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12 Sep 2011

Volume 99, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 113501 (2011); http://dx.doi.org/10.1063/1.3634072 (3 pages)

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan, Ramamoorthy Ramesh, and Sayeef Salahuddin
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Nonlinear thermal transport and negative differential thermal conductance in graphene nanoribbons

Jiuning Hu, Yan Wang, Ajit Vallabhaneni, Xiulin Ruan, and Yong P. Chen

Appl. Phys. Lett. 99, 113101 (2011); http://dx.doi.org/10.1063/1.3630026 (3 pages) | Cited 9 times

Online Publication Date: 12 September 2011

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We employ classical molecular dynamics to study the nonlinear thermal transport in graphene nanoribbons (GNRs). For GNRs under large temperature biases beyond linear response regime, we have observed the onset of negative differential thermal conductance (NDTC). NDTC is tunable by varying the manner of applying the temperature biases. NDTC is reduced and eventually disappears when the length of the GNR increases. We have also observed NDTC in triangular GNRs, where NDTC exists only when the heat current is from the narrower to the wider end. These effects may be useful in nanoscale thermal managements and thermal signal processing utilizing GNRs.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.

Electronic transport in single-walled carbon nanotube/graphene junction

Tian Pei, Haitao Xu, Zhiyong Zhang, Zhenxing Wang, Yu Liu, Yan Li, Sheng Wang, and Lian-Mao Peng

Appl. Phys. Lett. 99, 113102 (2011); http://dx.doi.org/10.1063/1.3636407 (3 pages) | Cited 7 times

Online Publication Date: 12 September 2011

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Graphene/carbon nanotube (CNT) junctions were fabricated by depositing mechanically exfoliated graphene on substrate followed by direct chemical vapor deposition growth of CNT, and their electronic transport properties were investigated. Unlike metallic CNT/graphene junction with good contact, there exists an obvious Schottky barrier between semiconducting CNT and graphene due to the difference of their work functions, which lead to typical rectification properties and directionally field-effect behavior.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ei Rectification
73.63.Fg Nanotubes
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Ion current rectification in a fluidic bipolar nanochannel with smooth junction

Kunwar Pal Singh, Kusum Kumari, and Manoj Kumar

Appl. Phys. Lett. 99, 113103 (2011); http://dx.doi.org/10.1063/1.3627181 (3 pages) | Cited 1 time

Online Publication Date: 12 September 2011

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We have simulated bipolar nanochannel based fluidic diode for different values of junction sharpness. We can obtain significant ion current rectification even for a smooth junction between oppositely charged zones. The rectification increases with junction sharpness due to increase in unipolar character of electrolyte but a sharp junction is not a necessary condition for rectification. The ion current rectification increases with surface charge density due to increase in unipolar character of electrolyte and decrease in reverse ion current. The fluid enters (exits) the nanochannel through the centre from (to) the opposite directions for reverse (forward) bias due to fluid pressure.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
07.10.Cm Micromechanical devices and systems
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Unique prospects for graphene-based terahertz modulators

Berardi Sensale-Rodriguez, Tian Fang, Rusen Yan, Michelle M. Kelly, Debdeep Jena, Lei Liu, and Huili (Grace) Xing

Appl. Phys. Lett. 99, 113104 (2011); http://dx.doi.org/10.1063/1.3636435 (3 pages) | Cited 13 times

Online Publication Date: 12 September 2011

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The modulation depth of two-dimensional electron-gas (2DEG) based terahertz (THz) modulators using AlGaAs/GaAs hetero-structures with metal gates is inherently limited to <30%. The metal gate not only attenuates the THz signal but also severely degrades modulation depth. Metal losses can be significantly reduced employing an alternative material with tunable conductivity. Graphene presents a unique solution to this problem due to its symmetric band structure and extraordinarily high hole mobility. In this work, we show that it is possible to achieve a modulation depth of >90% while simultaneously minimizing signal attenuation to <5% by tuning the Fermi level at its Dirac point.
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85.65.+h Molecular electronic devices
85.30.-z Semiconductor devices

Axial bandgap engineering in germanium-silicon heterostructured nanowires

Shadi A. Dayeh, Robert M. Dickerson, and S. Thomas Picraux

Appl. Phys. Lett. 99, 113105 (2011); http://dx.doi.org/10.1063/1.3634050 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2011

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Large composition changes along the nanowire axial direction provide an additional degree of freedom for tailoring charge transport in semiconductor devices. We utilize 100% axial composition modulated germanium to silicon semiconductor nanowires to demonstrate bandgap-engineered Schottky barrier heterostructured field-effect transistors that outperform their homogenous counterparts. The built-in electric field in the channel provided by the compositional change and asymmetric Schottky barrier heights enables high carrier injection in one transport direction but not the other, resulting in high on-currents of 50 μA/μm, 107 Ion/Ioff ratios, and no ambipolarity in transfer characteristics.
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85.30.Tv Field effect devices

