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12 Oct 2009

Volume 95, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 95, 153101 (2009); http://dx.doi.org/10.1063/1.3244597 (3 pages)

Geunjae Kwak, Mikyung Lee, Karuppanan Senthil, and Kijung Yong
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Grazing incidence fast atom diffraction: An innovative approach to surface structure analysis

H. Khemliche, P. Rousseau, P. Roncin, V. H. Etgens, and F. Finocchi

Appl. Phys. Lett. 95, 151901 (2009); http://dx.doi.org/10.1063/1.3246162 (3 pages) | Cited 12 times

Online Publication Date: 12 October 2009

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An alternative diffraction technique, based on grazing incidence scattering of high energy atoms, is applied to surface structure determination of crystalline surfaces. This technique, named GIFAD for grazing incidence fast atom diffraction, uses the same geometry as reflection high energy electron diffraction but is less invasive, more surface sensitive, and readily interpretable quantitatively. We present here a demonstration of this approach on a prototypical II–VI compound, ZnSe(001). Besides providing lattice parameter with high accuracy, we show that GIFAD gives straightforward access to the surface valence electron density profile, allowing clear identification of an electron transfer from Zn to Se.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Features of two-dimensional to three-dimensional growth mode transition of Ge in SiGe/Si(001) heterostructures with strained layers

D. V. Yurasov, Yu. N. Drozdov, M. V. Shaleev, and A. V. Novikov

Appl. Phys. Lett. 95, 151902 (2009); http://dx.doi.org/10.1063/1.3244202 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2009

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The results of the study of the effect of strained SiGe layers on the critical thickness of two-dimensional growth of Ge layer in different SiGe/Si(001) structures are presented. A significant influence of buried strained SiGe layer on the growth of Ge has been found out, which remains considerable even for SiGe layers capped by unstrained Si layer of thickness up to 3.5 nm. The experimental results are well described by the proposed model, where obtained features are explained by means of introducing a phenomenological parameter called “effective decay length” of the strain energy accumulated in the structure.
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68.55.ag Semiconductors
68.55.jd Thickness
81.05.Cy Elemental semiconductors

Thermal rectification at water/functionalized silica interfaces

Ming Hu, Javier V. Goicochea, Bruno Michel, and Dimos Poulikakos

Appl. Phys. Lett. 95, 151903 (2009); http://dx.doi.org/10.1063/1.3247882 (3 pages) | Cited 13 times

Online Publication Date: 13 October 2009

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Using nonequilibrium molecular dynamics simulations, we study the thermal diode effect in a system composed of silica, self-assembled monolayers (SAMs) at the silica surface and water surrounding this system, by imposing a series of positive and negative heat currents. We have found that in the limit of large heat currents, the thermal conductance at the SAMs-water interface is about 1000 MW/m2 K at room temperature for heat flowing from the SAMs to the water and 650 MW/m2 K for heat flowing from the water to the SAMs, respectively, resulting in a thermal rectification of up to 54%. Analysis of the radial distribution function of oxygen-oxygen atoms in water indicates that the origin of the thermal rectification resides in the strong temperature dependence of the hydrogen bonds in water.
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73.40.Ei Rectification
68.08.-p Liquid-solid interfaces

Large contrast enhancement of graphene monolayers by angle detection

V. Yu and M. Hilke

Appl. Phys. Lett. 95, 151904 (2009); http://dx.doi.org/10.1063/1.3247967 (3 pages) | Cited 8 times

Online Publication Date: 13 October 2009

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Exfoliated graphene monolayers are identified by optical inspection. In order to improve the monolayer detection, we investigate the angle dependence of the optical contrast of graphene on a 90 nm SiO2/Si substrate. We observe a significant enhancement of the visibility of graphene by changing the polarization and the angle of optical incidence. This method can be used to detect graphene on arbitrary substrates such as GaAs/AlAs based materials, which have a much cleaner surface.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
78.66.Tr Fullerenes and related materials
78.67.Ch Nanotubes

The significance of core-level electron binding energies on the proper analysis of InGaAs interfacial bonding

C. L. Hinkle, M. Milojevic, E. M. Vogel, and R. M. Wallace

Appl. Phys. Lett. 95, 151905 (2009); http://dx.doi.org/10.1063/1.3249577 (3 pages) | Cited 24 times

