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6 Apr 2009

Volume 94, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 141901 (2009); http://dx.doi.org/10.1063/1.3111813 (3 pages)

G. S. Huang (黄高山), S. Kiravittaya, V. A. Bolaños Quiñones, F. Ding (丁飞), M. Benyoucef, A. Rastelli, Y. F. Mei (梅永丰), and O. G. Schmidt
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DyScO3 buffer layer for a performing metal-ferroelectric-insulator-semiconductor structure with multiferroic BiFeO3 thin film

N. M. Murari, R. Thomas, S. P. Pavunny, J. R. Calzada, and R. S. Katiyar

Appl. Phys. Lett. 94, 142907 (2009); http://dx.doi.org/10.1063/1.3116088 (3 pages) | Cited 14 times

Online Publication Date: 9 April 2009

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Metal-ferroelectric-insulator-semiconductor structures with a BiFeO3 ferroelectric layer and DyScO3 insulating buffer layer were fabricated and characterized. BiFeO3 film was polycrystalline with rhombohedral structure and DyScO3 film was amorphous. The size of the capacitance-voltage memory window (ΔVFB) was investigated as a function of voltage sweep and frequency; ΔVFB increased to a saturation value of 1.7 V with the sweep voltage and it almost remained constant over a frequency range of 1 kHz to 1 MHz.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.50.Gk Non-volatile ferroelectric memories
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.J- Morphology of films

Enhanced magnetization and polarization in chemically modified multiferroic (1−x)BiFeO3–xDyFeO3 solid solution

W.-M. Zhu, L. W. Su, Z.-G. Ye, and W. Ren

Appl. Phys. Lett. 94, 142908 (2009); http://dx.doi.org/10.1063/1.3110971 (3 pages) | Cited 17 times

Online Publication Date: 10 April 2009

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In order to develop multiferroics with large magnetization and polarization, we have prepared the (1−x)BiFeO3–xDyFeO3 (BF-DF) solid solution and systematically studied its properties. A morphotropic phase transition from rhombohedral perovskite (R3c) to orthorhombic orthoferrite (Pbnm) was found at x around 0.1. The magnetic properties of BiFeO3 were improved by the introduction of Dy3+ on the perovskite A site. Chemically modified Bi0.9Dy0.1Fe1−xTixO3+x/2 ceramics by aliovalent ionic substitution of Ti4+ for Fe3+ with excess Bi2O3 exhibit weak ferromagnetism and a typical ferroelectric hysteresis loop with a large remnant polarization of 23 μC/cm2 at room temperature and a large saturated magnetization (Ms = 0.5 μB/f.u.) at 2 K. These properties entitle the BF-DF solid solution one of few multiferroic materials that exhibit both decent magnetization and electric polarization.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
81.20.-n Methods of materials synthesis and materials processing
77.80.Dj Domain structure; hysteresis
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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Counting graphene layers on glass via optical reflection microscopy

P. E. Gaskell, H. S. Skulason, C. Rodenchuk, and T. Szkopek

Appl. Phys. Lett. 94, 143101 (2009); http://dx.doi.org/10.1063/1.3115026 (3 pages) | Cited 28 times

Online Publication Date: 6 April 2009

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We show that optical reflection microscopy is a reliable method to simultaneously locate and count graphene layers deposited on bulk, transparent substrates such as soda-lime glass. The visible contrast in optical reflection versus graphene layer number is resolvable on bulk substrates. A simple Fresnel theory based on the universal optical conductance of graphene layers accurately models optical reflection images taken at a wavelength of 550±5 nm. We directly count one to nine layers of graphene using reflection microscopy.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.40.Ri Fullerenes and related materials
78.68.+m Optical properties of surfaces
81.07.Bc Nanocrystalline materials

Origin of low threshold field emission from nitrogen-incorporated nanocrystalline diamond films

Tomohiro Ikeda and Kungen Teii

Appl. Phys. Lett. 94, 143102 (2009); http://dx.doi.org/10.1063/1.3115767 (3 pages) | Cited 14 times

