For the past few years we have made transport measurements of pure nickel wires made by decomposing nickel carbonyl with the electrons from a scanning tunneling microscope (STM), which is a form of chemical vapor deposition (CVD). The need to align the tip with four micron-size contact pads resulted in a design incorporating a non-UHV scanning electron microscope (SEM), and a concomitant low throughput of samples. Nonetheless, we have continued to reduce our wires’ dimensions and improve their quality; we show these results and discuss the primary factors governing line quality. To improve throughput and reliability further, we have finished a novel design that utilizes a high power optical microscope instead of a SEM. Two key features of this design are a very compact x–y positioner and a custom window welded directly on the side of the chamber. The positioner is built into a standard fine-screw tripod. It provides over 150 μm of orthogonal motion by tilting a 0.25 in. ball bearing that holds a 0.188 in. ball bearing in an off-center position. The 2 in. sapphire window, which protrudes into the vacuum chamber, makes it possible to have the tip as close as 6 mm to the atmosphere side. This gives an excellent view of the whole STM and allows us to use a 40× (or 20×) objective lens with a 14 (or 19) mm working distance. The extra distance is important for viewing the sample from different angles and makes it possible to place the tip over any desired feature on the surface. We present results from the new STM demonstrating this capability.
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Rubel et al. (1995) studied this question.