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27 Aug 2012

Volume 101, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 091102 (2012); http://dx.doi.org/10.1063/1.4747168 (3 pages)

Hagay Shpaisman, Bhaskar Jyoti Krishnatreya, and David G. Grier
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Geometry-induced magnetoelectric effect enhancement and noise floor reduction in Metglas/piezofiber sensors

Yaojin Wang, Menghui Li, D. Hasanyan, Junqi Gao, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 101, 092905 (2012); http://dx.doi.org/10.1063/1.4737906 (4 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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The geometry-dependent magnetoelectric (ME) effect was theoretically and experimentally investigated for multi-push-pull mode Metglas/Pb(Zr,Ti)O3 sandwich-like laminates. Such structures hold promise for passive sensor applications. A geometry-induced significant enhancement in the ME coefficient and an effective reduction in the equivalent magnetic noise was observed due to an increase in the Metglas width fraction.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
75.85.+t Magnetoelectric effects, multiferroics

Electric field induced phase instability in typical (Na,K)(Nb,Sb)O3-LiTaO3 ceramics near orthorhombic and tetragonal phase boundary

Ruzhong Zuo, Jian Fu, G. Z. Yin, X. L. Li, and J. Z. Jiang

Appl. Phys. Lett. 101, 092906 (2012); http://dx.doi.org/10.1063/1.4748320 (4 pages) | Cited 2 times

Online Publication Date: 31 August 2012

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The Li, Ta, and Sb modified (Na,K)NbO3 ceramics were reported to exhibit excellent piezoelectric properties typically in the vicinity of orthorhombic (O) and tetragonal (T) phase boundaries. Ex- and in-situ synchrotron x-ray diffraction measurements have provided a direct evidence of the electric-field induced phase instability owing to reversible phase transition between monoclinic (Mc) phase and T phase. A low-symmetry Mc phase was irreversibly produced from the initial O phase after the electric field was applied. Experimental results suggested that the Mc-T phase coexistence and reversible Mc-T phase transition (phase instability) may be responsible for enhanced piezoelectric activity in these compositions.
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77.65.-j Piezoelectricity and electromechanical effects
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
64.70.K- Solid-solid transitions
77.84.Ek Niobates and tantalates
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Foucault imaging by using non-dedicated transmission electron microscope

Yoshifumi Taniguchi (谷口佳史), Hiroaki Matsumoto (松本弘昭), and Ken Harada (原田研)

Appl. Phys. Lett. 101, 093101 (2012); http://dx.doi.org/10.1063/1.4748124 (4 pages)

Online Publication Date: 27 August 2012

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An electron optical system for observing Foucault images was constructed using a conventional transmission electron microscope without any special equipment for Lorentz microscopy. The objective lens was switched off and an electron beam was converged by a condenser optical system to the crossover on the selected area aperture plane. The selected area aperture was used as an objective aperture to select the deflected beam for Foucault mode, and the successive image-forming lenses were controlled for observation of the specimen images. The irradiation area on the specimen was controlled by selecting the appropriate diameter of the condenser aperture.
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07.60.Pb Conventional optical microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.79.Bh Lenses, prisms and mirrors

Low bias short channel impurity mobility in graphene from first principles

Zi Wang, Youqi Ke, Dongping Liu, Hong Guo, and Kirk H. Bevan

Appl. Phys. Lett. 101, 093102 (2012); http://dx.doi.org/10.1063/1.4748326 (5 pages)

Online Publication Date: 27 August 2012

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In theory, graphene should exhibit very high carrier mobility, however its measured mobility is usually much lower. This discrepancy between theory and empirical observations is believed to be due to disordered scattering. We present a systematic first principles study of diffusive impurity scattering in short channel graphene. We achieve good agreement with experimental data and show that mobility in graphene is strongly influenced by impurity scattering. In general, the results show that diffusive scattering can play a key role in determining the carrier transport properties of short channel devices.
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72.80.Vp Electronic transport in graphene
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Nucleation features and energy levels of type-II InAsSbP quantum dots grown on InAs(100) substrate

