High 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.

Zirconium Oxynitride Thin Films for Photoelectrochemical Water Splitting.

Transition metal oxynitrides are a promising class of functional materials for photoelectrochemical (PEC) applications. Although these compounds are most commonly synthesized via ammonolysis of oxide precursors, such synthetic routes often lead to poorly controlled oxygen-to-nitrogen anion ratios, and the harsh nitridation conditions are incompatible with many substrates, including transparent conductive oxides. Here, we report direct reactive sputter deposition of a family of zirconium oxynitride thin films and the comprehensive characterization of their tunable structural, optical, and functional PEC properties. Systematic increases of the oxygen content in the reactive sputter gas mixture enable access to different crystalline structures within the zirconium oxynitride family. Increasing oxygen contents lead to a transition from metallic to semiconducting to insulating phases. In particular, crystalline Zr2ON2-like films have band gaps in the UV-visible range and are n-type semiconductors. These properties, together with a valence band maximum position located favorably relative to the water oxidation potential, make them viable photoanode candidates. Using chopped linear sweep voltammetry, we indeed confirm that our Zr2ON2 films are PEC-active for the oxygen evolution reaction in alkaline electrolytes. We further show that high-vacuum annealing boosts their PEC performance characteristics. Although the observed photocurrents are low compared to state-of-the-art photoanodes, these dense and planar thin films can offer a valuable platform for studying oxynitride photoelectrodes, as well as for future nanostructuring, band gap engineering, and defect engineering efforts.

Evaluation of High-Vacuum Annealing and Hot Isostatic Pressing on the Microstructure and Properties of an Additively Manufactured Niobium Alloy

Evaluation of High-Vacuum Annealing and Hot Isostatic Pressing on the Microstructure and Properties of an Additively Manufactured Niobium Alloy

Fabrication of silica glass for UV-transmission by gel-casting method

We present the gel casting preparation of sintered silica glass and analyze its structural and optical properties in both atmospheric and 10−4 Pa high-vacuum conditions, with annealed and non-annealed samples, alongside a comparison to synthetic silica glass. The crystallization temperature of SiO2 bodies sintered in high-vacuum is higher than that in atmosphere since high-vacuum sintered body has less β-OH, the suitable temperature range is on the high temperature side compared to in the atmosphere. Fluorescence spectrum, ESR spectra and the transmittance spectrum indicate the existence of NBOHC, POR and E′ center in atmospheric sintered silica glass as well as ODC(I) and E′ center in high-vacuum sintered silica glass. High-vacuum sintering and annealing in hydrogen atmosphere can eliminate oxygen defects, NBOHC, POR, and E’ centers, resulting in the transmittance reached 91.1 % at 265 nm and 87.3 % at 230 nm. These are equivalent to 98.9 % and 94.9 % of the synthetic silica glass, respectively.

Effects of Mo doping on the phase transformation behaviors and the magnetic properties of rare-earth-free MnBi alloy

The high-performance rare-earth-free low-temperature phase Mn–Bi-based permanent magnet alloys (LTP-MnBi) have gained widespread attention, but it still presents a challenge. Here, the LTP-MnBi alloy with Mo element doping was prepared by using arc-melting and subsequent high-vacuum annealing. The crystalline structure, phase transformation behavior, and magnetic properties were systematically investigated. The result showed that Mo element doping significantly improved the stability of the LTP in MnBi alloy. The investigation revealed that the disparity in atomic radius between Mo and Mn, Bi elements played a pivotal role in the formation and stability of the LTP-MnBi. With the increase of Mo content in the LTP-MnBi alloy, the coercivity value remarkably increased from 8.1 kOe to 11.7 kOe with a decrease of saturation magnetization from 71.6 emu/g to 56.5 emu/g, and the maximum energy product gradually reduced from 10.6 MGOe to 7.9 MGOe. The underlying mechanism revealed that magnetic properties were closely related to the fraction and crystal structure of LTP-MnBi. Therefore, magnetic properties of Mo-doped MnBi alloy make them an attractive candidate among the rare-earth-free permanent magnets.

