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31 Jan 2011

Volume 98, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 053101 (2011); http://dx.doi.org/10.1063/1.3549154 (3 pages)

Minggang Zeng, Lei Shen, Ming Yang, Chun Zhang, and Yuanping Feng
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Generation of correlated photon pairs in a chalcogenide As2S3 waveguide

C. Xiong, G. D. Marshall, A. Peruzzo, M. Lobino, A. S. Clark, D.-Y. Choi, S. J. Madden, C. M. Natarajan, M. G. Tanner, R. H. Hadfield, S. N. Dorenbos, T. Zijlstra, V. Zwiller, M. G. Thompson, J. G. Rarity, et al.

Appl. Phys. Lett. 98, 051101 (2011); http://dx.doi.org/10.1063/1.3549744 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2011

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We demonstrate a 1550 nm correlated photon-pair source in an integrated glass platform—a chalcogenide As2S3 waveguide. A measured pair coincidence rate of 80 s−1 was achieved using 57 mW of continuous-wave pump. The coincidence to accidental ratio was shown to be limited by spontaneous Raman scattering effects that are expected to be mitigated by using a pulsed pump source.
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42.79.Gn Optical waveguides and couplers
42.50.-p Quantum optics
61.43.Fs Glasses
78.30.Hv Other nonmetallic inorganics

Light absorption in textured thin film silicon solar cells: A simple scalar scattering approach versus rigorous simulation

C. Rockstuhl, S. Fahr, F. Lederer, F.-J. Haug, T. Söderström, S. Nicolay, M. Despeisse, and C. Ballif

Appl. Phys. Lett. 98, 051102 (2011); http://dx.doi.org/10.1063/1.3549175 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2011

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Rigorous diffraction theory is a reliable tool to quantify the absorption enhancement in textured thin film solar cells. We provide a line of arguments that make the insights from such an involved analysis accessible to a broader community by using a scalar approach. We show that the scattering response from a textured surface as calculated by a simple scalar model can be related to the measured external quantum efficiency of a solar cell and double-check this model by rigorous calculations. This approach allows estimating the performance of a textured thin film to a certain extent without any sophisticated numerical analysis.
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88.40.jj Silicon solar cells

Experimental validation of strong directional selectivity in nonsymmetric metallic gratings with a subwavelength slit

Semih Cakmakyapan, Humeyra Caglayan, Andriy E. Serebryannikov, and Ekmel Ozbay

Appl. Phys. Lett. 98, 051103 (2011); http://dx.doi.org/10.1063/1.3552675 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2011

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Strong directional selectivity is theoretically predicted and experimentally validated at the microwave frequencies in the beaming regime for a single subwavelength slit in nonsymmetric metallic gratings with double-side corrugations. The operation regime can be realized at a fixed angle of incidence when the surface-plasmon assisted transmission is significant within a narrow range of observation angles, if illuminating one of the grating interfaces, and tends to vanish for all observation angles, if illuminating the opposite interface. The studied effect is connected with asymmetry (nonreciprocity) in the beaming that occurs if the surface plasmon properties are substantially different for the two interfaces being well isolated from each other.
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42.79.Dj Gratings
42.25.Bs Wave propagation, transmission and absorption

Chaotic emission and tunable self-sustained pulsations in a two-section Fabry–Perot quantum dot laser

Charis Mesaritakis, Apostolos Argyris, Christos Simos, Hercules Simos, Alexandros Kapsalis, Igor Krestnikov, and Dimitris Syvridis

Appl. Phys. Lett. 98, 051104 (2011); http://dx.doi.org/10.1063/1.3552962 (3 pages)

Online Publication Date: 2 February 2011

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We present an experimental study on the intrinsic instabilities of a two electrode InAs/InGaAs Fabry–Perot quantum dot laser in the absence of optical feedback. By individually controlling the current injected in each electrode, different regimes of operation are allowed including tunable self-sustained pulsations and coherence collapse resulting to possible chaotic emission. The origin of these effects does not resign in the presence of optical feedback but is associated to the carrier dynamics of the quantum dot device. A numerical analysis on the time traces collected from the device reveals high complexity output in terms of correlation dimension.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Compact microdisk cavity laser with type-II GaSb/GaAs quantum dots

