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27 Feb 2012

Volume 100, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.
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Silicon layer intercalation of centimeter-scale, epitaxially grown monolayer graphene on Ru(0001)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.

Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages) | Cited 15 times

Online Publication Date: 27 February 2012

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We develop a strategy for graphene growth on Ru(0001) followed by silicon-layer intercalation that not only weakens the interaction of graphene with the metal substrate but also retains its superlative properties. This G/Si/Ru architecture, produced by silicon-layer intercalation approach (SIA), was characterized by scanning tunneling microscopy/spectroscopy and angle resolved electron photoemission spectroscopy. These experiments show high structural and electronic qualities of this new composite. The SIA allows for an atomic control of the distance between the graphene and the metal substrate that can be used as a top gate. Our results show potential for the next generation of graphene-based materials with tailored properties.
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68.55.ap Fullerenes
71.20.Tx Fullerenes and related materials; intercalation compounds
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Vacancy analysis in a Ni-Nb-Zr-H glassy alloy by positron annihilation spectroscopy

Mikio Fukuhara

Appl. Phys. Lett. 100, 093102 (2012); http://dx.doi.org/10.1063/1.3688303 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2012

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The positron lifetimes of Ni36Nb24Zr40 and (Ni0.36Nb0.24Zr0.40)90H10 glassy alloys are almost the same but longer than those of pure Zr, Nb, and Ni crystals, indicating that they have higher density of vacancies with smaller size than in crystals. The coincidence Doppler broadening spectrum for both specimens shows that the contribution of Ni around the vacancies is lower than that of Zr and Nb, suggesting that hydrogen atoms favour to exist between Ni atoms comprising neighboring distorted icosahedral Zr5Ni5Nb3 clusters. Thus, these results provide a substitute model of quantum dot tunneling along Ni–H–Ni atomic bond arrays among the clusters.
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61.72.jd Vacancies
78.67.Hc Quantum dots
78.70.Bj Positron annihilation
61.43.Dq Amorphous semiconductors, metals, and alloys
61.43.Fs Glasses

In-situ x-ray characterization of wurtzite formation in GaAs nanowires

Peter Krogstrup, Morten Hannibal Madsen, Wen Hu, Miwa Kozu, Yuka Nakata, Jesper Nygård, Masamitu Takahasi, and Robert Feidenhans’l

Appl. Phys. Lett. 100, 093103 (2012); http://dx.doi.org/10.1063/1.3688489 (4 pages) | Cited 7 times

Online Publication Date: 27 February 2012

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In-situ monitoring of the crystal structure formation during Ga-assisted GaAs nanowire growth on Si(111) substrates has been performed in a combined molecular beam epitaxy growth and x-ray characterization experiment. Under Ga rich conditions, we show that an increase in the V/III ratio increases the formation rate of the wurtzite structure. Moreover, the response time for changes in the structural phase formation to changes in the beam fluxes is observed to be much longer than predicted time scales of adatom kinetics and liquid diffusion. This suggests that the morphology of the growth interface plays the key role for the relative growth structure formation rates.
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81.07.Gf Nanowires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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)
81.05.Ea III-V semiconductors

Enhanced thermoelectric performance of graphene nanoribbons

H. Zheng, H. J. Liu, X. J. Tan, H. Y. Lv, L. Pan, J. Shi, and X. F. Tang

Appl. Phys. Lett. 100, 093104 (2012); http://dx.doi.org/10.1063/1.3689780 (5 pages) | Cited 3 times

Online Publication Date: 28 February 2012

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The thermoelectric properties of a series of armchair and zigzag graphene nanoribbons with narrow width are examined using nonequilibrium Green function method and molecular dynamics simulations. It is found that these nanoribbons are rather stable when the edge atoms are passivated by hydrogen and those with armchair edges exhibit much better thermoelectric performance than their zigzag counterparts. Moreover, the corresponding ZT value increases with decreasing ribbon width. By optimizing the doping level, a room temperature ZT of 6.0 can be achieved for the narrowest armchair nanoribbon. The significantly enhanced ZT value makes armchair graphene nanoribbon a promising candidate for thermoelectric applications.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
61.72.up Other materials
61.48.Gh Structure of graphene