Synthesis, crystal structure, and magnetic properties of CoMoFeAl and related compounds

We have carried out joint theoretical and experimental investigations of three Heusler compounds CoMoFeAl, CoMo0.5Fe1.5Al, and Co1.5Mo0.5FeAl. Our first-principle calculations show that all three compounds show either ferro- or ferrimagnetic order with CoMoFeAl and CoMo0.5Fe1.5Al exhibiting high spin polarization of almost 80%. The investigated samples were prepared using arc melting and high vacuum annealing. All the samples show cubic crystal structure with disorder. The parent compound CoMoFeAl shows a small saturation magnetization of 12 emu/g, and a Curie temperature of 440 K. The other two compounds, namely, Co1.5Mo0.5FeAl and CoMo0.5Fe1.5Al, show much higher saturation magnetizations of 62 emu/g and 59 emu/g, and substantially higher Curie temperatures of 950 K and 780 K, respectively.

Structural, electronic, and magnetic properties of CoFeVGe-based compounds: Experiment and theory

We have carried out a combined theoretical and experimental investigation of both stoichiometric and nonstoichiometric CoFeVGe alloys. In particular, we have investigated CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe bulk alloys. Our first principles calculations suggest that all four alloys show ferromagnetic order, where CoFeVGe, Co1.25Fe0.75VGe, and Co0.75Fe1.25VGe are highly spin polarized with spin polarization values of over 80%. However, the spin polarization value of CoFe0.75VGe is only about 60%. We have synthesized all four samples using arc melting and high-vacuum annealing at 600 °C for 48 hours. The room temperature x-ray diffraction of these samples exhibits a cubic crystal structure with disorder. All the samples show single magnetic transitions at their Curie temperatures, where the Curie temperature and high field (3T) magnetization are 288 K and 42 emu/g; 305 K and 1.5 emu/g; 238 K and 39 emu/g; and 306 K and 35 emu/g for CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe, respectively.

Co-doped In-Situ Engineered Carbon Nano-Onions Enabled High-Performance Supercapacitors

The feasibility of achieving in situ sulfur (S) and nitrogen (N) co-doped carbon nano-onions (CNOs and SN-CNOs) via a simple flame-pyrolysis technique without using sophisticated high-vacuum annealing or expensive nanodiamond-based complex processes is demonstrated for the first time. The characteristic onion-like feature of 0.34 nm remained intact with a high degree of ordering and graphitization, even though the S and N heteroatoms were co-doped simultaneously. The in situ co-doped SN-CNO demonstrated high supercapacitor device performance with a high energy density of 25 Wh kg-1 at a maximum power density of 18 kW kg-1, maintaining 98% specific capacitance over 10,000 cycles at 10 A g-1. These are the highest achieved device performance values of a fullerene family electrode material to date.

In-situ investigation on the oxygen vacancy-driven topotactic phase transition in charge-orbital ordered Nd0.5Sr0.5MnO3 films

The topotactic phase transition from perovskite to oxygen vacancies ordered brownmillerite structure in transition metal oxides intrigues various new application possibilities. However, the in-situ observation of the oxygen vacancies formation process accompanying the phase transition is still rare. Here in this article, we report the topotactic phase transition from the perovskite to a brownmillerite phase transition in the intermediate bandwidth- (101)-Nd0.5Sr0.5MnO3-δ films. The oxygen vacancies migration process in the films was identified by the TEM technique during the in-situ high vacuum annealing process. The TEM results demonstrate a vertical brownmillerite structure with the oxygen vacancies channel perpendicular to the film plane in the (101)-oriented films. Moreover, the in-situ investigation reveals that oxygen atoms in the {010}PV plane of the perovskite phase migrate out of the film along the out-of-plane <101>PV direction at first, and the formed oxygen vacancies become ordered by elongating the high-vacuum annealing process to 42 h, transforming to the brownmillerite structure. Further studies reveal that the associated physical properties of the topotactic phases can be controlled by the phase transition. The charge-orbital ordered antiferromagnetic insulating ground state transfers to a highly insulating state with a novel magnetic phase that is distinct from that of brownmillerite structure of other manganites. The present studies thus pioneered topotactic phase transition in a new manganite system and provide useful information for developing perovskite-based functional materials by defect engineering.

