BYU Physics and Astronomy

We have fabricated nanoscale tellurium fuses using electron beam lithography for long term data storage applications. The tellurium fuses contain a narrow resistive region(250 nm to 10 micron). Application of a sufficiently high voltage accross the tellurium fuse causes resistive heating of the narrow region. After a sufficient temperature is reached, the tellurium melts and begins to flow until a gap is formed in the material. After the gap is formed there is no longer a path for electric current flow, causing a large permanent change in the resistance of the device. We have measured teh resistance change following gap formation and have experimentally determined the effect of voltage on the resulting gap size. Finite element simulations have been used to estimate the effect of applied voltage on the temperature of the fuses.

This paper has provided details on the LE of the data on magnetic tape, hard-disc drives, flash memory, and optical discs. For archival purposes, only the M-DISC presently meets the requirement of long-term data retention (more than 100 years). This disc has been rigorously tested, and the results are very positive. The main weakness of the M-DISC is its relatively small capacity. This weakness is being addressed by our current research on a permanent solid-state solution, one whose density will enable a capacity of several terabytes in the format of a solid-state drive. Though it will be much more expensive than an M-DISC, the convenience of having several terabytes in a single, removable form of storage should be very attractive to the archival community.

Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as floating potential dielectrophoresis (FPD) allows for a self-limiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting mechanism of CNT localization and how it can be used advantageously as devices are scaled downwards to smaller sizes.

This paper examines the effect of iron catalyst thickness on the straightness of growth of carbon nanotubes (CNTs) for microelectromechanical systems fabricated using the CNT-templated-microfabrication (CNT-M) process. SEM images of samples grown using various iron catalyst thicknesses show that both straight sidewalls and good edge definition are achieved using an iron thickness between 7 and 8 nm. Below this thickness, individual CNTs are well aligned, but the sidewalls of CNT forests formed into posts and long walls are not always straight. Above this thickness, the CNT forest sidewalls are relatively straight, but edge definition is poor, with significantly increased sidewall roughness. The proximity of a device or feature to other regions of iron catalyst also affects CNT growth. By using an iron catalyst thickness appropriate for straight growth, and by adding borders of iron around features or devices, a designer can greatly improve straightness of growth for CNT-MEMS.

Crystalline films and isolated particles of vanadium dioxide (VO2) were obtained through solid phase crystallization of amorphous vanadium oxide thin films sputtered on silicon dioxide. Electron back-scattered diffraction (EBSD) was used to study the crystals obtained in the thin films, to differentiate them from different vanadium oxide stoichiometries that may have formed during the annealing process, and to study their phase and orientation. EBSD showed that the crystallization process yielded crystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated particles, and did not show evidence of other vanadium oxide stoichiometries present. Indexing of the crystals for the orientation study was performed using EBSD patterns for the tetragonal phase of vanadium dioxide, since it was observed that EBSD patterns for the monoclinic and tetragonal phases of vanadium dioxide are not distinguishable by computer automated indexing. Using the EBSD patterns for the tetragonal phase of vanadium dioxide, orientation maps showed that all VO2 crystals that were measurable (approximately the thickness of the film) had a preferred orientation with the c-axis of the tetragonal phase parallel to the plane of the specimen. (C) 2011 Elsevier B.V. All rights reserved.