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17 May 2010

Volume 96, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages)

Qimin Quan, Parag B. Deotare, and Marko Loncar
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High-order cumulants in the counting statistics of asymmetric quantum dots

Christian Fricke, Frank Hohls, Nandhavel Sethubalasubramanian, Lukas Fricke, and Rolf J. Haug

Appl. Phys. Lett. 96, 202103 (2010); http://dx.doi.org/10.1063/1.3430000 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2010

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Measurements of single electron tunneling through a quantum dot (QD) using a quantum point contact as charge detector have been performed for very long time traces with very large event counts. This large statistical basis is used for a detailed examination of the counting statistics for varying symmetry of the QD system. From the measured statistics we extract high order cumulants describing the distribution. Oscillations of the high order cumulants are observed when varying the symmetry. We compare this behavior to the observed oscillation in time dependence and show that the variation in both system variables lead to the same kind of oscillating response.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling
73.63.Kv Quantum dots
73.63.Rt Nanoscale contacts
02.50.-r Probability theory, stochastic processes, and statistics

Positive temperature coefficient resistor behavior in praseodymium-doped ZnO (000math)∣(000math) boundaries

Jong-Sook Lee, Yong Kim, Eui-Chol Shin, and Joachim Maier

Appl. Phys. Lett. 96, 202104 (2010); http://dx.doi.org/10.1063/1.3432444 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2010

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Clear positive temperature coefficient resistor (PTCR) dc behavior has been shown in Pr-doped ZnO (000math)∣(000math) bicrystals by electrical characterization over an unprecedentedly wide temperature range between 40 and 1070 K. With subtraction of the PTCR dc, the admittance can be described by a deep trap level at 0.26 eV but no clue to the origin of the PTCR behavior is provided. Capacitance-voltage characteristics revealed a maximum in the Schottky barrier heights consistent with the PTCR behavior. The PTCR behavior in Pr-doped ZnO c-axis oriented bicrystals is thus phenomenologically analogous to that of the ferroelectric BaTiO3.
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73.40.Ns Metal-nonmetal contacts
71.55.Gs II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge

Shengqiang Zhou, Danilo Bürger, Wolfgang Skorupa, Peter Oesterlin, Manfred Helm, and Heidemarie Schmidt

Appl. Phys. Lett. 96, 202105 (2010); http://dx.doi.org/10.1063/1.3428770 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2010

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In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 1018 to 2.1×1020 cm−3, the latter being the highest reported so far. Based on the magnetotransport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Cc Kinetics of defect formation and annealing

Band gap tuning in GaN through equibiaxial in-plane strains

L. Dong, S. K. Yadav, R. Ramprasad, and S. P. Alpay

Appl. Phys. Lett. 96, 202106 (2010); http://dx.doi.org/10.1063/1.3431290 (3 pages) | Cited 14 times

Online Publication Date: 19 May 2010

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Structural transformations and the relative variation in the band gap energy (ΔEg) of (0001) gallium nitride (GaN) films as a function of equibiaxial in-plane strains are studied by density functional theory. For relatively small compressive misfits (−6%–0%), the band gap is estimated to be around its strain-free value, while for small tensile strains (0%–6%), it decreases by approximately 45%. In addition, at large tensile strains (>14.5%), our calculations indicate that GaN may undergo a structural phase transition from wurtzite to a graphitelike semimetallic phase.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.55.ag Semiconductors

High-temperature thermoelectric properties of thallium-filled skutterudites

Adul Harnwunggmoung, Ken Kurosaki, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 96, 202107 (2010); http://dx.doi.org/10.1063/1.3430739 (3 pages) | Cited 11 times

Online Publication Date: 20 May 2010

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The high temperature thermoelectric (TE) properties of polycrystalline Tl-filled skutterudites TlxCo4Sb12 (x = 0, 0.05, 0.10, 0.15, 0.20, and 0.25) were examined from room temperature to 750 K. All samples exhibited negative Seebeck coefficients. The electrical resistivity, absolute values of the Seebeck coefficient, and the lattice thermal conductivity were found to decrease with increasing Tl content. Tl0.25Co4Sb12 exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.90 at 600 K.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors
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Strongly suppressed 1/f noise and enhanced magnetoresistance in epitaxial Fe–V/MgO/Fe magnetic tunnel junctions