Experimental and theoretical investigation of FeCrVAl and related compounds

We have carried out a combined theoretical and experimental investigation of FeCrVAl, and the effect of Mn and Co doping on its structural, magnetic, and electronic band properties. Our first principles calculations indicate that FeCrVAl, FeCr0.5Mn0.5VAl, and FeCr0.5Co0.5VAl exhibit nearly perfect spin polarization, which may be further enhanced by mechanical strain. At the same time, FeCrV0.5Mn0.5Al and FeCrV0.5Co0.5Al exhibit a relatively small value of spin polarization, making them less attractive for practical applications. Using arc melting and high vacuum annealing, we synthesized three compounds FeCrVAl, FeCr0.5Mn0.5VAl, and FeCr0.5Co0.5VAl, which are predicted to exhibit high spin polarization. The room temperature x-ray diffraction patterns of all samples are fitted with full B2 type disorder with a small amount of FeO2 secondary phase. All samples show very small saturation magnetizations at room temperature. The thermomagnetic curves M(T) of FeCrVAl and FeCr0.5Co0.5VAl are similar to that of a paramagnetic material, whereas that of FeCr0.5Mn0.5VAl indicates ferrimagnetic behavior with the Curie temperature of 135 K. Our findings may be of interest for researchers working on Heusler compounds for spin-based electronic applications.

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.

A highly tunable photoelectric response of graphene field-effect transistor with lateral P–N junction in channel

This paper reports a highly tunable photoelectric response of graphene field-effect transistor (GFET) with lateral P–N junction in channel. The poly(sulfobetaine methacrylate) (PSBMA) provides strong N-type doping on graphene due to the dipole moment of pendent groups after ultraviolet annealing in high vacuum. A lateral P–N junction is introduced into the channel of the GFET by partially covering the graphene channel with PSBMA. With such P–N junction in the channel, the GFET exhibits a highly tunable photoelectric response over a wide range of exciting photon wavelength. With a lateral P–N junction in the channel, the polarity of photocurrent (I ph) of the GFET switches three times as the back-gate voltage (V BG) scan over two Dirac-point voltages. The underlying physical mechanism of photoelectric response is attributed to photovoltaic and photo-induced bolometric effect, which compete to dominating I ph at various V BG. This provides a possible strategy for designing new phototransistors or optoelectronic device in the future.

Modifying magnetic properties of MnBi with carbon: an experimental and theoretical study

MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. One of the main issues with MnBi synthesis is the presence of residual Bi in the sample which reduces the net magnetization. We have found that MnBi synthesized in the presence of carbon substantially reduces the amount of residual Bi, improving its saturation magnetization. We have synthesized Mn55Bi45 and Mn55Bi45C x samples using arc melting and high-vacuum annealing. The room temperature x-ray diffraction patterns indicate that both Mn55Bi45 and Mn55Bi45C x crystallize in the hexagonal NiAs-type structure. The Rietveld analysis of the x-ray patterns shows that the amount of residual Bi reduces from 16 wt.% for Mn55Bi45 to 5 wt.% for Mn55Bi45Cx. The high-field (3 T) magnetizations measured at room temperature are 61 emu g−1 and 66 emu g−1 for Mn55Bi45 and Mn55Bi45C x , respectively. To understand the role of C in enhancing the magnetization of MnBi, we carried out the first-principles calculations of both stoichiometric and nonstoichiometric MnBi alloys, which suggests that the increase of magnetization in Mn55Bi45C x may be due to the coating of MnBi grains with C.