Modulating quantum transport by transient chaos

Rui Yang, Liang Huang, Ying-Cheng Lai, and Louis M. Pecora

Appl. Phys. Lett. 100, 093105 (2012); http://dx.doi.org/10.1063/1.3690046 (4 pages) | Cited 4 times

Online Publication Date: 29 February 2012

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We propose a scheme to modulate quantum transport in nanostructures based on classical chaos. By applying external gate voltage to generate a classically forbidden region, transient chaos can be generated, and the escape rate associated with the underlying non-attracting chaotic set can be varied continuously by adjusting the gate voltage. We demonstrate that this can effectively modulate the quantum conductance-fluctuation patterns. A theory based on self-energies and the spectrum of the generalized non-Hermitian Hamiltonian of the open quantum system is developed to understand the modulation mechanism.
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73.21.La Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots

Nonvolatile memory with graphene oxide as a charge storage node in nanowire field-effect transistors

David J. Baek, Myeong-Lok Seol, Sung-Jin Choi, Dong-Il Moon, and Yang-Kyu Choi

Appl. Phys. Lett. 100, 093106 (2012); http://dx.doi.org/10.1063/1.3690670 (4 pages) | Cited 2 times

Online Publication Date: 29 February 2012

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Through the structural modification of a three-dimensional silicon nanowire field-effect transistor, i.e., a double-gate FinFET, a structural platform was developed which allowed for us to utilize graphene oxide (GO) as a charge trapping layer in a nonvolatile memory device. By creating a nanogap between the gate and the channel, GO was embedded after the complete device fabrication. By applying a proper gate voltage, charge trapping, and de-trapping within the GO was enabled and resulted in large threshold voltage shifts. The employment of GO with FinFET in our work suggests that graphitic materials can potentially play a significant role for future nanoelectronic applications.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

How does folding modulate thermal conductivity of graphene?

Nuo Yang, Xiaoxi Ni, Jin-Wu Jiang, and Baowen Li

Appl. Phys. Lett. 100, 093107 (2012); http://dx.doi.org/10.1063/1.3690871 (4 pages) | Cited 5 times

Online Publication Date: 29 February 2012

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We study thermal transport in folded graphene nanoribbons using molecular dynamics simulations and the non-equilibrium Green’s function method. It is found that the thermal conductivity of flat graphene nanoribbons can be modulated by folding and changing interlayer couplings. The analysis of transmission reveals that the reduction of thermal conductivity is due to scattering of low frequency phonons by the folds. Our results suggest that folding can be utilized in the modulation of thermal transport properties in graphene and other two dimensional materials.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Rc Phonons in graphene
65.80.Ck Thermal properties of graphene
73.63.Bd Nanocrystalline materials

Optical-force-induced bistability in nanomachined ring resonator systems

Y. F. Yu, J. B. Zhang, T. Bourouina, and A. Q. Liu

Appl. Phys. Lett. 100, 093108 (2012); http://dx.doi.org/10.1063/1.3690955 (4 pages) | Cited 4 times

Online Publication Date: 29 February 2012

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This paper reports optical-force-induced bistability in a nanomachined ring resonator system. It consists of two ring resonators and a bus waveguide, whereby each ring resonator has a free-hanging arc that is perpendicularly deformable by an optical force and changes the effective refractive index of the system. Therefore, an optical bistability is induced into the nanomachined ring resonator system, in which the bistability band can reach 0.3 nm and 0.68 nm in the ring resonators 1 and 2, respectively. It has potential applications in optical signal processing area, such as all-optical switching and opto-mechanical memory.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers

