High-pressure Annealing Research Articles

Pressure Effect on Surface Roughness of Gradient Chromium-doped Diamond-like Carbon Coatings under High Temperature

Abstract In this paper, the pressure effect of surface roughness of four gradient chromium-doped diamond-like carbon (GCD-DLC) coating is systemically studied in argon annealing and high pressure annealing under high temperature. After HIPping annealing, the surface roughness of the hydrogen-free group (GCr and GCrSi) decreased slightly. However, for the two hydrogen-containing GCD-DLC coatings (DCr and DCrSi), especially the DCr coating, the roughness increased significantly. The changes in surface roughness of the hydrogen-free group and the hydrogen-containing group after high-pressure annealing are opposite. The surface roughness of the DCr coating increased significantly after 500°C HIP annealing, which is attributed to the pores on the coating surface. Only the surface morphology of the DCr coating exhibited significant changes. Numerous voids appeared on the surface of the DCr5H coating after 500°C HIP annealing. There were significant differences in the size and shape of these voids compared to those after 500°C argon annealing. The voids on the coating after argon annealing were larger than those after HIP annealing. The formation of pores is associated with the breaking of carbon-hydrogen bonds and the subsequent release of hydrogen. This is because high pressure slows down the transformation from sp3 carbon bonds to sp2 carbon bonds. Simultaneously, high pressure also slows down the release of hydrogen within the coatings.

Study on the fabrication of high-quality hafnium oxide thin films using spatial rotated atomic layer deposition and supercritical fluids treatment

This study explores the experimental outcomes and discussions surrounding the deposition of high-quality hafnium oxide (HfO2) thin films using spatial rotated atomic layer deposition (SRALD). The primary objective was to enhance the efficiency of ALD processes while maintaining film quality comparable to conventional methods. The SRALD system, developed by Kudos Nano Technology, was employed to deposit HfO2 films over a four-step process. Following deposition, the films underwent high-pressure annealing and supercritical fluids treatment, which are known for reducing thermal budgets. The key findings revealed that high-pressure annealing resulted in a significant reduction in the leakage current by up to 50%, while supercritical fluids treatment improved the dielectric constant of the films, reaching values as high as 23. These treatments also contributed to enhancing the uniformity and density of the films, as confirmed by cross-sectional transmission electron microscopy and x-ray reflectometry analyses. The electrical properties of the resulting metal–insulator–semiconductor capacitors were thoroughly investigated, demonstrating a marked improvement in capacitance-voltage characteristics with minimal hysteresis.

Investigation of the activation and diffusion of ion-implanted p-type and n-type dopants in germanium using high-pressure annealing

In this study, we investigate the effectiveness of high-pressure annealing (HPA) compared to microwave annealing (MWA) in activating n-type and p-type dopants in germanium. For phosphorus dopants, HPA at 500 °C significantly enhances the activation level, resulting in a reduction of sheet resistance to 120.1 ohms sq.−1 and a maximum active concentration of up to 5.76 × 1019 P cm−3. Similarly, for boron dopants, HPA at 800 °C reduces the sheet resistance to 80.6 ohms sq.−1 and achieves a maximum active concentration that maintains effective doping profiles. Transmission electron microscopy images reveal that the amorphous layers implanted with phosphorus and boron are significantly reduced, indicating that HPA is more effective in achieving solid-phase epitaxial regrowth compared to MWA. HPA demonstrates superior performance in minimizing dopant diffusion and reducing sheet resistance for both phosphorus and boron dopants, making it a preferable method for high-temperature annealing in germanium-based devices.

Two Perovskite Modifications of BiFe0.6Mn0.4O3 Prepared by High-Pressure and Post-Synthesis Annealing at Ambient Pressure

BiFeO3-related perovskite-type materials attract a lot of attention from the viewpoint of applications and fundamental science. In this work, we prepared two modifications of heavily Mn-doped BiFeO3 with the composition of BiFe0.6Mn0.4O3. A high-pressure (HP) modification was prepared at about 6 GPa and 1400 K. An ambient pressure (AP) modification was prepared by heating the HP modification at 780 K in the air at AP (post-synthesis annealing). Crystal structures of both modifications and in situ transformation were investigated with synchrotron powder X-ray diffraction. The transformation started at about 700 K and finished at about 780 K. The HP modification crystallized in space group Pnma with a = 5.57956 Å, b = 15.70576 Å, and c = 11.22557 Å, and the AP modification crystallized in space group Pbam with a = 5.63839 Å, b = 11.2710 Å, and c = 7.75923 Å (all parameters were at room temperature). Post-synthesis annealing of the HP modification (conversion polymorphism) is the only way to prepare the Pbam modification of oxygen stoichiometric BiFe0.6Mn0.4O3. Magnetic properties of both modifications have been reported. The Néel temperatures are TN = 350 K (HP) and TN = 335 K (AP). HP modification shows larger spin canting. Both modifications show negative magnetization phenomena at low temperatures in low magnetic fields.

