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28 Apr 2008

Volume 92, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 92, 173301 (2008); http://dx.doi.org/10.1063/1.2912822 (3 pages)

Takeo Minari, Masataka Kano, Tetsuhiko Miyadera, Sui-Dong Wang, Yoshinobu Aoyagi, Mari Seto, Takashi Nemoto, Seiji Isoda, and Kazuhito Tsukagoshi
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Whisker formation in Sn and Pb–Sn coatings: Role of intermetallic growth, stress evolution, and plastic deformation processes

E. Chason, N. Jadhav, W. L. Chan, L. Reinbold, and K. S. Kumar

Appl. Phys. Lett. 92, 171901 (2008); http://dx.doi.org/10.1063/1.2912528 (3 pages) | Cited 22 times

Online Publication Date: 28 April 2008

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We have simultaneously measured the evolution of intermetallic volume, stress, and whisker density in Sn and Pb–Sn alloy layers on Cu to study the fundamental mechanisms controlling whisker formation. For pure Sn, the stress becomes increasingly compressive and then saturates, corresponding to a plastically deformed region spreading away from the growing intermetallic particles. Whisker nucleation begins after the stress saturates. Pb–Sn layers have similar intermetallic growth kinetics but the resulting stress and whisker density are much less. Measurements after sputtering demonstrate the important role of the surface oxide in inhibiting stress relaxation.
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68.55.at Other materials
81.15.Cd Deposition by sputtering
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Lm Deformation, plasticity, and creep
68.60.Bs Mechanical and acoustical properties
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Theoretical determination of contact angle in quantum dot self-assembly

X. L. Li and G. W. Yang

Appl. Phys. Lett. 92, 171902 (2008); http://dx.doi.org/10.1063/1.2917796 (3 pages) | Cited 9 times

Online Publication Date: 28 April 2008

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We have established an analytic thermodynamic theory to elucidate the evolution of contact angle upon the quantum dot (QD) self-assembly. It is found that the balance between surface energy and elastic relaxation energy plays a crucial role in the determination of contact angle in the heteroepitaxial system. The size-dependent surface energy determines a low contact angle in the QDs with small volume at the initial stage of growth, while the elastic relaxation energy becomes more significant and induces a high contact angle in the QDs with large volume.
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81.16.Dn Self-assembly
68.35.Md Surface thermodynamics, surface energies
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.at Other materials
73.21.La Quantum dots

Electronic structure of a potential optical crystal YBa3B9O18: Experiment and theory

Z. H. Zhang, Jianjun Yang, Ming He, X. F. Wang, and Quan Li

Appl. Phys. Lett. 92, 171903 (2008); http://dx.doi.org/10.1063/1.2918131 (3 pages) | Cited 2 times

Online Publication Date: 28 April 2008

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Using valence electron energy loss spectroscopy and ab initio band structure calculations, we have studied the basic electronic structure of a potential optical crystal YBa3B9O18. Its optical band gap Eg is experimentally estimated as 6.3 eV and the origins of the individual interband transitions have been identified. In addition, the theoretical calculation reveals the strong anisotropic characteristic of the material band structure, accounting for its large birefringence.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
42.70.-a Optical materials

Structural and optical properties of nonpolar GaN thin films

Z. H. Wu, A. M. Fischer, F. A. Ponce, B. Bastek, J. Christen, T. Wernicke, M. Weyers, and M. Kneissl

Appl. Phys. Lett. 92, 171904 (2008); http://dx.doi.org/10.1063/1.2918834 (3 pages) | Cited 25 times

