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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages)

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng
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Characterization of piezoelectric ceramics and 1-3 composites for high power transducers

Hyeong Jae Lee, Shujun Zhang, Richard J. Meyer, Jr., Nevin P. Sherlock, and Thomas R. Shrout

Appl. Phys. Lett. 101, 032902 (2012); http://dx.doi.org/10.1063/1.4737651 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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The high power characteristics of various piezoelectric ceramics and 1-3 composites were investigated. In contrast to “hard” Pb(Zr,Ti)O3, modified (Bi0.5Na0.5)TiO3 based ceramics were found to show a relatively linear electromechanical response under high drive conditions due to their high stability of mechanical quality factor. The effects of high drive field and duty cycle on the behavior of 1-3 composites were analyzed by varying active and passive components. Improved high power characteristics of 1-3 composites were achieved by selection of optimized composite components, with enhanced electromechanical efficiency and thermal stability under high drive conditions.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
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Electrical properties of the graphitic carbon contacts on carbon nanotube field effect transistors

Masato Tamaoki, Shigeru Kishimoto, Yutaka Ohno, and Takashi Mizutani

Appl. Phys. Lett. 101, 033101 (2012); http://dx.doi.org/10.1063/1.4737169 (3 pages)

Online Publication Date: 16 July 2012

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Carbon nanotube field effect transistors (CNT-FETs) with graphitic carbon (G-C) contacts were fabricated and the electrical properties of the G-C contacts were studied. The CNT-FETs showed p-type conduction in air. However, the conduction type has changed to ambipolar in vacuum after annealing at 200 °C. This suggests that the p-type conduction in air is attributed to the adsorbed oxygen. The barrier heights at the G-C/CNT contacts in vacuum were ∼400 meV for electrons and ∼310 meV for holes. These values suggest that the Fermi level of G-C contacts is located at slightly below the midgap of the CNTs in vacuum.
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85.35.Kt Nanotube devices
81.40.Gh Other heat and thermomechanical treatments
85.30.Tv Field effect devices

30-kV spin-polarized transmission electron microscope with GaAs–GaAsP strained superlattice photocathode

M. Kuwahara, S. Kusunoki, X. G. Jin, T. Nakanishi, Y. Takeda, K. Saitoh, T. Ujihara, H. Asano, and N. Tanaka

Appl. Phys. Lett. 101, 033102 (2012); http://dx.doi.org/10.1063/1.4737177 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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A spin-polarized electron beam has been used as the probe beam in a transmission electron microscope by using a photocathode electron gun with a photocathode made of a GaAs–GaAsP strained superlattice semiconductor with a negative electron affinity (NEA) surface. This system had a spatial resolution of the order of 1 nm for at 30 keV and it can generate an electron beam with an energy width of 0.24 eV without employing monochromators. This narrow width suggests that a NEA photocathode can realize a high energy resolution in electron energy-loss spectroscopy and a longitudinal coherence of 3 × 10−7 m.
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85.60.Ha Photomultipliers; phototubes and photocathodes
68.37.Lp Transmission electron microscopy (TEM)
84.47.+w Vacuum tubes

Synthesis of graphene-based Pt nanoparticles by a one-step in situ plasma approach under mild conditions

Qi Wang, Mingming Song, Changlun Chen, Yu Wei, Xiao Zuo, and Xiangke Wang

Appl. Phys. Lett. 101, 033103 (2012); http://dx.doi.org/10.1063/1.4737421 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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Herein, a one-step in situ plasma approach to synthesize the highly dispersed Pt nanoparticles on graphene under mild conditions is reported. The graphene oxide (GO) was transformed into graphene and H2PtCl6 was simultaneously transformed into Pt nanoparticles under argon plasma conditions. The synthesized graphene-based Pt nanoparticles were characterized by scanning electron microscopy, atomic force microscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The analysis showed that the Pt nanoparticles were deposited on graphene as a form of face-centered cubical structure and the oxygen groups on graphene oxide were partially removed. The results of x-ray photoelectron spectroscopy analysis further confirmed the results.
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81.16.-c Methods of micro- and nanofabrication and processing
52.77.Dq Plasma-based ion implantation and deposition
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)
78.30.-j Infrared and Raman spectra
79.60.Jv Interfaces; heterostructures; nanostructures

