Surface Brillouin scattering on annealed ion-implanted CVD diamond

Single crystal <100> diamond samples were implanted with a total fluence of 1.5 × 10¹⁶  ions/cm² at single energy of 150 keV using carbon ions. This implantation fluence created a damage density that would not restore the diamond structure after annealing. Surface Brillouin scattering studies show that the elastic properties of the highly damaged diamond layer starts to transit from diamond-like to amorphous carbon state at an annealing temperature of 500 °C. The amorphous carbon layer is shown to have a sound velocity (elastic properties) similar to those reported for tetrahedral amorphous carbon (ta-C). Raman spectroscopy, EELS and HRTEM has been used in conjunction with the SBS data to monitor the changes in the carbon implanted diamond at different annealing temperatures.     

Si diffusion induced adhesion and corrosion resistance in annealed RF sputtered SiC films on graphite substrate

Silicon carbide (SiC) is one of the promising candidates for graphite protection in different applications involving high temperatures and a highly corrosive environment. An ideal Silicon carbide coating should withstand a corrosive environment without compromising its adhesion. Herein, RF magnetron sputtered silicon-rich SiC thin films were deposited on a graphite substrate followed by annealing at 1000 °C, 1200 °C, and 1400 °C in an inert atmosphere. The impact of annealing temperature on microstructure, adhesion and chemical stability of SiC thin films was demonstrated. Different analytical techniques like Scanning electron microscopy (SEM), X-Ray Diffraction (XRD), Fourier's Transform Infrared (FTIR) spectroscopy and nano-indentation were used to study microstructural evaluation and mechanical characteristics. Moreover, the electrochemical analysis (Tafel and Electrochemical impedance spectroscopy) was performed in 3.5% NaCl solution. The microstructural analysis revealed that the amorphous SiC thin film turned into a crystalline and dense film upon annealing. Scanning electron micrographs showed that silicon-rich regions at SiC film surface started to disappear as Si diffuses into graphite matrix at elevated temperatures. Both these factors contributed to improvement in the adhesion of SiC coating with graphite substrate as annealing temperature increased. In addition, the nano-indentation hardness of 5.2 GPa was obtained for as grown sample, which decreased at 1000 °C, and then increased at 1200 °C and 1400 °C. Furthermore, the electrochemical analysis confirmed the enhancement in corrosion resistance upon annealing at a temperature of 1200 °C and 1400 °C due to Si diffusion and film compactness in these samples.     

Study of the Ion‐Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

6H–SiC single crystals and two types of SiC fibers, Hi‐Nicalon type S and Tyranno SA3, have been irradiated with 4‐MeV Au³⁺ up to 2 × 10¹⁵ cm^?2 (4 dpa) at room temperature, 100°C and 200°C. These fibers are composed of highly faulted 3C–SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29 nm^?1 and 26–36 nm for the Hi‐Nicalon type S fibers and 0.18 nm^?1 and 141–210 nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro‐Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100°C and a remaining crystallinity when irradiated at 200°C. The latter observations reveal a multi‐band irradiated layer consisting in a partially amorphized band near the surface and an in‐depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi‐Nicalon type S fibers irradiated at 200°C.     

Kr ion irradiation study of polymer-derived SiFeOC–C–SiC nanocomposite

This study focuses on the pyrolysis and ion irradiation behaviors of polymer-derived SiFeOC–C–SiC ceramic. The pyrolyzed material is composed of SiO₂ and SiOC (amorphous), carbon (amorphous and turbostratic), and Fe₃Si and β-SiC (nanocrystalline). Irradiation was carried out at both room temperature and 600°C using 400 keV Kr ions with fluences of 4 × 10¹⁵ and 1 × 10¹⁶ ions cm⁻², respectively. The Fe₃Si and SiC nanocrystals are stable against irradiation up to 3 displacement per atom (dpa) at room temperature and up to 12 dpa at 600°C. The SiOC tetrahedrals show phase separation and minor carbothermal reduction. The high irradiation resistance and the dense, defect-free amorphous microstructure of SiFeOC–C–SiC after prolonged irradiation demonstrate its great potential for advanced nuclear reactor applications.     

