Evaluate the complexity of the user interface. It should be laid out in a straightforward, manner with easy-to-use controls. For example, the user interface should have buttons with names that represent commonly performed functions such as "APPROACH" and "IMAGE". After you have seen someone else demonstrate the instrument, ask to operate it yourself. You are then in the best position to evaluate the simplicity of the user interface.
Some SPMs are built upon operating systems that allow multi-tasking. If you can process data while collecting additional data, your throughput will be increased measurably.
All commercial SPMs now include optical microscopes to help monitor the tip-to-sample approach and to select the areas of interest on the sample surface. A good optical microscope speeds up your work because it enables you to position the tip quickly and accurately, exactly where you want to take an SPM image. If you intend to image very rough or oddly shaped samples (for example geological samples, or teeth), or cross sections of any kind that require landing the tip on a narrow edge, a good optical microscope is indispensable. Figure 5-1 shows a real-time video image of a cantilever positioned over an integrated circuit.
When evaluating the optical microscope, look for the following features:
Under normal operating conditions, an AFM tip should last for a couple of days, so changing the probe should be a straightforward process. However, the chips upon which cantilevers are mounted are very small and can be unwieldy to handle. New designs permit pre-aligned, pre-mounted probes to be changed very quickly, with minimal alignment of the beam-bounce detection system. As with the user interface, you should evaluate how difficult it is to change a probe. Change a probe yourself, instead of watching a highly skilled operator change it.
If you intend to perform unique experiments with an SPM, you may be very interested in having access to the software, the electronics, and the mechanics of the system in order to make your own modifications. Investigate the design of the system to see whether it is open enough for your customized work. Consider also the technical strength and availability of the technical support staff at the factory. You may want their advice more often than a user who is happy to operate the machine off-the-shelf.
