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26 Nov 2012

Volume 101, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 221101 (2012); http://dx.doi.org/10.1063/1.4767646 (5 pages)

Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso
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Solution processable carbon nanotube network thin-film transistors operated in electrolytic solutions at various pH

Tobias Haeberle, Alexandra M. Münzer, Felix Buth, Jose Antonio Garrido, Alaa Abdellah, Bernhard Fabel, Paolo Lugli, and Giuseppe Scarpa

Appl. Phys. Lett. 101, 223101 (2012); http://dx.doi.org/10.1063/1.4768683 (5 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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We investigate the electronic properties of solution-gated carbon nanotube (CNT) thin-film transistors, where the active layer consists of a randomly distributed single-walled CNT network of >90% semiconducting nanotubes, deposited from an aqueous solution by spin-coating. The devices are characterized in different electrolytic solutions, where a reference electrode immersed in the liquid is used to apply the gate potential. We observe a gate-potential shift in the transfer characteristic when the pH and/or ionic strength of the electrolytic solution is changed with a pH sensitivity of ≈19 mV/pH. This sensitivity is attributed to a surface charging effect at the CNT/electrolyte interface.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Continuous and scalable fabrication of flexible metamaterial films via roll-to-roll nanoimprint process for broadband plasmonic infrared filters

Jong G. Ok, Hong Seok Youn, Moon Kyu Kwak, Kyu-Tae Lee, Young Jae Shin, L. Jay Guo, Anton Greenwald, and Yisi Liu

Appl. Phys. Lett. 101, 223102 (2012); http://dx.doi.org/10.1063/1.4767995 (4 pages)

Online Publication Date: 26 November 2012

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We demonstrate the continuous fabrication of large-area flexible metamaterial films via roll-to-roll (R2R) nanoimprint lithography (NIL) technique that can be conducted in an ambient environment at high speed. The plasmonic metal-insulator-metal structure is successfully fabricated by R2R NIL to continuously pattern the sub-wavelength scale metal disk array on flexible substrates. The patterned metal disks having varying diameters and sub-micron spacing with few defects lead to the desired broadband IR filtering performance at the designed dual-band, which correlates well with simulation analysis. Our method realizes a simple and high-throughput fabrication of plasmonic metamaterials for scalable and flexible optoelectronic and photonic applications.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.-a Optical materials
42.79.Wc Optical coatings

Enhanced and persistent photoconductivity in vertical silicon nanowires and ZnS nanoparticles hybrid devices

Mushtaq Ahmad, Kamran Rasool, M. A. Rafiq, and M. M. Hasan

Appl. Phys. Lett. 101, 223103 (2012); http://dx.doi.org/10.1063/1.4768784 (4 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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We observe persistent photoconductivity, enhanced detectivity, responsivity, and external quantum efficiency (EQE) in hybrid ZnS nanoparticles (NPs) and vertical silicon nanowire (Si NW) devices. ZnS NPs (diameter ∼30 nm) were prepared by co-precipitation method. Si NWs (length ∼30 μm, diameter ∼30-400 nm) were prepared by electroless chemical etching. Hybrid device shows ∼10, 3, and 10 times enhancement of EQE, detectivity, and responsivity, respectively, as compared with the Si NWs only devices. The enhancement is attributed to presence of low refractive index ZnS around Si NWs causing funneling of photon energy into Si NWs.
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85.30.De Semiconductor-device characterization, design, and modeling

Field-effect transistors and intrinsic mobility in ultra-thin MoSe2 layers

Stefano Larentis, Babak Fallahazad, and Emanuel Tutuc

Appl. Phys. Lett. 101, 223104 (2012); http://dx.doi.org/10.1063/1.4768218 (4 pages) | Cited 2 times

Online Publication Date: 26 November 2012

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We report the fabrication of back-gated field-effect transistors (FETs) using ultra-thin, mechanically exfoliated MoSe2 flakes. The MoSe2 FETs are n-type and possess a high gate modulation, with On/Off ratios larger than 106. The devices show asymmetric characteristics upon swapping the source and drain, a finding explained by the presence of Schottky barriers at the metal contact/MoSe2 interface. Using four-point, back-gated devices, we measure the intrinsic conductivity and mobility of MoSe2 as a function of gate bias, and temperature. Samples with a room temperature mobility of ∼ 50 cm2/V·s show a strong temperature dependence, suggesting phonons are a dominant scattering mechanism.
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85.30.Tv Field effect devices

