Ablation Of SiC Research Articles

Numerical and experimental analysis of nanosecond laser ablation of SiC

This work presents a fundamental study on the melting threshold, ablation morphology and removal mechanism of single-crystal SiC during nanosecond laser processing. A thermal model was established to investigate the thermal behavior of single-crystal SiC at different wavelengths and pulse durations, and to predict the size and cross-sectional profile of ablation hole. The phase transitions and thermophysical parameters variation of silicon carbide with temperature were considered in the numerical analysis. To verify the reliability of the established model, the simulation data were compared with experimentally measured ablation depth under the same operating parameters. The investigation results indicated that the melting threshold of crystalline material increased with the increase of wavelength under the studied condition and was approximately linear distribution. Surface evaporation should be the dominant removal mechanism for nanosecond laser pulse ablation of SiC. By comparing the diameter and depth of ablated hole obtained from experiment and simulation calculation, it is found that the experimental/modeling coupling method had good consistency. Therefore, the established model can accurately simulate the interaction process between nanosecond laser pulse and silicon carbide.

Modeling chemical reactions in laser-induced plasmas

Under the assumption of local thermal equilibrium, a numerical algorithm is proposed to find the equation of state for laser-induced plasmas (LIPs) in which chemical reactions are permitted in addition to ionization processes. The Coulomb interaction in plasma is accounted for by the Debye–Huckel method. The algorithm is used to calculate the equation of state for LIPs containing carbon, silicon, nitrogen, and argon. The equilibrium reaction constants are calculated using the latest experimental and ab initio data of spectroscopic constants for the molecules $$\hbox {N}_2, \hbox {C}_2, \hbox {Si}_2, \hbox {CN}, \hbox {SiN}, \hbox {SiC}$$ and their ions. The algorithm is incorporated into a fluid dynamic numerical model based on the Navier–Stokes equations describing an expansion of LIP plumes into an ambient gas. The dynamics of LIP plumes obtained by the ablation of SiC, solid silicon, or solid carbon in an ambient gas containing $$\hbox {N}_2$$ and Ar is simulated to study formation of molecules and molecular ions.

Effect of high temperature heat treatment on the ablation of SiC–ZrB2–ZrC particles modified C/C composites in two heat fluxes

Effect of high temperature heat treatment on the ablation of carbon/carbon (C/C) composites modified by SiC–ZrB2–ZrC particles was investigated under oxyacetylene torch. The composites were prepared through thermal gradient chemical vapor infiltration at 900–1100°C and precursor infiltration and pyrolysis at 1400–1800°C. The SiC–ZrB2–ZrC particles modified C/C composites with and without heat treatment at 2100°C were named as C/C-ZSA and C/C-ZSB, respectively. Compared with C/C-ZSB, C/C-ZSA had four kinds of cracks, higher thermal conductivity, lower ablation rates in heat flux of 4.18MW/m2 and promoted ablation in 2.38MW/m2. Different thermal conductions induced various rises of surface temperature. The surface temperature and these four cracks determined local thermal stress and infiltration of oxidizing species, which dominated mechanical erosion of outer layer and oxidation of sub-layer. Compared with C/C-ZSB, the existence of these four cracks and lower surface temperature of C/C-ZSA reduced mechanical erosion in 4.18MW/m2 but resulted in enhanced oxidation in 2.38MW/m2.

Resistance to oxidation and ablation of SiC coating on graphite prepared by chemical vapor reaction

A thick SiC coating was prepared on graphite by chemical vapor reaction. The coating reveals a typical crystalline structure with limited porosity and combines well with the substrate. Oxidation tests demonstrate that the coating has a weak self-healing ability at 1100K and good self-healing ability at temperatures from 1623 to 1823K. An oxyacetylene torch test verifies that the prepared coating can effectively protect graphite from ablation for 50s. After the ablation test, the silica microspheres and other interesting silica structures such as microwires, microparticles, microflowers, nanowires and nanoparticles are formed at the ablation center and its surroundings.

Pulsed laser ablation of SiC in a nitrogen atmosphere: formation of CN

Optical emission lines from the plasma generated by a laser ablation process have been investigated to gather information on the nature of the chemical species present. In particular, the experiments were carried out during the laser ablation of a ceramic sintered SiC target, both in vacuum and in presence of controlled nitrogen atmosphere. Time integrated and spatially resolved emission spectra are dominated by the atomic emission lines from silicon and carbon species, either neutral, or singly ionized. When the ablation process was carried out in a nitrogen gas background direct evidence of the formation of the CN molecular specie was found. Fast photography imaging of the expanding plume revealed the formation of a shock wave at nitrogen pressure above 13.3 Pa, with the consequent heating of the shocked region and enhancement of the kinetics of ionization and excitation. Since the C2 specie was absent, a CN formation mechanism involving atomic carbon and nitrogen in the presence of a shock wave is suggested.

