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5 Jun 2006

Volume 88, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 233102 (2006); http://dx.doi.org/10.1063/1.2209157 (3 pages)

Zh. M. Wang, J. H. Lee, B. L. Liang, W. T. Black, Vas. P. Kunets, Yu. I. Mazur, and G. J. Salamo
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Quantitative photoacoustic tomography: Recovery of optical absorption coefficient maps of heterogeneous media

Zhen Yuan and Huabei Jiang

Appl. Phys. Lett. 88, 231101 (2006); http://dx.doi.org/10.1063/1.2209883 (3 pages) | Cited 48 times

Online Publication Date: 5 June 2006

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We report on experimental demonstration of photoacoustic tomography for reconstructing the optical absorption coefficient images of heterogeneous media. Photoacoustic images are obtained from a series of tissuelike phantom experiments using a finite element-based reconstruction algorithm coupled with a scanning photoacoustic imaging system. The experimental results show that optical absorption images can be quantitatively reconstructed when the photon diffusion model is coupled with the Helmholtz photoacoustic wave equation.
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87.63.L- Visual imaging
87.63.D- Ultrasonography
87.57.N- Image analysis
43.80.Vj
42.30.Wb Image reconstruction; tomography

Evanescent field on the surface of a negative-index planar lens

Cheng Liu, Changchun Yan, Hao Chen, Ying Liu, and Shumei Gao

Appl. Phys. Lett. 88, 231102 (2006); http://dx.doi.org/10.1063/1.2209885 (3 pages) | Cited 4 times

Online Publication Date: 5 June 2006

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The propagation of the evanescent waves in an imaging system formed by left-handed material (LHM) slab is studied with finite difference time domain method. It was found that four energy-stream loops were formed on the slab interfaces, and the evanescent waves circulated within these loops instead of propagating away along the interfaces, accordingly, they could sustain for remarkably long time after the light source was turned off. Thus, for lossless LHM slab under continuing illumination, the energy of evanescent waves on its interfaces would accumulate with the time, leading to the evanescent wave amplification. This result reveals the back physics of the evanescent wave resonance and amplification, which were used to explain the superimaging with LHM slab, and has the potential to explain some of the contradictories existing in related researches.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Bh Lenses, prisms and mirrors
42.70.-a Optical materials

Low resistance tunnel junctions with type-II heterostructures

N. Suzuki, T. Anan, H. Hatakeyama, and M. Tsuji

Appl. Phys. Lett. 88, 231103 (2006); http://dx.doi.org/10.1063/1.2210082 (3 pages) | Cited 6 times

Online Publication Date: 5 June 2006

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We propose tunnel junctions with type-II heterostructures to reduce the electrical resistance of vertical-cavity surface-emitting lasers. We fabricated the type-II tunnel junctions on GaAs substrates, which consist of highly C-doped GaAsSb on the p side and highly Si-doped InGaAs on the n side. We achieved an extremely low specific resistance of 4×10−6 Ω cm2, which corresponded to a resistance of 20 Ω for an aperture 5 μm in diameter. The specific resistance of the type-II tunnel junction was about 40% smaller than that of the type-I tunnel junction.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Tunable and frequency-stabilized diode laser using temperature-dependent energy pooling fluorescence

Liantuan Xiao, Tao Huang, Lirong Wang, Jianming Zhao, and Suotang Jia

Appl. Phys. Lett. 88, 231104 (2006); http://dx.doi.org/10.1063/1.2210454 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2006

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We have demonstrated a robust method of tuning and stabilizing a diode laser frequency to the fluorescence peaks of the energy pooling occurred at thermal cesium vapor-glass interface. This technique is based on temperature-dependent shift of the two off-core fluorescence peaks caused by 6P3/2+6P3/2→7P(3/2,1/2)/8S1/2+6S1/2 energy pooling collisions. We achieved laser linewidth of 1.1 MHz and continuous tunability over ±200–600 MHz within a temperature range of 360–420 K by applying the wavelength modulation technology. Tunable frequency locking in such a wide range was constructed inexpensively with low laser power. It can also be extended to other wavelengths by using different atomic species.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Transition metal atom heat processing for writing of crystal lines in glass

Tsuyoshi Honma, Yasuhiko Benino, Takumi Fujiwara, and Takayuki Komatsu

Appl. Phys. Lett. 88, 231105 (2006); http://dx.doi.org/10.1063/1.2212272 (3 pages) | Cited 38 times

