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14 Feb 2011

Volume 98, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 073101 (2011); http://dx.doi.org/10.1063/1.3554360 (3 pages)

Wei Xu, Rajesh Leeladhar, Yao-Tsan Tsai, Eui-Hyeok Yang, and Chang-Hwan Choi
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Evaporative self-assembly of nanowires on superhydrophobic surfaces of nanotip latching structures

Wei Xu, Rajesh Leeladhar, Yao-Tsan Tsai, Eui-Hyeok Yang, and Chang-Hwan Choi

Appl. Phys. Lett. 98, 073101 (2011); http://dx.doi.org/10.1063/1.3554360 (3 pages) | Cited 7 times

Online Publication Date: 14 February 2011

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In this letter, we report a site-specific self-assembly of nanowires during the evaporation of a colloid droplet of nanowires on nanoengineered superhydrophobic surfaces. The self-assembly of nanowires is achieved by the interactions between nanowires and the superhydrophobic surface engineered with sharp-tip latching nanostructures of micropillars, provided by the convective hydrodynamic flow and the receding three-phase contact line of the evaporating droplet. The experimental results show that the spatial density of surface structures, the relative dimension of surface patterns to nanowires, and the morphology of tip surface influence the self-assembly and alignment of nanowires on the evaporative superhydrophobic surface.
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81.16.Dn Self-assembly
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)
82.70.Dd Colloids

Imaging dissipation and hot spots in carbon nanotube network transistors

David Estrada and Eric Pop

Appl. Phys. Lett. 98, 073102 (2011); http://dx.doi.org/10.1063/1.3549297 (3 pages) | Cited 9 times

Online Publication Date: 14 February 2011

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We use infrared thermometry of carbon nanotube network (CNN) transistors and find the formation of distinct hot spots during operation. However, the average CNN temperature at breakdown is significantly lower than expected from the breakdown of individual nanotubes, suggesting extremely high regions of power dissipation at the CNN junctions. Statistical analysis and comparison with a thermal model allow the estimate of an upper limit for the average tube-tube junction thermal resistance, ∼ 4.4×1011 K/W (thermal conductance of ∼ 2.27 pW/K). These results indicate that nanotube junctions have a much greater impact on CNN transport, dissipation, and reliability than extrinsic factors such as low substrate thermal conductivity.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.07.De Nanotubes
85.35.Kt Nanotube devices
77.22.Jp Dielectric breakdown and space-charge effects

Fabrication of uniform Ge-nanocrystals embedded in amorphous SiO2 films using Ge-ion implantation and neutron irradiation methods

Q. Chen, T. Lu, M. Xu, C. Meng, Y. Hu, K. Sun, and I. Shlimak

Appl. Phys. Lett. 98, 073103 (2011); http://dx.doi.org/10.1063/1.3553770 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2011

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Uniform Ge-nanocrystals (Ge-ncs) embedded in amorphous SiO2 film were formed by using 74Ge+ ion implantation and neutron transmutation doping (NTD) method. Both experimental and theoretical results indicate that the existence of As dopants transmuted from 74Ge by NTD tunes the already stabilized (crystallized) system back to a metastable state and then activates the mass transfer processes during the transition form this metastable state back to the stable (crystallized) state, and hence the nanocrystal size uniformity and higher volume density of Ge-ncs. This method has the potential to open a route in the three-dimensional nanofabrication.
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81.16.-c Methods of micro- and nanofabrication and processing
68.55.-a Thin film structure and morphology
61.72.uf Ge and Si
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Spectroscopic investigation of confinement effects on optical properties of graphene oxide

Shobha Shukla and Sumit Saxena

Appl. Phys. Lett. 98, 073104 (2011); http://dx.doi.org/10.1063/1.3555438 (2 pages) | Cited 7 times

Online Publication Date: 14 February 2011

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The effect of electron confinement due to the formation of graphitic islands in graphene oxide has been studied using optical techniques. Photoluminescence studies indicate a strong ultraviolet (UV) emission at ∼ 356 nm along with a broadened feature in the green region of the visible electromagnetic spectrum. Strong UV emission suggests probable application of graphene oxide in photodynamic therapy and nanophotonic devices.
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78.67.Wj Optical properties of graphene
78.55.Hx Other solid inorganic materials
78.40.Ri Fullerenes and related materials

Confined high-mobility electron gas at the Ruddlesden–Popper type heterointerfaces

M. Matvejeff, K. Nishio, R. Takahashi, and M. Lippmaa

Appl. Phys. Lett. 98, 073105 (2011); http://dx.doi.org/10.1063/1.3552681 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2011

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We study the transport properties of Ruddlesden–Popper type interfaces grown on SrTiO3 substrates, showing that in contrast to perovskite-type interfaces, no mobile carriers are observed in the substrate even when La ions of the rocksalt layer are in direct contact with the Ti-terminated surface of SrTiO3. Annealing at 800 °C and above can, however, be used to perform local chemical doping of the interface by La-ion diffusion into the SrTiO3 substrate, forming a metallic interface with confined high-mobility carriers. The technique can be used to reliably fabricate δ-doped perovskite quantum wells with sheet carrier densities below 1013 cm−2.
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73.40.-c Electronic transport in interface structures
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
72.20.Fr Low-field transport and mobility; piezoresistance
73.21.Fg Quantum wells
FREE