K. M. Gambaryan, V. M. Aroutiounian, and V. G. Harutyunyan

Appl. Phys. Lett. 101, 093103 (2012); http://dx.doi.org/10.1063/1.4748574 (5 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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The nucleation features and measurements of holes energy levels of the InAsSbP type-II quantum dots (QDs) with respect to the InAs valence band edge by employing magnetospectroscopy and a photo- and electroluminescence measurements are reported. Three samples are prepared for investigations. The first and second samples consist of unencapsulated spherical and ellipsoidal QDs, respectively. Third sample is a n-InAs/p-InAsSbP heterostructure with QDs embedded into the p-n junction interface. The measured value for the holes first state is ∼33 meV above the InAs valence band. The hysteresis of 0.483 pF and contra-directional oscillations on the first sample’s capacitance-voltage characteristic is detected.
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81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.60.Fi Electroluminescence
78.20.Ls Magneto-optical effects
73.21.La Quantum dots

Generation of high-resolution kagome lattice structures using extreme ultraviolet interference lithography

Li Wang, Bernd Terhalle, Vitaliy A. Guzenko, Alan Farhan, Mohamad Hojeij, and Yasin Ekinci

Appl. Phys. Lett. 101, 093104 (2012); http://dx.doi.org/10.1063/1.4748758 (5 pages) | Cited 2 times

Online Publication Date: 27 August 2012

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High-resolution kagome lattice structures with feature sizes down to the sub-50 nm regime are fabricated using diffraction-based extreme ultraviolet interference lithography. The resulting interference pattern of multiple beams is sensitive to the relative phase of the interfering beams. The precise control of their phases is achieved by precise positioning of transmission diffraction gratings on a mask using a high-end electron beam lithography tool. The presented method may find applications in providing high-resolution and large-area kagome lattice structures for studies on frustrated magnetic systems, photonic crystals, and plasmonics.
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81.16.Nd Micro- and nanolithography
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

High-Q gold and silicon nitride bilayer nanostrings

T. S. Biswas, A. Suhel, B. D. Hauer, A. Palomino, K. S. D. Beach, and J. P. Davis

Appl. Phys. Lett. 101, 093105 (2012); http://dx.doi.org/10.1063/1.4748977 (5 pages)

Online Publication Date: 28 August 2012

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Low-mass, high-Q, silicon nitride nanostrings are at the cutting edge of nanomechanical devices for sensing applications. Here we show that the addition of a chemically functionalizable gold overlayer does not adversely affect the Q of the fundamental out-of-plane mode. Instead the device retains its mechanical responsiveness while gaining sensitivity to molecular bonding. Furthermore, differences in thermal expansion within the bilayer give rise to internal stresses that can be electrically controlled. In particular, an alternating current (AC) excites resonant motion of the nanostring. This AC thermoelastic actuation is simple, robust, and provides an integrated approach to sensor actuation.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Absorption spectroscopy of individual cadmium selenide nanowire

Fajun Xiao, Kaihui Liu, Yaqing Bie, Jianlin Zhao, and Feng Wang

Appl. Phys. Lett. 101, 093106 (2012); http://dx.doi.org/10.1063/1.4739786 (3 pages)

Online Publication Date: 29 August 2012

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We develop a technique to measure the absorption spectrum of individual nanowires with the supercontinuum laser based Fourier transform spectroscopy. It employs photocurrent of a nanowire as the signal for Fourier transform spectroscopy. We demonstrate this technique in obtaining absorption spectrum of individual cadmium selenide nanowires, and determine the nanowires absorption bandgap of 1.75 eV. This technique has high detection sensitivity. Potentially it will be able to measure absorption cross-section as small as 19 nm2 per μm for a focus laser spot of 1 μm, and could be a general method to detect the absorption spectrum of individual quasi-one-dimensional nanomaterials.
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07.60.-j Optical instruments and equipment
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
78.30.Fs III-V and II-VI semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

In situ transmission electron microscopy study of dielectric breakdown of surface oxides during electric field-assisted sintering of nickel nanoparticles

Cecile S. Bonifacio, Jorgen F. Rufner, Troy B. Holland, and Klaus van Benthem

Appl. Phys. Lett. 101, 093107 (2012); http://dx.doi.org/10.1063/1.4749284 (5 pages) | Cited 2 times

