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See detailMorphology and strain of self-assembled semipolar GaN quantum dots in (11-22) AlN
Dimitrakopulos, George; Kalesaki, Efterpi UL; Kioseoglou, Joseph et al

in Journal of Applied Physics (2010), 108

GaN quantum dots (QDs) grown in semipolar (11-22) AlN by plasma-assisted molecular-beam epitaxy were studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy ... [more ▼]

GaN quantum dots (QDs) grown in semipolar (11-22) AlN by plasma-assisted molecular-beam epitaxy were studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy techniques. The embedded (11-22)-grown QDs exhibited pyramidal or truncated-pyramidal morphology consistent with the symmetry of the nucleating plane, and were delimited by nonpolar and semipolar nanofacets. It was also found that, in addition to the (11-22) surface, QDs nucleated at depressions comprising {10-11} facets. This was justified by ab initio density functional theory calculations showing that such GaN/AlN facets are of lower energy compared to (11-22). Based on quantitative high-resolution TEM strain measurements, the three-dimensional QD strain state was analyzed using finite-element simulations. The internal electrostatic field was then estimated, showing small potential drop along the growth direction, and limited localization at most QD interfaces. [less ▲]

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See detailGrain-size-dependent magnetic susceptibility of nanocrystalline terbium
Philippi, S.; Markmann, J.; Birringer, R. et al

in Journal of Applied Physics (2009), 105(7), 7011-7013

This paper reports grain-size-dependent magnetic susceptibility data on nanocrystalline bulk Tb. We find that at small grain size Curie–Weiss behavior is not present for temperatures up to about 80 K ... [more ▼]

This paper reports grain-size-dependent magnetic susceptibility data on nanocrystalline bulk Tb. We find that at small grain size Curie–Weiss behavior is not present for temperatures up to about 80 K above the transition temperature and that the helical antiferromagnetic phase is absent. Possible origins for the suppression of the helix phase in nanoscaled Tb are discussed in terms of internal magnetostatic fields and competing length scales (grain size versus wavelength of the helix phase). [less ▲]

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See detailMagnetic-field-dependent optical transmission of nickel nanorod colloidal dispersions
Klein, Tobias; Laptev, Aleksej; Günther, Annegret UL et al

in Journal of Applied Physics (2009), 106

Aqueous dispersions of nickel nanorods, ~13 nm in diameter and 40–160 nm in length, were synthesized using ac electrodeposition into porous alumina templates. The nanorods in suspension can be aligned by ... [more ▼]

Aqueous dispersions of nickel nanorods, ~13 nm in diameter and 40–160 nm in length, were synthesized using ac electrodeposition into porous alumina templates. The nanorods in suspension can be aligned by modest magnetic fields, which leads to a change in the optical transmittance of the dispersion. Optical transmission measurements with polarized and unpolarized light as a function of magnetic field were performed on suspensions of different particle concentration and varying aspect ratio of the nanoparticles. The experimental results were compared with a theoretical model in which the optical absorption of the nanorods is calculated from the polarizability of prolate ellipsoids in the quasistatic approximation. The magnetic field dependence is introduced in terms of the static orientational distribution function of magnetic moments in an external field. In addition, the relaxation dynamics of the optical transmission was studied, which allowed us to determine the rotational diffusion coefficient of the nanorods in suspension. [less ▲]

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See detailSpatially resolved measurements of depletion properties of large gate two-dimensional electron gas semiconductor terahertz modulators
Kleine-Ostmann, T.; Pierz, K.; Hein, G. et al

in Journal of Applied Physics (2009), 105(9), 093707-1-093707-6

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See detailCharge and doping distributions by capacitance profiling in Cu(In,Ga)Se2 solar cells
Cwil, Michael; Igalson, Malgorzata; Zabierowski, Powel et al

in Journal of Applied Physics (2008), 103

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See detailMagnetic domains and annealing-induced magnetic anisotropy in nanocrystalline soft magnetic materials
Suzuki, K.; Ito, N.; Saranu, S. et al

in Journal of Applied Physics (2008), 103(7), 7301-7303

The magnetic domains of nanocrystalline Fe84Nb6B10 annealed under static and rotating magnetic fields have been investigated by means of magneto-optical Kerr effect (MOKE) microscopy in order to clarify ... [more ▼]