D. Herranz, F. Bonell, A. Gomez-Ibarlucea, S. Andrieu, F. Montaigne, R. Villar, C. Tiusan, and F. G. Aliev

Appl. Phys. Lett. 96, 202501 (2010); http://dx.doi.org/10.1063/1.3430064 (3 pages) | Cited 5 times

Online Publication Date: 17 May 2010

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Alloying Fe electrodes with V, through reduced FeV/MgO interface mismatch in epitaxial magnetic tunnel junctions with MgO barriers, notably suppresses both nonmagnetic (parallel) and magnetic (antiparallel) state 1/f noise and enhances tunneling magnetoresistance. A comparative study of the room temperature electron transport and low frequency noise in Fe1−xVx/MgO/Fe and Fe/MgO/Fe1−xVx magnetic tunnel junctions with 0 ≤ x ≤ 0.25 reveals that V doping of the bottom electrode for x<0.1 reduces in nearly two orders of magnitude the normalized nonmagnetic and magnetic 1/f noise. We attribute the enhanced TMR and suppressed 1/f noise to strongly reduced misfit and dislocation density.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport

Large exchange bias field in the Ni–Mn–Sn Heusler alloys with high content of Mn

H. C. Xuan, Q. Q. Cao, C. L. Zhang, S. C. Ma, S. Y. Chen, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 96, 202502 (2010); http://dx.doi.org/10.1063/1.3428782 (3 pages) | Cited 20 times

Online Publication Date: 17 May 2010

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The exchange bias properties have been investigated in bulk Mn50Ni40−xSn10+x (x = 0, 0.5, and 1) Heusler alloys with high content of Mn, in which the largest exchange bias field is up to 910 Oe for Mn50Ni40Sn10 alloy. In these alloys, the excess Mn atoms would occupy not only the Sn sites but also the Ni sites, and the moments of Mn on Sn or Ni sites are coupled antiferromagnetically to those on the regular Mn sites, respectively. The origin of this considerably large exchange bias field has been discussed.
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75.30.Et Exchange and superexchange interactions
71.70.Gm Exchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities

Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers

P. Poulopoulos, V. Kapaklis, P. E. Jönsson, E. Th. Papaioannou, A. Delimitis, S. D. Pappas, D. Trachylis, and C. Politis

Appl. Phys. Lett. 96, 202503 (2010); http://dx.doi.org/10.1063/1.3428791 (3 pages) | Cited 2 times

Online Publication Date: 17 May 2010

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Ni/NiO multilayers with excellent sequencing are grown via radiofrequency magnetron sputtering with the use of one Ni target and natural oxidation. Ni layers consist of very small Ni nanocrystals interrupted by amorphous NiO layers. When Ni is deposited at 0.3 Pa Ar-pressure, the hard-magnetization axis is the film normal and saturation field decreases by decreasing Ni layer thickness. Considerable positive surface anisotropy is found, which is remarkable for Ni-based multilayers. If Ni is deposited at 3 Pa Ar-pressure, perpendicular magnetic anisotropy is observed at low temperatures even for 5.4 nm thick Ni layers. This anisotropy results in the formation of stripe magnetic domains.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.78.Fg Dynamics of domain structures

C-axis critical current of a PrFeAsO0.7 single crystal

H. Kashiwaya, K. Shirai, T. Matsumoto, H. Shibata, H. Kambara, M. Ishikado, H. Eisaki, A. Iyo, S. Shamoto, I. Kurosawa, and S. Kashiwaya

Appl. Phys. Lett. 96, 202504 (2010); http://dx.doi.org/10.1063/1.3427464 (3 pages) | Cited 9 times

Online Publication Date: 18 May 2010

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The c-axis transport properties of a high-pressure synthesized PrFeAsO0.7 single crystal are studied using s-shaped junctions. Resistivity anisotropy of about 120 detected at 50 K shows the presence of strong anisotropy in the electronic states. The obtained critical current density for the c-axis of 2.9×105 A/cm2 is two orders of magnitude larger than that in Bi2Sr1.6La0.4CuO6+δ. The appearance of a hysteresis in the current-voltage curve below Tc is the manifestation of the intrinsic Josephson effect similar to that in cuprate superconductors. The suppression of the critical current-normal resistance (IcRn) product is explained by an inspecular transport in s±-wave pair potential.
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74.25.fc Electric and thermal conductivity
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.20.-z Theories and models of superconducting state