Online Publication Date: 30 August 2012

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The removal of ultra-thin oxide surface layers on nanometric nickel particles is investigated in the framework of electric field-induced dielectric breakdown. In situ transmission electron microscopy was used to directly apply electrical biasing to agglomerates of nanoparticles during simultaneous imaging of the contact area between two adjacent particles. The applied electrical field initiated dielectric breakdown of the surface layers through percolation of oxygen vacancies and the migration of oxygen away from the particle contact, which leads to the formation of metallic necks and their subsequent growth. The experimental results represent direct evidence for surface cleaning effects during electric field-assisted sintering.
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77.22.Jp Dielectric breakdown and space-charge effects
81.65.Cf Surface cleaning, etching, patterning
61.72.jd Vacancies
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Lp Transmission electron microscopy (TEM)

Exchange-coupled dopants in Si quantum dots

A. J. Almeida, R. N. Pereira, and M. S. Brandt

Appl. Phys. Lett. 101, 093108 (2012); http://dx.doi.org/10.1063/1.4748324 (4 pages)

Online Publication Date: 30 August 2012

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The electronic structure of exchange-coupled donors in Si quantum dots (QDs) is predicted using effective mass theory, enabling the calculation of many dopant configurations. We account for the statistical distribution of dopants in QD ensembles with a broad range of mean sizes and doping concentrations. A quenching of the magnetic resonance intensity of exchange-coupled donors is inferred, which is more pronounced for smaller QDs. We further show that in QDs smaller than ∼ 2.5 nm, the quantization (and broadness) of the distribution of exchange energies yields a step-like behavior in the magnetic resonance temperature dependence, as observed in recent experiments.
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71.20.Mq Elemental semiconductors
61.72.sh Impurity distribution
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.La Quantum dots
76.30.-v Electron paramagnetic resonance and relaxation

Small-scale effect on the mechanical properties of metallic nanotubes

Jin Zhang, Chengyuan Wang, Rajib Chowdhury, and Sondipon Adhikari

Appl. Phys. Lett. 101, 093109 (2012); http://dx.doi.org/10.1063/1.4748975 (4 pages) | Cited 1 time

Online Publication Date: 30 August 2012

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The residual stress and elastic modulus for the surface and core layers of metallic nanotubes (MNTs) are studied based on molecular dynamics simulations. The resultant small-scale effect is then demonstrated in a case study on the vibration of MNTs. In contrast to previous assumptions, it is found that the residual stresses at the inner and outer surfaces differ by several times and change sensitively with the geometric size of MNTs. In addition, the core layer stress ignored in most previous studies can also exert substantial influence on the structural response of MNTs. It is believed that these results can provide important guidance for the future study and potential applications of MNTs.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Robust mesoscopic fluctuations in disordered graphene

G. Bohra, R. Somphonsane, N. Aoki (青木伸之), Y. Ochiai (落合勇一), D. K. Ferry, and J. P. Bird

Appl. Phys. Lett. 101, 093110 (2012); http://dx.doi.org/10.1063/1.4748167 (5 pages) | Cited 2 times

Online Publication Date: 31 August 2012

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The temperature dependence of the mesoscopic conductance fluctuations is investigated for disordered graphene. The fluctuations are generated by varying either magnetic field or carrier density (via a back-gate). Very different temperature cut-offs are found for these two types of fluctuations, with the density-induced features persisting to much higher temperatures (beyond 100 K, even) than those observed when sweeping magnetic field. The robust character of the density-dependent fluctuations may cause them to play an important role in determining the operation of future graphene nanodevices, particularly as device sizes are reduced to the nanoscale.
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73.61.Wp Fullerenes and related materials
72.20.Fr Low-field transport and mobility; piezoresistance
73.23.-b Electronic transport in mesoscopic systems
72.80.Vp Electronic transport in graphene

Graphene cantilever beams for nano switches

Peng Li, Zheng You, and Tianhong Cui

Appl. Phys. Lett. 101, 093111 (2012); http://dx.doi.org/10.1063/1.4738891 (5 pages) | Cited 2 times

Online Publication Date: 31 August 2012

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A method named sacrificial beam is presented to fabricate graphene cantilever devices. The mechanical properties of graphene cantilevers are studied using atomic force microscopy. Graphene cantilever based 2-terminal nano-electro-mechanical systems switches are demonstrated, and their DC characteristics and switch performance are investigated. A 3-terminal switch based on a graphene cantilever is fabricated, and its electrical properties are also studied.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Sheaf-like-ZnO@Ag nanocomposite materials modified photoanode for low-cost metal-free organic dye-sensitized solid-state solar cells

