Performance of ion-figured silicon carbide SUMER telescope mirror in the vacuum ultraviolet

Measured and theoretical encircled energy and small-angle scatter of the telescope mirror (SST) of the solar ultraviolet measurements of emitted radiation (SUMER) instrument are compared at the wavelength of 123.6 nm. Mirror performance modeling was accomplished with the Optical Surface Analysis Code software package. The modeling is based on measured mirror-surface figure error data and roughness characteristics covering all important spatial frequencies that affect imaging in the vacuum ultraviolet wavelength region. Mirror-surface errors were measured with a Zygo Mark IV interferometer, Bauer Model 200 Profiler, and WYKO Topo 2-D (two-dimensional) interferometer. Performance of the SST mirror, including encircled energy and small-angle scatter, was also directly measured. A good agreement is found between measured and theoretical encircled energy within 6 arcsec and small-angle scatter up to ~50 arcmin from the peak. The 80% encircled energy diameter of the SST mirror is ~1.9 arcsec, and the amount of scattered light drops to approximately 1.0 × 10(-10) of peak irradiance (normalized to 1 arcsec(2) in the focal plane) 50 arcmin from the peak. Vacuum ultraviolet performance of the mirror is degraded primarily by midfrequency errors.     

Ion-beam-deposited boron carbide coatings for the extreme ultraviolet

The normal-incidence reflectance of ion-beam-deposited boron carbide thin films has been evaluated in the extreme ultraviolet (EUV) spectral region. High-reflectance coatings have been produced with reflectances greater than 30% between 67 and 121.6 nm. This high reflectance makes ion-beam-deposited boron carbide an attractive coating for EUV applications.     

Formation of high-density structure of self-bonded silicon carbide

An alternative method has been developed for fabricating high-density products from ceramics based on self-bonded silicon carbide. The product blanks are formed by slip molding of thermoplastic mixtures under pressure. The composition of the polyfractional mixture has been defined and new temporary binders, whose rheological properties ensure high density of the products, have been formulated.     

Mechanical properties of cast lead alloy/silicon carbide particulate composites

This paper describes a study of the mechanical properties of cast lead-antimony alloy composites containing silicon carbide (SiC) particles of size 90–150 μm and of contents ranging from 0% to 5% by weight. The ‘vortex method’ of production was employed in which the SiC particles were poured into the vortex created by stirring the molten metal at 400°C by means of a mechanical agitator. The results of this study revealed that as SiC composition was increased, there were significant increases in the ultimate tensile strength (UTS), hardness, torsional strength and impact strength of the composite, accompanied by a reduction in its ductility. An attempt is made in the paper to provide explanations for these phenomena.     

Extreme ultraviolet polarizing optics using bare and aluminum-coated silicon carbide

A deformable three-reflection system that uses a bare silicon carbide substrate can function as an in-line, high-throughput (>30%), 90° phase shifter in the 50-100 nm spectral range. For a given extreme ultraviolet wavelength, an aluminum thin film can be deposited on the silicon carbide substrate to suppress the parallel (p) or perpendicular (s) polarization on single reflection or to introduce quarter-wave retardation and equal reflectances for incident p- and s-polarized light.     

Defects in silicon carbide

Defects in various forms of SiC, both single crystal and polycrystalline, have been examined using transmission electron microscopy. Dislocations were not as common as stacking faults, which were observed in all materials examined. The mechanism of formation of stacking faults is discussed and two types of both intrinsic and extrinsic faults are shown possible. The stacking-fault energy of SiC was measured to be 1.9 ergs/cm² by the extended node method.     

应用紫外·极紫外

介绍长春光机所八、九十年代在短波光学方面的某些研究工作     

Electrodeposition of silicon carbide

Thin layers of SiC were electrodeposited from $\text{Li}{}_2\text{CO}{}_3\text{SiO}{}_2$ melts onto α-SiC substrates at 1000°–1050°C using potential differences around ?0.5V versus polycrystalline SiC anodes. The layers appear to be epitaxial. Although conditions were found under which the melt exhibited good long term stability, attempts to grow bulk SiC crystals were handicapped by the delamination of the seed crystals.     

Superconductivity in carrier-doped silicon carbide

Abstract

We report growth and characterization of heavily boron-doped 3C-SiC and 6H-SiC and Al-doped 3C-SiC. Both 3C-SiC:B and 6H-SiC:B reveal type-I superconductivity with a critical temperature T_c=1.5 K. On the other hand, Al-doped 3C-SiC (3C-SiC:Al) shows type-II superconductivity with T_c=1.4 K. Both SiC:Al and SiC:B exhibit zero resistivity and diamagnetic susceptibility below T_c with effective hole-carrier concentration n higher than 10²⁰ cm^?3. We interpret the different superconducting behavior in carrier-doped p-type semiconductors SiC:Al, SiC:B, Si:B and C:B in terms of the different ionization energies of their acceptors.     

Nonequilibrium heteroepitaxy of silicon carbide on silicon

A method of silicon carbide (SiC) deposition onto silicon via a nonequilibrium disilicon carbide (Si₂C) vapor phase is proposed, theoretically described, and experimentally verified. Estimates obtained using thermochemical calculations show that a sufficiently large number of SiC molecules, which are transported by mobile Si₂C species, are obtained using this method on the silicon surface. It is established that homogeneous epitaxial SiC layers can be grown on a Si(111) substrate surface.     