Potassium-doped BaFe2As2 superconducting thin films with a transition temperature of 40 K

Nam Hoon Lee, Soon-Gil Jung, Dong Ho Kim, and Won Nam Kang

Appl. Phys. Lett. 96, 202505 (2010); http://dx.doi.org/10.1063/1.3431583 (3 pages) | Cited 13 times

Online Publication Date: 18 May 2010

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We report the growth of potassium-doped BaFe2As2 thin films, where the major charge carriers are holes, on Al2O3 (0001) and LaAlO3 (001) substrates by using an ex situ pulsed laser deposition technique. The measured superconducting transition temperatures are 40 K and 39 K for the films grown on Al2O3 and LaAlO3, respectively, and diamagnetism indicates that the films have good bulk superconducting properties below 36 K and 30 K, respectively. The x-ray diffraction patterns for both films indicated a preferred c-axis orientation, regardless of the substrate structures of LaAlO3 and Al2O3. The upper critical field at zero temperature was estimated to be about 155 T.
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74.78.-w Superconducting films and low-dimensional structures
68.55.A- Nucleation and growth
74.62.-c Transition temperature variations, phase diagrams
81.15.Fg Pulsed laser ablation deposition
68.55.jm Texture

Reduced low frequency noise in electron beam evaporated MgO magnetic tunnel junctions

Z. Diao, J. F. Feng, H. Kurt, G. Feng, and J. M. D. Coey

Appl. Phys. Lett. 96, 202506 (2010); http://dx.doi.org/10.1063/1.3431620 (3 pages) | Cited 11 times

Online Publication Date: 18 May 2010

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We compare low frequency noise in magnetic tunnel junctions with MgO barriers prepared by electron-beam evaporation with those prepared by radiofrequency sputtering, both showing a high tunneling magnetoresistance. The normalized noise parameter in the parallel state of junctions with evaporated barriers is at least one order of magnitude lower than that in junctions with sputtered barriers, and exhibits a weaker bias dependence. The lowest normalized noise is in the 10−11 μm2 range. A lower density of oxygen vacancies acting as charge trap states in the evaporated MgO is responsible for the lower noise.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
61.72.jd Vacancies
72.20.My Galvanomagnetic and other magnetotransport effects

Enhanced microwave performance of cobalt nanoflakes with strong shape anisotropy

Fei Ma, Yong Qin, and Yun-Ze Li

Appl. Phys. Lett. 96, 202507 (2010); http://dx.doi.org/10.1063/1.3432441 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2010

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Co nanoflakes are synthesized through a low temperature hydrothermal method. The single-phased hexagonal close-packed Co nanoflakes have a diameter of several micrometers and a thickness about 80 nm. Magnetic hysteresis loops are quite different along different directions deviating from the nanoflakes plane, which shows Co nanoflakes have strong magnetic anisotropy. Flakelike morphology influence the performance of complex permeability in gigahertz frequency. Natural resonance peak happens at 5.74 GHz with the contribution of shape anisotropy. Multiple resonance phenomenon appears due to the exchange resonance effect, which makes Co nanoflakes a broadband candidate for microwave absorbing material.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Control of orbital ordered state in strained Nd0.25Sr1.75MnO4 films

K. S. Takahashi, J. Fujioka, Y. Ida, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 96, 202508 (2010); http://dx.doi.org/10.1063/1.3427428 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2010

