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11 Jun 2012

Volume 100, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages)

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci
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Semiconductor nanowires for highly sensitive, room-temperature detection of terahertz quantum cascade laser emission

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages) | Cited 7 times

Online Publication Date: 11 June 2012

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We report on the development of nanowire-based field-effect transistors operating as high sensitivity terahertz (THz) detectors. By feeding the 1.5 THz radiation field of a quantum cascade laser (QCL) at the gate-source electrodes with a wide band dipole antenna, we record a photovoltage signal corresponding to responsivity values >10 V/W, with impressive noise equivalent power levels <6 × 10−11 W/√Hz at room temperature and a wide modulation bandwidth. The potential scalability to even higher frequencies and the technological feasibility of realizing multi-pixel arrays coupled with QCL sources make the proposed technology highly competitive for a future generation of THz detection systems.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.Tv Field effect devices
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Energy dissipation in energy transfer mediated by optical near-field interactions and their interfaces with optical far-fields

Makoto Naruse, Petter Holmström, Tadashi Kawazoe, Kouichi Akahane, Naokatsu Yamamoto, Lars Thylén, and Motoichi Ohtsu

Appl. Phys. Lett. 100, 241102 (2012); http://dx.doi.org/10.1063/1.4729003 (4 pages) | Cited 1 time

Online Publication Date: 11 June 2012

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We theoretically and experimentally evaluated energy dissipation of nanophotonic devices based on energy transfer via near-field interactions and their interfaces with optical far-fields. The lower bound is about 104 times more energy-efficient than electronic devices. We also examined some fundamental differences between near-field-mediated optical energy transfer logic and electrical logic in terms of energy dissipation.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Optically addressed near and long-wave infrared multiband photodetectors

O. O. Cellek, J. L. Reno, and Y.-H. Zhang

Appl. Phys. Lett. 100, 241103 (2012); http://dx.doi.org/10.1063/1.4729004 (4 pages) | Cited 1 time

Online Publication Date: 11 June 2012

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Optically addressed dual-band photodetector incorporating of a 0.82 μm cut-off wavelength near-infrared (NIR) AlGaAs/GaAs p-i-n photodetector and a 8.2 μm peak wavelength long-wave infrared (LWIR) AlGaAs/GaAs quantum well infrared photodetector on GaAs substrate is fabricated and characterized. Switching between NIR and LWIR bands is demonstrated by using external light bias. The dual-band photodetector gives 65% quantum efficiency in NIR band and specific detectivity of 2 × 109 cm Hz1/2/W in LWIR band at 68 K. Spectral crosstalk is better than 25 dB. These devices enable the use of only a single indium-bump per pixel for multiband image sensor arrays to have maximum fill factor.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.67.De Quantum wells
85.60.Gz Photodetectors (including infrared and CCD detectors)

Enhanced optical transmission through tapered metallic gratings

Honghui Shen and Bjorn Maes

Appl. Phys. Lett. 100, 241104 (2012); http://dx.doi.org/10.1063/1.4729005 (3 pages) | Cited 1 time

Online Publication Date: 11 June 2012

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To achieve non-resonant behavior, we propose a metallic grating device with linearly tapered slits. The tapering provides a gradual impedance variation from the entrance to the exit of the slits, leading to broadband and wide-angle enhanced transmission in the infrared. In addition, the light is strongly localized and enhanced at the slit exits, in contrast with straight slits. We describe the phenomenon with a transmission line model, which is in accordance with rigorous simulations.
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42.79.Dj Gratings
42.25.Bs Wave propagation, transmission and absorption

Experimental demonstration of ultra-compact directional couplers based on silicon hybrid plasmonic waveguides

Fei Lou, Zhechao Wang, Daoxin Dai, Lars Thylen, and Lech Wosinski

Appl. Phys. Lett. 100, 241105 (2012); http://dx.doi.org/10.1063/1.4729018 (4 pages) | Cited 3 times

