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29 Oct 2012

Volume 101, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 183101 (2012); http://dx.doi.org/10.1063/1.4761935 (4 pages)

S. J. Kim, J. J. Lee, H. J. Kang, J. B. Choi, Y.-S. Yu, Y. Takahashi, and D. G. Hasko
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One electron-based smallest flexible logic cell

S. J. Kim, J. J. Lee, H. J. Kang, J. B. Choi, Y.-S. Yu, Y. Takahashi, and D. G. Hasko

Appl. Phys. Lett. 101, 183101 (2012); http://dx.doi.org/10.1063/1.4761935 (4 pages)

Online Publication Date: 29 October 2012

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A one electron-based operating half-adder, the smallest arithmetic block, has been implemented on silicon-on-insulator structure whose basic element is a nanoscale single-electron transistor (SET) with two symmetrical side-wall gates. Grayscale contour plots of the resulting cell output voltages exhibit the Coulomb blockade-induced periodic alternating high/low features. Their voltage transfer characteristics display typical Sum and Carry-Out functions for binary, multi-valued (MV), and binary-MV mixed input voltages. Moreover, the half-adder function converts into a subtraction mode by adjusting control gates of the SET element. This flexible multi-valued cell provides an arithmetic block for the SET MV logic family of high density integration, operating with ultra-low power.
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84.30.Sk Pulse and digital circuits
85.35.Gv Single electron devices

Primary energy dependence of secondary electron emission from graphene adsorbed on Ni(111)

P. Riccardi, A. Cupolillo, M. Pisarra, A. Sindona, and L. S. Caputi

Appl. Phys. Lett. 101, 183102 (2012); http://dx.doi.org/10.1063/1.4765053 (4 pages) | Cited 3 times

Online Publication Date: 29 October 2012

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We measured energy distribution and yields of electrons emitted from graphene adsorbed on a Ni(111) surface under the impact of 200–1200 eV electrons. The adsorption of graphene results in significant changes of the spectra of emitted electrons but not of the total emission yields. The electronic structure of the graphitic overlayer determines the final states of excited electrons transported by collision cascade from the bulk of the substrate.
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79.20.Hx Electron impact: secondary emission
73.22.Pr Electronic structure of graphene
68.43.Mn Adsorption kinetics

Electrostatics and electrical transport in semiconductor nanowire Schottky diodes

Cheng-Han Hsu, Qiaoming Wang, Xin Tao, and Yi Gu

Appl. Phys. Lett. 101, 183103 (2012); http://dx.doi.org/10.1063/1.4765653 (5 pages) | Cited 2 times

Online Publication Date: 29 October 2012

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The electrostatics and electrical transport characteristics in semiconductor nanowire Schottky diodes are studied using three-dimensional finite-element simulations. From the simulations, the dependences of the depletion region width on the bias and the doping level are found to deviate significantly from the relations in the bulk Schottky model, indicating different electrostatic properties in nanowire Schottky junctions. Furthermore, simulations of the current-voltage relation, which is corroborated by experimental measurements, demonstrate that the standard analytical model is not sufficient to describe current-voltage characteristics in nanowire Schottky diodes. An important implication is that the commonly used analytical model is not valid for extracting the ideality factor and the Schottky barrier height. These findings suggest that numerical simulations are critical to evaluating nanoscale device performance and guiding device development efforts.
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85.30.Kk Junction diodes
02.70.Dh Finite-element and Galerkin methods

Spectral patterns underlying polarization-enhanced diffractive interference are distinguishable by complex trigonometry

Drew DeJarnette, Justin Norman, and D. Keith Roper

Appl. Phys. Lett. 101, 183104 (2012); http://dx.doi.org/10.1063/1.4764943 (5 pages)

Online Publication Date: 1 November 2012

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Superpositioned modes from scatterers in periodic arrays that prescribe spectral interference patterns are distinguishable using an analytic description. Interference arising from irradiation of ordered lattices with polarizable components yields far-field spectral patterns in which extraordinary features appear at resonant frequencies associated with lattice geometry. Organization of nanostructures utilizing these features has been limited by complexity of electrodynamic descriptions for coupling between these plasmon resonance energies and diffracted spectral modes. The trigonometric description shows how changing lattice constant and incident wavelength to adjust coupling between phase-dependent constructive interference and isometric values of plasmonic gold nanostructure polarizability results in extraordinary spectral features.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
02.70.Bf Finite-difference methods

Large room-temperature quantum linear magnetoresistance in multilayered epitaxial graphene: Evidence for two-dimensional magnetotransport

Ram Sevak Singh, Xiao Wang, Wei Chen, Ariando, and Andrew T. S. Wee

Appl. Phys. Lett. 101, 183105 (2012); http://dx.doi.org/10.1063/1.4765656 (5 pages)

