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5 Nov 2012

Volume 101, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 193101 (2012); http://dx.doi.org/10.1063/1.4764508 (4 pages)

Ryan T. Tucker, Allan L. Beaudry, Joshua M. LaForge, Michael T. Taschuk, and Michael J. Brett
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Bound and anti-bound biexciton in site-controlled pyramidal GaInAs/GaAs quantum dots

C. Jarlov, P. Gallo, M. Calic, B. Dwir, A. Rudra, and E. Kapon

Appl. Phys. Lett. 101, 191101 (2012); http://dx.doi.org/10.1063/1.4765646 (4 pages)

Online Publication Date: 5 November 2012

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We present a detailed study of biexciton complexes formed in single, site-controlled pyramidal GaInAs/GaAs quantum dots (QDs). By using power dependent measurements and photon correlation spectroscopy, we identify the excitonic transitions of a large number of pyramidal QDs, exhibiting both positive and negative biexciton binding energies. Separation of charges within the QD, caused by piezoelectric fields, is believed to be responsible for the positive to negative crossover of the biexciton binding energy with increasing QD size. In particular, QDs exhibiting vanishing biexciton binding energies are evidenced, with potential applications in quantum information processing.
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71.35.-y Excitons and related phenomena
77.65.-j Piezoelectricity and electromechanical effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots

Can interference patterns in the reflectance spectra of GaN epilayers give important information of carrier concentration?

C. C. Zheng, S. J. Xu, F. Zhang, J. Q. Ning, D. G. Zhao, H. Yang, and C. M. Che

Appl. Phys. Lett. 101, 191102 (2012); http://dx.doi.org/10.1063/1.4766188 (3 pages)

Online Publication Date: 6 November 2012

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Low-temperature reflectance spectra of a series of Si-doped GaN epilayers with different doping concentrations grown on sapphire by metal-organic chemical vapour deposition were measured. In addition to the excitonic polariton resonance structures at the band edge, interference oscillating patterns were observed in the energy region well below the band gap. The amplitudes of these oscillation patterns show a distinct dependence on the doping concentrations of the samples. From the thin-film optical interference principle, an approach connecting the amplitude of the interference oscillations and the impurity scattering was established. Good agreement between experiment and theory is achieved.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Differential reflectance modulation sensing with diffractive microstructures

N. Kumawat and M. M. Varma

Appl. Phys. Lett. 101, 191103 (2012); http://dx.doi.org/10.1063/1.4766190 (4 pages)

Online Publication Date: 6 November 2012

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We present a method for differential ratiometric measurement of reflectance change due to molecular adsorption using a diffractive microstructure fabricated on a reflectance contrast enhancing substrate for bulk refractometry and surface molecular binding detection applications. The differential method suppresses signal fluctuations due to thermal or concentration gradients in the sample flow cell by more than 40× and enables the real-time measurement of molecular interactions on the surface with a noise floor of about 70 pm.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Hv Refractometers and reflectometers

Relevance of intra- and inter-subband scattering on the absorption in heterostructures

C. Ndebeka-Bandou, F. Carosella, R. Ferreira, A. Wacker, and G. Bastard

Appl. Phys. Lett. 101, 191104 (2012); http://dx.doi.org/10.1063/1.4766192 (4 pages) | Cited 1 time

Online Publication Date: 6 November 2012

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We analyze the absorption lineshape for inter-subband transitions in disordered quasi two-dimensional heterostructures by an exact calculation. The intra-subband scatterings control the central peak, while the tails of the absorption line are dominated by the inter-subband scattering terms. Our numerical study quantitatively assesses the magnitude of the free carrier absorption. The accuracy of different models currently used for gain/absorption is discussed.
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78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High single-spatial-mode pulsed power from 980 nm emitting diode lasers

Martin Hempel, Jens W. Tomm, Thomas Elsaesser, and Mauro Bettiati

Appl. Phys. Lett. 101, 191105 (2012); http://dx.doi.org/10.1063/1.4766267 (5 pages)

Online Publication Date: 7 November 2012

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Single-spatial-mode pulsed powers as high as 13 W and 20 W in 150 and 50 ns pulses, respectively, are reported for 980 nm emitting lasers. In terms of energy, single-spatial-mode values of up to 2 μJ within 150 ns pulses are shown. In this high-power pulsed operation, the devices shield themselves from facet degradation, being the main degradation source in continuous wave (cw) operation. Our results pave the way towards additional applications while employing available standard devices, which have originally been designed as very reliable cw fiber pumps.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrafast nonlinear optical responses of bismuth doped silicon-rich silica films

