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7 Mar 2011

Volume 98, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 98, 104101 (2011); http://dx.doi.org/10.1063/1.3560505 (3 pages)

Zhongchang Wang, Susumu Tsukimoto, Rong Sun, Mitsuhiro Saito, and Yuichi Ikuhara
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Indefinite permittivity and negative refraction in natural material: Graphite

Jingbo Sun, Ji Zhou, Bo Li, and Feiyu Kang

Appl. Phys. Lett. 98, 101901 (2011); http://dx.doi.org/10.1063/1.3562033 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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In this work, we report a nature indefinite permittivity in crystalline graphite that exhibits negative group refraction at ultraviolet region. A hyperbolic equifrequency contour was obtained from ellipsometry data at 254 nm and an all angle negative refraction was verified experimentally. The indefinite permittivity is attributed to extremely strong anisotropy in the crystal structure and the hybrid electronic transitions. This result not only explores a route toward natural negative-index materials, but also holds a promise for ultraviolet hyperlens, which may lead to a breakthrough in nanolithography for the next generation of electronics.
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81.05.uf Graphite
78.40.Ri Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
61.66.Bi Elemental solids

Distribution of bismuth atoms in epitaxial GaAsBi

D. L. Sales, E. Guerrero, J. F. Rodrigo, P. L. Galindo, A. Yáñez, M. Shafi, A. Khatab, R. H. Mari, M. Henini, S. Novikov, M. F. Chisholm, and S. I. Molina

Appl. Phys. Lett. 98, 101902 (2011); http://dx.doi.org/10.1063/1.3562376 (3 pages) | Cited 4 times

Online Publication Date: 7 March 2011

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The distribution of Bi atoms in epitaxial GaAs(1−x)Bix is analyzed through aberration-corrected Z-contrast images. The relation between the atomic number and the intensity of the images allows quantifying the distribution of Bi atoms in this material. A bidimensional map of Bi atoms is extracted showing areas where nanoclustering is possible and evidencing the location of Bi at As-substitutional positions in the lattice. The distribution of Bi atoms differs from a random spatial pattern of Bi atoms in the material.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Electronic origin of the phase transition in ternary alloy Mo(Si1−x,Alx)2

Zhengzheng Chen, Bin Shan, and Rong Chen

Appl. Phys. Lett. 98, 101903 (2011); http://dx.doi.org/10.1063/1.3562593 (3 pages)

Online Publication Date: 7 March 2011

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The structural stability of the ternary alloy Mo(Si1−x,Alx)2 with different x has been investigated using first-principles pseudopotential plane wave method. The electronic origin of the C11b→C40 phase transition is revealed by analyzing the density of states and d-band splitting induced by the crystal field. We further propose the feasibility of controlling the microscopic structure by adding a quaternary component according to the mechanism presented in this work.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
71.15.-m Methods of electronic structure calculations
71.20.Gj Other metals and alloys

Thermal conductivity of chalcogenide material with superlatticelike structure

H. Tong, X. S. Miao, X. M. Cheng, H. Wang, L. Zhang, J. J. Sun, F. Tong, and J. H. Wang

Appl. Phys. Lett. 98, 101904 (2011); http://dx.doi.org/10.1063/1.3562610 (3 pages) | Cited 6 times

Online Publication Date: 7 March 2011

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Thermal conductivity of chalcogenide material with superlatticelike (SLL) structure is investigated using the 3ω method and the molecular dynamics method. Both the measured and calculated results show that the thermal conductivity of SLL is lower than those of conventional chalcogenide materials and will decrease to a minimum as the number of interfaces increases. The Raman spectrum is introduced to study the phonon behavior of SLL and the “phonon mode vanishing” is proposed to explain its lower thermal conductivity. Finite-element analysis and phase change memory cell testing confirm the enhancement of cell performance for SLL with minimum thermal conductivity.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.30.Hv Other nonmetallic inorganics
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

A simple theoretical approach to analyze polarization properties in semipolar and nonpolar InGaN quantum wells

Atsushi A. Yamaguchi and Kazunobu Kojima

Appl. Phys. Lett. 98, 101905 (2011); http://dx.doi.org/10.1063/1.3561761 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2011

