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18 Jun 2012

Volume 100, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 100, 252401 (2012); http://dx.doi.org/10.1063/1.4727909 (4 pages)

Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez, and Riccardo Hertel
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Large-scale fabrication of plasmonic gold nanohole arrays for refractive index sensing at visible region

Ke Cheng, Shujie Wang, Zhonggang Cui, Qianqian Li, Shuxi Dai, and Zuliang Du

Appl. Phys. Lett. 100, 253101 (2012); http://dx.doi.org/10.1063/1.4728987 (4 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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We present the design and fabrication of large-scale gold nanohole arrays based on the versatile nanosphere lithography technique. The gold nanohole arrays exhibit two surface plasmonic resonance related transmission peaks and show a sensitive response to refractive index. The working wavelength and sensitivity can be tuned by changing the hole diameter and hole depth. A sensitivity of 125 nm/refractive index unit is obtained in the visible region. Our quasi-infinite gold nanohole arrays film can serve as an optical enhancing component while also can serve as a transparent conductive electrode for the opto-electric devices.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

Direct manipulation of the uncompensated antiferromagnetic spins in exchange coupled system by GeV ion irradiation

Amitesh Paul, N. Paul, C. Trautmann, S. Mattauch, Jaru Jutimoosik, Rattikorn Yimnirun, Saroj Rujirawat, Britta Höpfner, Iver Lauermann, M. Lux-Steiner, and P. Böni

Appl. Phys. Lett. 100, 253102 (2012); http://dx.doi.org/10.1063/1.4729472 (5 pages)

Online Publication Date: 18 June 2012

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Incident ion energy to matrix electrons of a material is dissipated within a narrow cylinder surrounding the swift heavy ion path. The temperature of the lattice exceeds the melting point and upon quenching causes nanometric modifications. We present here a unique ex situ approach in manipulating the uncompensated spins in antiferromagnetic layers of ferro-/antiferromagnetic exchange coupled systems on a nanometric scale. We use the impact of relativistic heavy ion (1–2 GeV) irradiation on such systems. We find an increase in the bias field and a restoration of the reversal via domain nucleation in the trained state. These are identified as plausible results of ion-induced antiferromagnetic ordering with little or no effect on the layer structure. This study demonstrates, therefore, the possibility of nanoscale tailoring of exchange coupled systems that survive even in the trained state.
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61.80.Jh Ion radiation effects
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions

Ultrafast photoluminescence from freestanding Si nanocrystals

Sung Kim, Dong Hee Shin, and Suk-Ho Choi

Appl. Phys. Lett. 100, 253103 (2012); http://dx.doi.org/10.1063/1.4729605 (3 pages)

Online Publication Date: 18 June 2012

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SiO1.2/SiO2 multilayers were grown on n-type (100) Si wafers by ion beam sputtering and subsequently annealed at 1100 °C to form SiO2-embedded Si (S-Si) nanocrystals (NCs). The SiO2 matrix was then removed from S-Si NCs by chemical treatments to prepare freestanding Si (F-Si) NCs. The photoluminescence (PL) peak of F-Si NCs at ∼657 nm (1.89 eV) is blue-shifted with respect to that of S-Si NCs at ∼816 nm (1.52 eV). The peak shift of ∼0.37 eV is much larger than what is expected by the quantum confinement effect. The PL lifetime of F-Si NCs (∼3 ns) is much shorter than that of S-Si NCs (∼50 μs). Possible physical mechanisms are discussed to explain the origin of the fast PL band found in F-Si NCs.
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78.55.Hx Other solid inorganic materials
81.16.Be Chemical synthesis methods
81.40.Gh Other heat and thermomechanical treatments
81.07.Bc Nanocrystalline materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.65.Ac Multilayers

Ultrathin metallic coatings can induce quantum levitation between nanosurfaces

Mathias Boström, Barry W. Ninham, Iver Brevik, Clas Persson, Drew F. Parsons, and Bo E. Sernelius

Appl. Phys. Lett. 100, 253104 (2012); http://dx.doi.org/10.1063/1.4729822 (4 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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There is an attractive Casimir-Lifshitz force between two silica surfaces in a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin (5–50 Å) metallic nanocoating to one of the surfaces results in repulsive Casimir-Lifshitz forces above a critical separation. The onset of such quantum levitation comes at decreasing separations as the film thickness decreases. Remarkably, the effect of retardation can turn attraction into repulsion. From that we explain how an ultrathin metallic coating may prevent nanoelectromechanical systems from crashing together.
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78.66.Bz Metals and metallic alloys