Eliminating metallurgical defects and achieving strength-ductility combination in selective laser melted martensitic stainless steel through high-pressure annealing

Due to high difficulty in fabricating and processing high-strength metals, additive manufacturing has been considered to have broad prospects compared to the traditional casting means. However, unavoidable metallurgical defects and strength–ductility trade-off dilemma have become Achilles' heels for their practical applications. In this work, one high-pressure annealing (HPA) strategy was introduced to process the selective laser melted (SLM) martensitic stainless steel. The microstructures and mechanical properties of as-built, high temperature annealing and HPA and as-rolled SLM samples were systematically investigated. It was found that the HPA treatment makes the stainless steel achieve the significant yield strength of 1828 MPa and the comparable plastic strain of 36.2% compared to other samples. The pores and laminar structures from the SLM process were eliminated by HPA. What is more, the HPA treatment results in uniform carbide precipitation, grain refinement and nanoscale heterogeneous structure comprising a series of coarse and fine grains. The physical mechanism for nanoscale heterogeneous structure induced by HPA was discussed from the perspective of the cooperative effect of temperature and pressure. Additionally, the strengthening contributions from grain refinement, carbide precipitation, dislocation hardening, heterogeneous structure and pore closure were quantitatively determined. The current study not only reveals the comprehensive effect of temperature and pressure on microstructure and mechanical properties, but also establishes HPA as an effective method to evade the strength-ductility trade-off in alloys fabricated by additive manufacturing.

Mechanism of quantum yield enhancement in Si quantum dots by high-pressure water vapor annealing from single-dot studies

High-pressure water vapor annealing (HWA) was recently demonstrated as a method that can substantially improve the photoluminescence quantum yield (PLQY) of silicon quantum dots (Si QDs) with the oxide shell. In this Letter, the mechanism of this enhancement is studied optically on a single-dot level. HWA treatment is performed on Si QDs formed on a silicon-on-insulator wafer, and their photoluminescence (PL) properties were examined before and after the treatment. Our experiments show a 2.5 time enhancement in the average blinking duty cycle of Si QDs after 2.6 MPa HWA treatment without changing the average ON-state PL intensity. This observation proves the carrier trapping process is suppressed on the HWA-built Si/SiO2 interface. We also discussed the mechanism behind the PLQY enhancement of HWA-treated Si QDs by comparing single-dot-level data to reported ensemble PL Si QDs results. HWA treatment is found to mainly brighten “grey” (not 100% efficient) QDs, a mechanism different from changing dark (non-emitting) to bright (100% efficient) Si QDs by ligand passivation.

High-pressure hydrogen annealing improving the cryogenic operation of Si (110)-oriented n-MOSFETs

This study experimentally investigated the effects of an additional high-pressure hydrogen annealing (HPHA) on the cryogenic operation of Si (110)-oriented n-MOSFETs. The HPHA induced improvements in the subthreshold swing (SS), threshold voltage (V th), and ON current at cryogenic temperatures. Further, we analyzed the SS-drain current curves using the analytical model and concluded that HPHA reduced the density of the band-edge states. In addition, the analysis of the temperature-dependent V th supported this conclusion. Furthermore, effective mobility analysis results indicated that the improvement in the ON current was attributable to the improvement in the band-edge states. Therefore, we conclude that the HPHA process positively affected the Si/SiO2 interface and reduced the interface-related band-edge states, thereby improving the cryogenic operation of MOSFETs.

The effects of high-pressure annealing on magnetostructural transitions and magnetoresponsive properties in stoichiometric MnCoGe

In this study, phase transitions (structural and magnetic) and associated magnetocaloric properties of stoichiometric MnCoGe have been investigated as a function of annealing pressure. Metastable phases were generated by annealing at 800 °C followed by rapid cooling under pressures up to 6.0 GPa. The x-ray diffraction results reveal that the crystal cell volume of the metastable phases continuously decreases with increasing thermal processing pressure, leading to a decrease in the structural transition temperature. The magnetic and structural transitions merge and form a first-order magnetostructural transition between the ferromagnetic orthorhombic and paramagnetic hexagonal phases over a broad temperature range (>80 K) spanning room temperature, yielding considerable magnetic entropy changes. These findings demonstrate the utility of thermal processing under high pressure, i.e., high-pressure annealing, to control the magnetostructural transitions and associated magnetocaloric properties of MnCoGe without altering its chemical composition.

