High-temperature Vacuum Annealing Research Articles

Characterization of a HPHT boron ion-implanted diamond X-ray mirror following high vacuum annealing

The incorporation of boron into a diamond lattice holds the potential to advance X-ray optics, offering the capability to manipulate various parameters of the lattice. This includes enhancing near-infrared absorption relative to pure diamond, thereby enabling Q-switchable optics. The use of MeV boron implantation emerges as a promising method for precisely doping the diamond lattice. However, for these optics to function effectively as Bragg-reflecting mirrors, ion implantation must be executed with meticulous attention to maintaining a strain-free, perfect diamond lattice. This study aimed to investigate the feasibility of utilizing a 9 MeV ion beam for high energy boron implantation. Different areas of a high-pressure, high-temperature (HPHT) diamond sample were subjected to irradiation with 9 MeV Boron ions, ranging in fluences from 5×1015 to 2.5×1016ions/cm2. Following boron implantation, high-temperature vacuum annealing was performed to restore the diamond lattice. Our assessment utilized X-ray rocking curve imaging, surface profilometry, and micro-Raman spectroscopy, with additional observations on near-infrared transmission properties. Our measurement of high-quality Bragg reflection through X-ray rocking curve imaging, sensitive to implantation-induced strain and defects, served as an key diagnostic for the effectiveness of this ion-implanted sample as a Bragg-reflecting optic.

Vliyanie usloviy navedeniya deformatsii na strukturno-fazovoe sostoyanie i termomekhanicheskie kharakteristiki svoystv splava Ni<sub>49,5</sub>Ti<sub>48</sub>Hf<sub>2,5</sub> s vysokotemperaturnym effektom pamyati formy

Complex studies of the properties of Ni49,5Ti48Hf2,5 alloy featuring high-temperature shape memory effect were carried out on samples made of 2,34 mm-thick strip after high-temperature annealing in vacuum (850 ºС, 1 h). Data on element, phase compositions and structure state was obtained. Results of studies of phase transition temperatures, mechanical and thermomechanical characteristics of the alloy are given. According to the results of studying the local phase composition of alloy samples, it was found that the main matrix of samples is formed by solid solution of Ti, Ni, Hf elements. When analyzing diffraction patterns, it was found that the main phase of samples is titanium nickelide in the low-temperature martensitic state TiNi (B19`) with a monoclinically distorted orthorhombic crystal lattice. It was found that the best average values of the shape memory characteristics εSME = 4,4 % and ηSME = 53 % were obtained for alloy samples with a previously induced total deformation of eо = 11 % in the temperature range tD=(–5 ÷ 23) ºС and deformation rate ε ≈ 2,8·10–3 s–1. The average values of temperatures of the start and the end of the main form recovery are Аs SME = 133 ºС, Аf SME = 149 ºС. These thermomechanical characteristics are suitable for alloy selected to create safety devices such as devices of pushing type.

SYNTHESIS, ELECTRONIC STRUCTURE, AND MAGNETIC PROPERTIES OF NANOCRYSTALLINE OXYGEN-DEFICIENT TiO2–δ(B)

Nanocrystalline TiO2 polymorphs with nonstoichiometry, i.e. having intrinsic and/or impurity structural defects, attract considerable interest due to enhanced optical and catalytic activity, improved electronic properties, and existence of room-temperature ferromagnetism. Herein, due to combination of hydrothermal technology, ion exchange process, and high-temperature vacuum annealing, a gray-colored bronze titanium dioxide with a belt-like nanostructure has been successfully shynthesized. The electron paramagnetic resonance data indicate that coloring of bronze polymorph during vacuum annealing is caused by the appearance of F-centers within a crystal lattice (electron trapped in the anionic vacancies). X-ray diffraction, electron-microscopic studies, and adsorption measurements has no reveal obvious changes in phase composition, microstructure, and texture during vacuum heat treatment (in comparison with bronze TiO2 treteated under air). Spectrophotometry experiments illustrate a "narrowing" of the TiO2(B) band gap from 3.23 to 3.04 eV and an evolution of the optical absorption in the visible and near infrared ranges due to appearance of oxygen vacancies. The study of magnetic characteristics showed that TiO2–δ(B) has a ferromagnetic ordering at room temperature, and the nature of ferromagnetism in it is clearly defective (magnetic properties are determined by the exchange interaction between electrons located in the vacancy zone). At low temperatures (4 K) the magnetic properties of oxygen-deficient bronze titanium dioxide become similar to those for quasi-stoichiometric TiO2(B) prepared through annealing under oxidizing atmosphere (air).