Threshold switching via electric field induced crystallization in phase-change memory devices

Jorge A. Vázquez Diosdado, Peter Ashwin, Krisztian I. Kohary, and C. David Wright

Appl. Phys. Lett. 100, 253105 (2012); http://dx.doi.org/10.1063/1.4729551 (4 pages) | Cited 4 times

Online Publication Date: 19 June 2012

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Phase-change devices exhibit characteristic threshold switching from the reset (off) to the set (on) state. Mainstream understanding of this electrical switching phenomenon is that it is initiated electronically via the influence of high electric fields on inter-band trap states in the amorphous phase. However, recent work has suggested that field induced (crystal) nucleation could instead be responsible. We compare and contrast these alternative switching “theories” via realistic simulations of device switching both with and without electric field dependent contributions to the system free energy. Results show that although threshold switching can indeed be obtained purely by electric field induced nucleation, the fields required are significantly larger than experimentally measured values.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
84.30.Sk Pulse and digital circuits

Design of a surface acoustic wave mass sensor in the 100 GHz range

Damiano Nardi, Elisa Zagato, Gabriele Ferrini, Claudio Giannetti, and Francesco Banfi

Appl. Phys. Lett. 100, 253106 (2012); http://dx.doi.org/10.1063/1.4729624 (4 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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A design for photoacoustic mass sensors operating above 100 GHz is proposed. The design is based on impulsive optical excitation of a pseudosurface acoustic wave in a surface phononic crystal with nanometric periodic grating and on time-resolved extreme ultraviolet detection of the pseudosurface acoustic wave frequency shift upon mass loading the device. The present design opens the path to sensors operating in a frequency range currently unaccessible to electro-acoustical transducers, providing enhanced sensitivity, miniaturization, and incorporating time-resolving capability while forgoing the piezoelectric substrate requirement.
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43.58.-e Acoustical measurements and instrumentation
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
85.60.Gz Photodetectors (including infrared and CCD detectors)

Plasma-assisted growth and nitrogen doping of graphene films

C. D. Wang, M. F. Yuen, T. W. Ng, S. K. Jha, Z. Z. Lu, S. Y. Kwok, T. L. Wong, X. Yang, C. S. Lee, S. T. Lee, and W. J. Zhang

Appl. Phys. Lett. 100, 253107 (2012); http://dx.doi.org/10.1063/1.4729823 (5 pages) | Cited 2 times

Online Publication Date: 20 June 2012

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Microwave plasmas were employed to synthesize single- or double-layer graphene sheets on copper foils using a solid carbon source, polymethylmetacrylate. The utilization of reactive plasmas enables the graphene growth at reduced temperatures as compared to conventional thermal chemical vapor deposition processes. The effects of substrate temperature on graphene quality were studied based on Raman analysis, and a reduction of defects at elevated temperature was observed. Moreover, a facile approach to incorporate nitrogen into graphene by plasma treatment in a nitrogen/hydrogen gas mixture was demonstrated, and most of the nitrogen atoms were verified to be pyridinelike in carbon network.
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81.05.ue Graphene
61.72.jd Vacancies
78.30.Na Fullerenes and related materials
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene

Controlled doping of graphene using ultraviolet irradiation

Zhengtang Luo, Nicholas J. Pinto, Yarely Davila, and A. T. Charlie Johnson

Appl. Phys. Lett. 100, 253108 (2012); http://dx.doi.org/10.1063/1.4729828 (4 pages) | Cited 3 times

Online Publication Date: 20 June 2012

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The electronic properties of graphene are tunable via doping, making it attractive in low dimensional organic electronics. Common methods of doping graphene, however, adversely affect charge mobility and degrade device performance. We demonstrate a facile shadow mask technique of defining electrodes on graphene grown by chemical vapor deposition (CVD) thereby eliminating the use of detrimental chemicals needed in the corresponding lithographic process. Further, we report on the controlled, effective, and reversible doping of graphene via ultraviolet (UV) irradiation with minimal impact on charge mobility. The change in charge concentration saturates at ∼2 × 1012 cm–2 and the quantum yield is ∼10−5 e/photon upon initial UV exposure. This simple and controlled strategy opens the possibility of doping wafer-size CVD graphene for diverse applications.
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61.72.up Other materials
72.80.Vp Electronic transport in graphene
81.05.ue Graphene
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
72.20.Fr Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Observation of the quantum Hall effect in epitaxial graphene on SiC(0001) with oxygen adsorption

