Nanostructures

There are two general types of nanostructured materials that may be scanned with an atomic force microscope. The first category, category I, are structures that are integrated or directly attached to a bulk structure. The second type, category II, are structures that must be attached to a substrate before imaging.

Category I
Category I samples can typically be imaged with an AFM without sample preparation. It is important that contamination resulting from preparation and handling be removed from the sample before scanning with the AFM. If there is residual contamination on the surface, the images of the sample will typically have streak marks.

Category II
Because an AFM scans a mechanical probe across the sample's surface, the structure being imaged must be directly attached to the surface i.e. the affinity of the nanostructure for the surface must be greater than the affinity of the nanostructure to the probe. When nanostructures do attach to the probe, the resulting images typically show reduced resolution. Also, if the nanostructure is not rigidly attached to a surface, streaking may occur.

Often nanostructures naturally attach to surfaces. For example, nanotubes naturally directly attach to many surfaces. They can be moved on the surface but only with considerable shear forces from the probe.

In instances where there is no "natural" substrate, it often helps to use sticky substrates. Many of the common microscopy sample mounting supplies are appropriately covered through the use of double sided conductive carbon discs, sheets, and tapes. However, the unique needs of the AFM probe require some additional accommodation to expose a flat and stable surface. Examples of the two most recently successful techniques are described below. Supplies may be purchased at several microscopy supply venders. The ones used in the following example were purchased from SPI Supplies, Inc.