Organic-free suspension of large-area graphene

E. Ledwosinska, P. Gaskell, A. Guermoune, M. Siaj, and T. Szkopek

Appl. Phys. Lett. 101, 033104 (2012); http://dx.doi.org/10.1063/1.4737415 (4 pages)

Online Publication Date: 17 July 2012

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We report an entirely organic-free method to suspend monolayer graphene grown by chemical vapour deposition over 10–20 μm apertures in a Cu substrate. Auger electron spectroscopy, Raman spectroscopy, scanning electron microscope, and transmission electron microscope measurements confirm high quality graphene with no measurable contamination beyond that resulting from air exposure. This method can be used to prepare graphene for fundamental studies and applications where the utmost cleanliness and structural integrity are required.
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82.70.Kj Emulsions and suspensions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene
81.05.ue Graphene
78.30.Na Fullerenes and related materials

First-principles study of hydrogenated carbon nanotubes: A promising route for bilayer graphene nanoribbons

Pengcheng Chen, Yuanchang Li, Chen Si, Jian Wu, Jisoon Ihm, and Wenhui Duan

Appl. Phys. Lett. 101, 033105 (2012); http://dx.doi.org/10.1063/1.4737427 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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Using combined density functional theory and nonequilibrium Green’s function techniques, we demonstrate that hydrogenated armchair single-walled carbon nanotubes (H-CNTs) can exhibit electronic, magnetic, and transport properties remarkably similar to zigzag graphene nanoribbons (ZGNRs). Hydrogen atoms break the circumferential periodic boundary condition of CNTs, incising them into two ZGNRs structurally. The staggered stacking ensures these two ZGNRs to be almost decoupled electronically and retain the electronic properties of monolayer ZGNRs. Interestingly, H-CNTs show unique advantages and application prospects over ZGNRs for their bilayer structure and diverse magnetic couplings between spin-polarized edge states.
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61.46.Fg Nanotubes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.25.-b Spin polarized transport
73.22.-f Electronic structure of nanoscale materials and related systems
75.70.Ak Magnetic properties of monolayers and thin films
75.75.-c Magnetic properties of nanostructures

Eco-friendly electron beam lithography using water-developable resist material derived from biomass

Satoshi Takei, Akihiro Oshima, Takanori Wakabayashi, Takahiro Kozawa, and Seiichi Tagawa

Appl. Phys. Lett. 101, 033106 (2012); http://dx.doi.org/10.1063/1.4737639 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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We investigated the eco-friendly electron beam (EB) lithography using a high-sensitive negative type of water-developable resist material derived from biomass on hardmask layer for tri-layer processes. A water developable, non-chemically amplified, high sensitive, and negative tone resist material in EB lithography was developed for environmental affair, safety, easiness of handling, and health of the working people, instead of the common developable process of trimethylphenylammonium hydroxide. The images of 200 nm line and 800 nm space pattern with exposure dose of 7.0 μC/cm2 and CF4 etching selectivity of 2.2 with hardmask layer were provided by specific process conditions.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Probing the three-dimensional strain inhomogeneity and equilibrium elastic properties of single crystal Ni nanowires

E. Fohtung, J. W. Kim, Keith T. Chan, Ross Harder, Eric E. Fullerton, and O. G. Shpyrko

Appl. Phys. Lett. 101, 033107 (2012); http://dx.doi.org/10.1063/1.4737440 (4 pages)

Online Publication Date: 18 July 2012

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We employ three dimensional x-ray coherent diffraction imaging to map the lattice strain distribution, and to probe the elastic properties of a single crystalline Ni (001) nanowire grown vertically on an amorphous SiO2∥Si substrate. The reconstructed density maps show that with increasing wire width, the equilibrium compressive stress in the core region decreases sharply while the surface tensile strain increases, and gradually trends to a nonzero constant. We use the retrieved projection of lattice distortion to predict the Young’s Modulus of the wire based on the elasticity theory.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.de Elastic moduli
62.20.F- Deformation and plasticity
81.16.-c Methods of micro- and nanofabrication and processing

Fast electrothermally activated micro-positioner using a high-aspect-ratio micro-machined polymeric composite

Gih-Keong Lau, Jiaping Yang, Borriboon Thubthimthong, Nyok-Boon Chong, Cheng Peng Tan, and Zhimin He