Online Publication Date: 8 April 2009

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Highly conductive, nitrogen-incorporated nanocrystalline diamond films with quasimetallic character emit electrons at low turn-on fields ( ∼ 3 V μm−1). These films exhibit stronger delocalization of carriers, indicative of smaller energy separation between the defect bands in the band gap. We show that the emission level derived from the measured emission characteristic and electron affinity shifts upward (up to a few eV) with increasing the film conductivity, thereby decreasing the effective potential barrier height for the emission. This is attributed to higher probabilities of electron injection into upper defect levels during the transport process, originating from internal band bending and increasing band continuity.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.22.-f Electronic structure of nanoscale materials and related systems
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ng Insulators
71.20.Ps Other inorganic compounds

Distribution control of 1.55 μm InAs quantum dots down to small numbers on truncated InP pyramids grown by selective area metal organic vapor phase epitaxy

Hao Wang, Jiayue Yuan, Torsten Rieger, Peter J. van Veldhoven, Peter Nouwens, Tom J. Eijkemans, Tjibbe de Vries, Barry Smalbrugge, Erik Jan Geluk, and Richard Nötzel

Appl. Phys. Lett. 94, 143103 (2009); http://dx.doi.org/10.1063/1.3116146 (3 pages) | Cited 7 times

Online Publication Date: 8 April 2009

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Distribution control of InAs quantum dots (QDs) on truncated InP pyramids by selective area growth is reported. The top surface of the pyramids is composed of a (100) facet and high-index facets aside. The arrangement of the facets is governed by the shape of the pyramid base and top surface area. The QDs preferentially nucleate on the high-index facets determining position and distribution. The QD number is reduced with shrinking top surface size. Positioning of four, three, two, and single QDs is realized depending on the top surface’s shape and size. Emission from single QDs is observed at 1.55 μm.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.47.Fg Semiconductor surfaces

Possible formation of interlayer nano-p-n junctions and quantum dot in double-walled carbon nanotube with electrode contacts to different layers

T. Shimizu, J. Haruyama, K. Nozawa, T. Sugai, and H. Shinohara

Appl. Phys. Lett. 94, 143104 (2009); http://dx.doi.org/10.1063/1.3108086 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2009

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We report findings on the asymmetrical current properties on both the source-drain and back-gate voltage (VBG) dependence (unconventional ambipolar behavior) found in a double-walled carbon nanotube (DWNT) field-effect transistor, which has electrode contacts to different layers. We also find Coulomb oscillations with a large charging energy observable only in +VBG region at low temperature. As origins for these phenomena, we discuss the possible presence of outer p- and inner n-type semiconducting layers, a corresponding interlayer nano-p-n junction, and a small quantum dot region in the inner n-layer exposed from the outer layer. Annealing of the DWNT in air atmosphere after synthesis allows change in only outer layer to p-type, remaining n-type behavior in the inner layer.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Effects of capping on GaN quantum dots deposited on Al0.5Ga0.5N by molecular beam epitaxy

M. Korytov, M. Benaissa, J. Brault, T. Huault, T. Neisius, and P. Vennéguès

Appl. Phys. Lett. 94, 143105 (2009); http://dx.doi.org/10.1063/1.3115027 (3 pages) | Cited 9 times

Online Publication Date: 10 April 2009

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The impact of the capping process on the structural and morphological properties of GaN quantum dots (QDs) grown on fully relaxed Al0.5Ga0.5N templates was studied by transmission electron microscopy. A morphological transition between the surface QDs, which have a pyramidal shape, and the buried ones, which have a truncated pyramid shape, is evidenced. This shape evolution is accompanied by a volume change: buried QDs are bigger than surface ones. Furthermore a phase separation into Al0.5Ga0.5N barriers was observed in the close vicinity of buried QDs. As a result, the buried QDs were found to be connected with the nearest neighbors by thin Ga-rich zones, whereas Al-rich zones are situated above the QDs.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.75.Qr Phase separation and segregation in semiconductors
81.07.Ta Quantum dots