Evolution of coating layers during high-temperature annealing and their effects on magnetic behavior of Fe(Si) soft magnetic composites

Low-loss Fe(Si) soft magnetic composites (SMCs) with atomic-layer-deposition coated layer were successfully prepared in this work. The continuous, compact and uniform Al2O3 layer is found to form tight bonding with the powder base. Evolution of the coating layers has been investigated under different annealing temperatures and closely linked to the magnetic performance of the composites. Results indicate that 1100 °C was the optimal annealing temperature, at which the Fe(Si) SMCs showed lowest core loss of 1237 mW/cm3 and the highest permeability of 99.7 simultaneously (100 mT/100 kHz). Integrity of the coating layer ensures the maximum grain growth and stress removal of powder particles at the highest possible temperature, so as to reduce the hysteresis loss. Formation of high resistivity oxides and silicates (Al2O3, Fe2SiO4 and 3Al2O3·SiO2) after annealing result in a low inter-particle eddy current loss. Besides, high temperature vacuum annealing is helpful to eliminate impurity atoms and decrease the anomalous eddy current loss. The improvement in effective permeability caused by high-temperature annealing is mainly attributed to the relaxation of residual stresses and the reduction of defects. While excessive temperature leads to the decomposition and destruction of the insulation layer, resulting in a significant increase in hysteresis loss, inter-particle and anomalous eddy current loss.

Ultrathin Ge epilayers on Si produced by low-temperature PECVD acting as virtual substrates for III-V / c-Si tandem solar cells

Ultrathin (20 nm) epitaxial films of germanium are deposited on crystalline silicon wafers, to act as virtual substrates for the growth of III-V materials, opening a low-cost approach to tandem solar cells. Such ultrathin layers allow for material cost reduction, along with the possibility of using the silicon wafer as the bottom cell in tandem devices. A simple plasma-enhanced chemical vapor deposition (PECVD) process at 175 °C has been optimized to deposit these heteroepitaxial germanium films, which grow directly on the silicon wafers without any intermediate silicon-germanium alloy. Thanks to an in-situ plasma cleaning step prior to Ge epitaxy, the films can sustain high-temperature annealing in vacuum (up to 800 °C) without any delamination. The suitability of the germanium heteroepitaxial films as virtual substrates is analyzed by depositing III-V layers on them by conventional growth methods like chemical beam epitaxy (CBE) and metalorganic chemical vapor deposition (MOCVD). The properties of the GaAs films deposited on the virtual substrates are comparable in terms of roughness, microstructure, and crystallinity to these of the III-V layers co-deposited on c-Ge wafers, pointing at the effectiveness of the ultrathin c-Ge epitaxial layers to act as virtual substrates for III-V epitaxial growth. Moreover, growing the c-Ge layers on c-Si substrates with 5° miscut avoids the formation of antiphase domains. These substrates are finally used to demonstrate proof of concept tandem solar cells, proving the suitability of our low temperature and ultrathin virtual substrate approach.

ДВУСЛОЙНЫЕ ПЛАСТИНЫ ИЗ СИНТЕТИЧЕСКИХ МОНОКРИСТАЛЛОВ АЛМАЗА, ЛЕГИРОВАННЫХ АЗОТОМ, ДЛЯ ВЫСОКОТЕМПЕРАТУРНЫХ ДИОДОВ ШОТТКИ n-ТИПА

