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9 Nov 2009

Volume 95, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 95, 193101 (2009); http://dx.doi.org/10.1063/1.3258663 (3 pages)

L. Gaudreau, A. Kam, G. Granger, S. A. Studenikin, P. Zawadzki, and A. S. Sachrajda
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Temperature dependence of ministop band in double-slots photonic crystal waveguides

Kaiyu Cui, Yidong Huang, Gengyan Zhang, Yongzhuo Li, Xuan Tang, Xiaoyu Mao, Qiang Zhao, Wei Zhang, and Jiangde Peng

Appl. Phys. Lett. 95, 191901 (2009); http://dx.doi.org/10.1063/1.3258072 (3 pages) | Cited 5 times

Online Publication Date: 10 November 2009

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We proposed and fabricated a double-slots photonic crystal waveguides (PCWGs) structure formed by introducing two slots into PCWGs with air-bridge structure on silicon-on-insulator substrate. The mode characteristics of double-slots PCWGs were investigated theoretically and experimentally. The transmission spectra present a sharp and deep dip (22 dB with bandwidth of 6 nm) caused by ministop band in the proposed structure, which is 15 dB deeper than that in the W3 PCWG. Additionally, dependence of the dip on temperature in the double-slots PCWG was measured and a temperature coefficient 0.159 nm/°C can be concluded.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques

Arrhenius behavior of hydrocarbon fuel photochemical reaction rates by thermal lens spectroscopy

N. G. C. Astrath, F. B. G. Astrath, J. Shen, J. Zhou, K. H. Michaelian, C. Fairbridge, L. C. Malacarne, P. R. B. Pedreira, P. A. Santoro, and M. L. Baesso

Appl. Phys. Lett. 95, 191902 (2009); http://dx.doi.org/10.1063/1.3258661 (3 pages) | Cited 3 times

Online Publication Date: 10 November 2009

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The temperature dependence of thermo-optical and photochemical reaction properties of hydrocarbon fuels is investigated using thermal lens spectroscopy. We consider the time dependence of the absorption coefficient due to the photoinduced chemical reaction (PCR) and species diffusion to evaluate nonequilibrium characteristics of the samples. The measured temperature dependences of the reaction rates are found to follow the Arrhenius correlation. Experimental results for thermophysical properties of the samples and an analysis of the connection between PCR properties and the chemistry of the samples are also presented.
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89.20.Kk Engineering

Local chemical states and thermal stabilities of nitrogen dopants in ZnO film studied by temperature-dependent x-ray photoelectron spectroscopy

X. H. Li, H. Y. Xu, X. T. Zhang, Y. C. Liu, J. W. Sun, and Y. M. Lu

Appl. Phys. Lett. 95, 191903 (2009); http://dx.doi.org/10.1063/1.3259644 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2009

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Local chemical states and thermal stabilities of N dopants in ZnO:N film are investigated by temperature-dependent x-ray photoelectron spectroscopy. Different types of N local states are detected, including N2 molecules occupying O sites [(N2)O], –NO species, substitutional N atoms in O- and N-rich local environments (α- and β-NO). Compared to the β-NO, the α-NO shows a better thermal stability up to 723 K. However, the transformation from α-NO acceptor to undesirable (N2)O donor occurs above 743 K. The variation of N local states also affects Zn and O binding energies. Photoluminescence studies indicate the shallow acceptor nature of α-NO.
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81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.60.Dv Thermal stability; thermal effects
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
61.50.Lt Crystal binding; cohesive energy
79.60.Dp Adsorbed layers and thin films

Dramatic excitation dependence of strong and stable blue luminescence of ZnO hollow nanoparticles

Haibo Zeng, Shikuan Yang, Xiaoxia Xu, and Weiping Cai

Appl. Phys. Lett. 95, 191904 (2009); http://dx.doi.org/10.1063/1.3263712 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2009

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Strong and stable blue luminescence was obtained from ZnO hollow nanoparticles. Significantly, dramatic excitation dependence was observed for blue emissions of ZnO: (1) band-gap energy (Eg) is the optimal excitation energy but smaller energies are still effective; (2) there exist several fixed emitting wavelengths in blue wave band, such as 412, 439, and 458 nm. These phenomena, combined with previously reported defect levels and formation thermodynamics, point out that the initial states of corresponding transitions to blue emissions could be zinc interstitials-related defect states, which were further verified by subsequent electron paramagnetic resonance examinations.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Nr Semiconductor compounds
71.55.Gs II-VI semiconductors