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Epitaxial strain effect has been studied for Nd0.25Sr1.75MnO4 thin films on (100) surfaces of two different isostructural (single-layered perovskite) substrates, LaSrAlO4 and LaSrGaO4. Due to the anisotropic strain in the MnO2 plane, the orientation-controlled films were stabilized with the structure consistent with that of C-type antiferromagnetic and d3x2−r2 ferro-orbital-ordered state. Measurements of highly anisotropic optical spectra show that the tensile strain in the MnO2 plane aligns ferroically the direction of d3x2−r2 orbitals parallel to the film plane, whereas compressive strain does those vertical to the film plane. These results indicate that the direction of the ferroic ordering of d3x2−r2 orbitals can be controlled by external uniaxial pressure, implying a potential for a switching device.
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68.55.-a Thin film structure and morphology
75.50.Ee Antiferromagnetics
77.80.-e Ferroelectricity and antiferroelectricity
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Shape-independent permeability model for uniaxially-anisotropic ferromagnetic thin films

Brice Jamieson, Terence O’Donnell, Santosh Kulkarni, and Saibal Roy

Appl. Phys. Lett. 96, 202509 (2010); http://dx.doi.org/10.1063/1.3430061 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2010

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A permeability model based on the three-dimensional shape demagnetization effect is developed to estimate the permeability of any uniaxially-anisotropic ferromagnetic thin-film for integrated micromagnetic structures. The model is validated by comparison to measured ferromagnetic thin films (NiFe and CoPRe) with different anisotropies and saturation magnetizations. The dependence of permeability on film-thickness is modeled as a function of the demagnetization effect and verified against fabricated samples of varying thicknesses.
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75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Current-induced domain wall motion in Co/Pt nanowires: Separating spin torque and Oersted-field effects

J. Heinen, O. Boulle, K. Rousseau, G. Malinowski, M. Kläui, H. J. M. Swagten, B. Koopmans, C. Ulysse, and G. Faini

Appl. Phys. Lett. 96, 202510 (2010); http://dx.doi.org/10.1063/1.3405712 (3 pages) | Cited 13 times

Online Publication Date: 20 May 2010

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We report on low temperature current induced domain wall depinning experiments on (Co/Pt) multilayer nanowires with perpendicular magnetization. Using a special experimental scheme, we are able to extract the different contributions of the Oersted field and spin torque from the dependence of the depinning field on the injected current for selected magnetization configurations. The spin torque contribution is found to be dominant with a small contribution of the Oersted field leading to a nonadiabaticity factor β in line with previous measurements.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
73.21.Ac Multilayers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of Mn concentration on the ac magnetically induced heating characteristics of superparamagnetic MnxZn1−xFe2O4 nanoparticles for hyperthermia

Minhong Jeun, Seung Je Moon, Hiroki Kobayashi, Hye Young Shin, Asahi Tomitaka, Yu Jeong Kim, Yasushi Takemura, Sun Ha Paek, Ki Ho Park, Kyung-Won Chung, and Seongtae Bae

Appl. Phys. Lett. 96, 202511 (2010); http://dx.doi.org/10.1063/1.3430043 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2010

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The effects of Mn2+ cation concentration on the ac magnetically induced heating characteristics and the magnetic properties of superparamagnetic MnxZn1−xFe2O4 nanoparticles (SPNPs) were investigated to explore the biotechnical feasibility as a hyperthermia agent. Among the MnxZn1−xFe2O4 SPNPs, the Mn0.5Zn0.5Fe2O4 SPNP showed the highest ac magnetically induced heating temperature (ΔTac,mag), the highest specific absorption rate (SAR), and the highest biocompatibility. The higher out of phase susceptibility (χm″) value and the higher chemical stability systematically controlled by the replacement of Zn2+ cations by the Mn2+ cations on the A-site (tetrahedral site) are the primary physical reason for the promising biotechnical properties of Mn0.5Zn0.5Fe2O4 SPNP.
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87.85.Rs Nanotechnologies-applications
87.19.Pp Biothermics and thermal processes in biology

Atomically resolved scanning tunneling microscopy on perovskite manganite single crystals

Sahana Rößler, B. Padmanabhan, Suja Elizabeth, H. L. Bhat, F. Steglich, and S. Wirth

Appl. Phys. Lett. 96, 202512 (2010); http://dx.doi.org/10.1063/1.3432753 (3 pages) | Cited 1 time

Online Publication Date: 21 May 2010

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Atomically resolved scanning tunneling microscopy was conducted on cleaved single crystals of the cubic perovskite Pr0.68Pb0.32MnO3. Several different surface configurations could be resolved including a frequent square arrangement with atomic distances in excellent agreement to the bulk lattice constant of the cubic structure. We also observed stripe formation and a surface reconstruction. The latter is likely related to a polar rare earth-oxygen terminated surface.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.bt Other materials
61.66.Fn Inorganic compounds
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Roles of lattice distortion in (1−x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics

Y. S. Sung, J. M. Kim, J. H. Cho, T. K. Song, M. H. Kim, and T. G. Park

Appl. Phys. Lett. 96, 202901 (2010); http://dx.doi.org/10.1063/1.3428580 (3 pages) | Cited 12 times

Online Publication Date: 17 May 2010

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Structure property relations in (1−x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics were investigated at x = 0–10 mol %. A solid solution with either rhombohedral or tetragonal symmetry was confirmed with a morphotropic phase boundary (MPB) at x = 5–7 mol %. Grains became small with increasing x possibly due to grain boundary pinning by BaBi′–BaNa•. Lattice distortion was a key factor affecting piezoelectric coefficient (d33) and depolarization temperature (Td). Both rhombohedral 90−α and tetragonal cT/aT lattice distortion became smaller toward the MPB causing poling by field and depoling by temperature to become easier subsequently resulting in higher d33 but lower Td, and vice versa.
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61.72.Mm Grain and twin boundaries
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Reversible plasma switching in epitaxial BiFeO3 thin films

Yunseok Kim, Ionela Vrejoiu, Dietrich Hesse, and Marin Alexe

Appl. Phys. Lett. 96, 202902 (2010); http://dx.doi.org/10.1063/1.3431585 (3 pages) | Cited 6 times

Online Publication Date: 17 May 2010

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Reversible plasma switching in epitaxial multiferroic BiFeO3 thin films was directly observed and analyzed using piezoresponse force microscopy. The polarization could be reversibly switched using oxygen plasma and a subsequent thermal annealing treatment in vacuum, respectively. The domain wall velocity during plasma switching, estimated to about 10−8 m/s, is much slower compared to the normal electrical switching, however a large area of square centimeter scale could be stably switched. The results demonstrate that reversible plasma switching can be achieved by oxygen plasma treatment and it can be a useful tool for an electrode-less control of ferroelectric switching on large area.
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77.80.Fm Switching phenomena
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
52.77.-j Plasma applications
81.40.Gh Other heat and thermomechanical treatments

Electrode material dependent breakdown and recovery in advanced high-κ gate stacks

X. Wu, K. L. Pey, G. Zhang, P. Bai, X. Li, W. H. Liu, and N. Raghavan

Appl. Phys. Lett. 96, 202903 (2010); http://dx.doi.org/10.1063/1.3429682 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2010

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In this paper, the mechanism and physics governing the breakdown and recovery in metal-gated high-κ (MG-HK) dielectric stacks is investigated. Postbreakdown recovery is observed in NiSi and TiN-gated, but not TaN-gated, HfO2-based logic devices in voltage-stress tests. Failure analysis studies reveal that metal-filamentation, besides oxygen vacancies, is responsible for the breakdown of these MG-HK dielectrics. First-principle studies show that the 5d orbitals of Hf and migrated metal atoms in the filamentation process reduce the band gap and increase the leakage current, eventually causing percolative breakdown of the dielectric. Postbreakdown recovery is feasible only for gate stacks with a low enough defect formation energy, which can be realized by selecting appropriate gate electrode materials, such as NiSi and TiN.
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85.30.Tv Field effect devices
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Temperature-dependent leakage current characteristics of Pr and Mn cosubstituted BiFeO3 thin films

Zheng Wen, Xuan Shen, Jingxian Wu, Di Wu, Aidong Li, Bin Yang, Zhu Wang, Hengzhi Chen, and Junling Wang

Appl. Phys. Lett. 96, 202904 (2010); http://dx.doi.org/10.1063/1.3432083 (3 pages) | Cited 11 times