For the first time, a vertical Schottky diamond diode with an electronic type of conductivity was manufactured and investigated on the basis of a two-layer single-crystal plate of synthetic diamond doped with nitrogen, in which a thin working layer of low-nitrogen-doped diamond was grown by the chemical vapor deposition method homoepitaxially on a heavily nitrogen-doped substrate cut in the plane {100} from a single crystal grown by the method of high-pressure-high-temperature growth on the seed. The concentration of nitrogen in the form of single substitution atoms (C-centers) in the working layer, grown by the chemical vapor deposition method, was 0.5 ppm, the layer thickness was 10 μm, the thickness of the substrate with a nitrogen concentration of ~ 200 ppm was 400 μm. 6 Schottky contacts with a diameter of 0.6 mm were made by magnetron sputtering of a platinum layer with a thickness of 200 nm through a contact mask. A rectangular ohmic contact was made to the substrate also by magnetron sputtering through a contact mask of a 5 nm thick Ti layer, followed by high-temperature annealing in vacuum to form titanium carbide, and subsequent deposition of a Pt layer with a thickness of 200 nm to prevent oxidation of titanium carbide in air. The current-voltage characteristics of the manufactured diodes were studied at a bias range of (-200 V) – (+200) V at temperatures up to 650 °C. The opening voltage of the manufactured diode structure is ~ 30 V, the maximum current of each diode in the open state reaches 1 mA at U = 200V, while the reverse current at T = 525-650 °C does not exceed 0.1 µA. The highest rectification coefficient value was ~104.

Periodic nano ripple fabricated on diamond and its structure damage repair

Surface nanocrystallization and adjusting chemical compositions are anticipated to be effective strategies for exploring potential applications of diamond in physics, chemistry and biology. In this paper, the morphology evolution of a polycrystalline chemical vapor deposition diamond (PCD) under Ar+ ion beam bombardment was studied. Nano ripple was formed on the substrate. The characteristic sizes, including amplitude (A) and wavelength (W), of ripples could be adjusted by changing ion energy. Meanwhile, chemical compositions of the diamond surface after the bombardment were investigated by Raman spectrum and XPS. Amounts of lattice damage or defects appeared on the surface region of PCD due to a conversion of sp3 C to sp2 C during the ion bombardment. Moreover, high temperature annealing in vacuum was adopted to remove the damage layer. It was proved to be an effective means to restore diamond structure here and the ripple pattern could be still preserved after the thermal treatment. In addition, the variations of the sheet resistance of the PCD, which significantly increases as the increasing annealing time, offer a direct evidence to reveal the extent of restoration of diamond structure.

Formation, evolution, and prevention of thermally induced defects on germanium and silicon upon high-temperature vacuum annealing

This Letter reports the formation, evolution, and prevention of thermally induced defects on germanium upon high-temperature (up to 890 °C) vacuum (2×10−6 Torr or 2.67×10−6 mbar) annealing. It is found that the shape of defects evolves depending on the annealing temperature and duration. The defect shape can be classified into three groups (pyramid, expanded pyramid, and doughnut), considering the interplay of chemical desorption and surface diffusion. The effects of annealing conditions on the density and size of defects are also investigated with scanning electron microscopy and atomic force microscopy. To prevent thermally induced defects, a simple covering method is proposed and demonstrated. In addition, formation and prevention of defects resulting from high-temperature (1150 °C) vacuum annealing are applied to silicon.

Impact of surface and laser-induced noise on the spectral stability of implanted nitrogen-vacancy centers in diamond

Scalable realizations of quantum network technologies utilizing the nitrogen vacancy center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by $^{15}$N ion implantation and high-temperature vacuum annealing. Origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near lifetime-limited optical linewidths ($<$ 60 MHz) are observed for the majority of the normal-implant (7$^\circ$, $\approx$ 100 nm deep) $^{15}$NV centers. Long-term stability of the NV$^-$ charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion-energy, and thus lattice damage profile. In contrast to the normal implant condition, NVs from an oblique-implant (85$^\circ$, $\approx$ 20 nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.

Influence of concentration-time parameters on nitride coatings formation on VT6 titanium alloy and their stability during subsequent treatment

The possibility of using a titanium nitride coating as a «protective» layer against the penetration of hydrogen into VT6 titanium alloy semi-finished or finished products was shown in this article. It was found that the titanium nitride coating does not dissolve during high-temperature vacuum annealing and «isolates» sample sides from hydrogen penetration, which allows to form a linear gradient structure during subsequent thermal hydrogen treatment.