Structural and optical properties of m-plane GaN/AlGaN quantum wires grown by metalorganic chemical vapor deposition

Xuelin Yang, Munetaka Arita, Satoshi Kako, and Yasuhiko Arakawa

Appl. Phys. Lett. 99, 113106 (2011); http://dx.doi.org/10.1063/1.3639278 (3 pages)

Online Publication Date: 13 September 2011

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We have investigated the structural and optical properties of GaN quantum wires grown by metalorganic chemical vapor deposition on m-plane AlGaN templates. The quantum wire formation can be attributed to the surface morphology of the AlGaN buffer layer and to the anisotropic lattice mismatch between wires and template. The quantum wires exhibit a triangular cross-sectional geometry with width and height fluctuations. The appearance of individual spectrally narrow emission lines in the micro-photoluminescence spectra clearly demonstrates the localizations in the quantum wires. We correlate the narrow emission lines with the structural fluctuations in the cross-sectional geometry of the quantum wires.
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81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.bg Semiconductors
78.67.Lt Quantum wires
78.55.Cr III-V semiconductors

Characterization of deep-levels in silicon nanowires by low-frequency noise spectroscopy

Abhishek Motayed, Sergiy Krylyuk, and Albert V. Davydov

Appl. Phys. Lett. 99, 113107 (2011); http://dx.doi.org/10.1063/1.3637049 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2011

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We have used low-frequency noise (LFN) spectroscopy to characterize generation-recombination (G-R) centers in silicon nanowires grown using chemical vapor deposition. The LFN spectra showed Lorentzian behavior with well-defined corner-frequency indicative of single G-R center in the bandgap. From the temperature-dependent LFN measurement a single deep level at 0.39 eV from the bandedge is identified, which matches closely with the Au donor level in Si. The trap concentration was estimated at 2.0 × 1012 cm−3 with electron and hole capture cross-sections of 9.5 × 10−17 cm2 and 1.4 × 10−16 cm2, respectively. This study demonstrates the potential of the LFN spectroscopy in characterization of deep-levels in nanowires.
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71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.20.Mq Elemental semiconductors

Trapping of a photoexcited electron by a donor in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors

Arief Udhiarto, Daniel Moraru, Takeshi Mizuno, and Michiharu Tabe

Appl. Phys. Lett. 99, 113108 (2011); http://dx.doi.org/10.1063/1.3637445 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2011

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We study interaction of single-electron current and incident photons in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors. Trapping events of a photoexcited-electron by a trap donor are observed as random telegraph signals in single-electron-tunneling current flowing through a current-path donor. Trapping causes a potential change at the current-path donor, inducing a current change. An opposite current change is caused by electron detrapping from the trap donor to the current-path donor. This indicates that only a few donors (two donors in this study) work in the interaction between single-electron transport and photoexcited-electron trapping, even in the presence of many donors.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices

Growth and optical properties of CdTe quantum dots in ZnTe nanowires

Piotr Wojnar, Elżbieta Janik, Lech T. Baczewski, Sławomir Kret, G. Karczewski, Tomasz Wojtowicz, Mateusz Goryca, Tomasz Kazimierczuk, and Piotr Kossacki

Appl. Phys. Lett. 99, 113109 (2011); http://dx.doi.org/10.1063/1.3630004 (3 pages)

Online Publication Date: 14 September 2011

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We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV–2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.
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81.16.Hc Catalytic methods
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Holey topological thermoelectrics

O. A. Tretiakov, Ar. Abanov, and Jairo Sinova

Appl. Phys. Lett. 99, 113110 (2011); http://dx.doi.org/10.1063/1.3637055 (3 pages) | Cited 12 times

Online Publication Date: 14 September 2011

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We study the thermoelectric properties of three-dimensional topological insulators with many holes (or pores) in the bulk. We show that at high density of these holes, the thermoelectric figure of merit, ZT, can be large due to the contribution of the conducting surfaces and the suppressed phonon thermal conductivity. The maximum efficiency can be tuned by an induced gap in the surface states dispersion through tunneling or external magnetic fields. The large values of ZT, much higher than unity for reasonable parameters, make this system a strong candidate for applications in heat management of nanodevices, especially at low temperatures.
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73.25.+i Surface conductivity and carrier phenomena
72.20.Pa Thermoelectric and thermomagnetic effects
63.20.-e Phonons in crystal lattices
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Scintillation of rare earth doped fluoride nanoparticles

L. G. Jacobsohn, C. L. McPherson, K. B. Sprinkle, E. G. Yukihara, T. A. DeVol, and J. Ballato

Appl. Phys. Lett. 99, 113111 (2011); http://dx.doi.org/10.1063/1.3638484 (3 pages) | Cited 2 times