E. Pallecchi, M. Ridene, D. Kazazis, C. Mathieu, F. Schopfer, W. Poirier, D. Mailly, and A. Ouerghi

Appl. Phys. Lett. 100, 253109 (2012); http://dx.doi.org/10.1063/1.4729824 (4 pages) | Cited 3 times

Online Publication Date: 21 June 2012

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In this letter, we report on transport measurements of epitaxial graphene on SiC(0001) with oxygen adsorption. In a 50×50μm2 size Hall bar, we observe the half-integer quantum Hall effect with a transverse resistance plateau quantized at filling factor around 2, an evidence of monolayer graphene. We find low electron concentration of 9×1011cm−2 and we show that a doping of 1013cm−2 which is characteristic of intrinsic epitaxial graphene can be restored by vacuum annealing. The effect of oxygen adsorption on carrier density is confirmed by local angle-resolved photoemission spectroscopy measurements. These results are important for understanding oxygen adsorption on epitaxial graphene and for its application to metrology and mesoscopic physics where a low carrier concentration is required.
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73.43.-f Quantum Hall effects
73.61.Wp Fullerenes and related materials
61.72.up Other materials
68.43.Mn Adsorption kinetics
79.60.Dp Adsorbed layers and thin films
81.40.Gh Other heat and thermomechanical treatments

Enhancement of the Purcell effect for colloidal CdSe/ZnS quantum dots coupled to silver nanowires by a metallic tip

Y. C. Wang, C. T. Yuan, M. Y. Kuo, M. C. Wu, Jau Tang, and M. H. Shih

Appl. Phys. Lett. 100, 253110 (2012); http://dx.doi.org/10.1063/1.4729890 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2012

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In this study, the Purcell effect for CdSe/ZnS quantum dots emission coupled to a silver nanowire cavity was investigated. We manipulated the interaction between colloidal quantum dots (QDs) and an Ag NW in the presence of a metallic tip. When a metal tip approaches the Ag NW, the Ag surface plasmon mode could be lifted away from the metallic NW so that a low optical loss could still be obtained. This work demonstrates enhancement of the spatial coupling between the plasmonic mode and light sources and reduction in metal Ohmic losses, resulting in an enhanced Purcell effect and coupling efficiency accompanied with increased fluorescence intensity.
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78.67.Hc Quantum dots
78.55.-m Photoluminescence, properties and materials
78.67.Uh Nanowires
82.70.Dd Colloids
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces

Doping and defects in YBa2Cu3O7: Results from hybrid density functional theory

U. Schwingenschlögl and C. Schuster

Appl. Phys. Lett. 100, 253111 (2012); http://dx.doi.org/10.1063/1.4729892 (4 pages) | Cited 2 times

Online Publication Date: 21 June 2012

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Modified orbital occupation and inhomogeneous charge distribution in high-Tc oxide compounds due to doping and/or defects play a huge role for the material properties. To establish insight into the charge redistribution, we address metallic YBa2Cu3O7 in two prototypical configurations: Ca doped (hole doping) and O deficient (electron doping). By means of first principles calculations for fully relaxed structures, we evaluate the orbital occupations. We find that the change of the charge density, in particular in the CuO2 planes, shows a complex spatial pattern instead of the expected uniform (de-)population of the valence states.
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74.20.Pq Electronic structure calculations
71.55.Ht Other nonmetals
61.72.up Other materials
74.72.Ek Electron-doped
74.72.Gh Hole-doped
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Hard x-ray scanning microscopy with coherent radiation: Beyond the resolution of conventional x-ray microscopes

A. Schropp, R. Hoppe, J. Patommel, D. Samberg, F. Seiboth, S. Stephan, G. Wellenreuther, G. Falkenberg, and C. G. Schroer

Appl. Phys. Lett. 100, 253112 (2012); http://dx.doi.org/10.1063/1.4729942 (3 pages) | Cited 9 times

