The Atomic Force Microscope

The Atomic Force Microscope consists of a microfabricated cantilever with a very sharp and well-defined tip of a few microns in diameter (see cartoon of tip scanning over film at right). A laser is aimed at the r eflective back of the cantilever, and as the laser is scanned across the surface the orientation of the cantilever changes due to interactions with species on the surface of the sample. The variations in the position of the cantilever causes a change in the angle and orientation of the reflected laser light. A photodetector records the changes in the orientation of the laser light and sends this data to the computer. Deflections of laser light as small as 0.001 nm can be detected. The three-dimensiona l topography of the sample can then be imaged from this data. At left is a diagram showing a vertical cross-section through a diblock copolymer film. The blue and tan regions represent different microdomains and t he squiggly line shows how a copolymer molecule might be arranged in the film, bridging between two adjacent microdomains. No current is required between the sample surface and the tip, and thus very fragile samples are not damaged as they may be by othe r types of nanometer-scale microscopy. This superb non-destructive imaging capability allows pictures of the same area of a polymer film to be imaged over multiple annealings.

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