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13 Dec 2010

Volume 97, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 241101 (2010); http://dx.doi.org/10.1063/1.3525583 (3 pages)

Kanghee Lee and Jaewook Ahn
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Giant exchange bias based on magnetic transition in γ-Fe2MnGa melt-spun ribbons

X. D. Tang (唐晓丹), W. H. Wang (王文洪), W. Zhu (朱伟), E. K. Liu (刘恩克), G. H. Wu (吴光恒), F. B. Meng (孟凡斌), H. Y. Liu (刘何燕), and H. Z. Luo (罗鸿志)

Appl. Phys. Lett. 97, 242513 (2010); http://dx.doi.org/10.1063/1.3526377 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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Giant exchange bias with a shift up to 3.86 kOe has been observed in γ-Fe2MnGa alloy in which a ferromagnetic to antiferromagnetic transition takes place at 250 K. The transition can be suppressed to lower temperatures by higher magnetic fields at a shift rate of 10.3 K/kOe. Exchange bias and enhanced coercivity occur simultaneously, revealing an exchange coupling between the coexisting antiferromagnetic and ferromagnetic phases. Meanwhile, the internal exchange coupling inside the antiferromagnetic clusters dynamically ensures their unidirectional anisotropy during their size changing following the external magnetic field.
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75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Enhancement of perpendicular exchange bias in [Pd/Co]/FeMn thin films by tailoring the magnetoelastically induced perpendicular anisotropy

Lin Lin, Naganivetha Thiyagarajah, Ho Wan Joo, Jang Heo, Ky Am Lee, and Seongtae Bae

Appl. Phys. Lett. 97, 242514 (2010); http://dx.doi.org/10.1063/1.3526735 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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The effects of magnetoelastically induced perpendicular anisotropy, KFM,me, on the perpendicular exchange bias (PEB) characteristics in [Pd/Co]5/Fe50Mn50 thin films have been explored by inserting ultrathin CoFe magnetic layers with different thicknesses, compositions, and Ar sputtering gas pressures (PAr,CoFe) at the interface between [Pd/Co]5 and FeMn. It was clearly found that the [Pd/Co]5/CoFe/FeMn with CoFe sputtered at a low PAr,CoFe showed great enhancement in PEB due to the development of intrinsic compressive stress in the CoFe resulting in improving KFM,me and interfacial exchange coupling. Additionally, this effect was more significant for Co80Fe20 insertion than Co90Fe10 due to its larger magnetostriction.
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75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
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Improved epitaxy of ultrathin praseodymia films on chlorine passivated Si(111) reducing silicate interface formation

S. Gevers, J. I. Flege, B. Kaemena, D. Bruns, T. Weisemoeller, J. Falta, and J. Wollschläger

Appl. Phys. Lett. 97, 242901 (2010); http://dx.doi.org/10.1063/1.3525175 (3 pages)

Online Publication Date: 13 December 2010

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Ultrathin praseodymia films have been deposited on both Cl-passivated and nonpassivated Si(111) substrates by molecular beam epitaxy. Comparative studies on the crystallinity and stoichiometry are performed by x-ray photoelectron spectroscopy, x-ray standing waves, and x-ray reflectometry. On nonpassivated Si(111) an amorphous silicate film is formed. In contrast, praseodymia deposited on Cl-passivated Si(111) form a well-ordered crystalline film with cubic-Pr2O3 (bixbyite) structure. The vertical lattice constant of the praseodymia film is increased by 1.4% compared to the bulk value. Furthermore, the formation of an extended amorphous silicate interface layers is suppressed and confined to only one monolayer.
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68.55.-a Thin film structure and morphology
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Atomic structure, electronic structure, and band offsets at Ge:GeO:GeO2 interfaces

L. Lin, K. Xiong, and J. Robertson

Appl. Phys. Lett. 97, 242902 (2010); http://dx.doi.org/10.1063/1.3525371 (3 pages) | Cited 4 times