Online Publication Date: 14 September 2011

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The scintillation response of rare earth (RE) doped core/undoped (multi-)shell fluoride nanoparticles was investigated under x-ray and alpha particle irradiation. A significant enhancement of the scintillation response was observed with increasing shells due: (i) to the passivation of surface quenching defects together with the activation of the REs on the surface of the core nanoparticle after the growth of a shell, and (ii) to the increase of the volume of the nanoparticles. These results are expected to reflect a general aspect of the scintillation process in nanoparticles, and to impact radiation sensing technologies that make use of nanoparticles.
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78.70.Ps Scintillation
61.80.Cb X-ray effects
81.40.Gh Other heat and thermomechanical treatments
81.65.Rv Passivation

Graphene based nickel nanocrystal flash memory

Ning Zhan, Mario Olmedo, Guoping Wang, and Jianlin Liu

Appl. Phys. Lett. 99, 113112 (2011); http://dx.doi.org/10.1063/1.3640210 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2011

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Graphene based flash memory was demonstrated by using nickel nanocrystals as storage nodes. As-grown graphene films were characterized by transmission electron microscopy and Raman spectroscopy to show good film quality. On/off operation of the transistor memory was acquired by static pulse response measurement. The memory window of the device was found up to be 23.1 V by back gate sweep. This memory effect is attributed to charging/discharging of nanocrystals. Furthermore, excellent retention and endurance performance were achieved.
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84.30.Sk Pulse and digital circuits

Optical routing and switching of energy flow in nanostructure systems

S. M. Sadeghi

Appl. Phys. Lett. 99, 113113 (2011); http://dx.doi.org/10.1063/1.3633270 (3 pages) | Cited 5 times

Online Publication Date: 15 September 2011

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We study optical routing and switching of energy transfer between semiconductor quantum dots and metallic nanostructures. We demonstrate that in the presence of a metallic nanoshell, one can use quantum coherence to direct or switch energy transfer flow from a quantum dot to another quantum dot or to the nanoshell. Our results show that a quantum dot-metallic nanoshell system can act as a bistable energy switch formed via quantum mechanical control of energy transfer processes.
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73.21.La Quantum dots
73.63.Kv Quantum dots
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Solution processed reduced graphene oxide ultraviolet detector

Basant Chitara, S. B. Krupanidhi, and C. N. R. Rao

Appl. Phys. Lett. 99, 113114 (2011); http://dx.doi.org/10.1063/1.3640222 (3 pages) | Cited 9 times

Online Publication Date: 16 September 2011

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Electronic properties of graphene have been studied more extensively than its photonic applications, in spite of its exciting optical properties. Recent results on solar cells, light emitting diodes and photodetectors show its true potential in photonics and optoelectronics. Here, we have explored the use of reduced graphene oxide as a candidate for solution processed ultraviolet photodetectors. UV detection is demonstrated by reduced graphene oxide in terms of time resolved photocurrent as well as photoresponse. The responsivity of the detectors is found to be 0.12 A/W with an external quantum efficiency of 40%.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Localized surface optical phonon mode in the InGaN/GaN multiple-quantum-wells nanopillars: Raman spectrum and imaging

J. H. Zhu, J. Q. Ning, C. C. Zheng, S. J. Xu, S. M. Zhang, and Hui Yang

Appl. Phys. Lett. 99, 113115 (2011); http://dx.doi.org/10.1063/1.3640233 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2011

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An interesting phonon mode at around 685–705 cm−1 was clearly observed in the Raman spectra of InGaN/GaN multiple-quantum-wells nanopillars with different diameters at room temperature. The Raman peak position of this mode is found to show a distinct dependence on the nanopillar size, which is in well agreement with theoretical calculation of the surface optical (SO) phonon modes of nanopillars. Moreover, this kind of SO phonon was evidenced to be located on the pillar surface by using scanning confocal micro-Raman microscopy.
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78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
68.65.Fg Quantum wells
68.35.Ja Surface and interface dynamics and vibrations

Ni filled flexible multi-walled carbon nanotube–polystyrene composite films as efficient microwave absorbers

Rajesh Kumar Srivastava, T. N. Narayanan, A. P. Reena Mary, M. R. Anantharaman, Anchal Srivastava, Robert Vajtai, and Pulickel M. Ajayan

Appl. Phys. Lett. 99, 113116 (2011); http://dx.doi.org/10.1063/1.3638462 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2011

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In this letter, we report flexible, non corrosive, and light weight nickel nanoparticle@multi-walled carbon nanotube–polystyrene (Ni@MWCNT/PS) composite films as microwave absorbing material in the frequency range of S band (2-4 GHz). Dielectric permittivity and magnetic permeability of composites having 0.5 and 1.5 wt. % filler amount were measured using the cavity perturbation technique. Reflection loss maxima of −33 dB (at 2.7 GHz) and −24 dB (at 2.7 GHz) were achieved for 0.5 and 1.5 wt. % Ni@MWCNT/PS composite films of 6 and 4 mm thickness, respectively, suggesting that low concentrations of filler provide significant electromagnetic interference shielding.
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81.07.Pr Organic-inorganic hybrid nanostructures
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ch Permittivity (dielectric function)
77.84.Lf Composite materials
81.05.Qk Reinforced polymers and polymer-based composites
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