Bernard Despax

Structural characteristics of RF-sputtered BaTiO3 thin films

Abstract In this work some structural characteristics of the thin films deposited by a radio frequency-magnetron sputtering technique from a hot pressed BaTiO3 ceramic target were studied. The Ba/Ti ratio was measured by means of X-ray fluorescence in order to determine the real chemical composition of the films. The results showed that this ratio varied along the radial axis of the discharge. Besides, the evolution in phase composition of the annealed films as a function of the thermal treatment conditions (temperature and plateau) as well as the structural characteristics (unit cell parameter and crystallite size) were investigated by X-ray diffraction (XRD). Infrared (IR) and Raman spectroscopies were used in order to obtain more details about the distorted structure of such fine-grained thin films. In the case of these films, Raman spectroscopy carried out from 99 to 473 K did not emphasize steep, distinct transitions between the different polycrystalline BaTiO3 forms when compared with the bulk BaTiO3.

Synthesis of goldcarbon composites by simultaneous sputtering and plasma polymerization of propane in r.f. capacitively coupled diode system (13.56 MHz)

Abstract The synthesis of gold-containing plasma carbon polymer by simultaneous gold sputtering and plasma polymerization in the same system has been carried out in a small propane partial pressure range. The polymer cathode coverage plays an important role in the gold sputtering process.

Hydrogenated aluminum nitride thin films prepared by r.f. reactive sputtering. Infrared and structural properties

Abstract Hydrogenated aluminum nitride thin films, AlN:H, were successfully deposited by radio-frequency reactive sputtering of an aluminum target under an argon-ammonia gas mixture. In-situ control of the nitrogen species was performed by emission spectroscopy. Optical spectroscopy of the gas phase revealed that growth processes depend on target nitriding. Specular reflectance Fourier transform infrared (FTIR) spectroscopy showed the evolution of AlN longitudinal and transverse optical modes as a function of temperature synthesis, film thickness and angle of incidence. A structural study was carried out by transmission electron microscopy and X-ray diffraction. FTIR and secondary ion mass spectrometry analyses showed that for samples exposed to room atmosphere, A1N:H reacts with air moisture, leading to the formation of a superficial layer of aluminum hydroxide Al(OH)3.

Internal r.f. plasma parameters correlated with structure and properties of deposited hydrocarbon films

Abstract Hydrogenated amorphous carbon films (a-C:H) have been prepared by r.f. plasma deposition from a C 3 H 8 –Ar gas mixture. Visible, infrared and Raman spectroscopy as well as electrical measurements are reported and used to characterize the bonding and electronic properties of these films. The gas phase discharge has been investigated by Langmuir probe and by optical emission spectroscopy diagnostics. Under constant self-bias voltage and total pressure, variations in the propane partial pressure brought into evidence the influence of gas phase scission of hydrocarbon bonds on the growth process and the layer composition. The change appears with the increase of the propane partial pressure, which leads to a decrease of both electron temperature and electron density. Simultaneously, CH optical emission increases with respect to the carbon emission. The decrease in the electron temperature results in a decrease of the discharge efficiency to break CH and carbon bonds, and thus, in a decrease of carbon atom production in the gas phase. The formation of more hydrogenated radical precursors, as a consequence of the above, enhances the plasma polymerization process with respect to graphitic nucleation. Films deposited at high electron temperatures were found to contain a large amount of graphite, while those prepared at lower temperatures were found to be polymer-like, with a high hydrogen content.

Polarization phenomena on a silica surface immersed in various gases

On a silica surface, polarization current intensity versus time and Thermostimulated Depolarization Current (TDC) spectra were recorded. This polarization depended on the nature of the ambient gas. Higher was the pressure or longer was the exposure time, higher was the polarization current intensity and larger was the TDC peak area. Nevertheless, when the gas pressure in the vessel was enough low during the depolarization, TDC peak temperature jumped to a higher value. According to polarization conditions, specimens could approach to an electret behaviour.