Effect of gas rarefaction on the performance of submicron fins

Suresh Ramanan and Ronggui Yang

Appl. Phys. Lett. 94, 143106 (2009); http://dx.doi.org/10.1063/1.3115786 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2009

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High thermal conductivity and high surface to volume ratios of nanostructures such as carbon nanotubes and metallic nanowires make them great candidates as micro/nano-fins and thus a potential solution to the ever-increasing thermal management challenges in electronics and photonics. With sizes ranging in the order of a few hundred nanometers or less, the fluid flow through these structures fall in the transition, slip, and even molecular transport regimes. The effects of the velocity and temperature slips (gas rarefaction) could not be neglected. In this study, a simple analytical model has been developed to predict the effect of gas rarefaction on the heat transfer performance of submicron fins. It is shown that the effects of gas rarefaction should be taken into account when designing micro/nano-fins since such effects can significantly reduce the heat transfer enhancement postulated for micro/nano-fins.
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44.10.+i Heat conduction

The effect of layer absorbance for complex surface enhanced Raman scattering substrates

Z.-Y. Zhang, Y.-J. Liu, Q. Zhao, and Y.-P. Zhao

Appl. Phys. Lett. 94, 143107 (2009); http://dx.doi.org/10.1063/1.3118525 (3 pages) | Cited 6 times

Online Publication Date: 10 April 2009

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The “hot spots” mechanism is a common wisdom for surface enhanced Raman scattering (SERS). We argue that this is true when the hot spots are directly exposed to the detector. For complex SERS substrates with layered structures such as nanorod arrays, the structure and the layer absorbance both play important roles, which make the effect of hot spots less significant. Using a numerical calculation of the local electric field distribution of an Ag nanorod array substrate, we demonstrate that the layer absorbance must be considered in order to obtain polarization-dependent SERS intensity that is consistent with experimental data.
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78.30.Er Solid metals and alloys
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.68.+m Optical properties of surfaces

Characteristics of 1.3 μm InAs/InGaAs/GaAs quantum dot electroabsorption modulator

C. Y. Ngo, S. F. Yoon, W. K. Loke, Q. Cao, D. R. Lim, Vincent Wong, Y. K. Sim, and S. J. Chua

Appl. Phys. Lett. 94, 143108 (2009); http://dx.doi.org/10.1063/1.3119186 (3 pages) | Cited 4 times

Online Publication Date: 10 April 2009

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We report the characteristics of 1.3 μm electroabsorption modulators (EAMs) utilizing the InAs/InGaAs/GaAs quantum dot (QD) structures. While extinction ratio of ∼ 10 dB was obtained, suppression of absorption at low reverse bias was observed. Theoretical analysis using a strained-modified, single-band, constant-potential three-dimensional model shows that this is due to the presence of In0.15Ga0.85As acting as potential barrier for the heavy hole. From the device point-of-view, this suggests that InAs/InGaAs/GaAs QD-EAMs are potentially feasible for higher optical power handling capability, which is crucial for high link gain in analog fiber links. We believe that the findings are beneficial to those working on QD-EAMs.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Hp Optical processors, correlators, and modulators
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Effects of amorphous semiconductor thickness on top gate staggered organic field-effect transistors

J. M. Verilhac, M. Benwadih, S. Altazin, S. Jacob, R. Gwoziecki, R. Coppard, and C. Serbutoviez

Appl. Phys. Lett. 94, 143301 (2009); http://dx.doi.org/10.1063/1.3111446 (3 pages) | Cited 6 times

Online Publication Date: 6 April 2009

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We have investigated the influence of the semiconductor thickness varying by almost two orders of magnitude on the transfer and output characteristics of top gate staggered organic field-effect transistors. We observe that the mobility in the saturation regime is almost constant in the thickness range studied. In contrast, the subthreshold slope and the threshold voltage are highly impacted by the semiconductor thickness, and in particular they showed a common optimum thickness value. On both sides of this optimum we observe a loss in performances, which are tentatively attributed to different mechanisms.
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85.30.Tv Field effect devices
FREE

