Results from a series of molecular dynamics simulations are reported in which a nanoscale tip was used to indent gold lattices subjected to external strains. The changes in the slope of the loading curves reflect the stress state of the sample. This was true even in the absence of material pile-up, suggesting that the change in loading reflects changes in elastic properties of materials and not a change in contact area due to pile-up. Shallow nanoindentation was also evaluated as a method to map residual surface stresses by simulating indentation at a series of points near a dislocation intersecting a surface. Correlations between the maximum force on the tip and the initial local stresses at the point of indentation were observed. Thus, preliminary atomistic simulations indicate that atomic-force microscopy can be used as a nondestructive, nanoscale probe of the surface stress distributions

Microploughing experiments were used as a method for better understanding the ploughing mechanism in gold and iridium single crystals. The plough depths ranged from 20 nm in iridium to 1600 nm in gold. Yield stress profiles and TEM analyses indicate that both materials strain harden even when very small volumes of material are involved. Strain hardening theory, as applied to bulk material, is useful in analyzing the results.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Fabrication of metallic Au nanopillars and linear arrays of Au-containing nanodots for plasmonic waveguides is reported in this article by two different processes—focused ion beam (FIB) milling of deposited thin films and electron beam-induced deposition (EBID) of metallic nanostructures from an organometallic precursor gas. Finite difference time domain (FDTD) modeling of electromagnetic fields around metallic nanostructures was used to predict the optimal size and spacing between nanostructures useful for plasmonic waveguides. Subsequently, a multi-step FIB fabrication method was developed for production of metallic nanorods and nanopillars of the size and geometry suggested by the results of the FDTD simulations. Nanostructure fabrication was carried out on planar substrates including Au-coated glass, quartz, and mica slides as well as cleaved 4-mode optical fibers. In the second fabrication process, EBID was utilized for the development of similar nanostructures on planar Indium Tin Oxide and Titanium-coated glass substrates. Each method allows formation of nanostructures such that the plasmon resonances associated with the nanostructures could be engineered and precisely controlled by controlling the nanostructure size and shape. Linear arrays of low aspect ratio nanodot structures ranging in diameter between 50–70 nm were fabricated using EBID. Preliminary dark field optical microscopy demonstrates differences in the plasmonic response of the fabricated structures. SCANNING 31: 139–146, 2009. © 2009 Wiley Periodicals, Inc.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Fabrication of a linear array of metallic nanodots and nanopillars for plasmonic waveguides is reported in this paper by two different processes - FIB milling of deposited thin films and electron beam-induced deposition of metallic nanostructures from a organometallic precursor gas introduced into the chamber. In the first FIB fabrication method, metallic nanorods and nanopillars were fabricated by depositing a 30-150 nm layer of a metallic (gold or silver) film on a planar substrate and subsequently employing FIB milling to pattern out the metallic nanopillars from the film. Employing FIB allowed formation of nanostructures such that the plasmon resonances associated with the nanostructures could be engineered and precisely controlled by controlling the nanostructure size and shape. Multistep FIB fabrication procedures were developed to form the nanostructures of complex geometries on planar substrates. The second fabrication processed used to create nanodots and nanopillars for plasmonic waveguides discussed in this paper is direct deposition of metal nanostructures, created when an electron beam (e-beam) is used to dissociate metal from an organometallic precursor gas in a predefined reaction region. Ionization energy required for decomposition of the Au precursor, i.e. Dimethyl Au (III) Fluoro Actylacetonate, is matched with that of the secondary electrons (between 5-50 eV) that are generated by exposing the substrate to a focused electron beam.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

This paper describes the fabrication of portable and robust fiber optic sensors - mainly chemical and biological sensors - on standard communication grade optical fibers. Metallic nanostructures such as nanoparticles, nanopillars, nanorods, and nanoholes in optically thick metallic films were employed to precisely control the enhancement and absorption of light so as to form sensitive and specific optical sensors based on optical fibers. The fiber-optic sensors employ localized plasmon resonances (LSPRs) of metallic nanostructures formed on the fiber end-face as well as surface plasmon resonances assoc1ated with nanoholes in optically thick metallic films as a means of transducing the input optical signal. These metallic nanostructures were formed on the cleaved end-face of multimode and single mode optical fibers and were employed in both reflection and transmission modes. Metallic nanoparticles, nanorods, and nanopillars were formed on the tip or surface of the optical fiber by either employing chemical means or by first depositing a 10-100 nm layer of metallic film on the tip or surface of the fiber and then employing focused ion beam (FIB) milling to pattern out the metallic nanoparticles and nanopillars from the film. Ordered arrays of nanoholes were formed in optically thick (150-230 nm) metallic films by employing FIB milling. Gold (Au) nanostructures are chemically stable and result in plasmon resonance related peaks in the transmission spectrum in the visible spectral region. Hence, gold was selected as the material of choice for the fabrication of the plasmon resonance sensors.

In the fabrication of InGaN∕GaN multiple quantum well light emitting diodes so-called V defects are common, but little is known about their electrical activity. Scanning transmission electron microscopy is capable of directly observing these defects, while electron beam induced current (EBIC) techniques can be used to probe electronic behavior of semiconductor defects. These techniques were combined to obtain localized measurements and our results indicate that V defects suppress the EBIC signal near the core of the defect and produce a displacement in the p-n junction location. Furthermore, the EBIC profile suggests that minority carrier diffusion lengths are longer inside the defect.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Single crystal niobium specimens of (100), (110) and (111) crystal orientations have been analyzed using TEM and SIMS. The TEM specimens were prepared using Focused Ion Beam (FIB) and show niobium oxide thicknesses ranging from 4.9 to 8.3 nm for the three specimens after buffer chemical polishing. The oxide layers appear uniform and no significant sub-oxide region was noted. SIMS analysis was made for all three orientations on hydrogen, carbon, and oxygen before and after heat treatments at 90, 600, and 1250 degrees C. Hydrogen is at a high level between the oxide layer and niobium, but at a relatively low level in the oxide. No high oxygen concentration region was noted in the mobium below the oxide. C contamination on the surface is detected mainly at the surface. Analysis after heat treatments showed some decrease in hydrogen after the 600 degrees C heat treatment and significant oxidation of the niobium after the 1250 degrees C heat treatment.

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007