J. Takadoum

Glancing angle deposition to modify microstructure and properties of sputter deposited chromium thin films

Abstract The glancing angle deposition (GLAD) technique was used to deposit chromium thin films by dc magnetron sputtering. With suitable operating conditions to favour a columnar microstructure and by controlling the orientation of the substrate relative to the impinging vapour flux, an inclined columnar film microstructure was produced. A systematic change of the angle ‘α’ between the incident atom flux and the substrate normal was correlated with the angle ‘β’ between the columns axis and the substrate normal. For every angular range (α increases from 0 to 50°), the results were corroborated with empirical relationships between angles α and β. The influence of the deposition at oblique incidence on the surface morphology and the microstructure was investigated by atomic force microscopy and by scanning electron microscopy. The evolution of the crystallographic structure was also examined by X-ray diffraction vs. the angle of the incident flux. Measurements of the conductivity and nano-indentation tests were also performed in order to discuss the change of the mechanical and electrical behaviours, as a function of the orientated microstructure of the coatings.

Water as reactive gas to prepare titanium oxynitride thin films by reactive sputtering

Thin films of titanium oxynitride were successfully prepared by dc reactive magnetron sputtering using a titanium metallic target, argon, nitrogen and water vapour as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas that of the water vapour was systematically changed from 0 to 0.1 Pa. The evolution of the deposition rate with an increasing amount of water vapour injected into the process was correlated with the target poisoning phenomenon estimated from the target potential. Structure and morphology of the films were analysed by X-ray diffraction and scanning electron microscopy. Films were poorly crystallised or amorphous with a typical columnar microstructure. Nitrogen, oxygen and titanium concentrations were determined by Rutherford backscattering spectroscopy and nuclear reaction analysis, and the amount of hydrogen in the films was also quantified. Optical transmittance in the visible region and electrical conductivity measured against temperature were gradually modified from metallic to semiconducting behaviour with an increasing supply of the water vapour partial pressure. Moreover, an interesting maximum of the electrical conductivity was observed in this transition, for a small amount of water vapour.

Surface charges and adhesion measured by atomic force microscope influence on friction force

Abstract A good correlation has been found between friction force measured using a ball-on-disc tribometer (normal load 200 mN) and adhesion hysteresis measured by atomic force microscopy. Both adhesion and friction forces were investigated in liquid media (water, ethanol, formamide, ethylene glycol) and involved interactions between silicon nitride and several materials (Si(1 0 0), Si(1 1 1), silica glass, DLC and TiN coatings). Despite the difference between the two scales of measurement, comparison between the measured friction force and the dissipated energy during the adhesion process has shown that the two quantities follow the same trend. Additional experiments were conducted in NaCl 10 −3 M at various pH values in order to investigate surface charge effect on adhesion and friction.

Nitrogen pulsing to modify the properties of titanium nitride thin films sputter deposited

TiNx thin films were grown on (100) Si and glass substrates by dc reactive magnetron sputtering. A titanium target was sputtered in Ar + N2 atmosphere using a pulsing flow rate of the nitrogen gas. A constant pulsing period was used for every deposition whereas the nitrogen injection time was changed. The systematic variation of the nitrogen injection time led to a gradual decrease of the deposition rate and to a controlled modulation of the chemical composition of the TiNx films (x between 0 and 1.05). Analysis of the crystallographic structure by X-ray diffraction showed that both Ti and TiN phases coexisted and a change of the preferential orientation from (200) to (111) occurred. The electrical conductivity and colour measurements in the CIE-L*a*b* system of colourimetry were also performed and correlated with the evolution of the N/Ti ratio.

The reactive gas pulsing process for tuneable properties of sputter deposited titanium oxide, nitride and oxynitride coatings

TiOx, TiNy and TiOxNy thin films were deposited by reactive sputtering. The reactive gas pulsing process was implemented to tune the chemical composition and consequently, the characteristics of the films. For TiOx coatings, oxygen concentration was progressively modified from pure titanium to TiO2 compound. Similarly, a gradual decrease of the deposition rate and a controlled modulation of the chemical composition of TiNy films (y between 0 and 1.05) were easily reached. A reverse evolution of the oxygen and nitrogen contents was produced in TiOxNy films, which was correlated with the smooth transition from metallic to semiconducting behaviours.