Electronic band structure and magnetism of CoFeV0.5Mn0.5Si

Half-metallic Heusler alloys have attracted significant attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV0.5Mn0.5Si, using arc melting and high-vacuum annealing at 600 °C for 24 hours. First principles calculation indicates that CoFeV0.5Mn0.5Si shows a nearly half-metallic band structure with a degree of spin polarization of about 93%. In addition, this value can be enhanced by the application of tensile strain. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without secondary phases. The annealed sample shows ferromagnetic order with the Curie temperature well above room temperature (Tc = 657 K) and a saturation magnetization of about 92 emu/g. Our results indicate that CoFeV0.5Mn0.5Si has a potential for room temperature spin-transport-based devices.

Recrystallization behavior, oxygen vacancy and photoluminescence performance of sputter-deposited Ga2O3 films via high-vacuum in situ annealing

Ga 2 O 3 films were deposited on Si substrates through radio-frequency magnetron sputtering at room temperature and were annealed in situ in a high-vacuum environment. The as-deposited Ga 2 O 3 film exhibited an island-like surface morphology and had an amorphous microstructure, with a few nanocrystalline grains embedded in it. After high-temperature in situ annealing, the films recrystallized and exhibited coalesced surfaces. Because of the thermally driven diffusion of Ga, the interfacial layer between Si and Ga 2 O 3 was composed of SiGaO x . Compared with ex situ annealing in air, in situ annealing in high vacuum is more advantageous because it enhances surface mobility and improves the crystallinity of the Ga 2 O 3 films. The higher oxygen vacancy concentration of in situ annealed films revealed that oxygen atoms were easily released from the Ga 2 O 3 lattice during high-vacuum annealing. Photoluminescence (PL) spectra exhibited four emission peaks centered in ultraviolet, blue, and green regions, and the peak intensities were significantly enhanced by thermal annealing at >600 °C. This work elucidates the effect of the in situ annealing treatment on the recrystallization behavior, interfacial microstructure, oxygen vacancy concentration, and PL performance of the Ga 2 O 3 films, making it significant and instructional for the further development of Ga 2 O 3 -based devices.

Исследование процесса формирования сверхпроводящих покрытий станнида триниобия методом магнетронного напыления для задач ускорительной техники

The article considers some regularities of the formation of niobium stannide coatings during their deposition by magnetron sputtering using a stoichiometric target. The optimal mode of operation of the magnetron source is determined, the element-phase composition, the microstructure of the formed films, as well as their change in the process of high-temperature annealing are investigated. The research results indicate that the coatings optimal in terms of elemental and phase composition were obtained in the deposition mode at an argon pressure in the working chamber of 0.3 Pa and a high-vacuum annealing temperature of 800 °C.

Superparamagnetism of potassium-doped tris(diphenacyl) iron

Synthesis and exploration of intriguing physical properties of alkali-metal-doped aromatic hydrocarbons have been the important research topics in the fields of physics, chemistry and materials science. In this work, a powder sample of potassium-doped tris(diphenacyl) iron molecular crystal is prepared by the high-vacuum annealing method. The X-ray diffraction results show that the crystal structure of the synthesized sample is different from that of pristine tris(diphenacyl)iron. The direct current (DC) magnetic susceptibilitiy shows a pronounced hump structure near 8.0 K, which is distinct from the paramagnetism of pristine material in the whole temperature range of 1.8–300 K. The alternating current (AC) magnetic susceptibility shows that the hump has a significant frequency dependence, which can safely rule out the possibility of antiferromagnetism. The combination of the Vogel-Fulcher law, the Néel-Brown model and the critical slowing down model reveals that the hump originates from superparamagnetism with a blocking temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;B&lt;/sub&gt;) of about 8.0 K. According to the results of Raman spectroscopy, it can be confirmed that the 4s electrons of potassium in the doped material are transferred to the benzene ring of tris(diphenacyl)iron, causing the characteristic Raman modes to be red-shifted and the local magnetic moment to form. Our work is of great significance in exploring alkali-metal-doped aromatic hydrocarbons, and provides a new route for searching organic magnetic materials.