The magnetic domains of nanocrystalline Fe84Nb6B10 annealed under static and rotating magnetic fields have been investigated by means of magneto-optical Kerr effect (MOKE) microscopy in order to clarify the origin of the dramatic magnetic softening brought about by rotating field annealing. The coercivity (Hc) values after static- and rotating-magnetic field annealings are 5.9 and 3.0  A/m, respectively. The MOKE image after static field annealing implies a highly coherent uniaxial anisotropy (Ku) in the sample whereas no sign of such a strong Ku is evident in the domain configuration after rotating field annealing. Our analytical solution of the random anisotropy model with additional Ku predicts that the fluctuating amplitude of the effective anisotropy (δK) in nanocrystalline Fe84Nb6B10 decreases from 20 to 11 J/m3 by removing Ku. The observed reduction of Hc may be attributed to this decrease in δK induced by rotating field annealing. [less ▲]

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See detailA neutron-scattering investigation of the magnetic structure and magnetic excitations in nanocrystalline Tb
Vecchini, C.; Moze, O.; Hoser, A. et al

in Journal of Applied Physics (2006), 99(8), 5021-5023

The magnetic structure and magnetic excitations in nanocrystalline Tb have been investigated by neutron diffraction and neutron spectroscopy. This is a report on the long-range magnetic order and the ... [more ▼]

The magnetic structure and magnetic excitations in nanocrystalline Tb have been investigated by neutron diffraction and neutron spectroscopy. This is a report on the long-range magnetic order and the magnetic excitations in a nanocrystalline elemental rare earth. Refinement of the neutron-diffraction data reveals an “average” magnetic structure of each crystallite which contains a significant out-of-plane component to the magnetic moment as well as a suppression of the high-temperature antiferromagnetic phase observed for coarse-grained Tb. The inelastic-neutron-scattering measurements reveal the presence of a magnetic excitation of approximately 10 meV at 2.5 K. The excitation energy decreases with increasing temperature. The origins of this excitation are discussed with particular reference to the magnetic modes at the zone center observed for single-crystal Tb. [less ▲]

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See detailTerahertz photonic mixers as local oscillators for hot electron bolometer and superconductor-insulator-superconductor astronomical receivers, ,
Cámara Mayorga, I.; Muñoz Pradas, P.; Michael, E. A. et al

in Journal of Applied Physics (2006), 100

A pump experiment of two astronomical heterodyne receivers, a superconductorinsulator- superconductor SIS receiver at 450 GHz and a hot-electron-bolometer HEB receiver at 750 GHz, is reported. A low ... [more ▼]

A pump experiment of two astronomical heterodyne receivers, a superconductorinsulator- superconductor SIS receiver at 450 GHz and a hot-electron-bolometer HEB receiver at 750 GHz, is reported. A low-temperature-grown GaAs metal-semiconductor-metal photonic local oscillator LO was illuminated by two near infrared semiconductor lasers, generating a beat frequency in the submillimeter range. I-V junction characteristics for different LO pump power levels demonstrate that the power delivered by the photomixer is sufficient to pump a SIS and a HEB mixer. SIS receiver noise temperatures were compared using a conventional solid-state LO anda photonic LO. In both cases, the best receiver noise temperature was identical Tsys=170 K . [less ▲]

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See detailExchange-stiffness constant in cold-worked and nanocrystalline Ni measured by elastic small-angle neutron scattering
Michels, Andreas UL; Weissmüller, J.; Wiedenmann, A. et al

in Journal of Applied Physics (2000), 87(9), 5953-5955

We present a new method for determining the exchange-stiffness constant A of a ferromagnetic bulk material by field-dependent elastic small-angle neutron scattering (SANS). In the limit of high applied ... [more ▼]

We present a new method for determining the exchange-stiffness constant A of a ferromagnetic bulk material by field-dependent elastic small-angle neutron scattering (SANS). In the limit of high applied magnetic field H, for which the scattering volume is a single magnetic domain and the magnetization is nearly aligned with the direction of the applied field, a combination of micromagnetics theory with neutron scattering formalism suggests closed-form expressions for the differential scattering cross section as a function of the scattering vector and of H. Based on these results it is suggested that the exchange-stiffness constant can be extracted from experimental SANS data recorded as a function of H. At ambient temperature we have applied this method to polycrystalline cold-worked Ni and nanocrystalline electrodeposited Ni, finding exchange-stiffness constants of (8.2±0.2)×10−12 and (7.6±0.3)×10−12  J/m, respectively. Measurement at 5 K yields a value of (9.2±0.2)×10−12 J/m for the nanocrystalline sample, a temperature dependence that agrees qualitatively with data in the literature. In addition to the value of A, the technique supplies information on the spatial structure of the magnetic anisotropy field. [less ▲]

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See detailSchottky Barrier Height Enhancement on n-In0.53Ga0.47As
Kordoš, P.; Marso, Michel UL; Meyer, R. et al

in Journal of Applied Physics (1992), 72(1992), 2347-2355

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