Determination of the Tribological Fundamentals of Silicon and Diamond for Micro- and Macromechanism Applications
Abstract
SEM tribometry was performed with (a) various Si crystallinities Si(100), Si(111) and poly-Si), and (b) polished, mostly C(100)-textured and acid-cleaned polycrystalline CVD diamond films PCDC(100) heated to 850 deg C (Si) or 950 deg C (PCD) then cooled to room temperature (RT). The initial test environment was approx. 1 x 10(exp -5) Torr moderate vacuum of the SEM column containing approx. 93% water vapor in its residual gas environment, followed by 26 Pa (0.2 Torr) total pressure of 99.999%-pure H2 (dry PH2) as the second test environment, and the same dry PH2 containing 2.6 Pa (-0.02 Torr) partial pressure of water vapor (wet PH2) as the third environment. The data indicate that both H2 and H2O can act as atomic level lubricants for Si and PCDC(100), but only from gas-phase dissociative chemisorption reactions at elevated temperatures well above the boiling point of water. The most effective thermal regions for reducing both the average and the maximum coefficient of friction are near the desorption temperatures of the hydrides, the -OH moieties as well as the bridge bonded Si-O-Si and C-O-C. The wet PH2 was particularly effective in reducing the wear rate of the various Si crystallinities from the 10(exp -12)cu m/N-m range found both in vacuum and in dry PH2 by one to two orders-of magnitude. The friction and wear of Si and PCD are dependent on the temperature- and gas-phase-induced dissociative chemisorption of H2 and H2O passivating the sliding-and heating-induced dangling bonds. The results dispel the current belief that water is harmful under all conditions to Si MEMS surfaces and reinforces the contention the PCD is a far better MEMS bearing material than Si.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 22, 1997
- Accession Number
- ADA334907
Entities
People
- Michael N. Gardos
Organizations
- Hughes Aircraft Company