Graduation Year

2008

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Alex A. Volinsky, Ph.D.

Keywords

Single crystal ripples, Moisture assisted wear, Scratch testing, Gold pattern

Abstract

In order to successfully incorporate the tremendous possibilities of nanoscale applications into devices and manufacturing, significant studies need to be conducted of the properties and mechanics of materials of this small scale. In this thesis, the effect of repeated scanning of KBr, aluminum, and gold was studied by using a nanoindenter and Atomic Force Microscope (AFM) in varying environments. Additional research was performed to study the environmental effects of gold film scratching using a Taber Shear/Scratch Tester. Scanning of KBr single crystal surface in air with a diamond tip in the Hysitron Triboindenter formed surface ripples 100 nm high, 1 micron apart. It has been observed that the nanoripple's initial height and period increase with the number of repeated scans. The surface ripples form perpendicular to the scanning direction, beginning at the bottom of sloped samples and working their way up the entire scan area. The addition of water to a wear experiment on gold film produced considerably deeper wear areas than its ambient air counterpart in both scanning machines. Scratch testing with a conical diamond tip of 77 µm radius with 125 g normal load also produced deeper wear tracks in water than in ambient air conditions. Several mechanisms may be responsible for the ripples formation, including dislocation dynamics, chatter, piezo hysteresis and others. Most likely there is a combination of effects, with a clear differentiation between nanoripple's origination and propagation. Mechanisms responsible for rippling, including system dynamic response and stick slip behavior are investigated. Topography modification appears to be the main result of ambient wear tests at the nanoscale, whereas much higher wear rate and nanoripples are observed in water. It is possible that this moisture is assisting grain fracture and pull off.

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