Online Publication Date: 13 December 2010

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The band gaps of GeO2 and GeO are calculated to be 6.1 and 4.0 eV, respectively, using hybrid density functionals that do not require band gap corrections. The conduction band offsets for Ge:GeO2 and Ge:GeO interfaces are calculated to be 0.8 and 0.4 eV, respectively, relatively small and similar to those found by photoemission. The atomic structure of solid GeO is found to have threefold coordinated Ge and O sites with planar oxygen sites.
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73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.35.Ct Interface structure and roughness

Low symmetry monoclinic MC phase in epitaxial BiFeO3 thin films on LaSrAlO4 substrates

Zuhuang Chen, Zhenlin Luo, Yajun Qi, Ping Yang, Shuxiang Wu, Chuanwei Huang, Tom Wu, Junling Wang, Chen Gao, Thirumany Sritharan, and Lang Chen

Appl. Phys. Lett. 97, 242903 (2010); http://dx.doi.org/10.1063/1.3525378 (3 pages) | Cited 5 times

Online Publication Date: 13 December 2010

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We reported that the tetragonal-like phase identified in strained epitaxial BiFeO3 films on a (001) LaSrAlO4 single crystal substrates is monoclinic MC, based on high resolution synchrotron x-ray studies and piezoresponse force microscopy measurements. This MC phase has different symmetry with the rhombohedral-like monoclinic MA phase found in BiFeO3 films grown on low mismatch SrTiO3 substrates. Transmission electron microscopy revealed that the films on LaSrAlO4 substrates have a high crystalline quality and coherent interface.
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68.55.-a Thin film structure and morphology
77.55.hn Other piezoelectric or electrostrictive films
77.55.Px Epitaxial and superlattice films
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Amplitude scaling of a static wrinkle at an oil-air interface created by dielectrophoresis forces

C. V. Brown, W. Al-Shabib, G. G. Wells, G. McHale, and M. I. Newton

Appl. Phys. Lett. 97, 242904 (2010); http://dx.doi.org/10.1063/1.3525708 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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Dielectrophoresis forces have been used to create a static periodic wrinkle with a sinusoidal morphology on the surface of a thin layer of 1-decanol oil. The surface deformation occurs when a voltage V is applied between adjacent coplanar strip electrodes in an interdigitated array onto which the oil film is coated. It has been shown experimentally that the peak-to-peak amplitude A of the wrinkle scales according to the functional form A∝V2 exp(-αmath/p) for a range of oil film thicknesses math (between 15 and 50 μm) and wrinkle pitches p (160, 240, and 320 μm).
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82.45.Mp Thin layers, films, monolayers, membranes
68.60.Bs Mechanical and acoustical properties
62.10.+s Mechanical properties of liquids
68.15.+e Liquid thin films
68.55.jd Thickness

Space-charge-limited leakage current in high dielectric constant and ferroelectric thin films considering the field-dependent permittivity

J. Sun, X. J. Zheng, W. Yin, M. H. Tang, and W. Li

Appl. Phys. Lett. 97, 242905 (2010); http://dx.doi.org/10.1063/1.3525711 (3 pages) | Cited 2 times

Online Publication Date: 13 December 2010

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Distinguishing from the traditional characterization on high-field leakage current density-voltage relationship, the field-dependent permittivity from the polarization derivative is used to solve the space-charge-limited conduction, and the simulated leakage current densities are compared with the previous experimental observations. The influences of the mobility, ferroelectric parameters, and film thickness on the leakage current densities are discussed. The results verify that the high-field quasi-Ohmic region observed experimentally may result from the field-dependent permittivity, and that the leakage current can be influenced by the ferroelectric polarization.
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77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
77.55.F- High-permittivity capacitive films
77.80.-e Ferroelectricity and antiferroelectricity
73.50.Fq High-field and nonlinear effects

Domain pattern and piezoelectric response across polymorphic phase transition in strained bismuth ferrite films

