High-temperature Vacuum Annealing Research Articles

Interface-engineered YBCO edge junctions

We have fabricated all YBCO edge junctions which do not require the deposition of an interlayer or barrier material. Rather, through appropriate high-temperature vacuum annealing and in-situ ion plasma treatments, we have modified the junction interface in such a way as to lead to reliable weak link behavior. These devices display RSJ-type I-V characteristics with excellent magnetic field modulation. I/sub c/R/sub n/ values over the range 0.5 to 3 mV and corresponding R/sub n/A values of 6/spl times/10/sup -8/ to 1.2/spl times/10/sup -9/ /spl Omega/-cm/sup 2/ at 20 K are easily attained by varying the process, which is not possible in most high-T/sub c/ junction technologies. These junctions can also be very uniform and appear to be quite stable. We have observed an unusual response to applied microwave radiation. We have investigated the microstructure of these junctions using transmission electron microscopy (TEM). Results of these analyses lead us to believe these junctions are feasible as the basic components of a high-T/sub c/ circuit technology.

Influence of reduction on the behavior kinetics of optical inhomogeneities in LiNbO3 single crystals

An investigation was made of the influence of high-temperature annealing in vacuum on the optical homogeneity of LiNbO3 single crystals. It was observed that the residual light transmission decreased appreciably and the temperature dependence of this parameter almost completely disappeared.

Conducting properties and structure of nonstoichiometric orthorhombic phase of YBa2Cu3O7−x obtained by high-temperature vacuum annealing

Neutron and x-ray diffraction studies are carried out which show when the orthorhombic phase of YBa2Cu3O7−x (x≈0.02) is heat treated at temperatures of 430–550 K under tunnel high-vacuum pumping, a partial emission of oxygen from the O(1) positions (with coordinates 0;0;0.1578) and O(4) positions (with coordinates 0;1/2;0) occurs with no change in the symmetry or in the unit cell parameters. The temperature dependence of the electrical resistivity in the temperature interval 77–300 K shows a semiconducting character.

A Low Temperature Silicon‐on‐Insulator Fabrication Process Using Si MBE on Double‐Layer Porous Silicon

A series of low temperature processes incorporated in the silicon on insulator (SOI) formation using Si molecular beam epitaxial growth on porous silicon dramatically reduces the impurity ramp‐up from the porous silicon substrate and lowers the doping level in the epitaxial Si layer. A double‐layer porous silicon system with a spongy microstructure layer on top of a dendritic microstructure layer was fabricated on a moderately doped p‐type Si wafer using a two‐step anodization process, and was used as the substrate for Si epitaxy. An extended low temperature annealing in high vacuum was found to be helpful in stabilizing the porous silicon and making it less susceptible to microstructure change during the subsequent heat‐treatment. Prior to epitaxy, a Ge‐beam treatment was used to lower the temperature necessary for the Si surface cleaning. A low temperature preoxidation process stabilized the porous silicon during the subsequent high temperature oxidation. The choice of a moderately doped substrate and all these low temperature processes helped to achieve a Si epitaxial layer doping of 6 to , which is very close to meeting the requirement for direct device fabrication in the SOI without any additional doping compensation.

Crystal growth and preparation of colourless MgNb 2O 6 single crystals

MgNb 2O 6 single crystals of several cubic centimetres have been grown by the Czochralski technique. The as-grown black crystals were annealed in oxygen at high temperature and became transparent. The process was reversible by high temperature vacuum annealing. The optical absorption observed in as-grown samples has been attributed to oxygen deficiency of the crystal. The grown crystals were resistant against strong mineral acids. The surface tension of the molten material was 0.35 N/m.

Surface enrichment of niobium on Inconel 718 (100) single crystals

The surface composition of an Inconel 718 (100) single crystal was investigated by X-ray photoelectron spectroscopy over the temperature range 300 to 1000 K in ultra-high vacuum (UHV). The surface composition of an ion etched surface closely resembled the bulk alloy composition determined by atomic absorption spectroscopy. The composition of the ion etched surface remained close to the bulk composition until the temperature was raised above 800 K. At temperatures above 800 K, a dramatic enrichment of surface niobium (Nb) occurred. The extent of Nb enrichment was highly influenced by the presence of trace amounts of surface or subsurface oxygen. Numerous cycles of ion etching and annealing led to nearly complete removal of oxygen from the surface and subsurface region. Surface enrichment of Nb at high temperatures on these oxygen-free surfaces was greatly reduced. However, extensive Nb enrichment could be easily reintroduced by pre-exposure of the surface to oxygen prior to high-temperature vacuum annealing. The evolution of CO during the high-temperature anneal suggested that oxygen attack of the Nb carbide particles played a role in the mechanism of surface enrichment.

