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4 Apr 2011

Volume 98, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen
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Universal stress-defect correlation at (100)semiconductor/oxide interfaces

M. Houssa, M. Scarrozza, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 98, 141901 (2011); http://dx.doi.org/10.1063/1.3575559 (3 pages) | Cited 2 times

Online Publication Date: 4 April 2011

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Interface models between various group IV and III-V (100)semiconductors and their oxides are generated from first-principles molecular dynamics simulations. The tensile strain at the interface (from the semiconductor side) is estimated, by comparing bond lengths at/near the interface and in the bulk semiconductor phase. A linear relationship between the calculated interface stress and the density of interface defects observed at such interfaces is revealed. These results suggest that the interface stress due to the volume mismatch between the semiconductor and its oxide likely plays an important role in the creation of interface defects. These findings can explain recent results pertaining to the passivation of various high-mobility channels for their integration in high-performance metal-oxide-semiconductor field-effect transistors.
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68.35.Ct Interface structure and roughness
68.35.Gy Mechanical properties; surface strains

Temperature dependence of single twin boundary motion in Ni–Mn–Ga martensite

L. Straka, H. Hänninen, and O. Heczko

Appl. Phys. Lett. 98, 141902 (2011); http://dx.doi.org/10.1063/1.3573860 (3 pages) | Cited 10 times

Online Publication Date: 4 April 2011

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Magnetic-field-induced reorientation in Ni–Mn–Ga five-layered martensite (10 M) mediated by the motion of single twin boundary was evaluated from magnetization measurements between 20 and 300 K. At 300 K, the single twin boundary moved in an exceptionally small field of 25 kA/m. Twinning stress, as a measure of the twin boundary mobility, was determined from the magnetization curves using a magnetic-energy-based model; it increased from ≈0.1 MPa at 300 K to ≈0.8 MPa at 20 K. The dependence is discussed in terms of thermal activation and the effect of intermartensitic transformation is considered.
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61.72.Mm Grain and twin boundaries
64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Growth temperature dependent graphene alignment on Ir(111)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen

Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2011

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The morphology of graphene monolayers on Ir(111) prepared by thermal decomposition of ethylene between 1000 and 1530 K was studied with high resolution low energy electron diffraction. In addition to a well-oriented epitaxial phase, randomly oriented domains are observed for growth temperatures between 1255 and 1460 K. For rotational angles of ±3° around 30° these domains lock-in in a 30° oriented epitaxial phase. Below 1200 K the graphene layer exhibits high disorder and structural disintegrity. Above 1500 K the clear moiré spots reflect graphene in a single orientation epitaxial incommensurate phase.
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68.55.-a Thin film structure and morphology
81.05.ue Graphene

Doping-type dependence of phonon dephasing dynamics in Si

Keiko Kato, Katsuya Oguri, Atsushi Ishizawa, Kouta Tateno, Takehiko Tawara, Hideki Gotoh, Masahiro Kitajima, Hidetoshi Nakano, and Tetsuomi Sogawa

Appl. Phys. Lett. 98, 141904 (2011); http://dx.doi.org/10.1063/1.3574533 (3 pages) | Cited 1 time

Online Publication Date: 5 April 2011

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We studied the dephasing dynamics of coherent phonons in n-type, p-type, and intrinsic Si using time-resolved reflectivity measurements with sub-10 fs laser pulses. The dephasing time of the coherent phonons increases (decreases) for n-type (p-type) doping compared with that of intrinsic Si, while the frequencies of the coherent phonons exhibit a redshift for both types of doping. These doping-induced changes in the coherent phonon dynamics are observed when the carrier concentration exceeds 1019 cm−3. The doping-type dependent changes in the dephasing time are attributed to the interconduction and intervalence band transitions in n-type and p-type Si, respectively.
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61.72.U- Doping and impurity implantation
78.47.D- Time resolved spectroscopy (>1 psec)
78.47.jg Time resolved reflection spectroscopy
71.20.Mq Elemental semiconductors
78.47.db Conduction electrons