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By using a simple theoretical approach, the previously reported experimental results of the polarization properties in semipolar and nonpolar InGaN quantum wells (QWs) were analyzed. On the basis of the k⋅p-perturbation theory, we derived a useful analytical expression for describing the polarization properties of these QWs, and used this expression to analyze experimental data reported from various research groups. Based on these analyses, we predicted that the negative polarization degree, which is favorable for laser diodes with cleaved-facet cavity mirrors, would appear in the blue- or green-InGaN QWs on the lower-angle semipolar planes (30°–40° inclined from the c-plane).
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
42.55.Px Semiconductor lasers; laser diodes

Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

M. W. Allen, D. Y. Zemlyanov, G. I. N. Waterhouse, J. B. Metson, T. D. Veal, C. F. McConville, and S. M. Durbin

Appl. Phys. Lett. 98, 101906 (2011); http://dx.doi.org/10.1063/1.3562308 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2011

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Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.
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71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.15.Nc Total energy and cohesive energy calculations

Detection of a ZnSe secondary phase in coevaporated Cu2ZnSnSe4 thin films

Alex Redinger, Katja Hönes, Xavier Fontané, Victor Izquierdo-Roca, Edgardo Saucedo, Nathalie Valle, Alejandro Pérez-Rodríguez, and Susanne Siebentritt

Appl. Phys. Lett. 98, 101907 (2011); http://dx.doi.org/10.1063/1.3558706 (3 pages) | Cited 23 times

Online Publication Date: 9 March 2011

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Cu2ZnSnSe4 (CZTSe) thin films are grown by coevaporation. Composition depth profiles reveal that a Zn rich phase is present at the CZTSe/Mo interface. Raman measurements on the as grown films are used to study the near surface region and the CZTSe/Mo interface, after mechanically removing the thin film from the Mo coated glass. These measurements provide direct experimental evidence of the formation of a ZnSe phase at the CZTSe/Mo interface. While the Raman spectra at the surface region are dominated by CZTSe modes, those measured at the CZTSe/Mo interface are dominated by ZnSe and MoSe2 modes.
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81.05.Hd Other semiconductors
81.15.Dj E-beam and hot filament evaporation deposition
68.55.ag Semiconductors
68.35.Ct Interface structure and roughness
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

In situ strain relaxation comparison between GaAsBi and GaInAs grown by molecular-beam epitaxy

R. France, C.-S. Jiang, and A. J. Ptak

Appl. Phys. Lett. 98, 101908 (2011); http://dx.doi.org/10.1063/1.3562952 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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The strain relaxation of GaAsBi is studied in order to determine both the maximum thickness before dislocations form for various misfits and the potential of GaAsBi for usage in the compositionally graded buffer of lattice-mismatched devices. Low-misfit GaAsBi epilayers are grown and compared with GaInAs, a well-studied material currently used in compositional grades. Relaxation behavior and dislocation energetics are compared using in situ wafer curvature. Samples are grown using molecular-beam epitaxy under similar conditions with misfit up to –0.81%. GaAsBi begins to relax at a lower thickness than GaInAs of the same mismatch. This leads to the majority of GaAsBi strain relaxation occurring with less material growth than comparable GaInAs. However, GaAsBi has greater residual strain than GaInAs after 2 μm of growth. These results indicate that GaAsBi requires less elastic energy to form dislocations and more elastic energy to either encourage glide or multiply dislocations than GaInAs. GaAsBi shows less surface roughness than GaInAs for all samples, ruling out roughness as a source of dislocations and hindered glide in these alloys.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties
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Picosecond time-resolved x-ray refectivity of a laser-heated amorphous carbon film

R. Nüske, A. Jurgilaitis, H. Enquist, S. Dastjani Farahani, J. Gaudin, L. Guerin, M. Harb, C. v. Korff Schmising, M. Störmer, M. Wulff, and J. Larsson

Appl. Phys. Lett. 98, 101909 (2011); http://dx.doi.org/10.1063/1.3562967 (3 pages) | Cited 4 times

