Pacific Nanotechnology Inc.

Surface Modification

Electrical Surface Modification

Electrically conducting AFM probes can be used to chemically modify a surface to "draw" an image. For example, applying an electrical bias between the conducting probe and a substrate can locally oxidize selected regions of the surface to form patterns.

Figure 2: By placing a bias between an electrically conductive probe and a surface, the surface can be modified.

The dimensions of the pattern drawn by electrically conducting techniques depends on:

Diameter of the probe
Potential between probe and surface

Figure 3: These patterns were drawn with an electrically conductive AFM probe using Anodic Oxidation. At the left the, line widths are 50 nm. At the right, two line widths were drawn using two different biases between the probe and sample.

For growing an oxide on silicon, the line-width of the pattern ranges up to tens of nanometers. The thickness can be controlled in the range of 10-50 nm. When the writing is done in ambient air, the line width depends on the relative humidity, because water adsorbed at the tip-substrate interface focuses the electric field and also acts as the anodization medium. The oxide thickness was found to depend on the electric field strength. Figure 3 shows two patterns written in silicon oxide with an AFM.