The graphite phase derived from polyimide at low temperature

This paper reports a novel method to produce the graphite phase derived from polyimide using Ni(Ac)₂ as catalyst at about 800 °C. The graphitization behavior was characterized by FTIR, X-ray diffraction, Raman spectra and N₂ sorption measurements. The results showed that β-cyclodextrin promoted the catalytic effect of Ni(Ac)₂ in graphitizing process, increased the degree of graphitization and micropore volume. The graphite structure was confirmed the pores distributed uniformly throughout by SEM.     

The character of FeMn-1# powder catalyst and its influence on the synthesis of diamond

In this paper industrial diamond crystal was synthesized using FeMn-1# powder catalyst in China-type cubic high-pressure apparatus at 5.7 GPa and 1400–1600 °C. The growth feature of diamond in the graphite–FeMn-1# system was researched. Optical microscope observation showed that all the diamond crystals were light yellow octahedral with grain size of 0.3–0.5 mm. There are also plenty of bubbles in the crystals. By SEM, we can see that the surface of diamond is smooth and the crystal is intact. Mössbauer spectrum was used to detect the impurity in the diamonds.     

GaN grown on (1 1 1) single crystal diamond substrate by molecular beam epitaxy

GaN epilayers are grown on (1 1 1) oriented single crystal diamond substrate by ammonia-source molecular beam epitaxy. Each step of the growth is monitored in situ by reflection high energy electron diffraction. It is found that a two-dimensional epitaxial wurtzite GaN film is obtained. The surface morphology is smooth: the rms roughness is as low as 1.3 nm for 2×2 μm² scan. Photoluminescence measurements reveal pretty good optical properties. The GaN band edge is centred at 3.469 eV with a linewidth of 5 meV. These results demonstrate that GaN heteroepitaxially grown on diamond opens new rooms for high power electronic applications.     

Surface and catalytic properties of acid metal-carbons prepared by the sol-gel method

The sol-gel method has been applied for the synthesis of a series of acid metal-carbon xerogels (with M = V, Cr, Mo and Ni) by polymerisation of resorcinol with formaldehyde in the presence of metallic precursors. A blank sample was also prepared without any metal addition. The xerogels were heated in nitrogen at 1000 °C to obtain the pyrolysed products. The samples were characterised by different techniques such as thermal-mass spectrometry analysis, gas physisorption, and mercury porosimetry. In addition, the acid character of the pyrolysed products was tested by the Claisen-Schmidt condensation between benzaldehyde and acetophenone for the formation of chalcones.     

AFM investigation on surface evolution of amorphous carbon during ion-beam-assisted deposition

Hydrogen-free amorphous carbons (a-C) have been prepared on mirror-polished Si(1 1 1) wafers through thermally evaporated C₆₀ with simultaneous bombardments of Ne⁺ ions. The time evolution of film surfaces has been characterized by atomic force microscopy (AFM) at two temperatures of 400 and 700 °C, respectively. Based on the topography images and the root-mean-square (rms) roughness analysis, it is found that the a-C surfaces present roughening growth at the initial stage. With increasing growth time, the cooperative nucleation of the islands and pits appears on the surfaces, suggesting three-dimensional growth, and then they continue to evolve to irregular mounds at 400 °C, and elongated mounds at 700 °C. At the steady growth stage, these surfaces further develop to the structures of bamboo joints and ripples corresponding to these two temperatures, respectively. It is believed that besides ion sputtering effect, the chemical bonding configurations in the amorphous carbon films should be taken into considerations for elucidating the surface evolutions.     

Influence of annealing on the physical properties of filtered vacuum arc deposited tin oxide thin films

Tin oxide (SnO₂) thin films were deposited on UV fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at room temperature (RT). As-deposited films were annealed at 400 and 600 °C in Ar for 30 min. The film structure, composition, and surface morphology were determined as function of the annealing temperature using X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the SnO₂ thin films deposited on substrates at RT indicated that the films were amorphous, however, after the annealing the film structure became polycrystalline. The grain size of the annealed films, obtained from the XRD analysis, increased with the annealing temperature, and it was in the range 8-34 nm. The AFM analysis of the surface revealed an increase in the film surface average grain size from 15 nm to 46 nm, and the surface roughness from 0.2 to 1.8 nm, as function of the annealing temperature. The average optical transmission of the films in the visible spectrum was >80%, and increased by the annealing ∼10%. The films’ optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the range 1.83-2.23 and 1.85-2.3, respectively. The extinction coefficients, k(λ), of as-deposited and annealed films were in the range same range ∼0-0.5. The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, increased with the annealing temperature from 3.90 to 4.35 eV. The lowest electrical resistivity of the as-deposited tin oxide films was 7.8 × 10⁻³ Ω cm, however, film annealing resulted in highly resistive films.     

Hard carbon coatings deposited on steel

We report results of steel substrates coated with hard amorphous carbon and with diamond films. In order to enhance the adherence to the substrate, steel substrates were pretreated by means of a silicon ion beam. Raman spectroscopy was used to analyze the structure of silicon interface while the elastic recoil detection analysis method was applied to determine their composition and thickness. The a-C adherence to the substrate and hardness were also tested. The diamond films were observed by SEM.     

The Two-Parameter Higher-Order Differential Calculus and Curvature on a Quantum Plane

We construct an associative differential algebra on a two-parameter quantum plane associated with a nilpotent endomorphism d in the two cases d ² = 0 and d ³ = 0 (d ² ≠ 0). The correspondent curvature is derived and the related non-commutative gauge field theory is introduced.     

Diamond coating deposition by synergy of thermal and laser methods—A problem revisited

Diamond coatings were deposited by synergy of the hot filament CVD method and the pulse TEA CO₂ laser, in spectroactive and spectroinactive diamond precursor atmospheres. Resulting diamond coatings are interpreted relying on evidence of scanning electron microscopy as well as microRaman spectroscopy. Thermal synergy component (hot filament) possesses an activating agent for diamond deposition, and contributes significantly to quality and extent of diamond deposition. Laser synergy component comprises a solid surface modification as well as the spectroactive gaseous atmosphere modification. Surface modification consists in changes of the diamond coating being deposited and, at the same time, in changes of the substrate surface structure. Laser modification of the spectroactive diamond precursor atmosphere means specific consumption of the precursor, which enables to skip the deposition on a defined substrate location. The resulting process of diamond coating elimination from certain, desired locations using the CO₂ laser might contribute to tailoring diamond coatings for particular applications. Additionally, the substrate laser modification could be optimized by choice of a proper spectroactive precursor concentration, or by a laser radiation multiple pass through an absorbing medium.