Well-defined sub-nanometer graphene ribbons synthesized inside carbon nanotubes

Graphene nanoribbons with sub-nanometer widths are extremely interesting for nanoscale electronics and devices as they combine the unusual transport properties of graphene with the opening of a band gap due to quantum confinement in the lateral dimension. Strong research efforts are presently paid to grow such nanoribbons. Here we show the synthesis of 6- and 7-armchair graphene nanoribbons, with widths of 0.61 and 0.74 nm, and excitonic gaps of 1.83 and 2.18 eV, by high-temperature vacuum annealing of ferrocene molecules inside single-walled carbon nanotubes. The growth of the so-obtained graphene nanoribbons is evidenced from atomic resolution electron microscopy, while their well-defined structure is identified by a combination of an extensive wavelength-dependent Raman scattering characterization and quantum-chemical calculations. These findings enable a facile and scalable approach leading to the controlled growth and detailed analysis of well-defined sub-nanometer graphene nanoribbons.

Investigations of Crystalline Phases in Glasses under Various Annealing Conditions

Studies of the temperature dependence of the electrical properties of glasses show that the high-temperature annealing in glasses observed irreversible processes. These processes lead to changes in electrical conductivity, dielectric permittivity, and hence the electrical capacitance, dielectric loss tangent, and other parameters. Obviously, this is due to structural changes in the glass as a result of high-temperature annealing. In this regard, this paper presents studies of structural and phase transformations in glasses used for the production of microchannel plates in the process of high-temperature annealing in vacuum and in the air atmosphere at different times. The studies were conducted by x-ray phase and X-ray diffraction analysis, as well as X-ray fluorescence elemental analysis.

Photoluminescence Spectra of the 580-nm Center in Irradiated Diamonds

The formation mechanisms of the zero-phonon line optical center at 580 nm (H19 center) in photoluminescence spectra of irradiated natural diamonds and those deposited from the vapor phase were studied after their high-temperature vacuum annealing. The photoluminescence band intensity of the H19 center was shown to increase exponentially as the annealing temperature increased. Temperature dependences of photoluminescence spectra and local mechanical stress effects on the position and full width at half-height of the 580-nm zero-phonon line optical peak led to the conclusion that the H19 optical center was a complex intrinsic vacancy defect.

Structural and Phase Transformations in Compact Titanium Nitride-Based Ceramics during High-Temperature Heating in Gaseous Media

We have studied structural and phase transformations in the surface layer of compact titanium nitride-based ceramics during high-temperature annealing in vacuum, nitrogen, and air. The formation of an oxide phase during heat treatment of TiNx ceramics in air is controlled by bulk oxygen diffusion from the gas phase across an initially forming dense rutile TiO2 layer. Annealing in vacuum or nitrogen in the range 400–800°C changes neither the phase composition nor the grain structure of the ceramics.

Phase Transformations in the Surface Layer of Compact Zirconium Nitride-Based Ceramics

We have studied structural, morphological, and phase transformations in the surface layer of compact zirconium nitride-based ceramics during high-temperature annealing in vacuum, nitrogen, and air. The formation of oxygen-containing phases during heat treatment of ZrN is controlled by bulk and grain-boundary oxygen diffusion. At the beginning of the process, oxygen is supplied by an amorphous surface layer, which always forms during the ceramic preparation process. In air, the process is driven by oxygen indiffusion from the gas phase across an initially forming porous oxide layer. Grain-boundary oxygen diffusion leads to the formation of a crystalline zirconium oxide layer on grain boundaries and crack nucleation.

