Jimmie A. Miller

Scanning tunneling microscopy bit making on highly oriented pyrolytic graphite: Initial results

A scanning tunneling microscope was used to modify the surface structure of highly oriented pyrolytic graphite in air. By superimposing 0.1‐μs pulses on the substrate bias, we consistently manufactured hole‐hill combinations (‘‘bits’’) of 2–3 nm. A 40‐nm L‐shaped structure was created. We describe the experiments and relevant results.

X-ray calibrated tunneling system utilizing a dimensionally stable nanometer positioner

To determine to what extent tunneling probes can be used for metrology or as position-sensitive transducers on the atomic scale, accurate characterization of tunneling current as a function of distance must be ascertained. This report describes a system for making such characterizations and observing their repeatability in air. Also, it is often necessary to position two objects to within nanometers in order to perform precision measurements. Included in the narrative, a dimensionally stable screw-wedge-lever system is described for manually moving a tunneling probe to within 15 nm of a conducting surface. The conducting surface is translated via a magnetically actuated single crystal flexure system previously calibrated through direct x-ray interferometry over a 20-nm range. This limited calibration range dictated dimensional positioning below 15 nm. Also, tunneling current measurements demanded dimensional stability below one nanometer. The complete system is demonstrated to hold the relative probe-surface separation to within 1 nm over a 15-minute duration. Also, the vibrational resonance of the structure is determined using the power spectrum analysis during electron tunneling. Resulting data using platinum, palladium, and silver tips in conjunction with a carbon surface show that current-displacement values vary from run to run with a positional difference of up to 1 nm for a given current. These variations suggest limitations for using tunneling probes in air to perform angstrom metrology.

A Technique for Enhancing Machine Tool Accuracy by Transferring the Metrology Reference From the Machine Tool to the Workpiece

High-speed machining (HSM) has had a large impact on the design and fabrication of aerospace parts and HSM techniques have been used to improve the quality of conventionally machined parts as well. Initially, the trend toward HSM of monolithic parts was focused on small parts, where existing machine tools have sufficient precision to machine the required features. But, as the technology continues to progress, the scale of monolithic parts has continued to grow. However, the growth of such parts has become limited by the inability of existing machines to achieve the tolerances required for assembly due to the long-range accuracy and the thermal environment of most machine tools. Increasing part size without decreasing the tolerances using existing technology requires very large and very accurate machines in a tightly controlled thermal environment. As a result, new techniques are needed to precisely and accurately manufacture large scale monolithic components. Previous work has established the fiducial calibration system (FCS), a technique, which, for the first time provides a method that allows for the accuracy of a coordinate measuring machine (CMM) to be transferred to the shop floor. This paper addresses the range of applicability of the FCS, and provides a method to answer two fundamental questions. First, given a set of machines and fiducials, how much improvement in precision of the finished part can be expected? And second, given a desired precision of the finished part, what machines and fiducials are required? The achievable improvement in precision using the FCS depends on a number of factors including, but not limited to: the type of fiducial, the probing system on the machine and CMM, the time required to make a measurement, and the frequency of measurement. In this paper, the sensitivity of the method to such items is evaluated through an uncertainty analysis, and examples are given indicating how this analysis can be used in a variety of cases.

Accurate measurement of trivalent silicon interface trap density using small signal steady‐state methods

The high–low‐frequency capacitance method for determining the interface trap density is widely used in studying the effects of ionizing radiation on thermally grown SiO2, and in verifying the trivalent silicon interface traps first discovered in electron paramagnetic resonance studies. It is shown that the high–low‐frequency capacitance method gives fictitious interface trap density peaks because of the departure of the 1‐MHz high‐frequency capacitance from the ideal high‐frequency capacitance. This method gives accurate values of the interface trap density near the center of the silicon band gap, but for a given high frequency, the range of band‐gap energy over which accurate values are obtained decreases with increasing interface trap density. Interface trap density is obtained over a band‐gap energy range with an accuracy that is independent of interface trap density from a comparison of the measured and calculated slopes of gate bias versus equilibrium band‐bending curves using the Q‐C (charge‐capacit...

