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7 Jun 2010

Volume 96, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages)

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi
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Nanoscale structural variation observed on the vicinal SrTiO3(001) surface

Susumu Shiraki, Masashi Nantoh, Satoshi Katano, and Maki Kawai

Appl. Phys. Lett. 96, 231901 (2010); http://dx.doi.org/10.1063/1.3447796 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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The vicinal (001) surface of a Nb-doped SrTiO3 single crystal has been investigated by scanning tunneling microscopy and low energy electron diffraction. The stepped surface prepared by annealing in ultrahigh vacuum at 250 °C exhibits a complex atomic structure composed of four types of reconstructions, which shows short-range variation within nanoscale regions. SrO layers show a c(6×2) structure being stable up to 1000 °C, while √13×√13-R33.7°, c(√13×√13)-R33.7°, and c(√2×√18)-R45° structures are formed on TiO2 layers, which disappear at 450–750 °C followed by the formation of 2×2 and √5×√5-R26.6° structures. These results indicate instability of the reconstructions on the TiO2 terminated surface due to the variation in Sr adatom density caused by multikinetic processes, in contrast to the thermodynamically stable SrO terminated surface.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments

Enhanced photoluminescence from self-organized rubrene single crystal surface structures

R. J. Stöhr, G. J. Beirne, P. Michler, R. Scholz, J. Wrachtrup, and J. Pflaum

Appl. Phys. Lett. 96, 231902 (2010); http://dx.doi.org/10.1063/1.3449124 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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We report on crystalline pyramidal structures grown via self-organization on the rubrene (001) surface. The analysis of their spectral response by means of photoluminescence with micrometer lateral resolution reveals an intensity enhancement on-top of the surface structures. As we demonstrate this intensity increase can be related to the excitation processes at the molecular level in combination with exciton confinement within the pyramids.
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78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena

Enhancing magnetorheology with nonmagnetizable particles

John C. Ulicny, Keith S. Snavely, Mark A. Golden, and Daniel J. Klingenberg

Appl. Phys. Lett. 96, 231903 (2010); http://dx.doi.org/10.1063/1.3431608 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2010

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Experimental results illustrate an enhancement in the field-induced yield stress of magnetorheological (MR) fluids caused by the presence of nonmagnetizable particles. Particle-level simulations in three dimensions show similar behavior. However, the enhancement does not appear in simulations in which the spheres are confined to a monolayer. A mechanistic explanation of these observations is currently lacking. Nonetheless, the ability to enhance the MR response by replacing magnetizable particles with nonmagnetizable particles offers several advantages for applications.
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75.50.Mm Magnetic liquids
83.80.Gv Electro- and magnetorheological fluids
75.50.Tt Fine-particle systems; nanocrystalline materials

First principles prediction of the metastability of the Ge2Mn phase and its synthesis pathways

E. Arras, I. Slipukhina, M. Torrent, D. Caliste, T. Deutsch, and P. Pochet

Appl. Phys. Lett. 96, 231904 (2010); http://dx.doi.org/10.1063/1.3446837 (3 pages) | Cited 2 times

Online Publication Date: 8 June 2010

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In this letter, we performed first principles calculations to investigate the stability of a [100]-compatible Ge2Mn compound. Based on a thermodynamical approach, we propose and assess the C16 structure (Al2Cu prototype) to be only slightly metastable as compared to the other Ge–Mn compounds. The reported structural and magnetic properties of this Ge2Mn compound make it a potentially interesting compound for spintronic applications, all the more since a simple way to stabilize it as a bulk film is proposed.
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71.10.Li Excited states and pairing interactions in model systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Planar semipolar (10math1) GaN on (11math3) sapphire

Stephan Schwaiger, Ilona Argut, Thomas Wunderer, Rudolf Rösch, Frank Lipski, Johannes Biskupek, Ute Kaiser, and Ferdinand Scholz

Appl. Phys. Lett. 96, 231905 (2010); http://dx.doi.org/10.1063/1.3442484 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2010

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We report on the growth of planar semipolar (10math1) GaN on (11math3) prepatterned sapphire. This is a method that allows the growth of semipolar oriented (10math1) GaN on large scale. Using x-ray diffraction only the peaks of the desired (10math1) plane could be observed. Scanning electron, transmission electron, and atomic force microscopy measurements show an atomically flat surface. Further investigations using photoluminescence spectroscopy show spectra that are dominated by the near band edge emission. The high crystal quality is furthermore confirmed by the small full width at half maximum values of x-ray rocking curve measurements of less than 400 arcsec.
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68.55.ag Semiconductors
68.35.Ct Interface structure and roughness
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Reduction of the transverse effective charge of optical phonons in ZnO under pressure

