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28 Dec 2009

Volume 95, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 95, 261901 (2009); http://dx.doi.org/10.1063/1.3268436 (3 pages)

Weiqiang Wang, Richard Clark, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta
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Low-temperature ballistic transport in nanoscale epitaxial graphene cross junctions

S. Weingart, C. Bock, U. Kunze, F. Speck, Th. Seyller, and L. Ley

Appl. Phys. Lett. 95, 262101 (2009); http://dx.doi.org/10.1063/1.3276560 (3 pages) | Cited 5 times

Online Publication Date: 28 December 2009

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We report on the observation of inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene grown on SiC(0001). Ballistic transport is indicated by a negative bend resistance of R12,43 ≈ −170 Ω, which is measured in a nonlocal, four-terminal configuration at 4.2 Κ and which vanishes as the temperature is increased above 80 K.
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73.23.Ad Ballistic transport
81.05.ue Graphene
73.63.Fg Nanotubes
68.55.ap Fullerenes
61.48.Gh Structure of graphene

High subthreshold field-emission current due to hydrogen adsorption in single-walled carbon nanotubes: A first-principles study

Parham Yaghoobi, Md. Kawsar Alam, Konrad Walus, and Alireza Nojeh

Appl. Phys. Lett. 95, 262102 (2009); http://dx.doi.org/10.1063/1.3275785 (3 pages) | Cited 2 times

Online Publication Date: 28 December 2009

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We investigate the effect of hydrogen adsorption on field-emission current from a single-walled carbon nanotube using first-principles calculations. The results show a new emission regime at field values around the field-emission threshold of bare nanotubes, with emission currents comparable to those of the high-field regime. This current enhancement can be explained with the surface dipole created as a result of the difference in electronegativity between carbon and hydrogen that contributes to electron extraction from the nanotube.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.43.Mn Adsorption kinetics
73.63.Fg Nanotubes
72.20.Ht High-field and nonlinear effects

Stress-enhancement in free-standing Si pillars through nonequilibrium dehydrogenation in SiN:H stress-liners by ultraviolet light irradiation

Takanori Tanaka, Taizoh Sadoh, Masashi Kurosawa, Masanori Tanaka, Masanori Yamaguchi, Shinji Suzuki, Tokuhide Kitamura, and Masanobu Miyao

Appl. Phys. Lett. 95, 262103 (2009); http://dx.doi.org/10.1063/1.3278596 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2009

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Tensile-strained Si pillars are desired to achieve three-dimensional (3D) transistors with high speed. Effects of ultraviolet (UV) light irradiation on tensile strains in Si pillars covered with SiN:H stress-liners are investigated as a function of the wavelength (172–436 nm). Tensile-stress enhancement is found at specific wavelengths (200–330 nm) under low-temperature heating (400 °C), where dehydrogenation in SiN:H is clearly detected by infrared absorption measurements. On the other hand, equilibrium dehydrogenation by high-temperature heating (>700 °C) without UV-irradiation does not cause tensile-stress enhancement. This nonequilibrium dehydrogenation at low temperatures opens up possibility of 3D transistors with high carrier mobility.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

The origin of 2.78 eV emission and yellow coloration in bulk AlN substrates

A. Sedhain, L. Du, J. H. Edgar, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 95, 262104 (2009); http://dx.doi.org/10.1063/1.3276567 (3 pages) | Cited 4 times

Online Publication Date: 29 December 2009

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The yellow color of bulk AlN crystals was found to be caused by the optical absorption of light with wavelengths shorter than that of yellow. This yellow impurity limits UV transparency and hence restricts the applications of AlN substrates for deep UV optoelectronic devices. Here, the optical properties of AlN epilayers, polycrystalline AlN, and bulk AlN single crystals have been investigated using photoluminescence (PL) spectroscopy to address the origin of this yellow appearance. An emission band with a linewidth of ∼ 0.3 eV (at 10 K) was observed at ∼ 2.78 eV. We propose that the origin of the yellow color in bulk AlN is due to a band-to-impurity absorption involving the excitation of electrons from the valence band to the doubly negative charged state, (VAl2−), of isolated aluminum vacancies, (VAl)3−/2− described by VAl2−+hν = VAl3−+h+. In such a context, the reverse process is responsible for the 2.78 eV PL emission.
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78.55.Cr III-V semiconductors
68.47.Fg Semiconductor surfaces
78.66.Fd III-V semiconductors
68.55.ag Semiconductors
61.72.jd Vacancies
78.40.Fy Semiconductors

Plasma-assisted molecular beam epitaxy of high quality In2O3(001) thin films on Y-stabilized ZrO2(001) using In as an auto surfactant

