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8 Dec 2008

Volume 93, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 93, 231101 (2008); http://dx.doi.org/10.1063/1.3040686 (3 pages)

Mads Brøkner Christiansen, Anders Kristensen, Sanshui Xiao, and Niels Asger Mortensen
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Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films

D. D’Angelo, L. Romano, I. Crupi, E. Carria, V. Privitera, and M. G. Grimaldi

Appl. Phys. Lett. 93, 231901 (2008); http://dx.doi.org/10.1063/1.3036899 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2008

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Solid phase epitaxial regrowth (SPER) of p-doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p- and n-type doping. We introduced a charged defect, whose energy level is independent of the dopant species.
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81.15.Np Solid phase epitaxy; growth from solid phases
61.72.sd Impurity concentration
71.55.Cn Elemental semiconductors
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Analysis on the mechanism of photoluminescence quenching in π-conjugated polymers in photo-oxidation process with broadband transient grating

Ying-hui Wang, Ya-jing Peng, Yue-qi Mo, Yan-qiang Yang, and Xian-xu Zheng

Appl. Phys. Lett. 93, 231902 (2008); http://dx.doi.org/10.1063/1.3045953 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2008

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Photoinduced oxidation process of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] is probed by using broadband transient grating technique. The results suggest that the damage of bonds in the side and main chains leads to the line shape variation and efficiency decreasing of luminescence in photoluminescence quenching, and their temporal evolution and damage rates are found to vary with molecular energy states.
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78.55.Kz Solid organic materials
81.65.Mq Oxidation
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Infrared analysis of hole properties of Mg-doped p-type InN films

Masayuki Fujiwara, Yoshihiro Ishitani, Xinqiang Wang, Song-Bek Che, and Akihiko Yoshikawa

Appl. Phys. Lett. 93, 231903 (2008); http://dx.doi.org/10.1063/1.3006052 (3 pages) | Cited 15 times

Online Publication Date: 9 December 2008

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Mg-doped InN films grown by plasma-assisted molecular beam epitaxy were characterized by infrared reflectance. Signatures of p-type conductivity in the spectra were obtained in the same doping density range where the existence of net acceptors was found by electrolyte capacitance-voltage measurements. Numerical spectrum analysis, which takes into account the large broadening factor of the normal mode energies of longitudinal optical phonon–plasmon coupling yielded high hole densities in the range of (0.1–1.2)×1019 cm−3 and optical mobilities in the range of 25–70 cm2/V s.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
63.20.kk Phonon interactions with other quasiparticles
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Single quantum dot emission by nanoscale selective growth of InAs on GaAs: A bottom-up approach

F. Patella, F. Arciprete, E. Placidi, M. Fanfoni, A. Balzarotti, A. Vinattieri, L. Cavigli, M. Abbarchi, M. Gurioli, L. Lunghi, and A. Gerardino

Appl. Phys. Lett. 93, 231904 (2008); http://dx.doi.org/10.1063/1.3040327 (3 pages) | Cited 3 times

Online Publication Date: 10 December 2008

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We report on single dot microphotoluminescence (μPL) emission at low temperature and low power from InAs dots grown by molecular beam epitaxy in nanoscale holes of a SiO2 mask deposited on GaAs(001). By comparing atomic force microscopy measurements with μPL data, we show that the dot sizes inside the nanoholes are smaller than those of the dots nucleated on the extended GaAs surface. PL of dots spans a wide energy range depending on their size and on the thickness and composition of the InGaAs capping layer. Time-resolved PL experiments demonstrate a negligible loss of radiative recombination efficiency, proving highly effective in the site-controlled dot nucleation.
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68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.47.jd Time resolved luminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Terahertz electromagnetic interference shielding using single-walled carbon nanotube flexible films

M. A. Seo, J. H. Yim, Y. H. Ahn, F. Rotermund, D. S. Kim, S. Lee, and H. Lim

Appl. Phys. Lett. 93, 231905 (2008); http://dx.doi.org/10.1063/1.3046126 (3 pages) | Cited 12 times