Mechanical Characterization of Annealed ZrB2–SiC Composites

Composites consisting of 70 vol% ZrB₂ and 30 vol% α‐SiC particles were hot pressed to near full density and subsequently annealed at temperatures ranging from 1000°C to 2000°C. Strength, elastic modulus, and hardness were measured for as‐processed and annealed composites. Raman spectroscopy was employed to measure the thermal residual stresses within the silicon carbide (SiC) phase of the composites. Elastic modulus and hardness were unaffected by annealing conditions. Strength was not affected by annealing at 1400°C or above; however, strength increased for samples annealed below 1400°C. Annealing under uniaxial pressure was found to be more effective than annealing without applied pressure. The average strength of materials annealed at 1400°C or above was ~700 MPa, whereas that of materials annealed at 1000°C, under a 100 MPa applied pressure, averaged ~910 MPa. Raman stress measurements revealed that the distribution of stresses in the composites was altered for samples annealed below 1400°C resulting in increased strength.     

Divacancy and silicon vacancy color centers in 4H-SiC fabricated by hydrogen and dual ions implantation and annealing

Silicon carbide (SiC), as a wide-band gap semiconductor, plays an important role in high temperature and high-power devices, and the spin defect has great application prospect in quantum technology. Divacancy in SiC (V_CV_Si, VV) has attracted more and more attention. There are a lot of experimental studies on color center preparation by ion implantation, but the mechanism of atomic scale defects in the experimental preparation process is not fully understood. EPI epitaxial 4H–SiC was implanted with 250 keV proton at room temperature under three fluence of 1E14 cm^?2, 1E15 cm^?2, 1E16 cm^?2. Defects of implanted 4H–SiC samples were characterized by photoluminescence spectrum and electron paramagnetic resonance (EPR). The existence of the optimal implantation fluence for V_Si and V_CV_Si (VV) color centers by hydrogen ion implantation was found. Molecular dynamics (MD) simulation by considering the ionization energy loss for swift ion implantation were used to study the defect distribution and transformation at atomic-scale during hydrogen ion implantation and post-annealing. The optimal implantation fluence was found and confirmed by comparing the atomic-scale implantation simulation with the experimental results. In the annealing simulation, the optimal annealing temperature for the color centers in 4H–SiC was verified, and its formation mechanism was analyzed by accurately calculating the defect transformation during the annealing process. Finally, in order to accurately control the depth of color center in 4H–SiC, dual ions implantation of carbon and proton has been studied to realize the optimal divacancy yield by SRIM and MD simulations. Molecular dynamics simulation results showed that low-fluence C pre-implantation is helpful to improve the color center yield for the dual ions implantation.     

Solidification of welded SiC–ZrB2–ZrC ceramics

A silicon carbide‐based ceramic, containing 50 vol% SiC, 35 vol% ZrB₂, and 15 vol% ZrC was plasma arc welded to produce continuous fusion joints with varying penetration depth. The parent material was preheated to 1450°C and arc welding was successfully implemented for joining of the parent material. A current of 138 A, plasma flow rate of ~1 L/min or ~0.5 L/min, and welding speed of ~8 cm/min were utilized for repeated joining, with full penetration fusion zones along the entire length of the joints. Solidification was determined to occur through the crystallization of β‐SiC (3C), then the simultaneous solidification of SiC and ZrB₂, and lastly through the simultaneous solidification of SiC, ZrB₂, and ZrC through a ternary eutectic reaction. The ternary eutectic composition was determined to be 35.3 ± 2.2 vol% SiC, 39.3 ± 3.8 vol% ZrB₂, and 25.4 ± 3.0 vol% ZrC. A dual fusion zone microstructure was always observed due to convective melt pool mixing. The SiC content at the edge of the fusion zone was 57 vol%, while SiC content at the center of the fusion zone was 42 vol% although the overall SiC content was still nominally 50 vol% throughout the entire fusion zone.     

Gradual modification of the YSZ structures by Au ion implantation and high-energy Si ion irradiation