G303 SiCアブレーション層による放射加熱の低減(G.S.3 特殊流れ)

G303 SiCアブレーション層による放射加熱の低減(G.S.3 特殊流れ)

Radiative Characteristics of Carbonaceous Ablation Layers with Reflection Effects.

The equilibrium composition and spectral absorption coefficient of SiC ablation layer plasmas have been calculated for temperature of 5000 to 7000 K, layer thickness of 0 to 7.5 mm, and pressure of 0.1 to 1.0 MPa. The radiations included were molecular bands, atomic lines, and continuum processes. The absorption coefficient thus calculated was applied to a simplified shock layer model for the Jupiter entry probe to investigate the effectiveness of the ablation layer in reducing the radiative heating from a shock layer to a body surface. It was found that the SiC ablation layer is very effective to protect the body from radiative heating and that the photoionization processes of atomic carbon and silicon were mainly responsible for radiative absorption at high photon energy range. Furthermore the molecular carbon bands were effectively absorptive in relatively low photon energy range, Particularly at low temperatures.

Radiative Characteristics of Carbonaceous Ablation Layers with Reflection Effects

The equilibrium composition and spectral absorption coefficient of SiC ablation layer plasmas have been calculated for temperature of 5000 to 7000 K, layer thickness of 0 to 7.5mm, and pressure of 0.1 to 1.0 MPa. The radiations included were molecular bands, atomic lines, and continuum processes. The absorption coefficient thus calculated was applied to a simplified model of the ablation layer for Jupiter entry probe. It was found that the molecular carbon bands were very effective in reducing the high-temperature radiative flux from a stagnation shock layer at low ablation-layer temperature, and the photoionization process in atomic elements (carbon, silicon) at high ablation-layer temperature.

Precise microfabrication of wide band gap semiconductors (SiC and GaN) by VUV–UV multiwavelength laser ablation

High-quality deep etching of single crystal 6H-SiC substrate and epitaxial GaN thin film by 266-nm laser ablation coupled with a vacuum ultraviolet (VUV) Raman laser (133–184 nm), followed by chemical treatment in HF for SiC and HCl solution for GaN is demonstrated. The etch rate was as high as 35 nm pulse −1 for SiC and 55 nm pulse −1 for GaN. Scanning probe microscopy measurement indicates that the surface of the etched films was structurally well defined and cleanly patterned. Micro-Raman measurement of ablated SiC samples, and micro-photoluminescence measurement of ablated GaN samples revealed no severe damage to the optical properties or the crystal structure. The mechanism of the VUV-266 nm laser ablation of SiC and GaN is discussed based on the band structure.

Growth of SiC and SiCxNy films by pulsed laser ablation of SiC in Ar and N2 environments

Amorphous SiC and SiCxNy films have been deposited by pulsed laser deposition on single crystal silicon substrates by KrF (248 nm) excimer laser ablation of a SiC sintered target in a vacuum system at room temperature using nonreactive, Ar, and reactive, N2, background gases at different pressures. The pressure range in the growth chamber was from 4×10−8 Torr to 80 mTorr. The optical properties and stoichiometry of films were varied by the introduction of a background gas. The resulting films are inspected by spectroellipsometry in the photon-energy range of 1.5<hv<5.0 eV. In situ high resolution x-ray photoemission spectroscopy characterization was performed on every film to obtain the atomic concentration and bonding constitution of the elements as a function of background gas pressure. The ideal stoichiometry for SiC films was obtained at Ar pressures higher than 30 mT. The existence of a new phase, given by SiCN2, was suggested from surface techniques and ellipsometric data in the deposition of SiCxNy films at N2 pressures higher than 30 mTorr.

Electroless metallization of sic after laser ablation

Experimental results are presented on the ablation of SiC ceramics in air under irradiation with XeCl and ArF excimer laser beam. X-Ray photoelectron spectroscopy analysis reveals the enrichment of the ablated areas in Si under laser beam energy densities of 1–3.5 J cm −2. At higher energy densities the ablated areas contain Si oxide. The non-stoichiometric ablation of SiC allows one to activate selectively the SiC surface for metal deposition from electroless plating solution. Both Ni and Cu deposits show excellent adherence to both SiC ceramics and single-crystal SiC.

Uncongruent laser ablation and electroless metallization of SiC

Experimental results on the ablation of a SiC single crystal in air under irradiation with a XeCl excimer laser beam are presented. XPS analysis reveals the Si enrichment of the ablated areas under an energy density of the laser beam of 1 to 3.5 J/cm2 and the formation of SiOx in the ablated areas. The nonstoichiometric ablation of SiC allows one to activate selectively the SiC surface for metal deposition from an electroless plating solution. Both Ni and Cu deposits show a good adherence to the SiC surface (up to 0.5 N/mm2). Similar results are observed with SiC ceramics with a better adherence of the electroless metal deposit. The adherence of the deposit to the ablated SiC samples increases upon HF treatment.