Anisotropic capillary instability of silicon nanostructures under hydrogen anneal

T. Barwicz, G. M. Cohen, K. B. Reuter, S. Bangsaruntip, and J. W. Sleight

Appl. Phys. Lett. 100, 093109 (2012); http://dx.doi.org/10.1063/1.3690869 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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Anneal in reduced pressure hydrogen ambient is known to induce morphological changes in silicon microstructures via markedly increased surface self-diffusivity on exposed silicon surfaces. Here, we investigate the capillary instability of silicon nanostructures under hydrogen anneal. We demonstrate that a surface diffusion mask can significantly improve stability by isolating vulnerable segments from large mass reservoirs. In addition, we find that Plateau-Rayleigh instability shows strong crystallographic dependence, which is explained by the surface energy anisotropy of silicon. We observe that nanowires are the least stable when their axial orientation corresponds to 〈100〉 and are increasingly stable for 〈111〉, 〈112〉, and 〈110〉.
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68.03.Cd Surface tension and related phenomena
68.35.Fx Diffusion; interface formation
68.47.Fg Semiconductor surfaces
81.40.Gh Other heat and thermomechanical treatments
66.30.Pa Diffusion in nanoscale solids

Mass detection by means of the vibrating nanomechanical resonators

I. Stachiv, A. I. Fedorchenko, and Y.-L. Chen

Appl. Phys. Lett. 100, 093110 (2012); http://dx.doi.org/10.1063/1.3691195 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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We present a theoretical analysis of the vibrating resonator in cantilever and bridge configurations operating as ultrasensitive mass sensors. An exact solution of the problem has been obtained. For the small mass ratio, the asymptotic solutions (which relate the frequency shift, mass ratio, and position of the attached particle) have been derived. It has been shown that the mass and position of the attached particle for the cantilever configuration can be unambiguously resolved by the use of three consecutive resonant frequencies. For the bridge configuration, the particle mass can be deduced by using only two measured resonant frequencies.
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07.10.Cm Micromechanical devices and systems

Lateral positioning of InGaAs quantum dots using a buried stressor

A. Strittmatter, A. Schliwa, J.-H. Schulze, T. D. Germann, A. Dreismann, O. Hitzemann, E. Stock, I. A. Ostapenko, S. Rodt, W. Unrau, U. W. Pohl, A. Hoffmann, D. Bimberg, and V. Haisler

Appl. Phys. Lett. 100, 093111 (2012); http://dx.doi.org/10.1063/1.3691251 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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We present a “bottom-up” approach for the lateral alignment of semiconductor quantum dots (QDs) based on strain-driven self-organization. A buried stressor formed by partial oxidation of (Al,Ga)As layers is employed in order to create a locally varying strain field at a GaAs(001) growth surface. During subsequent strained layer growth, local self-organization of (In,Ga)As QDs is controlled by the contour shape of the stressor. Large vertical separation of the QD growth plane from the buried stressor interface of 150 nm is achieved enabling high optical quality of QDs. Optical characterization confirms narrow QD emission lines without spectral diffusion.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

Scaling of Al2O3 dielectric for graphene field-effect transistors

B. Fallahazad, K. Lee, G. Lian, S. Kim, C. M. Corbet, D. A. Ferrer, L. Colombo, and E. Tutuc

Appl. Phys. Lett. 100, 093112 (2012); http://dx.doi.org/10.1063/1.3689785 (4 pages) | Cited 10 times

Online Publication Date: 1 March 2012

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We investigate the scaling of Al2O3 dielectric on graphene by atomic layer deposition (ALD) using ultra-thin, oxidized Ti and Al films as nucleation layers. We show that the nucleation layer significantly impacts the dielectric constant (k) and morphology of the ALD Al2O3, yielding k = 5.5 and k = 12.7 for Al and Ti nucleation layers, respectively. Transmission electron microscopy shows that Al2O3 grown using the Ti interface is partially crystalline, while Al2O3 grown on Al is amorphous. Using a spatially uniform 0.6 nm-thick Ti nucleation layer, we demonstrate graphene field-effect transistors with top dielectric stacks as thin as 2.6 nm.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
77.22.Ch Permittivity (dielectric function)