Isocompositional liquid-liquid transition in dilute aqueous LiCl solutions

We here demonstrate that small amounts of LiCl dissolved in water extend the existence window of deeply supercooled liquid water. This shift allows us to observe the isocompositional, sharp liquid-liquid transition (LLT), while this is not possible in pure water. Upon heating at ambient pressure, the hyperquenched and densified glass first turns into the high-density liquid (HDL) and then experiences the LLT to the low-density liquid (LDL) at 137–141 K and ambient pressure. At the LLT the viscosity suddenly jumps up by an order of magnitude, from ∼4.3×109Pas in HDL to ∼3.7×1010Pas in LDL for the 3.1 mol % solution based on our calorimetric analysis. That is, the LLT takes place clearly in the ultraviscous liquid domain at ambient pressure. By contrast, the viscosity of the emerging LDL at the LLT is still in the domain of the soft glass for pure water and for solutions exceeding 5 mol % LiCl that were studied in the past. This is owing to our observation that, first, the LDL's glass transition is lowered by about 8 K to 126 K in the presence of small amounts LiCl, whereas the HDL's glass transition remains at 118 K. Second, the stability of HDL at ambient pressure is increased by high-pressure annealing, shifting the LLT to higher temperatures. Published by the American Physical Society 2024

Novel strategies for low-voltage NAND flash memory with negative capacitance effect

Here, we present a novel approach to employing a negative capacitance (NC) phenomenon in the blocking oxide of charge trap flash (CTF) memory. To achieve this, we developed an inversible mono-domain like ferroelectric (IMFE) film through high-pressure post-deposition annealing in a forming gas at 200 atm (FG-HPPDA). The FG-HPPDA process enables to form a uniform alignment of domains and facilitates invertible domain switching behavior in ferroelectrics, generating an internal field by the flexo-electric effect as well as interface-pinned polarization by chemical reaction. Subsequently, to stabilize the NC effect, we fabricated the IMFE/Al2O3 heterostructure, which exhibits an outstanding capacitance-boosting feature. Finally, we successfully demonstrate unprecedented CTF memory with the NC effect in a blocking oxide. Our unique CTF device shows the improved performance (maximum incremental-step-pulse-programming (ISPP) slope ∼1.05) and a large MW (>8 V), attributed to the capacitance boosting by NC phenomenon.

Enhanced conductivity in Sr doped La3Ni2O7-δ with high-pressure oxygen annealing

The structural, electrical and magnetic properties of a series of La3-xSrxNi2O7-δ polycrystalline samples have been systematically investigated with and without high-pressure oxygen annealing. Without annealing, the introduction of Sr at La site leads to a moderate enhancement of conductivity. The high-pressure oxygen annealing leads to an increase of oxygen content by ∼1.08 %. Consequently, the conductivity of the annealing samples is significantly enhanced comparing to the untreated samples. The La3-xSrxNi2O7-δ samples exhibit metal-like behavior in the whole temperature range with annealing, which is due to the hole doping effect. The present results could contribute to the exploration of possible ambient superconductivity in La3Ni2O7-δ system.

High-Pressure Deuterium Annealing for Trap Passivation for a 3-D Integrated Structure

High-Pressure Deuterium Annealing for Trap Passivation for a 3-D Integrated Structure

Uncovering the universality of critical phenomenon in a ferromagnet Gd5Si4 prepared under high pressure

Manipulation of phase transition is of great interest not only because it can enhance the application ability of accompanying physical effects, but also because it allows us to uncover the physical connotations near the critical temperature point. In this work, we systematically examine the influence of high-pressure annealing (HPA) on critical phenomena in Gd5Si4 ferromagnet. A second-order magnetic phase transition is determined in the annealed sample under 3 GPa with a reduced Curie temperature. Various techniques including modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis are adopted to calculate critical exponents β, γ, and δ of HPA compound. Using the obtained parameters, we employ the renormalization group theory to calculate the spin exchange range, which satisfies J(r) ∼ r−4.454, exhibiting a longer-range-ordered ferromagnetic interaction. Our work indicates that HPA can manipulate the degree of order inside matter with a novel universality class, thus acquiring desired functionality through reasonable HPA treatment.

