We study the Casimir force between a nanoparticle and a substrate using a spectral representation formalism. We consider the interaction of metal nanoparticles with different substrates within the dipolar approximation. The force is calculated as a function of the distance between the particles and the substrate. The particles are made of gold or potassium spheres, and the substrate is titanium dioxide, sapphire or a perfect conductor.

Despite the extensive interest in its remarkable materials properties, the structure of spider dragline silk is not yet known. Indirect structural information is thus of particular interest. New data are presented here from two probe microscopy techniques – atomic force microscopy (AFM) and single-molecule force spectroscopy, or ‘molecular pulling.’ Using a soluble synthetic protein from dragline silk, segmented silk nanofibers have been observed by AFM. Molecular pulling (Force Spectroscopy) has revealed sawtooth-like rupture peaks, indicative of the sacrificial bonds and hidden lengths seen in molecules of other self-healing biomaterials. A model is presented for the folding of single dragline-silk molecules and the arrangement of these molecules into nanofibers. The relationship is discussed between these molecular / nanoscale results and the materials properties of natural and artificial dragline silks.

Luminescence imaging techniques such as Photoluminescence (PL) and Cathodoluminescence (CL) have been extensively used to characterize the optical properties of GaN. However, analysis using these techniques is limited to near surface regions and may not represent bulk material properties. This restricts the understanding of the defect-related yellow luminescence in GaN, which tends to originate at the interface region. In this work, we propose the use of MeV protons to probe several microns into a Epitaxial Lateral Overgrown GaN layer. Monte Carlo simulations of the ionization profile show that MeV ions have a much higher penetration depth than the keV electrons used in CL. The well-defined electronic energy loss peak or ‘Bragg peak’ at the end of range for MeV ions enables us to perform depth resolved imaging of the yellow luminescence distribution. Another advantage of using a MeV ion beam over keV electrons is the relatively small lateral spreading of ions in a material, making it a more suitable technique for providing high-resolution images of any buried defects in GaN.

Gold nanoclusters dispersed in single crystal MgO were prepared by ion implantation and subsequent annealing at 1000 °C. The morphological feature, size, crystallographic orientation of the Au nanoclusters with respect to the MgO matrix, and the interface structure between the Au nanoclusters and MgO were investigated using transmission electron microscopy. During annealing, the Au clusters nucleate coherently in the MgO lattice, leading to an epitaxial orientation relationship of [010] MgO// [010]Au and (200)MgO//(200)Au that is maintained for all the Au clusters. A critical size for the coherent-semicoherent interface transition is observed to be in the range from ∼5 to 8 nm for Au clusters in MgO. Au clusters larger than this critical size exhibit faceting on the {001} planes. The precipitated Au also exhibits internal dislocations.

The free carrier concentration of GaAs layers grown by MOCVD either on GaAs or Si substrates, by the conformal method in the last case, was obtained from the micro-Raman spectra using the hydrodynamic approach to fit the LO phonon-plasmon coupled Raman modes. The results on homoepitaxial layers were used as a calibration of the fitting method. The measurements in the selectively doped conformal layers were then compared with data obtained by micro-photoluminescence and cathodoluminescence spectroscopy and imaging. The doping data are compared with those deduced from the room temperature micro-photoluminescence and cathodolumiescence spectra.

The size dependence of the catalytic property of the gold catalysts has been reported. It is especially interesting that the catalytic property of gold suddenly changes to show a platinum-like behavior when the mean size of gold is below 2nm. This phenomenon should be owing to the change of the electronic structure of the gold, however its detail has not been cleared yet. We investigated the size dependence of the mean inner potential of gold catalysts supported on TiO2, which is affected by the outer valence electron, using electron holography and high-resolution electron microscopy. We found the following tendency. When the size of the gold particle is over 5nm, the values of the mean inner potential are the same level as the reported experimental values of the bulk gold (21–23V) and the calculated values of the bulk gold (25–30V). When the size is below 5nm, the mean inner potential begins to increase over 30V, and it begins to increase suddenly over 40V at the size below about 2nm. It indicates that the electronic structure of the gold particles varies from that of the bulk state as the size of the gold particles reduces. Due to the size reduction, the volume fraction of the surface atoms and the interface atoms increases, e.g., almost half of the atoms locate on the surfaces or at the interface in case of the top half of the octahedron particle with the size 1.6nm. The surface dipole and the interface dipole should be formed owing to the electron out of the surface to the vacuum and the local charge transfer from the gold particles to the TiO2 surface. These dipole effects might be effective and one of the reasons for the increase of the mean inner potential of gold particles.

