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27 Jul 2009

Volume 95, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 95, 043110 (2009); http://dx.doi.org/10.1063/1.3184784 (3 pages)

Felix Loske and Angelika Kühnle
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Improved photovoltaic performance of bilayer heterojunction photovoltaic cells by triplet materials and tetrapod-shaped colloidal nanocrystals doping

Yanqin Li, Rosanna Mastria, Kechang Li, Angela Fiore, Yue Wang, Roberto Cingolani, Liberato Manna, and Giuseppe Gigli

Appl. Phys. Lett. 95, 043101 (2009); http://dx.doi.org/10.1063/1.3186074 (3 pages) | Cited 5 times

Online Publication Date: 27 July 2009

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The aim of this work is to investigate the photovoltaic properties of indium tin oxide/poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) / poly(3-hexylthiophene-2,5-diyl) /fullerene/aluminum bilayer heterojunction solar cells when the active polymer layer is doped with triplet organic molecules (a platinum porphyrin complex) and tetrapod-shaped colloidal CdTe nanocrystals. In both cases, the device photovoltaic responses are greatly improved due to the enhanced triplet exciton population, in the case of molecular doping, and due to the improved charge transport and charge separation characteristics, for nanocrystal doping. The latter are related both to the relatively large nanostructured interface and to the high intrinsic carrier mobilities of nanocrystals.
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84.60.Jt Photoelectric conversion
61.72.up Other materials
81.16.-c Methods of micro- and nanofabrication and processing
82.70.Dd Colloids
71.35.-y Excitons and related phenomena
72.20.Fr Low-field transport and mobility; piezoresistance

Local temperature control of photonic crystal devices via micron-scale electrical heaters

Andrei Faraon and Jelena Vučković

Appl. Phys. Lett. 95, 043102 (2009); http://dx.doi.org/10.1063/1.3189081 (3 pages) | Cited 17 times

Online Publication Date: 27 July 2009

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We demonstrate a method to locally control the temperature of photonic crystal devices via micron-scale electrical heaters. The method is used to control the resonant frequency of InAs quantum dots strongly coupled to GaAs photonic crystal resonators. This technique enables independent control of large ensembles of photonic devices located on the same chip at tuning speed as high as hundreds of kilohertz.
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42.82.-m Integrated optics
42.70.Qs Photonic bandgap materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Single ricin detection by atomic force microscopy chemomechanical mapping

Guojun Chen, Jianfeng Zhou, Bosoon Park, and Bingqian Xu

Appl. Phys. Lett. 95, 043103 (2009); http://dx.doi.org/10.1063/1.3190197 (3 pages) | Cited 1 time

Online Publication Date: 27 July 2009

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The authors report on a study of detecting ricin molecules immobilized on chemically modified Au (111) surface by chemomechanically mapping the molecular interactions with a chemically modified atomic force microscopy (AFM) tip. AFM images resolved the different fold-up conformations of single ricin molecule as well as their intramolecule structure of A- and B-chains. AFM force spectroscopy study of the interaction indicates that the unbinding force has a linear relation with the logarithmic force loading rate, which agrees well with calculations using one-barrier bond dissociation model.
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87.15.B- Structure of biomolecules
36.20.Hb Configuration (bonds, dimensions)
82.37.Rs Single molecule manipulation of proteins and other biological molecules
87.14.E- Proteins
87.64.Dz Scanning tunneling and atomic force microscopy
87.15.Fh Bonding; mechanisms of bond breakage

Production of size-controlled Si nanocrystals using self-organized optical near-field chemical etching

Takashi Yatsui and Motoichi Ohtsu

Appl. Phys. Lett. 95, 043104 (2009); http://dx.doi.org/10.1063/1.3193536 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2009

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We demonstrate the selective photochemical etching of Si in a self-organized manner, which strongly depends on the distribution of the optical near field. This dependence was described by the virtual exciton-phonon-polariton model. The photoluminescence (PL) spectra from the etched Si exhibited a blueshifted PL peak at 1.8 eV, corresponding to Si nanocrystals of 2.8 nm diameter.
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81.16.Dn Self-assembly
78.55.Ap Elemental semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
81.07.De Nanotubes
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.-y Excitons and related phenomena
82.50.-m Photochemistry

Ion engineering of embedded nanostructures: From spherical to facetted nanoparticles

G. Rizza, E. A. Dawi, A. M. Vredenberg, and I. Monnet

Appl. Phys. Lett. 95, 043105 (2009); http://dx.doi.org/10.1063/1.3186030 (3 pages) | Cited 8 times

