AFM tipinduced modification of GaAs100 surface structure

The GaAs(lOO) surface can be modified by an AFM tip if it is scanned with relatively large force (10 riN) in 10 mM H2SO4 solution at various electrode potentials [24]. Figure 8 shows a typical AFM image of a p-GaAs(lOO) surface at an open-circuit potential after the tip was scanned at an open-circuit potential (1 pm x 1 pm) for 30 min in only the x-direction of 500 nm with a scan rate of 25 lines/s. It is clear that there is a wedge in the central part of the image where the tip was initially scanned with a strong force. Figure 9 shows the relation between the electrode potential and the depth of the fabricated wedge. The more positive the potential, the larger the anodic current and the deeper the depth of the wedge structure. However, when the electrode potential became more positive than +0.075 V, the wedge structure was not clearly observed because the dissolution process on the p-GaAs surface proceeded violently and large hill-and-valley structures were formed everywhere on the surface. On the other hand, if the potential was kept in the cathodic range, surface modification did not occur. These results suggest that the formation of wedge structures on the surface requires both the scanning of the tip and the flow of anodic current, i.e., the modification is the result of tip-induced electrochemical etching. The wedge structure was formed even at the open-circuit potential (Fig. 8), because a small anodic current corresponding to GaAs dissolution flowed to compensate the cathodic photocurrent which was generated by laser light used for sensing the deflection of the cantilever.

When Cu was electrochemically deposited onto the GaAs surface part of which was modified by the AFM tip, Cu was deposited selectively on the scratched portion. This result may lead to a novel technique for the submicron fabrication.

0 0

Post a comment