Interdiffusion Of Ti Research Articles

Titanium aluminides from cold-extruded elemental powders with Al-contents of 25–75 at% Al

Titanium aluminide alloys were prepared from cold-extruded elemental Ti and Al powders with compositions ranging from 25 to 75 at % Al. The production route in this study includes four essential steps: mixing, precompaction, cold-extrusion and reaction treatment. During reaction treatment, the intermetallic phases Ti3Al, TiAl and TiAl3 are formed by interdiffusion of Ti and Al, and pore formation takes place because of the different diffusivities of Ti and Al. The processes of phase formation, as well as pore formation, were studied by means of calorimetric, dilatometric and metallographic methods. In order to obtain nearly fully dense specimens, the technique of hot isostatic pressing was applied. The sintering behaviour and microstructures of the prepared alloys are reported.

SEM and TEM/EDX analysis of model interfaces in multicomponent electroceramics

Abstract The interfaces between (Ni,Zn)Fe 2 O 4 and MgTiO 3 as well as between MgTiO 3 and RuO 2 glass—models for the interfaces in multicomponent electroceramics—have been investigated by SEM and combined TEM/EDX analysis. Under the preparation conditions involved (1400 K, 2 h), the local properties of both interfaces are mainly thermodynamically controlled. In the case of the ferrite-titanate system, a μ m thick interface is formed, consisting of a compositionally modified, cation-exchanged spinel phase, Mg 1+ x Fe 2− 2x Ti x O 4 , with x = 0·66, and a pseudobrookite phase, Mg x Fe 2− 2x Ti 1+ x O 5 , with x = 0·75. Concerning the interface properties of MgTiO 3 -RuO 2 glass, interdiffusion of Ti and Mg appears to be the dominant process below 1100 K, whereas at higher temperature several new phases can be clearly identified in the 3 and PbTiO 3 .

Study on interdiffusion of FeTi compositionally modulated films by in situ X-ray diffraction

Study on interdiffusion of FeTi compositionally modulated films by in situ X-ray diffraction

Growth and interdiffusion of ultrathin films of Ti and Ni on Mo(110)

The growth and interdiffusion of Ti and Ni on a Mo(110) surface have been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and temperature programmed desorption spectroscopy (TPD). Ti grows layer-by-layer upon deposition on Mo(110) at 115 K, whereas annealing multilayers of Ti to 900 K causes formation of Ti three-dimensional clusters. Submonolayer Ti on Mo(110), annealed to 300–700 K, induces a LEED pattern interpreted to arise from a Ti overlayer with a distorted Ti (0001) lattice. This pattern disappears upon annealing above 700 K, consistent with a phase transition from a distorted Ti (0001) lattice to a pseudomorphic structure. On a Mo (110) surface first covered with Ni and then Ti (or deposited in the reverse order), Ti and Ni interdiffuse to form a Ti-Ni compound when annealed above 300 K.

Hole trap level in Pt-Ti/p-InGaAs/n-InP heterostructures due to rapid thermal processing

Low-resistance ohmic contacts of Pt/Ti to p-InGaAs/n-InP heterostructures were formed by rapid thermal processing (RTP). Deep level transient spectroscopy and current-voltage temperature (I-V-T) measurements were used to characterize this system in order to evaluate the stability of the Pt/Ti ohmic contact and the effects of different RTP temperatures on the device performance. A new hole trap level with activation energy of 0.89 eV was found in samples treated at temperatures above 500 °C but not in those treated at lower temperatures. This trap, featured by a higher density when closer to the junction, was thought to be caused by Ti interdiffusion at high RTP temperature, in agreement with the analysis from Auger depth profiling. Four electron trap levels with activation energies of 0.61, 0.45, 0.35, and 0.30 eV were observed for all samples and believed to be native defects in InP. I-V-T measurements revealed current mechanisms independent of the RTP temperatures indicating that the new hole trap does not influence current conduction mechanisms.

Interfacial microstructure and electrical properties of the Pt/Ti ohmic contact in p-In0.53Ga0.47As formed by rapid thermal processing

The interfacial microstructure and electrical properties of the Pt/Ti ohmic contact to p-In0.53Ga0.47As (Zn: 5×1018 cm−3) formed by rapid thermal processing (RTP) were intensively studied. Significant interdiffusion of Ti, In, and As across the interface, driven by RTP, occurred at temperatures of, or above, 350 °C for a heating duration of 30 s. A minimum specific contact resistance (9.0×10−6 Ω cm2) was achieved after heating at 450 °C. Cross-sectional transmission electron microscopy of this sample revealed an interfacial reaction zone with complicated microstructure, and the dominant interfacial compound was identified to be InAs. Further increase in RTP temperature resulted in a change in the microstructure, and degradation of the contact resistance. The temperature-dependence characteristic of the specific contact resistance of as-deposited Pt/Ti contact to InGaAs revealed a thermionic-emission-dominated carrier-transport mechanism with an effective barrier height φb, of 0.13 V. RTP treatment to the sample at elevated temperatures up to 450 °C decreased the temperature dependence of the contact resistance. This phenomenon strongly suggests a partial conversion of the dominant carrier-transport mechanism across the contact area from thermionic emission to field emission. This was further verified by fitting the temperature dependence of the measured contact resistance to a phenomenological theory based on a linear combination of the two different types of carrier-transport mechanisms operating at isolated area segments distributed uniformly across the interface.