Online Publication Date: 28 July 2009

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We show that the high-energy ion irradiation of embedded metallic spherical nanoparticles (NPs) is not limited to their transformation into prolate nanorods or nanowires. Depending on their pristine size, the three following morphologies can be obtained: (i) nanorods, (ii) facettedlike, and (iii) almost spherical nanostructures. Planar silica films containing nearly monodisperse gold NPs (8–100 nm) were irradiated with swift heavy ions (5 GeV Pb) at room temperature for fluences up to 5×1013 cm−2. The experimental results are accounted for by considering a liquid-solid transformation of the premelted NP surface driven by the in-plane stress within the ion-deformed host matrix. This work demonstrates the interest of using ion-engineering techniques to shape embedded nanostructures into nonconventional configurations.
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61.82.Rx Nanocrystalline materials
64.70.kd Metals and alloys
64.70.Nd Structural transitions in nanoscale materials
64.70.D- Solid-liquid transitions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Jh Ion radiation effects

Magnetic dead layer in ferromagnetic manganite nanoparticles

J. Curiale, M. Granada, H. E. Troiani, R. D. Sánchez, A. G. Leyva, P. Levy, and K. Samwer

Appl. Phys. Lett. 95, 043106 (2009); http://dx.doi.org/10.1063/1.3187538 (3 pages) | Cited 16 times

Online Publication Date: 28 July 2009

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We present experimental evidence on the physical origin of a magnetic dead layer (MDL) in manganite nanoparticles. The studied nanoparticles constitute the wall of La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 manganite nanotubes. Magnetic properties analysis and high resolution transmission electron microscopy show a shell of approximately 2 nm thickness with different properties from the core. In this shell the atoms are in a noncrystalline array that perfectly explains the 50% reduction of the magnetization compared to the bulk. Moreover, we present experimental evidence that the internal magnetic structure of the MDL is constituted by small ferromagnetic clusters in a frustrated configuration.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Photoconductance of aligned SnO2 nanowire field effect transistors

DaeIl Kim, Yong-Kwan Kim, Sung Chan Park, Jeong Sook Ha, Junghwan Huh, Junhong Na, and Gyu-Tae Kim

Appl. Phys. Lett. 95, 043107 (2009); http://dx.doi.org/10.1063/1.3190196 (3 pages) | Cited 16 times

Online Publication Date: 28 July 2009

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We report on the optoelectronic properties of the aligned SnO2 nanowire (NW) field effect transistors (FETs) fabricated via a sliding transfer of NWs grown by chemical vapor deposition. Photocurrent measurements with polarized UV light confirmed a well aligned NWs along the channels. UV photosensitivity of ∼ 107 at the gate voltage Vg = −40 V was obtained due to a small dark-current at the turn-off state of FET. The dynamic response of the photocurrent became faster for the higher mobility SnO2 NW FETs. We expect our aligned SnO2 NW FETs will be useful as polarized UV detectors with a high sensitivity.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
FREE

Nanosecond switching in GeTe phase change memory cells

G. Bruns, P. Merkelbach, C. Schlockermann, M. Salinga, M. Wuttig, T. D. Happ, J. B. Philipp, and M. Kund

Appl. Phys. Lett. 95, 043108 (2009); http://dx.doi.org/10.1063/1.3191670 (3 pages) | Cited 69 times

Online Publication Date: 28 July 2009

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The electrical switching behavior of GeTe-based phase change memory devices is characterized by time resolved experiments. SET pulses with a duration of less than 16 ns are shown to crystallize the material. Depending on the resistance of the RESET state, the minimum SET pulse duration can even be reduced down to 1 ns. This finding is attributed to the increasing impact of crystal growth upon decreasing switchable volume. Using GeTe or materials with similar crystal growth velocities, hence promises nonvolatile phase change memories with dynamic random access memorylike switching speeds.
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84.30.Sk Pulse and digital circuits

Bendable high-frequency microwave switches formed with single-crystal silicon nanomembranes on plastic substrates

Hao-Chih Yuan, Guoxuan Qin, George K. Celler, and Zhenqiang Ma

Appl. Phys. Lett. 95, 043109 (2009); http://dx.doi.org/10.1063/1.3176407 (3 pages) | Cited 9 times

Online Publication Date: 29 July 2009

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This letter presents realization of bendable rf switches operating at microwave frequencies formed with single-crystal Si nanomembranes (SiNMs) on a plastic substrate. Selectively doped 200-nm-thick SiNM is lifted off from silicon-on-insulator and transferred to a polymer substrate to form lateral P-intrinsic-N (PIN) diodes with minimized parasitic resistances. A single-pole single-throw switch, consisting of two PIN diodes connected in a shunt-series configuration, demonstrated very low insertion loss and high isolation from dc up to 20 GHz. The level of performance indicates a promise of properly processed single-crystal semiconductor nanomembranes for high-frequency applications in a number of consumer and military systems.
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85.30.Kk Junction diodes
81.07.Bc Nanocrystalline materials
84.32.Dd Connectors, relays, and switches
84.40.-x Radiowave and microwave (including millimeter wave) technology