Online Publication Date: 10 December 2008

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We performed time-domain terahertz spectroscopy on thin layers of single-walled carbon nanotubes (SWCNTs) coated on flexible films. The SWCNT layers demonstrate good shielding of electromagnetic waves in the terahertz range while maintaining good transparency for visible light. The shielding efficiency can be engineered through the thickness control and/or chemical treatment of SWCNT layers. The frequency-dependent dielectric constants of SWCNT layers are in good agreement with the Drude free-electron model.
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78.67.Ch Nanotubes
81.07.De Nanotubes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Real-time acoustic emission testing based on wavelet transform for the failure process of thermal barrier coatings

L. Yang, Y. C. Zhou, W. G. Mao, and C. Lu

Appl. Phys. Lett. 93, 231906 (2008); http://dx.doi.org/10.1063/1.3043458 (3 pages) | Cited 8 times

Online Publication Date: 10 December 2008

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The fracture type differentiation, quantification, and source identification are desirable and yet intractable in the acoustic emission (AE) testing of a complex coating system. In this letter, a technique combining wavelet transform and conventional AE parameter analysis was developed to study the tensile failure process of thermal barrier coatings in real time. It is demonstrated that the failure of thermal barrier coatings originates from surface vertical cracking and follows interface cracking, and that the AE count increases with tensile load following a power law. The cracking source identified from AE signals agrees well with that observed by optical microscopy. This technique provides a powerful tool for the study of failure processes of a wide range of coatings and thin films.
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68.60.Bs Mechanical and acoustical properties
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.mt Cracks
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Uniform InGaAs quantum dot arrays fabricated using nanosphere lithography

X. Qian, J. Li, D. Wasserman, and W. D. Goodhue

Appl. Phys. Lett. 93, 231907 (2008); http://dx.doi.org/10.1063/1.3040683 (3 pages) | Cited 12 times

Online Publication Date: 11 December 2008

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We demonstrate the fabrication of optically active uniform InGaAs quantum dot arrays by combining nanosphere lithography and bromine ion-beam-assisted etching on a single InGaAs/GaAs quantum well. A wide range of lateral dot sizes was achieved from an oxygen plasma nanosphere resizing process. The increased lateral confinement of carriers in the dots results in low temperature photoluminescence blueshifts from 0.5 to 11 meV. Additional quantization was achieved using a selective wet-etch process. Our model suggests the presence of a 70 nm dead layer in the outer InGaAs radial edge, which we believe to be a result of defects and dislocations introduced during the dry-etch process.
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81.16.Nd Micro- and nanolithography
78.67.De Quantum wells
78.67.Hc Quantum dots
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.15.Jj Ion and electron beam-assisted deposition; ion plating
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Effects of disorder and scaling of optical conductivity in Nd0.5Ca0.5−xBaxMnO3 (x = 0 and 0.02) thin films as observed by terahertz time-domain spectroscopy

K. R. Mavani, M. Nagai, D. S. Rana, H. Yada, I. Kawayama, M. Tonouchi, and K. Tanaka

Appl. Phys. Lett. 93, 231908 (2008); http://dx.doi.org/10.1063/1.3041638 (3 pages) | Cited 5 times

Online Publication Date: 11 December 2008

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We have explored the low energy charge dynamics of charge-ordered Nd0.5Ca0.5MnO3 and Ba-doped Nd0.5Ca0.48Ba0.02MnO3 manganite thin films by recording the complex optical spectra using terahertz time-domain spectroscopy. The extracted frequency- and temperature-dependent optical conductivity (σ) and dielectric constant (ε1) show distinct features at Néel’s ordering and the charge-ordering temperatures (TN and TCO). We found that the Ba-doping induced cation disorder effects on σ and ε1 are more pronounced above TCO, but these effects are subtle in a large temperature region below TCO. Both ε1 and σ increase as a function of temperature and form a scaling relationship ε1∝σ.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
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Bandgap engineering by tuning particle size and crystallinity of SnO2–Fe2O3 nanocrystalline composite thin films

M. B. Sahana, C. Sudakar, G. Setzler, A. Dixit, J. S. Thakur, G. Lawes, R. Naik, V. M. Naik, and P. P. Vaishnava

Appl. Phys. Lett. 93, 231909 (2008); http://dx.doi.org/10.1063/1.3042163 (3 pages) | Cited 17 times

