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25 Jun 2012

Volume 100, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 100, 261104 (2012); http://dx.doi.org/10.1063/1.4711253 (4 pages)

Marcelo Davanço, Jun Rong Ong, Andrea Bahgat Shehata, Alberto Tosi, Imad Agha, Solomon Assefa, Fengnian Xia, William M. J. Green, Shayan Mookherjea, and Kartik Srinivasan
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The importance of scattering, surface potential, and vanguard counter-potential in terahertz emission from gallium arsenide

D. L. Cortie and R. A. Lewis

Appl. Phys. Lett. 100, 261601 (2012); http://dx.doi.org/10.1063/1.4730954 (3 pages) | Cited 2 times

Online Publication Date: 25 June 2012

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It is well established that under excitation by short (<1 ps), above-band-gap optical pulses, semiconductor surfaces may emit terahertz-frequency electromagnetic radiation via photocarrier diffusion (the dominant mechanism in InAs) or photocarrier drift (dominant in GaAs). Our three-dimensional ensemble Monte Carlo simulations allow multiple physical parameters to vary over wide ranges and provide unique direct insight into the factors controlling terahertz emission. We find for GaAs (in contrast to InAs), scattering and the surface potential are key factors. We further delineate in GaAs (as in InAs) the role of a vanguard counter-potential. The effects of varying dielectric constant, band-gap, and effective mass are similar in both emitter types.
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78.70.Gq Microwave and radio-frequency interactions
63.20.-e Phonons in crystal lattices
68.35.Fx Diffusion; interface formation
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Characterization of the local crystallinity via reflectance of very slow electrons

Z. Pokorná, Š. Mikmeková, I. Müllerová, and L. Frank

Appl. Phys. Lett. 100, 261602 (2012); http://dx.doi.org/10.1063/1.4729879 (4 pages)

Online Publication Date: 25 June 2012

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The reflectance of very slow electrons from solids and its electron energy dependence are shown as characteristic for the crystal system and its spatial orientation so they can serve, e.g., to fingerprinting the orientation of grains in polycrystals. Measurements on single crystals and polycrystals are validated via electron backscatter diffraction analyses. Sensitivity of the method to fine details of crystallinity is demonstrated.
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61.66.Bi Elemental solids
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.20.Kz Other electron-impact emission phenomena

Electronic structure of delta-doped La:SrTiO3 layers by hard x-ray photoelectron spectroscopy

A. M. Kaiser, A. X. Gray, G. Conti, B. Jalan, A. P. Kajdos, A. Gloskovskii, S. Ueda, Y. Yamashita, K. Kobayashi, W. Drube, S. Stemmer, and C. S. Fadley

Appl. Phys. Lett. 100, 261603 (2012); http://dx.doi.org/10.1063/1.4731642 (4 pages) | Cited 1 time

Online Publication Date: 27 June 2012

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We have employed hard x-ray photoemission (HAXPES) to study a delta-doped SrTiO3 layer that consisted of a 3-nm thickness of La-doped SrTiO3 with 6% La embedded in a SrTiO3 film. Results are compared to a thick, uniformily doped La:SrTiO3 layer. We find no indication of a band offset for the delta-doped layer, but evidence of the presence of Ti3+ in both the thick sample and the delta-layer, and indications of a density of states increase near the Fermi energy in the delta-doped layer. These results further demonstrate that HAXPES is a powerful tool for the non-destructive investigation of deeply buried doped layers.
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71.20.Ps Other inorganic compounds
79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Micro-Raman spectroscopy of graphene grown on stepped 4H-SiC (0001) surface

K. Grodecki, R. Bozek, W. Strupinski, A. Wysmolek, R. Stepniewski, and J. M. Baranowski

Appl. Phys. Lett. 100, 261604 (2012); http://dx.doi.org/10.1063/1.4730372 (4 pages) | Cited 1 time

Online Publication Date: 28 June 2012

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Graphene grown by chemical vapor deposition on 4H-SiC (0001) was studied using micro-Raman spectroscopy and atomic force microscopy (AFM). AFM revealed that the graphene structure grown on on-axis substrates has a stepped morphology. This is due to step bunching, which results from etching in hydrogen as well as from the process of graphene formation itself. It was shown by micro-Raman spectroscopy that the properties of graphene present on step edges and on terraces are quite different. Graphene on terraces is uniform with a relatively small thickness and strain fluctuations. On the other hand, graphene on step edges has a large thickness and strain variations occur. A careful analysis of micro-Raman spatial maps led us to the conclusion that the carrier concentration on step edge regions is lowered when compared with terrace regions.
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78.30.Na Fullerenes and related materials
78.66.Tr Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Simultaneous flattening of Si(110), (111), and (001) surfaces for three-dimensional Si nanowires

Yukinori Morita and Hiroyuki Ota

Appl. Phys. Lett. 100, 261605 (2012); http://dx.doi.org/10.1063/1.4731789 (4 pages)

Online Publication Date: 28 June 2012

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We prepared atomically flat Si(110), (111), and (001) surfaces using identical preparation conditions for a low-pH (pH < 1) HF treatment and a subsequent low-temperature (∼800 °C) anneal in H2. Atomic-resolution scanning tunneling microscopy (STM) revealed that the treated Si(110) surfaces were atomically flat with a hydrogen-terminated 1 × 1 atomic arrangement. Similar features were also confirmed by STM analysis of 1 × 1:H on Si(111) and 2 × 1:H on Si(001) surfaces. Using this technique, well-ordered cross sections of three-dimensional Si nanowires surrounded by simultaneously flattened (110), (111), (001) facets were realized for nanowires with 〈100〉, 〈110〉, 〈111〉, and 〈112〉 long-axis orientations.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.07.Gf Nanowires
82.45.Vp Semiconductor materials in electrochemistry
61.72.Cc Kinetics of defect formation and annealing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
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