A. J. Silvestre

Influence of carbon content on the crystallographic structure of boron carbide films

Abstract Boron carbide thin films were synthesised by laser-assisted chemical vapour deposition (LCVD), using a CO 2 laser beam and boron trichloride and methane as precursors. Boron and carbon contents were measured by electron probe microanalysis (EPMA). Microstructural analysis was carried out by Raman microspectroscopy and glancing-incidence X-ray diffraction (GIXRD) was used to study the crystallographic structure and to determine the lattice parameters of the polycrystalline films. The rhombohedral–hexagonal boron carbide crystal lattice constants were plotted as a function of the carbon content, and the non-linear behaviour observed was interpreted on the basis of the complex structure of boron carbide.

Magnetic properties of Co-doped TiO2 anatase nanopowders

This letter reports on the magnetic properties of Ti1−xCoxO2 anatase phase nanopowders with different Co contents. It is shown that oxygen vacancies play an important role in promoting long-range ferromagnetic order in the material studied in addition to the transition-metal doping. Furthermore, the results allow ruling out the premise of a strict connection between Co clustering and the ferromagnetism observed in the Co:TiO2 anatase system.

Structure and morphology of titanium nitride films deposited by laser-induced chemical vapour deposition

Results on the deposition of titanium nitride on AISI M2 tool steel-type substrates by pyrolytic laser chemical vapour deposition are reported. Spots of TiN were deposited from a gas mixture of TiCl4, nitrogen and hydrogen using a continuous wave quasi-TEMoo CO2 laser beam. The morphology and the structure of the deposited material were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. The chemical composition was studied with a scanning electron microscope with an energy dispersive spectrometer, and with an electron probe microanalyser. The topography of the coating was analysed with a stylus profilometer and different thickness profiles were measured depending on the laser-power densities and irradiation times. The morphology of the films showed a strong dependence on the laser-power density, interaction time and partial pressure of TiCl4.

CO2 laser induced CVD of TiN

Abstract Dots and lines of titanium nitride have been deposited on an Incoloy 800H substrate by laser chemical vapour deposition, using a CO2 laser and a reactive atmosphere consisting of TiCl4, N2 and H2. The shape and the microstructure of the films were analyzed by profilometry and scanning electron microscopy (SEM), respectively. Depending on the deposition conditions, different types of profiles and microstructures are observed.

Laser-assisted deposition of r-B4C coatings using ethylene as carbon precursor

Abstract Rhombohedral B 4 C coatings were synthesised on fused silica substrates by CO 2 laser-assisted chemical vapour deposition (LCVD) using a dynamic reactive atmosphere of BCl 3 , C 2 H 4 and H 2 . Films with carbon content from 15 to 22 at.% were grown at deposition rates as high as 0.12 μm s −1 . The kinetics of the reactive system used to deposit the B 4 C films and the influence of growth conditions on the structure and morphology of the deposits were investigated.

Investigation of the microstructure, chemical composition and lateral growth kinetics of TiN films deposited by laser-induced chemical vapour deposition

A study of the laser direct writing of titanium nitride on mild steel substrates by pyrolytic laser-induced chemical vapour deposition was carried out under different operating conditions. Lines of TiN were deposited from a reactive gas mixture of TiCl4, N2 and H2 using a continuous wave TEM00CO2 laser beam as heat source. The deposited material was analysed by optical and scanning electron microscopies, wavelength-dispersive X-ray microanalysis and profilometry techniques. Golden coloured TiN films, close to the stoichiometric composition, were produced exhibiting good adherence, very fine grain size (∼100 nm) and broad gaussian profiles. A time kinetics study based on the lateral growth rate of the deposited lines is also presented. From the transient growth conditions, an empirical relation between the interaction time needed to achieve film deposition and the laser irradiance was established, which led to a value for the incubation period of 5.4 ns. This relation also gave a value for the threshold laser irradiance of 1.54×104W cm−2, in good agreement with the value found experimentally.

The spin polarization of CrO2 revisited

Here, we use Andreev reflection spectroscopy to study the spin polarization of high quality CrO2 films. We study the spin polarization as a function of growth temperature, resulting in grain size and electrical resistivity. In these films low temperature growth appears to be a necessary but not sufficient condition to guarantee the observation of high spin polarization, and this is only observed in conjunction with suppressed superconducting gap values and anomalously low interface properties. We suggest that this combination of observations is a manifestation of the long range spin triplet proximity effect.

TiN films deposited by laser CVD: a growth kinetics study

Abstract Results on the chemical composition, structure and growth kinetics of titanium nitride (TiN) films deposited on mild steel substrates by pyrolytic laser-induced chemical vapour deposition (LCVD) are presented. Golden-coloured lines of TiN were deposited from a reactive gas mixture of TiCl 4 , N 2 and H 2 using a continuous wave TEM 00 CO 2 laser beam as the heat source. The chemical composition and structure of the films were determined by electron probe microanalysis (EPMA) and glancing incidence X-ray diffraction (GIXRD). A non-contact laser profilometer was used to measure the thickness profiles of the films. Using the data obtained in the steady-state region of the TiN laser-written lines, growth rates in the range 3.7 to 6.9 μm s −1 were deduced. The Arrhenius relation between the deposition rate and the deposition temperature yields an apparent activation energy of 46.9 ± 3.8 kJ mol −1 . This result enabled us to conclude that under our deposition conditions, the LCVD of TiN is controlled by mass transport in the vapour phase.

The Role of Carbon Precursor in Boron Carbide Synthesis by Laser-CVD

This paper focuses on the synthesis of rhombohedral B4C (r-B4C) coatings by CO2 laser-assisted chemical vapour deposition (LCVD), using a dynamic reactive atmosphere of BCl3, H2 and CH4 or C2H4. The influence of the carbon precursor on the deposition kinetics is discussed. The use of ethylene as carbon precursor presents several advantages over the use of methane, which is the conventional carbon precursor in CVD processes. These advantages are mainly related to its high absorption coefficient at the laser wavelength and a higher sticking coefficient, which enables to attain higher deposition rates and film thickness control at lower carbon precursor concentration. Films with carbon content from 15 to 22 at.% were grown at a deposition rate as high as 0.12 ∝m.s -1 .

Comparing a current-carrying circular wire with polygons of equal perimeter : magnetic field versus magnetic flux

We compare the magnetic field at the centre and the self-magnetic flux through a current-carrying circular loop, with those obtained for current-carrying polygons with the same perimeter. As the magnetic field diverges at the position of the wires, we compare the self-fluxes utilizing several regularization procedures. The calculation is best performed utilizing the vector potential, thus highlighting its usefulness in practical applications. Our analysis answers some of the intuition challenges students face when they encounter a related simple textbook example. These results can be applied directly to the determination of mutual inductances in a variety of situations.