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29 Jan 2007

Volume 90, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages)

Biqin Huang, Igor Altfeder, and Ian Appelbaum
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Charge transfer effect in the polyaniline-gold nanoparticle memory system

Ricky J. Tseng, Christina O. Baker, Brian Shedd, Jiaxing Huang, Richard B. Kaner, Jianyong Ouyang, and Yang Yang

Appl. Phys. Lett. 90, 053101 (2007); http://dx.doi.org/10.1063/1.2434167 (3 pages) | Cited 53 times

Online Publication Date: 29 January 2007

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A composite system comprised of polyaniline nanofibers bonded with gold nanoparticles is shown to possess a memory effect via a charge transfer mechanism. The charge transfer occurs between the imine nitrogen in the polyaniline and the gold nanoparticles as confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy. This charge transfer enables a bistable electrical conductivity, allowing the material system to be used as a digital memory device. The charge transfer is further confirmed by the elimination of the conductance switching when the fully reduced form of polyaniline, leucoemeraldine, which possesses no imine nitrogens, is used in place of the emeraldine form.
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79.60.Jv Interfaces; heterostructures; nanostructures
78.30.-j Infrared and Raman spectra
72.80.Tm Composite materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

High thermal stability of cross-linked aromatic self-assembled monolayers: Nanopatterning via selective thermal desorption

A. Turchanin, M. El-Desawy, and A. Gölzhäuser

Appl. Phys. Lett. 90, 053102 (2007); http://dx.doi.org/10.1063/1.2437091 (3 pages) | Cited 32 times

Online Publication Date: 29 January 2007

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An extremely high thermal stability of electron cross-linked biphenyl self-assembled monolayers (SAMs) is reported. The authors found that pristine biphenylthiol SAMs desorb at ∼ 400 K from gold surfaces, which is induced by a breaking of C–S bonds. Despite of a similar bond cleavage in cross-linked SAMs, these remain on the surface up to 1000 K, which is the highest temperature reported for a SAM. When patterns of pristine and cross-linked SAMs are heated, the pristine regions desorb, and the cross-linked regions remain on the surface. The authors show that this thermal desorption lithography can be utilized for the fabrication of molecular surface nanostructures.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.43.Mn Adsorption kinetics

Direct probe of excitonic and continuum transitions in the photocurrent spectroscopy of individual carbon nanotube p-n diodes

Ji Ung Lee, Peter J. Codella, and Matthew Pietrzykowski

Appl. Phys. Lett. 90, 053103 (2007); http://dx.doi.org/10.1063/1.2435980 (3 pages) | Cited 12 times

Online Publication Date: 29 January 2007

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The authors show that a carbon nanotube p-n diode is a very sensitive probe of optical transitions in individual single-walled carbon nanotubes. In the photocurrent spectra, an alternating sequence of resonant peaks from dissociation of excitons and exciton-phonon bound states, for the lowest and higher electronic subbands, is observed. At an intermediate energy, the onset of continuum is observed that allows measurement of exciton binding energies. Both the binding energy and the onset of continuum follow the inverse diameter relation as expected from general theory of optical transitions in nanotubes.
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85.35.Kt Nanotube devices
85.60.Dw Photodiodes; phototransistors; photoresistors

γ-Ga2O3 quantum dots with visible blue-green light emission property

Tao Chen and Kaibin Tang

Appl. Phys. Lett. 90, 053104 (2007); http://dx.doi.org/10.1063/1.2437110 (3 pages) | Cited 8 times

Online Publication Date: 30 January 2007

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Visible blue-green light emission metastable γ-Ga2O3 quantum dots were prepared, and the light emission is clearly visible to the naked eyes. The UV-visible spectra present a blueshift phenomenon of the absorption edge as the particle sizes decrease; the fitted result of UV-visible data by Tauc function shows that the as-prepared γ-Ga2O3 is a wide-band-gap semiconductor with a direct band gap structure. The photoluminescence spectra show the evidence of quantum confinement and a blueshift when the crystal sizes decrease.
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78.67.Hc Quantum dots
78.55.Hx Other solid inorganic materials
78.40.Fy Semiconductors
73.21.La Quantum dots
71.20.Nr Semiconductor compounds

Efficient switching of Rashba spin splitting in wide modulation-doped quantum wells

D. M. Gvozdić and U. Ekenberg

Appl. Phys. Lett. 90, 053105 (2007); http://dx.doi.org/10.1063/1.2437132 (3 pages) | Cited 8 times

Online Publication Date: 30 January 2007

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The authors demonstrate that the size of the electric-field-induced Rashba spin splitting in an 80 nm wide modulation-doped InGaSb quantum well can depend strongly on the spatial variation of the electric field. In a slightly asymmetric quantum well it can be an order of magnitude stronger than for the average uniform electric field. For even smaller asymmetry spin subbands can have wave functions and/or expectation values of the spin direction that are completely changed as the in-plane wave vector varies. The Dresselhaus effect [ Phys. Rev. 100, 580 (1955) ] can give an anticrossing at which the spin rapidly flips.
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73.21.Fg Quantum wells
71.70.-d Level splitting and interactions
73.63.Hs Quantum wells

Mass sensor for in situ monitoring of focused ion and electron beam induced processes

Vinzenz Friedli, Christian Santschi, Johann Michler, Patrik Hoffmann, and Ivo Utke

