Amorphous Carbon-Silicon Alloys Prepared by a High Plasma Density Source
- PDF / 887,253 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 54 Downloads / 200 Views
ALLOYS PREPARED BY A HIGH
A. C. FERRARIa, B. RACINEab, N. A. MORRISONa, I. HUTCHINGSc, W. I. MILNEa, J. ROBERTSONa aEngineering Department, Cambridge University, Cambridge CB2 1PZ, UK bLaboratoire de Physique de la Matierie Condensee, Amiens, France CMaterials Science and Metallurgy Department, Cambridge University, UK ABSTRACT The addition of silicon to hydrogenated amorphous carbon can have the advantageous effect of lowering the compressive stress, improving the thermal stability of its hydrogen and maintaining a low friction coefficient up to high humidity. Most experiments to date have been on a-Ci.xSix:H alloys deposited by RF plasma enhanced chemical vapour deposition (PECVD). This method gives alloys with considerable hydrogen content and only moderate hardness. Here, we use a high plasma density source, the electron cyclotron wave resonance (ECWR) source, to prepare films with a high deposition rate. The composition and bonding in the alloys is determined by XPS, visible and UV Raman and FTIR spectroscopy. We find that it is possible to produce hard, low stress, low friction, almost humidity insensitive a-Cl. ,Si,:H alloys with a good optical transparency and a band gap over 2 eV. INTRODUCTION Amorphous C-Si (a-C1 .-Si,) and hydrogenated amorphous C-Si (a-Ci.×Si,:H) alloys are of both fundamental and technological interest. The fundamental interest arises from the possibility of studying the preference for chemical ordering or
heteroatom bonding in a tetrahedrally coordinated sp 3 bonded alloy system around
x=0.5, where the crystalline compounds exists. The technological interest arises from the possibility of obtaining low stress, low friction, humidity insensitive coatings [131. Moreover band calculations suggest that the band gap of C-rich alloys depends on the C-C bonding, not the C-Si bonding, so that band gap need not be reduced by the addition of silicon [1]. It should thus be possible to produce hard, low stress, low friction, almost moisture insensitive a-Cl.xSi,:H alloys with a good optical transparency and a band gap over 2 eV. Most of the studies conducted so far considered the introduction of Si into hydrogenated amorphous carbon (a-C:H) produced by PECVD or Electron Cyclotron Resonance, see ref. [4] for a review. Hydrogenated tetrahedral amorphous carbon (taC:H) can be deposited using a Plasma Beam Source [5] or an Electron Cyclotron Wave Resonance Source [6]. In a-C:H a high sp 3 content is obtained mainly by saturating C=C bonds as CH, groups rather than by increasing the fraction of C-C bonds. Ta-C:H differs in that a higher sp3 content occurs at a fixed lower H content of 25-30%. This results in ta-C:H having a higher density (up to 2.4 g/cm 3 [7]), Young's modulus (-300GPa [8]) and hardness [5] and a lower H content, compared to a-C:H with similar sp 3 content. On the other hand, the higher ion energy and ionisation obtained in the ECWR source, with respect to PECVD, results in much higher stresses of -6-7 GPa [6], similar to as-deposited ta-C, limiting the maximum achievable 523 Mat.
Data Loading...
