Raman Scattering from Confined Liquid Films in the Sub-Nanometre Regime
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Raman spectroscopy has been used to study the confinement of octamethylcyclotetrasiloxane (OMCTS) and n-hexadecane between a prism and a lens at contact pressures of 40 MPa. Both lens and prism surfaces were optically smooth but not atomically flat. A total internal reflection geometry was employed to provide the sensitivity needed to detect liquid films of sub-nanometre thickness. For both liquids, the thickness of the residual film under load corresponded to less than a monolayer of liquid. The Raman spectra of the confined liquids were identical or very similar to that of the bulk liquid. Similar results were obtained for hexadecane confined between two surfaces coated with a Langmuir-Blodgett monolayer of a fatty acid. We infer that the liquids do not form a boundary layer under these conditions but rather they are squeezed out of the contact under the modest pressure applied. We ascribe the residual signal to liquid trapped in scratches or other defects on the surfaces.
KeywordsSpectroscopy Raman Boundary lubrication Nanotribology Hexadecane OMCTS
The authors wish to thank the EPSRC, the Leverhulme Trust, and the British Ramsay Memorial Fellowship Trust for funding this work.
- 1.Bhushan, B.: Introduction to Tribology. Wiley, New York, 2002Google Scholar
- 24.Haydock, S.A.: In situ vibrational spectroscopy of thin organic films confined at the solid-solid interface, PhD Thesis, University of Oxford (2002)Google Scholar
- 27.Greene, P.A., Bain, C.D.: Spectrosc. Eur. 16, 8 (2004)Google Scholar
- 32.Heavens, O., Ditchburn, R.: Insight into Optics. Wiley, Chichester, (1991)Google Scholar
- 33.Johnson, K.L.: Contact Mechanics. Cambridge University Press, Cambridge (1987)Google Scholar
- 34.Harrick, N.J.: Internal Reflection Spectroscopy. Harrick Scientific Corp, Ossining, NY, (1967)Google Scholar
- 35.Taylor, J.R.: An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements. University Science Books, Mill Valley, CA; Oxford University Press, Oxford (1982)Google Scholar
- 40.Castaings, N., Blaudez, D., Desbat, B., Turlet, J.M.: Thin Solid Films 284–285, 631 (1996)Google Scholar
- 41.Du, Q., Xiao, X.D., Charych, D., Wolf, F., Frantz, P., Shen, Y.R., Salmeron, M.: Phys. Rev. B-Condens. Matter. 51, 7456 (1995)Google Scholar