Appl. Phys. Lett. 101, 033108 (2012); http://dx.doi.org/10.1063/1.4737644 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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Recently, silicon electrothermal micro-actuators have been developed for dual-stage micropositioning in hard disk drive. But, silicon with a low coefficient of thermal expansion (CTE) has a shortcoming of requiring a large temperature change (>300 °C) to expand adequately. This letter presented a high-CTE polymer composite to solve the shortcoming of silicon. The polymer composite consists of high-aspect-ratio micro-machined SU-8 thermal expander and silicon thermal conductor. A micro-positioner which embodies the proposed polymer composite can drive a slider to travel fast (>1 kHz) more than a 17 nm-pitch data track under a moderate temperature rise (<100 °C).
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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Graphene radio: Detecting radiowaves with a single atom sheet

M. Dragoman, D. Neculoiu, A. Cismaru, G. Deligeorgis, G. Konstantinidis, and D. Dragoman

Appl. Phys. Lett. 101, 033109 (2012); http://dx.doi.org/10.1063/1.4738762 (4 pages)

Online Publication Date: 20 July 2012

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We present the experimental evidence of RF demodulation by a graphene monolayer embedded in a coplanar structure. The demodulator was tested in the frequency range from 100 MHz to 25 GHz using amplitude modulated input signals. An input power of 0 dBm (1 mW) was used, which is the typical power emitted for short range wireless communication systems, such as Bluetooth. The graphene demodulator exhibits good signal responsivity in the frequency range associated to industrial, scientific and medical radio band with a peak of 1100 V/W at 3.5 GHz.
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84.40.Ua Telecommunications: signal transmission and processing; communication satellites
89.20.Kk Engineering

Enhanced magnetic anisotropy of Ni nanowire arrays fabricated on nano-structured silicon templates

P. Granitzer, K. Rumpf, T. Ohta, N. Koshida, M. Reissner, and P. Poelt

Appl. Phys. Lett. 101, 033110 (2012); http://dx.doi.org/10.1063/1.4738780 (4 pages) | Cited 1 time

Online Publication Date: 20 July 2012

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The magnetic function of a Ni-nanowire/silicon-template system has been explored in corporation with an advanced process. Arrays of nanopores with a mean diameter of 35 nm have been fabricated by anodization of silicon wafers under an external magnetic field (8 T) perpendicular to the substrate. Due to a guided supply of holes from the substrate during the anodization, well controlled straight nanopores have been formed with a high aspect ratio, and then isolated Ni nanowires have been grown along these nanopores by electrodeposition. The fabricated samples show a significantly enhanced magnetic anisotropy with little crosstalk between adjacent pores.
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75.30.Gw Magnetic anisotropy
81.15.Pq Electrodeposition, electroplating
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)
75.75.-c Magnetic properties of nanostructures
81.07.Gf Nanowires
75.75.Cd Fabrication of magnetic nanostructures
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Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng

Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages) | Cited 7 times

Online Publication Date: 16 July 2012

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In this work, hybrid heterojunction solar cells are demonstrated based on a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) directly spun-cast on micro-textured n-type crystalline silicon wafers. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency, leading to an average power conversion efficiency of 9.84%. A one-dimensional drift-diffusion model is then developed based on fitting the device characteristics with experimentally determined PEDOT:PSS parameters and projects an ultimate efficiency above 20% for organic/inorganic hybrid photovoltaics. The simulation results reveal the impacts of defect densities, back surface recombination, doping concentration, and band alignment.
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88.40.H- Solar cells (photovoltaics)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.07.Pr Organic-inorganic hybrid nanostructures
82.35.Cd Conducting polymers
82.45.Wx Polymers and organic materials in electrochemistry
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Top illuminated inverted organic ultraviolet photosensors with single layer graphene electrodes

Martin Burkhardt, Wei Liu, Christopher G. Shuttle, Kaustav Banerjee, and Michael L. Chabinyc

Appl. Phys. Lett. 101, 033302 (2012); http://dx.doi.org/10.1063/1.4733299 (4 pages)