Silicidation of Molybdenum and Titanium Double Layers

Silicidation of molybdenum and titanium double layers has been investigated by measuring sheet resistance, SIMS, and Auger depth profiles. Mo/Ti, , Ti/Mo, double layers, and Ti‐Mo cosputtered layer were annealed in Ar or atmosphere with a halogen lamp annealer or diffusion furnace. Listed in increasing order of sheet resistance, they are: Mo/Ti and , , Ti/Mo, Ti‐Mo cosputtered layer. These results were explained by SIMS observations. The variations of the sheet resistance of the annealed Mo/Ti double layers with annealing temperature were divided into three temperature regions. In the low annealing temperature region, sheet resistance of the unreacted Mo layer was dominant. In the intermediate region, sheet resistance of the titanium silicide layer formed by the reaction with Ti and Si substrate was dominant. In the high annealing temperature region, sheet resistance of the molybdenum and titanium silicide mixed layer formed by interdiffusion of Mo and Ti was dominant. The Mo/Ti double layer, annealed at 800°–900°C for 20s had the lowest sheet resistance and good etching resistance towards hydrofluoric acid.

Effects of carbon content on the diffusion bonding of iron and steel to titanium.

A commercially pure titanium has been diffusion-bonded to iron and steels of various carbon contents: low carbon steel with 0.01% C (ULC), mild steel with 0.19% C (S20C) and spheroidal graphite cast iron with 3.75% C (FCD). The tensile strength of joints bonded below 900°C was hardly influenced by the carbon content, and increased with the rise in bonding temperature. Above 900°C however, the strength of the ULC/Ti joint was almost independent of the bonding temperature, that of the S20C/Ti joint decreased with the rise in bonding temperature, and that of the FCD/Ti increased. The interlayer forming along the bond interface consisted only of TiC in the FCD/Ti joint and of TiFe and TiFe2 in the ULC/Ti. Since Ti and Fe diffused over much longer distances in the ULC/Ti than in the FCD/Ti, the TiC layer may be considered to interfere with the interdiffusion of Ti and Fe, and consequently to suppress the formation of TiFe and TiFe2 which decrease the joint strength more seriously than TiC. The interlayer in the S20C/Ti consisted of TiC as well as TiFe and TiFe2. The coexisting carbide and intermetallic compounds in the interlayer seems to have more detrimental effect on the joint strength than those formed individually.

Interfacial Microstructure and Carrier Conduction Process in Pt/Ti Ohmic Contact to P-In0.53Ga0.47As Formed by Rapid Thermal Processing

ABSTRACTThe strong dependence of electrical properties of Pt/Ti ohmic contact to p–In0.53Ga0.47 As (Zn: 5 × 1018 cm−3) on the interfacial microstructure formed by rapid thermal processing (RTP) were intensively studied by transmission electron microscopy, Auger Spectroscopy, and transmission line model (TLM) measurements. The rapid decrease of the specific contact resistance with an increase in RTP temperature was correlated with the development of an interfacial reaction zone. Significant interdiffusion of Ti, In and As across the interface occurred at temperature above, 350°C for a 30 second of RTP. A minimum specific contact resistance (3.4 × 10−6 Ω-cm2) was achieved at RTP temperature of 450°C. The corresponding interfacial microstructure revealed a complicated solid state reaction zone with InAs as one of the major interfacial compounds. The low contact resistance is attributed to the carrier conduction through the InAs regions. This is also consistent with the results of Pt/Ti contact experiments to p-type InAs, InP and GaAs binary surfaces, where the lowest contact resistance was achieved on InAs (3.0 × 10−7 Ω-cm2at Zn: 5 × 1018 cm−3). The temperature dependence of specific contact resistance of as-deposited Pt/Ti contact to InGaAs agrees very well with the thermionic emission dominated carrier transport mechanism with an effective barrier height, φb, of 0.13V. The rapid decrease in the contact resistance as well as its reduced temperature dependence after RTP treatment at elevated temperatures suggesting a partial conversion of thermionic emission dominated contact area to field emission dominated regions. A phenomenological theory of multiple parrallel carrier conduction processes was proposed to analyse the temperature dependence of specific contact resistance for contacts with complicated interfacial microstructure. It was found that, for low resistance contacts, majority of the carriers conducted through only a fraction of the contact area via a tunneling mechanism.