A. Pandikumar, K. M. Saranya, and R. Ramaraj

Appl. Phys. Lett. 101, 093112 (2012); http://dx.doi.org/10.1063/1.4748287 (4 pages)

Online Publication Date: 31 August 2012

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Sheaf-like-ZnO-Ag nanocomposite material (sheaf-like-(ZnO@Ag)NCM) was prepared and used as photoanode in dye-sensitized solar cell. Eosin-Y adsorbed photoanode was employed, and the overall efficiency (η) was found to be 1.39% under standard AM 1.5G simulated solar irradiation (100 mWcm−2) which is ∼2-fold higher than that of ZnO nanorods (ZnO NRs), owing to the presence of an effective interfacial charge transfer processes through the Ag from the excited state of eosin-Y to ZnO. The obtained efficiency is also compared to the sensitized with N719, whose efficiency (1.8%) is ∼30% higher than that of the cells sensitized with eosin-Y.
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88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics

Mobile acoustic streaming based trapping and 3-dimensional transfer of a single nanowire

Ning Li, Junhui Hu, Huaqing Li, Satyanarayan Bhuyan, and Yujie Zhou

Appl. Phys. Lett. 101, 093113 (2012); http://dx.doi.org/10.1063/1.4745846 (4 pages)

Online Publication Date: 31 August 2012

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Acoustic manipulations of single nanoscale entities were not realized before this work owing to the acoustic streaming which usually flushes a trapped entity away. Here, we demonstrate a strategy that uses mobile acoustic streaming to effectively trap and align a single nanowire within water film on substrate surface, and stably transfers a trapped nanowire through an arbitrary 3-dimensional path in the water film. The streaming is generated by a vibrating micro-probe with uniform diameter. In our experiments, a trapped nanowire is constantly on the side of the micro-probe tip, perpendicular to the micro-probe vibration, and symmetric about the micro-probe approximately.
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68.65.La Quantum wires (patterned in quantum wells)
81.16.Ta Atom manipulation
82.80.-d Chemical analysis and related physical methods of analysis
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.07.Gf Nanowires
43.25.Nm Acoustic streaming
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On the triplet distribution and its effect on an improved phosphorescent organic light-emitting diode

S. W. Liu, Y. Divayana, A. P. Abiyasa, S. T. Tan, H. V. Demir, and X. W. Sun

Appl. Phys. Lett. 101, 093301 (2012); http://dx.doi.org/10.1063/1.4749278 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2012

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We reported phosphorescent organic light-emitting diodes with internal quantum efficiency near 100% with significantly reduced efficiency roll-off. It was found that the use of different hole transporting layer (HTL) affects the exciton distribution in the emission region significantly. Our best device reaches external quantum efficiency (EQE), current, and power efficiency of 22.8% ± 0.1%, 78.6 ± 0.2 cd/A, 85 ± 2 lm/W, respectively, with half current of 158.2 mA/cm2. This considerably outperforms the control device with N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) (HTL) and 4,4′-N,N′-dicarbazole-biphenyl (host) with maximum EQE, current and power efficiency of 19.1% ± 0.1%, 65.6 ± 0.3 cd/A, 67 ± 2 lm/W, respectively, with half current of only 8.1 mA/cm2.
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85.60.Jb Light-emitting devices
FREE

Polymer light-emitting devices based on a polymer/salt mixture

Bathilde Gautier and Jun Gao

Appl. Phys. Lett. 101, 093302 (2012); http://dx.doi.org/10.1063/1.4749286 (4 pages)

Online Publication Date: 28 August 2012

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In this paper, we report on polymer light-emitting devices based on the mixture of a common luminescent polymer and a lithium salt. The sandwich polymer/salt devices with aluminum electrodes are poor emitters as constructed, but undergo a unique turn on process when a large voltage bias is applied at room temperature. Once activated, the devices exhibit vastly improved electroluminescence and prompt response to applied voltage. Moreover, the devices exhibit a luminance shelf life of approx. 150 h when stored at room temperature without bias. We show detailed device characteristics and discuss possible operating mechanisms for such devices. We also discuss the implication of such devices with regard to room-temperature frozen-junction devices.
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85.60.Jb Light-emitting devices
FREE

