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24 Sep 2012

Volume 101, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 101, 133101 (2012); http://dx.doi.org/10.1063/1.4752467 (5 pages)

Yen Husn Su and Wei-Yu Chen
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Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

S. Wicklein, A. Sambri, S. Amoruso, X. Wang, R. Bruzzese, A. Koehl, and R. Dittmann

Appl. Phys. Lett. 101, 131601 (2012); http://dx.doi.org/10.1063/1.4754112 (5 pages) | Cited 1 time

Online Publication Date: 24 September 2012

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By combining structural and chemical thin film analysis with detailed plume diagnostics and modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms determining the stoichiometry of the complex oxides model material SrTiO3 during pulsed laser deposition. Deviations between thin film and target stoichiometry are basically a result of two effects, namely, incongruent ablation and preferential scattering of lighter ablated species during their motion towards the substrate in the O2 background gas. On the one hand, a progressive preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective scattering of the lighter Ti plume species results in Sr rich films.
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81.15.Fg Pulsed laser ablation deposition
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.aj Insulators
78.70.En X-ray emission spectra and fluorescence
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films

Water droplets on a hydrophobic insulator surface under high voltages: A thermal perspective

Guoxin Xie, Jianbin Luo, Ye Yang, Dan Guo, and Lina Si

Appl. Phys. Lett. 101, 131602 (2012); http://dx.doi.org/10.1063/1.4754689 (4 pages)

Online Publication Date: 25 September 2012

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The thermal characteristics in the interaction process between water droplets on a hydrophobic insulator surface under high direct current voltages have been investigated with the infrared thermography. Discharge inception under a sufficiently high electric field resulted in the temperature rise between droplets and the formation of a liquid channel. The channel was transient for low conductivity droplets followed by their coalescence while stable for highly conductive ones. Asymmetric temperature distributions in the associated droplets appeared, and localized drying in the low conductivity droplet near the higher potential electrode initiated intermittent discharge. Mechanisms of these experimental phenomena have been discussed.
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66.25.+g Thermal conduction in nonmetallic liquids

Thermoelectric properties of YBa2Cu3O7−δ–La2/3Ca1/3MnO3 superlattices

S. Heinze, H.-U. Habermeier, G. Cristiani, S. Blanco Canosa, M. Le Tacon, and B. Keimer

Appl. Phys. Lett. 101, 131603 (2012); http://dx.doi.org/10.1063/1.4754707 (4 pages)

Online Publication Date: 26 September 2012

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We report measurements of the thermoelectric power and electrical resistivity of superlattices composed of the high-temperature superconductor YBa2Cu3O7−δ (YBCO) and the metallic ferromagnet La2/3Ca1/3MnO3 (LCMO) with individual layer thicknesses between 5 and 50 nm. Whereas YBCO and LCMO reference films prepared under the same conditions exhibit negative Seebeck coefficients, in excellent agreement with data on bulk compounds of identical composition, those of all superlattices are positive, regardless of the individual layer thickness. Having ruled out lattice strain and incomplete oxygenation, we attribute the observed sign reversal of the Seebeck coefficient to a long-range electronic reconstruction nucleated at the YBCO-LCMO interfaces.
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74.25.fg Thermoelectric effects
74.72.-h Cuprate superconductors

S-parameter and perfect pinning of the Fermi level at nonpolar (11-20) a-plane p-GaN surfaces

Yunju Choi, Keun Man Song, and Hyunsoo Kim

Appl. Phys. Lett. 101, 131604 (2012); http://dx.doi.org/10.1063/1.4755839 (3 pages) | Cited 1 time

Online Publication Date: 26 September 2012

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We investigated the Schottky barrier height and S-parameter at nonpolar (11-20) a-plane p-GaN surfaces by using Schottky diodes fabricated with various metals, including Ti, Cu, Ni, and Pt. A barrier inhomogeneity model was used to explain anomalous carrier transport behavior at the nonpolar p-GaN surfaces, yielding the mean barrier heights of 2.01, 1.73, 1.82, and 1.92 eV for the Ti, Cu, Ni, and Pt contacts, respectively. The extracted S-parameter was as low as 0.02, indicating perfect pinning of the surface Fermi level at around 1.9 eV above the valence band.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions

Superstructure of self-aligned hexagonal GaN nanorods formed on nitrided Si(111) surface

Praveen Kumar, Mohit Tuteja, Manoj Kesaria, U. V. Waghmare, and S. M. Shivaprasad

Appl. Phys. Lett. 101, 131605 (2012); http://dx.doi.org/10.1063/1.4751986 (4 pages) | Cited 1 time

Online Publication Date: 28 September 2012

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We present here the spontaneous formation of catalyst-free, self-aligned crystalline (wurtzite) nanorods on Si(111) surfaces modified by surface nitridation. Nanorods grown by molecular beam epitaxy on bare Si(111) and non-stoichiometric silicon nitride interface are found to be single crystalline but disoriented. Those grown on single crystalline Si3N4 intermediate layer are highly dense c-oriented hexagonal shaped nanorods. The morphology and the self-assembly of the nanorods shows an ordered epitaxial hexagonal superstructure, suggesting that they are nucleated at screw dislocations at the interface and grow spirally in the c-direction. The aligned nanorod assembly shows high-quality structural and optical emission properties.
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81.16.Dn Self-assembly
78.67.Qa Nanorods
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Manganese induced modifications in yttria stabilized zirconia

Manoj K. Mahapatra, Prabhakar Singh, and Scott T. Misture

Appl. Phys. Lett. 101, 131606 (2012); http://dx.doi.org/10.1063/1.4755776 (4 pages)

Online Publication Date: 28 September 2012

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We have investigated the role of manganese oxide on the crystallographic and morphological modifications of cubic 8 mol. % yttria stabilized zirconia (YSZ). X-ray diffraction studies indicate that manganese dissolution leads to partial transformation of cubic YSZ into the tetragonal polymorph along with contraction of the unit cell. Evolution of an undulated surface with 2–15 nm roughness has been observed using electron and atomic force microscopies.
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61.66.Fn Inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.75.Bc Solubility
68.35.bt Other materials
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