Gold nanoparticles (Au-NPs) were created in crystalline yttria-stabilized zirconia (YSZ). (100)-, (110)- and (111)-oriented YSZ samples were implanted by 1 MeV Au⁺ ions at room temperature and fluences ranging from 1.5 × 10¹⁶ cm⁻² to 7.5 × 10¹⁶ cm⁻². The prepared Au: YSZ structures were annealed at 1100 °C for 1 h on air to support the Au-NPs coalescence and YSZ structure recovery. Subsequent irradiation with the 10 MeV Si³⁺ ions with a fluence of 5.0 × 10¹⁴ cm⁻² was performed to enable gradual modification of Au-NPs. Au-depth profiles and YSZ structure modification in the produced samples were analysed via Rutherford backscattering spectrometry in channelling mode (RBS-C) and X-ray diffraction (XRD). RBS-C showed the gold distributed in the region of about 50–300 nm below the YSZ surface. The disorder was accumulated in the region with Au-NPs and the concentration of the disorder increases as a function of ion implantation fluence. The Zr-disorder was partially decreased after the annealing, while the subsequent Si-ion irradiation increased Zr-disorder again, however, the disorder does not reach values before the annealing. XRD measurement evidenced elastic deformation of the YSZ host lattice in the Au-implanted samples. Optical absorbance showed the appearance of the new absorption band at 550 nm for the Au-ion fluences above 5.0 × 10¹⁶ cm⁻² ascribed to the Au-NPs formation. After the annealing, the absorption band is shifted to the wavelength of 580 nm which could be connected to the proceeding clustering of Au. The maximum absorption peak intensity increases which is connected to the increasing amount of the Au-NPs. Transmission electron microscopy (TEM) with Energy dispersive spectroscopy (EDS) confirmed the presence of Au-NPs in the implanted layer after the annealing. The subsequent Si-ion irradiation did not change the Au-NP shape which remained spherical with a slight size increase.     

Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.     

Xenon ion implantation induced defects and amorphization in 4H–SiC: Insights from MD simulation and Raman spectroscopy characterization

Xenon Focused Ion Beam (Xe-FIB) processing of 4H–SiC is an emerging technique with great potential for various applications. In this study, we investigate the evolution mechanism of damage caused by xenon ion implantation in 4H–SiC using a combination of molecular dynamics (MD) simulation and Raman spectroscopy. The study explores the microscopic mechanisms of damage processing and repairs using the proper potential function and the optimized simulation model. The MD simulation reveals that the vacancy and interstitial sites of silicon and carbon atoms, as identified by the Wigner-Seitz defect method, increase linearly with implanted dose until the dose reaches 2 × 10¹⁴ ions/cm². Subsequently, the growth rate of each defect site in the damaged area slows down and eventually comes to a saturation state with a continuous increase in dose. The growth rate of the amorphous region also slows down with the constant increase in dose, similar to the results obtained through variable temperature Raman spectroscopy characterization experiments on 4H–SiC (0001) nitrogen-doped substrates implanted with different doses of xenon ions. Furthermore, unlike light ions such as hydrogen and helium, Xe ions cause significant damage to the inside of 4H–SiC, resulting in the inability to produce structurally complete silicon vacancy defects. Our findings provide insights into the fundamental mechanism of Xe-FIB processing and have implications for future applications in semiconductor technology.     

Amorphization and graphitization of single-crystal diamond — A transmission electron microscopy study

The amorphization and graphitization of single-crystal diamond by ion implantation were explored using transmission electron microscopy (TEM). The effect of ion implantation and annealing on the microstructure was studied in (100) diamond substrates Si⁺ implanted at 1 MeV. At a dose of 1 × 10¹⁵ cm^− 2, implants done at 77 K showed a damage layer that evolves into amorphous pockets upon annealing at 1350 °C for 24 h whereas room temperature implants (303 K) recovered to the original defect free state upon annealing. Increasing the dose to 7 × 10¹⁵ Si⁺/cm² at 303 K created an amorphous-carbon layer 570 ± 20 nm thick. Using a buried marker layer, it was possible to determine that the swelling associated with the amorphization process was 150 nm. From this it was calculated that the layer while obviously less dense than crystalline diamond was still 15% more dense than graphite. Electron diffraction is consistent with the as-implanted structure consisting of amorphous carbon. Upon annealing, further swelling occurs, and full graphitization is achieved between 1 and 24 h at 1350 °C as determined by both the density and electron diffraction analysis. No solid phase epitaxial recrystallization of diamond is observed. The graphite showed a preferred crystal orientation with the (002)g//(022)d. Comparison with Monte Carlo simulations suggests the critical displacement threshold for amorphization of diamond is approximately 6 ± 2 × 10²² vacancies/cm³.     