Structural analysis of the beta -SiC(100)-c(2 x 2) surface reconstruction by automated tensor low-energy electron diffraction.

The atomic structure of the \ensuremath{\beta}-SiC(100)-c(2\ifmmode\times\else\texttimes\fi{}2) surface was analyzed using dynamical calculations of low-energy electron-diffraction intensities. The c(2\ifmmode\times\else\texttimes\fi{}2) surface was prepared in ultrahigh vacuum by two different methods. The first utilized the removal of surface silicon by high-temperature annealing in ultrahigh vacuum. The second route utilized the deposition of surface carbon by exposing the stoichiometric (2\ifmmode\times\else\texttimes\fi{}1) surface at 1125 K to ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$. Our results showed that both methods produced a surface terminated with ${\mathrm{C}}_{2}$ groups in staggered silicon bridge sites. Weak silicon dimer bonds were found in the second atomic layer of the c(2\ifmmode\times\else\texttimes\fi{}2) surface produced by silicon sublimation, but not for the c(2\ifmmode\times\else\texttimes\fi{}2) surface produced by ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$ exposure. We postulate that hydrogen, released by the thermal decomposition of ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$, saturated silicon dangling bonds in the second atomic layer, suppressing dimer formation.

Void formation upon annealing of shaped sapphire crystals

Shaped sapphire crystals were grown from the melt by the Stepanov (EFG) technique. High-temperature vacuum annealing of crystals grown in a reducing atmosphere, performed by employing graphite elements in the heater unit of the crystallization chamber, led to the formation of voids of two different types: (1) well-faceted voids which are the result of vacancy coagulation and (2) pores of irregular form which decorate the subgrain boundaries. The formation of these defects may be prevented by suppressing the interaction between the alumina melt and carbon.

The effect of surface sulfur on the oxidation of zirconium

In order to examine the effect of surface sulfur on the oxidation of zirconium, we have tried to make a quantitative analysis of sulfur segregation on Zr and made a study of the oxidation of sulfur segregated Zr. Depth profiles of the S-segregated Zr surface determined after high temperature annealing in vacuum show that the saturated surface concentration of sulfur has an S/Zr atomic ratio of about 1 and the total amount of segregated S is about 1 monolayer. These values do not depend on the annealing time. The S-segregated surface is exposed to an oxygen atmosphere in a pressure range of 10 −6−10 −5 Pa up to a total exposure of 9000 L at RT. Changes of the surface concentration of S, O and Zr are monitored by in situ AES analysis. Depth profiling of O, S and Zr for the oxidized specimen is also carried out. Surface oxidation is clearly delayed by segregated sulfur. This effect, however, is not so significant as for the SFe system, and three oxidation stages are clearly distinguished in the same manner as in the oxidation of clean Zr surfaces. This is because S is simultaneously oxidized and removed in the form of a volatile oxide such as SO or SO 2.

The effect of surface sulfur on the oxidation of zirconium

Abstract In order to examine the effect of surface sulfur on the oxidation of zirconium, we have tried to make a quantitative analysis of sulfur segregation on Zr and made a study of the oxidation of sulfur segregated Zr. Depth profiles of the S-segregated Zr surface determined after high temperature annealing in vacuum show that the saturated surface concentration of sulfur has an S/Zr atomic ratio of about 1 and the total amount of segregated S is about 1 monolayer. These values do not depend on the annealing time. The S-segregated surface is exposed to an oxygen atmosphere in a pressure range of 10 −6 −10 −5 Pa up to a total exposure of 9000 L at RT. Changes of the surface concentration of S, O and Zr are monitored by in situ AES analysis. Depth profiling of O, S and Zr for the oxidized specimen is also carried out. Surface oxidation is clearly delayed by segregated sulfur. This effect, however, is not so significant as for the SFe system, and three oxidation stages are clearly distinguished in the same manner as in the oxidation of clean Zr surfaces. This is because S is simultaneously oxidized and removed in the form of a volatile oxide such as SO or SO 2 .