Online Publication Date: 7 June 2006

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A technique for the writing of crystal line in glass has been developed, in which a continuous-wave Nd:YAG laser (wavelength: λ = 1064 nm) is irradiated to the glasses containing transition metal (TM) ions such as Fe2+, Ni2+, and V4+. Laser energies are absorbed through d-d transitions of TM ions and dissipated to the lattice surrounding TM ions by nonradiative relaxation process, giving the increase in temperature in the laser irradiated region and inducing crystallization. This technique has been demonstrated for the writing of crystal lines consisting of nonlinear optical fresnoite-type Ba2TiGe2O8 and Ba2TiSi2O8 crystals in NiO-, Fe2O3-, and V2O5-doped (0.3–1 mol %) BaO–TiO2–GeO2 and BaO–TiO2–SiO2 glasses. It is confirmed that crystals in the crystal lines are highly oriented along the laser scanning direction. The technique developed in this study is proposed to be called “transition metal atom heat processing.”
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81.05.Kf Glasses (including metallic glasses)
42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions

Dynamics of a growing cell in an optical trap

Giovanni Volpe, Gajendra Pratap Singh, and Dmitri Petrov

Appl. Phys. Lett. 88, 231106 (2006); http://dx.doi.org/10.1063/1.2213015 (3 pages) | Cited 11 times

Online Publication Date: 7 June 2006

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We analyze the forward scattered light from a single optically trapped cell during its growth. We show that the cell continues adjusting itself to the applied optical force because of the growth processes, and hence it keeps changing its orientation in the trap. We point out the importance of taking this variation into account in the interpretation of spectroscopic data. This method can also be used as a means for cell identification and cell sorting.
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87.17.Ee Growth and division
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

All-optical bistable band-edge Bloch modes in a two-dimensional photonic crystal

A. M. Yacomotti, F. Raineri, G. Vecchi, P. Monnier, R. Raj, A. Levenson, B. Ben Bakir, C. Seassal, X. Letartre, P. Viktorovitch, L. Di Cioccio, and J. M. Fedeli

Appl. Phys. Lett. 88, 231107 (2006); http://dx.doi.org/10.1063/1.2207842 (3 pages) | Cited 17 times

Online Publication Date: 8 June 2006

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We demonstrate experimentally all-optical bistable operation in an InP-based two-dimensional photonic crystal slab lying on top of a Bragg reflector. Bistability is obtained around 1550 nm, using a low group velocity mode at the band edge of the photonic dispersion characteristic. The origin of the bistable regime is shown to be the fast (275 ps relaxation time), electronically induced nonlinear refraction index. A low intensity threshold of 4 kW/cm2 was observed, with a contrast of 65% between the high and low reflectivity states.
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42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors

Single mode cw operation of 658 nm AlGaInP lasers based on longitudinal photonic band gap crystal

I. I. Novikov, L. Ya. Karachinsky, M. V. Maximov, Yu. M. Shernyakov, S. M. Kuznetsov, N. Yu. Gordeev, V. A. Shchukin, P. S. Kop’ev, N. N. Ledentsov, U. Ben-Ami, V. P. Kalosha, A. Sharon, T. Kettler, K. Posilovic, D. Bimberg, et al.

Appl. Phys. Lett. 88, 231108 (2006); http://dx.doi.org/10.1063/1.2211948 (3 pages) | Cited 7 times

Online Publication Date: 8 June 2006

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GaInP–AlGaInP lasers with broad waveguide based on a longitudinal photonic band gap crystal have been studied. Lasers with 10 μm stripe width exhibit single transverse mode operation. The vertical beam divergence is about 8° and is insensitive to the drive current. The aspect ratio is ∼ 2:1. The quality factor for the lateral beam M2 is less than 2 in single mode regime under pulsed excitation. The total maximum continuous wave output power in the single mode regime at 20 °C is more than 115 mW (for high reflection/antireflection facet coatings), indicating a dramatic reduction in the catastrophic optical mirror damage problem.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Concentration evaluation method using broadband absorption spectroscopy for sulfur dioxide monitoring

F. Xu, Z. Lv, Y. G. Zhang, G. Somesfalean, and Z. G. Zhang

Appl. Phys. Lett. 88, 231109 (2006); http://dx.doi.org/10.1063/1.2211299 (3 pages) | Cited 16 times