Online Publication Date: 10 March 2011

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We demonstrate thin film x-ray reflectivity measurements with picosecond time resolution. Amorphous carbon films with a thickness of 46 nm were excited with laser pulses characterized by 100 fs duration, a wavelength of 800 nm, and a fluence of 70 mJ/cm2. The laser-induced stress caused a rapid expansion of the thin film followed by a relaxation of the film thickness as heat diffused into the silicon substrate. We were able to measure changes in film thickness as small as 0.2 nm. The relaxation dynamics are consistent with a model which accounts for carrier-enhanced substrate heat diffusivity.
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81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Analysis of interband, intraband, and plasmon polariton transitions in silver nanoparticle films via in situ real-time spectroscopic ellipsometry

S. A. Little, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 98, 101910 (2011); http://dx.doi.org/10.1063/1.3564894 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2011

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The dielectric function of Ag nanoparticle films, deduced from an analysis of in situ real-time spectroscopic ellipsometry (RTSE) measurements, is found to evolve with time during deposition in close consistency with the film structure, deduced in the same RTSE analysis. In the nucleation regime, the intraband dielectric function component is absent and plasmon polariton behavior dominates. Only at nuclei contact, does the intraband amplitude appear, increasing above zero. Both intraband and plasmon amplitudes coexist during surface smoothening associated with coalescence. The intraband relaxation time increases rapidly after surface smoothening is complete, also in consistency with the thin film structural evolution.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Elastic stiffness of L10 FePt thin film studied by picosecond ultrasonics

N. Nakamura, A. Uranishi, M. Wakita, H. Ogi, M. Hirao, and M. Nishiyama

Appl. Phys. Lett. 98, 101911 (2011); http://dx.doi.org/10.1063/1.3562031 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2011

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The elastic stiffness of epitaxial and polycrystalline L10 FePt films is studied by picosecond ultrasonics coupled with x-ray reflectivity analysis, and we find that C33 of L10 FePt is 309 GPa. The morphology of FePt films shows dependence on the film thickness; as the film thickness increases the mazelike structure changes to a continuous film. The elastic stiffness correlates with the morphology change, and it increases as the film thickness increases. When the film thickness exceeds 40 nm, the elastic stiffness becomes independent of the film thickness, and we define the saturated value as C33 of L10 FePt.
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68.55.A- Nucleation and growth
68.55.J- Morphology of films
61.66.-f Structure of specific crystalline solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Surfactant mediated growth of Ti/Ni multilayers

Mukul Gupta, S. M. Amir, Ajay Gupta, and Jochen Stahn

Appl. Phys. Lett. 98, 101912 (2011); http://dx.doi.org/10.1063/1.3565161 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2011

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The surfactant mediated growth of Ti/Ni multilayers is studied. They were prepared using ion beam sputtering at different adatom energies. It was found that the interface roughness decreased significantly when the multilayers were sputtered with Ag as surfactant at an ion energy of 0.75 keV. On the other hand, when the ion energy was increased to 1 keV, it resulted in enhanced intermixing at the interfaces and no appreciable effect of Ag surfactant could be observed. On the basis of the obtained results, the influence of adatom energy on the surfactant mediated growth mechanism is discussed.
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81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
68.35.Ct Interface structure and roughness

Low temperature reflectivity study of nonpolar ZnO/(Zn,Mg)O quantum wells grown on M-plane ZnO substrates

L. Béaur, T. Bretagnon, C. Brimont, T. Guillet, B. Gil, D. Tainoff, M. Teisseire, and J.-M. Chauveau

Appl. Phys. Lett. 98, 101913 (2011); http://dx.doi.org/10.1063/1.3565969 (3 pages) | Cited 4 times

Online Publication Date: 11 March 2011

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We report growth of high quality ZnO/Zn0.8Mg0.2O quantum wells on M-plane oriented ZnO substrates. The optical properties are studied by reflectance spectroscopy. The optical spectra reveal strong in-plane optical anisotropies, as predicted by group theory, and clear reflectance structures, as an evidence of good interface morphologies. Signatures of confined excitons built from spin-orbit split-off valence band, analogous to C-exciton in bulk ZnO, are detected using a light polarized along the c-axis. Experiments performed in orthogonal polarization, show confined states analogous to A and B bulk excitons. Envelope function calculations including excitonic interaction nicely match the experimental results.
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81.07.St Quantum wells
81.05.Dz II-VI semiconductors
73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.-y Excitons and related phenomena
78.67.De Quantum wells
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