Manipulation of C60 islands on the rutile TiO2 (110) surface using noncontact atomic force microscopy

Felix Loske and Angelika Kühnle

Appl. Phys. Lett. 95, 043110 (2009); http://dx.doi.org/10.1063/1.3184784 (3 pages) | Cited 4 times

Online Publication Date: 30 July 2009

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Regular, almost quadratic pits were created in an island of C60 molecules on a rutile TiO2 (110) surface using noncontact atomic force microscopy at room temperature. Upon gradually approaching the scanning tip toward the surface, the interaction between the tip and the C60 island was increased until manipulation was achieved. Analyzing the manipulation process unambiguously revealed that the manipulation was performed in the repulsive regime. Retracting the tip allowed for reproducible imaging the C60 island after the manipulation process. Moreover, whole islands could be reshaped or even removed when scanning with appropriate scanning parameters.
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68.37.Ps Atomic force microscopy (AFM)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Optical spin control in nanocrystalline magnetic nanoswitches

C. Echeverría-Arrondo, J. Pérez-Conde, and A. Ayuela

Appl. Phys. Lett. 95, 043111 (2009); http://dx.doi.org/10.1063/1.3193545 (3 pages) | Cited 1 time

Online Publication Date: 31 July 2009

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We investigate the optical properties of (Cd,Mn)Te quantum dots (QDs) by looking at the excitons as a function of the Mn impurities positions and their magnetic alignments. When doped with two Mn impurities, the Mn spins, aligned initially antiparallel in the ground state, have lower energy in the parallel configuration for the optically active spin-up exciton. Hence, the photoexcitation of the QD ground state with antiparallel Mn spins induces one of them to flip and they align parallel. This suggests that (Cd,Mn)Te QDs are suitable for spin-based operations handled by light.
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72.25.-b Spin polarized transport
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.50.Pp Magnetic semiconductors
75.60.-d Domain effects, magnetization curves, and hysteresis
61.72.U- Doping and impurity implantation
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena

Mn3O4 precipitates in laser-ablated manganite films

T. Higuchi, T. Yajima, L. Fitting Kourkoutis, Y. Hikita, N. Nakagawa, D. A. Muller, and H. Y. Hwang

Appl. Phys. Lett. 95, 043112 (2009); http://dx.doi.org/10.1063/1.3193667 (3 pages) | Cited 12 times

Online Publication Date: 31 July 2009

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Precipitates formed during the growth of manganite thin films by pulsed laser deposition have been an obstacle for fabricating high quality devices incorporating these ferromagnetic metals. In order to analyze the nature of these precipitates, we have investigated their spectroscopic and structural properties by scanning transmission electron microscopy. For LaMnO3 films, crystallites of Mn3O4 are found to segregate out from stoichiometric films to accommodate a net cation off-stoichiometry during growth. By tuning the laser spot conditions, these precipitates can be eliminated.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition
81.30.Mh Solid-phase precipitation
64.75.St Phase separation and segregation in thin films
68.55.aj Insulators

Split ring resonator sensors for infrared detection of single molecular monolayers

Ertugrul Cubukcu, Shuang Zhang, Yong-Shik Park, Guy Bartal, and Xiang Zhang

Appl. Phys. Lett. 95, 043113 (2009); http://dx.doi.org/10.1063/1.3194154 (3 pages) | Cited 37 times

Online Publication Date: 31 July 2009

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We report a surface enhanced molecular detection technique with zeptomole sensitivity that relies on resonant coupling of plasmonic modes of split ring resonators and infrared vibrational modes of a self-assembled monolayer of octadecanthiol molecules. Large near-field enhancements at the gap of split ring resonators allow for this resonant coupling when the molecular absorption peaks overlap spectrally with the plasmonic resonance. Electromagnetic simulations support experimental findings.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.16.Dn Self-assembly
82.45.Mp Thin layers, films, monolayers, membranes
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Enhanced reactivity of nanoenergetic materials: A first-principles molecular dynamics study based on divide-and-conquer density functional theory

Fuyuki Shimojo, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta

Appl. Phys. Lett. 95, 043114 (2009); http://dx.doi.org/10.1063/1.3189143 (3 pages) | Cited 10 times

Online Publication Date: 31 July 2009

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Integration of nanowires and nanoparticles of energetic materials into semiconducting structures is giving birth to “nanoenergetics-on-a-chip” technology. Understanding and controlling the reactions of nanoenergetic materials pose a theoretical challenge for combining quantum-mechanical accuracy with large scales to capture nanostructural effects. Recent developments in linear-scaling density functional theory have set a stage for first-principles molecular dynamics simulation of thermite reaction at an Al/Fe2O3 interface. Here, we report the finding of a concerted metal-oxygen flip mechanism that enhances mass diffusion and reaction rate at the interface. This mechanism leads to two-stage reactions, which may explain recent experimental observation in thermite nanowire arrays.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
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