Hoon-Sik Jang

In-situ Resistance Measurements during Tensile Test of Carbon Nanotube using Nano-manipulator

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

In situ characterization of the field-emission behaviour of individual carbon nanotubes

The current–voltage (I–V) characteristics of carbon nanotubes (CNTs) during field emission were investigated by in situ imaging and field-emission (FE) measurement inside a field-emission scanning electron microscope (FE-SEM). A primary electron of the FE-SEM could induce and enhance a large stimulated electron emission from a CNT which might be due to the strong local field on the tip of the CNT in the presence of an applied voltage. FE of bent nanotubes (BNTs) can initially occur after they are fully straightened or it can start in the bent state (during geometrical straightening) as the applied field increases. The FE from a single CNT follows FN (Fowler–Nordheim) behaviour with a single linear slope in the FN plot. The FE from two nanotubes with a geometrical change during FE showed transition of the FN slope from the low voltage to the high voltage region, which could be due to interactions between two dynamic neighbouring BNTs.

Tensile properties of carbon nanotube with different growth methods

We have attempted to observe straining responses of a multi-walled carbon nanotube (MWCNT) with different growth methods by performing an in situ tensile testing in a scanning electron microscope. Linear deformation and fracture behaviors of MWNT were successfully observed and its force-displacement curve was also measured from the bending stiffness and displacement of the force sensor and manipulator, respectively. We obtained different tensile strength of MWCNTs with different growth methods and the elastic modulus of MWCNTs was also calculated and compared with each other.

On the Characterization of Thin Film-only Mechanical Property Based on the Indentation Image Analysis

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.