Online Publication Date: 14 October 2009

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The detection and removal of interfacial oxides on InGaAs semiconductors is of critical importance for their implementation as high-mobility channels for improved complementary metal oxide semiconductor device performance. X-ray photoelectron spectroscopy is a powerful tool to determine the chemical bonding at these interfaces. To correctly analyze these spectra, one must consider the binding energies and escape depths of the core-level electrons being detected, as monolayer level interfacial oxides (As–O and Ga–O) are detectable only in certain surface sensitive spectral regions. Also, inherent asymmetries associated with the In spectra must be taken into account for analysis of In-oxide bonding.
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61.50.Lt Crystal binding; cohesive energy
85.30.Tv Field effect devices
79.60.Jv Interfaces; heterostructures; nanostructures

High temperature strain glass in Ti50(Pd50−xCrx) alloy and the associated shape memory effect and superelasticity

Yumei Zhou, Dezhen Xue, Xiangdong Ding, Kazuhiro Otsuka, Jun Sun, and Xiaobing Ren

Appl. Phys. Lett. 95, 151906 (2009); http://dx.doi.org/10.1063/1.3249580 (3 pages) | Cited 8 times

Online Publication Date: 15 October 2009

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Strain glass has recently been reported in Ti50−xNi50+x (x ≥ 1.5 at %) alloys and caused by the existence of point defects. This strain glass alloy, being nonmartensitic, exhibits shape memory effect (SME) and superelasticity (SE) around the freezing temperature T0. However, the T0 of Ti50−xNi50+x (x ≥ 1.5 at %) strain glass alloy is very low ( ∼ 160 K), thus restricting its potential applications. In the present letter, we report a strain glass system, Ti50(Pd50−xCrx) (x ≥ 9 at %), which has a significantly higher freezing temperature. It is based on a high-temperature martensitic system TiPd (with Ms ∼ 810 K) and dopant Cr (as point defect). For Ti50(Pd40Cr10) strain glass, the freezing transition occurs at T0 ∼ 250 K, being close to the room temperature. Correspondingly, it exhibits SME and SE around its high T0. We further clarified that T0 of strain glass alloy is controlled by the martensitic transformation temperature Ms (i.e., martensite stability) of its corresponding host alloy without point defect. Our work provides insight into how to develop strain glass with desired T0 and the associated SME and SE for applications.
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81.30.Kf Martensitic transformations
62.20.fg Shape-memory effect; yield stress; superelasticity
81.40.Lm Deformation, plasticity, and creep
64.70.kj Glasses
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.J- Point defects and defect clusters

Temperature dependence of the band gap of ZnSe1−xOx

R. Broesler, E. E. Haller, W. Walukiewicz, T. Muranaka, T. Matsumoto, and Y. Nabetani

Appl. Phys. Lett. 95, 151907 (2009); http://dx.doi.org/10.1063/1.3242026 (3 pages) | Cited 8 times

Online Publication Date: 15 October 2009

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We have studied the temperature dependence of the band gap of molecular-beam-epitaxy-grown ZnSe1−xOx films (x = 0–0.021) using photoluminescence spectroscopy from 15 to 280 K. The temperature dependence of the band gap decreases with increasing oxygen concentration, which can be quantitatively explained by an anticrossing interaction between the highly localized oxygen defect states and the extended states of the conduction band.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors

Influence of heat treatments on electrical properties of ZnO films grown by molecular-beam epitaxy

D. C. Oh, S. H. Park, H. Goto, I. H. Im, M. N. Jung, J. H. Chang, T. Yao, J. S. Song, C. H. Bae, C. S. Han, and K. W. Koo

Appl. Phys. Lett. 95, 151908 (2009); http://dx.doi.org/10.1063/1.3247889 (3 pages) | Cited 3 times

