In this paper, adhesion force of graphene layers on 300 nm silicon oxide is studied. A simple model for measuring adhesion force for a flat surface with sub-nanometer roughness was developed and is shown that small surface roughness decreases adhesion force while large roughness results in an effectively larger adhesion forces. We also show that surface roughness over scales comparable to the tip radius increase by nearly a factor of two, the effective adhesion force measured by the atomic force microscopy. Thus, we demonstrate that surface roughness is an important parameter that should be taken into account in analyzing the adhesion force measurement results.
This work focuses on understanding the behavior of 3D hemispherical shells operating in wineglass resonance mode through finite element modeling (FEM). Fabrication of the hemispherical shells was done using micromachining technique. The quality factor of the device was in excess of 10,000 when operated in 50mT vacuum. The shell showed better than 95% sphericity and had an rms surface roughness of ~5nm. The separation in the degenerate frequencies of 4-node wineglass resonance was 5 Hz at a resonant frequency of 22 kHz. Modeling of the device behavior relates the frequency mismatch to the asymmetry in the shell and quantifies it.
This article reports on the evolution of contact resistance (R c ) of metal contacts over 100,000 cycles. A contact-mode atomic force microscope connected to a current versus voltage (I-V) measurement system was used and successive I-V measurements between a Crcoated AFM conducting tip and Ir, Pt, W, Ni, Cr, Ti, Cu or Al thin-film metals on silicon nitride coated silicon in a nitrogen ambient were carried out. Adhesion forces between the samples and the conducting AFM tip was also measured. The best cyclic I-V performers were Ir, Pt, W & Ti. The trend in changing R c seen in Ir, Pt and W are similar and can be attributed to factors such as their high Young's modulus, high melting temperatures and high density and low adhesion forces. Ti yeilded the best I-V behavior where contact resistance improved slightly as a function of cycling. A relationship between adhesion forces and defect generation in the contact region is observed and the results of both sets of experiments are detailed here.
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