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9 Jul 2012

Volume 101, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages)

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei
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Power factor enhancement in light valence band p-type skutterudites

Jiong Yang, R. Liu, Z. Chen, L. Xi, Jihui Yang, W. Zhang, and L. Chen

Appl. Phys. Lett. 101, 022101 (2012); http://dx.doi.org/10.1063/1.4733663 (4 pages) | Cited 2 times

Online Publication Date: 9 July 2012

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The heavy band feature in 3d p-type skutterudites causes strong electron-phonon interactions and reduces the power factor. We present band structures of Ru- and Os-containing skutterudites, which show that valence band near the Fermi levels composed of 4d or 5d states is much lighter. In these skutterudites, high Seebeck coefficient can be achieved at low hole concentrations, while the corresponding density of states at the Fermi level as well as electron-phonon interactions are greatly reduced. We demonstrate that LaIr1Os3Sb12 could possess sufficiently high Seebeck coefficient, and its power factor at high temperatures is estimated to be over 50 μW cm−1K−2.
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72.15.Jf Thermoelectric and thermomagnetic effects
71.20.Gj Other metals and alloys
63.20.kd Phonon-electron interactions

Substrate orientation dependent fine structure splitting of symmetric In(Ga)As/GaAs quantum dots

J. Treu, C. Schneider, A. Huggenberger, T. Braun, S. Reitzenstein, S. Höfling, and M. Kamp

Appl. Phys. Lett. 101, 022102 (2012); http://dx.doi.org/10.1063/1.4733664 (4 pages) | Cited 4 times

Online Publication Date: 10 July 2012

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We present a comparative investigation of the fine structure splitting (FSS) from self-organized In(Ga)As quantum dots (QDs) grown on GaAs substrates with different lattice orientations. QDs grown on (111)B- and (112) oriented substrates are analyzed and compared to small QDs on commonly used (001) substrates. Mean values for the FSS as low as (5.6 ± 0.6) μeV are obtained for QDs on (111)B-GaAs, comparing favorably to the other two approaches ((11.8 ± 1.7) μeV for (112)-surfaces and (14.0 ± 2.2) μeV for (001)-surfaces). Single photon emission from (111)B QDs grown by droplet epitaxy is demonstrated via photon autocorrelation studies with a g(2)(0) value of 0.07.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.21.La Quantum dots

Single-shot nuclear magnetization recovery curves with force-gradient detection

Dimitri A. Alexson, Steven A. Hickman, John A. Marohn, and Doran D. Smith

Appl. Phys. Lett. 101, 022103 (2012); http://dx.doi.org/10.1063/1.4730610 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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We measure the spin-lattice relaxation time as a function of sample temperature in GaAs in a real-time single-shot inversion recovery experiment using spin force gradients acting on a magnetic tipped cantilever. After inverting 69Ga spins localized near the magnet with a single 20 ms adiabatic rapid passage sweep, the spins’ magnetization recovery was passively tracked by recording the cantilever’s frequency change, which is proportional to the longitudinal component of the spins’ magnetization. The cantilever’s frequency was recorded for a time 3*T1 for sample temperatures ranging from 4.8 to 25 K. The temperature dependence was observed for the 69Ga quadrupolar relaxation interaction.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.60.Es Relaxation effects
75.50.Ss Magnetic recording materials

Metal-to-insulator transition in anatase TiO2 thin films induced by growth rate modulation

T. Tachikawa, M. Minohara, Y. Nakanishi, Y. Hikita, M. Yoshita, H. Akiyama, C. Bell, and H. Y. Hwang

Appl. Phys. Lett. 101, 022104 (2012); http://dx.doi.org/10.1063/1.4733724 (4 pages)

Online Publication Date: 10 July 2012

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We demonstrate control of the carrier density of single phase anatase TiO2 thin films by nearly two orders of magnitude by modulating the growth kinetics during pulsed laser deposition, under fixed thermodynamic conditions. The resistivity and the intensity of the photoluminescence spectra of these TiO2 samples, both of which correlate with the number of oxygen vacancies, are shown to depend strongly on the growth rate. A quantitative model is used to explain the carrier density changes.
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71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
61.72.jd Vacancies
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Determination of graphene work function and graphene-insulator-semiconductor band alignment by internal photoemission spectroscopy

Rusen Yan, Qin Zhang, Wei Li, Irene Calizo, Tian Shen, Curt A. Richter, Angela R. Hight-Walker, Xuelei Liang, Alan Seabaugh, Debdeep Jena, Huili Grace Xing, David J. Gundlach, and N. V. Nguyen

Appl. Phys. Lett. 101, 022105 (2012); http://dx.doi.org/10.1063/1.4734955 (4 pages) | Cited 6 times

Online Publication Date: 11 July 2012

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We determined the band alignment of a graphene-insulator-semiconductor structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage, we infer a 4.6× 1011 cm−2 negative extrinsic charge present on the graphene surface. Also, we extract the graphene work function to be 4.56 eV, in excellent agreement with theoretical and experimental values in literature. Electron and hole injection from heavily doped p-type silicon (Si) are both observed. The barrier height from the top of the valence band of Si to the bottom of the conduction band of silicon dioxide (SiO2) is found to be 4.3 eV. The small optical absorption in graphene makes it a good transparent contact to enable the direct observation of hole injection from Si to graphene. The barrier height for holes escaping from the bottom of Si conduction band to the top of SiO2 valence band is found to be 4.6 eV.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
65.40.gh Work functions
73.30.+y Surface double layers, Schottky barriers, and work functions
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