This article was downloaded by: [North Carolina State University] On: 22 April 2013, At: 09:24 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Advances in Physics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tadp20 Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films Jacqueline Krim a a Physics Department, North Carolina State University, Raleigh, NC, 27695, USA Version of record first published: 13 Aug 2012. To cite this article: Jacqueline Krim (2012): Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films, Advances in Physics, 61:3, 155-323 To link to this article: http://dx.doi.org/10.1080/00018732.2012.706401 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Advances in Physics Vol. 61, No. 3, May–June 2012, 155–323 REVIEW ARTICLE Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films Jacqueline Krim* Physics Department, North Carolina State University, Raleigh, NC 27695, USA (Received 21 June 2012; final version received 22 June 2012) This review provides an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales. Topics covered include a historical overview of the fundamental understanding of macroscopic friction, the- oretical treatments of phononic and electronic energy dissipation mechanisms in thin films, and current experimental methods capable of probing such phenomena. Measurements per- formed on adsorbates sliding in unconfined geometries with the quartz crystal microbalance technique receive particular attention. The final sections review the experimental literature of how measurements of sliding friction in thin films reveal energy dissipation mechanisms and how the results can be linked to film-spreading behavior, lubrication, film phase transitions, superconductivity-dependent friction, and microelectromechanical systems applications. Mate- rials systems reported on include adsorbed films comprised of helium, neon, argon, krypton, xenon, water, oxygen, nitrogen, carbon monoxide, ethane, ethanol, trifluoroethanol, methanol, cyclohexane, ethylene, pentanol, toluene, tricresylphosphate, t-butylphenyl phosphate, ben- zene, and iodobenzene. Substrates reported on include silver, gold, aluminum, copper, nickel, lead, silicon, graphite, graphene, fullerenes, C60, diamond, carbon, diamond-like carbon, and YBa2Cu3O7, and self-assembled monolayers consisting of tethered polymeric molecules. PACS: 68.35.Af Atomic scale friction, 68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggre- gation, 68.43.Pq Adsorbate vibrations, 81.40.Pq Friction, lubrication, and wear, 63.22.Kn Clusters and nanocrystals, 46.55.+d Tribology and mechanical contacts Keywords: nanotribology; adsorbed films; electronic friction; phononic friction; electrostatic friction; physical adsorption; chemical adsorption; energy dissipation; nano-lubrication; quartz crystal microbalance; diffusive Brownian motion Contents PAGE List of Acronyms 158 Downloaded by [North Carolina State University] at 09:24 22 April 2013 List of Symbols 159 1 Introduction 161 1.1. Fundamentals of macroscopic friction 162 1.2. Introductory examples 165 1.2.1. Unconfined contact: nanoscale transport and atomic machinery 165 1.2.2. Confined contact: static friction and jamming effects 167 1.2.3. Multiasperity contact: macroscopic blocks on planes 168 1.3. Review articles on closely related topics 169 1.3.1. Adatom vibrations 169 1.3.2. Diffusion 169 *Email: [email protected] ISSN 0001-8732 print/ISSN 1460-6976 online © 2012 Taylor & Francis http://dx.doi.org/10.1080/00018732.2012.706401 http://www.tandfonline.com 156 J. Krim 1.3.3. Adsorbed monolayers 170 1.3.4. Confined monolayers 170 1.3.5. Asperity contacts 170 1.3.6. Multiasperity contacts 171 1.3.7. Hydrodynamic slip 171 1.3.8. Statistical mechanics and molecular dynamics 172 1.3.9. Nanotribology: topical comments, updates, and monographs 172 2 Experimental techniques 172 2.1. Frictional damping of atomic vibrations 173 2.1.1. Helium atom scattering 173 2.1.2. Surface resistivity 177 2.2. Diffusion 178 2.2.1. Field emission microscopy 179 2.2.2. Field ion microscopy 180 2.2.3. Laser-induced thermal desorption 180 2.2.4. Scanning tunneling microscopy 180 2.2.5. Optical techniques: photoemission electron spectroscopy, linear