Tailoring the electronic properties of SrRuO3 films in SrRuO3/LaAlO3 superlattices

Z. Q. Liu, Y. Ming, W. M. Lü, Z. Huang, X. Wang, B. M. Zhang, C. J. Li, K. Gopinadhan, S. W. Zeng, A. Annadi, Y. P. Feng, T. Venkatesan, and Ariando

Appl. Phys. Lett. 101, 223105 (2012); http://dx.doi.org/10.1063/1.4768230 (5 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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The electronic properties of SrRuO3/LaAlO3 (SRO/LAO) superlattices with different interlayer thicknesses of SRO layers were studied. As the thickness of SRO layers is reduced, the superlattices exhibit a metal-insulator transition implying transformation into a more localized state from its original bulk metallic state. The strain effect on the metal-insulator transition was also examined. The origin of the metal-insulator transition in ultrathin SRO film is discussed. All the superlattices, even those with SRO layers as thin as 2 unit cells, are ferromagnetic at low temperatures. Moreover, we demonstrate field effect devices based on such multilayer superlattice structures.
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73.21.Cd Superlattices
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions

Structural study of Bi2Sr2CaCu2O8+δ exfoliated nanocrystals

A. Lupascu, Renfei Feng, L. J. Sandilands, Zixin Nie, V. Baydina, Genda Gu, Shimpei Ono, Yoichi Ando, D. C. Kwok, N. Lee, S.-W. Cheong, K. S. Burch, and Young-June Kim

Appl. Phys. Lett. 101, 223106 (2012); http://dx.doi.org/10.1063/1.4768234 (4 pages)

Online Publication Date: 26 November 2012

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We demonstrate that structural and spectroscopic information can be obtained on exfoliated nanocrystals as thin as 6 nm. This can be achieved by using a combination of micro X-ray fluorescence (μXRF), micro X-ray absorption near-edge spectroscopy (μXANES), and X-ray microdiffraction (μXRD) techniques. Highly focused, tunable X-ray beams available at synchrotron sources enable one to use these non-invasive characterization tools to study exfoliated samples on a variety of substrates. As an example, we focused on exfoliated nanocrystals of the high temperature superconductor Bi2Sr2CaCu2O8+δ. μXRF is used to locate the sample of desired thickness; μXANES and μXRD are used to obtain electronic and structural information, respectively. We find that the “4.7b” structural modulation, characteristic of the bulk crystals, is drastically suppressed for exfoliated crystals thinner than 60 nm.
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61.46.-w Structure of nanoscale materials
74.72.-h Cuprate superconductors
78.70.Dm X-ray absorption spectra
74.25.Jb Electronic structure (photoemission, etc.)
74.25.Gz Optical properties
78.55.Hx Other solid inorganic materials

Designer Ge quantum dots on Si: A heterostructure configuration with enhanced optoelectronic performance

M. H. Kuo, C. C. Wang, W. T. Lai, Tom George, and P. W. Li

Appl. Phys. Lett. 101, 223107 (2012); http://dx.doi.org/10.1063/1.4768292 (5 pages)

Online Publication Date: 26 November 2012

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An otherwise random, self-assembly of Ge quantum dots (QDs) on Si has been controlled by nano-patterning and oxidation to produce QDs with desired sizes, locations, and depths of penetration into the Si substrate. A heterostructure consisting of a thin amorphous interfacial oxide between the Ge QD and the Si substrate is shown to improve crystalline quality by de-coupling the lattice-matching constraint. A low dark current density of 1.1 μA/cm2 and a high photocurrent enhancement up to 35 000 and 1500, respectively, for 1.5 mW incident illumination at 850 nm and 1160 nm was measured on our Ge QD-based metal-oxide-semiconductor photodiodes.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
78.67.Hc Quantum dots
81.16.Dn Self-assembly
81.16.Rf Micro- and nanoscale pattern formation
72.40.+w Photoconduction and photovoltaic effects
79.60.-i Photoemission and photoelectron spectra

Direct measurement of radiative scattering of surface plasmon polariton resonance from metallic arrays by polarization-resolved reflectivity spectroscopy