Online Publication Date: 11 June 2012

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Hybrid plasmonic waveguides and directional couplers have been experimentally demonstrated. Using a direct measurement method, the propagation loss of a 170 nm wide waveguide is measured to be 0.08 dB/μm at 1550 nm when the thickness of low-index region is 56 nm. Ultra-compact directional couplers based on such hybrid plasmonic waveguides are demonstrated with gaps of 140 nm, 185 nm, 235 nm, and 290 nm. The corresponding coupling lengths measured are 1.55 μm, 2.2 μm, 3.2 μm, and 4.8 μm, respectively, which are in very good agreement with the simulations. These ultra-compact devices can be potentially used in future ultra-dense photonic integrated circuits.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics

Graphene-based photonic crystal to steer giant Faraday rotation

Haixia Da and Cheng-Wei Qiu

Appl. Phys. Lett. 100, 241106 (2012); http://dx.doi.org/10.1063/1.4729134 (4 pages) | Cited 2 times

Online Publication Date: 11 June 2012

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We present a graphene-based photonic-crystal schematic of enhancing and steering Faraday rotation angle of graphene. This concept is counter-intuitive because the giant Faraday rotation and high transmission can be simultaneously pronounced, which is distinguished from exisitng graphene structures reported before. It is found that chemical potential can be tailored to generate a controllable giant Faraday rotation via graphene with atomic thickness. By engineering the individual component thickness in the photonic crystal, the magneto-optical performance can be significantly improved. This is of fundamental importance in a wide range of magneto-optical applications, simply because the Faraday rotation makes sense only when the transmittivity is decently high.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
65.40.G- Other thermodynamical quantities
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene
78.20.Ls Magneto-optical effects

Terahertz Faraday rotation in a magnetic liquid: High magneto-optical figure of merit and broadband operation in a ferrofluid

Mostafa Shalaby, Marco Peccianti, Yavuz Ozturk, Matteo Clerici, Ibraheem Al-Naib, Luca Razzari, Tsuneyuki Ozaki, Anna Mazhorova, Maksim Skorobogatiy, and Roberto Morandotti

Appl. Phys. Lett. 100, 241107 (2012); http://dx.doi.org/10.1063/1.4729132 (3 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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We report on the demonstration of a high figure of merit (FOM) Faraday rotation in a liquid in the terahertz (THz) regime. Using a ferrofluid, a high broadband rotation (11 mrad/mm) is experimentally demonstrated in the frequency range of 0.2–0.9 THz at room temperature. Given the low absorption of the liquid, a high magneto-optical figure of merit (5-16 rad.cm/T) is obtained.
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78.20.Ls Magneto-optical effects
78.70.Gq Microwave and radio-frequency interactions
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
75.50.Mm Magnetic liquids

Pump dependence of the dynamics of quantum dot based waveguide absorbers

Evgeny A. Viktorov, Thomas Erneux, Tomasz Piwonski, Jaroslaw Pulka, Guillaume Huyet, and John Houlihan

Appl. Phys. Lett. 100, 241108 (2012); http://dx.doi.org/10.1063/1.4729155 (4 pages)

Online Publication Date: 13 June 2012

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The nonlinear two stage recovery of quantum dot based reverse-biased waveguide absorbers is investigated experimentally and analytically as a function of the initial ground state occupation probability of the dot. The latter is controlled experimentally by the pump pulse power. The slow stage of the recovery is exponential and its basic timescale is independent of pump power. The fast stage of the recovery is a logistic function which we analyze in detail. The relative strength of slow to fast components is highlighted and the importance of higher order absorption processes at the highest pump level is demonstrated.
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42.79.Gn Optical waveguides and couplers

Excitonic enhancement of nonradiative energy transfer from a quantum well in the optical near field of energy gradient quantum dots

Sedat Nizamoglu, Pedro Ludwig Hernández-Martínez, Evren Mutlugun, Durmus Ugur Karatay, and Hilmi Volkan Demir

Appl. Phys. Lett. 100, 241109 (2012); http://dx.doi.org/10.1063/1.4724109 (4 pages)

