Papers
"Impact of substrate corrugation on the sliding friction levels of adsorbed films"
T. Coffey and J. Krim, Physical Review Letters, Vol. 95 (2005) article no. 076101
"Nanotribology," T. Coffey and J. Krim, from the Encyclopedia of Nanoscience and Nanotribology, from American Scientific Publishers.
Characterization of the effects of soft X-ray irradiation on polymers
1 * T. Coffey, S.G. Urquhart , H. Ade
Journal of Electron Spectroscopy and Related Phenomena, Vol. 122 (2002) pg 65-78.
Abstract
The physical and chemical effects of the soft X-ray irradiation of polymers have been systematically evaluated for photon
energies just above the C 1s binding energy. This exposure causes radiation damage in the form of the loss of mass and
changes to the chemical structure of the polymers. These effects are evident in the Near Edge X-ray Absorption Fine
Structure (NEXAFS) spectra of the exposed polymers, posing a fundamental limit to the sensitivity of NEXAFS
spectroscopy for chemical microanalysis. Quantitative understanding of the chemistry and kinetics of radiation damage in
polymers is necessary for the successful and validated application of NEXAFS microscopy. This paper outlines a method for
quantifying this radiation damage as a function of X-ray dose, and applies these methods to characterize the loss of mass and
loss of carbonyl group functionality from a diverse series of polymers. A series of simple correlations are proposed to
rationalize the observed radiation damage propensities on the basis of the polymer chemical structure. In addition, NEXAFS
spectra of irradiated and virgin polymers are used to provide a first-order identification of the radiation chemistry.
A scanning probe and quartz crystal microbalance study of the impact of C60 on friction at solid–liquid interfaces
T Coffey, M Abdelmaksoud and J Krim,
Journal of Physics: Condensed Matter, Vol. 13 (2001) pg 4991-4999.
Abstract
We have investigated the changes in interfacial friction of toluene on mica
and Ag(111) both in the presence and in the absence of interfacial C60 layers
employing atomic force microscope (AFM) and quartz crystal microbalance
(QCM) techniques. The lateral force measurements fail to detect C60 at the
toluene/mica interface, presumably because the C60 is dislodged by the slowmoving
probe tip. In contrast, QCM measurements of interfacial friction and
slippage for toluene/Ag(111) are sensitive to the presence of interfacial C60.
We see the friction double when C60 is present. The results are discussed in the
light of the full-slip boundary condition which had been previously reported for
surface forces apparatus (SFA) measurements on toluene/mica in the presence
and absence of interfacial C60.
Dissertation - T. Coffey (2004)
Nanotribology Fundamentals: Predicting the Viscous Coefficient of Friction
Abstract
COFFEY, TONYA SHEA. Nanotribology Fundamentals: Predicting the Viscous
Coefficient of Friction. (Under the supervision of Professor Jacqueline Krim.)
In this work, I have used the Quartz Crystal Microbalance (QCM) to study nanoscale
friction of monolayer adsorbates on (111) metals. The friction of these systems is viscous
friction, defined as ( ) f
m F v v η τ = = . Here, η is the viscous coefficient of friction, v is the
velocity of the adsorbate, m is adsorbate mass, and τ is the slip time, which is the time
required for the film’s speed to fall to 1/e of its original value. The main focus of this
dissertation is to determine the factors that control η, the viscous coefficient of friction. I
have examined three different parameters in order to determine their effect on η.
An equation for predicting the viscous coefficient of friction has been proposed:
2
subs o aU η η = + . Here, ηsubs is the damping of adsorbate sliding energy within the substrate, a
is a constant depending on mainly temperature and adsorbate film coverage, and Uo is the
atomic-scale surface corrugation. I have closely examined the effect of varying Uo while
holding the lattice spacing relatively constant by studying the slippage of xenon films on
Cu(111), Ni(111), graphene, and C60 substrates at 77.4 K. I have also examined the effect of
varying ηsubs while controlling other parameters by studying the slippage of n-octane films on
Cu(111) vs. Pb(111) surfaces at room temperature.