H. Y. Kuo, Y. C. Shu, H. Z. Chen, C. J. Hsueh, C. H. Wang, and Y. H. Chu

Appl. Phys. Lett. 97, 242906 (2010); http://dx.doi.org/10.1063/1.3525926 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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A model is developed to investigate the domain pattern and piezoelectric response across the polymorphic phase transition in strained epitaxial bismuth ferrite films. The orientations of stripelike pattern of the mixed rhombohedral and tetragonal phases are predicted as the consequence of competition between elastic and depolarization energies. The abnormally large piezoelectric response is attributed to the strain-driven softening in dielectric stiffness. The results are in good agreement with recent experimental observations and provide a guidance for developing similar strain-driven polymorphic phase transition in other related perovskite material systems.
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77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
77.55.Nv Multiferroic/magnetoelectric films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
64.70.K- Solid-solid transitions

Defect-related room-temperature ferroelectricity in tensile-strained SrTiO3 thin films on GdScO3 (110) substrates

Yong Su Kim, J. S. Choi, J. Kim, S. J. Moon, B. H. Park, J. Yu, J.-H. Kwon, M. Kim, J.-S. Chung, T. W. Noh, and J.-G. Yoon

Appl. Phys. Lett. 97, 242907 (2010); http://dx.doi.org/10.1063/1.3525963 (3 pages) | Cited 2 times

Online Publication Date: 14 December 2010

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We investigate room-temperature (RT) ferroelectricity in tensile-strained SrTiO3 (STO) thin films grown on GdScO3 (110) substrates. To separate the strain and the defect dipole effect, we apply an electric field to measure the polarization in the direction perpendicular to the elongation axis, and the RT ferroelectric polarization is found to be perpendicular to that axis. These results clearly demonstrate the importance of the contribution of defect dipoles to the RT ferroelectricity observed in STO thin films.
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77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Orientation of colloidally suspended LiNbO3 nanocrystals in externally applied electric fields

D. Schütze, B. Knabe, M. Ackermann, and K. Buse

Appl. Phys. Lett. 97, 242908 (2010); http://dx.doi.org/10.1063/1.3526372 (3 pages)

Online Publication Date: 14 December 2010

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Electric fields are applied to lithium niobate nanoparticles of 41 nm radius colloidally suspended in heptane. Interferometric measurements of field-induced refractive index changes show that the particle orientation is dominated by induced dipole moments. There are indications that a permanent dipole moment of the nanoparticles of 10−26 C m along their crystallographic c-axis is present as well. An electric field of 2 kV/mm is sufficient to align 80% of the particles, such that the angle between their c-axis and the applied electric field direction is less than 70°, making applications of such a liquid with electrically controlled optical properties feasible.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
82.70.Dd Colloids
77.80.-e Ferroelectricity and antiferroelectricity
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Grain size effect on the nonlinear dielectric properties of barium titanate ceramics

Lavinia Curecheriu, Maria Teresa Buscaglia, Vincenzo Buscaglia, Zhe Zhao, and Liliana Mitoseriu

Appl. Phys. Lett. 97, 242909 (2010); http://dx.doi.org/10.1063/1.3526375 (3 pages) | Cited 3 times

Online Publication Date: 16 December 2010

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The nonlinear dielectric properties of dense BaTiO3 ceramics with grain size of 1 μm–90 nm were investigated. In the finest ceramics, the permittivity reduces below 1000 and a remarkable nonhysteretic linear dc-tunability [ε(E)] is obtained at high field, above 40 kV/cm. The observed behavior was explained by considering the nanostructured ceramic as a composite formed by ferroelectric grains, whose nonlinearity is reducing, and by low-permittivity nonferroelectric grain boundaries, whose volume fraction increases when decreasing the grain size. Reducing the grain size in ferroelectric dense materials is an alternative route to accomplish the application requirements: nonhysteretic tunability and permittivity below 1000.
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77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
72.20.Ht High-field and nonlinear effects
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
61.72.Mm Grain and twin boundaries

Defects responsible for the Fermi level pinning in n+ poly-Si/HfO2 gate stacks

Byungki Ryu and K. J. Chang

Appl. Phys. Lett. 97, 242910 (2010); http://dx.doi.org/10.1063/1.3527929 (3 pages)