Cascade-energy-level alignment based organic photovoltaic cells by utilizing copper phthalocyanine as bipolar carrier transporting layer

Guang Zhang, Wenlian Li, Bei Chu, Lili Chen, Fei Yan, Jianzhuo Zhu, Yiren Chen, and C. S. Lee

Appl. Phys. Lett. 94, 143302 (2009); http://dx.doi.org/10.1063/1.3114379 (3 pages) | Cited 8 times

Online Publication Date: 6 April 2009

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We demonstrate a cascade-energy-level alignment based organic photovoltaic cell by using stacking three materials with appropriate energy levels. A cell with a structure of ITO/4,4′,4″-tris[N,(3-methylphenyl)-N-phenylamino]-triphenylamine (m-MTDATA)/copper phthalocyanine (CuPc)/fullerene (C60)/4,4′-N,N′-dicarubreneazolebiphenyl (BCP)/LiF/Al was shown to have a power efficiency enhancement in more than 30% over that of a standard reference cell (ITO/CuPc/C60/BCP/LiF/Al), which has only one exciton-dissociation interface. The efficiency improvement was mainly ascribed to the ingenious cascade-energy-level alignment and the application of the bipolar carrier transporting property.
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84.60.Jt Photoelectric conversion
FREE

Field dependent and high light sensitive organic phototransistors based on linear asymmetric organic semiconductor

Yunlong Guo, Chunyan Du, Chong-an Di, Jian Zheng, Xiangnan Sun, Yugeng Wen, Lei Zhang, Weiping Wu, Gui Yu, and Yunqi Liu

Appl. Phys. Lett. 94, 143303 (2009); http://dx.doi.org/10.1063/1.3115794 (3 pages) | Cited 15 times

Online Publication Date: 6 April 2009

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The authors reported organic phototransistors (PTs) with octadecyltrichlorosilane treated SiO2/Si substrate based on anthra[2,3-b]benzo[d]thiophene. The organic PTs show a high mobility of 0.4 cm2 V−1 s−1, a maximum photoresponsivity of about 1000 A/W, and photocurrent/dark-current ratio of around 800 under white light irradiation with 30 μW/cm2. The data are comparable with those of PTs based on amorphous silicon. Meanwhile, it is interesting to see that the devices show a high air-stable property and high photosensitivity via electric-field enhanced process. All these phenomena were attributed to the intrinsic optic-electronic property of the organic semiconductor and optic-electric field effect.
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85.60.Dw Photodiodes; phototransistors; photoresistors
FREE

Improvement of subthreshold current transport by contact interface modification in p-type organic field-effect transistors

Masataka Kano, Takeo Minari, and Kazuhito Tsukagoshi

Appl. Phys. Lett. 94, 143304 (2009); http://dx.doi.org/10.1063/1.3115826 (3 pages) | Cited 30 times

Online Publication Date: 6 April 2009

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The charge injection efficiency of organic field-effect transistors (OFETs) is found to be a critical factor determining the subthreshold characteristics of these devices. OFETs fabricated using a wide band gap organic semiconductor and gold source/drain contacts display large threshold voltage and poor subthreshold characteristics. Insertion of a metal-oxide charge injection layer at the contact/semiconductor interface lower the injection barrier height, resulting in marked improvements in threshold voltage and subthreshold slope and strong suppression of the short-channel effect. The improved subthreshold characteristics are attributed to enhanced charge injection and the consequent promotion of charge accumulation.
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85.30.Tv Field effect devices
FREE

Single-crystal-like organic heterojunction with 40 nm thick charge accumulation layers

Feng Zhu, Jianbing Yang, De Song, Chunhong Li, and Donghang Yan

Appl. Phys. Lett. 94, 143305 (2009); http://dx.doi.org/10.1063/1.3118581 (3 pages) | Cited 17 times