Kenji Imakita, Yuya Tsuchihashi, Ryo Naruiwa, Minoru Fujii, Hong-Tao Sun, Jianrong Qiu, and Shinji Hayashi

Appl. Phys. Lett. 101, 191106 (2012); http://dx.doi.org/10.1063/1.4766269 (4 pages)

Online Publication Date: 7 November 2012

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Nonlinear optical responses of bismuth (Bi) doped silicon-rich silicon dioxide (Si-rich SiO2) films were studied by a z-scan and an optical Kerr gate method under femtosecond excitation around 800 nm. It was found that the Bi-doping enhances the nonlinear optical response of Si-rich SiO2 films by several orders of magnitudes. The nonlinear refractive index was of the order of 10−11 cm2/W and the response time was shorter than our time resolution of 100 fs. The nonlinear refractive index was independent of the wavelength in the range from 750 to 835 nm, suggesting that virtual transitions are involved in the nonlinear optical processes.
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78.66.Nk Insulators
78.47.jh Coherent nonlinear optical spectroscopy
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Silicon-based three-dimensional photonic crystal nanocavity laser with InAs quantum-dot gain

Daoshe Cao, Aniwat Tandaechanurat, Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa

Appl. Phys. Lett. 101, 191107 (2012); http://dx.doi.org/10.1063/1.4766288 (4 pages)

Online Publication Date: 7 November 2012

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We report on the demonstration of lasing oscillation in a silicon-based three-dimensional photonic crystal nanocavity using InAs quantum dots as gain material by pulsed optical pumping at 11 K. An active layer embedding InAs quantum dots was inserted in the cavity using micromanipulation technique. The highest quality factor for silicon-based three-dimensional photonic crystal cavities (∼22 000) was achieved. We also evaluated the spontaneous emission coupling factor of the laser to be ∼0.78 by fitting the experimental light-in light-out curve with coupled rate equations. This result would pave the way to the realization of CMOS-compatible high-density three-dimensional photonic integrated circuits.
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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
42.70.Qs Photonic bandgap materials
42.82.-m Integrated optics
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping

Shaoqiang Chen, Makoto Okano, Baoping Zhang, Masahiro Yoshita, Hidefumi Akiyama, and Yoshihiko Kanemitsu

Appl. Phys. Lett. 101, 191108 (2012); http://dx.doi.org/10.1063/1.4766290 (3 pages) | Cited 1 time

Online Publication Date: 7 November 2012

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We report the demonstration of the picosecond-pulse lasing in blue region from an optically pumped gain-switched InGaN vertical-cavity-surface-emitting laser (VCSEL). Through 150-fs optical pulse excitations at room temperature, multimode pulse lasing with a main mode at 436.5 nm from the InGaN VCSEL was observed. The output pulse widths were measured to be as short as 9.8 ps for the total lasing spectra and 6.0 ps for the main mode. Since the obtained short pulses were still not limited by its photon lifetime of 0.7 ps or band-width of 0.8 nm, possible ways to generate even shorter pulses have been examined.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

A bi-functional quantum cascade device for same-frequency lasing and detection

Benedikt Schwarz, Peter Reininger, Hermann Detz, Tobias Zederbauer, Aaron Maxwell Andrews, Stefan Kalchmair, Werner Schrenk, Oskar Baumgartner, Hans Kosina, and Gottfried Strasser

Appl. Phys. Lett. 101, 191109 (2012); http://dx.doi.org/10.1063/1.4767128 (4 pages)

Online Publication Date: 8 November 2012

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We demonstrate a bi-functional quantum cascade device that detects at the same wavelength as it coherently emits. Our fabricated device operates at room-temperature with a pulsed peak power emission of 45 mW and a detector responsivity of 3.6 mA/W. We show how to compensate the intrinsic wavelength mismatch between the laser and the detector, based on a bound-to-continuum design. An overlap between the laser and the detector spectra was observed from 6.4 μm to 6.8 μm. The electro-luminescence spectrum almost perfectly matches the detector spectrum, overlapping from 6.2 μm to 7.1 μm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.60.Gz Photodetectors (including infrared and CCD detectors)