J. S. Reparaz, L. R. Muniz, M. R. Wagner, A. R. Goñi, M. I. Alonso, A. Hoffmann, and B. K. Meyer

Appl. Phys. Lett. 96, 231906 (2010); http://dx.doi.org/10.1063/1.3447798 (3 pages) | Cited 6 times

Online Publication Date: 9 June 2010

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From Raman scattering on a-plane wurtzite ZnO crystals we obtained a decreasing splitting between longitudinal and transversal optical phonons with A1 and E1 symmetry as a function of hydrostatic pressure up to 5.5 GPa. Consequently, the transverse effective charge (eT∗) exhibits a strong reduction with increasing pressure, yielding 2.17–14.6×10−3 P/GPa and 2.04–13.7×10−3 P/GPa (in units of the elementary charge) for the A1 and E1 phonons, respectively. We find a clear systematic in the linear pressure coefficient of eT∗ with bond polarity for the series of wide-band gap semiconductors SiC, AlN, GaN, and ZnO.
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78.30.Fs III-V and II-VI semiconductors
63.20.-e Phonons in crystal lattices
62.50.-p High-pressure effects in solids and liquids

Origin of pyramidal hillocks on GaN thin films grown on free-standing m-plane GaN substrates

R. M. Farrell, D. A. Haeger, X. Chen, C. S. Gallinat, R. W. Davis, M. Cornish, K. Fujito, S. Keller, S. P. DenBaars, S. Nakamura, and J. S. Speck

Appl. Phys. Lett. 96, 231907 (2010); http://dx.doi.org/10.1063/1.3447926 (3 pages) | Cited 8 times

Online Publication Date: 9 June 2010

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The relationship between pyramidal hillocks and dislocations was studied for GaN thin films grown by metalorganic chemical vapor deposition on low-dislocation-density free-standing m-plane GaN substrates. Four-sided pyramidal hillocks were observed on GaN thin films grown on nominally on-axis m-plane GaN substrates. Cathodoluminescence measurements revealed the presence of a dislocation at the apex of each pyramidal hillock. High-resolution atomic force microscopy images showed a pinned step at the apex of each pyramidal hillock and a spiral ramp around the termination of the step, indicating that the pyramidal hillocks arise from spiral growth around screw-component dislocations intersecting the surface of the crystal.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence

Microstructure of gallium nitride films grown on silicon (110)

F. Ruiz-Zepeda, O. Contreras, A. Dadgar, and A. Krost

Appl. Phys. Lett. 96, 231908 (2010); http://dx.doi.org/10.1063/1.3449126 (3 pages) | Cited 1 time

Online Publication Date: 9 June 2010

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The microstructure of GaN layers grown on Si(110) is studied by transmission electron microscopy. The GaN layers were grown by metal-organic vapor phase epitaxy using low-temperature AlN interlayers and a high-temperature AlN seed layer. Anisotropic misfit strain originating at the AlN/Si(110) interface is notably reflected in the microstructure of the GaN layers. The stress produced in GaN/Si(110) films is relieved by bending of edge type threading dislocations over the basal plane, generating horizontal segments aligned all along the closely lattice matched direction [1math00]. It is proposed that the horizontal defects are generated by a driven force with glide- and climb-components manifested on some of the prismatic slip planes of GaN. The general mechanism of the change in the propagation direction of dislocations is discussed.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

The formation, stability, and suitability of n-type junctions in germanium formed by solid phase epitaxial recrystallization

R. Duffy, M. Shayesteh, M. White, J. Kearney, and A.-M. Kelleher

Appl. Phys. Lett. 96, 231909 (2010); http://dx.doi.org/10.1063/1.3452345 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2010

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Design and optimization of n-type doped regions in germanium by solid phase epitaxial recrystallization (SPER) have been studied by the authors. A systematic study is presented of process variables that influence activation and thermal stability, including preamorphization, coimplants, recrystallization temperature, and postrecrystallization thermal treatments. Unlike silicon, activation after recrystallization in germanium is not optimum where the postrecrystallization thermal budget is kept to a minimum. With the aid of modeling, a maximum peak activation of 7×1019 cm−3 was extracted. A steady increase in sheet resistance during postrecrystallization anneals confirms the formation of metastable activation by SPER. It is predicted that active concentrations of 6–8×1019 cm−3 are sufficient to meet targets for sub-20 nm technologies.
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61.72.uf Ge and Si
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
81.05.Cy Elemental semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
71.55.Cn Elemental semiconductors
81.40.Gh Other heat and thermomechanical treatments