On the Contact Optimization of ALD-Based MoS2 FETs: Correlation of Processing Conditions and Interface Chemistry with Device Electrical Performance

Despite the extensive ongoing research on MoS2 field effect transistors (FETs), the key role of device processing conditions in the chemistry involved at the metal-to-MoS2 interface and their influence on the electrical performance are often overlooked. In addition, the majority of reports on MoS2 contacts are based on exfoliated MoS2, whereas synthetic films are even more susceptible to the changes made in device processing conditions. In this paper, working FETs with atomic layer deposition (ALD)-based MoS2 films and Ti/Au contacts are demonstrated, using current–voltage (I–V) characterization. In pursuit of optimizing the contacts, high-vacuum thermal annealing as well as O2/Ar plasma cleaning treatments are introduced, and their influence on the electrical performance is studied. The electrical findings are linked to the interface chemistry through X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) analyses. XPS evaluation reveals that the concentration of organic residues on the MoS2 surface, as a result of resist usage during the device processing, is significant. Removal of these contaminations with O2/Ar plasma changes the MoS2 chemical state and enhances the MoS2 electrical properties. Based on the STEM analysis, the observed progress in the device electrical characteristics could also be associated with the formation of a continuous TiSx layer at the Ti-to-MoS2 interface. Scaling down the Ti interlayer thickness and replacing it with Cr is found to be beneficial as well, leading to further device performance advancements. Our findings are of value for attaining optimal contacts to synthetic MoS2 films.

On a new Ti-carbooxinitride redistribution driven microcrack healing mechanism in an annealed 14YWT nanostuctured ferritic alloy

FCRD NFA-1 is a larger best practice heat of Fe-14Cr nanostructured ferritic alloy (NFA) dispersion strengthened by a large population of nano-scale Y2Ti2O7 nano-oxides. NFA-1 was produced by ball milling FeO with argon atomized Fe-14Cr-3W-0.35Ti-0.25Y (wt.%) powders, followed by hot extrusion at 850 °C, followed by 1 h annealing and multipass cross-rolling at 1000 °C to form an ≈ 10 mm thick plate. Cross-rolling results in a large population of {001}<110> cleavage system microcracks (MCs) running on planes parallel to the plate faces. A series of high temperature vacuum anneals were carried out from 1100 to 1300 °C for 1 and 5 h to explore the possibility of self-healing, not only of the MCs, but also macroscopic fatigue cracks. Most notably, a new crack self-healing mechanism was discovered, involving the redistribution and coarsening of initially fine matrix Ti, C, O and N precipitates (TiCONs) to bridging sites on the crack faces. The relocated TiCONs grow and coarsen, thereby consuming a volume of the adjoining Fe-Cr matrix. The displaced matrix atoms diffuse to further fill the crack. Extensive microstructural, fractographic and mechanical property characterization measurements show that MC self-healing begins at 1100 °C/1 h, increasing with annealing time and temperature, up to completion at 1300 °C. The NFA-1 grains and texture are relatively stable. However, at 1300 °C the nano-oxides and dislocations coarsen or recover, respectively, leading to significant softening.

Review on fabrication methods of SrTiO3-based two dimensional conductive interfaces

The SrTiO3-based two dimensional conductive interfaces have attracted considerable attention in the last decade owing to the emergence of novel physical phenomena. These heterointerfaces are generally formed by depositing the films on SrTiO3 substrates. Particularly, the controllable and precise characteristics of pulsed laser deposition (PLD) allow the deposition of an atomically flat oxide films and control the growth layer-by-layer. Recently, the deposition methods of atomic layer deposition (ALD) and spin coating have exhibited an excellent practicability and many interesting results are obtained by analyzing the chemical reaction pathway. In addition, the surface treatment methods (such as high vacuum annealing, Ar+ ion irradiation and photoirradiation etc.) can also obtain the two dimensional conductive SrTiO3 effectively. Furthermore, owing to the difference of fabrication method, the SrTiO3-based two dimensional conductive interfaces significantly show different performances of the same oxides. Thus, this review compares the characteristics of different methods in preparing the SrTiO3-based interfaces. The appropriate method and process is the precondition to obtain high-quality oxide films and establish the foundation for the development of oxide and interface electronics.