Online Publication Date: 29 April 2008

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A correlation between the structural and optical properties of GaN thin films grown in the [11math0] direction has been established using transmission electron microscopy and cathodoluminescence spectroscopy. The GaN films were grown on an r-plane sapphire substrate, and epitaxial lateral overgrowth was achieved using SiO2 masks. A comparison between the properties of GaN directly grown on sapphire and GaN laterally grown over the SiO2 mask is presented. The densities and dimensions of the stacking faults vary significantly with a high density of short faults in the window region and a much lower density of longer faults in the wing region. The low-temperature luminescence spectra consist of peaks at 3.465 and 3.41 eV, corresponding to emission from donor-bound excitons and basal-plane stacking faults, respectively. A correlation between the structural defects and the light emission characteristics is presented.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.ag Semiconductors
71.35.-y Excitons and related phenomena

Phonon polariton of InN observed by infrared synchrotron radiation

Takashi Inushima, Kazutoshi Fukui, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 92, 171905 (2008); http://dx.doi.org/10.1063/1.2918848 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2008

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Temperature dependence of the reflectivity of InN with a carrier concentration of (3.5–4.7)×1017 cm3 is investigated from 50 to 750 cm−1 using infrared synchrotron radiation. E1 phonon is separately observed from plasma oscillation, and in the energy range below E1(TO), phonon polariton is observed up to 104 cm−1. The lifetime of the E1(TO) phonon is directly determined by the reflectivity measurements. From the temperature dependence of the lifetime, the E1(TO) phonon primarily decays into phonons with a renormalized frequency of 177 cm−1. From the plasma edge position the electron effective mass is estimated to be me⊥ = 0.076m0 for the intrinsic InN.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.20.-e Optical properties of bulk materials and thin films
78.66.Fd III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Indium stability on InGaAs during atomic H surface cleaning

F. S. Aguirre-Tostado, M. Milojevic, C. L. Hinkle, E. M. Vogel, R. M. Wallace, S. McDonnell, and G. J. Hughes

Appl. Phys. Lett. 92, 171906 (2008); http://dx.doi.org/10.1063/1.2919047 (3 pages) | Cited 18 times

Online Publication Date: 30 April 2008

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Atomic H exposure of a GaAs surface at 390 °C is a relatively simple method for removing the native oxides without altering the surface stoichiometry. In-situ reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to show that this procedure applied to In0.2Ga0.8As effectively removes the native oxides resulting in an atomically clean surface. However, the bulk InGaAs stoichiometry is not preserved from this treatment. The In:Ga ratio from the substrate is found to decrease by 33%. The implications for high-mobility channel applications are discussed as the carrier mobility increases nearly linearly with the In content.
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81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors
68.47.Fg Semiconductor surfaces

On the origin of photoluminescence in indium oxide octahedron structures

Mukesh Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh

Appl. Phys. Lett. 92, 171907 (2008); http://dx.doi.org/10.1063/1.2910501 (3 pages) | Cited 19 times

Online Publication Date: 1 May 2008

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A sixfold decrease in photoluminescence signal intensity at 590 nm with increase in deposition time from 3 to 12 h has been observed in single crystalline indium oxide octahedron structures grown by vapor-phase evaporation method. Electron paramagnetic resonance and energy dispersive x-ray analysis confirm that the concentration of oxygen vacancies increases with deposition time. These results are contrary to the previous reports where oxygen vacancies were shown to be responsible for photoluminescence in indium oxide structures. Our results indicate that indium interstitials and their associated complex defects other than oxygen vacancies are responsible for the photoluminescence in In2O3 microstructures.
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78.55.Hx Other solid inorganic materials
81.10.Bk Growth from vapor
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
76.30.-v Electron paramagnetic resonance and relaxation
61.72.jd Vacancies
61.72.jj Interstitials

An optical limiter based on ferrofluids

Swapna S. Nair, Jinto Thomas, C. S. Suchand Sandeep, M. R. Anantharaman, and Reji Philip

Appl. Phys. Lett. 92, 171908 (2008); http://dx.doi.org/10.1063/1.2919052 (3 pages) | Cited 21 times