Nano-precipitation in hot-pressed silicon carbide

Heat treatments at 1300°C, 1400°C, 1500°C, and 1600°C in Ar were found to produce nanoscale precipitates in hot-pressed silicon carbide containing aluminum, boron, and carbon sintering additives (ABC-SiC). The precipitates were studied by transmission electron microscopy (TEM) and nano-probe energy-dispersive X-ray spectroscopy (nEDS). The precipitates were plate-like in shape, with a thickness, length and separation of only a few nanometers, and their size coarsened with increasing annealing temperature, accompanied by reduced number density. The distribution of the precipitates was uniform inside the SiC grains, but depleted zones were observed in the vicinity of the SiC grain boundaries. A coherent orientation relationship between the precipitates and the SiC matrix was found. Combined high-resolution electron microscopy, computer simulation, and nEDS identified an Al₄C₃-based structure and composition for the nano-precipitates. Most Al ions in SiC lattice exsolved as precipitates during the annealing at 1400 to 1500°C. Formation mechanism and possible influences of the nanoscale precipitates on mechanical properties are discussed.     

Crack-healing in reaction-bonded silicon carbide

Crack healing in reaction-bonded silicon carbide (RBSC) was investigated by introducing cracks with the depth of 2.0–2.3 mm into flexure specimens and subsequently heat-treating the specimens at temperatures up to 1300 °C. Results showed that the cracks were healed by being filled with amorphous silica produced by the oxidation of silicon and silicon carbide. As the cracks were healed, the strength of cracked specimens was recovered to as much as 60% of the strength of as-machined specimens.     

Polytype distribution in silicon carbide

Silicon carbide is a candidate material for high-performance applications. It exists as a composite of many structurally distinct but related polytypes with differing physical properties, It is well known, for example, that the flexural strength of formed SiC composites is strongly dependent on the relative amounts of the various polytypes present in the composite. X-ray powder diffraction is the method of choice to determine polytype distribution. Each of the SiC polytypes gives a unique diffraction pattern; unfortunately, the patterns for the various polytypes superimpose in part, making interpretation difficult. The authors have developed a method to separate the superimposed patterns to give quantitative information on the distribution of the polytypes in the composite. This approach provides a useful tool in relating preparation conditions to performance properties.     

Bidirectional reflectance distribution function of diffuse extreme ultraviolet scatterers and extreme ultraviolet baffle materials

Bidirectional reflectance distribution function (BRDF) measurements of a number of diffuse extreme ultraviolet (EUV) scatterers and EUV baffle materials have been performed with the Goddard EUV scatterometer. BRDF data are presented for white Spectralon SRS-99 at 121.6 nm; the data exhibit a non-Lambertian nature and a total hemispherical reflectance lower than 0.15. Data are also presented for an evaporated Cu black sample, a black Spectralon SRS-02 sample, and a Martin Optical Black sample at wavelengths of 58.4 and 121.6 nm and for angles of incidence of 15 degrees and 45 degrees. Overall Martin Optical Black exhibited the lowest BRDF characteristic, with a total hemispherical reflectance of the order of 0.01 and measured BRDF values as low as 2 x 10(-3) sr(-1).     

Nanorods of silicon carbide from silicon carbide powder by high temperature heat treatment

Nanorods of silicon carbide were found to be produced directly from silicon carbide powder when subjected to high temperature heat treatment. The powder with 20–50 μm grain size was kept in a graphite crucible (enclosed in a chamber/furnace) and heated from its bottom at 2700 °C for 15 min by employing a typical configuration of arc plasma (Ar). The heating was then followed by chamber cooling (up to room temperature) for 2 h. Silicon carbide nanorods of 10–120 nm diameter and 5–20 μm length grew within the powder when the graphite crucible was kept 90% closed at its top end during the heat treatment. The heat treated powder and nanorods were evaluated by XRD, SEM, AFM, HRTEM and micro Raman spectroscopy. A catalyst (Fe) driven two stage VLS mechanism is proposed to understand the growth of the nanorods.     

Study the formation mechanism of silicon carbide polytype by silicon carbide nanobelts sintered under high pressure

In this paper, in order to reveal the formation mechanism of SiC polytype, four SiC specimens sintered under high pressure has been investigated, after being prepared from SiC nanobelts as initial powders. The structure and morphology variation dependence of SiC specimens with temperature and pressure was studied based on experimental data obtained by XRD, SEM, and Raman. The results show that SiC lattice structure and the crystallite size are greatly affected by pressure between 2 and 4 GPa under different sintering temperatures of 800 and 1200 degrees C. At the largest applied pressure and temperature, 4 GPa and 1200 degrees C, 3C-SiC crystal structure can be changed into to R-SiC due to the stress resulted in dislocations instead of planar defects. Based on our results, the multiquantum-well structure based a single one-dimensional nanostructure can be achieved by applying high pressure at certain sintered temperature.     

Preparation of silicon carbide whiskers from silicon nitride

Silicon carbide whiskers have been prepared by sintering silicon nitride powder in a graphite reactor at 1800°C under a nitrogen atmosphere. The whiskers differ in morphology: tubular needles, hollow faceted fibers with a square cross section, and solid fibers with a triangular cross section. The average diameter of the needles is 0.5?5 μm, and that of the faceted fibers is up to 20 μm. The fibers range in length up to several millimeters. Such silicon carbide whiskers can be used as reinforcing agents for structural ceramics based on nonoxide materials.