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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Spectroscopic investigation of nitrogen doped graphene

R. Podila, J. Chacón-Torres, J. T. Spear, T. Pichler, P. Ayala, and A. M. Rao

Appl. Phys. Lett. 101, 123108 (2012); http://dx.doi.org/10.1063/1.4752736 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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Current research efforts are aimed at controlling the electronic properties via doping graphene. Previously, dopant-induced changes in the Fermi velocity were observed to result in an effectively downshifted Raman peak below the G′-band for n-doped carbon nanotubes. However, in the case of N-doped graphene, we find that several Raman features vary depending upon both dopant concentration and its bonding environment. For instance, only pyridinic/pyrrolic dopants were observed to result in intense D/D′-bands with a concomitant downshift in the G′-band. Here, we correlate x-ray photoelectron measurements with Raman spectra to elucidate effects of dopant bonding configuration on vibrational properties of graphene.
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78.67.Wj Optical properties of graphene
61.72.up Other materials
63.22.Rc Phonons in graphene
73.22.Pr Electronic structure of graphene
78.30.Na Fullerenes and related materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Intrinsic effect of porosity on mechanical and fracture properties of nanoporous ultralow-k dielectrics

K. Vanstreels, C. Wu, P. Verdonck, and M. R. Baklanov

Appl. Phys. Lett. 101, 123109 (2012); http://dx.doi.org/10.1063/1.4753972 (3 pages)

Online Publication Date: 19 September 2012

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The intrinsic effect of porosity on the mechanical and fracture properties of ultralow-k dielectrics is demonstrated using a special curing process that allows a separate control of porosity and matrix properties. The stiffness and fracture energy highly depend on the precise pore structure of the film. A change in relative Young's modulus behavior with open porosity and average pore diameter was found and attributed to the percolation of mesopores.
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77.55.Bh Low-permittivity dielectric films
81.05.Rm Porous materials; granular materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
62.20.mm Fracture

Tunable electroluminescence from polymer-passivated 3C-SiC quantum dot thin films

B. Xiao, X. L. Wu, W. Xu, and Paul K. Chu

Appl. Phys. Lett. 101, 123110 (2012); http://dx.doi.org/10.1063/1.4753995 (4 pages)

Online Publication Date: 19 September 2012

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Strong room-temperature photoluminescence in the wavelength range of 400-540 nm is achieved from a thin film containing polymer encapsulated 3C-SiC quantum dots (QDs). The QD surface is completely passivated by the polymer so that the QD film possesses voltage-tunable electroluminescence. The electroluminescence spectrum blue-shifts from 490 to 460 nm when the applied voltage is increased from 5 to 10 V. The tunable electroluminescence is attributed to carrier recombination in the core quantum confinement states as a result of Pool-Frenkel emission. Owing to the environmental friendliness, nontoxicity, easy fabrication, and stability, the polymer passivated 3C-SiC QD thin films have promising applications.
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78.67.Hc Quantum dots
81.65.Rv Passivation
68.55.ag Semiconductors
78.55.Hx Other solid inorganic materials
78.60.Fi Electroluminescence
78.66.Li Other semiconductors

Highly tunable electron transport in epitaxial topological insulator (Bi1-xSbx)2Te3 thin films

Xiaoyue He, Tong Guan, Xiuxia Wang, Baojie Feng, Peng Cheng, Lan Chen, Yongqing Li, and Kehui Wu

Appl. Phys. Lett. 101, 123111 (2012); http://dx.doi.org/10.1063/1.4754108 (5 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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Atomically smooth, single crystalline (Bi1−xSbx)2Te3 films have been grown on SrTiO3(111) substrates by molecular beam epitaxy. A full range of Sb-Bi compositions have been studied in order to obtain the lowest possible bulk conductivity. For the samples with optimized Sb compositions (x = 0.5±0.1), the carrier type can be tuned from n-type to p-type across the whole thickness with the help of a back-gate. Linear magnetoresistance has been observed at gate voltages close to the maximum in the longitudinal resistance of a (Bi0.5Sb0.5)2Te3 sample. These highly tunable (Bi1−xSbx)2Te3 thin films provide an excellent platform to explore the intrinsic transport properties of the three-dimensional topological insulators.
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73.61.Ng Insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Direct actuation of cantilever in aqueous solutions by electrostatic force using high-frequency electric fields