Oliver Bierwagen, Mark E. White, Min-Ying Tsai, and James S. Speck

Appl. Phys. Lett. 95, 262105 (2009); http://dx.doi.org/10.1063/1.3276910 (3 pages) | Cited 11 times

Online Publication Date: 29 December 2009

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The surface roughness of In2O3(001) films is a roadblock to potential semiconductor applications of this material. Using plasma-assisted molecular beam epitaxy we found that In2O3(001) films grow rough by the formation of {111} facets and In2O3(111) films grow smooth without facetting due to the conventionally used (oxygen-rich) conditions. This behavior indicates that the (111) surface is thermodynamically prefered over the (001) surface. We demonstrate that under indium-rich growth conditions these thermodynamics are changed allowing In2O3(001) films to grow smoothly without facetting. Surface indium plays a key role by acting as an auto surfactant that lowers the surface free energy difference between the (001) and the (111) surface.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.35.Md Surface thermodynamics, surface energies
65.40.gp Surface energy
81.05.Hd Other semiconductors
68.35.bg Semiconductors

Changes in VO2 band structure induced by charge localization and surface segregation

Changhong Chen and Zhaoyang Fan

Appl. Phys. Lett. 95, 262106 (2009); http://dx.doi.org/10.1063/1.3280375 (3 pages) | Cited 8 times

Online Publication Date: 30 December 2009

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Vanadium vacancies introduce acceptor doping with hole localization, while oxygen vacancies cause electron localization and donor doping. As deposition temperature increases, donor concentration stays constant, whereas acceptor concentration significantly increases, leading to enhanced (011) lattice-plane compression and surface segregation. Localized charges result in shifts of O 1s and V4+ 2p core levels toward higher binding energies, and O 2p and V4+ 3d valence bands toward the Fermi level, but egπ bands lifting and a1g bands splitting energies are both insensitive to charge localization. Particularly, band-gap energy decreases with increasing V–V pair distance, and is significantly reduced by band tailing.
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71.20.Ps Other inorganic compounds
61.72.sd Impurity concentration
71.55.Ht Other nonmetals
61.72.up Other materials
61.72.jd Vacancies
68.35.Dv Composition, segregation; defects and impurities
73.20.Fz Weak or Anderson localization

Morphology and defect properties of the Ge–GeO2 interface

L. Tsetseris and S. T. Pantelides

Appl. Phys. Lett. 95, 262107 (2009); http://dx.doi.org/10.1063/1.3280385 (3 pages) | Cited 14 times

Online Publication Date: 30 December 2009

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Ge-based devices, currently being pursued as replacement of their Si counterparts, typically contain a germanium oxide layer next to the substrate. Here we show using first-principles calculations that, in contrast to Si technology, hydrogenation and fluorination are not effective ways of passivating Ge–GeO2 interfacial Pb centers with a Ge dangling bond (DB). Moreover, we identify DB geometries that differ from the Pb structures and we find that the Ge–GeO2 boundary has a higher atomic-scale roughness than the Si–SiO2 interface. These key differences in interface morphology and defect properties are consistent with experimental data.
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68.35.Ct Interface structure and roughness
81.65.Rv Passivation
81.05.Cy Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Cn Elemental semiconductors
71.15.-m Methods of electronic structure calculations

High-field Hall effect and magnetoresistance in Fe3O4 epitaxial thin films up to 30 Tesla

A. Fernández-Pacheco, J. Orna, J. M. De Teresa, P. A. Algarabel, L. Morellon, J. A. Pardo, M. R. Ibarra, E. Kampert, and U. Zeitler

Appl. Phys. Lett. 95, 262108 (2009); http://dx.doi.org/10.1063/1.3276696 (3 pages) | Cited 8 times

Online Publication Date: 31 December 2009

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We have measured the Hall effect and the magnetoresistance of epitaxial Fe3O4 thin films grown on MgO (001) in magnetic fields up to 30 T. Using such high fields, it is possible to magnetically saturate films thicker than 40 nm, providing access to intrinsic conduction properties. We find an effective electron density corresponding to 1 electron per f.u. A smaller value is obtained for thinner films, caused by the increasing density of antiphase boundaries defects. The magnetoresistance is not saturating at 30 T, showing linear dependence at high fields, and peaks at the Verwey transition.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Ng Insulators

The effect of temperature on the secondary electron emission yield from single crystal and polycrystalline diamond surfaces

A. Stacey, S. Prawer, S. Rubanov, R. Ahkvlediani, Sh. Michaelson, and A. Hoffman

Appl. Phys. Lett. 95, 262109 (2009); http://dx.doi.org/10.1063/1.3275729 (3 pages)

