Hoon-Sik Jang

Conventional nanoindentation testing generally uses a peak penetration depth of less than 10 % of thin-film thickness in order to measure film-only mechanical properties, without considering the critical depth for a given thin film-substrate system. The uncertainties in this testing condition make hardness measurement more difficult. We propose a new way to determine the critical relative depth for general thin-film/substrate systems; an impression volume analyzed from the remnant indent image is used here as a new parameter. Nanoindents made on soft Cu and Au thin films with various indentation loads were observed by atomic force microscope. The impression volume calculated from 3D remnant image was normalized by the indenter penetration volume. This indent volume ratio varied only slightly in the shallow regime but decreased significantly when the indenter penetration depth exceeded the targeted critical relative depth. Thus, we determined the critical relative depth by empirically fitting the trend of the indent volume ratio and determining the inflection point. The critical relative depths for Cu and Au films were determined as 0.170 and 0.173, respectively, values smaller than 0.249 and 0.183 determined from the hardness variation of the two thin films. Hence the proposed indent volume ratio is highly sensitive to the substrate constraint, and stricter control of the penetration depth is needed to measure film-only mechanical properties.

A variety of outstanding experimental results on mechanical properties of carbon nanotube (CNT) are fast appearing. Nevertheless, mechanical properties of CNT have been rarely understood because of measurement difficulties. The response of multi walled carbon nanotube (MWNT) to mechanical strain applied with a nano-manipulator was investigated inside scanning electron microscope (SEM). MWNTs were produced by arc-discharge method and the protruded sample for tensile test was selected among the MWNTs fragment which has rectilinearity and purity above 40%. The average diameter of MWNT was approximately 15 nm. In order to measure the resistance of a MWNT during tensile test, an individual MWNT was attached at the tungsten (W) tip using electron beam induced deposition. We confirmed that the contact resistance between a MWNT and the W tip decrease during the exposure of electron beam. And then the W tip were manipulated and controlled by nano-manipulator and personal computer. We observed that resistance of sample was significantly changed until the MWNT fracture