Annealing and Strain Effects on Tl-Ba-Ca-Cu-O Crystals and Ceramics

ABSTRACTSuperconducting transition temperatures (Tc'S) in the Tl-Ba-Ca-Cu-O system are shown to be a function of processing for both single crystals and bulk ceramics. Crystals with the identical structural phase and nominal composition but slightly different lattice constants can have significant differences in Tc. We report the effects of high temperature annealing in vacuum or flowing oxygen on Tc for single crystal plates of two common phases with nominal stochiometries Tl2Ba2Ca1Cu2O8 and Tl2Ba2Ca2Cu3O10. Contradictory results on nominally similar crystals suggest that strain, Tl content and TI/Ca site disorder are as important as the oxygen stoichiometry in determining Tc This interpretation is supported by complementary annealing studies in bulk ceramic, including a powder where Tc increased by 5 K following high-pressure shock loading which introduced substantial residual strain.

Xps Analysis of the Sapphire Surface as a Function of High Temperature Vacuum Annealing

ABSTRACTFor the first time the (1102) surface of sapphire has been investigated by X-ray photoelectron spectroscopy to ascertain chemical changes resulting from annealing in vacuum at 1300° C and 1450° C. As received substrates had a substantial surface C contaminant. For substrates that were chemically cleaned before inserting them into the MBE system no trace of carbon is detected. A residual flourine contaminant results from the cleaning procedure and is desorbed by the vacuum annealing. Spectra of annealed substrates are compared to the unannealed chemically cleaned substrates. The annealed substrates exhibit 0.4 to 0.5 eV shift to higher binding energy of the Al peak and a 0.3 eV shift to higher binding energy of the O peak. In addition, a 2% depletion of oxygen from the surface occurs.

Increasing the heat resistance of vanadium by siliciding

The purpose of this article was to evaluate the influence of modifier metals on the protective properties of silicide coatings in heating of vanadium in air and also on the mechanical properties of type VnM-2 unalloyed vanadium and VTsU alloy. Coatings were produced by diffusion impregnation from molten sodium with silicon or silicides of the modifying elements. The silicides of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, chromium, tungsten, rhenium, and nickel were investigated using x-ray spectrometric and hardness investigations and x-ray diffractometric analysis. The protective properties of the coatings were determined from the relative change in weight of the samples with and without coatings during isothermal oxidation in air at 1073/sup 0/K and also by differential thermal analysis. The influence of the coating on the mechanical properties of the material was also investigated using a borosilicide coating. High-temperature vacuum annealing was assessed as a method for restoring the plastic properties and relieving the stresses of vanadium and VTsU alloy subsequent to coating.

Anomalous fading of thermoluminescence in oligoclase

Abstract In a discussion of the TL properties of meteorites Hasan et al. (1986) suggested that anomalous fading is only exhibited by those samples in which the feldspar is in the low-temperature form. They further suggested that the fading proceeded via tunnelling. This study tests the above hypotheses. A low/high-form phase change in oligoclase is induced by high-temperature vacuum annealing and the fading properties of the two forms so-produced compared. The TL decay is also analysed using both the tunnelling model and the localised transition model, recently proposed by Templer (1986a, b). The data indicate that both the low-temperature and the high-temperature forms of the oligoclase samples examined display anomalous fading. The properties of the fading are not consistent with tunnelling. Instead the qualitative features are well explained by the localised transition model. Quantitative agreement is not obtained, however. This is probably due to the use of an unrealistic energy level distribution in the localised transition model calculations.

Highly transparent and conducting zinc oxide films deposited by activated reactive evaporation

Highly transparent and conducting undoped zinc oxide films have been obtained with a best resistivity of ∼1.1 × 10-3 Ω cm, a carrier density of ∼1.5 × 1020 cm−3 and a mobility of ∼38 cm2V−1s −1. These were produced by activated reactive evaporation at a deposition rate of 2 to 8A/s with a substrate temperature ≤200° C. The films deposited by this process were found to have resistivities that were thickness independent and also were relatively insensitive to deposition parameters. In terms of conductivity, it was found that films deposited at higher temperatures (T > 300°+ C) were always inferior to the films deposited below 200° C. High temperature vacuum annealing (350° C) significantly degraded the resistivity of the undoped films deposited at low temperature; this was attributable to a drop in both the electron concentration and the mobility. Aluminum doping was found to be able to stabilize the electron concentration while the drop in mobility was found to be related to the choice of substrate.