Online Publication Date: 1 May 2008

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We report an optical limiter based on ferrofluids which has a very high shelf life and remarkable thermal stability, which are important requirements for sustainable use with intense lasers. The colloidal suspensions contain nanosized particles of approximately 80 Å diameter, with a number density of the order of 1022/m3. The nonlinear optical transmission of the samples is studied using nanosecond and femtosecond laser pulses. Excited state absorption phenomena contribute to enhanced limiting in the nanosecond excitation regime. An advantageous feature of ferrofluids in terms of device applications is that their optical properties are controllable by an external magnetic field.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.-e Optical elements, devices, and systems
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.70.Kj Emulsions and suspensions
75.50.Mm Magnetic liquids

Dynamic fracture instability of tough bulk metallic glass

J. X. Meng, Z. Ling, M. Q. Jiang, H. S. Zhang, and L. H. Dai

Appl. Phys. Lett. 92, 171909 (2008); http://dx.doi.org/10.1063/1.2913206 (3 pages) | Cited 15 times

Online Publication Date: 2 May 2008

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We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit.1) bulk metallic glass (BMGs) under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young’s modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.43.Fs Glasses
62.20.M- Structural failure of materials
62.20.de Elastic moduli

Electron effective mean free path and thermal conductivity predictions of metallic thin films

Jae Sik Jin, Joon Sik Lee, and Ohmyoung Kwon

Appl. Phys. Lett. 92, 171910 (2008); http://dx.doi.org/10.1063/1.2917454 (3 pages) | Cited 7 times

Online Publication Date: 2 May 2008

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A simple model of the electron effective mean free path (MFP) in thin metal films is proposed, and the thermal conductivities of aluminum and copper thin films are calculated by solving the Boltzmann transport equation (BTE). In the modeling of the electron effective MFP, the combined contributions of the bulk MFP and the film MFP are taken into account. The proposed effective electron MFP model is incorporated with the gray version of BTE through the “transport” relaxation time. The present model is verified against the experimental thermal conductivity data as a function of the film thickness.
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73.61.At Metal and metallic alloys
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.15.Lh Relaxation times and mean free paths
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Hardening of a metallic glass during cyclic loading in the elastic range

C. E. Packard, L. M. Witmer, and C. A. Schuh

Appl. Phys. Lett. 92, 171911 (2008); http://dx.doi.org/10.1063/1.2919722 (3 pages) | Cited 16 times

Online Publication Date: 2 May 2008

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Although fatigue failure is well documented in metallic glasses, the mechanism responsible for damage accumulation during cyclic loading below the yield point remains elusive. This letter describes a high-resolution nanomechanical study of an Fe-based bulk metallic glass subjected to cyclic loading in the nominal elastic range. An increase in the yield load was observed with an increasing number of subyield loading cycles, providing a clean documentation of kinematic irreversibility in very small volumes of material that experience no shear bands either prior to or during cyclic loading.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.me Fatigue
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

An orthogonal surface phase in semipolar GaN/r-plane sapphire

Kazuhide Kusakabe, Daisuke Terui, Takashi Yamazaki, Iwao Hashimoto, and Kazuhiro Ohkawa

Appl. Phys. Lett. 92, 171912 (2008); http://dx.doi.org/10.1063/1.2917570 (3 pages) | Cited 4 times

Online Publication Date: 2 May 2008

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This paper reports structural characterization on semipolar GaN films grown on r-plane sapphire substrates by metalorganic vapor-phase epitaxy. The polar orientation of semipolar GaN is assigned that the N-polar plane faces the surface side. The epitaxial relationship of the semipolar GaN/r-plane sapphire is determined as [000math]GaN∥[1math13]sapphire and [1math00]GaN∥[1math0math]sapphire. An anomalous phase orthogonal-twisted around the c-axis is revealed by transmission electron microscope, which is almost localized at the surface.
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68.55.-a Thin film structure and morphology
68.37.Og High-resolution transmission electron microscopy (HRTEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
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