Accession Number : ADA323320

Title :   Investigations of Metal Adhesion and Reactions on Solid Lubricant Surfaces Using Scanned Probe Microscopies.

Descriptive Note : Final rept. 1 Nov 93-31 Oct 96,

Corporate Author : HARVARD UNIV CAMBRIDGE MA DEPT OF CHEMISTRY

Personal Author(s) : Lieber, Charles M.

PDF Url : ADA323320

Report Date : JAN 1997

Pagination or Media Count : 23

Abstract : Scanning tunneling and atomic force microscopy studies of metal dichalcogenide materials demonstrate that wear proceeds via surface oxidation, and that wear rates are directly related to the oxidative stability of the surfaces. Surface oxidation was also shown to produce oriented MoO3 nanocrystals on MoS2 surfaces. This system was shown to be uniquely suited for nanotribology studies because the interface structure and contact area are atomically deformed and the MoO3 nanocrystals can be moved controllably with lateral force microscope tip. Highly anisotropic friction has been observed whereby MoO3 nanocrystals moved along only specific directions of the MoS2 surface lattice. An atomic model of the interface was developed to explain these In addition, chemical force microscopy has been used to measure adhesion and friction forces between probe tips and substrates covalently modified with self-assembled monolayers (SAMs) that terminate in distinct functional groups such as COOH, CH3,and NH2 in ethanol and water solvents. The measured adhesive forces were found to agree well with predictions of the Johnson, Kendall, and Roberts (JKR) theory of adhesive contact, and thus show that the observed adhesion forces correlate with the surface free energy. Electrostatic contributions to adhesive forces have also been characterized using COOH/NH2 functionalized tip/surface that exists as COO(-)/NH3(+) in aqueous solution. The dependence of friction forces on the tip and sample functionality has also been shown to be the basis for chemical force microscopy in which lateral force images are interpreted in terms of the strength of adhesive interactions between functional groups. Chemically sensitive imaging of photopatterned monolayers using probe tips modified with different functional groups has been demonstrated.

Descriptors :   *SCANNING ELECTRON MICROSCOPES, *ADHESION, *SOLID LUBRICANTS, *SURFACE CHEMISTRY, SCANNING, INTERFACES, OXIDATION, ANISOTROPY, FRICTION, FREE ENERGY, ELECTROSTATIC CHARGE, MOLYBDENUM COMPOUNDS, SURFACE ENERGY.

Subject Categories : Physical Chemistry
      Adhesives, Seals and Binders
      Lubricants and Hydraulic Fluids

Distribution Statement : APPROVED FOR PUBLIC RELEASE