Online Publication Date: 9 June 2006

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We report on an approach for sulfur dioxide monitoring using broadband absorption spectroscopy in the ultraviolet spectral range. The method was applied in real-time measurements and has the advantage of straightforward data evaluation, limited susceptibility for interference from other gases, and low degree of complexity compared with other real-time optical detection techniques having the same precision. Concentration measurement is demonstrated at atmospheric pressure, which is of interest for pollution emission monitoring, yielding a detection limit of about 1 ppm with 3 s integration time. Comparison is made with low pressure measurements for validation of the accuracy of the method.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
92.60.Sz Air quality and air pollution
82.80.-d Chemical analysis and related physical methods of analysis
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Integrated non-SO2 underlayer and improved line-edge-roughness dielectric etch process using 193 nm bilayer resist

Parijat Bhatnagar, Siddhartha Panda, Nikki L. Edleman, Scott D. Allen, Richard Wise, and Arpan Mahorowala

Appl. Phys. Lett. 88, 231501 (2006); http://dx.doi.org/10.1063/1.2210086 (2 pages) | Cited 6 times

Online Publication Date: 6 June 2006

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We present an integrated reactive ion etch (RIE) process using bilayer (a top imaging layer and a bottom underlayer) thin film imaging system to push the limits of 193 nm wavelength photolithography. Minimizing the line-edge roughness (LER) and maintaining the critical dimension (CD) of the transferred pattern are important in high-resolution RIE. Along with LER and CD issues and shrinking ground rules, deleterious effects of SO2 in the underlayer etch chemistry necessitated the development of non-SO2 chemistry. Thus a N2–H2–CO chemistry was developed and integrated with the etch process of underlying borophosphosilicate glass using Ar–O2–C4F8–CO–CH3F chemistry.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Fuel gas production by microwave plasma in liquid

Shinfuku Nomura, Hiromichi Toyota, Michinaga Tawara, Hiroshi Yamashita, and Kenya Matsumoto

Appl. Phys. Lett. 88, 231502 (2006); http://dx.doi.org/10.1063/1.2210448 (3 pages) | Cited 16 times

Online Publication Date: 7 June 2006

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We propose to apply plasma in liquid to replace gas-phase plasma because we expect much higher reaction rates for the chemical deposition of plasma in liquid than for chemical vapor deposition. A reactor for producing microwave plasma in a liquid could produce plasma in hydrocarbon liquids and waste oils. Generated gases consist of up to 81% hydrogen by volume. We confirmed that fuel gases such as methane and ethylene can be produced by microwave plasma in liquid.
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52.77.Dq Plasma-based ion implantation and deposition
52.50.Dg Plasma sources
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Plasma treatment of diamond nanoparticles for dispersion improvement in water

Qingsong Yu, Young Jo Kim, and Hongbin Ma

Appl. Phys. Lett. 88, 231503 (2006); http://dx.doi.org/10.1063/1.2208279 (3 pages) | Cited 9 times

Online Publication Date: 9 June 2006

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Low-temperature plasmas of methane and oxygen mixtures were used to treat diamond nanoparticles to modify their surface characteristics and thus improve their dispersion capability in water. It was found that the plasma treatment significantly reduced water contact angle of diamond nanoparticles and thus rendered the nanoparticles with strong water affinity for dispersion enhancement in polar media such as water. Surface analysis using Fourier transform infrared spectroscopy confirmed that polar groups were imparted on nanoparticle surfaces. As a result, improved suspension stability was observed with plasma treated nanoparticles when dispersed in water.
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52.77.Dq Plasma-based ion implantation and deposition
82.35.Np Nanoparticles in polymers
81.05.U- Carbon/carbon-based materials
68.03.Cd Surface tension and related phenomena
78.35.+c Brillouin and Rayleigh scattering; other light scattering
82.70.Kj Emulsions and suspensions
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Dependence of the IR reflectance LO absorption bands on the crystalline texture of AlN films

E. Iborra, M. Clement, L. Vergara, A. Sanz-Hervás, J. Olivares, and J. Sangrador

Appl. Phys. Lett. 88, 231901 (2006); http://dx.doi.org/10.1063/1.2209205 (3 pages) | Cited 5 times