Probing Site Symmetry Around Eu3+ in Nanocrystalline ThO2 Using Time Resolved Emission Spectroscopy

ThO₂:Eu³⁺ nanoparticles were synthesized at 300°C by combustion route using urea as a fuel and characterized by thermogravimetric/differential thermal analysis, X‐ray diffraction, transmission electron microscopy, and photoluminescence techniques. To investigate the effect of annealing temperature, as synthesized powder were heated further at 500°C, 700°C, and 900°C. It was observed that extent of asymmetry around Eu³⁺ at 700°C/900°C is very high as compared to as‐prepared or 500°C annealed sample. Based on the time resolved emission spectroscopic investigations, it was inferred that two different types of Eu³⁺ ions were present in the ThO₂ nanoparticles. In ThO₂ structure, Eu³⁺ ions occupy two sites; cubic (O_h) and noncubic (<C_2v) as can be confirmed from our emission studies. Short‐lived species T₁ (~1.3–3.4 ms) predominates at higher annealing temperature arises because of Eu³⁺ ions occupying noncubic (<C_2v) sites without inversion symmetry, whereas long‐lived species T₂ (~4.6–6.6 ms) can be ascribed to Eu³⁺ ions occupying cubic sites (O_h) with inversion symmetry.     

Electrically conductive SiC ceramics processed by pressureless sintering

Polycrystalline SiC ceramics with 10 vol% Y₂O₃-AlN additives were sintered without any applied pressure at temperatures of 1900-2050°C in nitrogen. The electrical resistivity of the resulting SiC ceramics decreased from 6.5 × 10¹ to 1.9 × 10⁻² Ω·cm as the sintering temperature increased from 1900 to 2050°C. The average grain size increased from 0.68 to 2.34 μm with increase in sintering temperature. A decrease in the electrical resistivity with increasing sintering temperature was attributed to the grain-growth-induced N-doping in the SiC grains, which is supported by the enhanced carrier density. The electrical conductivity of the SiC ceramic sintered at 2050°C was ~53 Ω⁻¹·cm⁻¹ at room temperature. This ceramic achieved the highest electrical conductivity among pressureless liquid-phase sintered SiC ceramics.     

Structural and compositional characterization of 6H–SiC implanted with N+ and Al+ ions using optical methods

Using plane-view and cross-sectional Raman spectroscopy, polarized infra-red spectroscopy and photothermal spectroscopy, the structure, composition and internal stress of 6H–SiC crystal implanted sequentially with N⁺ and Al⁺ ions to form a (SiC)_1−x(AlN)_x solid solution were studied non-destructively and self-consistently. The optimum implantation temperature for the synthesis of a (SiC)_1−x(AlN)_x solid solution with a 6H structure was found to be 600 °C.     

The structural properties of B–O codoped diamond films

Using Raman spectroscopy and positron annihilation technology (PAT), we investigate the structural properties of the codoped samples by implanting boron and oxygen ions into the intrinsic diamond films (called BO series) and by implanting oxygen ions into the diamond films doped with small amounts of boron in chemical vapor deposition (called CVDBO series). It is found that after 1000 °C annealing, the full width at half maximum (FWHM) value of diamond peak in Raman spectrum reduces, the amount of diamond increases above 99.6% and the stress changes from compression to tension. More important, the FWHM value in CVDBO series decreases by 1.6 cm^{? 1} after 1000 °C annealing, which is larger than that in the BO series with a decrease of 0.2 cm^{? 1}, showing that the annealing prefers to more significantly reduce the defect concentration in CVDBO series. Also, the PAT measurements indicate that the S_n value of CVDBO series is smaller than that of BO series after 800 °C annealing, suggesting that CVDBO series has lower defect concentrations. It is revealed that the co-doping that implanting oxygen ions into the low concentration B-doped diamond films can give a better restoration of the damaged diamond lattice by oxygen ion implantation after high temperature annealing. The intrinsic mechanism is also discussed.     

Spectroscopic characterization of thin SiC films

The electrical, structural and optical properties of thin SiC films were investigated. A new approach based on high temperature annealing of layered carbon–silicon structures was used for the formation of the films. The SiC films were prepared by deposition of 30 nm thick carbon films on crystalline silicon (c-Si) and on porous silicon layers grown on c-Si. The layers were annealed to temperatures between 800 and 1400°C for different annealing times ranging between 15 and 180 s. The structure of the resulting SiC films was analyzed by Raman spectroscopy. The Raman spectra of as-deposited films consist of two broad bands at 1350 and 1580 cm⁻¹ characteristic of the presence of amorphous carbon. These bands were shifted to lower frequencies in the spectra of annealed layers and were assigned to the hexagonal and cubic SiC phases. The photoluminescence spectra of the studied layers show a broad band at 550 nm. The most intense photoluminescence was observed from non-annealed porous silicon layers covered with thin carbon films. A degradation of the luminescence and a simultaneous increase of the conductivity of the layers with increasing annealing temperature and/or duration of annealing was observed. This behavior strongly suggests the creation of defect states which determine the conductivity of the layers and at the same time act as non-radiative centers. The increase of defect states was explained as originating from the dehydrogenation of the silicon carbide layers by annealing.     