Online Publication Date: 15 October 2009

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We report on the influence of heat treatments on the electrical properties of ZnO films grown by molecular-beam epitaxy. We note that the electrical resistance of the ZnO films is significantly changed by the heat treatments: the electrical resistance increases with the increase of ambient temperature, but above a critical temperature the resistance decreases with the increase of temperature, irrespective of ambient gases. On the other hand, it is found that the large amount of photocurrent is generated in the ZnO films, exposed to white sources: the photocurrent decreases with the increase of the obtained resistance, and the current increases with the decrease of the resistance. Also, it is shown that the x-ray diffraction linewidth of the ZnO films is significantly decreased by the heat treatments. These indicate that the increase/decrease of the electrical resistance is ascribed to the annihilation/formation of the residual donor-type defects in the ZnO films by the heat treatments. It is suggested that the increase of the electrical resistance is due to the annihilation of Zni-complex defects, while the decrease of the electrical resistance is due to the formation of VO-complex defects.
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73.61.Ga II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
68.55.ag Semiconductors
72.80.Ey III-V and II-VI semiconductors

X-ray linear dichroism of defects in GaN:Mg using hard x-ray nanoprobe

G. Martínez-Criado, R. Tucoulou, P. Cloetens, J. A. Sans, and J. Susini

Appl. Phys. Lett. 95, 151909 (2009); http://dx.doi.org/10.1063/1.3238557 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2009

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In this study, we report the application of synchrotron radiation nanoprobe techniques to the structural analysis of pyramidal defects in Mg doped GaN. A combination of fluorescence mapping with spectroscopic techniques enabled us to examine not only the elemental nature but also their crystallographic orientation on the submicron scale. Our observations provide strong evidence for the diffusion and subsequent segregation of background impurities of Fe and Cr on the sample surface, with the absence of pronounced sequential stacking compared with Ga atoms. The strong polarization-dependent x-ray absorption near-edge structure features showed the preservation of the hexagonal crystalline structure in both defect-free and hexagonal pyramids. From the spatially resolved x-ray linear dichroism, no preferential disorder was observed in the direction parallel or perpendicular to the crystal growth.
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78.20.Fm Birefringence
61.72.uj III-V and II-VI semiconductors
66.30.H- Self-diffusion and ionic conduction in nonmetals
78.70.Dm X-ray absorption spectra
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
61.46.-w Structure of nanoscale materials

Understanding the relation between stress and surface morphology in sputtered films: Atomistic simulations and experiments

Luis A. Zepeda-Ruiz, Eric Chason, George H. Gilmer, Yinmin Wang, Hongwei Xu, Abbas Nikroo, and Alex V. Hamza

Appl. Phys. Lett. 95, 151910 (2009); http://dx.doi.org/10.1063/1.3246791 (3 pages) | Cited 7 times

Online Publication Date: 16 October 2009

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The relation between stress evolution and surface morphology during deposition of sputtered films is examined by combining kinetic Monte Carlo simulations and stress measurements. We find that the surface morphology is susceptible to an instability, which transforms from layer-by-layer growth to the formation of pillarlike columns. The gaps between these columns prevent complete densification and can lead to a network of pores in the layer. We propose that the formation of this structure changes the stress in the growing layers from compressive to tensile.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Bn Structural modeling: serial-addition models, computer simulation
81.15.Cd Deposition by sputtering
61.72.Mm Grain and twin boundaries

Comparison of the magnetic properties of GeMn thin films through Mn L-edge x-ray absorption

S. Ahlers, P. R. Stone, N. Sircar, E. Arenholz, O. D. Dubon, and D. Bougeard

Appl. Phys. Lett. 95, 151911 (2009); http://dx.doi.org/10.1063/1.3232245 (3 pages) | Cited 4 times

Online Publication Date: 16 October 2009

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X-ray absorption spectroscopy of epitaxial GeMn thin films reveals an experimentally indistinguishable electronic configuration of Mn atoms incorporated in Ge1−xMnx nanoclusters and in precipitates of the intermetallic compound Mn5Ge3, respectively. However, the average magnetic response of thin films containing Ge1−xMnx nanoclusters is lower than the response of films containing Mn5Ge3 precipitates. This reduced magnetic response of Ge1−xMnx nanoclusters is explained in terms of a fraction of Mn atoms being magnetically inactive due to antiferromagnetic coupling or the presence of structural disorder. A determination of the role of magnetically inactive Mn atoms in the self-assembly of the thermodynamically metastable Ge1−xMnx nanoclusters seems to be an essential ingredient for an enhanced control of this promising high Curie temperature magnetic semiconductor.
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78.70.Dm X-ray absorption spectra
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
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