Online Publication Date: 13 June 2012

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We report strong exciton migration with an efficiency of 83.3% from a violet-emitting epitaxial quantum well (QW) to an energy gradient colloidal construct of layered green- and red-emitting nanocrystal quantum dots (NQDs) at room temperature, enabled by the interplay between the exciton population and the depopulation of states in the optical near field. Based on the density matrix formalization of near-field interactions, we theoretically model and demonstrate that the energy gradient significantly boosts the QW-NQDs exciton transfer rate compared to using mono-dispersed NQDs, which is in agreement with the observed experimental results.
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73.21.Fg Quantum wells
73.21.La Quantum dots
82.70.Dd Colloids
73.22.Lp Collective excitations
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Terahertz scattering by dense media

Mayank Kaushik, Brian W.-H. Ng, Bernd M. Fischer, and Derek Abbott

Appl. Phys. Lett. 100, 241110 (2012); http://dx.doi.org/10.1063/1.4720078 (4 pages)

Online Publication Date: 14 June 2012

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Frequency dependent absorption of a given material at distinct frequencies in the terahertz (THz) range is commonly used as a spectral fingerprint for material identification and classification. However, in the presence of strong scattering, these features can often become distorted or altered. Thus, there is an important need to understand how scattering from a sample alters the THz signal. In this letter, we propose an iterative algorithm that builds on the effective field theory proposed by P. C. Waterman and R. Truell [J. Math. Phys. 2, 512–537 (1961)] and offers a rather simple and computationally efficient method for accurately explaining the multiple scattering response of a medium.
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78.70.Gq Microwave and radio-frequency interactions
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Afterpulse-like noise limits dynamic range in time-gated applications of thin-junction silicon single-photon avalanche diode

A. Dalla Mora, D. Contini, A. Pifferi, R. Cubeddu, A. Tosi, and F. Zappa

Appl. Phys. Lett. 100, 241111 (2012); http://dx.doi.org/10.1063/1.4729389 (4 pages) | Cited 3 times

Online Publication Date: 14 June 2012

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We describe a source of noise in thin-junction silicon single-photon avalanche diode arising after strong illumination either during the ON (voltage above breakdown) or the OFF (voltage below breakdown) time. It increases the background noise with respect to primary dark count rate similarly to the afterpulsing process, but it is not related to a previous detector ignition. The amount of noise is linearly dependent on the power of light impinging on the detector and time constants are independent of the electric field. This phenomenon is the main limiting factor for the dynamic-range during time-gated measurements in condition of strong illumination.
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85.30.Kk Junction diodes
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Crack-free InGaN multiple quantum wells light-emitting diodes structures transferred from Si (111) substrate onto electroplating copper submount with embedded electrodes

Tufu Chen, Yunqian Wang, Peng Xiang, Ruihong Luo, Minggang Liu, Weimin Yang, Yuan Ren, Zhiyuan He, Yibin Yang, Weijie Chen, Xiaorong Zhang, Zhisheng Wu, Yang Liu, and Baijun Zhang

Appl. Phys. Lett. 100, 241112 (2012); http://dx.doi.org/10.1063/1.4729414 (4 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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Crack-free InGaN multiple quantum wells (MQWs) light-emitting diodes with embedded electrode structures (EE-LEDs) were transferred from Si (111) substrate onto the electroplating copper submount. Crystalline quality was investigated by the high resolution x-ray diffraction (HR-XRD) measurement, in which no obvious deteriorations were found in the MQWs structure after the LEDs transferred from silicon substrate onto copper except for a partial residual strain relaxation in the film. The strain relaxation after silicon removal leads to a reduction in quantum confined stark effect (QCSE), which results in the enhancement of internal quantum efficiency (IQE). In comparison to the conventional LEDs on silicon substrate, the light output of the EE-LEDs on copper was enhanced by 122% at an injection current of 350 mA. Besides the enhancement of IQE, the improvement is also attributed to the following factors: the removal of the absorptive substrate, the inserting of the metal reflector between the EE-LEDs structure and the copper submount, the elimination of the electrode-shading, and the rough surface of the exposed AlN buffer layer.
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85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices
82.45.Qr Electrodeposition and electrodissolution
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Far-infrared intersubband photodetectors based on double-step III-nitride quantum wells

Faisal F. Sudradjat, Wei Zhang, Jeffrey Woodward, Habibe Durmaz, Theodore D. Moustakas, and Roberto Paiella

