Micro∕nanotribological study of perfluorosilane SAMs for antistiction and low wear

Abstract

In micro/nanoelectromechanical systems ͑MEMS/NEMS͒, surface-dominated forces, such as stiction/adhesion and friction, play an important role because of the large surface-area-to-volume ratio. In order to control these forces and wear properties, optimal lubricant systems have been extensively investigated. Perfluoroalkyl self-assembled monolayers ͑SAMs͒ are considered to be a strong candidate since the fluorinated carbon backbones are expected to show lower adhesion and friction. In this paper, surface properties of perfluoroalkylsilane SAMs are investigated and compared with those of standard alkylsilane SAMs. The SAMs are deposited on silicon with a native oxide layer and silica substrates by a vapor deposition process. Surface properties, such as surface energy, water contact angle, roughness, adhesive and friction forces, and wear resistance, are evaluated. An atomic force microscope ͑AFM͒ is used for evaluations of the micro/nanotribological properties. The influence of humidity, temperature, and sliding velocity is also examined. In addition, the tribological mechanisms of the SAMs on molecular scale are discussed based on the AFM observations to aid the design and selection of proper lubricants for MEMS/NEMS.

Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion

“…PF 3 was chosen because of its hydrophobic nature. The thickness and standard deviation of the SAM of PF 3 were 1.8 and 0.14 nm, respectively (Kasai et al 2005). An optical profiler was used to measure the surface topography of the patterned surfaces , 2008.…”

Nanotribological characterization of perfluoroalkylphosphonate self-assembled monolayers deposited on aluminum-coated silicon substrates

“…The efficiency, power output and steady state operation of MEMS/NEMS devices can be critically influenced by adhesion, friction, and wear (Bhushan 1998(Bhushan , 2003(Bhushan , 2004(Bhushan , 2005Liu and Bhushan 2004a, b;Bhushan and Liu 2004a). Further, adhesion and friction are known to show dependence on the operating parameters, such as relative sliding velocity and environmental conditions, e.g., relative humidity (RH) and temperature (Liu et al 1996;Lio et al 1997;Schoenherr and Vancso 1999;Tian et al 1999;Clear and Nealey 2001;Bhushan 2002, 2003;Bhushan and Liu 2004b;Bhushan et al 2004;Kasai et al 2005;Bhushan 2004, 2005a, b, c, d). This has necessitated the application of low friction and low adhesion, ultrathin lubricant films for the protection of contacting surfaces in MEMS/NEMS.…”

Nanotribology and nanomechanics in nano/biotechnology

“…For wear performance studies, experiments were conducted on various films. Figure 9b shows the relationship between the decrease in surface height and the normal load for various SAMs and corresponding substrates (Kasai et al 2005;Tambe & Bhushan 2005;Bhushan et al 2006b). As shown in the figure, the SAMs exhibit a critical normal load beyond which point the surface height drastically decreases.…”

“…Several studies of liquid perfluoropolyether (PFPE) lubricant films and SAMs have been carried out for the purpose of minimizing adhesion, friction and wear (Bhushan et al 1995b(Bhushan et al , 2006bKoinkar & Bhushan 1996a,b;Henck 1997;Bhushan 1999aLiu & Bhushan 2002Kasai et al 2005;Lee et al 2005b;Tambe & Bhushan 2005;Tao & Bhushan 2005a,b). Many variations of these films are hydrophobic (low surface tension and high contact angle) and have low shear strength which provide low adhesion, friction and wear.…”