Online Publication Date: 31 December 2009

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The effect of temperature in the 293–473 K range, on the secondary electron emission (SEE) yield of single crystal and polycrystalline diamond film surfaces is reported. For the polycrystalline films the SEE yield was found to decay as function of electron irradiation dose while for the single crystal an increase occurs first, followed by a decrease. For both surfaces, the SEE yield increases significantly upon heating and obtained a nearly constant value with electron dose at 473 K. These effects are explained as due to the temperature dependence of the electron beam induced hydrogen desorption and surface band bending.
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79.20.Hx Electron impact: secondary emission
81.40.Gh Other heat and thermomechanical treatments
61.80.Fe Electron and positron radiation effects
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Nr Desorption kinetics

Role of germanium in the reduced temperature dependence of Ti-based nanocrystals formation for nonvolatile memory applications

Li-Wei Feng, Chun-Yen Chang, Ting-Chang Chang, Chun-Hao Tu, Pai-Syuan Wang, Yao-Feng Chang, Min-Chen Chen, and Hui-Chun Huang

Appl. Phys. Lett. 95, 262110 (2009); http://dx.doi.org/10.1063/1.3279131 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2009

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We investigated the physical and electrical characteristics of Ti-based nanocrystals (NCs) with composition of germanium fabricated by cosputtering titanium silicide and germanium targets for low temperature applications of nonvolatile memory. The addition of Ge significantly reduces the thermal budget necessary for Ti-based NCs formation to 500 °C in 2 min due to the rise of its morphological instability and agglomeration properties. Compositions characteristics were analyzed by x-ray photon-emission spectroscopy and formations of NCs were observed by transmission electron microscopy. Additionally, capacitance-voltage characteristics, data retention, and endurance properties are characterized to demonstrate its advantages for nonvolatile memory device applications.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
84.30.Sk Pulse and digital circuits
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Lp Transmission electron microscopy (TEM)

Oxygen vacancies in N doped anatase TiO2: Experiment and first-principles calculations

Abdul K. Rumaiz, J. C. Woicik, E. Cockayne, H. Y. Lin, G. Hassnain Jaffari, and S. I. Shah

Appl. Phys. Lett. 95, 262111 (2009); http://dx.doi.org/10.1063/1.3272272 (3 pages) | Cited 29 times

Online Publication Date: 31 December 2009

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We have determined the electronic and atomic structure of N doped TiO2 using a combination of hard x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Our results reveal that N doping of TiO2 leads to the formation of oxygen vacancies and the combination of both N impurity and oxygen vacancies accounts for the observed visible light catalytic behavior of N doped TiO2.
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61.72.jd Vacancies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials
79.60.-i Photoemission and photoelectron spectra

Influence of Si precursor on Ge segregation during ultrathin Si reduced pressure chemical vapor deposition on Ge

B. Vincent, W. Vandervorst, M. Caymax, and R. Loo

Appl. Phys. Lett. 95, 262112 (2009); http://dx.doi.org/10.1063/1.3280075 (3 pages) | Cited 2 times

Online Publication Date: 31 December 2009

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This letter reports on the Ge segregation mechanism occurring during ultrathin (few monolayers) Si cap growth on Ge substrates by reduced pressure chemical vapor deposition. Thanks to extremely low energy secondary ion mass spectroscopy, we have highlighted that Ge segregation in Si-covered Ge does not depend on the growth temperature (in the 350–500 °C range) or on the carrier gas (H2,N2) used during Si growth. Solely the Si precursor used, i.e., the Si incorporation mechanism, impacts the Ge segregation rate. A multi-Ge segregation model is proposed, considering probabilities of sites exchanges in between all Si–Ge stacked atoms within the first nanometer of the layers.
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64.75.Qr Phase separation and segregation in semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Resistive switching characteristics of ZnO thin film grown on stainless steel for flexible nonvolatile memory devices

Seunghyup Lee, Heejin Kim, Dong-Jin Yun, Shi-Woo Rhee, and Kijung Yong

Appl. Phys. Lett. 95, 262113 (2009); http://dx.doi.org/10.1063/1.3280864 (3 pages) | Cited 30 times

Online Publication Date: 31 December 2009

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This paper reports a resistive switching device of Au/ZnO/stainless steel (SS) and its applicability as a flexible resistive random access memory (ReRAM). The Au/ZnO/SS structure was fabricated by radio frequency sputtering deposition of a ZnO thin film on the SS substrate. The fabricated device showed stable unipolar and bipolar resistive switching behaviors with reliable switching responses over 100 cycles. The device performance was not degraded upon bending, which indicates high potential for flexible ReRAM applications.
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73.61.Ga II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
73.40.Sx Metal-semiconductor-metal structures
84.30.Sk Pulse and digital circuits
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