Orest J. Glembocki

Carbon nanotube growth for field-emission cathodes from graphite paste using Ar-ion bombardment

Multiwall carbon nanotubes (MW-CNT) have been synthesized from solid-phase graphite. The graphite is deposited as a thick-film paste and irradiated with a 1.2keV flood Ar-ion beam, transforming the graphite surface to a composite of MW-CNT embedded in the graphite matrix. Micro-Raman measurements have verified that the nanotubes are metallic in nature. The technique was used to make printed field-emission cathodes. Emission from these cathodes demonstrates Fowler–Nordheim tunneling characteristics. The irradiated film emits at an extraction field of 5.0V∕μm, which is less than one-sixth of the minimum extraction field of the nonirradiated graphite film, and exhibit lower noise and greater emission uniformity.

Experimental demonstration of the optical lattice resonance in arrays of Si nanoresonators

Optical resonances of crystalline Si nanopillar arrays on a Si substrate are studied using optical reflectivity and Raman spectroscopy. When the nanopillars are arranged in a two-dimensional lattice, a collective resonance is observed in the reflection spectra which is absent for randomly distributed nanopillars. The resonance is due to coherent oscillations in nanopillars, can be tuned spectrally by the nanopillar diameter and lattice period, and strongly suppresses reflection from the Si surface. Raman scattering demonstrates that the reduced reflectivity is accompanied by increased electromagnetic field confined in Si, thus suggesting potential application of the lattice resonance in surface enhanced spectroscopy and thin film solar cells.

Aspect-ratio driven evolution of high-order resonant modes and near-field distributions in localized surface phonon polariton nanostructures

Polar dielectrics have garnered much attention as an alternative to plasmonic metals in the mid- to long-wave infrared spectral regime due to their low optical losses. As such, nanoscale resonators composed of these materials demonstrate figures of merit beyond those achievable in plasmonic equivalents. However, until now, only low-order, phonon-mediated, localized polariton resonances, known as surface phonon polaritons (SPhPs), have been observed in polar dielectric optical resonators. In the present work, we investigate the excitation of 16 distinct high-order, multipolar, localized surface phonon polariton resonances that are optically excited in rectangular pillars etched into a semi-insulating silicon carbide substrate. By elongating a single pillar axis we are able to significantly modify the far- and near-field properties of localized SPhP resonances, opening the door to realizing narrow-band infrared sources with tailored radiation patterns. Such control of the near-field behavior of resonances can also impact surface enhanced infrared optical sensing, which is mediated by polarization selection rules, as well as the morphology and strength of resonator hot spots. Furthermore, through the careful choice of polar dielectric material, these results can also serve as the guiding principles for the generalized design of optical devices that operate from the mid- to far-infrared.

Observation of coherent oscillations in plasma-enhanced atomic layer deposition Ag films

Acoustic oscillations were observed in ultrafast transient absorption of nanostructured Ag films produced by plasma-enhanced atomic layer deposition (PEALD). The oscillations are attributed to modulations of localized surface plasmon resonance (SPR) bands that naturally arise in the PEALD films and can be described as two lateral modes (∼50 and 100 GHz) with different dephasing times. Contributions from electron-phonon coupling and lattice dynamics in the transient response vary systematically with the probe wavelength relative to the SPR maximum (500–1000 nm).

On the Driving Force of Shockley Stacking Fault Motion in 4H-SiC

Shockley stacking faults (SSFs) are extended, planar defects in silicon carbide SiC that are the cause of the observed drift in the forward voltage that occurs during bipolar injection within both bipolar or unipolar SiC devices. Efforts to understand the primary driving force for SSF nucleation and expansion have been put forth in an effort to eradicate the incorporation of the basal plane dislocations from which the SSFs nucleate and/or to minimize the expansion of the SSFs themselves. Up until recently, the reported driving force models were all based on the hypothesis that SSFs were thermodynamically stable with respect to the 4H-SiC host lattice. Therefore, these prior models focused on explaining the reason for the improved stability of the material in the faulted state. However, annealing 4 and high temperature device operation 5 experiments illustrated that SSFs could be contracted and the Vf drift recovered. The results of these experiments therefore clearly showed that SSFs are not the preferred state of 4H-SiC at thermal equilibrium and T>30C. Here, we introduce and discuss a possible mechanism describing the primary driving force governing SSF expansion and contraction that is consistent with the previously reported experimental observations. Further, we also will present further experimental and simulation results that strengthen support for this model. Finally, we report simulation results that imply SSF-induced degradation of the Vf is due to a reduction in the carrier lifetime within the 3C-SiC material of the SSFs, which act as electron traps within the host lattice material. The model we present builds upon the mechanisms reported by Lambrecht and Miao and Galeckas et al., where the relative energy associated with the filling of the two-dimensional density of states of the SSFs under

Clusters on semiconductor surfaces

Recent theoretical analysis and experimental investigations indicate that the physics of clusters deposited on semiconductor surfaces such as Silicon may be a promising future avenue for nanostructure science. Clusters of small number (5 - 10) of atoms in free space have also been shown to have interesting energy structures as well as magnetic and electrical moments. We report on the formation of Mn islands on Si(111) surfaces and their optical scattering response. We show that Mn islands of diameter 15 to 30nm exhibit paramagnetism at low temperatures, while thick films of Mn do not. In addition, our experiments verify previous theoretical suggestions that polarized optical scattering can be used to detect magnetism in small clusters. We will discuss some of these along with possible future applications of cluster physics.