optic diffraction, and second harmonic diffraction 181 2.2.6. Quasi-elastic helium atom scattering 182 2.2.7. Quartz crystal microbalance 183 2.2.7.1 Island diffusion coefficients 183 2.2.7.2 Spreading diffusion of an adsorbed monolayer as determined by QCM 184 2.2.8. Impact of surface defects, pinning on diffusion coefficients 184 2.3. Adsorbed layers in unconfined geometries 185 2.3.1. The QCM technique 185 2.3.1.1 Spreading, wetting, and slip lengths 192 2.3.1.2 Response of an immersed QCM with an adsorbed boundary layer 196 2.3.2. The blowoff apparatus 198 2.4. Thin films confined between parallel surfaces 200 2.4.1. The SFA 200 2.5. Sliding friction of single-asperity contacts 201 2.5.1. Atomic force microscopy 201 2.5.2. Friction laws for dry and lubricated AFM asperity contacts 202 2.5.3. STM–QCM and related geometries 204 Downloaded by [North Carolina State University] at 09:24 22 April 2013 2.6. Few-asperity contact 205 2.6.1. Mesoscale friction tester 206 2.6.2. MEMS sidewall tribometer 207 2.6.2.1 Determination of normal and frictional forces in an MEMS tribometer 208 2.6.2.2 Capacitive ringdown measurement technique to measure force of friction 209 2.7. Summary comments 211 3 Fundamental theories of sliding friction 211 3.1. Overview 211 3.2. Periodic substrate potentials 213 3.2.1. Defect-free periodic potentials 213 3.2.2. Impact of an external load on a periodic potential: a case study of confined rare gases 216 Advances in Physics 157 3.2.3. Impact of coverage on periodic potentials: a case study of confined Xe/Ni(111) 216 3.2.4. Impact of defects on a periodic potential: a case study of Ne adsorption on Mg 217 3.3. Phononic mechanisms of friction 217 3.3.1. Prandtl–Tomlinson, or independent oscillator model 218 3.3.2. Frenkel–Kontorova and Frenkel–Kontorova–Tomlinson models 220 3.3.3. Beyond Frenkel–Kontorova 221 3.3.3.1 Composite oscillators and hybrid models 221 3.3.3.2 MD simulations 222 3.3.4. Commensurability/corrugation effects 225 3.3.5. Temperature and velocity dependencies 226 3.3.6. Confined films and quantized friction 231 3.3.7. Phononic treatments of the impact of disorder, vibration, and thermal noise 234 3.3.7.1 Disorder 235 3.3.7.2 Vibration 236 3.3.7.3 Thermal noise 236 3.4. Electronic mechanisms of friction 236 3.4.1. Surface contributions to sliding friction and changes in thin-film resistivity 237 3.4.2. Electronic contributions to sliding friction inferred from rare-gas adlayer transitions 239 3.4.2.1 Monolayer to bilayer transitions 239 3.4.2.2 Liquid to solid monolayer transitions 241 3.4.3. Superconductivity-dependent friction 241 3.4.3.1 Popov’s ohmic damping model 243 3.4.3.2 Novotny, Velicky, and Sokoloff’s ohmic damping models 245 3.4.3.3 Persson’s model for surface and bulk electronic contributions 246 3.4.3.4 Rekhviashvili’s thermodynamic model 247 3.4.3.5 Bruch’s ohmic damping model for an adsorbed monolayer 248 3.5. A dislocation drag model of friction 250 3.6. Summary comments 251 4 Numerical and experimental results for specific material systems 251 4.1. Adsorbed rare-gas atoms 253 4.1.1. Helium films 253 4.1.2. Neon films 255 4.1.3. Argon films 257 Downloaded by [North Carolina State University] at 09:24 22 April 2013 4.1.4. Krypton films 257 4.1.5. Xe films 260 4.2. Adsorbed diatomic molecules 262 4.2.1. Hydrogen and deuterium films 262 4.2.2. Physisorbed nitrogen films 263 4.2.3. Oxygen and carbon monoxide films 265 4.3. Other adsorbed species 268 4.3.1. Water films 268 4.3.2. Hydrocarbons, triflouroethanol, and iodobenzene 272 4.3.3. Large molecular lubricants: t-butylphenyl phosphate, TCP, and perfluoropolyether 273 4.4. Adsorbed metal clusters 275 4.5. Metal substrates 276 158 J. Krim 4.5.1. Ag(111) substrates (Table 12) 276 4.5.2. Au(111) substrates (Table 13) 276 4.5.3. Cu(111) and Ni(111) substrates (Table 14) 278 4.5.4. Pb(111) substrates (normal and superconducting) (Table 15) 279 4.5.5. YBa2Cu3O7 substrates 280 4.6. Graphite-, graphene-, and carbon-based substrates (Table 16) 282 4.6.1. Carbon/diamond/graphite/graphene/nanotubes 282 4.6.2. Rotating and fixed fullerenes and related materials 284 4.7. Silicon-, semiconductor-, SAM-, and MEMS-related materials (Table 18) 285 4.7.1.