K. S. Hsu, T. T. Chiu, Wei-Hsun Lin, K. L. Chen, M. H. Shih, Shih-Yen Lin, and Yia-Chung Chang

Appl. Phys. Lett. 98, 051105 (2011); http://dx.doi.org/10.1063/1.3543839 (3 pages)

Online Publication Date: 3 February 2011

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Microdisk lasers with active region made of type-II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. A microdisk cavity with diameter of 3.9 μm was fabricated from a 225-nm-thick GaAs layer filled with GaSb quantum dots. Lasing at wavelengths near 1000 nm at 150 K was achieved for this microdisk. A high threshold characteristic temperature of 77 K was also observed. It is found that the lasing wavelength matches closely with the first-order whispering-gallery mode of the cavity as obtained from the finite-element method simulation.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.86.+b Optical workshop techniques

Enhanced optical output power of green light-emitting diodes by surface plasmon of gold nanoparticles

Chu-Young Cho, Sang-Jun Lee, Jung-Hoon Song, Sang-Hyun Hong, Song-Mae Lee, Yong-Hoon Cho, and Seong-Ju Park

Appl. Phys. Lett. 98, 051106 (2011); http://dx.doi.org/10.1063/1.3552968 (3 pages) | Cited 9 times

Online Publication Date: 3 February 2011

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We demonstrate the surface plasmon (SP) enhanced green light-emitting diodes (LEDs). The Au nanoparticles were embedded in the p-GaN of LEDs. The photoluminescence and electroluminescence measurements showed improved optical properties of LEDs with Au nanoparticles due to an increase in the spontaneous emission rate by resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Au nanoparticles. The optical output power of SP-enhanced green LEDs with Au nanoparticles was increased by 86% without showing degradation of the electrical characteristics of LEDs compared to LEDs without Au nanoparticles.
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85.60.Jb Light-emitting devices
78.68.+m Optical properties of surfaces
78.60.Fi Electroluminescence

Temperature dependence of a high-performance narrow-stripe (1 μm) single quantum-well transistor laser

M. Feng, N. Holonyak, Jr., and A. James

Appl. Phys. Lett. 98, 051107 (2011); http://dx.doi.org/10.1063/1.3528206 (3 pages)

Online Publication Date: 3 February 2011

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Data are presented on the thermal behavior of a high performance 1 μm wide stripe quantum-well (QW) transistor laser in continuous-wave single-mode operation up to 40 °C, multimode to 55 °C. The electrical and optical outputs of the TL are found to be complementary across temperature, directly correlated with the spontaneous and stimulated radiative recombination process. The QW transistor laser operates on two states, lower and upper, at two characteristic temperatures, T0 (ITH = I0 exp(T/T0)). On the lower state transition, T00 = 40 K, and on the upper state, T01 = 70 K, the difference in performance and speed (bandwidth) connected directly to the different recombination lifetimes on each state and the confining barrier heights of the lower |0〉 and upper state |1〉.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems

Self-established noncollinear oscillation and angular tuning in a quasi-phase-matched mirrorless optical parametric oscillator

Gustav Strömqvist, Valdas Pasiskevicius, and Carlota Canalias

Appl. Phys. Lett. 98, 051108 (2011); http://dx.doi.org/10.1063/1.3551526 (3 pages)

Online Publication Date: 3 February 2011

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We experimentally demonstrate self-established noncollinear interactions in a quasi-phase-matched mirrorless optical parametric oscillator using a periodically-poled KTiOPO4 crystal with submicrometer periodicity. It is shown that the oscillation is established in a very specific geometric configuration where the two possible solutions of the energy and momentum conservation conditions become spatially degenerate and contribute coherently to the gain. In this configuration, the signal and the idler remain mutually counter-propagating. The tuning capabilities of a noncollinear mirrorless optical parametric oscillator are investigated.
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42.65.Yj Optical parametric oscillators and amplifiers
42.70.Mp Nonlinear optical crystals

Terahertz metasurfaces with high Q-factors

Christian Jansen, Ibraheem A. I. Al-Naib, Norman Born, and Martin Koch

Appl. Phys. Lett. 98, 051109 (2011); http://dx.doi.org/10.1063/1.3553193 (3 pages) | Cited 8 times