Fluctuation electron microscopy studies have been performed on several aluminum oxides exposed to different electrochemical conditions. Little is known about amorphous aluminum oxide structures and their relationship with their passivation behaviors. Corrosion studies have shown that exposure of aluminum oxide films to Cl ions in solution reduces the oxide's passivity, and this results in the onset of pitting corrosion. The physical changes that occur in the oxide as a result of Cl exposure have not been previously identified due to the difficulty in investigating the structure of this amorphous material. Fluctuation microscopy is a new electron microscopy technique that is able to detect the presence of medium range order structures in amorphous systems. In this paper, we will report fluctuation microscopy results on amorphous aluminum oxides that have been exposed to Cl ions in solution and compare them with oxides that have seen no electrolyte exposure or that have been exposed to electrolytes that do not contain Cl-,such as SO42- containing electrolytes. We will also compare the Cl-exposed oxides with oxides that have been implanted with Cl ions. The differences in pitting behaviors for these oxidesare consistent with our previous speculation on the effect of medium range order on the passivation behavior of aluminum oxides grown using ozone.

STM stimulated light emissions (STM-LE) from cleaved surfaces of GaAs(110) were investigated using a UHV-STM combined with a light detection system. Clean surfaces of Zn doped GaAs (p=5×1018) were obtained by mechanical cleavage in UHV. Light emission from the cleavage surface showed a single peak in a spectrum, which corresponds to luminescence by the conduction band to acceptor level transition in GaAs. In STM image Zn acceptors show bright tri angular-shaped contrasts, while in photon map they show dark contrasts when taken with a sample bias voltage of 2.0 V and 2.2 V at 80K. This contrast can be explained from the local band bending due to the charging effect or strain effect of the Zn acceptor.

Thin films and arrays of lines of magnetic CoNiFe alloy have been produced by electrodeposition. A magnetic field was applied during the electrodeposition process in order to induce a magnetic anisotropy in the sample. The dependence of the magnetic properties and the magnetic domain structures on the thickness of the films is reported. In addition to this, the magnetic properties and the domain structure of a thin film and an array of lines, with the same thickness and deposited in the same conditions, have been compared. An increase in the coercivity of the array of lines has been shown.

A simple method was demonstrated to tune surface plasmon resonance wavelength of silver island films by introducing an underlayer. The tunability can be much enhanced by varying the underlayer medium. In combination with the size effects of metallic islands the plasmon wavelength can be readily adjusted throughout the visible spectral regions. The experimental results were interpreted based on a generalized Maxwell-Garnett theory.

Time-resolved luminescence measurements on silicon nanocrystal waveguides have revealed a fast recombination dynamics, related to population inversion which leads to net optical gain. The waveguide samples were obtained by thermal annealing of plasma enhanced chemical vapour deposited thin layers of silicon rich oxide Variable stripe length measurements performed on the fast emission signal have shown an exponential growth of the amplified spontaneous emission, with net gain values of about 10 cm-1. Both the fast component intensity and its temporal width revealed threshold behaviour as a function of the incident pump intensity. A modelling of the decay dynamics is suggested within an effective four level rate equation treatment including the delicate interplay among stimulated emission and Auger recombinations.

The atomic and electronic structures of Au/TiO2(110) systems have been theoretically investigated based on the density functional theory. We have examined Au adsorption on the stoichiometric TiO2(110) surface and on the Ti-rich surface formed by the removal of bridging-oxygen atoms (VOB surface) and the O-rich surface formed by the removal of 6-fold titanium and bridging-oxygen atoms (VTi6OB surface). For the stoichiometric surface, the stable site for the Au adatom is the hollow site of one bridging-oxygen and two in-plane oxygen atoms or the on-top site above 5-fold titanium atom. For the Ti-rich VOB surface, the bridging site of 6-fold titanium atoms along [001] direction is the most stable. In addition, the vacant site of 6-fold titanium atom is the most stable for the O-rich VTi6OB surface. The adhesive energies between the Au adlayer and the TiO2 surface are larger for the non-stoichiometric surfaces than that for the stoichiometric surface. The charge transfer between the Au adatom and the substrate is small for stoichiometric surface. For the Ti-rich VOB surface, the electron transfer occurs from the 6-fold Ti to the Au, while from the Au to the in-plane oxygen for the O-rich VTi6OB surface. It can be said that the TiO2 surface conditions such as defects or non-stoichiometry strongly affect the adsorption energy and electron structure of the Au adsorbed system. This point should be closely related the catalytic property of the Au/TiO2 system.

Electron Tomography is shown to be applicable to problems of materials science if a contrast mechanism is used which provides a projection relationship for crystals not depending on lattice plane orientation. Energy filtered TEM (EFTEM) in its mode of electron spectroscopic imaging (ESI) and STEM-EDX-Mapping are, subject to limitations, suitable image formation techniques. The spectroscopic operation not only allows to overcome Bragg scattering artefacts, but offers the possibility of recording 4-dimensional data (volume and energy) of a region of interest, otherwise only known from NMR and XAS/XANES tomography at larger length-scales and from field-ion microscopy (atom probe) under restrictive conditions.

In this paper, we report the leakage current characterization of HfO2 high-k dielectric thin films by using tunneling AFM, which utilizes a conducting AFM probe to detect current passing through the sample and the probe while simultaneously acquiring a topographic image. We have studied tunneling current behavior of HfO2 films by characterizing the hot spots, which are characterized by excessive local leakage current, as well as the overall current distribution. Tunneling AFM results show sensitive dependence of tunneling current with variation of film thickness. The current distribution can be described approximately by a log-normal distribution, which is consistent with the characteristics of the thickness variation. Furthermore, the film structure and thickness were also characterized with TEM and spectroscopic ellipsometry.