Ken-ichi Umeda, Kei Kobayashi, Kazumi Matsushige, and Hirofumi Yamada

Appl. Phys. Lett. 101, 123112 (2012); http://dx.doi.org/10.1063/1.4754289 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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We recently developed a method to directly actuate a cantilever in aqueous solutions by electrostatic force [K.-I. Umeda et al., Appl. Phys. Express 3, 065205 (2010)]. However, the cantilever was actuated by surface stress in a low frequency regime. We solved this problem by applying amplitude-modulated high-frequency electric fields, which actuates the cantilever solely by electrostatic force. The time variations of the self-oscillation frequency of a cantilever and the Au(111) surface images by frequency-modulation atomic force microscopy using acoustic, photothermal, and the improved electrostatic actuation methods were compared, which demonstrates the advantages of the last method such as stability and simplicity in instrumentation.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Imaging current paths in complex conductors by scanning fluorescence microscopy

L. Aigouy, J. Lesueur, N. Bergeal, and M. Mortier

Appl. Phys. Lett. 101, 123113 (2012); http://dx.doi.org/10.1063/1.4754553 (3 pages)

Online Publication Date: 20 September 2012

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Using a fluorescence-based scanning thermal microscope, we observed the Joule heating of a complex circuit made of submicron-wide rectangular stripes interconnected between them. The thermal images reveal the presence of localized hot spots which allow to visualize the main current paths in the networks. By suppressing a single elementary conductive element in the device, we observed a different hot spot repartition showing the new electrical current paths. The experimental results are in good agreement with simulations and open the way to directly characterize the electrical and thermal behaviour of complex devices and metal-dielectric composites.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
07.79.-v Scanning probe microscopes and components

Study of ferromagnetic transition in Pd nanometer-scale constrictions using a mechanically controllable break junction technique

K. Ienaga, N. Nakashima, Y. Inagaki, H. Tsujii, T. Kimura, and T. Kawae

Appl. Phys. Lett. 101, 123114 (2012); http://dx.doi.org/10.1063/1.4754565 (4 pages) | Cited 2 times

Online Publication Date: 20 September 2012

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We measured the magnetoresistance (MR) of Pd nanometer-scale constrictions while changing the constriction size by stretching the Pd wire using a mechanically controllable break junction technique. In large constrictions, the resistance is constant for |H| ≤ 400 Oe, reflecting bulk Pd paramagnetic properties. As size decreases to ∼ 10 nm, the MR effect with hysteresis is observed with a sweeping field, indicating the ferromagnetic transition in Pd constrictions. We proposed this technique to detect ferromagnetic transitions caused by downsizing in paramagnetic metals and to study magnetic properties after the transitions.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Efficient broadband energy transfer via momentum matching at hybrid junctions of guided-waves

Charles Lin, Herman M. K. Wong, Benedict Lau, Mohamed A. Swillam, and Amr S. Helmy

Appl. Phys. Lett. 101, 123115 (2012); http://dx.doi.org/10.1063/1.4753985 (4 pages)

Online Publication Date: 20 September 2012

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Momentum matching at hybrid junctions is examined for efficient broadband energy transfer between internal reflection guided waves and evanescence-based plasmonic-gap guided waves. We demonstrate a nanoscale orthogonal junction coupler between 50 nm air-filled plasmonic slot waveguides (PSWs) and 450 nm silicon rib waveguides. Non-resonant junction coupling efficiency of 50 ± 2 % between 1450 nm and 1650 nm is achieved experimentally and PSW propagation loss is directly measured to be only 2.5 dB/μm. This taperless hybrid junction reduces PSW-based device footprint and enhances device tolerance to temperature and fabrication process variations, serving as a potential platform for hybrid silicon-plasmonic interconnects.
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42.79.Gn Optical waveguides and couplers
42.82.Ds Interconnects, including holographic interconnects

Improving the field emission of carbon nanotubes by lanthanum-hexaboride nano-particles decoration

Monika Kumari, S. Gautam, P. V. Shah, S. Pal, U. S. Ojha, A. Kumar, A. A. Naik, J. S. Rawat, P. K. Chaudhury, Harsh, and R. P. Tandon

Appl. Phys. Lett. 101, 123116 (2012); http://dx.doi.org/10.1063/1.4754110 (5 pages) | Cited 1 time