Magnetic-field dependent differential capacitance of polymer diodes

Thaddee K. Djidjou, Tek Basel, and Andrey Rogachev

Appl. Phys. Lett. 101, 093303 (2012); http://dx.doi.org/10.1063/1.4748797 (4 pages)

Online Publication Date: 28 August 2012

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Using admittance spectroscopy, we found that bipolar organic diodes based on pi-conjugated polymer, 2-methoxy-5-(2′-ethylhexyloxy), MEH-PPV, have strong divergent contribution to the device differential capacitance. It is positive at low bias voltages, turns negative at intermediate biases, and becomes positive again at stronger biases. In addition, we found that at certain biases, a small magnetic field can change the capacitance from divergent negative to divergent positive. Possible physical processes responsible for this anomalous behavior of the capacitance and its relation to the phenomenon of organic magnetoresistance are discussed.
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85.60.Jb Light-emitting devices
FREE

Time-of-flight mobility of charge carriers in position-dependent electric field between coplanar electrodes

Egon Pavlica and Gvido Bratina

Appl. Phys. Lett. 101, 093304 (2012); http://dx.doi.org/10.1063/1.4742149 (5 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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Time-of-flight measurements of the photocurrent in thin organic semiconductor layers represent an effective way to extract charge carrier mobility. A common method to interpret the time-dependence of the photocurrent in these material systems assumes a position-independent electric field between two coplanar electrodes. In this letter, we compare time-dependence of the photocurrent, measured in the samples comprising thin layers of poly-3-hexylthiophene, with the Monte Carlo simulations. In the simulations, we have used both, a position-independent and a position-dependent electric field. We obtained a favorable agreement between the simulations and the measurements only in the case of position-dependent electric field. We demonstrate that the charge carrier mobility may be underestimated by more than one order of magnitude, if a position-independent electric field is used in the calculations of the mobility.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.40.+w Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
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Work function recovery of air exposed molybdenum oxide thin films

Irfan Irfan, Alexander James Turinske, Zhenan Bao, and Yongli Gao

Appl. Phys. Lett. 101, 093305 (2012); http://dx.doi.org/10.1063/1.4748978 (4 pages) | Cited 2 times

Online Publication Date: 29 August 2012

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We report substantial work function (WF) recovery of air exposed molybdenum oxide thin films with vacuum annealing. We observed a sharp reduction in the MoOx WF (from 6.8 eV to 5.6 eV) as well as a very thin layer of oxygen rich adsorbate on the MoOx film after an hour of air exposure. The WF of the exposed MoOx film started to gradually recover with increasing annealing temperature in vacuum, and the saturation in the WF recovery was observed at 450 °C with WF ∼6.4 eV. We further studied the interface formation between the annealed MoOx and copper phthalocyanine (CuPc). The highest occupied molecular orbital (HOMO) level of CuPc was observed to be almost pinned to the Fermi level, strongly suggesting the possibility of efficient hole injection with the vacuum annealed MoOx film.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states
71.20.Ps Other inorganic compounds
68.43.Mn Adsorption kinetics
FREE

High-efficiency organic light-emitting diodes utilizing thermally activated delayed fluorescence from triazine-based donor–acceptor hybrid molecules

Sae Youn Lee, Takuma Yasuda, Hiroko Nomura, and Chihaya Adachi

Appl. Phys. Lett. 101, 093306 (2012); http://dx.doi.org/10.1063/1.4749285 (4 pages) | Cited 2 times

Online Publication Date: 30 August 2012

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We have designed and synthesized a high-efficiency purely organic luminescent material, 2,4-bis{3-(9 H-carbazol-9-yl)-9 H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA) comprising the bicarbazole donor and phenyltriazine acceptor units, which is capable of emitting thermally activated delayed fluorescence. The molecular design of CC2TA allows spatial separation of HOMO and LUMO on the donor and acceptor fragments, respectively, leading to an exceptionally small singlet–triplet exchange energy (ΔEST = 0.06 eV) together with a high triplet energy. Furthermore, a high external electroluminescence quantum efficiency as high as 11% ± 1% has been achieved in the sky-blue organic light-emitting diodes employing CC2TA as an emitter.
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85.60.Jb Light-emitting devices
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High output current in vertical polymer space-charge-limited transistor induced by self-assembled monolayer

