friction at the nanoscale - american chemical societyfriction at the nanoscale discovered fricon...

Izabela Szlufarska, Department of Materials Science and Engineering, University of Wisconsin-Madison Motivation: Understanding of fundamental mechanisms of friction and wear of ultrananocrystalline diamond (UNCD). Promising material for coating drill bits for oil recovery. Approach: Massively parallel molecular dynamics simulations using realistic potentials (background picture) Friction at the nanoscale Discovered fric,on laws at the nanoscale. Determined dependence of fric,on force on load and contact area. Proposed a physical explana,on for experimentally observed isotope effect on solid fric,on. Mo, Turner, and Szlufarska, Nature, 457, 1116 (2009) Mo, Müser, and Szlufarska, Physical Review B (in press) Discovered friction laws at the nanoscale. Proposed a physical explanation of why deuterium lowers friction of diamond Increase adhesion sub-linear Increase roughness H Reaction coordinate D Exp 3h Theory 5.5h Atoms in contact • We demonstrated that behavior of nanoscale contacts is described by roughness theories instead of con,nuum mechanics •Fric,on force is controlled by the short range chemical interac,ons. Demonstrated a transi,on from a linear to sublinear fric,on – load dependence. Explained previously reported experiments. Fric,on force – Real contact area Mo,va,on: Experiment reported fric,on reduc,on of 20% by passiva,ng diamond with deuterium instead of hydrogen D is chemically more stable than H on diamond surface Surface coverage of H/D decreases during annealing • The isotope effect on solid fric,on is consistent with differences in chemical stability of H and D on diamond • A few percent of surface vacancies has a large effect on fric,on.

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Page 1: Friction at the nanoscale - American Chemical SocietyFriction at the nanoscale Discovered fricon laws at the nanoscale. Determined dependence of fricon force on load and contact area

Izabela Szlufarska, Department of Materials Science and Engineering, University of Wisconsin-Madison

Motivation: Understanding of fundamental mechanisms of friction and wear of ultrananocrystalline diamond (UNCD). Promising material for coating drill bits for oil recovery. Approach: Massively parallel molecular dynamics simulations using realistic potentials (background picture)

Friction at the nanoscale

Discoveredfric,onlawsatthenanoscale.Determineddependenceoffric,onforceonloadandcontactarea.

Proposedaphysicalexplana,onforexperimentallyobservedisotopeeffectonsolidfric,on.

Mo,Turner,andSzlufarska,Nature,457,1116(2009) Mo,Müser,andSzlufarska,PhysicalReviewB(inpress)

Discovered friction laws at the nanoscale. Proposed a physical explanation of why deuterium lowers friction of diamond

Increaseadhesionsub-linear

Increaseroughness

Reaction coordinate

D Exp 3h Theory

5.5h

Atomsincontact

• Wedemonstratedthatbehaviorofnanoscalecontactsisdescribedbyroughnesstheoriesinsteadofcon,nuummechanics• Fric,onforceiscontrolledbytheshortrangechemicalinterac,ons.

Demonstratedatransi,onfromalineartosublinearfric,on–loaddependence.Explainedpreviouslyreportedexperiments.

Fric,onforce–Realcontactarea Mo,va,on:Experimentreportedfric,onreduc,onof20%bypassiva,ngdiamondwithdeuteriuminsteadofhydrogenDischemicallymorestablethanHondiamondsurface

SurfacecoverageofH/Ddecreasesduringannealing

• Theisotopeeffectonsolidfric,onisconsistentwithdifferencesinchemicalstabilityofHandDondiamond• Afewpercentofsurfacevacancieshasalargeeffectonfric,on.

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