Online Publication Date: 10 April 2009

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Single-crystal-like organic heterojunction films of copper phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F16CuPc) were fabricated by weak-epitaxy-growth method. The intrinsic properties of organic heterojunction were revealed through threshold voltage shift of field-effect transistors and measurement of single-crystal-like diodes. At both sides of the heterojunction interface 40 nm thick charge accumulation layers formed, which showed that the long carriers’ diffusion length is due to the high crystallinity and low density of deep bulk traps of single-crystal-like films. This also indicated the electronic properties of organic heterojunction can be adjusted by controlling the growth condition.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.ag Semiconductors
85.30.Kk Junction diodes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
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Poly(3-hexylthiophene)/ZnO hybrid pn junctions for microelectronics applications

E. Katsia, N. Huby, G. Tallarida, B. Kutrzeba-Kotowska, M. Perego, S. Ferrari, F. C. Krebs, E. Guziewicz, M. Godlewski, V. Osinniy, and G. Luka

Appl. Phys. Lett. 94, 143501 (2009); http://dx.doi.org/10.1063/1.3114442 (3 pages) | Cited 14 times

Online Publication Date: 6 April 2009

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Hybrid poly(3-hexylthiophene)/ZnO devices are investigated as rectifying heterojunctions for microelectronics applications. A low-temperature atomic layer deposition of ZnO on top of poly(3-hexylthiophene) allows the fabrication of diodes featuring a rectification ratio of nearly 105 at ±4 V and a current density of 104 A/cm2. Electrical characteristics are discussed taking into account the chemical structure of the stack and the energy band diagram.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Ei Rectification
85.40.Sz Deposition technology

Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures

Day-Shan Liu, Tan-Wei Lin, Bing-Wen Huang, Fuh-Shyang Juang, Po-Hsun Lei, and Chen-Ze Hu

Appl. Phys. Lett. 94, 143502 (2009); http://dx.doi.org/10.1063/1.3116613 (3 pages) | Cited 15 times

Online Publication Date: 8 April 2009

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Amorphous titanium oxide (a-TiOx:OH) films prepared by plasma-enhanced chemical-vapor deposition at 200 and 25 °C are in turn deposited onto the GaN-based light-emitting diode (LED) to enhance the associated light extraction efficiency. The refractive index, porosity, and photocatalytic effect of the deposited films are correlated strongly with the deposition temperatures. The efficiency is enhanced by a factor of ∼ 1.31 over that of the uncoated LEDs and exhibited an excellent photocatalytic property after an external UV light irradiation. The increase in the light extraction is related to the reduction in the Fresnel transmission loss and the enhancement of the light scattering into the escape cone by using the graded-refractive-index a-TiOx:OH film with porous structures.
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85.60.Jb Light-emitting devices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
82.50.Hp Processes caused by visible and UV light
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Highly selective left-handed transmission line loaded with split ring resonators and wires

A. L. Borja, J. Carbonell, V. E. Boria, and D. Lippens

Appl. Phys. Lett. 94, 143503 (2009); http://dx.doi.org/10.1063/1.3116647 (3 pages) | Cited 4 times

Online Publication Date: 8 April 2009

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The frequency selectivity of coplanar transmission lines loaded with split ring resonators and shunt strips was dramatically improved owing to a blueshift of the electrical plasma frequency by oversizing the strip width. Beyond a higher rejection level, which was expected as a consequence of the deepening of the forbidden gap between the left- and right-handed dispersion branches, a huge enhancement in the loaded Q quality factors, while maintaining low insertion losses were also pointed out. This Q factor improvement was a consequence of a decrease in the coupling between the resonators and the transmission line.
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84.40.Az Waveguides, transmission lines, striplines

A polarizer-free three step switch using distinct dye-doped liquid crystal gels

Yi-Hsin Lin and Chih-Ming Yang

Appl. Phys. Lett. 94, 143504 (2009); http://dx.doi.org/10.1063/1.3111790 (3 pages) | Cited 7 times