Online Publication Date: 1 November 2012

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We report magnetoresistance (MR) properties from room temperature (300 K) to 2 K in multilayered epitaxial graphene (EG) prepared on C-face of SiC substrate. A large (∼50%) and linear MR is observed at 300 K, which is distinctively different from other carbon materials. This linear MR is attributed to the two-dimensional (2D) transport in the material as inferred from our angular dependence magnetotransport experiments. Furthermore, negative MR behaviour at a low field regime for temperatures ≤20 K is recognised as a weak localization in EG. This study underlines the potential of exploiting multilayered EG on C-face SiC for room temperature magneto-electronic device applications.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Vp Electronic transport in graphene

A suspended nanogap formed by field-induced atomically sharp tips

Jun Hyun Han, Kyung Song, Shankar Radhakrishnan, Sang Ho Oh, and Chung Hoon Lee

Appl. Phys. Lett. 101, 183106 (2012); http://dx.doi.org/10.1063/1.4764562 (3 pages)

Online Publication Date: 2 November 2012

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A sub-nanometer scale suspended gap (nanogap) defined by electric field-induced atomically sharp metallic tips is presented. A strong local electric field (>109 V/m) across micro/nanomachined tips facing each other causes the metal ion migration in the form of dendrite-like growth at the cathode. The nanogap is fully isolated from the substrate eliminating growth mechanisms that involve substrate interactions. The proposed mechanism of ion transportation is verified using real-time imaging of the metal ion transportation using an in situ biasing in transmission electron microscope (TEM). The configuration of the micro/nanomachined suspended tips allows nanostructure growth of a wide variety of materials including metals, metal-oxides, and polymers.
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71.20.Be Transition metals and alloys
73.63.Bd Nanocrystalline materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Effective large-area free-standing graphene field emitters by electrophoretic deposition

Angel T. T. Koh, Y. M. Foong, Likun Pan, Zhuo Sun, and Daniel H. C. Chua

Appl. Phys. Lett. 101, 183107 (2012); http://dx.doi.org/10.1063/1.4765070 (4 pages) | Cited 1 time

Online Publication Date: 2 November 2012

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Large area graphene field emitters were fabricated using electrophoretic deposition. By varying the deposition time, we were able to fabricate emitters with varied field enhancement factors. The turn-on field increased when the deposition time increased, and it was observed that a monolayer of graphene flakes covered on the substrate gave the best results. The low emission turn-on field obtained from the graphene field emitters was attributed to the random orientation of graphene flakes which give protruded edges that acted as field enhancing spots. Graphene emitters produced by this method present a low cost cold cathode that can be mass produced.
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85.45.Db Field emitters and arrays, cold electron emitters

Influence of p-doping on the temperature dependence of InAs/GaAs quantum dot excited state radiative lifetime

Edmund Harbord, S. Iwamoto, Y. Arakawa, P. Spencer, E. Clarke, and R. Murray

Appl. Phys. Lett. 101, 183108 (2012); http://dx.doi.org/10.1063/1.4765349 (4 pages)

Online Publication Date: 2 November 2012

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The radiative lifetime of the excited state transition of undoped and p-doped InAs/GaAs quantum dots (QDs) is estimated from measurements of time-integrated and time-resolved luminescence from both ground and excited states. The radiative lifetime of the undoped QDs increases from 500 ps at 10 K to almost 3 ns at room temperature, consistent with a Boltzmann redistribution of holes over the available energy states. The rate of increase can be suppressed by a factor of ∼2 by p-doping the QDs to maintain a hole population in the lowest confined dot states to high temperatures.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.47.jd Time resolved luminescence
73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

Charging of nanostructured and partially reduced graphene oxide sheets

Yue Shen, Shouwu Guo, Jun Hu, and Yi Zhang

Appl. Phys. Lett. 101, 183109 (2012); http://dx.doi.org/10.1063/1.4765359 (4 pages)

Online Publication Date: 2 November 2012

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We report on the charging of individual graphene oxide (GO) sheets with varied degrees of reduction by using electrically biased atomic force microscope (AFM) tips. AFM measurements indicate that the apparent height of reduced GO (rGO) sheets increases sharply after charging, while the charging ability is enhanced when the GO sheets are deeply reduced. In addition, the rGO sheets tend to be extracted with electrons (or to be injected with holes) with a positively biased AFM tip, in contrast to that with a negatively biased tip. Charging on isolated areas with tunable shape and size on single-layered GO has also been achieved.
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73.61.Wp Fullerenes and related materials
61.48.Gh Structure of graphene
72.80.Vp Electronic transport in graphene
61.46.-w Structure of nanoscale materials

Direct probing of density of states of reduced graphene oxides in a wide voltage range by tunneling junction

Sheng-Tsung Wang, Yen-Fu Lin, Ya-Chi Li, Pei-Ching Yeh, Shiow-Jing Tang, Baruch Rosenstein, Tai-Hsin Hsu, Xufeng Zhou, Zhaoping Liu, Minn-Tsong Lin, and Wen-Bin Jian

Appl. Phys. Lett. 101, 183110 (2012); http://dx.doi.org/10.1063/1.4765361 (4 pages)