Diffusion and growth mechanism of Nb3Sn superconductor grown by bronze technique

T. Laurila, V. Vuorinen, A. K. Kumar, and A. Paul

Appl. Phys. Lett. 96, 231910 (2010); http://dx.doi.org/10.1063/1.3453502 (3 pages) | Cited 1 time

Online Publication Date: 10 June 2010

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The rather surprising position of the Kirkendall pores in Nb3Sn superconductor grown by bronze technique is clarified. It is shown that Sn is the fastest diffusing species, which seems to be unusual considering the crystal structure of Nb3Sn. Further, we explain the dramatic change in the growth rate and the activation energy for growth of the product phase, when the Sn composition in the Cu(Sn) bronze alloy is changed from 7 to 8 at. %.
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74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Electromigration-driven surface morphological stabilization of a coherently strained epitaxial thin film on a substrate

Georgios I. Sfyris, M. Rauf Gungor, and Dimitrios Maroudas

Appl. Phys. Lett. 96, 231911 (2010); http://dx.doi.org/10.1063/1.3447371 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2010

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We analyze the surface morphological stability of a coherently strained thin film grown epitaxially on a thick elastic substrate under the simultaneous action of an electric field that drives surface electromigration. A model of driven film surface morphological evolution is developed and a linear stability analysis is carried out of the planar film surface morphology. The analysis reveals that surface electromigration can inhibit surface morphological instabilities due to the lattice mismatch between the film and the substrate. The critical electric-field strength for surface stabilization and the optimal electric-field direction are determined and the effects of surface diffusional anisotropy are examined.
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66.30.Qa Electromigration
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Stacking fault formation in the long wavelength InGaN/GaN multiple quantum wells grown on m-plane GaN

Feng Wu, You-Da Lin, Arpan Chakraborty, Hiroaki Ohta, Steven P. DenBaars, Shuji Nakamura, and James S. Speck

Appl. Phys. Lett. 96, 231912 (2010); http://dx.doi.org/10.1063/1.3447940 (3 pages) | Cited 17 times

Online Publication Date: 10 June 2010

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Nonpolar GaN-based light emitting diodes (LEDs) and laser diodes (LDs) show great promise. However, long wavelength emitters (λ>500 nm) have reduced performance in comparison with violet and blue nonpolar emitters. We present results of transmission electron microscopy studies of long wavelength (1math00) m-plane GaN LED series and m-plane GaN LDs grown on high quality bulk GaN substrates. I1 basal plane stacking faults form in the high In content InxGa1−xN quantum wells (x ∼ 0.26) for thicker wells. The I1 faults are bounded by sessile Frank–Shockley partial dislocations that likely limit the radiative efficiency of long wavelength m-plane emitters.
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85.60.Jb Light-emitting devices
42.55.Px Semiconductor lasers; laser diodes

Band gap of sphalerite and chalcopyrite phases of epitaxial ZnSnP2

P. St-Jean, G. A. Seryogin, and S. Francoeur

Appl. Phys. Lett. 96, 231913 (2010); http://dx.doi.org/10.1063/1.3442917 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2010

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Using contactless electroreflectance, we determined the band gap of the two known phases of epitaxial ZnSnP2. Induced by small changes in Sn/Zn flux ratio during epitaxy, the order-disordered transition between the chalcopyrite and sphalerite phases reduces the band gap by 300 meV. The chalcopyrite ordered phase, unambiguously identified from x-ray diffraction, exhibits a band gap of 1.683 eV at 293 K. The band gap of the disordered sphalerite phase is 1.383 eV. Using the volume-averaged order parameter measured on the chalcopyrite sample, we find that its morphology is best described by the presence of perfectly ordered domains inside a disordered matrix.
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71.20.Nr Semiconductor compounds
78.20.Jq Electro-optical effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Striated surface morphology and crystal orientation of m-plane GaN films grown on γ-LiAlO2(100)

K. R. Wang, M. Ramsteiner, C. Mauder, Q. Wan, T. Hentschel, H. T. Grahn, H. Kalisch, M. Heuken, R. H. Jansen, and A. Trampert

Appl. Phys. Lett. 96, 231914 (2010); http://dx.doi.org/10.1063/1.3449133 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2010