Online Publication Date: 5 June 2006

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The infrared reflectance spectra of polycrystalline sputtered AlN films are analyzed in relation to their crystalline texture. AlN films with perfect c-axis orientation and good piezoelectric response exhibit a single peak at 887 cm−1 corresponding to the A1–longitudinal-optical (LO) vibrational mode. However, {0001}-textured films with traces of 10math1, 10math2, and 10math3 reflections in their x-ray diffraction patterns show an additional peak at 905 cm−1 that we assign to an E1-A1 quasi-LO mode due to interaction of light with non-⟨0001⟩-oriented grains. The piezoelectric response deteriorates as the amplitude of the quasi-LO mode increases with respect to the A1(LO) mode.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films

Long wavelength emitting InAs/Ga0.85In0.15NxAs1−x quantum dots on GaAs substrate

M. Richter, B. Damilano, J.-Y. Duboz, J. Massies, and A. D. Wieck

Appl. Phys. Lett. 88, 231902 (2006); http://dx.doi.org/10.1063/1.2209879 (3 pages) | Cited 15 times

Online Publication Date: 5 June 2006

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InAs quantum dots (QDs) overgrown by a Ga0.85In0.15NxAs1−x (0 ⩽ x ⩽ 0.017) layer have been realized on GaAs substrate by molecular beam epitaxy. When the nitrogen composition increases, the photoluminescence (PL) wavelength redshifts up to 1.52 μm. It is shown that PL properties of InAs/Ga0.85In0.15N0.012As0.988 QDs are improved by thermal annealing. Finally, 1.45 μm PL emission with a 38.5 meV full width at half maximum is obtained at room temperature.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing

Detection of explosive materials by differential reflection spectroscopy

Rolf E. Hummel, Anna M. Fuller, Claus Schöllhorn, and Paul H. Holloway

Appl. Phys. Lett. 88, 231903 (2006); http://dx.doi.org/10.1063/1.2210077 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2006

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It is shown that traces of 2,4,6-trinitrotoluene (TNT) display strong and distinct structures in differential reflectograms, near 420 and 250 nm. These characteristic peaks are not observed from moth balls, nail polish, polyvinyl chloride, starch, soap, paper, epoxy, aspirin, polycarbonate, aspartame, polystyrene, polyester, fertilizer, or sugar, to mention a few substances which may be in or on a suitcase. The described technique for detection of TNT is fast, inexpensive, reliable, and portable and does not require contact with the surveyed substance. Moreover, we have developed a curve recognition program for field applications of the technique. The origin of the spectra is discussed.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.20.-e Optical properties of bulk materials and thin films

Electronic structure and energetics of the quaternary hydride Li4BN3H10

J. F. Herbst and L. G. Hector

Appl. Phys. Lett. 88, 231904 (2006); http://dx.doi.org/10.1063/1.2210083 (3 pages) | Cited 17 times

Online Publication Date: 6 June 2006

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Li4BN3H10 has been synthesized recently from LiNH2/LiBH4 mixtures and its crystal structure determined. We have calculated the electronic structure of this complex hydride and investigated its thermodynamic stability and decomposition energetics. We find that its enthalpy of formation is −708 kJ/mole with respect to the elemental constituents and −8 kJ/mole relative to a 3:1 molar LiNH2/LiBH4 mixture, in qualitative agreement with experiment. Reaction enthalpies computed for several decomposition pathways suggest Li4BN3H10→Li3BN2+½Li2NH+½NH3+4H2 as the likely dehydriding route.
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71.20.Ps Other inorganic compounds
61.66.Fn Inorganic compounds
64.75.-g Phase equilibria
82.60.Cx Enthalpies of combustion, reaction, and formation
65.40.-b Thermal properties of crystalline solids

Inversion domain boundaries and phase separation in p-AlGaN layers with high Al contents

Hyung Koun Cho, Bo Hyun Kong, Z. Ren, J. Han, and S.-R. Jeon

Appl. Phys. Lett. 88, 231905 (2006); http://dx.doi.org/10.1063/1.2210450 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2006

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The effect of Mg incorporation and Al composition on the formation of inversion domain boundaries (IDBs) and self-assembled superlattices in Mg-doped p-AlxGa1−xN epilayers grown on undoped Al0.3Ga0.7N was investigated by transmission electron microscopy. The formation, initiating position, and shape of the faceted IDBs strongly depended on the Mg and Al contents. Horizontally well-aligned self-assembled superlattices with large composition modulation by phase separation were also observed in the Mg-doped p-AlGaN before the formation of the faceted IDBs. The periodicity of the modulation obtained from the diffused streaks is ∼ 40 Å.
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68.65.Cd Superlattices
64.75.-g Phase equilibria
68.37.Lp Transmission electron microscopy (TEM)

