AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP15
Conformation of Model Self-assembled Monolayers Studied by Sum-frequency Generation Spectroscopy

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: M.B. Raschke, University of California, Berkeley
Authors: M.B. Raschke, University of California, Berkeley
P.B. Miranda, University of California, Berkeley
X. Wei, University of California, Berkeley
Y.R. Shen, University of California, Berkeley
Correspondent: Click to Email
Potential technological applications of self-assembled monolayers (SAM) as lithography resists, lubricants or biosensors make detailed surface strucural analysis of these materials highly desirable. In this respect chemisorbed films of model self-assembling n-alkyl monolayers have been investigated by means of infrared-visible sum-frequency generation spectroscopy providing information about chain orientation and internal molecular conformation. The trans-gauche transformation behavior of n-Octadecyltrichlorosilane (OTS) and Octadecyldimethyl(3-trimethoxysilyl-propyl)ammonium chloide (DMOAP) adsorbed on quartz with different surface molecular densities has been studied in vacuum for temperatures between 100 and 450 K. Whereas tight packing sterically prevents low energy excitations (e.g. molecular tilt, gauche defects), for low chain-densities large number of gauge conformations are found even at low temperatures. This corresponds to an observed increase in the onset temperature for chain melting with increasing surface density. For high chain densities metastable conformations (e.g. entanglement with neighboring molecules) can persist even at T=300 K and may be annealed at elevated temperatures. The observed behavior will be discussed in terms of the thermodynamics describing linear chain molecules.@FootnoteText@ Work supported by DOE.