Influence of Surface Morphology on the Shear-Induced Wear of Alkylsilane Monolayers: Molecular Dynamics Study.

Chemisorbed alkylsilane monolayer coatings have been shown to possess favorable lubrication properties; however, film degradation prevents the widespread use of these materials as lubricants in micro- and nanoelectromechanical systems (MEMS/NEMS). In this work, molecular dynamics (MD) simulations are used to provide insight into the conditions that promote the degradation and wear of these materials. This is achieved through removal of interfacial chain-substrate bonds during shear and the examination of the mobility of the resulting free, unbound chains. Specific focus is given to the effects of surface morphology, which has been shown previously to strongly influence frictional forces in monolayer systems. In-plane order of chain attachments is shown to lead to pressure-induced orientational ordering of monolayers, promoting film stability. This behavior is lost as nonideality is introduced into the substrate and chain patterning on the surface becomes disordered. The presence of surface roughness is found to reduce film stability, with localization of wear observed for chain attachment sites nearest the interface of contact. The influence of substrate nonideality on monolayer degradation is shown to diminish as chain length is increased.

[1]  C. Allen,et al.  Boundary layer lubrication: monolayer or multilayer , 1969 .

[2]  Paul J. Mcwhorter,et al.  Materials issues in microelectromechanical devices: science, engineering, manufacturability and reliability , 2003 .

[3]  Clare McCabe,et al.  Frictional properties of mixed fluorocarbon/hydrocarbon silane monolayers: a simulation study. , 2012, Langmuir : the ACS journal of surfaces and colloids.

[4]  A. V. Duin,et al.  ReaxFF: A Reactive Force Field for Hydrocarbons , 2001 .

[5]  Steve Plimpton,et al.  Fast parallel algorithms for short-range molecular dynamics , 1993 .

[6]  G. Grest,et al.  Systematic study of the effect of disorder on nanotribology of self-assembled monolayers. , 2004, Physical review letters.

[7]  B. Bhushan,et al.  Investigation of the adhesion, friction, and wear properties of biphenyl thiol self-assembled monolayers by atomic force microscopy , 2001 .

[8]  B. Bhushan,et al.  Micro∕nanotribological study of perfluorosilane SAMs for antistiction and low wear , 2005 .

[9]  X. Zhu,et al.  Tribological properties of self-assembled monolayers on Au, SiOx and Si surfaces , 2000 .

[10]  Mark E. Tuckerman,et al.  Reversible multiple time scale molecular dynamics , 1992 .

[11]  H. Zuilhof,et al.  Highly wear-resistant ultra-thin per-fluorinated organic monolayers on silicon(1 1 1) surfaces , 2013 .

[12]  S. Nosé A unified formulation of the constant temperature molecular dynamics methods , 1984 .

[13]  Massimo G Noro,et al.  Simulation studies of stratum corneum lipid mixtures. , 2009, Biophysical journal.

[14]  B. Luan,et al.  Contact and friction of nanoasperities: effects of adsorbed monolayers. , 2009, Physical review. E, Statistical, nonlinear, and soft matter physics.

[15]  S. Granick,et al.  Formation and Characterization of a Highly Ordered and Well- Anchored Alkylsilane Monolayer on Mica by Self -Assembly , 1991 .

[16]  M. Stevens,et al.  Friction between Alkylsilane Monolayers: Molecular Simulation of Ordered Monolayers , 2002 .

[17]  E. Kumacheva,et al.  Confinement-Induced Phase Transitions in Simple Liquids , 1995, Science.

[18]  Steven G. Vilt,et al.  Tribological durability of silane monolayers on silicon. , 2011, Langmuir : the ACS journal of surfaces and colloids.

[19]  Hisae Yoshizawa,et al.  Recent advances in molecular level understanding of adhesion, friction and lubrication , 1993 .

[20]  B. Bhushan Nanotribology and nanomechanics of MEMS/NEMS and BioMEMS/BioNEMS materials and devices , 2007 .

[21]  Sriram Sundararajan,et al.  Nanoscale friction switches: friction modulation of monomolecular assemblies using external electric fields. , 2009, Langmuir : the ACS journal of surfaces and colloids.

[22]  Clare McCabe,et al.  Simulation study of the structure and phase behavior of ceramide bilayers and the role of lipid head group chemistry. , 2013, Journal of chemical theory and computation.

[23]  H. Kuisma,et al.  Effect of alkylsilane coating on sliding wear of silica-silicon contacts with small amplitude motion , 2002 .

[24]  Xiaoli Hu,et al.  Atomistic simulation of the effect of roughness on nanoscale wear , 2015 .

[25]  Water penetration of damaged self-assembled monolayers. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[26]  G. Grest,et al.  Probe-Tip Induced Damage in Compliant Substrates , 2010 .

[27]  G. Grest,et al.  Tribological properties of alkylsilane self-assembled monolayers. , 2005, Langmuir.

[28]  M. Berkowitz,et al.  Ewald summation for systems with slab geometry , 1999 .