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Polarized in-plane and cross-sectional Raman spectra have been used to determine the crystal orientation of m-plane GaN grown on γ-LiAlO2(100) (LAO) using a three-step metalorganic vapor phase epitaxy process. The epitaxial relationship is found to be GaN(1math00)∥LAO(100) and GaN[11math0]∥LAO[001]. However, the stripes on the GaN surface are oriented parallel to [0001], i.e., perpendicular to the one found on striated m-plane GaN surfaces in previous studies. This unusual orientation is attributed to the changes in the Ga adatom kinetics due to the presence of a 2-nm-thick interlayer observed at the GaN/LAO interface in transmission electron microscopy.
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68.55.J- Morphology of films
68.35.Ja Surface and interface dynamics and vibrations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.55.ag Semiconductors

TiO2-coated carbon nanotubes: A redshift enhanced photocatalysis at visible light

Sheng-Yi Lu, Chiung-Wen Tang, Yu-Hsien Lin, Hsin-Fu Kuo, Yao-Cheng Lai, Meng-Yen Tsai, Hao Ouyang, and Wen-Kuang Hsu

Appl. Phys. Lett. 96, 231915 (2010); http://dx.doi.org/10.1063/1.3454908 (3 pages) | Cited 7 times

Online Publication Date: 11 June 2010

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Annealing of carbon nanotubes coated with thin and uniform TiO2 results in carbon diffusion into oxygen lattices and doping induced redshift is evident by an efficient photocatalysis at visible light. The underlying mechanism is discussed.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
82.50.Hp Processes caused by visible and UV light
81.07.De Nanotubes
78.67.Ch Nanotubes

Band engineering of bilayer graphene by metal atoms: First-principles calculations

D.-H. Oh, B. G. Shin, and J. R. Ahn

Appl. Phys. Lett. 96, 231916 (2010); http://dx.doi.org/10.1063/1.3451465 (3 pages) | Cited 4 times

Online Publication Date: 11 June 2010

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The continuous change in the electronic band structure of metal-adsorbed bilayer graphene was calculated as a function of metal coverage using first-principles calculations. Instead of modifying the unit cell size as a function of metal coverage, the distance between the metal atoms and bilayer graphene in the same 2×2 unit unit cell was controlled to change the total charges transferred from the metal atoms to bilayer graphene. The validity of the theoretical method was confirmed by reproducing the continuous change in the electronic band structure of K-adsorbed epitaxial bilayer graphene, as shown by Ohta et al. [Science 313, 951 (2006)] . In addition, the changes in the electronic band structures of undoped, n-type, and p-type bilayer graphene were studied schematically as a function of metal coverage using the theoretical method.
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68.43.Bc Ab initio calculations of adsorbate structure and reactions
71.20.Tx Fullerenes and related materials; intercalation compounds
61.48.Gh Structure of graphene
73.21.Ac Multilayers

Absolute spectral gaps for infrared light and hypersound in three-dimensional metallodielectric phoxonic crystals

N. Papanikolaou, I. E. Psarobas, and N. Stefanou

Appl. Phys. Lett. 96, 231917 (2010); http://dx.doi.org/10.1063/1.3453448 (3 pages) | Cited 11 times

Online Publication Date: 11 June 2010

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By means of full electrodynamic and elastodynamic multiple-scattering calculations we study the optical and acoustic properties of three-dimensional lattices of metallic nanospheres implanted in a dielectric host. Our results show that such structures exhibit omnidirectional spectral gaps for both telecom infrared light and hypersound, with relatively low absorptive losses. This class of dual (phoxonic) band-gap materials is an essential step toward the hypersonic modulation of light and could lead to the development of efficient acousto-optical devices.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
62.65.+k Acoustical properties of solids
63.22.Np Layered systems
78.30.Er Solid metals and alloys

Semipolar GaN films on patterned r-plane sapphire obtained by wet chemical etching

P. de Mierry, N. Kriouche, M. Nemoz, S. Chenot, and G. Nataf

Appl. Phys. Lett. 96, 231918 (2010); http://dx.doi.org/10.1063/1.3454278 (3 pages) | Cited 8 times

Online Publication Date: 11 June 2010

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It is shown that (11math2)-oriented GaN films can be achieved from r-sapphire patterned by chemical etching. Growth first occurs selectively from the inclined c-facet of sapphire, leading finally to a fully coalesced layer with (11math2) orientation. The structural and optical quality of these layers was assessed by x-ray diffraction, cathodoluminescence and photoluminescence measurements. The results clearly show that the quality of (11math2) GaN on patterned r-sapphire is markedly improved in comparison with (11math2) GaN on m-sapphire.
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81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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