Hsiao-Wen Zan, Yuan-Hsuan Hsu, Hsin-Fei Meng, Chian-Hao Huang, Yu-Tai Tao, and Wu-Wei Tsai

Appl. Phys. Lett. 101, 093307 (2012); http://dx.doi.org/10.1063/1.4748284 (4 pages) | Cited 1 time

Online Publication Date: 30 August 2012

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We present a promising solution-processed vertical transistor which exhibits high output current, high on/off current ratio, and low operation voltage. Numerous poly(3-hexylthiophene) vertical channels are embedded in vertical nanometer pores. Treating the sidewalls of pores by self-assemble monolayer with long alkyl chains enhances the pore-filling and inter-chain order of poly(3-hexylthiophene). The channel current is therefore greatly increased. A grid metal inside the porous template controls the channel potential profile to turn on and turn off the vertical transistor. Finally, the transistor delivers an output current density as 50–110 mA/cm2 at 2 V with an on/off current ratio larger than 10 000.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
85.30.Tv Field effect devices
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Influence of dielectric-dependent interfacial widths on device performance in top-gate P(NDI2OD-T2) field-effect transistors

Hongping Yan, Torben Schuettfort, Auke J. Kronemeijer, Christopher R. McNeill, and Harald W. Ade

Appl. Phys. Lett. 101, 093308 (2012); http://dx.doi.org/10.1063/1.4748976 (4 pages) | Cited 2 times

Online Publication Date: 30 August 2012

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Resonant soft x-ray reflectivity (R-SoXR) is employed to determine the interfacial widths of the semiconductor/dielectric interface in P(NDI2OD-T2)-based top-gate organic field-effect transistors (OFETs). It is shown that the deposition of a polymer dielectric on top of a semiconducting polymer layer can affect the interface structure, even when cast from an orthogonal solvent. The observed differences in the interfacial widths for different dielectrics explain the insensitivity of OFET performance to dielectric choice for OFETs fabricated using an identical fabrication protocol. The R-SoXR results demonstrate that differences in the physical interface structure should be taken into account when considering the influence of polymer dielectrics on the performance of all solution-processed OFETs. Specifically, the importance of the choice of solvent for the deposition is highlighted.
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85.30.Tv Field effect devices
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An experimental investigation of electrically induced-birefringence of Kerr effect in polymer-stabilized blue phase liquid crystals resulting from orientations of liquid crystals

Hung-Shan Chen, Shih-Ya Ni, and Yi-Hsin Lin

Appl. Phys. Lett. 101, 093501 (2012); http://dx.doi.org/10.1063/1.4748117 (4 pages)

Online Publication Date: 27 August 2012

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The electrically induced-birefringence (EIB) of Kerr effect of polymer-stabilized blue phase liquid crystals (PSBP-LCs) is experimentally investigated by discussing the orientations of liquid cryastal (LC) molecules. The results show that the EIB of Kerr effect of PSBP-LCs mainly results from the orientations of LC molecules when the voltage is larger than the voltage of disappearance of the lattice deformation; otherwise, lattice deformation is also involved in the contribution of EIB besides the orientations of LC molecules. This study proves that the orientations of liquid crystals indeed play roles in the EIB of Kerr effect in PSBP-LCs.
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78.20.Jq Electro-optical effects
61.30.Mp Blue phases and other defect-phases
78.20.Fm Birefringence

Electromagnetically induced transparencies in a closed waveguide with high efficiency and wide frequency band

Xian Qi Lin, Jia Wei Yu, Yuan Jiang, Jun Ye Jin, and Yong Fan

Appl. Phys. Lett. 101, 093502 (2012); http://dx.doi.org/10.1063/1.4748121 (3 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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We propose an effective method to alleviate the conflict between large group delay and wide frequency band in electromagnetically induced transparency (EIT) design. Two kinds of electrically induced transparency (E-IT) and magnetically induced transparency (M-IT) are proposed, respectively. Then an EIT with wide transparency window is developed by combining the independent E-IT and M-IT structures. All of the transparencies are designed in a closed waveguide system, and high efficiency is obtained at the same time. One sample is fabricated and the bandwidth is increased to more than 3 times without decrease of the group delay and increase of the size.
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42.79.Gn Optical waveguides and couplers
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
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