Hydrogen Permeation Properties and Hydrothermal Stability of Sol–Gel‐Derived Amorphous Silica Membranes Fabricated at High Temperatures

The sol–gel method was applied to the fabrication of amorphous silica membranes for use in hydrogen separation at high temperatures. The effects of fabrication temperature on the hydrogen permeation properties and the hydrothermal stability of amorphous silica membranes were evaluated. A thin continuous silica separation layer (thickness = <300 nm) was successfully formed on the top of a deposited colloidal silica layer in a porous glass support. After heat treatment at 800°C for an amorphous silica membrane fabricated at 550°C, however, it was quite difficult to distinguish the active separation layer from the deposited colloidal silica layer in a porous glass support, due to the adhesion of colloidal silica caused by sintering at high temperatures. The amorphous silica membranes fabricated at 700°C were relatively stable under steam atmosphere (500°C, steam = 70 kPa), and showed steady He and H₂ permeance values of 4.0 × 10^?7 and 1.0 × 10^?7 mol·m^?2·s^?1·Pa^?1 with H₂/CH₄ and H₂/H₂O permeance ratios of ~110 and 22, respectively. The permeance ratios of H₂/H₂O for membranes fired at 700°C increased drastically over the range of He/H₂ permeance ratios by factors of ~3–4, and showed a value of ~30, which was higher than those fired at 500°C. Less permeation of water vapor through amorphous silica membranes fabricated at high temperatures can be ascribed to the dense amorphous silica structure caused by the condensation reaction of silanol groups.     

Raman Scattering and Backscattering Studies of Silicon Nanocrystals Formed Using Sequential Ion Implantation

Silicon nanocrystals were produced using a two-stage gold ion implantation technique. The first stage implantation using low energy ions led to the formation of an amorphous Si (a-Si) layer. A subsequent high energy Au irradiation in the second stage was found to produce strained Si NCs. An annealing step at a temperature as low as 500 °C was seen to result in strain free NCs. Higher temperature annealing of the samples was found to result in a growth in size from recrystallization of the a-Si matrix. Raman Scattering, X-Ray diffraction and Rutherford Backscattering Spectrometry have been used to study the effect of annealing on the samples and the size of the Si NCs formed. The data can be well explained using a phonon confinement model with an extremely narrow size distribution. The XRD results are in line with the Raman analysis.     

SiC nanograins stabilized Si–C–B–N fibers with ultrahigh-temperature resistance

Continuous ceramic fibers with ultrahigh-temperature stability are in high demand for applications in advanced space propulsion and thermal protection systems. In this study, SiC nanograins stabilized Si–C–B–N ceramic fibers were prepared using chemically modified polyborosilazane via a polymer-derived method. The fabricated Si–C–B–N fibers exhibited a rather high tensile strength of approximately 1.8 GPa and a high strength retention of approximately 90% after annealing at 2100°C for 0.5 h under a nitrogen atmosphere. The ultrahigh-temperature stability can be contributed to the presence of thermodynamically stable SiC nanograins and the encapsulation of SiC nanograins by the BN(C) phase and amorphous Si–C–B–N matrix. Our work offers a convenient strategy for preparing Si-based ceramic fibers with ultrahigh-temperature stability at beyond 2000°C.     

Metal–insulator transition in boron-ion implanted type IIa diamond

Electrical conductivity measurements for selected boron-ion dopant concentrations have been made on type IIa diamond specimens in the temperature range 1.5–30 K. Samples have been implanted using the CIRA (cold implantation–rapid annealing) process, in which small implantation increments were used followed by high-temperature annealing to achieve a significant reduction in the levels of implantation-induced radiation damage and to obtain maximum boron activation. Further post anneals at temperatures up to 1700°C were carried out. Using this procedure, we have recorded, for the first time, metallic conductivity behaviour in implanted surface layers in single-crystal diamond specimens with boron concentrations measured by secondary-ion mass spectrometry to be of the order of n=10²¹ cm⁻³. The occurrence of a metal–insulator transition in this system is discussed.