission properties of various groupings of emitters thus formed were investigated using an accurately positioned counterelectrode. The counterelectrode was made of tungsten coated with nickel and had a well-defined tip geometry. Measurements were performed on individual groups of one, four, or nine field emitters. Fowler-Nordheim plots were made for a variety of coating materials, emitter-to-electrode spacings, and tip geometries. It is concluded that, for many applications, tip optimization should not be aimed solely at the achievement of high field strengths but that the emitting area should also be as large as possible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tantalum as a diffusion barrier between copper and silicon

We have investigated the effectiveness and failure mechanism of thin tantalum layers as diffusion barriers to copper. 50 nm tantalum films were sputtered onto unpatterned single-crystal 〈100〉 Si wafers and overlaid with 100 nm Cu. Material reactions in these films were followed as a function of annealing temperature by in situ resistance measurements, and characterized by Rutherford backscattering spectroscopy and cross-section transmission electron microscopy. While pure Cu on Si reacts at 200 °C, the Ta film prevents Cu silicon interaction up to 600 °C. At higher temperatures, reaction of the Si substrate with Ta forms a planar layer of hexagonal TaSi2. Cu rapidly penetrates to the Si substrate, forming η″-Cu3Si precipitates at the Ta-Si2-Si interface.

Direct observation of anodic film growth on superimposed aluminium and tantalum metallic layers

Abstract A direct electron optical study has been made of anodic film growth on substrates comprising a tantalum layer superimposed on aluminium and the reverse situation (i.e. an aluminium layer superimposed on tantalum). To achieve the latter, the system comprised an ion-plated aluminium layer superimposed above a tantalum layer which had been ion-plated initially onto an electropolished aluminium substrate. For the tantalum-above-aluminium situation, observations of ultramicrotomed anodic film sections revealed a dark band in the outer region of film, consistent with the initial development of an anodic tantalum oxide followed by uniform anodizing of aluminium to form the usual anodic alumina film material. In the case of aluminium superimposed above tantalum, direct observation clearly showed the development of tantalum oxide fingers which penetrated the initially formed anodic alumina to different extents. The non-uniform tantalum oxide film growth may ultimately short-circuit the alumina and result ...

Quadrupled nondestructive outputs from magnetoresistive memory cells using reversed word fields

A new operating mode has been discovered in transverse magnetoresistive (MR) memory cells which increases the usable nondestructive sense output by more than a factor of 4 over the original mode described, which employed a unipolar word field. The new mode allows for increased cell density, decreased memory access time, and increased margins. This new operating mode was examined experimentally and analytically for experimental cells ranging in size from 1.5×5 μm to 1.8×18 μm. The MR material used in the cells consisted of two 150-Å-thick magnetic layers (65% Ni, 15% Fe, 20% Co) separated by a 50-Å-thick reacted tantalum layer to break the exchange. In the new operating mode, a word field of one polarity is used for writing (parallel to the edge magnetization) and a reversed polarity is used for reading. During the reading process, 120°–225° paired ‘‘walls’’ are formed at the edges. The energy in the walls is sufficient to restore the elements to their original states even if switching occurs (in a direction opposite to the normal rotation during writing). The operating margins are improved because while reading only one and not both the word field and the sense field are in a direction to cause normal switching.

Tantalum and Tantalum Nitride as Diffusion Barriers Between Copper and Silicon

ABSTRACTWe have investigated the effectiveness of thin tantalum layers as diffusion barriers to copper. Fifty nm Ta films were sputtered onto unpatterned single crystal Si wafers and overlaid with 100 nm Cu. Material reactions in these films were followed as a function of annealing temperature by in-situ resistance measurements, and characterized by by Rutherford Backscattering and cross-section TEM. The effect of the incorporation of nitrogen was explored by reactively depositing Ta(5 at.% N) and Ta2N. Pure Ta prevents Cu - silicon interaction to at least 600 °C. At higher temperatures, reaction of the Si substrate with Ta forms a planar TaSi2 layer. Cu rapidly penetrates to the Si substrate, forming Cu silicide precipitates at the TaSi2 - Si interface. A study performed on the Si/Ta(N)/Cu film had very similar results. Ta2N is an even more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 700 °C.

Sputter deposition of thin tantalum layers and low temperature interactions between tantalum and SiO 2 and tantalum and silicon

Tantalum layers were sputter deposited, in a d.c. triode system, onto SiO 2 or silicon substrates to examine the chemical nature of the interactions between tantalum and SiO 2 or silicon for low temperatures of substrate heating during deposition (50–500 °C). The thick tantalum layers (700 nm) deposited onto various substrates were amorphous when grown at 50 °C and polycrystalline when grown at 500 °C. In addition, X-ray diffraction showed that the crystallites of the tetragonal β-Ta phase had a preferential orientation on smooth substrates. The resistivity of these tantalum layers (around 200 μΩ cm) was independent of their structural state. Analysis by Auger electron spectrometry (AES) of the thin tantalum layers (35 nm) deposited at 500 °C or 50 °C onto oxidized SiO 2/Si substrates showed the presence, in the TaSiO 2 interface region, of silicon or tantalum silicide (TaSi x ) and suggested a reduction of SiO 2 by tantalum with formation of tantalum oxide (TaO y ). AES depth profiles of the thin tantalum layers deposited onto Si(111) substrates at 500 °C showed that the interaction between tantalum and silicon was consistent with a short-distance diffusion of silicon into tantalum (2–3 nm), irrespective of the etching process (chemical etching or in situ ion etching) and the deposition time. In addition, the shape of the silicon Auger peak for the TaSi interface region showed the presence of TaSi bonds and suggested the local formation of a TaSi x phase as a result of the short-distance diffusion of silicon.

Silicon transport in sputter-deposited tantalum layers grown under ion bombardment

Tantalum was sputter deposited on (111) Si substrate under low‐energy ion bombardment in order to study the effects of the ion energy on the silicon transport into the Ta layer. The Si substrate was heated up to 500 °C during growth. For ion energies up to 180 eV silicon is not transported into tantalum and the growth temperature has no effect. An ion bombardment energy of 280 eV enhances the transport of silicon throughout the tantalum layer. Growth temperatures up to 300 °C have no effect on the silicon transport which is mainly enhanced by the ion bombardment. For growth temperatures between 300 and 500 °C, the silicon transport is also enhanced by the thermal diffusion. The experimental depth distribution of silicon is similar to the theoretical depth distribution calculated for the case of an interdiffusion. The ion‐enhanced process of silicon transport is characterized by an activation energy of 0.4 eV. Silicon into the layers as‐grown at 500 °C is in both states, amorphous silicide and microcrystal...