Appl. Phys. Lett. 100, 241113 (2012); http://dx.doi.org/10.1063/1.4729470 (4 pages) | Cited 2 times

Online Publication Date: 14 June 2012

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Far-infrared photoconductive detectors based on intersubband transitions in III-nitride semiconductor quantum wells are demonstrated. The device active material is based on a double-step quantum-well design, where two different (Al)GaN compositions are used both in the wells and in the barriers. With this approach, one can create a virtually flat multiple-quantum-well potential energy profile, where the deleterious effects of the intrinsic spontaneous and piezoelectric fields of nitride heterostructures are almost completely eliminated. Photocurrent spectra centered at a wavelength of 23 μm (13 THz frequency) are resolved up to 50 K, with responsivity of approximately 7 mA/W.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Efficient measurement of broadband terahertz optical activity

Daniel J. Aschaffenburg, Michael R. C. Williams, Diyar Talbayev, Daniel F. Santavicca, Daniel E. Prober, and Charles A. Schmuttenmaer

Appl. Phys. Lett. 100, 241114 (2012); http://dx.doi.org/10.1063/1.4729148 (5 pages)

Online Publication Date: 15 June 2012

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We report a method to determine the four Stokes parameters of each spectral component in a broadband terahertz (THz) pulse by using a continuously rotating analyzer and a standard THz time domain spectroscopy (THz-TDS) instrument. A complete characterization of the polarization state at each frequency is obtained through a single time-domain measurement. Our method requires no specialized THz emitters or detectors; it is, therefore, perfectly general and suitable for any existing THz-TDS apparatus.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Resonant slot nanoantennas for surface plasmon radiation in optical frequency range

Jiasen Zhang, Weiwei Zhang, Xinli Zhu, Jing Yang, Jun Xu, and Dapeng Yu

Appl. Phys. Lett. 100, 241115 (2012); http://dx.doi.org/10.1063/1.4729552 (4 pages)

Online Publication Date: 15 June 2012

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We demonstrate resonant slot nanoantennas on Ag film for surface plasmon (SP) radiation in optical frequency range. Radiation spectra of the nanoantennas and resonant mode patterns for different mode orders with high spatial resolution are obtained using cathodoluminescence spectroscopy. The dispersions are obtained from the experimental data, and the far-field angular distributions of the radiation are simulated for the four lowest modes. The nanoantennas, which can realize resonant conversion between free space light and SPs at nanoscale, should find applications in nanophotonic devices and integrated optical circuits.
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84.40.Ba Antennas: theory, components and accessories
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Electronic and quantum phase coherence properties of bismuth thin films

M. Rudolph and J. J. Heremans

Appl. Phys. Lett. 100, 241601 (2012); http://dx.doi.org/10.1063/1.4729035 (4 pages)

Online Publication Date: 11 June 2012

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We present a method to deposit bulk-like Bi films by thermal evaporation and study the electrical, quantum coherence, and physical properties. A two stage growth procedure was found to optimize the film properties, with an initial wetting layer deposited at lower temperature followed by an active layer at higher temperature. Transport measurements indicate carrier properties comparable to molecular beam epitaxial films and display weak-antilocalization, from which the quantum phase coherence lengths are deduced. A 76 nm film is found to optimally exhibit both bulk-like Bi characteristics and the 2-dimensional quantum coherence properties desired for Bi-based quantum devices.
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71.20.Gj Other metals and alloys
72.15.Rn Localization effects (Anderson or weak localization)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.aj Insulators
68.08.Bc Wetting

Graphene monolayer rotation on Ni(111) facilitates bilayer graphene growth

Arjun Dahal, Rafik Addou, Peter Sutter, and Matthias Batzill

Appl. Phys. Lett. 100, 241602 (2012); http://dx.doi.org/10.1063/1.4729150 (4 pages) | Cited 3 times

Online Publication Date: 11 June 2012

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Synthesis of bilayer graphene by chemical vapor deposition is of importance for graphene-based field effect devices. Here, we demonstrate that bilayer graphene preferentially grows by carbon-segregation under graphene sheets that are rotated relative to a Ni(111) substrate. Rotated graphene monolayer films can be synthesized at growth temperatures above 650 °C on a Ni(111) thin-film. The segregated second graphene layer is in registry with the Ni(111) substrate and this suppresses further C-segregation, effectively self-limiting graphene formation to two layers.
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81.05.ue Graphene
68.35.Dv Composition, segregation; defects and impurities
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Pq Graphene films