Morphological degradation of TiSi2 on 〈100〉 silicon

Evidence of instability of TiSi2 layers during high-temperature high vacuum annealing has been observed. Rutherford backscattering and scanning electron microscopy measurements showed that at high vacuum annealing conditions, the laterally homogeneous silicide layer breaks up into islands. In between these TiSi2 islands, growth of an epitaxial silicon layer was observed.

Electron microscopic and AES studies on thin layers of NiCr

In order to understand the parameters affecting the properties of NiCr resistors prepared by various methods, the annealing properties of NiCr thin films were studied. TEM and electron diffraction were used to determine the structure of the films deposited onto SiO x coated microgrids, while electrical measurements and AES indepth profiling were carried out on the samples deposited under identical conditions onto silica substrates. The effect of a SiO x protective coating on the structural changes was investigated during high temperature annealing in vacuum. In the NiCr samples annealed without a protective layer the selective oxidation of chromium led to a rather metallic type of conduction, while in the protected samples the stabilization of the conduction was observed after the same annealing. By hindering oxidation and surface diffusion processes the protective layer resulted in the development of a more stable structure in the NiCr films.

Chromium depletion from stainless steels during vacuum annealing

AbstractDuring selective chromium Oxidation of stainless steels the changes in chromium concentration at the metal surface and in the metal have an important bearing on the overall oxidation performance. It has been proposed that an analogue of chromium behaviour during selective oxidation is obtained from volatilisation of chromium during high temperature vacuum annealing. In the present report the evaporation of chromium from 316 type of steel, vacuum annealed at 1000 °C, has been investigated by menas of energy dispersive X‐ray analysis and by neutron activation analysis. It was established that chromium loss from austenitic stainless steels is rate controlled by interdiffusion in the alloy. As predicted the chromium concentration at the metal surface decreased with increasing vacuum annealing time. The chromium depletion profile in the metal was in good agreement with the previously derived model apart from an anomalous region near the surface. Here the higher resolution of the neutron activation technique indicated a zone within ∼2μm of the surface where the chromium concentration decreased more steeply than expected.

A low energy electron diffraction study of the (100), (110) and (111) surfaces of gold

The technique of low energy electron diffraction has been used to determine the structure of (100), (110) and (111) surfaces of single crystals of gold. Following short periods of argon ion bombardment, 1 × 1 bulk type structures are generated on all three surfaces. Subsequent low temperature annealing or extended ion bombardment, without annealing, results in the formation of the anomalous structures, (100) 5 × 1 and (110) 1 × 2; no change is observed in the (111) surface structure. The anomalous structures were observed to transform reversibly as follows: 5×1 ⇄ 800°C 1×1(100) 1×2 ⇄ 600°C 1×1(110) Based on the assumption that these structures arise from the interaction of an impurity with the gold substrate, a surface dislocation model is proposed that qualitatively accounts for the superperiodic character of these structures. A theory which invokes impurity layer roughening (disordering) is advanced to account for the reversible transformations. Evidence is presented that suggests that the impurity is derived from the bulk of the crystals and is brought to the surface by a combination of selective sputtering, volume and surface diffusion processes. A second type of impurity structure, resulting in “ring” type diffraction features for all three orientations, is observed after extended high temperature annealing in vacuum. Results describing the thermal desorption of impurities from electropolished surfaces of gold are also presented.

471. Removal of nitrogen and carbon in high temperature vacuum annealing of cold-rolled transformer steel: V E Kochnovet al, Ref Zh Met I, Metalloved i Term Obrabotka, 1965, Abstr No 71421

471. Removal of nitrogen and carbon in high temperature vacuum annealing of cold-rolled transformer steel: V E Kochnovet al, Ref Zh Met I, Metalloved i Term Obrabotka, 1965, Abstr No 71421