Photoreflectance and Fourier transform infrared spectroscopy study of intersubband transitions of a ZnxCd1−xSe/Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well structure for quantum cascade laser application

J. D. Wu, C. T. Huang, Y. S. Huang, W. O. Charles, A. Shen, and M. C. Tamargo

Appl. Phys. Lett. 95, 191905 (2009); http://dx.doi.org/10.1063/1.3263951 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2009

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Photoreflectance (PR) and Fourier transform infrared (FTIR) spectroscopy were used to study the intersubband (ISB) transitions of a ZnxCd1−xSe/Znx′Cdy′Mg1−x′−y′Se asymmetric coupled quantum well (ACQW) structure for quantum cascade laser (QCL) application. The PR spectrum revealed a wide range of possible optical transitions in the ACQW structure. A comprehensive analysis of the PR spectrum led to the identification of various interband transitions. The ISB transitions were estimated and confirmed by FTIR absorption measurements. The results demonstrated the use of PR as a complimentary technique to FTIR for the contactless and nondestructive characterization of ACQW structures for QCL application.
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78.30.Fs III-V and II-VI semiconductors
78.67.De Quantum wells
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Size effect on the lattice parameters of nanocrystalline anatase

Md. Imteyaz Ahmad and S. S. Bhattacharya

Appl. Phys. Lett. 95, 191906 (2009); http://dx.doi.org/10.1063/1.3261754 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2009

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Crystallite size dependence on the lattice parameters of nanocrystalline anatase was examined by x-ray diffraction pattern analysis, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The lattice parameter a increased while the parameter c decreased with reducing crystallite sizes. However, the cell volume increased with decreasing crystallite size indicating an overall expansion due to confinement effect. The observed shift in Eg Raman mode (at 144 cm−1) was in accordance with an empirical phonon confinement model while no substoichiometric titania could be detected by XPS. It was concluded that the lattice expansion was purely due to electrostatic relaxation as a result of size confinement.
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61.46.Hk Nanocrystals
63.22.Kn Clusters and nanocrystals
78.30.Hv Other nonmetallic inorganics
79.60.Jv Interfaces; heterostructures; nanostructures
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Giant changes in atomic dynamics on microalloying metallic melt

S. M. Chathoth, B. Damaschke, J. P. Embs, and K. Samwer

Appl. Phys. Lett. 95, 191907 (2009); http://dx.doi.org/10.1063/1.3263950 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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We report unexpectedly strong variations in the relaxational dynamics in a glass-forming metallic melt while microalloying. Analysis of quasielastic neutron scattering data revealed that changes in the values of stretching of the self-correlation function and the temperature dependence of self-diffusivity showed an Arrhenius to non-Arrhenius transition. The intermediate structure of the melts did not show any prepeak or indication of short range order. These observations are correlated with the enhanced glass-forming ability of metallic melts on microalloying.
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66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
64.70.pm Liquids

Study of minority carrier diffusion length in multicrystalline silicon solar cells using photoassisted Kelvin probe force microscopy

Masaki Takihara, Takuji Takahashi, and Toru Ujihara

Appl. Phys. Lett. 95, 191908 (2009); http://dx.doi.org/10.1063/1.3264081 (3 pages) | Cited 6 times

Online Publication Date: 13 November 2009

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We evaluated the minority carrier diffusion length in multicrystalline silicon solar cells by means of photoassisted Kelvin probe force microscopy to investigate the influence of the multicrystalline material grains and the grain boundaries on solar cell performance. We observed a reduction in the diffusion length in the vicinity of the grain boundary and differences in the diffusion lengths between grains even when considering the influence of lateral diffusion.
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88.40.jj Silicon solar cells
61.72.Mm Grain and twin boundaries
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Transformation pathways in the solid-solid phase transitions of iron nanowires

