Heat Treatment In High Vacuum Research Articles

Reducing two-level systems dissipations in 3D superconducting niobium resonators by atomic layer deposition and high temperature heat treatment

Superconducting qubits have arisen as a leading technology platform for quantum computing, which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency niobium resonators by atomic layer deposition of a 10 nm aluminum oxide Al2O3 thin films, followed by a high vacuum heat treatment at 650 °C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by x-ray photoelectron spectroscopy plus scanning and conventional high resolution transmission electron microscopy coupled with electron energy loss spectroscopy and energy dispersive spectroscopy, we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3.

Influence of atmosphere during vacuum heat treatment of stainless steels AISI 304 and 446

Specimens of austenitic AISI 304 and ferritic 446 (contains 1.7 wt.% Al) underwent heat treatments up to 1200 °C in ultrahigh vacuum (UHV) in an analysis chamber with a base pressure of 10-10 mbar and high vacuum (HV) in an industrial vacuum brazing furnace with a base pressure of 10-6 mbar. The effect of the two oxygen partial pressure ranges on surface and bulk composition was determined by XPS, AES and EDX, imaging was provided by SEM.For AISI 304, we observe similar behavior for both atmospheres and the removal of the surface oxide layer. For AISI 446, we observe a strong dependency on the atmosphere. Heat treatment in high vacuum yielded a thick aluminum oxide layer on the surface that inhibited wetting with copper silver eutectic. Heat treatments in ultrahigh vacuum did not lead to aluminum oxide formation but rather carbide formation of foreign elements such as titanium was observed on the surface.

Effect of high vacuum heat treatment on microstructure and cyclic oxidation resistance of HVOF-CoNiCrAlY coatings

CoNiCrAlY coatings were deposited on IN-738 LC substrates using HVOF technique. The microstructure of these coatings is composed of a single γ phase. A two-step high vacuum heat treatment transformed the single γ phase into a two-phase γ+β microstructure. The result of cyclic oxidation test at 1100 °C on the coated samples indicated a higher oxidation resistance in as-sprayed coatings than heat-treated samples. At initial oxidation cycles of the as-sprayed coatings, fine grain size and high dislocation density of single γ phase could enhance the diffusion rate of aluminum into the surface and increase the probability of alumina formation as the first oxide layer.Whereas two-phase microstructure together with coarse grain size and low dislocation density of the heat-treated coatings reduced the aluminum diffusion rate and decreased the possibility of having a single layer of alumina.After 50 oxidation cycles, a single layer of alumina oxide formed on the as-sprayed coatings with a more uniform thickness compared to a dual-layer oxide of alumina and spinel on the heat-treated coatings. At 260th oxidation cycle, the growth of initiated cracks in previous cycles reached a critical stage which led to spallation of the oxide layer.

Thermal boundary conductance between refractory metal carbides and diamond

The thermal boundary conductance (TBC) between thin films of Cr, Mo, Nb and W and diamond substrates has been measured using time domain thermoreflectance before and after a high-vacuum heat treatment at 800°C for 2h. While no signs of carbide formation could be detected in as-deposited layers by scanning transmission electron microscopy energy dispersive X-ray spectroscopy elemental analysis, the heat treatment led to partial (W,Mo) or full conversion (Cr,Nb) of the film into carbide. The measured TBC values on as-deposited samples of 315, 220, 220 and 205MWm-2K-1 measured for, respectively, the Cr, Mo, Nb and W samples, were found to not be significantly altered by the heat treatment.

Surface hardening of biocompatible ultrafine-grained niobium zirconium alloy by two-stage oxidation treatment