Online Publication Date: 4 February 2011

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We propose asymmetric D-split resonators as unit cells for high Q metasurfaces. In such resonators, current trapped modes lead to in-phase oscillations of antisymmetric currents. Thus, radiation losses are suppressed, enabling Q-factors beyond the ones obtainable in symmetric designs. We compare the proposed structure against both asymmetric and symmetric split ring metasurfaces and find an improvement in terms of Q by a factor of two and ten, respectively. Transmission measurements in a terahertz spectrometer provide experimental proof of the high Q-factors and agree well with numerical simulations. In the future, asymmetric D-split metasurfaces could be employed as high-performance sensors or filters.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.-e Optical elements, devices, and systems
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Nonlinear dynamics of relativistic charged particle beams

R. P. Nunes and F. B. Rizzato

Appl. Phys. Lett. 98, 051501 (2011); http://dx.doi.org/10.1063/1.3549690 (3 pages)

Online Publication Date: 31 January 2011

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The idea behind this work is to analyze the transversal dynamics of a relativistic charged particle beam. The beam is azimuthally symmetric, focused by a constant magnetic field and supposed to be initially cold. While mismatched, nonrelativistic, and homogeneous beams oscillate with an invariant cold density profile, it is shown that relativistic homogeneous beams progressively heat and lose an important amount of constituents during its magnetic confinement. This heating process starts with phase-space wave-breaking, a mechanism observed before in initially inhomogeneous beams. The results have been obtained with full self-consistent N-particle beam numerical simulations.
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41.75.-i Charged-particle beams
41.85.Ja Particle beam transport

Child–Langmuir law in the Coulomb blockade regime

Yingbin Zhu and L. K. Ang

Appl. Phys. Lett. 98, 051502 (2011); http://dx.doi.org/10.1063/1.3549868 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2011

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The one-dimensional (1D) classical Child–Langmuir (CL) law has been extended to the Coulomb blockade (single to few electrons) regime, including the effect of single-electron charging. It is found that there is a threshold of voltage (Vth) equals to one-half of the single-electron charging energy for electron injection assuming zero barrier at the interface. For voltage in the range of 1<V/Vth<2, there is only one electron inside the gap, and the time-averaged single-electron injected current is equal or higher than the 1D CL current.
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73.23.Hk Coulomb blockade; single-electron tunneling

Raman scattering analysis of silicon dioxide single crystal treated by direct current plasma discharge

D. M. Popovic, V. Milosavljevic, A. Zekic, N. Romcevic, and S. Daniels

Appl. Phys. Lett. 98, 051503 (2011); http://dx.doi.org/10.1063/1.3543838 (3 pages)

Online Publication Date: 1 February 2011

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Low-k materials such as silicon dioxide (SiO2) play an important role in the semiconductor industry. Plasma has become indispensable for advanced materials processing. In this work a treatment of SiO2 single crystal by direct current plasma discharge is studied in detail. Offline metrology is conducted for silicon dioxide wafers by Raman scattering, energy-dispersive x-ray spectroscopy, and ellipsometry. Broad Raman peak at around 2800 cm−1 is observed for the treated SiO2 wafers. Effects of plasma treatment on position of this peak are reported in the paper. An analysis of this correlation could be a framework for creating virtual etch rate sensors, which might be of importance in managing plasma etching processes.
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78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
77.55.D- High-permittivity gate dielectric films
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Impact of electromagnetic radiation on cascaded failure in high voltage insulators

A. Bojovschi, K. L. Wong, and W. S. T. Rowe

Appl. Phys. Lett. 98, 051504 (2011); http://dx.doi.org/10.1063/1.3551544 (3 pages)

Online Publication Date: 4 February 2011

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A cause of aging and cascaded failure of high voltage insulators is investigated by assessing the radiation propagating from a faulty insulator. The transfer of electromagnetic energy from corona discharge to healthy insulators situated on the same power pole is assessed. The results show that the high intensity of electric field associated with corona discharge on faulty insulators can lead to aging and finally failure of high voltage infrastructure.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
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Kinetics of ejected particles during breakdown in fused silica by nanosecond laser pulses

