Shirley Turner

Restructuring tungsten thin films into nanowires and hollow square cross-section microducts

We report on the growth of nanowires and unusual hollow microducts of tungsten oxide by thermal treatment of tungsten films in a RF H2/Ar plasma at temperatures between 550-620 °C. Nanowires with diameters of 10-30 nm and lengths between 50-300 nm were formed directly from the tungsten film, while under certain specific operating conditions hollow microducts having edge lengths ~ 0.5 μm and lengths between 10-200 μm were observed. Presence of a reducing gas such as H2 was crucial in growing these nanostructures as was trace quantities of oxygen necessary to form a volatile tungsten species. Preferential restructuring of the film surface into nanowires or microducts appeared to be significantly influenced by the rate of mass-transfer of gas phase species to the surface. Nanowires were also observed to grown on tungsten wires under similar condition. A surface containing nanowires, annealed at 500 °C in air, exhibited capability of sensing trace quantities of nitrous oxides (NOx).

A microarray approach for optimizing localized deposition of carbon nanotubes using microhotplate arrays

A 340-element array of microhotplates was used to characterize the chemical vapour deposition growth of carbon nanotubes and nanofibres under a variety of process conditions. One dimension of the 17 by 20 element array was used to vary the thickness of a Ni catalyst layer. The second dimension was used for temperature control. Growth took place in an ambient temperature gas flow system, with processes only occurring on activated heaters. This allowed different process sequences to be defined on different columns of the array. Four parameters were varied: pre-anneal temperature of the catalyst, growth temperature of the carbon nanostructures, growth pressure, and growth time. Scanning electron microscope images of each array element revealed trends in microstructure as these parameters, together with the catalyst thickness, were varied.

Characterization of SiGe films for use as a National Institute of Standards and Technology Microanalysis Reference Material (RM 8905).

Bulk silicon-germanium (SiGe) alloys and two SiGe thick films (4 and 5 microm) on Si wafers were tested with the electron probe microanalyzer (EPMA) using wavelength dispersive spectrometers (WDS) for heterogeneity and composition for use as reference materials needed by the microelectronics industry. One alloy with a nominal composition of Si0.86Ge0.14 and the two thick films with nominal compositions of Si0.90Ge0.10 and Si0.75Ge0.25 on Si, evaluated for micro- and macroheterogeneity, will make good microanalysis reference materials with an overall expanded heterogeneity uncertainty of 1.1% relative or less for Ge. The bulk Ge composition in the Si0.86Ge0.14 alloy was determined to be 30.228% mass fraction Ge with an expanded uncertainty of the mean of 0.195% mass fraction. The thick films were quantified with WDS-EPMA using both the Si0.86Ge0.14 alloy and element wafers as reference materials. The Ge concentration was determined to be 22.80% mass fraction with an expanded uncertainty of the mean of 0.12% mass fraction for the Si0.90Ge0.10 wafer and 43.66% mass fraction for the Si0.75Ge0.25 wafer with an expanded uncertainty of the mean of 0.25% mass fraction. The two thick SiGe films will be issued as National Institute of Standards and Technology Reference Materials (RM 8905).

Characterization of SiGe Bulk Compositional Standards with Electron Probe Microanalysis

Bulk SiGe wafers cut from single‐crystal boules were evaluated with the electron probe microanalyzer (EPMA) for micro‐ and macroheterogeneity for use as primary standards for future characterization of SiGe thin films on Si that are needed by the microelectronics industry as reference standards. Specimens with nominal compositions of 14 at. %, 6.5 at. %, and 3.5 at. % Ge were rigorously tested with wavelength dispersive spectrometers (WDS) using multiple point, multiple sample, and duplicate data acquisitions. The SiGe14 is a good bulk reference material for evaluation of SiGe thin films.

Transmission electron microscopy and electron holography of nanophase TiO{sub 2} generated in a flame burner system

Nanophase TiO{sub 2} (n-TiO{sub 2}) particles were generated in a flame burner system under three experimental conditions. Selected individual nanoparticles were identified and characterized using selected area electron diffraction, bright-field and, in some cases, dark-field imaging to determine morphology and microstructural features. Previously unknown TiO{sub 2} particles with unusual central features were identified as rutile. Electron holography was used to characterize the central features which were found to be consistent with voids. More extensive characterization of individual particles may lead to improved understanding of n-TiO{sub 2} nucleation and growth.

Systematic Characterization of Reciprocal Space by SAED: Advantages of a Double-Tilt, Rotate Holder

Characterization of reciprocal space by selected area electron diffraction (SAED) has been limited by the conventional transmission electron microscope (TEM) sample holders available for sample manipulation. Traditional sample holders include the double-tilt holder and rotate-tilt holder, each of which has two degrees of freedom for sample manipulation. These holders allow for orientation of samples down zone axes. However, the microscopist commonly cannot easily tilt around a crystallographic direction of interest within the resultant electron diffraction patterns unless the sample is fortuitously oriented in the sample holder. Multiple diffraction patterns, however, can be collected from the same sample. This is done, especially for higher symmetry metallurgic samples, by combining the available tilt or rotate-tilt capabilities [1]. The angles between zones can be only estimated. Alternatively, software available for the FEI CompuStage allows for tilt around a specified crystallographic direction (FEI CM k-Space Control) [2,3]. The capability is limited to those instruments with a CompuStage. In this work, the applicability of a double-tilt, rotate (2TR) holder to characterization of reciprocal space is tested. This holder has a third degree of freedom for sample manipulation and it was expected that this would allow for systematic characterization of reciprocal space by SAED.

Characterization of the Morphology of Faceted Particles by Transmission Electron Microscopy

Abstract : Faceting in a polyhedral rutile particle was modeled from transmission electron microscopy images. A double-tilt, rotate transmission electron microscope (TEM) sample holder was used to manipulate the particle. Using this holder, it was possible to align the c axis of the particle along one of the axes of the sample holder. This alignment allowed images to be obtained of the particle in several orientations around its c axis. Assuming symmetrical growth perpendicular to the c axis of the rutile particle, comparison of dimensions and angles obtained to those obtained for hypothetical models of the particle gives information about its likely prismatic and pyramidal faceting. This approach to facet modeling in combination with thickness information should be useful for more complete determination of the faceting in individual euhedral particles using transmission electron microscopy.