Growth kinetics of amorphous interlayer formed by interdiffusion of polycrystalline Ti thin-film and single-crystal silicon

The growth kinetics of amorphous interlayer (a interlayerbb) in polycrystalline Ti films on single-crystal-silicon has been studied by cross-sectional transmission electron microscopy. The growth was found to follow a linear growth law initially in samples annealed at 350–425 °C. The activation energy of the linear growth was measured to be 1.6±0.3 eV. Maximum thicknesses of the a interlayers were measured to be of the order of 10 nm. The formation of an a interlayer was observed in samples annealed at a temperature as high as 600 °C. The formation and growth kinetics of a interlayers in Ti/Si and Ni/Zr systems are compared. Essential factors for the formation and growth of an a interlayer are discussed. The results represent the first report on the growth kinetics of an a interlayer in metal thin films on single-crystal silicon.

Nitriding of bulk titanium and thin titanium films in a NH3 low pressure plasma

Abstract Nitriding of bulk titanium and titanium thin films deposited on silicon was investigated under low pressure NH 3 plasma conditions. Kinetic studies of bulk titanium nitriding allowed the mechanisms of titanium nitride formation to be elucidated. The evolution of the thin surface oxide layer during the treatment was examined by means of photoelectrochemistry experiments. The mechanisms of transport of nitrogen (migration and/or diffusion) are studied for different plasma parameters and sample temperatures, using the general laws of protective layer growth. Nitriding study of thin films of titanium (1000 A) deposited on silicon substrates pointed out that two competitive processes can occur. At the Ti-plasma interface, titanium was nitrided; at the TiSi interface, titanium silicide was formed by a solid state reaction. The use of a barrier layer, SiO 2 (1 μm), enhanced nitriding of the titanium film by preventing Ti and Si interdiffusion.

Niobium-titanium superconducting wires with ultrafine filaments (A role of SC filament-matrix boundaries)

The influence of boundaries in superconducting Nb-Ti filaments in a Cu matrix upon critical current density and upper critical magnetic field is presented. The copper-matrix wires 25000 and 480000 Nb-Ti filaments. The wires were manufactured by cold deformation without any annealing. It was found that the current-carrying capacity and the magnetic hysteresis curve of these ultrafine-filament wires are determined by the fluxoid pinning on the Nb-Ti filament-matrix boundaries. The pinning can be reduced by interdiffusion of Cu and Ti.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Schottky-barrier behavior of a Ti-W alloy on Si(100)

The Schottky-barrier height of a Ti-W alloy of 23 at. % Ti concentration, on both n-type and p-type Si(100), has been measured in the temperature range 170–295 K using current-voltage technique. Auger electron spectroscopy/depth-composition profiling, Rutherford backscattering spectroscopy, and glancing-angle x-ray diffraction were used to monitor the reaction between the alloy and Si. The results showed that the interdiffusion of Ti and Si dominates the interfacial reaction in this alloy-Si (100) system. Further, Ti rather than W dominated the barrier height. The n- and p-type barrier heights for both the metal and the silicide phase were found to decrease with increasing temperature with the sum equal, within the experimental error, to the Si indirect energy gap at any measured temperature. These results indicate that the change in barrier heights with temperature are mainly due to the temperature dependence of the indirect energy gap in Si. Further, the temperature coefficients of the n- and p-type barrier heights were found to be the same within the experimental error, and they were approximately equal to one-half the temperature coefficient of the Si indirect gap, consistent with the predictions of a recent model of barrier formation based on Fermi-level pinning in the center of the indirect gap.

鉄鋼のチタンとの拡散接合性に及ぼす炭素の影響

A commericially pure titanium has been diffusion-bonded to iron and steels of various carbon contents ; low carbon steel with 0.01%C(ULC), mild steel with 0.19%C(S20C) and spheroidal graphite cast iron with 3.75%C(FCD). The tensile strength of joints bonded below 900°C was hardly influenced by the carbon content, and increased with the rise in bonding temperature. Above 900°C, however, the strength of the Ti-to-ULC joint showed a constant value, that of the Ti-to-S20C joint decreased, and that of the Ti-to-FCD increased with the rise in bonding temperature. The interlayer forming along the bond interface consisted only of TiC in the Ti-to-FCD joint and of TiFe and TiFe2 in the Ti-to-ULC. Since Ti and Fe diffused over much longer distances in the Ti-to-ULC than in the Ti-to-FCD, the TiC layer may be considered to interfere with the interdiffusion of Ti and Fe, and consequently to suppress the formation of TiFe and TiFe2 which decrease the joint strength more seriously than TiC. The interlayer in the Ti-to-S20C consisted of TiC as well as TiFe and TiFe2. The coexisting carbide and intermetallic compounds in the interlayer, seems to reduce the joint strength to a more extent than those formed individually.