Graphene Q-switched, tunable fiber laser

D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, and A. C. Ferrari

Appl. Phys. Lett. 98, 073106 (2011); http://dx.doi.org/10.1063/1.3552684 (3 pages) | Cited 34 times

Online Publication Date: 15 February 2011

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We demonstrate a wideband-tunable Q-switched fiber laser exploiting a graphene saturable absorber. We get ∼ 2 μs pulses, tunable between 1522 and 1555 nm with up to ∼ 40 nJ energy. This is a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.62.-b Laser applications

Theoretical analysis of postbuckling behavior with experimental validation using electrothermal microbeams

Xing Chen, LianSheng Ma, YingMei Zheng, and Dong-Weon Lee

Appl. Phys. Lett. 98, 073107 (2011); http://dx.doi.org/10.1063/1.3555441 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2011

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A comprehensive theoretical and experimental investigation of the postbuckling behavior of beams is presented. A nonlinear equation representing thermal postbuckling of beams is solved by deriving a closed-form solution. The proposed analytical method offers a simple yet efficient way to analyze the postbuckling behavior of microbeam structures. Measurements using electrothermal microbeams are performed to validate the theoretical model, and are shown to be superior to conventional measurement techniques. Excellent agreements between exact solutions and experimental results prove the validity of our theoretical analysis, and the potential for applying the proposed method to postbuckling behavior in the field of microelectromechanical systems.
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46.32.+x Static buckling and instability

Prediction of extremely long mobile electron spin lifetimes at room temperature in wurtzite semiconductor quantum wells

N. J. Harmon, W. O. Putikka, and Robert Joynt

Appl. Phys. Lett. 98, 073108 (2011); http://dx.doi.org/10.1063/1.3555628 (3 pages)

Online Publication Date: 17 February 2011

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Many proposed spintronics devices require mobile electrons at room temperature with long spin lifetimes. One route to achieving this is to use quantum wells with tunable spin-orbit (SO) parameters. Research has focused on zinc-blende materials such as GaAs which do not have long spin lifetimes at room temperature. We show that wurtzite (w) materials, which possess smaller SO coupling due to being low-Z, are better suited for spintronics applications. This leads to predictions of spin lifetimes in w-AlN exceeding 2 ms at helium temperatures and, relevant to spintronic devices, spin lifetimes up to 0.5 μs at room temperature.
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72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Method for probing the magnetic state of nanomaterials encapsulated in carbon nanotubes

Satoru Konabe and Susumu Okada

Appl. Phys. Lett. 98, 073109 (2011); http://dx.doi.org/10.1063/1.3556274 (3 pages) | Cited 2 times

Online Publication Date: 17 February 2011

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We propose a method for optically probing the magnetic states of metallic atoms encapsulated in single-walled carbon nanotubes. The absorption spectrum is calculated by solving the Bethe–Salpeter equation, which includes the effects of magnetic atoms, under the tight-binding approximation. Due to the exchange interaction between excitons and polarized spins in ferromagnets, triplet excitons acquire a finite oscillator strength and can thus be excited by light. This mechanism is promising for detecting magnetic ordering of materials encapsulated in carbon nanotubes.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
71.35.-y Excitons and related phenomena

The catalytic potential of high-κ dielectrics for graphene formation

Andrew Scott, Arezoo Dianat, Felix Börrnert, Alicja Bachmatiuk, Shasha Zhang (张莎莎), Jamie H. Warner, Ewa Borowiak-Paleń, Martin Knupfer, Bernd Büchner, Gianaurelio Cuniberti, and Mark H. Rümmeli

Appl. Phys. Lett. 98, 073110 (2011); http://dx.doi.org/10.1063/1.3556639 (3 pages) | Cited 9 times

Online Publication Date: 17 February 2011

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The growth of single and multilayer graphene nanoflakes on MgO and ZrO2 at low temperatures is shown through transmission electron microscopy. The graphene nanoflakes are ubiquitously anchored at step edges on MgO (100) surfaces. Density functional theory investigations on MgO (100) indicate C2H2 decomposition and carbon adsorption at step-edges. Hence, both the experimental and theoretical data highlight the importance of step sites for graphene growth on MgO.
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81.05.ue Graphene
81.07.Bc Nanocrystalline materials
81.16.Hc Catalytic methods
61.48.Gh Structure of graphene

Wavelength selective plasmonic thermal emitter by polarization utilizing Fabry-Pérot type resonances

Pei-En Chang, Yu-Wei Jiang, Hung-Hsin Chen, Yi-Tsung Chang, Yi-Ting Wu, Lawrence Dah-Ching Tzuang, Yi-Han Ye, and Si-Chen Lee

Appl. Phys. Lett. 98, 073111 (2011); http://dx.doi.org/10.1063/1.3537807 (3 pages) | Cited 2 times