Online Publication Date: 11 December 2008

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We report the structural and optical properties of xSnO2–yFe2O3 nanocrystalline composite thin films. SnO2 and Fe2O3 exhibit strong phase separation instability and their particle size and crystallinity are tunable by changing their composition and annealing temperature. The bandgap for these composites continuously increases from 2.3 to 3.89 eV. We discuss the increasing bandgap values in terms of the quantum confinement effect manifested by the decreasing size of Fe2O3 crystallites. The method provides a generic approach for the tuning of the bandgap in nanocomposite systems.
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61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.-f Electronic structure of nanoscale materials and related systems
64.75.Jk Phase separation and segregation in nanoscale systems
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Measurement and evaluation of the interfacial thermal resistance between a metal and a dielectric

Heng-Chieh Chien, Da-Jeng Yao, and Cheng-Ting Hsu

Appl. Phys. Lett. 93, 231910 (2008); http://dx.doi.org/10.1063/1.3039806 (3 pages) | Cited 6 times

Online Publication Date: 11 December 2008

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We used a sandwiched film structure of dielectric, metal, and dielectric to measure and also to estimate theoretically the metal-dielectric interfacial thermal resistance. In this structure, a metal layer with a thickness of about 10 nm, including chromium, titanium, aluminum, nickel, and platinum, is sandwiched between two SiO2 layers with a thickness of 100 nm prepared by plasma enhanced chemical vapor deposition. The estimates, 10−10–10−9 m2 K W−1, calculated with a continuum two-fluid model are significantly smaller than the measured values, ∼ 10−8 m2 K W−1. The continuum two-fluid model, according to the phenomena of electron-phonon nonequilibrium near the interface in a metal, cannot explain completely the cause of this metal-dielectric interfacial thermal resistance. From photographs of the transmission electron microscopy cross section, we argue that defects at an interface likely play an important role in the magnitude of the interfacial thermal resistance.
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73.40.Ns Metal-nonmetal contacts
77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.jd Thickness
71.38.-k Polarons and electron-phonon interactions
63.20.kd Phonon-electron interactions
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Residual strain in nonpolar a-plane Zn1−xMgxO (0<x<0.55) and its effect on the band structure of (Zn,Mg)O/ZnO quantum wells

J.-M. Chauveau, J. Vives, J. Zuniga-Perez, M. Laügt, M. Teisseire, C. Deparis, C. Morhain, and B. Vinter

Appl. Phys. Lett. 93, 231911 (2008); http://dx.doi.org/10.1063/1.3046783 (3 pages) | Cited 13 times

Online Publication Date: 12 December 2008

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We investigate the dependence on Mg content of the lattice parameters and the surface morphology of nonpolar a-(11math0) Zn1−xMgxO (x ≤ 0.55) grown by molecular beam epitaxy. The anisotropy of the lattice parameters gives rise to an unusual in-plane strain state in the ZnO QWs: tensile strain along [1math00] and compressive strain along [0001]. For a Zn0.6Mg0.4O barrier, the strain in a ZnO QW reaches −1.3% along [0001] and +0.3% along [1math00]. This induces a strong blueshift of the excitonic transitions, in addition to the confinement effects, which we observe in photoluminescence excitation experiments.
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73.21.Fg Quantum wells
68.35.bg Semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
78.55.Et II-VI semiconductors
78.67.De Quantum wells
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Invariant critical stress for shear banding in a bulk metallic glass

Z. Han, H. Yang, W. F. Wu, and Y. Li

Appl. Phys. Lett. 93, 231912 (2008); http://dx.doi.org/10.1063/1.3048869 (3 pages) | Cited 6 times

Online Publication Date: 12 December 2008

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Through uncovering the macroscopic true stress after correction with the instant load-bearing area, we found that the critical stress for continuous shear banding of a bulk metallic glass (BMG) maintains invariant on and after yielding as the plastic deformation progresses. This finding is in strong contrast with the previous reports of either “strain hardening” or “strain softening” associated with the plastic deformation of BMGs. Our results point out that atomic cohesive energy constantly serves to be the controlling factor of the critical stress for shear banding.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
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