Low temperature plasma processing for cell growth inspired carbon thin films fabrication.

The recent bio-applications (i.e. bio-sensing, tissue engineering and cell proliferation etc.) are driving the fundamental research in carbon based materials with functional perspectives. High stability in carbon based coatings usually demands the high density deposition. However, the standard techniques, used for the large area and high throughput deposition of crystalline carbon films, often require very high temperature processing (typically >800 °C in inert atmosphere). Here, we present a low temperature (<150 °C) pulsed-DC plasma sputtering process, which enables sufficient ion flux to deposit dense unhydrogenated carbon thin films without any need of substrate-bias or post-deposition thermal treatments. It is found that the control over plasma power density and pulsed frequency governs the density and kinetic energy of carbon ions participating during the film growth. Subsequently, it controls the contents of sp(3) and sp(2) hybridizations via conversion of sp(2) to sp(3) hybridization by ion's energy relaxation. The role of plasma parameters on the chemical and surface properties are presented and correlated to the bio-activity. Bioactivity tests, carried out in mouse fibroblast L-929 and Sarcoma osteogenic (Saos-2) bone cell lines, demonstrate promising cell-proliferation in these films.

Structural and electrical properties of ZnO films deposited with low-temperature facing targets magnetron sputtering (FTS) system with changes in H2 and O2 flow rate.

ZnO has been studied as a strong candidate for high-quality TCO in accordance with increasing demand to replace ITO. The origin of n-doping in ZnO is not clearly understood, but recently, the H2 effect has received attention due to the role it plays in O-rich and O-poor conditions. In spite of recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. To control the electrical conductivity of ZnO, this study was performed using an FTS system with H2 and O2 addition at low processing temperature. The structural and electrical properties of ZnO thin films deposited at various H2 and O2 flow rates were investigated using XRD and a sheet resistance meter. In response to changes in H2 and O2 flow rates, the crystallization and related grain size of the ZnO films were somewhat changed. The sheet resistance increased from approximately 10(-1) to approximately 10(4) M ohm/sq. when the O2 flow rate was increased, and the resistance decreased from approximately 10(-1) to approximately 10(-4) M ohm/sq. when the H2 flow rate was increased. The increase of sheet resistance with O2 flow rates could be explained by decrease of oxygen vacancies. The decrease of sheet resistance with H2 flow rates could be explained by increase of the electrons from interstitial hydrogen atoms. The plasma characteristics were analyzed using optical emission spectroscopy (OES). But, the overall spectrum did not change with the H2 and O2 gas flow rates. So, the dramatic changes in the electrical properties of ZnO thin films could be considered to be a result of changes in chemical composition of the thin films rather than the plasma status.