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Title: Effect of Self-Assembled Monolayer Film Order on Nanofriction

Abstract

Self-assembled monolayers have increasingly been explored as potential protective films in devices against friction and adhesion. However, detailed characterization of the monolayer film structure is difficult. This article utilizes a combination of near edge x-ray absorption fine structure (NEXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy to determine the film structure in order to explain the observed nanofriction measurement results. A series of n-alkyltrichlorosilane self-assembled monolayer films with various chain lengths (C5-C30) was prepared on silicon (100) surfaces. Nanofriction measurements were conducted using an atomic force microscope. Results showed that the lowest friction was obtained with a C12 film with higher friction values observed for C5 and C30 films. To explain these observations, the x-ray absorption technique NEXAFS was used to quantitatively measure the surface molecular orientation (order) of these films. It was observed that C12, C16, and C18 films were highly ordered with a molecular orientation of the carbon backbone nearly perpendicular to the surface. C5 and C30 films were less oriented and C10 film showed partial orientation. FTIR spectra suggested that these films possessed different degrees of order. This combination of molecular orientation and order supports and confirms that nanofriction results were heavily influenced by the order andmore » structure of these films.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
913967
Report Number(s):
BNL-78535-2007-JA
Journal ID: ISSN 0734-2101; JVTAD6; TRN: US0801437
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Vac. Sci. Technol., A; Journal Volume: 24; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ABSORPTION; ADHESION; CARBON; CHAINS; FINE STRUCTURE; FRICTION; ORIENTATION; SILICON; SPECTRA; SPECTROSCOPY; NSLS; national synchrotron light source