Spontaneous formation of highly regular superlattice structure in InGaN epilayers grown by molecular beam epitaxy

Z. H. Wu, Y. Kawai, Y.-Y. Fang, C. Q. Chen, H. Kondo, M. Hori, Y. Honda, M. Yamaguchi, and H. Amano

Appl. Phys. Lett. 98, 141905 (2011); http://dx.doi.org/10.1063/1.3574607 (3 pages) | Cited 1 time

Online Publication Date: 5 April 2011

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In this letter, we have investigated the structural properties of thick InGaN layers grown on GaN by plasma-assisted molecular beam epitaxy, using two growth rates of 1.0 and 3.6 Å/s. A highly regular superlattice (SL) structure is found to be spontaneously formed in the film grown at 3.6 Å/s but not in the film grown at 1.0 Å/s. The faster grown film also exhibits superior structural quality, which could be due to the surface roughness suppression caused by kinetic limitation, and the inhibition of the Frank–Read dislocation generation mechanism within the spontaneously formed SL structure.
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81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.65.Cd Superlattices
68.55.ag Semiconductors
68.35.bg Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Type II detwinning in NiTi

Tawhid Ezaz and Huseyin Sehitoglu

Appl. Phys. Lett. 98, 141906 (2011); http://dx.doi.org/10.1063/1.3574775 (3 pages) | Cited 8 times

Online Publication Date: 5 April 2011

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Shape memory effect in nickel-titanium (NiTi) alloys depends on phase transformation between two phases and growth of twin variants in martensite called detwinning. An outstanding issue regarding detwinning in NiTi has been the lack of fundamental understanding of its mechanism at the atomistic level. The present article resolves this issue via first-principles energetics calculations of twin nucleation and growth. Our results based on ion relaxation and valence charge distribution point to a distinct energy barrier during detwinning process and the mechanism is mediated by a complex conjunction of shear and shuffle.
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61.72.Mm Grain and twin boundaries
64.70.kd Metals and alloys
62.20.fg Shape-memory effect; yield stress; superelasticity
81.30.Kf Martensitic transformations

Influence of Mn dopants on InAs/GaAs quantum dot electronic states

V. D. Dasika, A. V. Semichaevsky, J. P. Petropoulos, J. C. Dibbern, A. M. Dangelewicz, M. Holub, P. K. Bhattacharya, J. M. O. Zide, H. T. Johnson, and R. S. Goldman

Appl. Phys. Lett. 98, 141907 (2011); http://dx.doi.org/10.1063/1.3567510 (3 pages) | Cited 2 times

Online Publication Date: 6 April 2011

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We have investigated the influence of Mn dopants on the electronic states in the vicinity of InAs/GaAs quantum dots (QDs) and the surrounding GaAs matrix. A comparison of cross-sectional scanning tunneling microscopy, scanning tunneling spectroscopy, and tight binding calculations of the local density of states reveals that the Mn dopants primarily influence the electronic states at the QD edges and the surrounding GaAs matrix. These results suggest that the Mn dopants reside at the QD edge, consistent with the predictions of a thermodynamic model for the nanoscale-size dependence of dopant incorporation in nanostructures.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.21.La Quantum dots
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

High resolution cathodoluminescence hyperspectral imaging of surface features in InGaN/GaN multiple quantum well structures

Jochen Bruckbauer, Paul R. Edwards, Tao Wang, and Robert W. Martin

Appl. Phys. Lett. 98, 141908 (2011); http://dx.doi.org/10.1063/1.3575573 (3 pages) | Cited 8 times

Online Publication Date: 6 April 2011

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InGaN/GaN multiple quantum wells (MQWs) have been studied by using cathodoluminescence hyperspectral imaging with high spatial resolution. Variations in peak emission energies and intensities across trenchlike features and V-pits on the surface of the MQWs are investigated. The MQW emission from the region inside trenchlike features is redshifted by approximately 45 meV and more intense than the surrounding planar regions of the sample, whereas emission from the V-pits is blueshifted by about 20 meV and relatively weaker. By employing this technique to the studied nanostructures it is possible to investigate energy and intensity shifts on a 10 nm length scale.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Depth progression of dissociation reaction of the 1.014-eV photoluminescence copper center in copper-diffused silicon crystal measured by deep-level transient spectroscopy