Online Publication Date: 20 September 2012

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Field emission of carbon nanotubes (CNTs) was remarkably improved by lanthanum-hexaboride (LaB6) nano-particles (NPs) decoration. CNTs were grown on the silicon substrate by chemical vapor deposition. Field emission of bare CNTs and LaB6-NPs decorated CNTs was carried out under same conditions. Physical, morphological, elemental, and graphitic nature changes were ascertained by scanning electron microscope, transmission electron microscope, energy dispersive x-ray spectroscopy, and Raman analysis. LaB6-NPs decorated CNTs show significant reduction of turn-on electric-field from 3.0 to 2.1 V/μm. A remarkable improvement of more than six-fold from 2.05 to 13.19 mA/cm2 at a field of 4.6 V/μm was also observed in the current-density.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.Fg Nanotubes
78.30.Hv Other nonmetallic inorganics

Negative and positive photoconductivity modulated by light wavelengths in carbon nanotube film

Jia-Lin Zhu, Guowei Zhang, Jinquan Wei, and Jia-Lin Sun

Appl. Phys. Lett. 101, 123117 (2012); http://dx.doi.org/10.1063/1.4754624 (4 pages)

Online Publication Date: 21 September 2012

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We explore the photoconductive properties of double-walled carbon nanotube film under laser illumination at different wavelengths in both ambient air and vacuum. In our experimental measurements, the photoconductivity of the film shows a strong dependence on the wavelength of light and can be changed from negative to positive by fully removing oxygen. We propose that competition among photoexcitation, photodesorption, and surface plasmon polaritons is responsible for these interesting phenomena. Our results are expected to provide potential applications in the field of nano-optoelectronic sensors based on carbon nanotubes.
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72.40.+w Photoconduction and photovoltaic effects
73.22.Lp Collective excitations
73.50.Pz Photoconduction and photovoltaic effects
73.61.Wp Fullerenes and related materials
73.63.Fg Nanotubes
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
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Ambipolar charge transport in polymer:fullerene bulk heterojunctions for different polymer side-chains

S. Fall, L. Biniek, N. Leclerc, P. Lévêque, and T. Heiser

Appl. Phys. Lett. 101, 123301 (2012); http://dx.doi.org/10.1063/1.4754590 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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We use field-effect transistors to investigate electron and hole mobilities in polymer:fullerene blends. Low-band-gap polymers with a common conjugated backbone and differing side-chains are utilized in order to clarify the link between the side-chain molecular structure and grafting position, and the power-conversion efficiency of related bulk heterojunction solar cells. The results show that, at a fixed polymer:fullerene weight ratio, the electron mobility increases by more than four orders of magnitude when changing from linear to branched side-chains. As a consequence, the photovoltaic performances are highest at low fullerene contents for branched chains while the opposite is true for linear chains.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
88.40.hj Efficiency and performance of solar cells
88.40.jp Multijunction solar cells
FREE

Reverse bias degradation in dye solar cells

Simone Mastroianni, Alessandro Lanuti, Thomas M. Brown, Roberto Argazzi, Stefano Caramori, Andrea Reale, and Aldo Di Carlo

Appl. Phys. Lett. 101, 123302 (2012); http://dx.doi.org/10.1063/1.4754116 (4 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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A prolonged reverse bias (RB) stress forcing a short-circuit current through a dye solar cell, corresponding to the harshest test a shadowed cell may experience in real conditions, can cause the RB operating voltage VRB to drift with time, initially slowly but accelerating for VRB < (−1.65 ± 0.15)V when gas bubbles, identified as H2 (gas chromatography), are produced inside the cell, leading to breakdown. A close connection between VRB, cell performance, and stability was established. Contributions to RB degradation include triiodide depletion and impurities, in particular water. Acting upon these components and setting up protection strategies is important for delivering long-lasting modules.
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88.40.H- Solar cells (photovoltaics)
82.80.Bg Chromatography
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Unipolar behavior of asymmetrically doped strained Si0.5Ge0.5 tunneling field-effect transistors