An EBSD analysis of a commercial immiscible Cu43%Cr alloy after high-pressure torsion processing and annealing

ABSTRACT The influence of high-pressure torsion (HPT) and annealing on microstructure, texture and thermal stability of an immiscible composite Cu43%Cr alloy was studied using electron backscatter diffraction, X-ray diffraction and microhardness measurements. As-received alloy samples were subjected to HPT and subsequent annealing treatment in the range of 210–850°C for 1 h in order to develop ultrafine-grained (UFG) microstructures and highlight their thermal stability. The Cu and Cr grains were refined to ∼0.45 and ∼0.39 µm, respectively and exhibited equiaxed morphology. The crystallographic texture was of shear type in both Cu and Cr with the domination of C and F orientations, respectively. The UFG microstructure and texture were retained in the Cu43%Cr alloy up to 850°C. The global results show that the immiscible composite Cu43%Cr alloy exhibits a high thermal stability up to 850°C. The evolution of the microstructure, texture and thermal stability of the UFG Cu43%Cr alloy was compared to published data and available models.

(Invited) Application of Synchrotron X-Ray Topography Techniques to the Analysis of Defect Microstructures in Bulk GaN Substrates and Epilayers for Power Devices

Wide bandgap semiconductor gallium nitride (GaN), along with silicon carbide (SiC) are replacing silicon materials in the applications for power electronic devices. While SiC-based power technologies are based on bulk SiC substrates, GaN-based power technologies have until recently been based on GaN layers grown on foreign substrates such as sapphire, SiC and Si substrates. To achieve the full potential of GaN power devices, devices on bulk GaN substrates are desirable. In this review, the use of synchrotron X-ray topography techniques to evaluate defects and strain in bulk GaN substrates for vertical device development is presented. Ray tracing simulations is shown to effectively identify the Burgers vectors of all dislocations on X-ray topographs from GaN materials. Ammonothermal-grown GaN substrate wafers show the best quality among all the wafers. These wafers, which are free of basal plane dislocations (BPDs), have low curvature and threading mixed dislocations (TMDs) dominant among the TDs. However, certain ammonothermal substrates contain growth sectors with different impurity concentrations that are likely inherited from prior seed expansion growth runs. Patterned hydride vapor phase epitaxy (HVPE) GaN reveal a starkly heterogeneous distribution of dislocations with large areas containing low threading dislocation densities in between a grid of strain centers with higher threading dislocation densities and BPDs. These substrates also contain growth sector boundaries separating core regions growing in <11-22> directions and surrounding regions growing along [0001]. HVPE GaN substrates are characterized by high lattice distortion and dislocation densities of the order of 105-106 cm-2, which is much higher than 103-104 cm-2 of ammonothermal samples and dislocation-free areas in the patterned HVPE samples. Epitaxial growth and other processes involving heat treatment (including annealing) does not nucleate new defects but can result in interactions of dislocations (threading screw dislocations(TSDs)/threading mixed dislocations (TMDs)/threading edge dislocations (TEDs)) with point defects leading to changes in dislocation configurations. Mg-ion implantation for p-type doping does not change the distribution of dislocation but introduces lattice damage. By Rocking curve Analysis by Dynamical Simulation (RADS) analysis of X-ray rocking curves, the depth profile of strain can be obtained and correlated with doping profile. During annealing the implanted samples to heal lattice damage and activate the Mg ions, proper capping is necessary to limit loss of matter and introduction of additional lattice distortion. However, high pressure annealing has been shown to eliminate the need for capping. The effect on microstructure from other selectively area doping techniques such as etch and regrowth, diffusion and neutron transmutation will also be discussed.

Realizing metallicity in Sr2IrO4 thin films by high-pressure oxygen annealing

Perovskite iridates are a promising material platform for hosting unconventional superconductivity. Transport measurements of Sr2IrO4 thin-film field-effect transistors are expected to provide irrefutable evidence for the existence of superconductivity. However, these experiments have revealed a remarkably robust insulating state over wide electron and hole doping ranges; this finding is in contrast to the case of the bulk material, in which metallicity appears upon moderate electron doping by substituting cations in place of Sr. The nature of this robust insulating state and whether any metallic state can be realized in the Sr2IrO4 thin film are two remaining challenges that preclude further progress in the search for superconductivity in this system. Here, we show that this insulating state is enhanced in Sr2IrO4 thin films by thermal annealing under vacuum conditions, while it can be destroyed upon annealing in an oxygen atmosphere within restricted ranges of oxygen pressure, annealing temperature and ion substitution levels. The resulting films exhibit metallic transport behavior near room temperature and a metal–insulator crossover at ~200 K. Our results point to the potentially important roles of the oxygen vacancies at different atomic sites in the formation of the robust insulating state and the new metallic state and to their interplay in the Sr2IrO4 thin film. This finding opens new possibilities in the search for unconventional superconductivity by further tailoring the as-found metallic state in properly oxygen-annealed Sr2IrO4 thin films.

