Thomas Haensel

HREELS Investigation of the Surfaces of Nanocrystalline Diamond Films Oxidized by Different Processes

This article reports on the use of high-resolution electron energy loss spectroscopy (HREELS) for the investigation of as-grown (hydrogen-terminated) and oxidized nanocrystalline diamond films (NCD) using chemical, physical, and electrochemical approaches. The results indicate that the nature and number of oxygen-related chemical groups generated on the NCD surface depend strongly on the oxidation process. A high concentration of C-O functions has been obtained on the NCD surface oxidized by rf (radio frequency) oxygen plasma, whereas the highest C═O/C-O ratio has been achieved by electrochemical oxidation. The NCD surface oxidized by rf plasma was totally free of C═O groups. Traces of surface hydroxyl groups (C-OH) have been detected upon annealing in air or through UV/ozone oxidation.

Raman Spectroscopy of Amorphous Carbon Prepared by Pulsed Arc Discharge in Various Gas Mixtures

To meet various application requirements, it is important to enable an improvement of a-C structure and properties, such as hardness, adhesion, and wear resistance. In this study, we used the Raman spectroscopy to investigate the a-C thin films structure dependence on the different deposition parameters. The effect of nitrogen, argon, and hydrogen gas flow rate was analyzed to determine the influence on the film properties. The change in the gas type, combination, and flow had a significant influence on the D and G bands of the a-C Raman spectra. The addition of N2 into the chamber promoted the sp2 creation, while with adding hydrogen the layer contained more sp3 bonds. The depositions of a-C thin films were carried out in pulsed arc discharge vacuum installation. Micro-Raman measurements of the deposited materials were performed using an ISA Dilor-Jobin Yvon-Spex Labram confocal system with 632.8 nm radiation from a He-Ne laser using a back-scattering geometry.

Interaction of Hydrogen and Oxygen with Nanocrystalline Diamond Surfaces

Nanocrystalline diamond films (NCD) are strong candidates for applications in a wide variety of fields. An important concern in all these applications is to understand the properties of variously prepared NCD surfaces. This contribution is focussed on the surface science study of hydrogen and oxygen containing NCD films using X-ray photoelectron spectroscopy (XPS) as well as high resolution electron energy loss spectroscopy (HREELS). Previous studies have demonstrated that hydrogen, oxygen, and gases from the ambient environment as well as water can result in drastic surface changes affecting conductivity, wettability, tribological properties, etc. In this contribution we analyzed differently prepared NCD surfaces as a function of parameters such as the annealing temperature under ultrahigh vacuum conditions (UHV). We are able to identify the thermal stability of a number of species at the interface, which are related to different characteristics of C-H, C-OH, C=O, and C=C bonds. Furthermore, a formation of graphitic-like species appears at higher annealing temperatures. An atomic hydrogen treatment was also applied to the NCD surface to obtain further information about the surface composition.