Valerie J. Leppert

Spectroscopic and structural characterization of electrochemically grown ZnO quantum dots

We report a novel method for the synthesis of stable, OH free zinc oxide quantum dots, using an electrochemical route. The optical properties of these quantum dots were studied at room temperature, by taking the optical absorption and luminescencespectra. The band gapluminescence is predominant in ZnOquantum dots synthesized by the present technique, while the green defect induced luminescence, typical of ZnO, is strongly quenched. The role of defects in photoluminescence emission is discussed.

Pulsed laser deposition of amorphous diamond-like carbon films with ArF (193 nm) excimer laser

Abstract : We have deposited hydrogen-free diamond-like amorphous carbon (amorphous diamond) films by ArF (193 nm) pulsed laser ablation of graphite. The deposition process is performed with the laser power density of only 5x10(8) W/cm2 at room temperature without any auxiliary energy source incorporation. The resulting films possess remarkable physical, optical and mechanical properties which are close to those of diamond and distinct from the graphite target used. The films have a mechanical hardness up to 38 GPa, an optical energy band gap of 2.6 eV and excellent thermal stability. Analysis of electron energy loss spectroscopy reveals the domination of diamond-type tetrahedral bonding structure in the films with the Sp3 bond fraction over 95%. Compared to other reported results of pulsed laser deposited diamond-like carbon films, our experimental results confirm that the laser wavelength or photon energy plays a crucial role in controlling the properties of the pulsed laser deposited diamond-like carbon films.

Oxidative stress and NFκB activation in the lungs of rats: A synergistic interaction between soot and iron particles

Particulate matter (PM) has been associated with a variety of adverse health effects primarily involving the cardiopulmonary system. However, the precise biological mechanisms to explain how exposure to PM exacerbates or directly causes adverse effects are unknown. Particles of varying composition may play a critical role in these effects. To study such a phenomenon, a simple, laminar diffusion flame was used to generate aerosols of soot and iron particles in the ultrafine size range. Exposures of healthy adult rats were for 6 h/day for 3 days. Conditions used included exposure to soot only, iron only, or a combination of soot and iron. We found animals exposed to soot particles at 250 microg/m3 had no adverse respiratory effects. Exposure to iron alone at a concentration of 57 microg/m3 also had no respiratory effects. However, the addition of 45 microg/m3 of iron to soot with a combined total mass concentration of 250 microg/m3 demonstrated significant pulmonary ferritin induction, oxidative stress, elevation of IL-1beta, and cytochrome P450s, as well as activation of NFkappaB. These findings suggest that a synergistic interaction between soot and iron particles account for biological responses not found with exposure to iron alone or to soot alone.

ULTRAVIOLET-BLUE EMISSION AND ELECTRON-HOLE STATES IN ZNSE QUANTUM DOTS

We observed the quantum-confined band edge emission from ZnSe quantum dots and the size dependence of the energy states, spin-orbit interaction, and Stokes shift. The band edge emission occurs in the ultraviolet blue. The energy gap=Eg+C/dn where d is the diameter and n is 1.19±0.13 and 1.21±0.13 for the first and second electron-hole transitions, respectively. The separation between these transitions approaches the bulk spin-orbit splitting, while the Stokes shift decreases with particle size. Effective mass theories cannot explain these results. Trap emission is observed in some samples in the green and red, resulting from Se-related traps.

Blue luminescence from amorphous GaN nanoparticles synthesized in situ in a polymer

Amorphous GaN nanoparticles were synthesized by the in situ thermal decomposition of cyclotrigallazane incorporated into a polystyrene–poly(N,N-dimethyl-4-vinylaniline) copolymer. Transmission electron microscopy, energy dispersive x-ray spectrometry, and x-ray photoelectron spectroscopy show that the composite material consists of amorphous GaN nanoparticles (average diameter ∼40 nm) well dispersed in the copolymer. The photoluminescence spectra show blue light emission from the amorphous GaN nanoparticles, peaked at ∼426 nm.