Structured surfaces for enhanced pool boiling heat transfer

Kuang-Han Chu, Ryan Enright, and Evelyn N. Wang

Appl. Phys. Lett. 100, 241603 (2012); http://dx.doi.org/10.1063/1.4724190 (4 pages) | Cited 2 times

Online Publication Date: 11 June 2012

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We experimentally investigated surface roughness-augmented wettability on critical heat flux (CHF) during pool boiling with horizontally oriented surfaces. Microstructured surfaces with a wide range of well-defined surface roughness were fabricated, and a maximum CHF of ∼208 W/cm2 was achieved with a surface roughness of ∼6. An analytical force-balance model was extended to explain the CHF enhancement. The excellent agreement found between the model and experimental data supports the idea that roughness-amplified capillary forces are responsible for the CHF enhancement on structured surfaces. The insights gained from this work suggest design guidelines for new surface technologies with high heat removal capability.
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47.55.dd Bubble dynamics
47.55.dp Cavitation and boiling
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena

Atomic intermixing in short-period InAs/GaSb superlattices

Y. Ashuach, Y. Kauffmann, D. Isheim, Y. Amouyal, D. N. Seidman, and E. Zolotoyabko

Appl. Phys. Lett. 100, 241604 (2012); http://dx.doi.org/10.1063/1.4729058 (4 pages) | Cited 3 times

Online Publication Date: 12 June 2012

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High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and laser-assisted local-electrode atom-probe (LEAP) tomography are utilizing for characterizing short-period InAs/GaSb superlattices with an emphasis on obtaining the atomic concentration profiles with sub-nm resolution. HAADF-STEM permits direct visualization and counting of atomic columns in individual sub-layers. The spatial resolution of HAADF-STEM is sufficient to resolve the anion-cation dumbbells and, on this basis, to follow the atomic distributions across a superlattice. Both methods confirm that InAs-on-GaSb interfaces are wider than GaSb-on-InAs interfaces. The interfacial widths deduced from LEAP tomographic measurements are slightly larger than those extracted from HAADF-STEM micrographs, with the maximum total width not exceeding 4.5 monolayers. LEAP tomographic analysis shows the presence of about 7 at. % of Sb atoms in the middle of the InAs sub-layers, as a result of As/Sb substitutions during growth.
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68.65.Cd Superlattices
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.35.Ct Interface structure and roughness

Electrical growth of metallic nanoparticles in mesoporous silica films using atomic force microscopy

Christophe Hubert, Hamza Amrani, Murtaza Ali Khan, Francis Vocanson, and Nathalie Destouches

Appl. Phys. Lett. 100, 241605 (2012); http://dx.doi.org/10.1063/1.4729039 (3 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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We report the formation of silver nanoparticles in mesoporous silica films under a polarized micro-tip. By applying a bias voltage between an atomic force microscope conductive tip and an indium tin oxide substrate, reduction of silver ions initially impregnated in a mesoporous silica film occurs and leads to the creation of silver nanoparticles. This technique allows both the precise positioning of the nanoparticles via the control of the tip position and the control of the nanoparticles size by varying the bias voltage applied to the tip or the contact time.
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81.16.-c Methods of micro- and nanofabrication and processing
61.43.Gt Powders, porous materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Ps Atomic force microscopy (AFM)

Graphene on Rh(111): Scanning tunneling and atomic force microscopies studies

E. N. Voloshina, Yu. S. Dedkov, S. Torbrügge, A. Thissen, and M. Fonin

Appl. Phys. Lett. 100, 241606 (2012); http://dx.doi.org/10.1063/1.4729549 (4 pages) | Cited 8 times

Online Publication Date: 14 June 2012

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The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.
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73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
71.20.-b Electron density of states and band structure of crystalline solids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)

The influence of substrate morphology on thickness uniformity and unintentional doping of epitaxial graphene on SiC