Efficient spectral broadening of supercontinuum in photonic crystal fiber with self-phase modulation induced by femtosecond laser pulse

Masayuki Suzuki, Motoyoshi Baba, Shin Yoneya, and Hiroto Kuroda

Appl. Phys. Lett. 101, 191110 (2012); http://dx.doi.org/10.1063/1.4767143 (3 pages)

Online Publication Date: 8 November 2012

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The authors experimentally demonstrated the generation of a supercontinuum (SC) in a photonic crystal fiber (PCF) using laser power of 0.8 W with 100 fs pulse duration at 1028 nm wavelength. The SC spectrum extended from 420 nm to 1650 nm using a 10 cm long PCF, for a wavelength difference of 275 nm between the pump laser and the zero dispersion wavelength (ZDW). This extension of the SC originates from the self-phase modulation induced broadening in the PCF of the femtosecond laser pulse. This study shows the effectiveness of this technique to extend the SC spectrum.
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42.81.Wg Other fiber-optical devices
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Qs Photonic bandgap materials
42.81.Dp Propagation, scattering, and losses; solitons

Electrical and optical interconnection for mechanically stacked multi-junction solar cells mediated by metal nanoparticle arrays

Hidenori Mizuno, Kikuo Makita, and Koji Matsubara

Appl. Phys. Lett. 101, 191111 (2012); http://dx.doi.org/10.1063/1.4766339 (4 pages)

Online Publication Date: 8 November 2012

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An interconnection approach for mechanical stacking of solar cells is described. In this approach, block copolymer-templated fabrication of metal nanoparticle arrays and van der Waals bonding were integrated to design interfaces which permit both high interfacial conductivities and minimal transmission losses upon interconnections of solar cells. A series of electrical and optical characterizations verified that the approach potentially provides resistances of as low as 3.7 Ω-cm2 with transmission losses of less than 2%. The demonstrative two-junction solar cell exhibited promising open-circuit voltage and fill factor, suggesting the possibility of achieving high-efficiency multi-junction solar cells based on this unique strategy.
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88.40.jp Multijunction solar cells
73.40.Ns Metal-nonmetal contacts
81.16.Dn Self-assembly

Using quantum memory techniques for optical detection of ultrasound

D. L. McAuslan, L. R. Taylor, and J. J. Longdell

Appl. Phys. Lett. 101, 191112 (2012); http://dx.doi.org/10.1063/1.4766341 (4 pages) | Cited 1 time

Online Publication Date: 8 November 2012

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Quantum memories are inherently highly efficient and display low noise, making them particularly suitable for the optical detection of ultrasound. Here, we use an atomic-frequency-comb based quantum memory to demonstrate sensitive ultrasound detection, realising a 49 dB discrimination between the sidebands and the carrier. The method remains valid in the case of optically thin samples and thus represents a significant improvement over other ultrasound detection methods based on rare-earth-ion-doped crystals. Furthermore, we show that this non-destructive non-contact approach is also compatible with highly scattering samples and suggest its particular suitability for the real-time imaging of biological tissues.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
87.63.D- Ultrasonography
87.63.L- Visual imaging

Optical logic gates using coherent feedback

Zhifan Zhou, Cunjin Liu, Yami Fang, Jun Zhou, Ryan T. Glasser, Liqing Chen, Jietai Jing, and Weiping Zhang

Appl. Phys. Lett. 101, 191113 (2012); http://dx.doi.org/10.1063/1.4767133 (4 pages)

Online Publication Date: 9 November 2012

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We experimentally demonstrate optical logic “or” and “nor” gates via coherent feedback. Based on a four-wave mixing process in hot rubidium vapor, two feedback beams are capable of fulfilling an optical “nor” gate for the feedback-suppressed state and an optical “or” gate for the feedback-boosted state simultaneously. The logic gates exhibit transition times faster than previously demonstrated in rubidium vapor. Coherent photon conversion between the two logic states, due to the atomic coherence, is observed in the coherent feedback process.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Buried anti resonant reflecting optical waveguide based on porous silicon material for an integrated Mach Zehnder structure