Schottky-barrier height of a Ti-W alloy on n-type and p-type Si.

Impurity effects on Schottky barriers have been investigated using a concentrated Ti-W alloy for barrier-height measurements on both n-type and p-type Si(100). The measurements were performed in the temperature range 175\char21{}295 K using forward current-voltage characteristics. Silicide-formation reaction was monitored by Rutherford backscattering spectroscopy, Auger-electron spectroscopy, and glancing-angle x-ray diffraction. The results showed that Ti dominates the barrier height, and that W does not play any role in barrier formation. The interdiffusion of Ti and Si dominated the reaction between the alloy and Si at the interface. For both the metal and the reacted silicide phase the n- and p-type barrier heights were found to decrease with increasing temperature with the sum equal, within the experimental accuracy, to the indirect energy gap of Si in the range of temperature measured. These results indicate that the temperature dependence of the barrier heights is mainly due to that of the indirect energy gap in Si.

Thermal stability of Al–Si/TiSi2/Si Schottky diodes

We have examined the thermal stability of Al–Si/TiSi2/Si Schottky diodes both with and without a sputter-deposited W–Ti (10 wt. %) diffusion barrier after furnace annealing up to 550 °C, 30 min. The diodes having the diffusion barrier exhibit stable Schottky barrier heights up to 550 °C, 30 min. In contrast, after 450 °C, 30 min annealing, diodes which do not have a diffusion barrier exhibit Schottky barrier heights typical of Al/n-Si. Metallurgical interactions have been investigated by He backscattering spectroscopy which shows a stable W–Ti/TiSi2 interface up to 550 °C, 30 min annealing in samples having the diffusion barrier. The samples without a diffusion barrier show evidence of Al–Ti interdiffusion after 450 °C, 30 min annealing. Residual gas incorporation in the barrier layers was investigated by Ar ion sputter-depth profiling Auger electron spectroscopy. Sheet resistance measurements and x-ray diffraction analysis were used to investigate intermetallic phase formation. Selective wet etching combined with scanning electron microscopy were used to determine morphological changes at the TiSi2/Si interface as a result of annealing.

Hot wall experiment in Microtor II

Panels made out of 304 SS, Mo, Inconel 600, α-Ti and Ti6A14Mo were installed on the outer walls in Microtor II and heated up to a maximum temperature of 800°C. No significant H α-light emission was observed near the hot panels during tokamak discharges. When carefully outgassed and properly surface conditioned (Ti deposition and discharge cleaning), these hot surfaces do not have a deleterious impact on tokamak discharges. Carbon originating from the bulk materials is the most abundant impurity that accumulates on the hot surfaces. Ti layers at 800°C are able to retain bulk oxygen, but carbon can diffuse out of the substrate materials and through the film to segregate at the Ti-vacuum surface. Inconel 600 substrates released the smallest amount of carbon during discharges. Impurity control with Ti, deposited onto cold panels, remains beneficial even at higher temperatures. Previously observed long term effects such as flaking and peeling are avoided due to interdiffusion of Ti and the panel matrix. Furthermore, hydrogen retention is eliminated.

Diffusion in the titanomagnetite solid solution series

AbstractIn order to be able to use the nature and scale of the exsolution microstructures developed in titanomagnetites as quantitative indicators of thermal history, it is necessary to have available accurate diffusion data for the system. Diffusion data for pure magnetite and Ti-poor titanomagnetites are available, but no data for diffusion in the centre of the solid-solution series exist. In order to obtain values for the activation energy (ΔE) and the pre-exponential factor (D0) for the interdiffusion of Fe and Ti in ulvöspinel-rich titanomagnetites, the natural microstructures developed in titanomagnetites from the Taberg intrusion, Sweden, were homogenized over a range of temperatures from 490 to 730 °C. From the model describing homogenization, values of 49.8 kcal mole−1 and 2.38 × 10−3 cm2 s−1 were calculated for ΔE and D0 respectively. Although the results obtained from these homogenization experiments are slightly less accurate than those which could be obtained by more conventional methods, the homogenization technique has several advantages which outweigh this drawback, namely the ease with which the experiment can be performed and the fact that the diffusion data can be obtained at significantly lower temperatures than is usually possible with more conventional methods.

Studies on the Al2O3−Ti−Mo−Au metallization system

The behavior of Ti−Mo−Au metallization on Al2O3 and C has been investigated by backscattering spectrometry. Results show that Mo−Au bimetal films typically mix during deposition. Diffusion of Ti in Mo film occurs at 600°C, but is inhibited by the presence of oxygen in the Ti film. Even 1000 Å of Mo is not a barrier against interdiffusion of Ti and Au during 20−min anneals at 600°C. The amount of mixing observed also depends on the nature of the substrate which supports the Ti−Mo−Au metallization.