Jens Eriksson, Ruth Pearce, Tihomir Iakimov, Chariya Virojanadara, Daniela Gogova, Mike Andersson, Mikael Syväjärvi, Anita Lloyd Spetz, and Rositza Yakimova

Appl. Phys. Lett. 100, 241607 (2012); http://dx.doi.org/10.1063/1.4729556 (5 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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A pivotal issue for the fabrication of electronic devices on epitaxial graphene on SiC is controlling the number of layers and reducing localized thickness inhomogeneities. Of equal importance is to understand what governs the unintentional doping of the graphene from the substrate. The influence of substrate surface topography on these two issues was studied by work function measurements and local surface potential mapping. The carrier concentration and the uniformity of epitaxial graphene samples grown under identical conditions and on substrates of nominally identical orientation were both found to depend strongly on the terrace width of the SiC substrate after growth.
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68.35.bt Other materials
73.30.+y Surface double layers, Schottky barriers, and work functions
65.40.gh Work functions
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Optical manipulation of shape-morphing elastomeric liquid crystal microparticles doped with gold nanocrystals

Yaoran Sun, Julian S. Evans, Taewoo Lee, Bohdan Senyuk, Patrick Keller, Sailing He, and Ivan I. Smalyukh

Appl. Phys. Lett. 100, 241901 (2012); http://dx.doi.org/10.1063/1.4729143 (5 pages) | Cited 3 times

Online Publication Date: 12 June 2012

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We demonstrate facile optical manipulation of shape of birefringent colloidal microparticles made from liquid crystal elastomers. Using soft lithography and polymerization, we fabricate elastomeric microcylinders with weakly undulating director oriented on average along their long axes. These particles are infiltrated with gold nanospheres acting as heat transducers that allow for an efficient localized transfer of heat from a focused infrared laser beam to a submicrometer region within a microparticle. Photothermal control of ordering in the liquid crystal elastomer using scanned beams allows for a robust control of colloidal particles, enabling both reversible and irreversible changes of shape. Possible applications include optomechanics, microfluidics, and reconfigurable colloidal composites with shape-dependent self-assembly.
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42.70.Jk Polymers and organics
61.30.Vx Polymer liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
82.35.Ej Nonlinear optics with polymers
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
42.70.Df Liquid crystals

A polymer electrolyte with high luminous transmittance and low solar throughput: Polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide with In2O3:Sn nanocrystals

İ. Bayrak Pehlivan, E. L. Runnerstrom, S.-Y. Li, G. A. Niklasson, D. J. Milliron, and C. G. Granqvist

Appl. Phys. Lett. 100, 241902 (2012); http://dx.doi.org/10.1063/1.4728994 (4 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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Chemically prepared ∼13-nm-diameter nanocrystals of In2O3:Sn were included in a polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide electrolyte and yielded high haze-free luminous transmittance and strong near-infrared absorption without deteriorated ionic conductivity. The optical properties could be reconciled with effective medium theory, representing the In2O3:Sn as a free electron plasma with tin ions screened according to the random phase approximation corrected for electron exchange. This type of polymer electrolyte is of large interest for opto-ionic devices such as laminated electrochromic smart windows.
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81.16.-c Methods of micro- and nanofabrication and processing
82.45.Gj Electrolytes
66.30.hk Polymers
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.Jw Organic compounds, polymers
81.07.Bc Nanocrystalline materials

Strain-assisted bandgap modulation in Zn based II-VI semiconductors

S. K. Yadav and R. Ramprasad

Appl. Phys. Lett. 100, 241903 (2012); http://dx.doi.org/10.1063/1.4729153 (4 pages) | Cited 2 times

Online Publication Date: 14 June 2012

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The electronic structure of bulk ZnX (X = O, S, Se, and Te) under uniaxial strain along the [0001] direction or equibiaxial strain along the (0001) plane is investigated using hybrid density functional theory calculations and many-body perturbation theory. It is shown that compressive uniaxial (or tensile equibiaxial) strains lead to a structural phase transition in all the ZnX systems. This is accompanied by large reductions in the bandgap of ZnSe and ZnTe, spanning the entire visible spectrum.
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71.20.Nr Semiconductor compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.70.kg Semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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