Rajesh N. Raman, Raluca A. Negres, and Stavros G. Demos

Appl. Phys. Lett. 98, 051901 (2011); http://dx.doi.org/10.1063/1.3549193 (3 pages)

Online Publication Date: 31 January 2011

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The temporal evolution and kinetic properties of material particles ejected from the surface of fused silica under nanosecond laser irradiation are investigated using a time-resolved microscope system. The experiments provide information on the particle size, shape, and speed as a function of delay time, as well as on the duration of the material ejection process. The results suggest that the processes involved are much more complex than those predicted by current models.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
78.47.D- Time resolved spectroscopy (>1 psec)
79.20.Ds Laser-beam impact phenomena

Partial strain relaxation by stacking fault generation in InGaN multiple quantum wells grown on (1math01) semipolar GaN

Z. H. Wu, T. Tanikawa, T. Murase, Y.-Y. Fang, C. Q. Chen, Y. Honda, M. Yamaguchi, H. Amano, and N. Sawaki

Appl. Phys. Lett. 98, 051902 (2011); http://dx.doi.org/10.1063/1.3549561 (3 pages) | Cited 2 times

Online Publication Date: 31 January 2011

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We have investigated the structural properties and relaxation phenomenon of InGaN multiple quantum wells (QWs) on (1math01) semipolar GaN templates grown on patterned (001) silicon substrates by selective area growth technique. Our studies by transmission electron microscopy and x-ray diffraction reciprocal space mapping reveal that QWs emitting light at 540 nm experience significant strain relaxation along the in-plane [1math0math] direction by the generation of an array of basal stacking faults (BSF). The generation of BSFs in 540 nm QWs could be an important factor limiting its luminescence efficiency.
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68.65.Fg Quantum wells
61.72.Nn Stacking faults and other planar or extended defects
78.67.De Quantum wells

Ligament and joint sizes govern softening in nanoporous aluminum

A. C. To, J. Tao, M. Kirca, and L. Schalk

Appl. Phys. Lett. 98, 051903 (2011); http://dx.doi.org/10.1063/1.3549858 (3 pages)

Online Publication Date: 31 January 2011

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The present computational study demonstrates that softening of an open cell nanoporous aluminum structure subjected to tensile loading can be significantly reduced when the size of ligaments and the joints that connect them in the structure is designed to be sufficiently small. It is found using molecular dynamics simulations that the softening becomes slightly slower with increasing porosity for the structures with porosity less than or equal to 72%, and stress localization is observed during softening. In contrast, for structures with more than 75% porosity, softening is much slower, and stress delocalization occurs during softening. It is argued that at relatively high porosity, softening is governed by both the ligament size and the joint size because their compliance becomes high enough to allow the overloading stress due to ligament rupture to be redistributed more effectively throughout the structure.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials

Universal Ti-rich termination of atomically flat SrTiO3 (001), (110), and (111) surfaces

A. Biswas, P. B. Rossen, C.-H. Yang, W. Siemons, M.-H. Jung, I. K. Yang, R. Ramesh, and Y. H. Jeong

Appl. Phys. Lett. 98, 051904 (2011); http://dx.doi.org/10.1063/1.3549860 (3 pages) | Cited 1 time

Online Publication Date: 31 January 2011

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We have studied the surface termination of atomically flat SrTiO3 surfaces treated by chemical etching and subsequent thermal annealing, for all commercially available orientations (001), (110), and (111). Atomic force microscopy confirms that our treatment processes produce unit cell steps with flat terrace structures. We have also determined the topmost atomic layer of SrTiO3 surfaces through time-of-flight mass spectroscopy. We found that all three orientations exhibit a Ti-rich surface. Our observation opens doors for interface engineering along the [110] and [111] directions in addition to a well known [100] case, which widens the range of functional heterostructures and interfaces.
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81.65.Cf Surface cleaning, etching, patterning
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)
82.80.Rt Time of flight mass spectrometry
68.35.bt Other materials

Transmission electron microscopy observations of dislocation annihilation and storage in nanograins