Online Publication Date: 17 December 2010

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Based on density functional calculations, we propose a defect model that can explain flat band voltage shifts, especially in n+ poly-Si/HfO2 gate stacks. For two interface structures, with Si electrodes on top of crystalline and amorphous HfO2, we find the formation of O-vacancies at the interface, which exhibit weak Si–Si dimer bonds and low formation energies, very different from those in the oxide. Due to weak dimer bonds, charge trap levels lie near the Si conduction band edge, leading to the Fermi level pinning and flat band voltage shifts in n+ poly-Si gate electrodes.
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81.05.Cy Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Ct Interface structure and roughness
61.72.jd Vacancies
61.50.Lt Crystal binding; cohesive energy
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Enhancement and suppression effect of molecules on nanocavity plasmon emissions excited by tunneling electrons

Y. Zhang, F. Geng, H. Y. Gao, Y. Liao, Z. C. Dong, and J. G. Hou

Appl. Phys. Lett. 97, 243101 (2010); http://dx.doi.org/10.1063/1.3525603 (3 pages)

Online Publication Date: 14 December 2010

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We use tunneling electron induced luminescence techniques to investigate the role of adsorbed molecules in nanocavity plasmon (NCP) mediated emissions. Porphyrin molecules directly adsorbed on metals are found to suppress NCP emissions, while molecules on top of an inserted ultrathin oxide layer on the metal substrate yield enhanced NCP emissions. We attribute such difference in enhancement versus suppression to a competing mechanism of two major roles of molecules on the local field enhancement: geometrical spacer and dynamic dipole oscillator. The latter could become dominant when molecules are sufficiently decoupled from the substrate, leading to the overall enhancement of NCP emissions.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
78.55.Kz Solid organic materials
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

J. N. Shapiro, A. Lin, P. S. Wong, A. C. Scofield, C. Tu, P. N. Senanayake, G. Mariani, B. L. Liang, and D. L. Huffaker

Appl. Phys. Lett. 97, 243102 (2010); http://dx.doi.org/10.1063/1.3526734 (3 pages) | Cited 5 times

Online Publication Date: 14 December 2010

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We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAs nanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy (EDS) indicates formation of axial InxGa1−xAs (x ∼ 0.20) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth. Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillar heterostructures is crucial for optimized device integration.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
78.70.-g Interactions of particles and radiation with matter
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Optimization of branched resonant nanostructures illuminated by a strongly focused beam

Juan Elezgaray, Lotfi Berguiga, and Françoise Argoul

Appl. Phys. Lett. 97, 243103 (2010); http://dx.doi.org/10.1063/1.3526753 (3 pages)

Online Publication Date: 14 December 2010

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In the design of nanostructures to perform single molecule surface enhanced Raman spectroscopy (SM-SERS), metallic structures with very narrow gaps (<1 nm) have been shown to contain regions with electric fields compatible with SM-SERS. However, this geometrical condition does not allow many biomolecules to reach the hot-spot regions. Here, we show that optimized branched structures formed by appropriate arrangements of gold nanoparticles with gaps ≥ 2 nm display field enhancements >102, compatible with SM-SERS.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.Er Solid metals and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon-coated Magnéli-phase TinO2n−1 nanobelts as anodes for Li-ion batteries and hybrid electrochemical cells

Wei-Qiang Han and Xiao-Liang Wang

Appl. Phys. Lett. 97, 243104 (2010); http://dx.doi.org/10.1063/1.3525369 (3 pages)

Online Publication Date: 15 December 2010

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We describe a method for preparing carbon-coated Ti9O17 nanowires using H2Ti3O7 nanobelts as precursors to react with ethane and hydrogen at high-temperature. The carbon-coating layers play a key role in restraining the sintering growth of the core during the phase transformation from H2Ti3O7 to Magnéli-phase TinO2n−1, and in retaining the morphology of nanobelts. We demonstrated that the initial reversible capacity of these Ti9O17 nanobelts attained 182 mA h g−1, a value even higher than the theoretical value of a-TiO2 (167 mA h g−1). Cyclic-voltammetry measurement supports the pseudocapacitive lithium-storage behavior of these Magnéli-phase Ti9O17 nanobelts. Furthermore, the nanobelts exhibit high power density along with excellent cycling stability in their application as hybrid electrochemical cells.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
73.61.Le Other inorganic semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology
82.47.Aa Lithium-ion batteries
81.16.-c Methods of micro- and nanofabrication and processing