We report on the use of surface enhanced Raman scattering (SERS) for the detection of dipicolinic acid (DPA) adsorbed on a silver (Ag) nanoparticle substrate. We have examined the interaction of DPA with Ag nanoparticles in a slightly basic, aqueous solution and determined that the molecule adsorbs as a dipicolinate anion on the metal surface. For micro molar or lower DPA concentrations in the colloid solution, no SERS activity from the adsorbed molecule was observed until nanoparticle aggregation was induced by reducing the pH with the addition of nitric acid. Following aggregation, the SERS response exhibited vibrational bands associated with both the pyridine ring and the carboxylate moieties in the adsorbed dipicolinate species. With proper control of the colloidal solution chemistry, the dipicolinate vibrational features could be observed in the SERS spectra at concentrations as low as 20 nano molar, a limit determined by the presence of solution-based contaminants on the Ag surface. In addition to the controlled DPA analyte studies, SERS was also able to detect the release of this molecule from Bacillus globigii spores, a non-toxic simulant for Bacillus anthracis, which demonstrated the potential of this optical spectroscopy for the detection of biological and chemical agents.

A combination of Kelvin Probe Microscopy (KPM) and Cathodoluminescence (CL) microanalysis has been used to characterize ultra pure silicon dioxide (SiO2) exposed to electron irradiation in a Scanning Electron Microscope. Charged beam irradiation of poorly conducting materials results in the trapping of charge at pre-existing or irradiation induced defects thereby inducing a localized electric field within the irradiated micro-volume of specimen. The residual surface potentials associated with the localized electric field have been mapped using KPM. Evidence of electro-diffusion and defect micro-segregation in charged beam irradiated SiO2 is observed. The associated mobile defect species are identified using CL microanalysis techniques. The high correlation between KPM and CL images confirms the significant influence of localized potentials on the microstructure of technologically important SiO2.

Imaging critical features by using transmission electron microscopy (TEM) or scanning electron microscopy (SEM) provides a versatile approach for nanostructure characterization. The combination of focused ion beam (FIB) technology for exposing defective sites beneath the surface is shown. Reliability testing and defect analysis by localized characterization of multilayered structures is demonstrated. TEM-imaging of a transistor gate with a locally confined radiation damage demonstrates target preparation by FIB yielding high-resolution TEM samples. The TEM imaging requires a longer sample preparation but provides high image quality (TEM). Investigation of materials previously processed with FIB revealed amorphization damage by the high energetic Ga-ion beam. This damage layer with a thickness in the range of 50 to 100 nm was confirmed in simulation. This disadvantageous damage by amorphization originating from FIB preparation of the cross-section could be removed by soft sputtering with a 250 V Ar+ ion beam. This combined method using FIB for microsample preparation and TEM for imaging and analysis was proven to be a powerful tool the exploitation of nanostructured devices and for defect analysis on a highly localized scale.

We report on the structure of and elemental distributions within various magnetic nano-particles synthesized using organometallic precursors. The characterization was carried out using high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS), with spectral imaging to investigate elemental distributions within the particles. The crystallinity and oxidation of Fe, Co and Fe-Co particles are discussed. We observe heavy oxidation of Fe particles, while Co particles show, at most, only a thin surface layer of oxide. When Fe and Co are combined to form Fe-Co particles, they are seen to be inhomogeneous, consisting of an Fe core, surrounded by a Co-rich shell.

Pulsed laser ablation has been used to produce silicon nanocrystals. Variation of the laser fluence, backing gas type and pressure result in nanocrystals with controllable size distributions. Properties of nanocrystals produced with this method also depend on the distance of the nanocrystal from the center of the laser plume. Correlated atomic force microscopy and in-situ micro-Raman measurements confirm that particle size decreases as distance from the plume center increases. Silicon peaks in the micro raman spectra taken at increasing distance from plume center show considerable differences in both center energy and width. Confocal micro raman spectra from thicker (> 10 micron) samples show little variation with depth, in contrast with porous silicon samples.

The ability to determine the in-situ optoelectronic behavior of semiconductor materials has become especially important as the size of device architectures is reduced and the development of complex microsystems has increased. Scanning Tunneling Optical Resonance Microscopy or STORM has the ability to interrogate the optical bandgap as a function of position within a semiconductor microstructure. This technique uses a tunable solid-state Ti sapphire laser whose output is “chopped” using a spatial light modulator and is coupled by a fiber optic to a scanning tunneling microscope in order to illuminate the tip-sample junction. The photoenhanced portion of the tunneling current is spectroscopically measured using a lock-in technique. The capabilities of this technique were verified using semiconductor microstructure calibration standards that were grown by organometallic vapor phase epitaxy (OMVPE) at the NASA Glenn Research Center. Bandgaps characterized by STORM measurements were found to be in good agreement with the bulk values determined by transmission spectroscopy, photoluminescence, and with the theoretical values that were based on x-ray diffraction results.