Online Publication Date: 9 April 2009

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multimedia

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A polarizer-free three step switch using distinct dye-doped liquid crystal (LC) gels is demonstrated in reflective mode. By controlling the spatial distribution of the density of polymer networks, the distinct dye-doped LC gels can produce multiple states: bright, dark, and information states without patterning indium-tin oxide. The multiple states are generated by adapting different polymer network density in different display regions. The dark state is due to the combination of scattering and absorption. It can be further extended for a four step switch. The potential applications are decorative displays, electrically tunable iris, and electrically tunable low pass or high pass filter.
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42.79.Kr Display devices, liquid-crystal devices
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Efficiency improvement of blended poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 solar cells by nanoimprinting

C. F. Shih, K. T. Hung, J. W. Wu, C. Y. Hsiao, and W. M. Li

Appl. Phys. Lett. 94, 143505 (2009); http://dx.doi.org/10.1063/1.3117226 (3 pages) | Cited 21 times

Online Publication Date: 9 April 2009

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This work demonstrates the effects of nanoimprinting on poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (P3HT:PCBM)-blended organic solar cells at room temperature. Textured Si wafer was used as a stamp. Nanoimprinting significantly increased the open-circuit voltage, the short-circuit current, and the fill factor, increasing the power conversion efficiency by ∼ 50%. The fill factor contributed most to the cell efficiency. Upon nanoimprinting, not only the surface structure but also the applied pressure contributed to the performance of the device. The origin of the hydrostatic pressure-induced efficiency improvement was also investigated. The proposed approach has potential to be applied in the future to improve the efficiency of various organic solar cells.
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84.60.Jt Photoelectric conversion
81.16.Nd Micro- and nanolithography

Doping tuned rectifying properties in La2−xSrxCuO4/Nb:SrTiO3 heterojunctions

Y. F. Guo, X. Guo, M. Lei, L. M. Chen, W. H. Tang, P. G. Li, X. L. Fu, and L. H. Li

Appl. Phys. Lett. 94, 143506 (2009); http://dx.doi.org/10.1063/1.3115788 (3 pages) | Cited 5 times

Online Publication Date: 10 April 2009

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Here, we carried out a study on strontium doping effect on the rectifying properties of La2−xSrxCuO4 (LSCO)/NSTO heterojunctions. The intimate relationship between the change in electronic structure of LSCO and the variation of diffusion potential (Vd) of the junction supports opportunities for detecting Fermi level shift and superconducting gap evolution of LSCO upon hole doping. The results agree well to generally perceived viewpoints obtained by other methods. Even the suppression of Fermi level shift in the underdoped regime and weak-coupling d-wave BCS superconductivity behavior in the overdoped regime of LSCO are clearly exhibited by the tuned rectifying behaviors. This work not only reveals rich properties of LSCO/NSTO but also opens an alternative route to monitor the Fermi level and superconducting gap of high-temperature superconductors.
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74.25.Jb Electronic structure (photoemission, etc.)
74.20.Rp Pairing symmetries (other than s-wave)
74.62.Dh Effects of crystal defects, doping and substitution
61.72.U- Doping and impurity implantation
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Nanostructured zinc oxide platform for cholesterol sensor

Pratima R. Solanki, Ajeet Kaushik, Anees A. Ansari, and B. D. Malhotra

Appl. Phys. Lett. 94, 143901 (2009); http://dx.doi.org/10.1063/1.3111429 (3 pages) | Cited 19 times