Quantitative analysis of CO-humidity gas mixtures with self-heated nanowires operated in pulsed mode

J. D. Prades, F. Hernández-Ramírez, T. Fischer, M. Hoffmann, R. Müller, N. López, S. Mathur, and J. R. Morante

Appl. Phys. Lett. 97, 243105 (2010); http://dx.doi.org/10.1063/1.3515918 (3 pages)

Online Publication Date: 15 December 2010

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Self-heating effect in individual metal oxide nanowires can be used to activate their response to gases with power consumptions below tenths of microwatts. The thermal response time of these devices is extremely fast (a few milliseconds) and it makes it possible to observe the kinetics of the interactions between the gas molecules and the metal oxide. In this work we demonstrate that such effects enable an experimental methodology to improve the selectivity of metal oxide-based sensors based on the analysis of their fast response dynamics. Specifically, this work jointly analyzes the magnitude and response time of SnO2 nanowire-based sensors to carbon monoxide (CO) and humidity (H2O) mixtures, proving that a quantitative analysis of CO–H2O gas blends can be achieved by modulating their work temperature through the self-heating effect.
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82.80.-d Chemical analysis and related physical methods of analysis
78.47.D- Time resolved spectroscopy (>1 psec)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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)

Graphene quantum dots formed by a spatial modulation of the Dirac gap

G. Giavaras and Franco Nori

Appl. Phys. Lett. 97, 243106 (2010); http://dx.doi.org/10.1063/1.3525858 (3 pages)

Online Publication Date: 15 December 2010

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An electrostatic quantum dot cannot be formed in monolayer graphene because of the Klein tunneling. However, a dot can be formed with the help of a uniform magnetic field. As shown here, a spatial modulation of the Dirac gap leads to confined states with discrete energy levels, thus defining a dot, without applying external electric and magnetic fields. Gap-induced dot states can coexist and couple with states introduced by an electrostatic potential. This property allows the region in which the resulting states are localized to be tuned with the potential.
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81.05.ue Graphene
81.07.Ta Quantum dots
73.63.Kv Quantum dots
73.40.Gk Tunneling
73.22.Pr Electronic structure of graphene
73.21.La Quantum dots

Controlled B-site ordering in Sr2CrReO6 double perovskite films by using pulsed laser interval deposition

S. Chakraverty, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 97, 243107 (2010); http://dx.doi.org/10.1063/1.3525578 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2010

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We have investigated the effects of growth interval in pulsed laser deposition on structural, magnetic, and electrical transport properties of (111)-oriented Sr2CrReO6 double perovskite films. It was found that the degree of B-site ordering varied in a wide range by just changing the growth interval. Magnetization under 1 T and metallicity (the ratio of room-temperature resistivity to minimum resistivity at low temperatures) monotonically increased with increasing degree of ordering and reached values nearly identical to bulk. This technique, called pulsed laser interval deposition, may provide more efficient way to study relations between structural and physical properties in double perovskites than controlling growth parameters, such as temperature and oxygen partial pressure.
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81.15.Fg Pulsed laser ablation deposition
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth

Effect of current on Coulomb oscillation in a Ni–Nb–Zr–H glassy alloy with multiple junctions

Mikio Fukuhara and Akihisa Inoue

Appl. Phys. Lett. 97, 243108 (2010); http://dx.doi.org/10.1063/1.3527084 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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The effect of current on Coulomb oscillation in a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy was carried out under currents of 1 nA, 10 nA, 100 nA, 1 μA, 10 μA, 100 μA, 1 mA, 10 mA, and 100 mA in the temperature range of 300–6 K. The amplitude of the Coulomb oscillation showed maximum values at around 1 μA. The discrete variation of the oscillation can be described as E = 2×10−4 exp(2.34 N) (r2 = 0.993), showing clear quantization of Coulomb oscillation, where E and N are the units of h/2e2 and step number, respectively. We suggested that this would be associated with nanometer-sized RC circuits in the alloy.
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73.23.Hk Coulomb blockade; single-electron tunneling

