(Color online) Dipole moment on CNTs and particles in nonuniform electric field. Dielectrophoresis, which is the translation motion of neutral matter caused by the polarization effect in a nonuniform electric field, should be carefully distinguished from electrophoresis, which is a motion caused by the response to a free charge on a particle in an electric field. A neutral particle polarized in an electric field such as MWNTs moves to the region of highest field intensity in a nonuniform electric field (Ref. 14).
(Color online) Schematic of the electrochemical assembly apparatus with ac electric source. The apparatus consists of two parts: a processing part and an inducing part. In the processing part, the holder of AFM tip was fixed to the axis translation stage for maintaining the distance from the counter electrode. This stage is able to be operated in rolling and pitching directions with a tilting angle of 0 to 90 deg. The inducing part comprised a signal generator and signal detector such as an oscilloscope and an ohmmeter.
(a) (Color online) FESEM images of AFM tip used in this research. The shape of the tip remained conical with a curvature of 100–150 nm. (b) The simulation result of the electric field. The area where the dielectrophoretic force is zero is the area where the gradient of the electric field is zero.
(a) (Color online) FESEM images of CNT AFM tips with a single MWNT attached. These tips were fabricated under an ac electric field with at 5 MHz and, in the case of inner figure, at 5 MHz, gap distance. (b) Some of tips have the bundle CNTs on the end of the tips. The contact area between the MWNTs and the tip was covered by impurities. It caused a strong bonding between the MWNT and the tip. (c) The distribution of the yield in this experiment is shown. CNT AFM tip with a single MWNT attached has a 35% yield.
(Color online) Noncontact mode AFM images and line profiles obtained with (a) bare tip ( width) and (b) CNT-attached tip ( width). As shown in the AFM images, the cross-sectional line profile measured with the bare tip deviates significantly from the real profile, whereas the profile measured with the CNT AFM tip with a single MWNT attached resembles that of the standard sample. By verifying the existence of the MWNT after scanning, we have demonstrated that the MWNT tip made by this method is able to be used as a measurement tip.
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