H. Y. Lo, C. Y. Chan, and H. C. Ong

Appl. Phys. Lett. 101, 223108 (2012); http://dx.doi.org/10.1063/1.4764543 (4 pages) | Cited 2 times

Online Publication Date: 27 November 2012

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We have measured the radiative scattering from two-dimensional metallic arrays by using polarization-resolved reflectivity spectroscopy. We find the reflectivity spectra follow the Fano-like model that can be derived from temporal coupled mode theory and Jones matrix calculus. By orthogonally orienting the incident polarizer and the detection analyzer, reflectivity dips flip into peaks and the radiative scattering efficiency can be determined accordingly. The dependence of total radiative scattering efficiency on wavelength and hole diameter is found to agree well with Rayleigh scattering by single hole.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Modulation of external electric field on surface states of topological insulator Bi2Se3 thin films

Genhua Liu, Guanghui Zhou, and Yong-Hai Chen

Appl. Phys. Lett. 101, 223109 (2012); http://dx.doi.org/10.1063/1.4767998 (4 pages)

Online Publication Date: 27 November 2012

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We study theoretically surface band structure and topological phase transition for Bi2Se3 thin films under an external electric field. It is demonstrated that an electric field vertical to the film surface can close or reopen a gap for surface states. We also study the spin-dependent transport property through an interface junction between regions without and with electric field on the film. Interestingly, the opacity and transparency of spin-down Dirac fermions through the junction can be modulated by changing the incident angle and the electric field strength. On the contrary, the spin-up Dirac fermions always penetrate through the junction.
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73.20.At Surface states, band structure, electron density of states
78.66.Nk Insulators
73.61.Ng Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Growth of In0.25Ga0.75As quantum dots on GaP utilizing a GaAs interlayer

G. Stracke, A. Glacki, T. Nowozin, L. Bonato, S. Rodt, C. Prohl, A. Lenz, H. Eisele, A. Schliwa, A. Strittmatter, U. W. Pohl, and D. Bimberg

Appl. Phys. Lett. 101, 223110 (2012); http://dx.doi.org/10.1063/1.4768294 (4 pages) | Cited 2 times

Online Publication Date: 27 November 2012

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Coherent In0.25Ga0.75As quantum dots (QDs) are realized on GaP(001) substrates by metalorganic vapor phase epitaxy in the Stranski-Krastanow mode utilizing a thin GaAs interlayer prior to In0.25Ga0.75As deposition. Luminescence is observed between 2.0 eV and 1.83 eV, depending on the thickness of the In0.25Ga0.75As layer. The critical thickness for the two-dimensional to three-dimensional transition of the layer is determined to 0.75 to 1.0 monolayers. A mean activation energy of 489 meV for holes captured by In0.25Ga0.75As quantum dots is measured by deep-level transient spectroscopy, yielding a hole storage time of 3 µs at room temperature.
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81.07.Ta Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.60.Hk Cathodoluminescence, ionoluminescence
78.67.Hc Quantum dots

Universal scaling of resistivity in bilayer graphene

Kalon Gopinadhan, Young Jun Shin, and Hyunsoo Yang

Appl. Phys. Lett. 101, 223111 (2012); http://dx.doi.org/10.1063/1.4769042 (4 pages)

Online Publication Date: 27 November 2012

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We report the temperature dependent electrical transport properties of gated bilayer graphene devices. We see a clear evidence of insulating behavior due to electron-hole charge puddles. The electrical resistivity increases while the mobility decreases with decreasing temperature, a characteristic due to carrier inhomogeneity in graphene. The theoretical fittings using an empirical formula of single electron tunneling indicate that electrical resistivity follows a universal curve with a scaling parameter. The scaling parameter is determined to be a measure of the fluctuations in the electron-hole puddle distribution.
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85.65.+h Molecular electronic devices
85.35.Gv Single electron devices

Nanotwins and stacking faults in high-strength epitaxial Ag/Al multilayer films

D. Bufford, Z. Bi, Q. X. Jia, H. Wang, and X. Zhang

Appl. Phys. Lett. 101, 223112 (2012); http://dx.doi.org/10.1063/1.4768000 (5 pages) | Cited 1 time