Lihua Wang, Ze Zhang, En Ma, and X. D. Han

Appl. Phys. Lett. 98, 051905 (2011); http://dx.doi.org/10.1063/1.3549866 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2011

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A detailed in situ investigation of dislocation processes has been rare for nanograined materials with grain sized near or less than 10 nm. Here, we report a time-resolved and atomic-scale in situ transmission electron microscopy observation of the nucleation, motion, annihilation, and storage of full dislocations in nanograins with diameters less than ∼ 10 nm. Annihilation of dislocation dipoles appears to be a major contributor to the reduction in dislocation density, in addition to annihilation at grain boundary sinks. The accumulation of a high density of dislocations inside nanograins is found to be possible when they are surrounded by neighboring grains.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Color center formation in vacuum sintered Nd3xY3−3xAl5O12 transparent ceramics

Adam J. Stevenson, Brad C. Bittel, Christopher G. Leh, Xin Li, Elizabeth C. Dickey, Patrick M. Lenahan, and Gary L. Messing

Appl. Phys. Lett. 98, 051906 (2011); http://dx.doi.org/10.1063/1.3549872 (3 pages) | Cited 3 times

Online Publication Date: 31 January 2011

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Color center formation was studied in vacuum sintered Nd3xY3−3xAl5O12 transparent ceramics. The primary color centers were F- and F+-centers as evidenced by optical absorption in the 250–400 nm wavelength range and the presence of an electron spin resonance (ESR) line at g = 1.9977. Annealing in air at 1600 °C for 10 h reduced the number of color centers to below the detection limit of ESR. Color center formation is controlled by oxidation and reduction of Fe2+/3+ impurities.
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61.72.jn Color centers
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.40.Ha Other nonmetallic inorganics
76.30.Mi Color centers and other defects

Transmission electron microscopy of transparent conductive oxide films made by atmospheric pressure chemical vapor deposition

G. J. A. Mannie, J. van Deelen, J. W. Niemantsverdriet, and P. C. Thüne

Appl. Phys. Lett. 98, 051907 (2011); http://dx.doi.org/10.1063/1.3551523 (3 pages) | Cited 1 time

Online Publication Date: 31 January 2011

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The properties of crystalline films are strongly dependent on the morphology development during the first stages of growth, that is, the nucleation and growth of the first crystallites. The ideal method to investigate such films at atomic resolution is transmission electron microscopy (TEM). However, this technique usually requires extensive sample preparation. In this study we present a simple method to investigate thin film morphology with TEM. The key to this approach is the use of TEM membranes as growth substrates. As an illustration we describe fine grains of SnO2 deposited on these TEM membranes by atmospheric pressure chemical vapor deposition.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.J- Morphology of films

Improvement of UV emission from highly crystalline ZnO nanoparticles by pulsed laser ablation under O2/He glow discharge

Qiang Ma, Teguh Endah Saraswati, Akihisa Ogino, and Masaaki Nagatsu

Appl. Phys. Lett. 98, 051908 (2011); http://dx.doi.org/10.1063/1.3551534 (3 pages) | Cited 2 times

Online Publication Date: 31 January 2011

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Pulsed laser ablation under an O2/He glow discharge was studied to improve the surface crystallinity and UV luminescence of ZnO nanoparticles ∼ 10 nm in size. X-ray photoemission spectroscopy, scanning transmission electron microscopy, and cathodoluminescence spectroscopy were used to analyze the crystalline structures and chemical components. The results indicated that highly crystalline ZnO nanoparticles were fabricated under the O2/He plasma discharge. The near band gap UV emission intensities from these particles were roughly five times those of samples fabricated under O2 gas. The present results suggest the possibility of synthesize high quality ZnO quantum dots or nanoparticles without requiring any post-treatment.
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81.07.Bc Nanocrystalline materials
81.16.Mk Laser-assisted deposition
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.65.Hb Quantum dots (patterned in quantum wells)

Intrinsic metastability of orthorhombic HfTiO4 in thin film hafnia-titania

Massiel Cristina Cisneros-Morales and Carolyn Rubin Aita

Appl. Phys. Lett. 98, 051909 (2011); http://dx.doi.org/10.1063/1.3551543 (3 pages) | Cited 2 times