Hydrolytic Lignin: It’s Activated and Fluorinated Forms

The hydrolytic lignin (HL) derivatives have been prepared via its physical activation (high-temperature annealing in vacuum) followed by chemical modification (fluorination). It was found that the graphitized product of thermal activation up to 1000 °C at a low temperature gain rate of &lt; 2 °C/min under high vacuum shows an enhanced specific surface area (215 m2/g), that makes it potentially useful as sorbent, catalytic substrate, or electrode material. It was revealed from the experimental data the manufactured graphitized material consists of nanometric structural blocks, possibly nanographites and/or few-layer nanographenes. The edges of graphenes in agglomerates in activated hydrolytic lignin (AHL) have armchair and zigzag shapes. The nontrivial electronic structure of the zigzag edges, along with the electronic conductivity and the ability of AHL to absorb oxygen, can cause an increase in the energy intensity of lithium battery (LB) manufactured using AHL.The carbon-fluorine bond of semi-ionic type was detected in HL and AHL fluorinated in the temperature range of synthesize 60 – 300 oC. The fluorinated forms of both HL and its thermally activated product show increased values of operating voltage due to the participation of fluorine bound to carbon in the electrochemical process.

Engineering atomically flat rutile TiO2(100) over a centimeter scale

Atomically well-defined TiO2 is the prerequisite for both interfacial-physics engineering and photocatalytic-mechanism understanding. Here, we report the preparation of atomically flat rutile TiO2(100) over a centimeter scale by high-temperature annealing in ultrahigh vacuum and detailedly traced its microscopic evolution dynamics towards atomic smoothness. The reflection high-energy electron-diffraction pattern and the scanning topographic image both show an atomically flat surface over a sub–square-centimeter area. These results provide a microscopic understanding of the methodologies for obtaining atomically well-defined surfaces.

Sulfur‐Deficient TiS2‐x for Promoted Polysulfide Redox Conversion in Lithium‐Sulfur Batteries

AbstractSulfur‐deficient TiS2–x is prepared through high temperature vacuum annealing. Electron spin resonance (ESR) and X‐ray photoelectron spectroscopy (XPS) data confirm the presence of sulfur vacancies in TiS2–x. Effective polysulfide adsorption and promotion to polysulfide redox conversion was proven by adsorption simulation experiments and electrochemical measurements. Thus, TiS2–x is used as cathode promoter for Li−S half‐cells to improve the overall electrochemical performance. As expected, the TiS2–x/S electrode shows a high and stable capacity of 751 mAh g−1 even after 500 cycles and a fade rate as low as 0.04 % per cycle at 1 C. Besides, the high sulfur loading of the electrode of 4 mg cm−2 also displays an admirable cycling performance of 963 mAh g−1 with a capacity retention up to 91.7 % over 50 cycles at 0.2 C.

Effect of thermo-hydrogen-treatment on the surface oxide film and the compaction temperature of Ti-47Al-2Cr-2Nb pre-alloyed powders during hot-isostatic-pressing

In this study, a new hot-isostatic-pressing process was proposed, combining with the thermo-hydrogen-treatment process. Effects of hydrogen-atoms on the surface-oxide-film and the compaction-temperature of Ti-47Al-2Cr-2Nb pre-alloyed powders were investigated during hot-isostatic-pressing. Results show that the surface-oxide-film of powders of thermo-hydrogen-treatment can be effectively removed. For samples prepared by the new hot-isostatic-pressing process, the oxygen content decreased by 130 ppm and the compaction-temperature reduced by 50–100 °C, comparing with samples prepared by the traditional hot-isostatic-pressing process. After high-temperature vacuum annealing, the compressive fracture strength and ratio of samples prepared by the new hot-isostatic-pressing process is as high as 2830 MPa and 34.5%.

Lead-related quantum emitters in diamond

We report on quantum emission from Pb-related color centers in diamond following ion implantation and high temperature vacuum annealing. First-principles calculations predict a negatively-charged Pb-vacancy center in a split-vacancy configuration, with a zero-phonon transition around 2.3 eV. Cryogenic photoluminescence measurements performed on emitters in nanofabricated pillars reveal several transitions, including a prominent doublet near 520 nm. The splitting of this doublet, 2 THz, exceeds that reported for other group-IV centers. These observations are consistent with the PbV center, which is expected to have the combination of narrow optical transitions and stable spin states, making it a promising system for quantum network nodes.