M. Hiraoui, M. Guendouz, N. Lorrain, L. Haji, and M. Oueslati

Appl. Phys. Lett. 101, 191114 (2012); http://dx.doi.org/10.1063/1.4766729 (5 pages)

Online Publication Date: 9 November 2012

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A buried anti resonant reflecting optical waveguide for an integrated Mach Zehnder structure based on porous silicon material is achieved using a classical photolithography process. Three distinct porous silicon layers are then elaborated in a single step, by varying the porosity (thus the refractive index) and the thickness while respecting the anti-resonance conditions. Simulations and experimental results clearly show the antiresonant character of the buried waveguides. Significant variation of the reflectance and light propagation with different behavior depending on the polarization and the Mach Zehnder dimensions is obtained. Finally, we confirm the feasibility of this structure for sensing applications.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
07.60.Ly Interferometers

Rare earth doped Si-rich ZnO for multiband near-infrared light emitting devices

Emanuele Francesco Pecora, Thomas I. Murphy, and Luca Dal Negro

Appl. Phys. Lett. 101, 191115 (2012); http://dx.doi.org/10.1063/1.4766947 (5 pages) | Cited 4 times

Online Publication Date: 9 November 2012

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We demonstrate a light emitting material platform based on rare-earth doping of Si-rich ZnO thin films by magnetron sputtering, and we investigate the near-infrared emission properties under both optical and electrical injection. Er and Nd radiative transitions were simultaneously activated due to energy transfer via the ZnO direct bandgap and its luminescent defect centers. Moreover, by incorporating Si atoms, we demonstrate Si-mediated enhancement of photoluminescence in Er-doped ZnO and electroluminescence. These results pave the way to novel Si-compatible light emitters that leverage the optically transparent and electrically conductive ZnO matrix for multiband near-IR telecom and bio-compatible applications.
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85.60.Jb Light-emitting devices
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Ultrathin Si/C graded layer to improve tribological properties of Co magnetic films

Ehsan Rismani, M. Abdul Samad, Sujeet K. Sinha, Reuben Yeo, Hyunsoo Yang, and C. Singh Bhatia

Appl. Phys. Lett. 101, 191601 (2012); http://dx.doi.org/10.1063/1.4765054 (5 pages)

Online Publication Date: 6 November 2012

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An ultrathin Si layer (≤1 nm) deposited on Co magnetic films was bombarded with energetic C+ ions to form a Co/Si/C mixed layer. This layer improved the tribological properties of the Co film as compared with those of a commercial hard disk media with 3.0 nm carbon overcoat and 1.4 nm of lubricant. Formation of a network of C-C and Si-C bonds at the outermost layer and the bulk of the Si/C film as well as formation of chemical bonds between the Co surface and the mixed layer was found as the main factors to improve the tribological properties.
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81.40.Pq Friction, lubrication, and wear
68.55.A- Nucleation and growth
62.20.Qp Friction, tribology, and hardness
68.60.Bs Mechanical and acoustical properties

Domain formation in anatase TiO2 thin films on LaAlO3 substrates

Shijian Zheng, Craig A. J. Fisher, Takeharu Kato, Yuki Nagao, Hiromichi Ohta, and Yuichi Ikuhara

Appl. Phys. Lett. 101, 191602 (2012); http://dx.doi.org/10.1063/1.4766338 (5 pages)

Online Publication Date: 7 November 2012

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Using advanced Cs-corrected scanning transmission electron microscopy, we have observed the atomic structures of coherent TiO2/LaAlO3 heterointerfaces in anatase TiO2 thin films deposited on single-crystal LaAlO3. Two epitaxial relationships are identified: (001)[100] TiO2//(001)[100] LaAlO3 and (001)[010] TiO2//(001)[100] LaAlO3. These epitaxial relationships and the terrace steps on the substrate surface result in the formation of multidomains in the anatase TiO2 thin films. Three types of domain boundaries are identified, namely, 90° rotation domain boundaries, translation domain boundaries, and mixtures of the two. These domain boundaries are expected to have a profound effect on the properties of the thin film.
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68.35.Ct Interface structure and roughness

Fast photo-switchable surfaces for boiling heat transfer applications

C. N. Hunter, D. B. Turner, M. L. Jespersen, M. H. Check, P. T. Borton, N. R. Glavin, and A. A. Voevodin

Appl. Phys. Lett. 101, 191603 (2012); http://dx.doi.org/10.1063/1.4766345 (4 pages)