M. Schmidt, R. A. Minamisawa, S. Richter, A. Schäfer, D. Buca, J. M. Hartmann, Q.-T. Zhao, and S. Mantl

Appl. Phys. Lett. 101, 123501 (2012); http://dx.doi.org/10.1063/1.4751356 (4 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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We investigate here the impact of the dopant concentration in the source and drain regions on the ambipolar behavior of band-to-band tunneling field-effect transistors with compressively strained Si0.5Ge0.5 channels grown on Si on insulator. Source and drain areas were formed by BF2+ and As+ ion implantation to doses of 1 × 1013, 1 × 1014, and 1 × 1015 cm−2. We show that the dopant concentration impacts the energy band alignment of source/drain and the channel region, and thus influences the tunneling current. The ambipolar device behavior is strongly reduced toward unipolar for source-to-drain implantation dose ratio of 100, but at the expense of the on-current, as compared to symmetric implanted devices. Moreover, our results indicate that for SiGe devices, the change of the B doping concentration has a greater impact on the tunneling currents than the variation of the As concentration.
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85.30.Tv Field effect devices

Light/negative bias stress instabilities in indium gallium zinc oxide thin film transistors explained by creation of a double donor

Piero Migliorato, Md Delwar Hossain Chowdhury, Jae Gwang Um, Manju Seok, and Jin Jang

Appl. Phys. Lett. 101, 123502 (2012); http://dx.doi.org/10.1063/1.4752238 (5 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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The analysis of current-voltage (I-V) and capacitance-voltage (C-V) characteristics for amorphous indium gallium zinc oxide Thin film transistors as a function of active layer thickness shows that negative bias under illumination stress (NBIS) is quantitatively explained by creation of a bulk double donor, with a shallow singly ionized state ε(0/+) > EC-0.073 eV and a deep doubly ionized state ε(++/+) < EC-0.3 eV. The gap density of states, extracted from the capacitance-voltage curves, shows a broad peak between EC–E = 0.3 eV and 1.0 eV, which increases in height with NBIS stress time and corresponds to the broadened transition energy between singly and doubly ionized states. We propose that the center responsible is an oxygen vacancy and that the presence of a stable singly ionized state, necessary to explain our experimental results, could be due to the defect environment provided by the amorphous network.
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85.30.Tv Field effect devices

Coherent terahertz radiation from high-harmonic component of modulated free-electron beam in a tapered two-asymmetric grating structure

Ya-Xin Zhang, Yu-Cong Zhou, Liang Dong, and Sheng-Gang Liu

Appl. Phys. Lett. 101, 123503 (2012); http://dx.doi.org/10.1063/1.4752730 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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Based on the mechanism of incoherent diffraction radiation excited by an electron bunch in a waveguide with periodic structure, this paper presents the concept of coherent terahertz (THz) radiation from the high-harmonic component of a modulated free-electron beam in a tapered two-asymmetric grating structure. The results show that in this mechanism 0.43 THz radiation can be generated with 10 A/cm2 current density, and the efficiency can reach 0.5%. Because of the low required current density and relative high efficiency, this concept shows the application potential for electron-beam-driven terahertz sources.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.Dj Gratings
41.75.Fr Electron and positron beams
84.40.Az Waveguides, transmission lines, striplines

Recovery improvement of graphene-based gas sensors functionalized with nanoscale heterojunctions

Il-Suk Kang, Hye-Mi So, Gyeong-Sook Bang, Jun-Hyuk Kwak, Jeong-O Lee, and Chi Won Ahn

Appl. Phys. Lett. 101, 123504 (2012); http://dx.doi.org/10.1063/1.4753974 (4 pages)

Online Publication Date: 18 September 2012

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We report a development of reduced graphene oxide (rGO)-based gas sensors with a practical recovery by facile functionalization with tin dioxide nanoclusters. Upon the introduction of UV illumination to this nanostructure, the reaction on surfaces of tin dioxide nanoclusters was activated and thereby the nanoscale heterojunction barriers between the rGO sheet and the nanoclusters were developed. This lowered the conductance to quickly recover, which was intensified as the cluster density has reached to the percolation threshold. However, after the formation of the cluster percolating network, the sensor response has totally changed into a deterioration of the sensitivity as well as the recovery.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.ue Graphene

High field carrier transport in graphene: Insights from fast current transient

Kausik Majumdar, Sangeeth Kallatt, and Navakanta Bhat

Appl. Phys. Lett. 101, 123505 (2012); http://dx.doi.org/10.1063/1.4754103 (4 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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In this work, we observe gate tunable negative differential conductance (NDC) and current saturation in single layer and bilayer graphene transistor at high source-drain field, which arise due to the interplay among (1) self-heating, (2) hot carrier injection, and (3) drain induced minority carrier injection. The magnitude of the NDC is found to be reduced for a bilayer, in agreement with its weaker carrier-optical phonon coupling and less efficient hot carrier injection. The contributions of different mechanisms to the observed results are decoupled through fast transient measurements with nanosecond resolution. The findings provide insights into high field transport in graphene.
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72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.30.Tv Field effect devices
81.05.ue Graphene