Online Publication Date: 16 July 2012

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Inverted, top-illuminated organic photodiodes are demonstrated using transparent electrodes including single layer graphene (SLG) and thin gold or silver with poly(3-hexylthiophene) and 1 -(3-methoxycarboyl)-propyl-1-phenyl-(6,6)C61 as active layer. The devices are free of both indium-tin-oxide and poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate). The maximum solar power conversion efficiencies were 0.3% for SLG due to its series resistance and ∼2% for gold and silver. The organic photodiodes with SLG electrodes had good external quantum efficiency at incident illumination less than 10 mW/cm2 and better performance than gold and silver at wavelengths below 300 nm making them attractive for ultraviolet photosensors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
FREE

Hysteresis mechanism in low-voltage and high mobility pentacene thin-film transistors with polyvinyl alcohol dielectric

Wei Wang, Dongge Ma, Su Pan, and Yudan Yang

Appl. Phys. Lett. 101, 033303 (2012); http://dx.doi.org/10.1063/1.4737173 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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In this letter, the hysteresis mechanism of organic thin-film transistors (OTFTs) with polyvinyl alcohol (PVA) as gate dielectric is studied. By examining OTFTs with a blocking polymer layer between gate and PVA or between channel and PVA, we confirm that the origin of the hysteresis is caused by the holes injected from the gate and/or from the channel and trapped in the interface of pentacene/PVA and the PVA bulk. A method is proposed to reduce the hysteresis. As a result, a pentacene OTFT with free-hysteresis and high mobility of 1.8 cm2/Vs is achieved by a triple-layer polymer dielectric at low-operating voltages.
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85.30.Tv Field effect devices
77.80.Dj Domain structure; hysteresis
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Origin of multiple memory states in organic ferroelectric field-effect transistors

Benjamin Kam, Xiaoran Li, Claudio Cristoferi, Edsger C. P. Smits, Alexander Mityashin, Sarah Schols, Jan Genoe, Gerwin Gelinck, and Paul Heremans

Appl. Phys. Lett. 101, 033304 (2012); http://dx.doi.org/10.1063/1.4737176 (5 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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In this work, we investigate the ferroelectric polarization state in metal-ferroelectric-semiconductor-metal structures and in ferroelectric field-effect transistors (FeFET). Poly(vinylidene fluoride-trifluoroethylene) and pentacene was used as the ferroelectric and semiconductor, respectively. This material combination in a bottom gate—top contact transistor architecture exhibits three reprogrammable memory states by applying appropriate gate voltages. Scanning Kelvin probe microscopy in conjunction with standard electrical characterization techniques reveals the state of the ferroelectric polarization in the three memory states as well as the device operation of the FeFET.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.30.Sk Pulse and digital circuits
FREE

Surface doping in pentacene thin-film transistors with few monolayer thick channels

Tatjana Hählen, Claudio Vanoni, Christian Wäckerlin, Thomas A. Jung, and Soichiro Tsujino

Appl. Phys. Lett. 101, 033305 (2012); http://dx.doi.org/10.1063/1.4737214 (4 pages)

Online Publication Date: 17 July 2012

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Molecular surface doping was studied for organic thin film transistors consisting of an active layer of few monolayers pentacene, as prepared by physical vapor deposition. In situ transport measurements with different dopants revealed both positive (tetrafluoro-tetracyanoquinodimethane – F4TCNQ) and negative (manganese(III)-tetraphenylporphyrin-chloride), as well as zero value (cobalt(II)-tetraphenylporphyrin and fullerene) gate threshold shifts. For F4TCNQ, a high doping efficiency of 25% was observed. The maximum gate threshold shift was more than halved with pentacene thickness increasing from 2.5 to 5 monolayers, indicating that the doping effect decays above ∼2.5 monolayers. Charge transfer has been discussed based on complementary x-ray photoelectron experiments.
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85.30.Tv Field effect devices
FREE

Controllable threshold voltage shifts of polymer transistors and inverters by utilizing gold nanoparticles

Su-Ting Han, Ye Zhou, Zong-Xiang Xu, and V. A. L. Roy

Appl. Phys. Lett. 101, 033306 (2012); http://dx.doi.org/10.1063/1.4737422 (5 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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We have demonstrated controllable threshold voltage (Vth) shifts of gold nanoparticles (Au NPs)/poly (3-hexylthiophene) (P3HT) based composite transistors that are fabricated through a low temperature facile technique. By varying the doping concentration of gold nanoparticles in P3HT matrix, Vth has been tuned from 12 V to 27 V without device degradation. Using this technique, the switching voltages of unipolar inverters have also been systematically tuned. Efficient hole conduction and a variation in P3HT crystallinity was observed due to different concentrations of Au NPs which eventually shift the threshold voltage of the devices in a controlled manner.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
84.30.Jc Power electronics; power supply circuits
FREE