Online Publication Date: 7 November 2012

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Several milligrams of the ruthenium-centered organometallic complex, ruthenium bis-4,4′-di(thiomethyl)-2,2′-bipyridine, mono-2 -(2-pyridyl)-1,3-oxathiane ([Ru{(HS-CH2)2-bpy}2{pox}](PF6)2) were synthesized and used to produce a self assembled monolayer film on a gold substrate. X-ray photoelectron spectroscopy analysis of the film detected the presence of bound thiolate, which is an indication of a chemisorbed film. Water contact angle measurements were performed before and after 5 min of visible light irradiation using an ozone-free 1000 W Xe(Hg) arc source with a 425-680 nm long pass mirror. The contact angle changed from 52° pre-irradiation (hydrophilic state) to 95° post-irradiation (hydrophobic state).
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
64.70.fh Boiling and bubble dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.03.Cd Surface tension and related phenomena
79.60.Dp Adsorbed layers and thin films

High-resolution x-ray absorption studies of core excitons in hexagonal boron nitride

Lu Hua Li, Mladen Petravic, Bruce C. C. Cowie, Tan Xing, Robert Peter, Ying Chen, Chen Si, and Wenhui Duan

Appl. Phys. Lett. 101, 191604 (2012); http://dx.doi.org/10.1063/1.4767135 (4 pages) | Cited 2 times

Online Publication Date: 8 November 2012

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In the K-shell excitation spectroscopy studies of hexagonal boron nitride, a sharp π* resonance at 192.0 eV in the B K-edge region due to the B 1s–π* transition has been widely observed and accepted for three decades. However, our high-resolution near-edge x-ray absorption fine-structure studies disclose that this characteristic exciton peak actually consists of an asymmetric double-peak structure. Notable differences have been revealed in the polarization character of the two split peaks. These fine structures are explained by the coupling of core excitons to lattice vibrations with the inclusion of Jahn-Teller effect which breaks down Franck-Condon principle.
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78.70.Dm X-ray absorption spectra
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.35.-y Excitons and related phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.55.Cr III-V semiconductors

Evolution of local work function in epitaxial VO2 thin films spanning the metal-insulator transition

Ahrum Sohn, Haeri Kim, Dong-Wook Kim, Changhyun Ko, Shriram Ramanathan, Jonghyurk Park, Giwan Seo, Bong-Jun Kim, Jun-Hwan Shin, and Hyun-Tak Kim

Appl. Phys. Lett. 101, 191605 (2012); http://dx.doi.org/10.1063/1.4766292 (3 pages)

Online Publication Date: 8 November 2012

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Transport and Kelvin probe force microscopy measurements were simultaneously conducted on epitaxial VO2 thin films. The sample's work function abruptly dropped from 4.88 eV to 4.70 eV during heating from 333 K to 353 K, suggesting a significant change in its electronic band structure spanning the metal insulator transition. The work function showed nearly no statistical deviation across the film's surface during the transition, likely due to band bending at the boundaries of the small domains. Resistance profiles confirmed that the local work function corresponded closely to the resistance of the corresponding area.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.55.Px Epitaxial and superlattice films
71.20.Ps Other inorganic compounds
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Imaging of a patterned and buried molecular layer by coherent acoustic phonon spectroscopy

Mike Hettich, Karl Jacob, Oliver Ristow, Chuan He, Jan Mayer, Martin Schubert, Vitalyi Gusev, Axel Bruchhausen, and Thomas Dekorsy

Appl. Phys. Lett. 101, 191606 (2012); http://dx.doi.org/10.1063/1.4767141 (4 pages)

Online Publication Date: 9 November 2012

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A molecular layer of aminopropyltriethoxysilane is patterned with a focused ion beam and subsequently covered by a gold film. The gold-polymer-substrate structures are afterwards imaged by ultrafast coherent acoustic phonon spectroscopy in reflection geometry. We demonstrate that the lateral structure of the covered polymer layer can be detected via the damping time of the vibrational mode of the gold film. Furthermore, we utilize Brillouin oscillations originating from the silicon substrate to map the structures and to estimate the molecular layer thickness.
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63.20.-e Phonons in crystal lattices
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.47.J- Ultrafast spectroscopy (<1 psec)