Online Publication Date: 31 January 2011

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Orthorhombic (o) HfTiO4 is crystallized when sputter deposited hafnia-titania nanolaminates with ultrathin layers and bilayer (HfO2)0.5(TiO2)0.5 composition are annealed between 573 and 1173 K. However, o-HfTiO4 demixes after annealing at 1273 K, a result not predicted from bulk thermodynamics. X-ray diffraction and Raman microscopy are used here to study structural changes as o-HfTiO4 demixes upon long-term annealing at 1273 K into Ti-doped monoclinic HfO2 and Hf-doped rutile TiO2. We conclude that o-HfTiO4 crystallized at low temperature is intrinsically metastable. A space group symmetry analysis shows that demixing can be accomplished by a continuous phase transition chain.
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64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering
68.55.aj Insulators
64.75.Ef Mixing

Probing residual strain in epitaxial graphene layers on 4H-SiC(000math) with Raman spectroscopy

A. J. Strudwick, G. L. Creeth, N. A. B. Johansson, and C. H. Marrows

Appl. Phys. Lett. 98, 051910 (2011); http://dx.doi.org/10.1063/1.3551625 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2011

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Raman microspectroscopy was used to measure compressive strain within epitaxial graphene (EG) grown on the carbon-terminated SiC(000math) face as a function of annealing time for a growth temperature of 1400 °C. A maximum strain of −0.5% was seen at the longest time of 55 min. This differs from the −0.9% expected for strain caused by cooling from the growth temperature due to the differential thermal contraction between the SiC and EG layer, despite good agreement between this model and data on EG on SiC(0001). We suggest that this is due to the different EG bonding mechanisms on the two SiC faces.
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81.05.ue Graphene
68.65.Pq Graphene films
78.30.Na Fullerenes and related materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.67.Wj Optical properties of graphene
68.55.ap Fullerenes

Stress control during thermal annealing of copper interconnects

C.-C. Yang, C. Witt, P.-C. Wang, D. Edelstein, and R. Rosenberg

Appl. Phys. Lett. 98, 051911 (2011); http://dx.doi.org/10.1063/1.3551627 (3 pages)

Online Publication Date: 31 January 2011

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Grain growth of Cu interconnects in an ultralow k dielectric was achieved at an elevated anneal temperature of 300 °C without stress voiding related problems. For this, a TaN metal passivation layer was deposited on the Cu interconnect surface prior to the thermal annealing process, which suppressed void formation within the Cu features during the anneal process and reduced inelastic deformation within the interconnects after cooling down to room temperature. As compared to the conventional anneal process at 100 °C, the passivation layer enabled further Cu grain growth at elevated temperatures, which then resulted in lower electrical resistance in the Cu interconnects.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Structural and elemental characterization of high efficiency Cu2ZnSnS4 solar cells

Kejia Wang, Byungha Shin, Kathleen B. Reuter, Teodor Todorov, David B. Mitzi, and Supratik Guha

Appl. Phys. Lett. 98, 051912 (2011); http://dx.doi.org/10.1063/1.3543621 (3 pages) | Cited 8 times

Online Publication Date: 1 February 2011

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We have carried out detailed microstructural studies of phase separation and grain boundary composition in Cu2ZnSnS4 based solar cells. The absorber layer was fabricated by thermal evaporation followed by post high temperature annealing on hot plate. We show that inter-reactions between the bottom molybdenum and the Cu2ZnSnS4, besides triggering the formation of interfacial MoSx, results in the out-diffusion of Cu from the Cu2ZnSnS4 layer. Phase separation of Cu2ZnSnS4 into ZnS and a Cu–Sn–S compound is observed at the molybdenum-Cu2ZnSnS4 interface, perhaps as a result of the compositional out-diffusion. Additionally, grain boundaries within the thermally evaporated absorber layer are found to be either Cu-rich or at the expected bulk composition. Such interfacial compound formation and grain boundary chemistry likely contributes to the lower than expected open circuit voltages observed for the Cu2ZnSnS4 devices.
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88.40.hj Efficiency and performance of solar cells
88.40.jn Thin film Cu-based I-III-VI2 solar cells
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