Online Publication Date: 2 November 2012

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Reduced graphene oxide (rGO) sheets are synthesized and tunneling junction devices are fabricated with an aluminum oxide layer inserted in between electrodes and rGO sheets. Differential conductances, revealing density of states (DOS), of rGO sheets are measured in a wide voltage range. A difference in DOS of rGO sheets with different thickness is identified. For the single-layer rGO, the DOS shows a whole band with band edges in line with theoretical predictions, and gating DOS is used to estimate electron's Fermi velocity. Disorder effects on conductance and DOS of rGO sheets are explored and compared with each other.
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81.05.ue Graphene
73.40.Gk Tunneling
73.63.-b Electronic transport in nanoscale materials and structures
73.22.Pr Electronic structure of graphene

High magnetoresistance in graphene nanoribbon heterojunction

S. Bala Kumar, M. B. A. Jalil, and S. G. Tan

Appl. Phys. Lett. 101, 183111 (2012); http://dx.doi.org/10.1063/1.4765364 (4 pages)

Online Publication Date: 2 November 2012

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We show a large magnetoresistance (MR) effect in a graphene heterostructure consisting of a metallic and semiconductor-type armchair-graphene-nanoribbon. In the heterostructure, the transmission across the first subband of the semiconducting armchair-graphene-nanoribbon and metallic armchair-graphene-nanoribbon is forbidden under zero magnetic-field, due to the orthogonality of the wavefunctions. A finite magnetic-field introduces the quantum hall-like effect, which distorts the wavefunctions. Thus, a finite transmission occurs across the heterojunction, giving rise to a large MR effect. We study the dependence of this MR on temperature and electron energy. Finally, we design a magnetic-field-effect-transistor which yields a MR of close to 100% (85%) at low (room) temperature.
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81.05.ue Graphene
72.20.My Galvanomagnetic and other magnetotransport effects
73.63.-b Electronic transport in nanoscale materials and structures
81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
85.30.Tv Field effect devices

Removing the effects of elastic and thermal scattering from electron energy-loss spectroscopic data

N. R. Lugg, M. Haruta, M. J. Neish, S. D. Findlay, T. Mizoguchi, K. Kimoto, and L. J. Allen

Appl. Phys. Lett. 101, 183112 (2012); http://dx.doi.org/10.1063/1.4765657 (4 pages)

Online Publication Date: 2 November 2012

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Electron energy-loss spectroscopy (EELS) studies in scanning transmission electron microscopy are widely used to investigate the location and bonding of atoms in condensed matter. However, the interpretation of EELS data is complicated by multiple elastic and thermal diffuse scattering of the probing electrons. Here, we present a method for removing these effects from recorded EELS spectrum images, producing visually interpretable elemental maps and enabling direct comparison of the spectral data with established first-principles energy-loss fine structure calculations.
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79.20.Uv Electron energy loss spectroscopy

Self-aligned graphene field-effect transistors with polyethyleneimine doped source/drain access regions

Hema C. P. Movva, Michael E. Ramón, Chris M. Corbet, Sushant Sonde, Sk. Fahad Chowdhury, Gary Carpenter, Emanuel Tutuc, and Sanjay K. Banerjee

Appl. Phys. Lett. 101, 183113 (2012); http://dx.doi.org/10.1063/1.4765658 (4 pages)

Online Publication Date: 2 November 2012

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We report a method of fabricating self-aligned, top-gated graphene field-effect transistors (GFETs) employing polyethyleneimine spin-on-doped source/drain access regions, resulting in a 2X reduction of access resistance and a 2.5X improvement in device electrical characteristics, over undoped devices. The GFETs on Si/SiO2 substrates have high carrier mobilities of up to 6300 cm2/Vs. Self-aligned spin-on-doping is applicable to GFETs on arbitrary substrates, as demonstrated by a 3X enhancement in performance for GFETs on insulating quartz substrates, which are better suited for radio frequency applications.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices

Direct observation of blocked nanoscale surface evaporation on SiO2 nanodroplets

Neng Wan, Jun Xu, Li-Tao Sun, Matteo Martini, Qing-An Huang, Xiao-Hui Hu, Tao Xu, Heng-Chang Bi, and Jun Sun

Appl. Phys. Lett. 101, 183114 (2012); http://dx.doi.org/10.1063/1.4765662 (5 pages)

Online Publication Date: 2 November 2012

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Nano-scale surface evaporation of SiO2 nanodroplets from a volcano-shaped tip (tip diameter d ∼ 20 nm to 70 nm) was observed directly using an in situ transmission electron microscopy method. Au nanoparticles, those precipitated in the SiO2 matrix after an Au catalyzed growth, diffused and pinned onto the evaporation surface, which induced blocked evaporation dynamics. Our observations provide direct evidences of blocked evaporation dynamics caused by small-sized nanoparticles at the nanometer scale.
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64.70.fm Thermodynamics studies of evaporation and condensation
64.75.Jk Phase separation and segregation in nanoscale systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.35.Fx Diffusion; interface formation
81.30.Mh Solid-phase precipitation
81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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