Single charge detection in capacitively coupled integrated single electron transistors based on single-walled carbon nanotubes

Xin Zhou and Koji Ishibashi

Appl. Phys. Lett. 101, 123506 (2012); http://dx.doi.org/10.1063/1.4752240 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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Single charge detection is demonstrated in the capacitively coupled integrated single electron transistors (SETs) in single-walled carbon nanotubes (SWCNTs) quantum dots. Two SETs are fabricated based on two different SWCNTs aligned in parallel, by taking advantage of the aligned growth of SWCNTs and subsequent transfer-printed techniques. In order to make both two SETs be capacitively coupled, a metal finger is fabricated on the top of them. The charge sensing is proved by the response of a detector current in one SWCNT-SET when the number of electrons in the other SWCNT-SET is changed by sweeping the corresponding gate voltages. In this integrated device, shifts of Coulomb oscillation peaks due to the single electron event are also observed.
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85.35.Gv Single electron devices
85.35.Kt Nanotube devices

Heat flow control in thermo-magnetic convective systems using engineered magnetic fields

Jaewook Lee, Tsuyoshi Nomura, and Ercan M. Dede

Appl. Phys. Lett. 101, 123507 (2012); http://dx.doi.org/10.1063/1.4754119 (4 pages)

Online Publication Date: 19 September 2012

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We present the design of a magnetically controlled convective heat transfer system. The underlying thermo-magnetic instability phenomenon is described, and enhanced convective fluid flow patterns are determined using non-linear programming techniques plus a design sensitivity analysis. Specifically, the magnetic fluid body force is computed by finding the optimal distribution and magnetization direction of a magnetic field source, where the objective is to minimize the maximum temperature of a closed loop heat transfer system. Sizeable fluid recirculation zones are induced by arranging magnetic field generation elements in configurations similar to Halbach arrays. Applications include improved heat flow control for electromechanical systems.
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47.85.L- Flow control
47.27.te Turbulent convective heat transfer
47.65.Cb Magnetic fluids and ferrofluids

White light emission with red-green-blue lasing action in a disordered system of nanoparticles

Shujing Chen, Xiaoye Zhao, Yanrong Wang, Jinwei Shi, and Dahe Liu

Appl. Phys. Lett. 101, 123508 (2012); http://dx.doi.org/10.1063/1.4754286 (4 pages)

Online Publication Date: 20 September 2012

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White light emission from a disordered system with intensity feedback is investigated. The gain material is an ethanol solution with three laser dyes (Coumarin 440, Coumarin 6, Oxazine), and titanium dioxide (TiO2) nanoparticles to provide feedback. A single pulsed laser beam at 355 nm with 8 ns pulse duration is used to pump the dyes. Coumarin 440 and Coumarin 6 are excited first by the pump beam, and part of the Coumarin 6 peak pumps Oxazine. Bright white light emission is obtained by combining blue, green, and red beams with a threshold effect. The working properties and system emission characteristics are discussed.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Hj Laser materials
78.55.Bq Liquids
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Electro-optic polymer/TiO2 multilayer slot waveguide modulators

Y. Enami, B. Yuan, M. Tanaka, J. Luo, and A. K.-Y. Jen

Appl. Phys. Lett. 101, 123509 (2012); http://dx.doi.org/10.1063/1.4754597 (4 pages)

Online Publication Date: 21 September 2012

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We report an all-dielectric electro-optic (EO) polymer/TiO2 multilayer slot waveguide modulator with low optical insertion loss for high-speed operations. The EO polymer is sandwiched between thin TiO2 slot waveguide films to improve mode confinement in the EO polymer. The structure increased the mode confinement in the TiO2 and EO polymer slot layers and reduced the electrode distance between the Au electrodes without introducing optical loss from the metal electrodes. The half-wave voltage of the modulator was 6.5 V for a 5-mm-long electrode at a wavelength of 1550 nm. The half-wave voltage and length product was 3.25 V·cm.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers

Dislocation-limited open circuit voltage in film crystal silicon solar cells

Kirstin Alberi, Howard M. Branz, Harvey Guthrey, Manuel J. Romero, Ina T. Martin, Charles W. Teplin, Paul Stradins, and David L. Young

Appl. Phys. Lett. 101, 123510 (2012); http://dx.doi.org/10.1063/1.4754142 (4 pages)

Online Publication Date: 21 September 2012

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Carrier recombination at dislocations is a major source of efficiency loss in epitaxial film Si solar cells and significantly affects the open circuit voltage, VOC. We develop a simple empirical model that yields a logarithmic relationship between VOC and the dislocation density, which fits well to our data. Straightforward evaluation of device performance with this model provides qualitative information about the recombination activity at dislocations.
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88.40.jj Silicon solar cells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
88.40.hj Efficiency and performance of solar cells
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Thermally switchable adhesions of polystyrene-block-poly(n-isopropylacrylamide) copolymer pillar array mimicking climb attitude of geckos

Jem-Kun Chen, Jing-Hong Wang, Jia-Yaw Chang, and Shih-Kang Fan

Appl. Phys. Lett. 101, 123701 (2012); http://dx.doi.org/10.1063/1.4754135 (5 pages) | Cited 1 time

Online Publication Date: 21 September 2012

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Inspired by the gecko foot pad, we fabricated polystyrene-block-poly(N-isopropylacrylamide) (PS-b-PNIPAAm) copolymer pillar array to mimic climbing attitude of a gecko, alternately attach to and detach from a surface. The pillar array structure of the PS segment significantly enhances both of the hydrophilic and hydrophobic property of PNIPAAm segment tips at 25 and 50 °C, respectively, which could generate alternating adhesive forces of approximately 120 and 11 nN. The dramatic change in adhesive and friction force difference at 25 and 50 °C may guide the design of bio-inspired artificial analogues, which could approach gecko's climbing behavior.
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68.35.Np Adhesion
81.40.Pq Friction, lubrication, and wear
82.35.Gh Polymers on surfaces; adhesion
61.41.+e Polymers, elastomers, and plastics
62.20.Qp Friction, tribology, and hardness
68.08.Bc Wetting

Probing radiation damage by alternated current conductivity as a method to characterize electron hopping conduction in DNA molecules

Paulo J. Gomes, Margarida Coelho, Madalena Dionísio, Paulo António Ribeiro, and Maria Raposo

Appl. Phys. Lett. 101, 123702 (2012); http://dx.doi.org/10.1063/1.4754287 (4 pages)

Online Publication Date: 21 September 2012

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Analysis of AC electrical conductivity of deoxyribonucleic acid (DNA) thin films, irradiated with ultraviolet (UV) light, revealed that electrical conduction arises from DNA chain electron hopping between base-pairs and phosphate groups. The hopping distance calculated from correlated barrier hopping model equals the distance between DNA base-pairs, which is consistent with the loss of conductivity with irradiation time arising from a decrease in phosphates groups. In the high frequency regime, at a given frequency, real part of conductivity strongly depends on irradiation time particularly for low dose levels suggesting the use of DNA based films for UV radiation sensors.
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87.15.M- Spectra of biomolecules
87.15.Pc Electronic and electrical properties
87.53.-j Effects of ionizing radiation on biological systems
87.14.gk DNA
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An energy-harvesting scheme utilizing Ga-rich CuIn(1−x)GaxSe2 quantum dots for dye-sensitized solar cells

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He

Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Online Publication Date: 17 September 2012

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Ga-rich CuIn(1−x)GaxSe2 (CIGS) quantum dots (QDs) with a wide bandgap of 1.58 eV were utilized in dye-sensitized solar cells for energy harvesting. Ga-rich CIGS QDs at TiO2 photoanodes afford the recombination reduction and thus suppress the dark current, leading to the increase of short-circuit current from 14.47 to 15.27 mA·cm−2 and open-circuit voltage from 751 to 762 mV. This is due to well-adjusted conduction band minimum of Ga-rich CIGS QDs between that of TiO2 and excited state oxidation potential of N719, enhancing the photoelectron collection and suppressing electron back-transfer from TiO2 to oxidized redox species in the electrolyte.
Show PACS
88.40.hj Efficiency and performance of solar cells
88.40.J- Types of solar cells
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