Online Publication Date: 17 February 2011

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The experimental results of dispersion relations and thermal emittance spectra of a metal/insulator/metal (MIM) structure with rectangle metallic patch arrays as top layer are demonstrated. The structure exhibits wide-angle, multipeak and polarized emission characteristics caused by Fabry-Pérot type resonances of surface plasmons. Emission modes in x- and y-polarization are totally distinct, and their position depends on the width and length of the rectangular metallic patch. Therefore the designing of mode positions has two degrees of freedom and could be applied to wavelength selective light sources.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

Resonant optical reflection by a periodic system of the quantum well excitons at the second quantum state

V. V. Chaldyshev, Yuechao Chen, A. N. Poddubny, A. P. Vasil’ev, and Zhiheng Liu

Appl. Phys. Lett. 98, 073112 (2011); http://dx.doi.org/10.1063/1.3554429 (3 pages) | Cited 3 times

Online Publication Date: 18 February 2011

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A periodic multiple quantum well GaAs/AlGaAs structure was designed, grown, and characterized in order to reveal resonant features in optical spectra when the Bragg resonance was tuned to the second quantum state x(e2-hh2) of the heavy-hole exciton-polaritons in the multiple quantum wells. This double resonance was demonstrated by tuning the incident angle of the light as well as by comparison with a single quantum well structure. A significant enhancement of the light-matter interaction was observed, which manifests itself by strong resonant optical reflection and electroreflection.
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78.67.De Quantum wells
71.35.-y Excitons and related phenomena
78.20.Jq Electro-optical effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.St Quantum wells
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Graphitized carbon on GaAs(100) substrates

J. Simon, P. J. Simmonds, J. M. Woodall, and M. L. Lee

Appl. Phys. Lett. 98, 073113 (2011); http://dx.doi.org/10.1063/1.3555442 (3 pages)

Online Publication Date: 18 February 2011

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We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp2-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5–3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.
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81.05.uf Graphite
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Hv Other nonmetallic inorganics
81.65.Cf Surface cleaning, etching, patterning

Edge-enhanced Raman scattering effect from Au deposited nanoedge array

Li Liu, Mingwang Shao, Liang Cheng, Shujuan Zhuo, Ronghui Que, and Shuit Tong Lee

Appl. Phys. Lett. 98, 073114 (2011); http://dx.doi.org/10.1063/1.3556649 (3 pages) | Cited 1 time

Online Publication Date: 18 February 2011

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Edge-enhanced Raman scattering effect was demonstrated on nanoedge array, depositing Au film on the profile of anodized aluminum oxide template with the pore diameter of 30 nm and the channel length of 50 μm. The results showed a prominent superior Raman enhancement from the nanoedge array on the highly reproducible, uniform, and sensitive substrate with an enhancement factor of 107, which suggested the potential applications in ultrasensitive edge-enhanced Raman detection.
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78.30.Er Solid metals and alloys
81.07.Bc Nanocrystalline materials

Stabilizing and activating dopants in 〈112〉 silicon nanowires by alkene adsorptions: A first-principles study

H. Xu, X. B. Yang, C. Zhang, A. J. Lu, and R. Q. Zhang

Appl. Phys. Lett. 98, 073115 (2011); http://dx.doi.org/10.1063/1.3557067 (3 pages) | Cited 1 time

Online Publication Date: 18 February 2011

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The B dopant stability and doping level tunability of 〈112〉 silicon nanowires (SiNWs) with alkene adsorption are revealed based on first-principles calculations. It is found that the alkenyl chains favor the middle location of (111) facet, and the B dopants prefer to locate at (110) facet of the 〈112〉 SiNW. Interestingly, the B doping levels are activated upon an alkene adsorption which introduces an intermediate energy level. This finding sheds light on how SiNWs can achieve effective doping.
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71.55.Cn Elemental semiconductors
71.15.-m Methods of electronic structure calculations
61.72.U- Doping and impurity implantation
68.43.Mn Adsorption kinetics

An ultrasensitive and low-cost graphene sensor based on layer-by-layer nano self-assembly

Bo Zhang and Tianhong Cui

Appl. Phys. Lett. 98, 073116 (2011); http://dx.doi.org/10.1063/1.3557504 (3 pages) | Cited 9 times

Online Publication Date: 18 February 2011

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The flexible cancer sensor based on layer-by-layer self-assembled graphene reported in this letter demonstrates features including ultrahigh sensitivity and low cost due to graphene material properties in nature, self-assembly technique, and polyethylene terephthalate substrate. According to the conductance change of self-assembled graphene, the label free and labeled graphene sensors are capable of detecting very low concentrations of prostate specific antigen down to 4 fg/ml (0.11 fM) and 0.4 pg/ml (11 fM), respectively, which are three orders of magnitude lower than carbon nanotube sensors under the same conditions of design, manufacture, and measurement.
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87.85.Rs Nanotechnologies-applications
87.19.xj Cancer
87.85.fk Biosensors
87.85.J- Biomaterials
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