[29]  Bharat Bhushan,et al.  AFM study of perfluoroalkylsilane and alkylsilane self-assembled monolayers for anti-stiction in MEMS/NEMS , 2005 .

[30]  R. Maboudian,et al.  Tribological Challenges in Micromechanical Systems , 2013 .

[31]  R. J. Collins,et al.  Performance impact of monolayer coating of polysilicon micromotors , 1995, Proceedings IEEE Micro Electro Mechanical Systems. 1995.

[32]  J. Harrison,et al.  Packing-Density Effects on the Friction of n-Alkane Monolayers , 2001 .

[33]  Sharon C. Glotzer,et al.  Characterizing complex particle morphologies through shape matching: Descriptors, applications, and algorithms , 2011, J. Comput. Phys..

[34]  G. Grest,et al.  Simulations of nanotribology with realistic probe tip models. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[35]  R. Howe,et al.  Alkyltrichlorosilane-based self-assembled monolayer films for stiction reduction in silicon micromachines , 1998 .

[36]  J. Li,et al.  The influence of an OTS self‐assembled monolayer on the wear‐resistant properties of polysilicon based MEMS , 2006 .

[37]  D. F. Ogletree,et al.  Atomic Force Microscopy Study of the Pressure-Dependent Structural and Frictional Properties of n-Alkanethiols on Gold , 1997 .

[38]  David N Reinhoudt,et al.  Engineering silicon oxide surfaces using self-assembled monolayers. , 2005, Angewandte Chemie.

[39]  T. Xu,et al.  Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon , 2002 .

[40]  Maarten P. de Boer,et al.  Role of interfacial properties on MEMS performance and reliability , 1999, Industrial Lasers and Inspection.

[41]  Gary S. Grest,et al.  Frictional dynamics of perfluorinated self-assembled monolayers on amorphous SiO2 , 2005 .

[42]  H. D. Cochran,et al.  Molecular simulation of the transition from liquidlike to solidlike behavior in complex fluids confined to nanoscale gaps , 2001 .

[43]  M. Dugger,et al.  Nanotribology and MEMS , 2007 .

[44]  J. Israelachvili,et al.  Identification of a Second Dynamic State During Stick-Slip Motion , 1993, Science.

[45]  Clare McCabe,et al.  Molecular dynamics study of alkylsilane monolayers on realistic amorphous silica surfaces. , 2015, Langmuir : the ACS journal of surfaces and colloids.

[46]  Hoover,et al.  Canonical dynamics: Equilibrium phase-space distributions. , 1985, Physical review. A, General physics.

[47]  K. Kojio,et al.  Molecular aggregation state of n-octadecyltrichlorosilane monolayer prepared at an air/water interface , 1998 .

[48]  M. Loy,et al.  Humidity and Temperature Effect on Frictional Properties of Mica and Alkylsilane Monolayer Self-Assembled on Mica , 1999 .

[49]  Steven G. Vilt,et al.  Tribology of monolayer films: comparison between n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon. , 2009, Langmuir : the ACS journal of surfaces and colloids.

[50]  A. Ulman,et al.  Formation and Structure of Self-Assembled Monolayers. , 1996, Chemical reviews.

[51]  W. Merlijn van Spengen,et al.  MEMS reliability from a failure mechanisms perspective , 2003, Microelectron. Reliab..

[52]  Bharat Bhushan,et al.  Micro-/nanoscale tribological and mechanical characterization for MEMS/NEMS , 2003, SPIE MOEMS-MEMS.

[53]  O. Borodin,et al.  Frictional dynamics of fluorine-terminated alkanethiol self-assembled monolayers. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[54]  Bruno Marchon,et al.  Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives , 2010 .

[55]  D. A. Hook,et al.  Tribological degradation of fluorocarbon coated silicon microdevice surfaces in normal and sliding contact , 2008 .

[56]  E. Kumacheva,et al.  Simple liquids confined to molecularly thin layers. I. Confinement-induced liquid-to-solid phase transitions , 1998 .

[57]  K. Kanazawa,et al.  Structure and tribological properties of ultrathin alkylsilane films chemisorbed to solid surfaces , 1993 .

[58]  C. McCabe,et al.  Examining the frictional forces between mixed hydrophobic-hydrophilic alkylsilane monolayers. , 2012, The Journal of chemical physics.

[59]  A. Ulman,et al.  Self‐assembled monolayers of alkyltrichiorosilanes: Building blocks for future organic materials , 1990 .

[60]  R. Maboudian,et al.  Self-assembled monolayers as anti-stiction coatings for MEMS: characteristics and recent developments , 2000 .

[61]  Sharon C. Glotzer,et al.  Characterizing Structure Through Shape Matching and Applications to Self Assembly , 2010, ArXiv.

[62]  W. L. Jorgensen,et al.  Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids , 1996 .

[63]  M. Stevens Thoughts on the structure of alkylsilane monolayers , 1999 .