Lowering of Schottky Barrier Height in a Vertical Pillar MOSFET by Deuterium Annealing

The Schottky barrier height (Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) is lowered by high-pressure deuterium annealing (HPDA), in a vertical pillar (VP) metal-oxide-semiconductor field effect transistor (MOSFET). Typical device characteristics were comparatively studied before and after HPDA. A change of contact resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) at a Schottky junction was also analyzed by using a transmission line method (TLM). Moreover, HPDA effects on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> were characterized on different crystal orientations of silicon, which has a different number of traps. HPDA is more effective to lower the Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> at (111) orientation than at (100) orientation because a greater number of interface traps can be passivated for an orientation with a high Miller index. Finally, a deuterium peak was physically profiled across the Schottky junction by use of time-of-flight secondary ion mass spectrometry (ToF-SIMS).

The pressure-induced crystal structure transformations in the high-pressure annealed Bi1− xTbxFeO3 compounds (x = 0.05, 0.1, and 0.3)

The substitution of Bi by rare-earth ions is one of the common approaches for improving the electrical, magnetic, and multiferroic properties of the most studied multiferroic material BiFeO3. In this work, Bi1−xTbxFeO3 compounds with x = 0.05, 0.1, and 0.3 were synthesized using a two-step process: standard solid-state synthesis and high-pressure annealing. The obtained samples were studied by means of x-ray diffraction at normal pressure and neutron powder diffraction at high pressure. It was shown that high-pressure annealing could increase the Tb solubility limit to 10 at. %. It is proposed that the maximum solubility limit is even higher and could be achieved with high-pressure annealing in bulk samples. The transition from the R3c phase to the Pnma phase for the compounds with x = 0.05, 0.1 occurs through a two-phase region and starts at P≈4.4 and 1.7 GPa, respectively. The Pnma phase is stable in the compound with x = 0.3 up to P≈3.2 GPa. The values of Fe magnetic moments decrease with an increase in the Tb concentration or with external pressure for the compounds with x=0.05,0.3 in one-phase regions. The results will help to optimize the synthesis of multiferroic materials with improved magnetoelectric coupling for use in technological applications.

93 at.% of Na extraction from a Na24Si136 single crystal via anisotropic ion diffusion control method

An allotrope of Si, Si136, is a promising semiconductor for photovoltaics due to its direct bandgap. Si136 is synthesized via Na extraction from Na24Si136. In this study, 93 at.% of Na extraction from a single crystal of Na24Si136 was achieved using high-pressure-annealed zeolite as an ion absorber. The residual amount of Na is the least record among Na extraction from a single-crystalline Na24Si136. Na diffusion between the grains of amorphous phases of zeolite was suggested to be improved due to high-pressure annealing.

Glass Polymorphism in Hyperquenched Aqueous LiCl Solutions

We investigate the glass polymorphism of dilute LiCl-H2O in the composition range of 0-5.8 mol % LiCl. The solutions are vitrified at ambient pressure (requires hyperquenching with ∼106 K s-1) and transformed to their high-density state using a special high-pressure annealing protocol. Ex situ characterization was performed via isobaric heating experiments using X-ray diffraction and differential scanning calorimetry. We observe signatures from a distinct high-density and a distinct low-density glass for all solutions with a mole fraction xLiCl of ≤ 4.3 mol %, where the most notable are (i) the jumplike polyamorphic transition from high-density to low-density glass and (ii) two well-separated glass-to-liquid transitions Tg,1 and Tg,2, each pertaining to one glass polymorph. These features are absent for solutions with xLiCl ≥ 5.8 mol %, which show only continuous densification and relaxation behavior. That is, a switch from water-dominated to solute-dominated region occurs between 4.3 mol % LiCl and 5.8 mol % LiCl. For the water-dominated region, we find that LiCl has a huge impact only on the low-density form. This is manifested as a shift in halo peak position to denser local structures, a lowering of Tg,1, and a significant change in relaxation dynamics. These effects of LiCl are observed both for hyperquenched samples and low-density samples obtained via heating of the high-density glasses, suggesting path independence. Such behavior further necessitates that LiCl is distributed homogeneously in the low-density glass. This contrasts earlier studies in which structural heterogeneity is claimed: ions were believed to be surrounded by only high-density states, thereby enforcing a phase separation into ion-rich high-density and ion-poor low-density glasses. We speculate the difference arises from the difference in cooling rates, which are higher by at least 1 order of magnitude in our case.