SYNTHESIS OF GALLIUM NITRIDE QUANTUM DOTS THROUGH REACTIVE LASER ABLATION

Nanocrystalline GaN was synthesized through reactive laser ablation of gallium metal in a N2 atmosphere. X-ray diffraction, selected-area electron diffraction, and transmission electron microscopy measurements show that the GaN crystallites are as small as 2 nm in diameter, and follow a log-normal size distribution with a mean particle diameter of 12 nm. Size-selective photoluminescence and photoluminescence excitation spectroscopy reveal a continuous range of blueshifted band-edge emissions and absorptions starting from the bulk value for gallium nitride and continuing to below 300 nm. These results are consistent with a GaN particle size distribution that encompasses regions above and below the excitonic-Bohr radius of GaN, such that the GaN material shows combined bulk and quantum confined optical properties.

ZnO nanoparticles embedded in polymeric matrices

Highly stable, wurtzite quantum sized ZnO colloids encapsulated in polymers have been synthesized. The particles can be obtained in a powder form and are partially redissolvable in organic media. A shift in the optical absorption spectrum confirms quantum size effects. Stationary fluorescence measurements exhibit excitonic as well as trapped fluorescence. The intensity of trapped fluorescence changes with capping. The time resolved fluorescence measurements indicate considerably short decay times.

Feline Vaccine-associated Fibrosarcoma: An Ultrastructural Study of 20 Tumors (1996–1999)

Twenty feline vaccine-associated sarcomas were examined by transmission electron microscopy. Tumors contained pleomorphic spindle cells, histiocytoid cells, and giant cells. Most tumors contained myofibroblasts, which had morphologic features similar to those of fibroblasts. These cells were further distinguished by subplasmalemmal dense plaques and thin cytoplasmic actin myofilaments organized as elongated bundles concentrated at irregular intervals forming characteristic dense bodies. Intracellular crystalline particulate material was found in 5 of the 20 tumors. Energy dispersive X-ray spectroscopy was used to identify the crystalline material within one tumor as aluminum-based. One tumor from a feline leukemia virus-infected cat contained budding and immature retroviral particles.

Energetics of X-ray-amorphous zirconia and the role of surface energy in its formation

Abstract X-ray-amorphous zirconia was synthesized by a low temperature process. The difference in the energetics of monoclinic and amorphous zirconia was calculated based on drop solution calorimetry of amorphous and monoclinic zirconia in lead borate (2PbO·B2O3) at 1073 K. X-ray-amorphous zirconia is about 58 kJ/mol less stable in enthalpy than the monoclinic phase. Amorphous zirconia heated to 573 K shows crystalline nanoparticles (cubic or tetragonal) of 3.8 nm average diameter. Formation of amorphous zirconia at low temperatures can be explained by its surface energy stabilization relative to monoclinic zirconia, with a difference Δσ∼1.19±0.08 J / m 2 .

Reduced Lung Cell Proliferation Following Short-Term Exposure to Ultrafine Soot and Iron Particles in Neonatal Rats: Key to Impaired Lung Growth?

Particulate matter (PM) has been associated with a variety of negative health outcomes in children involving the respiratory system and early development. However, the precise mechanisms to explain how exposure to airborne particles may cause adverse effects in children are unknown. To study their influence on early postnatal development, a simple, laminar diffusion flame was used to generate an aerosol of soot and iron particles in the size range of 10 to 50 nm. Exposure of 10-day-old rat pups to soot and iron particles was for 6 h/day for 3 days. The lungs were examined following a single injection of bromodeoxyuridine (BrdU) 2 h prior to necropsy. Neonatal rats exposed to these particles demonstrated no effect on the rate of cell proliferation within terminal bronchioles or the general lung parenchyma. In contrast, within those regions arising immediately beyond the terminal bronchioles (defined as the proximal alveolar region), the rate of cell proliferation was significantly reduced compared with filtered air controls. These findings strongly suggest exposure to airborne particles during early neonatal life has significant direct effects on lung growth by altering cell division within critical sites of the respiratory tract during periods of rapid postnatal development. Such effects may result in altered growth in the respiratory system that may be associated with lifelong consequences.