Minoru Nakamura and Susumu Murakami

Appl. Phys. Lett. 98, 141909 (2011); http://dx.doi.org/10.1063/1.3575574 (3 pages) | Cited 3 times

Online Publication Date: 6 April 2011

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Changes in the concentration depth profiles of the 1.014-eV photoluminescence (PL) copper center and its dissociation product by annealing were measured by deep-level transient spectroscopy (DLTS). The transformation reaction between these centers by annealing was not homogeneous throughout; it started at the sample surface and extended deeper with increasing annealing time. From this finding, the precipitation of interstitial copper in the surface region and its out-diffusion in the bulk are analyzed as the underlying processes to dissociate the center. The origin of the difference in the dissociation energies of the center obtained by DLTS and PL measurements is discussed.
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71.55.Cn Elemental semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.35.Fx Diffusion; interface formation
61.72.jj Interstitials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Role of microstructure in initiation of Ni–Al reactive multilayers

Joshua C. Crone, Jaroslaw Knap, Peter W. Chung, and Betsy M. Rice

Appl. Phys. Lett. 98, 141910 (2011); http://dx.doi.org/10.1063/1.3575576 (3 pages) | Cited 4 times

Online Publication Date: 6 April 2011

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Through molecular dynamics simulations, the effects of microstructure on reaction initiation are studied in nickel-aluminum (Ni–Al) reactive multilayers. Ni–Al multilayer systems of varying misfit strain and layer thickness are created and the ignition temperature is estimated by heating and thermalizing over small temperature increments until a reaction is observed. Results show that ignition temperatures drop significantly with increasing misfit strain. Our results indicate that the sensitivity of reactive multilayers can be controlled, in part, by microstructure, with changes of the order of 350 K.
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68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments

Fabrication and characterization of topological insulator Bi2Se3 nanocrystals

S. Y. F. Zhao, C. Beekman, L. J. Sandilands, J. E. J. Bashucky, D. Kwok, N. Lee, A. D. LaForge, S. W. Cheong, and K. S. Burch

Appl. Phys. Lett. 98, 141911 (2011); http://dx.doi.org/10.1063/1.3573868 (3 pages) | Cited 6 times

Online Publication Date: 6 April 2011

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In the recently discovered class of materials known as topological insulators, the presence of strong spin-orbit coupling causes certain topological invariants in the bulk to differ from their values in vacuum. The sudden change in invariants at the interface results in metallic, time reversal invariant surface states whose properties are useful for applications in spintronics and quantum computation. However, a key challenge is to fabricate these materials on the nanoscale appropriate for devices and probing the surface. To this end we have produced 2 nm thick nanocrystals of the topological insulator Bi2Se3 via mechanical exfoliation. For crystals thinner than 10 nm we observe the emergence of an additional mode in the Raman spectrum. The emergent mode intensity together with the other results presented here provide a recipe for production and thickness characterization of Bi2Se3 nanocrystals.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.-c Methods of micro- and nanofabrication and processing
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
78.30.Hv Other nonmetallic inorganics

Thermal-vacancy-assisted phase transition in FePt thin films

X. H. Li, F. Q. Wang, B. T. Liu, D. F. Guo, and X. Y. Zhang

Appl. Phys. Lett. 98, 141912 (2011); http://dx.doi.org/10.1063/1.3575558 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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Understanding the ordering transition from A1 to L10 structure in FePt thin films is of great significance for developing L10-FePt films as ultrahigh density magnetic recording media. Here, the L10-ordering transition of FePt films has been investigated based on activation volume measurements. A large activation volume ΔV∗ = 10–11 Å3 = (0.75–0.8) Ω, where Ω is average atomic volume of FePt, is determined for atomic diffusions in the L10-ordering transition, indicating a thermal-vacancy-assisted phase transition. This transition is suggested to be predominantly dependent on the diffusion of Fe atoms. These findings have direct implications for yielding L10-FePt films at low temperatures and optimizing their microstructures.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
66.30.Fq Self-diffusion in metals, semimetals, and alloys
75.50.Ss Magnetic recording materials

Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

K. Zhao, X. X. Xia, H. Y. Bai, D. Q. Zhao, and W. H. Wang

Appl. Phys. Lett. 98, 141913 (2011); http://dx.doi.org/10.1063/1.3575562 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2011

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We report a high entropy metallic glass of Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.
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81.05.Kf Glasses (including metallic glasses)
64.70.pe Metallic glasses
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Spontaneous polarization estimation from the soft mode in strain-free epitaxial polar axis-oriented Pb(Zr,Ti)O3 thick films with tetragonal symmetry

Yoshitaka Ehara, Satoru Utsugi, Mitsumasa Nakajima, Tomoaki Yamada, Takashi Iijima, Hiroki Taniguchi, Mitsuru Itoh, and Hiroshi Funakubo

Appl. Phys. Lett. 98, 141914 (2011); http://dx.doi.org/10.1063/1.3575565 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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See Also: Erratum

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The ferroelectric property, crystal structure, and A1(1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal lead zirconate titanate thick films grown on CaF2 substrates were investigated by changing the Zr/(Zr+Ti) ratio and the temperature. The square of spontaneous polarization (Ps), Ps2, monotonically increased as tetragonal distortion, (c/a)−1, increased where a and c are the lattice parameters of the films and as the square of frequency in A1(1TO), ω2[A1(1TO)], increased. Additionally, the relationships of Ps2, (c/a−1), and ω2[A1(1TO)] were experimentally obtained, which confirmed the Ps value obtained from (c/a−1) and ω[A1(1TO)] without direct polarization measurements.
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77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
77.84.Cg PZT ceramics and other titanates
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.80.Dj Domain structure; hysteresis
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Electronic-grade GaN(0001)/Al2O3(0001) grown by reactive DC-magnetron sputter epitaxy using a liquid Ga target

M. Junaid, C.-L. Hsiao, J. Palisaitis, J. Jensen, P. O. Å. Persson, L. Hultman, and J. Birch

Appl. Phys. Lett. 98, 141915 (2011); http://dx.doi.org/10.1063/1.3576912 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2011

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Electronic-grade GaN (0001) epilayers have been grown directly on Al2O3 (0001) substrates by reactive direct-current-magnetron sputter epitaxy (MSE) using a liquid Ga sputtering target in an Ar/N2 atmosphere. The as-grown GaN epitaxial films exhibit low threading dislocation density on the order of ≤ 1010 cm−2 determined by transmission electron microscopy and modified Williamson–Hall plot. X-ray rocking curve shows narrow full-width at half maximum (FWHM) of 1054 arc sec of the 0002 reflection. A sharp 4 K photoluminescence peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. The high structural and optical qualities indicate that MSE-grown GaN epilayers can be used for fabricating high-performance devices without the need of any buffer layer.
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81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors

Manipulating stress in Cu/low-k dielectric nanocomposites

Conal E. Murray, Paul R. Besser, E. Todd Ryan, and Jean L. Jordan-Sweet

Appl. Phys. Lett. 98, 141916 (2011); http://dx.doi.org/10.1063/1.3578192 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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The interaction of x-rays with organic dielectric materials, which alters their mechanical properties, affects values of stress generated within encapsulated Cu structures. In particular, the evolution of stress within submicron Cu interconnect structures encapsulated by an organosilicate glass can be investigated in situ using synchrotron-based x-ray diffraction. The overall geometry of the composite, along with the amount of irradiation, dictates the change in stress of the Cu features. A quantitative comparison of these findings to mechanical modeling results reveals two modes of modification within the dielectric film: a densification that changes the effective eigenstrain followed by an increase in elastic modulus.
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68.60.Bs Mechanical and acoustical properties
62.23.Pq Composites (nanosystems embedded in a larger structure)
62.20.de Elastic moduli
77.55.Bh Low-permittivity dielectric films

