E. E. Ehrichs

Direct writing of submicron metallic features with a scanning tunneling microscope

We demonstrate for the first time that the scanning tunneling microscope can be used to write metallic features on a surface without further process steps. Using organometallic gases we have obtained features down to 20 nm in size.

Direct writing of 10 nm features with the scanning tunneling microscope

A scanning tunneling microscope (STM) has been used to write metallic lines and carbon lines with linewidths as small as 10 nm. Organometallic gases or surface organic contamination can be decomposed to deposit these lines in a single step. Computer control of the STM allows precise patterning of these lines on a silicon substrate.

Direct writing with the scanning tunneling microscope

A scanning tunneling microscope has been used to write metallic features directly on metallic and semiconducting surfaces without further process steps. Organometallic gases were used to obtain features as small as 20 nm.

Etching of silicon (111) with the scanning tunneling microscope

It has recently been demonstrated that the scanning tunneling microscope can be used to break organometallic molecules on a scale of tens of nanometers [E. E. Ehrichs, S. Yoon, and A. L. Lozanne, Appl. Phys. Lett. 53, 2287 (1988)]. This process has been used to write dots, lines, crisscross patterns, and letters on silicon surfaces. Thus far, dimethyl cadmium, trimethyl aluminum, and tungsten hexafluoride have been used as precursor gases. Organic surface contaminants can also be polymerized by this process, yielding stable structures with linewidths down to 10 nm. All these fabricated structures are conductive enough to drain the tunneling current. More information is currently being obtained by measuring the resistance of lines written by this technique. More recently, it has been observed that WF6 can produce either deposits or etch pits in silicon. The smallest pit obtained thus far is 20 nm in diameter and 12 nm deep. The parameter that determines whether deposition or etching takes place is probably...

Nanofabrication and rapid imaging with a scanning tunneling microscope

Nanowires have been made by decomposing organometallic gases in a UHV scanning tunneling microscope (STM); this process is a form of chemical vapor deposition (CVD). Our STM is coupled to a commercial scanning electron microscope (SEM), which allows us to align the tip with pre‐existing contact pads for electrical measurements of the nanowires. Thus four‐contact measurements on two wires have been performed, a first for STM‐fabricated structures. The resistivity of the first wire made from a nickel carbonyl precursor gas is 34±10 μΩ cm at room temperature. This is remarkably close to the bulk value of 7.8 μΩ cm, since the wire is only 5 nm thick, 190 nm wide and 3.7 μm long. This indicates that the nickel deposits are fairly pure, and is consistent with Auger analysis made on micron‐size deposits: there is at least 95% nickel in these deposits. This is a substantial improvement over previous results from our group and the few other groups using this technique. The second wire is 1.45 μm long and 100 nm wi...

Four-probe resistance measurements of nickel wires written with a scanning tunneling microscope/scanning electron microscope system

Abstract We have used a scanning tunneling microscope (STM)/scanning electron microscope (SEM) system in ultra-high vacuum (UHV) to write nickel wires on silicon, forming connections between prefabricated four-probe contact pads. We leak nickel carbonyl into the STM chamber to a set pressure. We then use the STM tip as a local source of electrons to decompose the nickel carbonyl which has adsorbed to the surface of the substrate. Auger analysis indicates that 95% of the material in our deposits is nickel. Nickel wires as small as 50 nm in width have been fabricated in this way. Previously, we have fabricated nonmetallic wires as small as 10 nm in width, thus demonstrating the potential for the technique. A low-temperature, four point resistance measurement indicates that our nickel wires are conductive and metallic. We estimate that their resistivity at 77 K is approximately 25 μΩ·cm. This is the first report of a four-point measurement on an STM-written structure.

Nanofabrication of nickel wires with the scanning tunnelling microscope

The authors present a brief review of their work by generating structures with sizes down to 10 nm by breaking organometallic molecules with the electrons from a scanning tunnelling microscope.

Direct Writing with a Combined STM/SEM System

We review our work on the use of the Scanning Tunneling Microscope (STM) for the fabrication of nano-scale metallic wires. Our process is essentially a very localized chemical vapor deposition (CVD), where the organic precursor gas is broken with the electrons coming from the STM tip. This process has produced lines as narrow as 10 nm. We have also etched holes in silicon with diameters down to 20 nm. More recently we have built an STM inside a Scanning Electron Microscope (SEM). The latter allows us to accurately align the STM tip with contact pads on the surface of the substrate. This has made it possible to measure the electrical properties of narrow nickel wires, which is the first four-point measurement of a structure made by STM. The work of other groups in this field will also be reviewed briefly.

Synthesis and Study of Nanostructures

We briefly review our work on the use of the scanning tunneling microscope (STM) for the synthesis and study of structures down to the 10 nm scale. In particular, we have demonstrated for the first time that the STM can dissociate organometallic gas molecules and thus produce a pattern of a desired metal. The smallest patterns thus far have been obtained by polymerizing residual organic contaminants on the surface. We have also found that it is possible to etch pits in silicon by using the appropriate halogen gas. More recently, we have built a new ultra high vacuum STM inside a commercial scanning electron microscope. This STM/SEM is a powerful tool to align the STM tip with contact pads which will allow the measurement of the transport properties of 10 nm wires written with the STM.

Four-Point Resistance Measurements of Wires Written with a Scanning Tunneling Microscope

We review briefly our work on using the Scanning Tunneling Microscope (STM) to break down organometallic precursor gases to form metallic lines. We are particularly interested in the transport properties of wires smaller than 100 nm. This requires four-probe measurements of the wires and therefore a good method for locating the probes on the substrate and for bringing the STM tip to the probes. We have built a UHV STM inside a commercial Scanning Electron Microscope in order to accomplish this. This instrument is briefly described here.