Nanofabrication with the scanning tunneling microscope

We have developed a technique to use the scanning tunneling microscope (STM) to create nanometer-scale structures. We use the STM tip as a localized source of electrons to decompose an organometallic gas, leaving metal atoms on the substrate. By scanning the STM tip over the surface of the substrate, we can create any desired pattern.;We have used the technique in two different STM/vacuum system combinations. The first system which we designed and built to quickly test this deposition scheme, operated in high vacuum. Using this system, we deposited cadmium, aluminum, tungsten, and carbon lines with linewidths down to 10 nm, onto silicon and copper substrates. Using other organometallic gases, we etched 20 nm pits in silicon substrates. We measured the two-probe electrical resistivity of some of the wires as a function of temperature.;The first system was not able to produce high-purity metal lines, nor was it possible to align the structures with pre-existing contact pads. To remedy these problems, we built a new, ultra-high-vacuum (UHV), scanning electron microscope (SEM)/STM combination. The system combines a conventional, high vacuum SEM with a separate UHV chamber for the STM. This instrument has a range of magnifications from 25x to 25,000,000x. The combination allows us to access any area on a substrate within a 2 mm x 2 mm area with the STM tip. Using this instrument, we have written wires with 95% nickel content on silicon substrates. This is by far the highest purity level achieved to date using this technique. Since the wires were aligned with a four-probe contact pad pattern, we were able to measure their four-point resistivity. This measurement, made on a 190 nm linewidth wire, confirmed the high nickel content of the wires.;By varying the tip-to-sample voltage bias, we can adjust the linewidth of the deposited lines. Working at lower bias voltages, we have fabricated nickel wires down to a linewidth of 35 nm although we have not yet succeeded in making these narrow wires electrically continuous. This technique shows great promise for the fabrication of novel devices.