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Phonon decay channels and anharmonicities in embedded domains in MgZnO film were studied via selective resonant Raman scattering at the elevated temperature regime up to 870 K. The resonant conditions provided by excitation with different ultraviolet laser lines enabled the detection of longitudinal optical (LO) phonons from domains with the wurtzite structure, and domains with the cubic rocksalt structure which lack inversion symmetry due to alloying. The phonon behavior was modeled in terms of three- and four-phonon decay processes using Ridley and Klemens type decay processes. It is found that the wurtzite phase displays dominantly three-phonon decay with a small four-phonon component. In contrast, the cubic phase displays a higher degree of anharmonicity in which the four-phonon processes contribute significantly to the temperature dependent frequency shift. At the elevated temperature range, the LO frequency shift rate is ~–2.6×10–2 cm–1/K for the wurtzite structure while that of the cubic exhibits a much larger shift rate of ~–1.6×10–1 cm–1/K. The larger anharmonicity of the domains with the cubic structure is discussed in terms of strain and deformation effects. [ABSTRACT FROM AUTHOR]

The synthesis of KCl nanowires has been achieved by atomic layer deposition inside high aspect ratio channels of microchannel glass. The average diameter of the KCl nanowires is 250 nm, with a minimum observed diameter of 50 nm, and lengths up to 5 μm. The Cl precursor was TaCl5, while the source of K was determined to be impurities in the microchannel glass substrate. The process for KC1 nanowire formation is a three-step chemical process that simultaneously etches K from the substrate concomitant with the formation of chlorine gas. It is postulated that the curvature of the channels may influence the diameters of the KCl nanowires. [ABSTRACT FROM AUTHOR]

Impurities play a major role in determining the optical and electrical properties of semiconductor nanoparticles. In this work, the presence and source of CO2 impurities in ZnO nanoparticles were studied by IR absorption spectroscopy. Isotopic substitution was used to verify the vibrational frequency assignment. Isochronal annealing experiments were performed to study the formation and stability of the molecular impurities. Our results indicate that the molecules are much more stable than CO2 adsorbed on bulk ZnO surfaces. By comparing our observations with similar results from IR spectroscopy of CO2 trapped in carbon nanotubes [C. Matranga, L. Chen, M. Smith, E. Bittner, J. K. Johnson, and B. Bockrath, J. Phys. Chem. B 107, 12930 (2003)], we conclude that the molecules are trapped in the ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

A method for the direct observation of the early stages of growth of superconducting films by transmission electron microscopy (TEM) is reported. The technique uses well-characterized, single-crystal TEM foils as substrates for the deposition process. Ultrathin films of YBa2Cu3O6+x (YBCO) were prepared by pulsed laser deposition from stoichiometric bulk samples directly onto (001) oriented MgO thin-foil substrates. Observation of the film by TEM is possible without any post-deposition specimen preparation. The epitactic nature of the film growth is shown by analysis of the moiré fringe pattern and by selected area diffraction. In addition to an interconnected film, copper oxide particles and stoichiometric ablated clusters were observed. [ABSTRACT FROM AUTHOR]

Strong, repeatable Terahertz (THz) signatures are measured in small samples of DNA solution using a THz photomixing spectrometer with custom conical-horn coupling. The DNA specimen is linear, single-stranded (ss), 13-mer polynucleotide, and is diluted in buffer solution to have a concentration of 0.15 μmol/ml. The strongest signature is centered ∼717 GHz, and has a strength of 2.5 × 1016 cm-1/mol, linewidth 48 GHz, and damping time of 6.6 ps. The origin of the signature is attributed to the hydrogen bond of locally cross-linked ssDNAs. [ABSTRACT FROM AUTHOR]