Strong luminescence of two-dimensional electron gas in tensile-stressed AlGaN/GaN heterostructures grown on Si substrates

Ki-Won Kim, Dong-Seok Kim, Ki-Sik Im, Jung-Hee Lee, Bong-Joon Kwon, Ho-Sang Kwack, Seol Beck, and Yong-Hoon Cho

Appl. Phys. Lett. 98, 141917 (2011); http://dx.doi.org/10.1063/1.3578399 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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We have investigated the photoluminescence (PL) characteristics of AlGaN/GaN heterostructure with an extremely high two-dimensional electron gas (2DEG) density. A very high 2DEG density was obtained by controlling the tensile stress during the growth of the heterostructure on silicon substrate. Strong PL emission peaks corresponding to both the band edge and the 2DEG were observed in the highly tensile-stressed heterostructure. Furthermore, the strong longitudinal optical (LO) phonon replicas (1-LO2DEG and 2-LO2DEG) of the 2DEG peak were also observed in the heterostructure.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
68.35.Gy Mechanical properties; surface strains
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effect of impurities on thermal stability of pseudomorphically strained Si:C layer

Yao-Teng Chuang, Sheng-Hao Wang, and Wei-Yen Woon

Appl. Phys. Lett. 98, 141918 (2011); http://dx.doi.org/10.1063/1.3572339 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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We investigate the thermal stability of pseudomorphically strained Si:C layer using high resolution x-ray diffraction (HRXRD) and Fourier transform infrared (FTIR) spectroscopy. Far below β-SiC precipitation threshold, almost complete strain relaxation is found without significant substitutional carbon (Csub) loss. FTIR shows the strain relaxation is related to volume compensation by Csub-interstitial complex formation through oxidation injection of interstitial. By multilayer HRXRD kinematical simulation, we find correlation of the enhanced strain relaxation to P distribution, implying P’s role as additional interstitial promoter during postannealing treatment. We relate our findings to recent reports on strain relaxation issues in Si:C devices fabrication.
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71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
81.40.Gh Other heat and thermomechanical treatments

Lattice thermal conductivity of graphene nanoribbons: Anisotropy and edge roughness scattering

Z. Aksamija and I. Knezevic

Appl. Phys. Lett. 98, 141919 (2011); http://dx.doi.org/10.1063/1.3569721 (3 pages) | Cited 10 times

Online Publication Date: 7 April 2011

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We present a calculation of the thermal conductivity of graphene nanoribbons (GNRs), based on solving the Boltzmann transport equation with the full phonon dispersions, a momentum-dependent model for edge roughness scattering, as well as three-phonon and isotope scattering. The interplay between edge roughness scattering and the anisotropy of the phonon dispersions results in thermal conduction that depends on the chiral angle of the nanoribbon. Lowest thermal conductivity occurs in the armchair direction and highest in zig-zag nanoribbons. Both the thermal conductivity and the degree of armchair/zig-zag anisotropy depend strongly on the width of the nanoribbon and the rms height of the edge roughness, with the smallest and most anisotropic thermal conductivities occurring in narrow GNRs with rough edges.
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66.70.Df Metals, alloys, and semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Effect of postgrowth hydrogen treatment on defects in GaNP

D. Dagnelund, X. J. Wang, C. W. Tu, A. Polimeni, M. Capizzi, W. M. Chen, and I. A. Buyanova

Appl. Phys. Lett. 98, 141920 (2011); http://dx.doi.org/10.1063/1.3576920 (3 pages) | Cited 3 times

Online Publication Date: 8 April 2011

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Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment ( ≤ 100 eV H ions). Among them, two defect complexes are identified to contain a Ga interstitial. Possible mechanisms for the H-induced defect activation and creation are discussed. Carrier recombination via these defects is shown to efficiently compete with the near band-edge PL, explaining the observed degraded optical quality of the alloys after the H treatment.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.jj Interstitials
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