Post-growth surface smoothing of thin films of diindenoperylene

A. Hinderhofer, T. Hosokai, K. Yonezawa, A. Gerlach, K. Kato, K. Broch, C. Frank, J. Novák, S. Kera, N. Ueno, and F. Schreiber

Appl. Phys. Lett. 101, 033307 (2012); http://dx.doi.org/10.1063/1.4737168 (4 pages) | Cited 3 times

Online Publication Date: 18 July 2012

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We applied in situ x-ray reflectivity and ultraviolet photoelectron spectroscopy to study the impact of annealing on low temperature (200 K) deposited organic thin films of diindenoperylene (DIP) on SiO2 and indium tin oxide (ITO). At 200 K, DIP is crystalline on SiO2 and amorphous on ITO. Upon heating to room temperature, the roughness of DIP is reduced on both substrates, from 1.5 nm to 0.75 nm (SiO2) and from 0.90 nm to 0.45 nm (ITO). The smoothing is accompanied by crystallization of the surface molecules, whereas the bulk structure of the films does not strongly reorganize.
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68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.15.Aa Theory and models of film growth
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
FREE

Efficient, bulk heterojunction organic photovoltaic cells based on boron subphthalocyanine chloride-C70

Richa Pandey, Yunlong Zou, and Russell J. Holmes

Appl. Phys. Lett. 101, 033308 (2012); http://dx.doi.org/10.1063/1.4737902 (4 pages) | Cited 4 times

Online Publication Date: 19 July 2012

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In this work, we describe the performance of organic photovoltaic cells (OPVs) based on the electron donor-acceptor pairing of boron subphthalocyanine chloride (SubPc) and C70. As an acceptor, C70 is a promising alternative to C60 due to its red-shifted absorption edge and large extinction coefficient, permitting increased photocurrent generation. In uniformly mixed OPVs based on SubPc:C70, peak power conversion efficiency is realized in devices containing 80 wt. % C70. Further enhancement in device performance can be realized through the use of a continuously graded donor-acceptor heterojunction. The optimized graded heterojunction OPV shows a power conversion efficiency of ηP = (5.4 ± 0.2)% under simulated AM1.5 G solar illumination at 100 mW/cm2. This efficiency is significantly larger than the value of ηP = (4.5 ± 0.1)% realized using C60 due to a substantial increase in the short-circuit current density.
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84.60.Jt Photoelectric conversion
85.60.-q Optoelectronic devices
FREE

Hybrid graphene/organic semiconductor field-effect transistors

Tae-Jun Ha, Deji Akinwande, and Ananth Dodabalapur

Appl. Phys. Lett. 101, 033309 (2012); http://dx.doi.org/10.1063/1.4737939 (3 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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In this letter, we report on the improvement of the electronic properties of graphene by capping with π-conjugated organic semiconductor molecules. The off-state current is reduced while the on-state current and mobility are either unaffected or increased. The semiconductors employed included α-sexithiophene and hexadecafluorocopperphthallocyanine. Removal of the organic semiconductor layer results in a return to the original electronic properties. This suggests that weak electronic interactions with organic semiconductors can be a promising approach to favorably alter the transport properties of graphene.
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85.30.Tv Field effect devices
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Improved memory characteristics by NH3-nitrided GdO as charge storage layer for nonvolatile memory applications

L. Liu, J. P. Xu, F. Ji, J. X. Chen, and P. T. Lai

Appl. Phys. Lett. 101, 033501 (2012); http://dx.doi.org/10.1063/1.4737158 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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Charge-trapping memory capacitor with nitrided gadolinium oxide (GdO) as charge storage layer (CSL) is fabricated, and the influence of post-deposition annealing in NH3 on its memory characteristics is investigated. Transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction are used to analyze the cross-section and interface quality, composition, and crystallinity of the stack gate dielectric, respectively. It is found that nitrogen incorporation can improve the memory window and achieve a good trade-off among the memory properties due to NH3-annealing-induced reasonable distribution profile of a large quantity of deep-level bulk traps created in the nitrided GdO film and reduction of shallow traps near the CSL/SiO2 interface.
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81.20.-n Methods of materials synthesis and materials processing
81.40.Gh Other heat and thermomechanical treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
84.32.Tt Capacitors
71.55.Ht Other nonmetals
79.60.-i Photoemission and photoelectron spectra