Improving the Accuracy of Large Scale Monolithic Parts Using Fiducials

Monolithic machined components are rapidly replacing sheet metal assemblies to reduce labor costs. As these monolithic parts become larger, maintaining the accuracy required for further assembly operations becomes difficult. The long-range accuracy and the thermal environment of most machine tools become the limiting factors for part size. This paper describes a solution to this problem using fiducials, the spacing of which is based on the machine accuracy and part tolerance. Experimental results demonstrate the validity of the technique. This technique can be extended to allow small machines to manufacture large components and is also applicable in high volume manufacturing environments.

Surface morphology of epitaxial Ge on Si grown by plasma enhanced chemical vapor deposition

Heteroepitaxial Ge films have been deposited on (100) Si substrates at low temperature (325 °C) by electron cyclotron resonance plasma enhanced chemical vapor deposition. The substrates were subjected to an in situ hydrogen/argon plasma etch prior to film growth to remove carbon and oxygen. The surface morphology has been observed with optical and scanning electron and scanning tunneling microscopy. Surface roughness due to three dimensional growth is strongly influenced by ion flux and arrival rate of reactive species on the growth surface. Surface roughness has a detrimental effect on the crystallinity of the deposited films as determined by reflection high‐energy electron diffraction and x‐ray diffraction measurements.

A double-pass interferometer for measurement of dimensional changes

A double-pass interferometer was developed for measuring dimensional changes of materials in a nanoscale absolute interferometric dilatometer. This interferometer realized the double-ended measurement of a sample using a single-detection double-pass interference system. The nearly balanced design, in which the measurement beam and the reference beam have equal optical path lengths except for the path difference caused by the sample itself, makes this interferometer have high stability, which is verified by the measurement of a quasi-zero-length sample. The preliminary experiments and uncertainty analysis show that this interferometer should be able to measure dimensional changes with characteristic uncertainty at the nanometer level.

Low temperature epitaxial growth of Ge using electron‐cyclotron‐resonance plasma‐assisted chemical vapor deposition

Epitaxial Ge films have been deposited on Si and Ge substrates at 300 °C using electron‐cyclotron‐resonance plasma‐assisted chemical vapor deposition. Helium was fed into the resonance chamber, and a mixture of helium and germane were fed downstream at a location above the substrate. Surface roughness increased with energetic ion bombardment as quantified by the number of ions striking the surface per Ge atom deposited. Surface roughness also increased with increasing substrate temperature. Films with very rough surface morphology were found to be polycrystalline. The large hydrogen content of the films, particularly those deposited on Si, appeared to prevent the reduction of the epitaxial temperature below 300 °C. In the temperature range between 300 and 325 °C, hydrogen bubbles formed at the Ge/Si interface and caused the films to pucker from the surface. Increasing the substrate temperature above 325 °C eliminated this problem by decreasing the surface coverage of hydrogen during deposition.

In-situ infrared detection and heating of metallic phase of silicon during scratching test

A new method of in-situ detection of the high pressure phase transformation of silicon during dead-load scratching is described. The method is based on the simple fact that single crystal silicon is transparent to infrared light while metallic materials are not. Infrared heating during scratching has also been performed to thermally soften and deform the transformed metallic material and some promising results were obtained. The sample material used here is silicon, but the same approach can be applied to germanium and other materials, such as ceramics (SiC), which have appropriate optical properties.

Quick and dynamic measurements of geometric errors of CNC machines

In this paper, a system that is used to measure dynamically all kinds of geometric errors of CNC machines is introduced, and some experiment results are given. The experiment results showed some significant differences between the static and dynamic error characteristics. Through analyses of the dynamic signals in both time and space fields, some error resources of the CNC machines can be found. In addition, any shape of contouring errors can be directly measured by this system without using a ball bar on other devices, which provides a simple and practical way to evaluate contouring errors of CNC machines.