Joao Roberto Moro

Cylindrical CVD diamond as a high-performance small abrading device

Columnar grain structure studies have been carried out on a small-curvature radius cylinder substrate for the development of small abrading devices. An enhanced hot filament-assisted technique was used. The substrate holder has a movable mechanism magnetically coupled to a d.c. motor placed outside the reactor chamber. Free-standing diamond films as thick as 1 mm were obtained on molybdenum wire substrates. The substrates varied from 500 up to 1200 μm diameter and were as long as 50 mm. A relationship of the curvature radius of the substrate surface with the growth rate and the spread of the column volume has been observed. A preferential diamond (111) surface morphology has been obtained, which is strongly dependent on diamond growth parameters, including the substrate position and its angular velocity. Grain size up to around 0.15 mm was obtained. In this work we also report an interesting application involving the characteristics of the (111) diamond surface as a small abrading device. Some results of cylindrical diamond burrs and diamond drills for non-ferrous wear are shown.

Infrared photoluminescence at deep centres in polycrystalline CdSe layers

A systematic study of the infrared photoluminescence from deep centres in polycrystalline CdSe layers is presented. The authors observe two emission bands at about 0.92 mu m and about 1.22 mu m. The evolution of the band shape and emission intensity quenching with temperature is analysed using a semiclassical model, and the characteristic parameters of the centres are obtained. The results are shown to be consistent with transitions involving selenium vacancies VSe and oxygen impurities OSe.

Optical losses in solar photoelectrochemical cells

Abstract Calculations and experiments clarifying the origin of optical losses in photoelectrochemical cells are reported. Losses due to reflection at the interfaces are examined in both front-wall and back-wall illuminated cells, and it is shown that they can be drastically reduced in the latter. Losses due to absorption within non-transparent electrolytes, which exist only in front-wall cells are also considered. The cell photocurrent has been measured as a function of incident light wavelength and, under white light, as a function of window-electrode separation, for three different electrolyte concentrations. Several quantitative conclusions about the cell configuration are drawn.

Effect of Heat Treatment on Microstructure and Mechanical Property of Diamonds Substrates Brazed with Active Filler Metal

This study aims to identify the effects caused by diffusion through heat treatment in diamonds, brazed components with metals and its effects on mechanical properties and microstructure. It will be used diamond films produced by CVD process, brazed by active filler metals with metallic substrate, using a high vacuum furnace at MAT / LNLS / CNPEM; the samples were heat treated in the atmosphere furnace at MAT too. The characterizations are carried out by hardness testing, vacuum sealing equipment at the MAT / LNLS / CNPEM facilities, and chemical and microstructural characterization will be performed using the scanning electron microscopes and EDS at LNNano / CNPEM.

On the Diffusion Profile at the Brazed Interface between Active Filler Metal and CVD Diamond Plates

Diamonds films have characteristics that are interesting for many optical applications, such as transparency to ultraviolet, visible and infrared light. These applications include use in detectors and windows in processes that involve high temperatures, microelectronics applications and wear-resistant components [. Polycrystalline diamond films can be made in the vapor phase at low-pressure, relatively low temperatures and in the form of auto-supported films, using the CVD process (Chemical Vapor Deposition) [. These films have a significant number of industrial applications, but often have problems with adhesion to metallic substrates. Diamond films can be deposited directly over some metals, but other techniques, such as brazing, can be used [.

Crescimento de diamante CVD em substratos de silício de grande área

Diamond fi lms were grown through Chemical Vapor Deposition (CVD) in silicon substrates (100) of large area (80 cm²), in a hot fi lament chemical vapor deposition (HFCVD), with growth rates over 1,5 μm/h. The growth of samples was made with different gaseous fl uxes and different methane percentages (CH 4 ) in hydrogen (H 2 ). The samples were analyzed through optical microscopy, Scanning Electron Microscopy and Raman spectroscopy scattering. Such analyzes showed the presence of a high purity diamond in all samples.