Millimeter-wave on-chip solenoid inductor by on-demand three-dimensional printing of colloidal nanoparticles

Niklas C. Schirmer, Jan Hesselbarth, Stefan Ströhle, Brian R. Burg, Manish K. Tiwari, and Dimos Poulikakos

Appl. Phys. Lett. 97, 243109 (2010); http://dx.doi.org/10.1063/1.3527923 (3 pages)

Online Publication Date: 16 December 2010

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Millimeter-wave on-chip solenoid inductor structures with wire diameters of O(1 μm) are investigated. The wires are formed by on-demand three-dimensional printing of nanoparticle laden droplets with known droplet size, deposition frequency, and evaporation time. After thermal annealing and morphological characterization, the solenoids are evaluated using two-port S parameter based electrical transmission measurements. The measurements over 0.1–110 GHz, combined with finite-element based electromagnetic field modeling, reveal a quality factor of 0.8 at 110 GHz for an 80 pH coil resulting in an inductance-per-area value of 80 nH/mm2, which is the highest reported value at these scales.
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84.32.Hh Inductors and coils; wiring
84.40.-x Radiowave and microwave (including millimeter wave) technology

Nonlinear optical spectrum of bilayer graphene in the terahertz regime

Yee Sin Ang, Shareef Sultan, and C. Zhang

Appl. Phys. Lett. 97, 243110 (2010); http://dx.doi.org/10.1063/1.3527934 (3 pages)

Online Publication Date: 17 December 2010

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We demonstrate that the nonlinear optical response in bilayer graphene is among the strongest, especially in the important frequency regime of terahertz to far-infrared. Furthermore, we show that both the single frequency and frequency tripled nonlinear response become comparable to the linear response at very moderate electric field. The field strength for the onset of nonlinear effect in bilayer graphene is well within the experimental achievable range in laboratories. Our result suggests that bilayers are preferred structures for developing graphene-based nonlinear photonics and optoelectronics devices.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics
78.30.Na Fullerenes and related materials
78.67.Wj Optical properties of graphene
78.70.Gq Microwave and radio-frequency interactions

Radio frequency electrical transduction of graphene mechanical resonators

Yuehang Xu, Changyao Chen, Vikram V. Deshpande, Frank A. DiRenno, Alexander Gondarenko, David B. Heinz, Shuaimin Liu, Philip Kim, and James Hone

Appl. Phys. Lett. 97, 243111 (2010); http://dx.doi.org/10.1063/1.3528341 (3 pages) | Cited 7 times

Online Publication Date: 17 December 2010

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We report radio frequency (rf) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ∼ 34 MHz, quality factor ∼ 10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Quantum pumping in graphene with a perpendicular magnetic field

Rakesh P. Tiwari and M. Blaauboer

Appl. Phys. Lett. 97, 243112 (2010); http://dx.doi.org/10.1063/1.3528457 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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We consider quantum pumping of Dirac fermions in a monolayer of graphene in the presence of a perpendicular magnetic field in the central pumping region. The two external pump parameters are electrical voltages applied to the graphene sheet on either side of the pumping region. We analyze this pump within scattering matrix formalism and calculate both pumped charge and spin currents. The predicted charge currents are of the order of 1000 nA, which is readily observable using current technology.
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72.80.Vp Electronic transport in graphene
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Charge accumulation dynamics in organic thin film transistors

X. Y. Chen, H. Zhu, and S. D. Wang

Appl. Phys. Lett. 97, 243301 (2010); http://dx.doi.org/10.1063/1.3526374 (3 pages) | Cited 4 times

Online Publication Date: 14 December 2010

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We have developed a transient current model to quantitatively describe the charge accumulation dynamics in organic thin film transistors. This model indicates that the charge accumulation process is faster at higher gate bias and/or higher field-effect mobility, and the experimental results are consistent with the theoretical expectations. A strong gate bias dependence of the field-effect mobility is observed, which suggests that the charge traps in the charge accumulation layer may limit the device performance not only at steady state but also at transient state.
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85.30.Tv Field effect devices
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