PhD Oral Examination :: Wesley Smith (Wednesday, June 16th, 2pm)

Wes Smith wessmith at
Fri Jun 11 10:43:44 PDT 2010

Stanford University Ph.D. Oral Defense
Department of Mechanical Engineering

Title: Shear adhesion, friction, and wear at multi-point micro- and  
nano-scale contacts

Speaker: Wesley Smith
Advisor: Prof. Thomas W. Kenny

Date: Wednesday, June 16th, 2010
Time: 2pm (Refreshments and snacks at 1:45pm)
Location: Allen Building (formerly CIS-X) Auditorium, Room 101


Building an understanding of the fundamental mechanisms that  
contribute to adhesion, friction, and wear at the micro- and nano- 
scales is vitally important to develop reliable micro-devices that  
involve contacting and sliding surfaces. When dimensions are reduced  
down to the micro- and nano-scale, the surface area-to-volume ratio  
increases significantly and surface forces begin to play a dominant  
role in adhesion and friction.

The complicated and often unreliable behavior of contacting and  
sliding surfaces has limited their adoption in many  
microelectromechanical systems (MEMS). This study examines the effects  
of the contact conditions on the friction forces and wear rate to  
enhance the current understanding of friction at the small scale and  
lead to the design of reliable sliding surfaces in MEMS devices.

In this presentation, I will discuss the development of a unique  
experimental setup where friction forces are solely responsible for  
the measured motion. Friction is measured between an array of single  
crystal silicon MEMS probe tips and a flat silicon surface. Contact  
between the surfaces occurs at AFM-like tips that are located at the  
end of compliant cantilevers. Friction force results from arrays with  
varying numbers of tips show that the friction forces depend heavily  
on the true contact area between two sliding surfaces. This work also  
takes a careful look at the conditions that affect the wear rate of  
the tips. Methods such as reducing the contact pressure per tip and  
allowing mechanical compliance of the contacting surface are shown to  
minimize the detrimental effects of wear. 
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