Online Publication Date: 21 June 2012

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We demonstrate x-ray scanning coherent diffraction microscopy (ptychography) with 10 nm spatial resolution, clearly exceeding the resolution limits of conventional hard x-ray microscopy. The spatial resolution in a ptychogram is shown to depend on the shape (structure factor) of a feature and can vary for different features in the object. In addition, the resolution and contrast are shown to increase with increasing coherent fluence. For an optimal ptychographic x-ray microscope, this implies a source with highest possible brilliance and an x-ray optic with a large numerical aperture to generate the optimal probe beam.
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07.85.Tt X-ray microscopes
07.60.Pb Conventional optical microscopes
07.79.-v Scanning probe microscopes and components
07.85.-m X- and γ-ray instruments

Fabrication of double-walled carbon nanotube film/Cu2O nanoparticle film/TiO2 nanotube array heterojunctions for photosensors

Mingjie Yang, Jia Xu, Jinquan Wei, Jia-Lin Sun, Wei Liu, and Jia-Lin Zhu

Appl. Phys. Lett. 100, 253113 (2012); http://dx.doi.org/10.1063/1.4730399 (4 pages) | Cited 1 time

Online Publication Date: 21 June 2012

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A structure for visible photosensors based on double-walled carbon nanotube (DWCNT) film/Cu2O nanoparticle (NP) film/TiO2 nanotube array (TNA) heterojunctions has been fabricated. Cu2O nanoparticles reduce dark current and enhance photoresponse of the heterojunctions. Consequently, the optoelectric performance is significantly enhanced compared to that of the heterojunctions without Cu2O nanoparticles. The photocurrent-to-dark current ratio reaches ∼1 × 104 under illumination at 405 nm and ∼3 × 104 under illumination at 532 nm, which is two orders of magnitude higher than the results of double-walled carbon nanotube film/TiO2 nanotube array heterojunctions under the same illumination density. Moreover, the response speed of the heterojunctions is greatly improved.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Pressure-induced positive electrical resistivity coefficient in Ni-Nb-Zr-H glassy alloy

M. Fukuhara, C. Gangli, K. Matsubayashi, and Y. Uwatoko

Appl. Phys. Lett. 100, 253114 (2012); http://dx.doi.org/10.1063/1.4729574 (3 pages)

Online Publication Date: 21 June 2012

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Measurements under hydrostatic pressure of the electrical resistivity of (Ni0.36Nb0.24Zr0.40)100−xHx (x = 9.8, 11.5, and 14) glassy alloys have been made in the range of 0–8 GPa and 0.5–300 K. The resistivity of the (Ni0.36Nb0.24Zr0.40)86H14 alloy changed its sign from negative to positive under application of 2–8 GPa in the temperature range of 300–22 K, coming from electron-phonon interaction in the cluster structure under pressure, accompanied by deformation of the clusters. In temperature region below 22 K, the resistivity showed negative thermal coefficient resistance by Debye-Waller factor contribution, and superconductivity was observed at 1.5 K.
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74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Kc Phonons
63.20.kd Phonon-electron interactions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride

Hyoungki Park, Amita Wadehra, John W. Wilkins, and Antonio H. Castro Neto

Appl. Phys. Lett. 100, 253115 (2012); http://dx.doi.org/10.1063/1.4730392 (4 pages) | Cited 9 times

Online Publication Date: 22 June 2012

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We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics.
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75.30.Cr Saturation moments and magnetic susceptibilities
71.55.Eq III-V semiconductors
75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
78.20.Ls Magneto-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Giant Goos-Hänchen shift in graphene double-barrier structures

Yu Song, Han-Chun Wu, and Yong Guo

Appl. Phys. Lett. 100, 253116 (2012); http://dx.doi.org/10.1063/1.4730440 (4 pages) | Cited 5 times

Online Publication Date: 22 June 2012

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We report giant Goos-Hänchen shifts [Goos and Hänchen, Ann. Phys. 436, 333 (1947)] for electron beams tunneling through graphene double barrier structures. We find that inside the transmission gap for the single barrier, the shift displays sharp peaks with magnitudes up to the order of electron beam width and rather small full-widths-at-half-maximum, which may be utilized to design valley and spin beam splitters with wide tunability and high energy resolution. We attribute the giant shifts to quasibound states in the structures. Moreover, an induced energy gap in the dispersion can increase the tunability and resolution of the splitters.
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73.40.Gk Tunneling
73.61.Wp Fullerenes and related materials
72.80.Vp Electronic transport in graphene
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