Cantilever driving low frequency piezoelectric energy harvester using single crystal material 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3

Chundong Xu, Bo Ren, Wenning Di, Zhu Liang, Jie Jiao, Lingying Li, Long Li, Xiangyong Zhao, Haosu Luo, and Dong Wang

Appl. Phys. Lett. 101, 033502 (2012); http://dx.doi.org/10.1063/1.4737170 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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We present a high performance piezoelectric energy harvester CANtilever Driving Low frequency Energy harvester (CANDLE) consisting of cantilever beam and cymbal transducers based on piezoelectric single crystal 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3. Electrical properties of CANDLE under different proof masses, excitation frequencies, and load resistances are studied systematically. Under an acceleration of 3.2g (g = 9.8 m/s2), a peak voltage of 38 V, a maximum power of 3.7 mW were measured at 102 Hz with a proof mass of 4.2 g. Low resonance frequency and high power output performance demonstrate the promise of the device in energy harvesting for wireless sensors and low-power electronics.
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84.60.-h Direct energy conversion and storage
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Modeling of a vertical tunneling graphene heterojunction field-effect transistor

S. Bala Kumar, Gyungseon Seol, and Jing Guo

Appl. Phys. Lett. 101, 033503 (2012); http://dx.doi.org/10.1063/1.4737394 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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Vertical tunneling field-effect-transistor (FET) based on graphene heterojunctions with layers of hBN is simulated by self-consistent quantum transport simulations. It is found that the asymmetric p-type and n-type conduction is due to work function difference between the graphene contact and the tunneling channel material. Modulation of the bottom-graphene-contact plays an important role in determining the switching characteristic of the device. Due to the electrostatic short-channel-effects stemming from the vertical-FET structure, the output I-V characteristics do not saturate. The scaling behaviors the vertical-FET as a function of the gate insulator thickness and the thickness of the tunneling channel material are examined.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Selective mode suppression in a W-band second harmonic coaxial-waveguide gyrotron backward-wave oscillator

C. L. Hung, M. F. Syu, M. T. Yang, and K. L. Chen

Appl. Phys. Lett. 101, 033504 (2012); http://dx.doi.org/10.1063/1.4737398 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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A gyrotron backward-wave oscillator (gyro-BWO) encounters increasingly severe mode competition problems during development toward the goal of higher power at high frequencies. A coaxial interaction waveguide with distributed losses is proposed to enhance the stability and frequency tunability of a W-band second harmonic gyro-BWO. The losses of the inner and outer cylinders complement each other and effectively stabilize all of the competing modes while having minor effects on the operating mode. Under stable operating conditions, the W-band second harmonic coaxial gyro-BWO has a predicted peak output power of 71 kW with a magnetic tuning bandwidth of 1.0 GHz.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

Very high thermoelectric power factor in a Fe3O4/SiO2/p-type Si(100) heterostructure

Z. Viskadourakis, M. L. Paramês, O. Conde, M. Zervos, and J. Giapintzakis

Appl. Phys. Lett. 101, 033505 (2012); http://dx.doi.org/10.1063/1.4737409 (4 pages)

Online Publication Date: 17 July 2012

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Show Abstract
The thermoelectric and transport properties of a Fe3O4/SiO2/p-Si(100) heterostructure have been investigated between 100 and 300 K. Both Hall and Seebeck coefficients change sign from negative to positive with increasing temperature while the resistivity drops sharply due to tunneling of carriers into the p-Si(100). The low resistivity and large Seebeck coefficient of Si give a very high thermoelectric power factor of 25.5 mW/K2m at 260 K which is an underestimated, lower limit value and is related to the density of states and difference in the work functions of Fe3O4 and Si(100) that create an accumulation of majority holes at the p-Si/SiO2 interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.40.Gk Tunneling
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