Surface effects on the radiation response of nanoporous Au foams

E. G. Fu, M. Caro, L. A. Zepeda-Ruiz, Y. Q. Wang, K. Baldwin, E. Bringa, M. Nastasi, and A. Caro

Appl. Phys. Lett. 101, 191607 (2012); http://dx.doi.org/10.1063/1.4764528 (5 pages)

Online Publication Date: 9 November 2012

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We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results.
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61.80.Jh Ion radiation effects
82.70.Rr Aerosols and foams
61.72.Nn Stacking faults and other planar or extended defects
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Excitonic luminescence in two-dimensionally confined layered sulfide oxides

Hiraku Ogino, Jun-ichi Shimoyama, Kohji Kishio, Yukari Katsura, Mizuki Tsuboi, Kohei Yamanoi, Marilou Cadatal-Raduban, Tomoharu Nakazato, Toshihiko Shimizu, and Nobuhiko Sarukura

Appl. Phys. Lett. 101, 191901 (2012); http://dx.doi.org/10.1063/1.4764941 (3 pages)

Online Publication Date: 5 November 2012

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A layered sulfide oxide, Sr2ScCuSO3, is synthesized and its electronic structure and luminescence properties are investigated. Sr2ScCuSO3 is composed of alternating layers of antifluoride type sulfide and perovskite-like oxide. Electronic structure calculations reveal that Sr2ScCuSO3 is a direct band gap semiconductor with a relatively large band gap. Excitonic luminescence was observed from Sr2ScCuSO3 and Sr3Sc2Cu2S2O5. The temperature stability of the luminescence intensity of Sr2ScCuSO3 was higher than that of Sr3Sc2Cu2S2O5. Control of the crystal structure might allow the excitonic luminescence properties of such two-dimensional compounds to be enhanced.
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71.35.-y Excitons and related phenomena
78.55.Hx Other solid inorganic materials
71.20.Nr Semiconductor compounds

Direct imaging of atomic clusters in an amorphous matrix: A Co-C granular thin film

Kazuhisa Sato, Masaki Mizuguchi, Ruihe Tang, Jung-Goo Kang, Manabu Ishimaru, Koki Takanashi, and Toyohiko J. Konno

Appl. Phys. Lett. 101, 191902 (2012); http://dx.doi.org/10.1063/1.4765362 (3 pages)

Online Publication Date: 6 November 2012

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The atomic structure of extremely small cobalt (Co) nanoparticles embedded in an amorphous carbon (C) matrix has been studied by spherical aberration (Cs) corrected high-resolution transmission electron microscopy and focal-series restoration. The Co nanoparticles, 1–3 nm in diameter, are crystalline with the face centered cubic structure, while the radial distribution function analysis revealed the existence of a Co–C bond. The reconstructed phase images of the exit-wave function clearly show the projected potential distribution within the Co nanoparticles. The Cs-correction has hence a benefit to visualize embedded crystalline clusters unambiguously, which are responsible for the magnetotransport properties of the Co-C films.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.75.-c Magnetic properties of nanostructures

Enhanced broadband emission from Er-Tm codoped ZnO film due to energy transfer processes involving Si nanocrystals

Yu Pu, Fei Xu, Zuimin Jiang, Zhongquan Ma, Fang Lu, and Dandan Chen

Appl. Phys. Lett. 101, 191903 (2012); http://dx.doi.org/10.1063/1.4766348 (4 pages) | Cited 2 times

Online Publication Date: 7 November 2012

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Er-Tm-Si codoped ZnO film was synthesized by co-sputtering, in which Si nanocrystals (Si-NCs) were observed to form by annealing at 1173 K for 30 min. A fairly flat emission with ∼375 nm bandwidth is achieved, and its intensity is enhanced by nearly an order of magnitude by the Si-NCs, which acted as broadband sensitizers, compared with that without Si-NCs. The film also exhibits broadband emission with relatively stable spectral shape under different excitation lines. The 1.80 μm emission intensity increases by a factor of 3 while the 1.53 μm emission is almost constant with decreasing the operating temperature from 300 to 20 K, attributed to competition between three energy transfer processes from Si-NCs to Er3+/Tm3+ and from Er3+ to Tm3+, and their back transfer processes.
Show PACS
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.40.Gh Other heat and thermomechanical treatments
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
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