Online Publication Date: 8 April 2009

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Nanostructured zinc oxide (nano-ZnO) film has been fabricated onto indium tin oxide (ITO) containing preferred (002) plane and 10 nm crystallite size using sol-gel technique for immobilization of cholesterol oxidase (ChOx). Electrochemical response of ChOx/nano-ZnO/ITO bioelectrode determined as a function of cholesterol concentration using cyclic voltammetry technique reveals improved detection range (5–400 mg/dl), low detection limit (0.5 mg/dl), fast response time (10 s), sensitivity (0.059 μA/mg dl−1 cm−2), and low value (0.98 mg/dl) of Michaelis–Menten constant (Km). It is shown that nano-ZnO film provides better environment and enhanced electron transfer between ChOx and electrode.
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87.85.Rs Nanotechnologies-applications
81.16.-c Methods of micro- and nanofabrication and processing
82.47.Rs Electrochemical sensors
82.80.Fk Electrochemical methods
82.45.Fk Electrodes
87.15.ht Ultrafast dynamics; charge transfer

DNA-quantum dot sensing platform with combined Förster resonance energy transfer and photovoltaic effect

Huijie Qi, Lixiang Wang, Ka-wai Wong, and Zuliang Du

Appl. Phys. Lett. 94, 143902 (2009); http://dx.doi.org/10.1063/1.3117193 (3 pages)

Online Publication Date: 10 April 2009

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A special DNA sensing platform based on a network of hybrid DNA-quantum dot system was designed and fabricated. Upon attachment of hybridized complementary DNA sequences, the molecular switch system can exhibit both photoinduced Förster resonance energy transfer (FRET) and photovoltaic (PV) effects simultaneously, but will give much weakened or no effect for the capture of hybridized products from “mismatched” DNA sequences. This dual sensing scheme based on combined FRET and PV effects can safeguard the accuracy of sensing, as FRET and PV can be singly induced even in the case of mismatch.
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87.85.jc Electrical, thermal, and mechanical properties of biological matter
87.15.Pc Electronic and electrical properties
85.65.+h Molecular electronic devices
87.15.Qt Sequence analysis
87.14.gk DNA
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Effects of N2–CO polarization beating on femtosecond coherent anti-Stokes Raman scattering spectroscopy of N2

Sukesh Roy, Daniel Richardson, Paul J. Kinnius, Robert P. Lucht, and James R. Gord

Appl. Phys. Lett. 94, 144101 (2009); http://dx.doi.org/10.1063/1.3116087 (3 pages) | Cited 6 times

Online Publication Date: 6 April 2009

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The effects of broadband excitation employing femtosecond laser pulses on the coherent anti-Stokes Raman scattering (CARS) spectroscopy of N2 are investigated. We have previously demonstrated that the dephasing rate of the coherence, established by the impulsive excitation of N2 using femtosecond pump and Stokes beams, can be used for measuring gas-phase temperature in chemically reacting flows. The objective of the current work is to investigate the effects of polarization beating between N2 and CO on the measured gas-phase temperature using time-resolved femtosecond CARS spectroscopy of N2.
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78.30.-j Infrared and Raman spectra
78.47.D- Time resolved spectroscopy (>1 psec)

Time-resolved pump-probe experiments beyond the jitter limitations at FLASH

A. Azima, S. Düsterer, P. Radcliffe, H. Redlin, N. Stojanovic, W. Li, H. Schlarb, J. Feldhaus, D. Cubaynes, M. Meyer, J. Dardis, P. Hayden, P. Hough, V Richardson, E. T. Kennedy, et al.

Appl. Phys. Lett. 94, 144102 (2009); http://dx.doi.org/10.1063/1.3111789 (3 pages) | Cited 21 times

Online Publication Date: 7 April 2009

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Using a noninvasive, electro-optically based electron bunch arrival time measurement at FLASH (free electron laser in Hamburg) the temporal resolution of two-color pump-probe experiments has been significantly improved. The system determines the relative arrival time of the extended ultraviolet pulse of FLASH and an amplified Ti:sapphire femtosecond-laser pulse at the interaction region better than 90 fs rms. In a benchmarking pump-probe experiment using two-color above threshold ionization of noble gases, an enhancement in the timing resolution by a factor of 4 compared to the uncorrected data is obtained.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
32.80.-t Photoionization and excitation
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