Microstructure of relaxed InN quantum dots grown on GaN buffer layers by molecular-beam epitaxy

Lin Zhou, Tao Xu, David J. Smith, and T. D. Moustakas

Appl. Phys. Lett. 88, 231906 (2006); http://dx.doi.org/10.1063/1.2205166 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2006

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Electron microscopy has been used to characterize the microstructure of InN quantum dots (QDs) grown by molecular-beam epitaxy on GaN(0001)/AlN(0001)/sapphire substrates at 425 °C under slightly group III-rich conditions. Observations in plan-view and cross-section geometries established that the large majority of the InN QDs were invariably associated with threading dislocations in the underlying GaN buffer layer having edge components. Periodic, primarily hexagonal, arrays of misfit dislocations separated by ∼ 2.8 nm were observed at the InN QD/GaN interface, indicating that the QDs were almost completely relaxed. No evidence for an InN wetting layer was obtained either in situ by reflection high-energy electron diffraction or ex situ by transmission electron microscopy.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Strong photoluminescence at 1.3 μm with a narrow linewidth from nitridized InAs/GaAs quantum dots

Y. D. Jang, N. J. Kim, J. S. Yim, D. Lee, S. H. Pyun, W. G. Jeong, and J. W. Jang

Appl. Phys. Lett. 88, 231907 (2006); http://dx.doi.org/10.1063/1.2210789 (3 pages)

Online Publication Date: 7 June 2006

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Nitridized quantum dots (QDs) were prepared by metal-organic chemical vapor deposition. These QDs all showed strong photoluminescence (PL) emission at 1.3 μm at room temperature, narrow spectral widths of 30 meV, and large separations of 98 meV between the ground and first excited states. Interestingly, the PL peak positions of the nitridized QDs were all around 1.3 μm, despite the QDs having been prepared using significantly different amounts of nitrogen. Time-resolved PL revealed no electronic coupling between the QDs. These properties could potentially make these nitridized QDs very useful candidates for the fabrication of devices emitting at 1.3 μm.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Achievement of alternative amorphous AlAs/crystalline AlGaAs multilayers

Hao Wang, Changjun Liao, Shuwen Zheng, and Songhao Liu

Appl. Phys. Lett. 88, 231908 (2006); http://dx.doi.org/10.1063/1.2210790 (3 pages)

Online Publication Date: 7 June 2006

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A hybrid multilayer, composed of ten period amorphous AlAs/crystalline GaAlAs stacks, is realized by metalorganic chemical vapor deposition method on a GaAs substrate. Cross-sectional transmission electron microscopy shows the presence of sharp amorphous/crystalline interfaces. The electron diffraction patterns reveal the coexistence of both amorphous and crystalline phases and the perfect coherence of atom arrows between substrate and crystalline AlGaAs layers was also demonstrated. Perfect crystalline AlGaAs quality was further confirmed by x-ray rocking curves. The potential application of such hybrid multilayers is discussed and its behavior as a Bragg reflector is explored with a stop band gap of 75% reflectance.
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68.65.Ac Multilayers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Diffusion of adatom in the selective epitaxial growth of Si(100): A molecular dynamics study

Gun-Do Lee, Sukwon Hong, Hyun-Woo Kim, and Euijoon Yoon

Appl. Phys. Lett. 88, 231909 (2006); http://dx.doi.org/10.1063/1.2210971 (3 pages)

Online Publication Date: 8 June 2006

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Tight-binding molecular dynamics simulation is performed for a Si adatom on the surface containing the {311} facet and the Si(100) surface to reproduce and explain the behavior of the {311} facet in the selective epitaxial growth of Si(100). In the simulation the adatom is observed to diffuse from the {311} facet to the Si(100) surface along the pathway of a trough between the dimer rows on Si(100) surface. By the tight-binding total energy calculation, it is also clarified that adatoms easily diffuse to the Si(100) surface because, after the adatom surmounts the first energy barrier to diffuse to the step edge near the {311} facet, there is no additional Schwoebel barrier and the other energy barriers gradually decrease to the top of the dimer row of Si(100). The pathway of the trough between dimer rows on the Si(100) surface is found to be energetically more favorable than the direct pathway to the dimer row from the tight-binding total energy calculation. Our tight-binding molecular dynamics simulation elucidates the mechanism responsible for the behavior of the {311} facet in the selective epitaxial growth of Si(100).
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68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology

First principles study of CdSe quantum dots: Stability, surface unsaturations, and experimental validation

M. Yu, G. W. Fernando, R. Li, F. Papadimitrakopoulos, N. Shi, and R. Ramprasad

Appl. Phys. Lett. 88, 231910 (2006); http://dx.doi.org/10.1063/1.2209195 (3 pages) | Cited 15 times

Online Publication Date: 9 June 2006

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Ab initio computational studies were performed for CdSe nanocrystals over a wide range of sizes and topologies. Substantial relaxations and coordination of surface atoms were found to play a crucial role in determining the nanocrystal stability and optical properties. While optimally (threefold) coordinated surface atoms resulted in stable closed-shell structures with large optical gaps, suboptimal coordination gave rise to lower stability and negligible optical gaps. These computations are in qualitative agreement with recent chemical etching experiments suggesting that closed-shell nanocrystals contribute strongly to photoluminescence quantum yield while clusters with nonoptimal surface coordination do not.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations
73.22.-f Electronic structure of nanoscale materials and related systems
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
61.46.Hk Nanocrystals

Dislocations in nanocrystalline grains

Xiao-Lei Wu and En Ma

Appl. Phys. Lett. 88, 231911 (2006); http://dx.doi.org/10.1063/1.2210295 (3 pages) | Cited 33 times

Online Publication Date: 9 June 2006

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Dislocation behavior inside the very small grains of nanocrystalline metals has so far eluded high-resolution transmission electron microscopy (TEM) examinations. We have identified full dislocations using high-resolution TEM, and the different ways they reside in the 20–30 nm Ni grains. The thermally activated propagation of dislocations, their interactions with twin/grain boundaries and dislocation loops, as well as their storage in nanocrystalline grains are demonstrated and discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.46.Hk Nanocrystals
68.37.Lp Transmission electron microscopy (TEM)
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Mm Grain and twin boundaries
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Exciton dissociation at the indium tin oxide-N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine interface: A transient photovoltage study

Q. L. Song, H. R. Wu, X. M. Ding, X. Y. Hou, F. Y. Li, and Z. G. Zhou

Appl. Phys. Lett. 88, 232101 (2006); http://dx.doi.org/10.1063/1.2209203 (3 pages) | Cited 16 times

Online Publication Date: 5 June 2006

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Transient photovoltage measured from the device of indium tin oxide (ITO)/N,N′-Bis(naphthalene-1-yl)-N,N′-bis(phenyl) benzidine (NPB) (600 nm)/Al (Al grounded) exhibits an abnormal polarity change from negative to positive upon pulsed laser irradiation. A simple model including interfacial exciton dissociation is proposed to describe the phenomenon observed. The initial negative signal is interpreted as a result of more electrons than holes injected into ITO by dissociation of excitons at the ITO-NPB interface, and the subsequent positive signal can be attributed to carrier separation by the built-in field in NPB. Further experiments confirm that it is the combination of interfacial exciton dissociation and built-in field that determines the polarity of the transient photovoltage. The amount of excitons dissociated at the ITO-NPB interface is much larger than that of free carriers created in other processes, with the ratio in the order of 103 for the device studied.
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71.35.-y Excitons and related phenomena
73.40.-c Electronic transport in interface structures
72.40.+w Photoconduction and photovoltaic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Pb-for-Bi substitution for enhancing thermoelectric characteristics of [(Bi,Pb)2Ba2O4±ω]0.5CoO2

K. Sakai, M. Karppinen, J. M. Chen, R. S. Liu, S. Sugihara, and H. Yamauchi

Appl. Phys. Lett. 88, 232102 (2006); http://dx.doi.org/10.1063/1.2206134 (3 pages) | Cited 4 times

Online Publication Date: 5 June 2006

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Show Abstract
We report strongly enhanced thermoelectric characteristics for a misfit-layered oxide, [Bi2Ba2O4±ω]0.5CoO2, in a wide temperature range, as achieved through substituting up to 20% of Bi by Pb. The Pb substitution kept the thermal conductivity (κ) unchanged but decreased the electrical resistivity (ρ) and increased the Seebeck coefficient (S) simultaneously, such that a three-fold enhancement in the thermoelectric figure of merit, Z ( ≡ S2/ρκ), was realized. At the same time x-ray absorption near-edge structure data indicated that the valence and spin states of Co are not affected by the Pb-for-Bi substitution.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.70.Dm X-ray absorption spectra
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