Luis Sandoval and Herbert M. Urbassek

Appl. Phys. Lett. 95, 191909 (2009); http://dx.doi.org/10.1063/1.3258002 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Using molecular dynamics simulations, we study the solid-solid phase transitions induced by strain in Fe nanowires. These show an intricate dependence on the crystallographic orientation of the wire. 〈001〉 oriented nanowires exhibit a bcc→fcc transition and preferably follow the Nishiyama–Wassermann path. In 〈011〉 and 〈111〉 oriented nanowires the transformation is bcc→hcp and proceeds according to the Burgers path. Additionally we show that it is possible to obtain multiple phase transitions accompanied with reorientations.
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64.70.Nd Structural transitions in nanoscale materials
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
64.70.kd Metals and alloys

Practical approach for a rod-connected diamond photonic crystal operating at optical wavelengths

Kanna Aoki

Appl. Phys. Lett. 95, 191910 (2009); http://dx.doi.org/10.1063/1.3264088 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Production of a rod-connected diamond (RCD) photonic crystal structure in a semiconductor material is proposed. Periodic shifting of only one building block can create a complicated three-dimensional network, with a RCD structure exhibiting a full bandgap as wide as 0.20 on a gap/midgap (Δω/ωM) basis. A point defect cavity in the structure sustains single-mode resonance throughout the operative range because of its low symmetry. The resonant mode’s highest quality factor (Q-factor) was calculated as 1.5×104 for a crystal of 11.5ax×4.25ay×12az for ai (i = x,y,z) representing three axes’ period lengths.
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42.70.Qs Photonic bandgap materials

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Sunil Kumar, M. Anija, N. Kamaraju, K. S. Vasu, K. S. Subrahmanyam, A. K. Sood, and C. N. R. Rao

Appl. Phys. Lett. 95, 191911 (2009); http://dx.doi.org/10.1063/1.3264964 (3 pages) | Cited 24 times

Online Publication Date: 13 November 2009

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Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pump-probe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, β of ( ∼ 2–9)×10−8 cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130–330 fs (related to carrier-carrier scattering) followed by a slower one in 3.5–4.9 ps range (associated with carrier-phonon scattering) are observed.
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78.47.J- Ultrafast spectroscopy (<1 psec)
82.70.Kj Emulsions and suspensions
63.20.-e Phonons in crystal lattices
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Water vapor interaction with silicon oxide films thermally grown on 6H-SiC and on Si

G. V. Soares, I. J. R. Baumvol, S. A. Corrêa, C. Radtke, and F. C. Stedile

Appl. Phys. Lett. 95, 191912 (2009); http://dx.doi.org/10.1063/1.3262971 (3 pages) | Cited 3 times

Online Publication Date: 13 November 2009

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Thermally induced incorporation of isotopically labeled water vapor (D2 18O) species in 7 nm thick SiO2 films thermally grown on 6H-SiC(0001) and on Si(001) were investigated. Higher incorporation of hydrogen and higher isotopic exchange were observed in SiO2/SiC as compared to SiO2/Si, at temperatures above 600 °C, which can lead to electrical instabilities, especially in high-temperature devices. At any annealing temperature, oxygen is incorporated in the oxide films, reaching the SiO2/SiC interface, in contrast with SiO2/Si. The present observations show that strict control of water vapor contents in SiO2/SiC is mandatory in order to achieve further improvements in the SiC-based device technology.
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82.20.Tr Kinetic isotope effects including muonium
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
81.40.Gh Other heat and thermomechanical treatments
68.47.Fg Semiconductor surfaces

Robust atomic resolution imaging of light elements using scanning transmission electron microscopy

S. D. Findlay, N. Shibata, H. Sawada, E. Okunishi, Y. Kondo, T. Yamamoto, and Y. Ikuhara

Appl. Phys. Lett. 95, 191913 (2009); http://dx.doi.org/10.1063/1.3265946 (3 pages) | Cited 55 times

Online Publication Date: 13 November 2009

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We show that an annular detector placed within the bright field cone in scanning transmission electron microscopy allows direct imaging of light elements in crystals. In contrast to common high angle annular dark field imaging, both light and heavy atom columns are visible simultaneously. In contrast to common bright field imaging, the images are directly and robustly interpretable over a large range of thicknesses. We demonstrate this through systematic simulations and present a simple physical model to obtain some insight into the scattering dynamics.
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68.37.Ma Scanning transmission electron microscopy (STEM)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
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