Martynas Audronis

Pulsed-bias magnetron sputtering of non-conductive crystalline chromia films at low substrate temperature

Chromia coatings were produced by biased pulsed-dc sputter deposition in a dual-frequency (2F) mode, pulsing the target and substrate at frequencies of 130 kHz and 250 kHz, respectively. Crystalline α-Cr2O3 coatings were deposited at substrate temperatures as low as 90 °C, significantly less than the values reported in the literature (~250 °C and more), exhibiting the potential to coat temperature sensitive substrates, such as polymers, with crystalline oxide films.We found that generating optimal ion bombardment conditions at the growing film surface is a critical factor in defining the structure of Cr2O3 coatings. Too low or too high energy ion bombardment can result in amorphous coatings, while a narrow window of optimal ion energies exists within which strongly crystalline coatings can be deposited at very low substrate temperatures.Also, we found that the conventional trend of decreasing deposition rate with increasing substrate bias voltage can be reversed when operating in 2F-pulsed-dc configuration, providing a combined benefit of both energetic ion-assisted deposition and a high deposition rate.The Cr2O3 films produced were found to possess hardness values of 23–27 GPa, approaching that of bulk Cr2O3 and remaining approximately constant over the range of deposition parameters (and resultant coating structures) investigated.Results show that the 2F-pulsed-dc mode enhances the deposition process, in turn allowing an enhanced control of film structure and texture. Significantly less enhancement of the deposition process (and a reduced capability to manipulate beneficially the coating structure) is obtained when operating in one frequency (1F) synchronous pulsed-dc mode. The relative efficacy of the 2F-pulsed-dc processing configuration we believe to be due to additional plasma enhancement and to the fact that, in contrast to 1F-synchronous pulsed-dc configuration, the whole range of charged species (positive ions, negative ions, electrons, etc) abundant in such discharges can be deployed to beneficially modify coating growth conditions at the surface of the film. 2F-pulsed-dc sputter deposition therefore offers a straightforward, reproducible and easily scalable deposition process which, in addition to significant process improvements, also allows complex substrate heating and/or RF biasing systems to be avoided. The findings of this study are expected to be of general validity and applicability to certain other oxide (such as Al2O3, TiO2 and HfO2) and non-oxide coatings of scientific and commercial interest.

Structure and mechanical properties of nitrogen-containing Zr?Cu based thin films deposited by pulsed magnetron sputtering

Pulsed-dc magnetron sputtered zirconium?copper films were deposited with a range of different compositions (of varying Zr/Cu ratio and nitrogen content). Adding nitrogen to the low-miscibility binary Zr?Cu system as a solution hardening and/or nitride-forming element permits the deposition of two- (or multi-) phase nanostructured coatings. Structure and morphology of the coatings was studied by means of x-ray diffraction and scanning electron microscopy. Elemental compositions and Zr/Cu atomic ratios were obtained by quantitative energy-dispersive x-ray analysis. Nanoindentation measurements were made to evaluate coating hardness and elastic modulus. Coating structure was found to depend on the chemical composition; at low nitrogen contents coatings exhibited a columnar morphology, while the maximum N2 flow rate used resulted in a compact and fully dense coating structure. ZrCu(N) films produced with little or no nitrogen (N2 gas flow rates of 0 and 1?sccm) showed a partially amorphous structure with broad, low intensity Zr and Cu x-ray diffraction peaks. An increase in N2 flow rate (3?sccm) developed coatings with nanocrystalline Zr and ZrN phases for the Zr-rich coatings, while increased amorphization, followed by Cu segregation, was observed for Cu-rich coatings deposited at the same N2 flow rate. At the highest N2 flow rate of 5?sccm crystalline ZrN-based coatings were produced. Zr-rich coatings deposited at 0, 1 and 3?sccm N2 flow rates (with Zr/Cu ratios of ~2.2?6.2) demonstrated slightly higher hardness values than coatings exhibiting lower Zr/Cu ratios, while the elastic modulus in the majority of cases showed an opposite trend. This behaviour is shown to correlate well with film chemical composition and the expected mechanical properties of the resulting constituent phases?the exception being the nitrogen-free coatings which (surprisingly) appeared to develop a lower elastic modulus with increasing copper content.

Nb2O5-SiO2 mixtures produced by reactive DC and RF magnetron sputtering

Optical and physical properties of magnetron sputtered Nb2O5-SiO2 mixtures are reported. Deposition rate and properties of mixtures produced were improved significantly by using fast feedback reactive sputtering process control.