Online Publication Date: 20 May 2010

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Leakage current characteristics of (Bi0.86Pr0.14)(Fe0.95Mn0.05)O3 (BPFMO) thin films are studied at various temperatures from 293 down to 93 K. Space charge limited current and Poole–Frenkel (PF) emission are found to be the dominant mechanism in the low and the high electric fields, respectively. The trap ionization energy at zero-field in BPFMO films is deduced to be around 0.29 eV, which indicates the existence of shallow traps. A negative differential resistivity behavior is observed before the onset of PF emission at 93 K, which is discussed in terms of the competition between electron trapping and field-assisted thermal emission.
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77.55.-g Dielectric thin films
73.50.Fq High-field and nonlinear effects
72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.70.+q Field emission, ionization, evaporation, and desorption

An in situ examination of atomic layer deposited alumina/InAs(100) interfaces

A. P. Kirk, M. Milojevic, J. Kim, and R. M. Wallace

Appl. Phys. Lett. 96, 202905 (2010); http://dx.doi.org/10.1063/1.3432749 (3 pages) | Cited 13 times

Online Publication Date: 21 May 2010

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Undoped InAs(100) wafers were either passivated with sulfur from a (NH4)2Sx solution or etched with NH4OH and then characterized with monochromatic x-ray photoelectron spectroscopy (XPS) before and after in situ deposition of Al2O3 by atomic layer deposition. Sulfur passivation minimized oxidation. Trimethyl aluminum (TMA) exposure reduced trivalent indium and arsenic oxidation states. The In1+ chemical state persisted while elemental arsenic remained at the Al2O3/InAs interface prior to TMA exposure and possibly a mixture of As–As and As–Al bonds were present afterwards. The In 3d5/2 peak line shape from bulk InAs differed from previous XPS experiments on epitaxial InxGa1−xAs.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
81.65.Rv Passivation
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.aj Insulators
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Nanograss and nanostructure formation on silicon using a modified deep reactive ion etching

M. Mehran, S. Mohajerzadeh, Z. Sanaee, and Y. Abdi

Appl. Phys. Lett. 96, 203101 (2010); http://dx.doi.org/10.1063/1.3428360 (3 pages) | Cited 4 times

Online Publication Date: 17 May 2010

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Silicon nanograss and nanostructures are realized using a modified deep reactive ion etching technique on both plane and vertical surfaces of a silicon substrate. The etching process is based on a sequential passivation and etching cycle, and it can be adjusted to achieve grassless high aspect ratio features as well as grass-full surfaces. The incorporation of nanostructures onto vertically placed parallel fingers of an interdigital capacitive accelerometer increases the total capacitance from 0.45 to 30 pF. Vertical structures with features below 100 nm have been realized.
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81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
81.07.Bc Nanocrystalline materials
81.65.Rv Passivation
52.77.Bn Etching and cleaning

Photonic crystal nanobeam cavity strongly coupled to the feeding waveguide

Qimin Quan, Parag B. Deotare, and Marko Loncar

Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages) | Cited 36 times

Online Publication Date: 17 May 2010

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A deterministic design of an ultrahigh Q-factor, wavelength-scale photonic crystal nanobeam cavity is proposed and experimentally demonstrated. Using this approach, cavities with Q>106 and on-resonance transmission T>90% are designed. The devices, fabricated in silicon and capped with a low refractive index polymer, have experimental Q = 80 000 and T = 73%. This is, to the best of our knowledge, the highest transmission measured in deterministically designed, wavelength-scale high-Q cavities.
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42.82.Gw Other integrated-optical elements and systems
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials

Liquid cell with plasmon lenses for surface enhanced Raman spectroscopy

V. Vlasko-Vlasov, A. Joshi-Imre, J. T. Bahns, L. Chen, L. Ocola, and U. Welp

Appl. Phys. Lett. 96, 203103 (2010); http://dx.doi.org/10.1063/1.3429605 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2010

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High-fidelity surface enhanced Raman spectra (SERS) of Rhodamine 6G and 2-mercaptopyrimidine liquid solutions are measured using a microfluidic delivery system constructed on a flat silver substrate. Microscopic plasmon lenses patterned in the silver film focus surface plasmons into a subwavelength spot which yields the light amplification required for SERS. The system provides an efficiency similar to traditional colloidal substrates, and allows multiple sample loading. We find that the main contribution to the spectra comes from the molecules directly attached to the silver surface, which gives strong evidence for the chemical enhancement of SERS.
Show PACS
42.79.Bh Lenses, prisms and mirrors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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