Citation Formats

Sambasivan,S., Shieh, S., Fischer, D., and Hsu, S. Effect of Self-Assembled Monolayer Film Order on Nanofriction. United States: N. p., 2006. Web. doi:10.1116/1.2204920.
Sambasivan,S., Shieh, S., Fischer, D., & Hsu, S. Effect of Self-Assembled Monolayer Film Order on Nanofriction. United States. doi:10.1116/1.2204920.
Sambasivan,S., Shieh, S., Fischer, D., and Hsu, S. Sun . "Effect of Self-Assembled Monolayer Film Order on Nanofriction". United States. doi:10.1116/1.2204920.
@article{osti_913967,
title = {Effect of Self-Assembled Monolayer Film Order on Nanofriction},
author = {Sambasivan,S. and Shieh, S. and Fischer, D. and Hsu, S.},
abstractNote = {Self-assembled monolayers have increasingly been explored as potential protective films in devices against friction and adhesion. However, detailed characterization of the monolayer film structure is difficult. This article utilizes a combination of near edge x-ray absorption fine structure (NEXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy to determine the film structure in order to explain the observed nanofriction measurement results. A series of n-alkyltrichlorosilane self-assembled monolayer films with various chain lengths (C5-C30) was prepared on silicon (100) surfaces. Nanofriction measurements were conducted using an atomic force microscope. Results showed that the lowest friction was obtained with a C12 film with higher friction values observed for C5 and C30 films. To explain these observations, the x-ray absorption technique NEXAFS was used to quantitatively measure the surface molecular orientation (order) of these films. It was observed that C12, C16, and C18 films were highly ordered with a molecular orientation of the carbon backbone nearly perpendicular to the surface. C5 and C30 films were less oriented and C10 film showed partial orientation. FTIR spectra suggested that these films possessed different degrees of order. This combination of molecular orientation and order supports and confirms that nanofriction results were heavily influenced by the order and structure of these films.},
doi = {10.1116/1.2204920},
journal = {J. Vac. Sci. Technol., A},
number = 4,
volume = 24,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • The selectivity, sensitivity, and reproducibility of SAW chemical sensors functionalized with a carboxylate-coordinated Cu{sup 2+}-terminated surface are examined in relation to the interfacial properties of these organomercaptan self-assembled monolayer (SAM) films, prepared from the solution phase for adsorption times of 36, 84, or 180 h on Au surfaces having variable, controlled grain sizes. SAM adsorption time and the grain size of the Au film can dramatically affect the response to adsorption from the vapor phase onto the composite monolayer-modified SAW device. It is proposed that the varied response results from differences in molecular packing and, particularly, in the ordering ofmore » the end groups of the monolayer film that provide the chemically sensitive interface. These studies provide an important step toward reliably fabricating chemical sensors that respond to specific classes of organic analytes. 46 refs., 7 figs.« less
  • The synthesis and characterization of p-HS(CH{sub 2}){sub 11}OC{sub 6}H{sub 4}N=NC{sub 6}H{sub 5}, compound 1d, is reported. Compound 1d self-assembles onto Au(111) substrates into highly ordered monolayer films. Self-assembled monolayer films (SAMs) of 1d on Au(111)/mica have been characterized by ellipsometry, surface-enhanced Raman spectroscopy (SERS), and atomic force microscopy (AFM). We also report the characterization of SAMs of 1d on bulk single crystal Au(111) by synchrotron in-plane X-ray diffraction (XRD) measurements. AFM and in-plane XRD suggest that a SAM of 1d is comprised of domains of 1d which form a hexagonal lattice (4.50 {+-} 0.06 A nearest neighbor spacing) that ismore » incommensurate with the underlying Au(111) lattice. A model is proposed to describe the SAM structure. In such a model, small bundles (nearly 80 molecules) of ordered azobenzene moieties that rest over a set of inward tilting alkyl surface tethering groups make up the individual domains. Thermal annealing of the as-deposited SAM of 1d results in a modest increase in domain size from nearly 45 to around 55 A and a change in azobenzene tilt angle from 20-30{degree} to approximately 0{degree} with no change in nearest neighbor spacing. The redox activity of the azobenzene group is significantly affected by monolayer film structure. Only 2% of the azobenzene groups within a SAM of 1d are electrochemically accessible through cyclic voltammetry in a THF/0.1 M n-Bu{sub 4}NPF{sub 6} electrolyte. 46 refs., 13 figs.« less
  • Docosanoic acid in solution spontaneously forms an ordered self-assembled (SA) monolayer on the silver(111) surface, exposing methyl groups to the atmosphere. The contact wetting angles for water and hexadecane are 116[degrees] and 55[degrees], respectively. Surface X-ray diffraction shows that the in-plane structure of the SA monolayer is p(2 [times] 2). The SA monolayer is present in domains of about 215 A with a mosaic spread of 0.85[degrees]C. The chains within the monolayer are titled at 27 [+-] 1[degrees] from the surface normal toward the near neighbors. We conclude that the carboxylate group is bound nearly normal to specific sites onmore » the Ag surface and that this determines the interchain spacing. The tilt angle is a consequence of this interchain spacing. 17 refs., 6 figs., 1 tab.« less
  • We use surface x-ray diffraction to study the structure of organic-organic heterojunctions grown by organic molecular-beam deposition. In particular, we study films of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) grown on a decanethiol self-assembled monolayer (SAM) on a Au(111) surface. The deposition of several ({approx_equal}16) monolayers of PTCDA results in unstrained crystalline films whose (012) lattice planes are rotated 21.6 degree sign with respect to the <112(bar sign)> Au azimuthal direction. This alignment, which is different from that of PTCDA on the bare Au(111) surface, is most likely caused by the corrugation of the SAM surface [with the c(4x2) superlattice of the (sqmore » root)(3)x{radical}(3)R30 degree sign unit cell]. The SAM structure was found to be unaltered by the presence of the PTCDA overlayer. In addition, the heterogeneous PTCDA/SAM/Au structure, acting as an x-ray interferometer with the SAM as a spacer, allows for the precise determination of the SAM thickness. (c) 2000 The American Physical Society.« less