The present study reports on an optimized surface hardening process for biocompatible ultrafine-grained (UFG) niobium 2.3 wt% zirconium (NbZr) alloy, a promising candidate implant material. The as-received material of conventional grain size (CG) was processed using multipass equal channel angular processing at room temperature to obtain an UFG microstructure featuring high strength and ductility. Subsequent surface hardening was performed by a heat treatment leading to internal oxidation. Using a thermogravimetric system, the influence of temperatures, time, and partial pressure of oxygen ( $$ p_{{\text{O}}_2} $$ ) on the oxidation kinetics were investigated. Metallographic and microscopic analyses and hardness measurements were employed to evaluate maximum hardness, penetration-depth and scale formation under various conditions. Heat treatment at 620 °C for 6 h at a $$ p_{{\text{O}}_2} $$ of 0.2 hPa led to sufficiently rapid oxidation kinetics yielding a relatively high depth of penetration without formation of loose Nb2O5 on the surface, which was observed at higher $$ p_{{\text{O}}_2} $$ . As compared to CG material, improved hardness profiles were reached using the same heat treatment parameters, since the UFG structure significantly changes diffusion conditions and therefore oxidation kinetics. After a second heat treatment in high vacuum the high maximum hardness of 820 HV0.01 in the UFG material was reduced effectively and a less steep hardness gradient was achieved, both contributing to a less brittle behavior under mechanical loading. High-cycle fatigue tests performed on surface-hardened UFG NbZr samples showed a substantial improvement of fatigue life in tests conducted near the endurance limit. Especially when high fatigue and wear resistance are key issues for a given application, the internal oxidation process offers an effective way to further improve the properties of UFG NbZr.

Comparison of the redox properties of iron incorporated in different amounts into MCM-41

Mesoporous Fe-MCM-41 samples with different framework iron contents were tested as catalysts in CO oxidation and characterized by TPR,Mossbauer and FTIR spectroscopies after heat treatment in high vacuum and reductive or oxidative atmospheres. In samples with Si/Fe ratiosof 20 and 12 all of the iron was found to be reducible with H2, but only a part of Fe(III) species could be reduced to Fe(II) in materialswith lower iron content. In neither of the materials could Fe(III) be fully converted with CO to the divalent oxidation state. A significant part ofiron can be reversibly reduced and reoxidized in successive redox cycles. Large Fe-O clusters could not be detected.

High Resolution Surface Structure of Porous Silicon

The work demonstrates that the surface atom layers of variously-prepared samples of porous silicon can, after high-temperature heat treatment in high vacuum, yield low energy electron diffraction patterns and also atomic resolution in scanning tunneling microscopy. The (100) surfaces show some patches of 2 × 1 reconstruction but no clear reconstructions are visible on (111) surfaces. We also show that although evaporated metal contacts give poor reproducibility of current–voltage characteristics, the latter can be made stable and reproducible if the surfaces are first coated with a conducting polymer

Characterization of Activated States of Ruthenium-Containing Zeolite NaHY

As has been proven earlier, ruthenium-containing NaHY zeolites are able to catalyze the decomposition of ammonia at temperatures from 300 to 450°C. In such catalysts, ruthenium cations are still present, even after heat treatment in high vacuum at 400°C; they can be detected using ammonia and/or pyridine as probes for Fourier transform IR spectroscopy. They reside both in supercages and in sodalite cages. Various intermediates of the decomposition of the Ru(NH3)6NaY complex on heat treatment in high vacuum were identified viain situIR spectroscopy; in particular, evidence for the formation of complexes with nitrosyl ligands was obtained. It was shown that partially decomposed (deammoniated) Ru(NH3)6NaY complexes can be recovered to some extent by readsorption of ammonia. Ruthenium-containing species were localized either in the supercages or in the small cavities as shown by IR spectroscopy employing ammonia and pyridine as probes. The acidic properties of variously treated Ru(NH3)6NaY zeolites were characterized via temperature-programmed desorption (TPD) of ammonia, which was monitored by mass spectrometry. A strong interaction between ruthenium-containing species and the zeolite framework, leading to a lack of overtone and combination modes in the near infrared, is confirmed. Investigations of Ru(NH3)6NaY samples by X-ray photoelectron spectroscopy under the same conditions as applied for IR and TPD studies revealed that, at variance with the results usually obtained after heat treatment of Ru(NH3)6NaY in high vacuum, no significant formation of ruthenium metal species through autoreduction occurred. Rather, a particular form of a cation-exchanged Ru, Na-Y zeolite was obtained.