Quasi first-principles Monte Carlo modeling of energy dissipation by low-energy electron beams in multi-walled carbon nanotube materials

Dimitris Emfietzoglou, Ioanna Kyriakou, Rafael Garcia-Molina, Isabel Abril, and Kostas Kostarelos

Appl. Phys. Lett. 100, 093113 (2012); http://dx.doi.org/10.1063/1.3688307 (5 pages) | Cited 2 times

Online Publication Date: 2 March 2012

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The energy dissipation pattern of low-energy electron beams (0.3–30 keV) in multi-walled carbon nanotube (MWCNT) materials is studied by Monte Carlo simulation taking into account secondary-electron cascade generation. A quasi first-principles discrete-energy-loss model deduced from a dielectric response function description of electronic excitations in MWCNTs is employed whereby both single-particle and plasmon excitations are included in a unified and self-consistent manner. Our simulations provide practical analytical functions for computing depth-dose curves and charged-carrier generation volumes in MWCNT materials under low-energy electron beam irradiation.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.22.Lp Collective excitations
71.15.-m Methods of electronic structure calculations
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Surface-dependent chemical properties of silicon nanowires: The acceleration of copper oxidation

Fan Liao, Shanshan Liu, Mingwang Shao, and Shuit-tong Lee

Appl. Phys. Lett. 100, 093114 (2012); http://dx.doi.org/10.1063/1.3691943 (4 pages) | Cited 1 time

Online Publication Date: 2 March 2012

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HF-treated silicon nanowires exhibited surface-dependent chemical property and accelerated the oxidation rate of copper with the enhancement factor of 10 000, confirmed by x-ray diffraction semi-quantitative analysis. This unexpected oxidation characteristic would make HF-treated silicon nanowires valuable for catalysis applications.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.46.Np Structure of nanotubes (hollow nanowires)
81.65.Mq Oxidation

Metal-enhanced fluorescence: The role of quantum yield, Q0, in enhanced fluorescence

Anatoliy I. Dragan and Chris D. Geddes

Appl. Phys. Lett. 100, 093115 (2012); http://dx.doi.org/10.1063/1.3692105 (4 pages) | Cited 2 times

Online Publication Date: 2 March 2012

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Metal-enhanced fluorescence has attracted enormous research and commercial interest in recent years, due to the ability to significantly enhance fluorescence signatures in the near-field as well as protect fluorophores against photobleaching. In this article, we address one of the major unresolved questions, whether far-field fluorophore quantum yield, Q0, has a direct relationship to fluorescence enhancement factors in metal-enhanced fluorescence.
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78.55.Kz Solid organic materials

Photoresponse in epitaxial graphene with asymmetric metal contacts

Ram Sevak Singh, Venkatram Nalla, Wei Chen, Wei Ji, and Andrew T. S. Wee

Appl. Phys. Lett. 100, 093116 (2012); http://dx.doi.org/10.1063/1.3692107 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2012

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We report photoresponse observations in epitaxial graphene (EG) devices with asymmetric metals (Au, Al) contacted in planar Au/EG/Al device format. The transient photocurrent measurements on the zero-bias device show photocurrent maxima at the Au/EG contact and minima at the EG/Al contact. This observed significant difference between the two types of junctions is responsible for the overall efficient device photoresponse. We have also found that the number of EG layers influences the photocurrent magnitude and response time regardless of incident photon energy or intensity. An external photoresponsivity (or efficiency) of ∼31.3 mA W−1 is achieved with a biased Au/EG/Al photodetector at excitation wavelength of 632.8 nm.
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78.67.Wj Optical properties of graphene
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
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