Online Publication Date: 29 November 2012

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Epitaxial Ag/Al multilayer films have high hardness (up to 5.5 GPa) in comparison to monolithic Ag and Al films (2 and 1 GPa). High-density nanotwins and stacking faults appear in both Ag and Al layers, and stacking fault density in Al increases sharply with decreasing individual layer thickness, h. Hardness increases monotonically with decreasing h, with no softening. In comparison, epitaxial Cu/Ni multilayers reach similar peak hardness when h ≈ 5 nm, but soften at smaller h. High strength in Ag/Al films is primarily a result of layer interfaces, nanotwins, and stacking faults, which are strong barriers to dislocation transmission.
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68.35.Gy Mechanical properties; surface strains
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Gate tunable graphene-silicon Ohmic/Schottky contacts

Chun-Chung Chen, Chia-Chi Chang, Zhen Li, A. F. J. Levi, and Stephen B. Cronin

Appl. Phys. Lett. 101, 223113 (2012); http://dx.doi.org/10.1063/1.4768921 (4 pages)

Online Publication Date: 29 November 2012

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We show that the I-V characteristics of graphene-silicon junctions can be actively tuned from rectifying to Ohmic behavior by electrostatically doping the graphene with a polymer electrolyte gate. Under zero applied gate voltage, we observe rectifying I-V characteristics, demonstrating the formation of a Schottky junction at the graphene-silicon interface. Through appropriate gating, the Fermi energy of the graphene can be varied to match the conduction or valence band of silicon, thus forming Ohmic contacts with both n- and p-type silicon. Over the applied gate voltage range, the low bias conductance can be varied by more than three orders of magnitude. By varying the top gate voltage from −4 to +4 V, the Fermi energy of the graphene is shifted between −3.78 and −5.47 eV; a shift of ±0.85 eV from the charge neutrality point. Since the conduction and valence bands of the underlying silicon substrate lie within this range, at −4.01 and −5.13 eV, the Schottky barrier height and depletion width can be decreased to zero for both n- and p-type silicon under the appropriate top gating conditions. I-V characteristics taken under illumination show that the photo-induced current can be increased or decreased based on the graphene-silicon work function difference.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
81.05.Cy Elemental semiconductors
82.45.Gj Electrolytes
73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Probing molecular interactions on carbon nanotube surfaces using surface plasmon resonance sensors

Nurbek Kakenov, Osman Balci, Sinan Balci, and Coskun Kocabas

Appl. Phys. Lett. 101, 223114 (2012); http://dx.doi.org/10.1063/1.4768927 (5 pages) | Cited 1 time

Online Publication Date: 30 November 2012

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In this work, we present a method to probe molecular interactions on single-walled carbon nanotube (SWNT) surfaces using a surface plasmon sensor. SWNT networks were synthesized by chemical vapor deposition and transfer-printed on gold surfaces. We studied the excitation of surface plasmon-polaritons on nanotube coated gold surfaces with sub-monolayer, monolayer, and multilayer surface coverage. Integrating the fabricated sensor with a microfluidic device, we were able to obtain binding dynamics of a bovine serum albumin (BSA) protein on SWNT networks with various tube densities. The results reveal the kinetic parameters for nonspecific binding of BSA on SWNT coated surfaces having various tube densities.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Single electron transport through site-controlled InAs quantum dots

K. M. Cha, K. Shibata, and K. Hirakawa

Appl. Phys. Lett. 101, 223115 (2012); http://dx.doi.org/10.1063/1.4769039 (5 pages)

Online Publication Date: 30 November 2012

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We have grown site- and size-controlled InAs quantum dots (QDs) in shallow nanoholes prepared using atomic force microscope-assisted anodic nano-oxidation and subsequent etching, and investigated their transport properties by depositing metal nanogap electrodes on a single QD. We have observed clear diamond-like patterns in Coulomb stability diagrams, indicating that the fabricated single QD transistors operate as single electron transistors and that the site-controlled QDs have a good crystalline quality. Furthermore, we show that the charging energies and the orbital quantization energies can be controlled over a wide range by controlling the size of the QDs.
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81.05.Ea III-V semiconductors
73.63.Kv Quantum dots
78.67.Hc Quantum dots
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.65.Mq Oxidation
81.07.Ta Quantum dots
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