アルミニウム合金熱処理炉

アルミニウム合金熱処理炉

Very high-vacuum heat treatment facility

Very high-vacuum heat treatment facility

Investigation of ferromagnetic phase precipitation on the surface of some constructional materials for thermonuclear reactors

Austenitic stainless steels are considered as a prospective material for the first wall of the thermonuclear reactors. Radiation and temperature influence erosion of material, and contamination of the plasma.This paper describes the results of investigations on the process of ferromagnetic layer formation on the surface of Cr-Mn and Cr-Ni austenitic steels after annealing at the working temperatures of the first wall (≈ 500°C) or at high temperature (≈ 1000°C), which can arise on the surface of blisters.The results of magneto-optic studies show that in the original samples with electropolished surface the ferromagnetic phase precipitations are absent. Ferromagnetic α-phase forms on the surface of Cr-Mn steel after heat treatment in high vacuum as a result of selective evaporation of the austenizing components. The parameters of evaporation of these components were investigated using thermogravimetry, and the re-distribution of the elements in the surface layers were studied by Auger electron spectroscopy.From these results it can be concluded that thin ferromagnetic layers can be formed on the surface of constructional materials during the reactor's run. This layer must be considered in calculations of the configuration of magnetic fields, working regimes of thermonuclear reactors, and plasma stability.

High-vacuum heat treatment furnace

The proposed design makes it possible to attain a vacuum of 3×10−7 mm Hg free of hydrocarbons after heating 8–10 h at 2000°C. This furnace makes it possible to heat treat metals and alloys under conditions excluding interactions with residual gases.

Properties of Clean Silicon Surfaces by Paramagnetic Resonance

Silicon crystals crushed in ultrahigh vacuum (∼10−9 Torr) display an electron spin resonance signal close to g=2.0055 with a width of 7.0 Oe. The signal is strongly affected by exposure to 10−2 Torr of molecular hydrogen (increase ≈60%) and oxygen (increase ≈80%), indicating that it is associated with surfaces. From surface area measurements, the ratio of dangling bonds to surface atoms was found to be approximately 1 to 5. High-vacuum heat treatment causes an irreversible decrease in the surface resonance at 380°C (1-h heating), but the signal is still increased by gas exposure. Above approximately 610°C the relatively weak remaining signal is now decreased by oxygen exposure, indicating a second surface transformation which correlates with that observed in this temperature region by low-energy electron diffraction. It is concluded that the surface structures for both cleaved and annealed clean silicon surfaces involve dangling bonds, the concentrations being of order 20% and 2%, respectively. Consequences with respect to surface atom arrangements are discussed.

Temperature Dependence of the Work Function of Single-Crystal Faces of Copper

Measurements of the temperature dependence of the work functions of the (100), (110), (111), (211), and (221) crystal faces of copper have been made in the temperature range 20 to 700\ifmmode^\circ\else\textdegree\fi{}C. The measurements were obtained by a diode retarding-field method in vacuo below ${10}^{\ensuremath{-}9}$ torr. Constant current operating conditions permitted a direct continuous monitoring of changes in the anode work function. While absolute work function measurements could not be obtained by this method, a precision measurement of the temperature dependence was possible. The single-crystal anodes were given rigorous heat treatment in high vacuum resulting in drift-free measurements which were reproducible. The results from the (100) and (111) faces, when combined with previously reported values of the absolute work function, demonstrate a relationship in which the work function smoothly approaches a value independent of crystallographic orientation at the melting point. A simple thermodynamic argument is presented to explain the results. Published measurements of the temperature dependence of the work function of single-crystal faces of tungsten are shown to be consistent with this interpretation.

Contact Potential Difference between Iron and Nickel and their Photoelectric Work Functions

Specimens of electrolytic iron and electrolytic nickel were outgassed by intensive heat treatment in high vacuum and the contact potential difference between them measured by the Kelvin null method. An apparatus is described by means of which the photoelectric long wave limits could be determined on the same specimens and under identical conditions as used for the contact potential measurements. The photoelectric long wave limits were determined in one case by using filters in the path of the light and in a second case by the method of plotting the photoelectric sensitivity curves obtained using monochromatic illumination of the metals. The results remained unchanged between 300 and 750 hours of heating in the first case and between 400 and 600 hours in the second. The equilibrium value of the contact potential difference was Fe-Ni+0.21\ifmmode\pm\else\textpm\fi{}0.01 volt. The photoelectric long wave limits determined by the second method were 2620A\ifmmode\pm\else\textpm\fi{}10A for the iron and 2500A\ifmmode\pm\else\textpm\fi{}10A for the nickel. The corresponding work functions are 4.71\ifmmode\pm\else\textpm\fi{}0.02 volts for the iron and 4.93\ifmmode\pm\else\textpm\fi{}0.02 volts for the nickel. Using the method published by Fowler the work functions were 4.77 volts for the iron and 5.01 volts for the nickel. The difference in these work functions by either method is equal to the measured contact potential difference between the metals within the limits of error of the photoelectric measurements.