Appl. Phys. Lett. 90, 053106 (2007); http://dx.doi.org/10.1063/1.2435611 (3 pages) | Cited 13 times

Online Publication Date: 31 January 2007

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A cantilever-based mass sensor for in situ monitoring of deposition and milling using focused ion and electron beams is presented. Carefully designed experiments allowed for mass measurements with a noise level of ±10 fg by tracking the resonance frequency of a temperature stabilized piezoresistive cantilever using phase locking. The authors report on measurements of precursor surface coverage, residence time, mass deposition rates, yields, and deposit density using the (CH3)3PtCpCH3 precursor.
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06.30.Dr Mass and density
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.20.Wk Machining, milling

Metal-enhanced fluorescence: Surface plasmons can radiate a fluorophore’s structured emission

Yongxia Zhang, Kadir Aslan, Michael J. R. Previte, and Chris D. Geddes

Appl. Phys. Lett. 90, 053107 (2007); http://dx.doi.org/10.1063/1.2435661 (3 pages) | Cited 30 times

Online Publication Date: 31 January 2007

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In this letter, the authors report the observation of metal-enhanced structured fluorescence emission. Perylene in close proximity to silver island films (SiFs) enhances the structured fluorescence emission intensity. In this regard, an approximately two-fold higher perylene fluorescence intensity was observed from SiFs as compared to a glass control sample, containing no silver nanoparticles. The findings strongly suggest that surface plasmons can radiate a fluorophore’s vibrational structure. This observation is helpful in the authors’ understanding, not only for studying the interactions between plasmons and lumophores but also for their laboratories’ continued efforts to develop a unified plasmon-lumophore theory.
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78.55.Kz Solid organic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads

K. Hamaya, S. Masubuchi, M. Kawamura, T. Machida, M. Jung, K. Shibata, K. Hirakawa, T. Taniyama, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 90, 053108 (2007); http://dx.doi.org/10.1063/1.2435957 (3 pages) | Cited 41 times

Online Publication Date: 31 January 2007

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The authors have fabricated a lateral double barrier magnetic tunnel junction (MTJ) which consists of a single self-assembled InAs quantum dot (QD) with ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance (TMR) effect, which is evidence for spin transport through a single semiconductor QD. The TMR ratio and the curve shapes are varied by changing the gate voltage.
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73.40.Ns Metal-nonmetal contacts
73.63.Kv Quantum dots
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Cc Other ferromagnetic metals and alloys

Hole spin relaxation in neutral InGaAs quantum dots: Decay to dark states

K. C. Hall, E. J. Koerperick, Thomas F. Boggess, O. B. Shchekin, and D. G. Deppe

Appl. Phys. Lett. 90, 053109 (2007); http://dx.doi.org/10.1063/1.2437063 (3 pages) | Cited 8 times

Online Publication Date: 1 February 2007

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The authors report measurements of hole spin relaxation in neutral InGaAs quantum dots using polarization-dependent time-resolved photoluminescence experiments. The single-particle hole spin relaxation was isolated from other spin flip processes in the electron-hole system by detecting the initial transfer of population from optically active to dark states. The results indicate that electron-hole exchange interactions play a negligible role in the carrier spin kinetics, and are consistent with a mechanism of hole spin relaxation via phonon-mediated virtual scattering between confined quantum dot states.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.70.Gm Exchange interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Simultaneous observation of magnetic domain structure and topography of Fe70Co30 using scanning Lorentz force microscopy

Seiichi Suzuki, Yasuo Azuma, and Yutaka Majima

Appl. Phys. Lett. 90, 053110 (2007); http://dx.doi.org/10.1063/1.2437654 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2007

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The surface topography and the distribution of stray magnetic flux density of Fe70Co30 are observed simultaneously by using scanning Lorentz force microscopy (SLFM). The SLFM images of the magnetic domain of Fe70Co30 have been observed repeatedly, and they were found to be unaffected by the surface roughness and friction force. As compared to the magnetic force microscopy image, it can be inferred that small stray magnetic flux loops were detected near the sample surface in the SLFM image.
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75.60.Ch Domain walls and domain structure
68.37.Ps Atomic force microscopy (AFM)
75.50.Bb Fe and its alloys
75.70.Rf Surface magnetism

Giant magnetoresistance behavior of an iron/carbonized polyurethane nanocomposite

Zhanhu Guo, Sung Park, H. Thomas Hahn, Suying Wei, Monica Moldovan, Amar B. Karki, and David P. Young

Appl. Phys. Lett. 90, 053111 (2007); http://dx.doi.org/10.1063/1.2435897 (3 pages) | Cited 37 times

Online Publication Date: 1 February 2007

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This letter describes the magnetoresistance (MR) behavior of the heat treated polyurethane composites reinforced with iron nanoparticles. The flexible nanocomposites were fabricated by the surface-initiated-polymerization method. The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning electron microscopy, favor a continuous carbon matrix formation, rendering the transition from insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic properties. By simply annealing in a reducing environment, the obtained nanocomposites possess a MR of 7.3% at room temperature and 14% at 130 K occurring at a field of 90 kOe.
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75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
82.35.-x Polymers: properties; reactions; polymerization
81.16.Be Chemical synthesis methods
81.40.Gh Other heat and thermomechanical treatments
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

C. B. Soh, H. Hartono, S. Y. Chow, S. J. Chua, and E. A. Fitzgerald

Appl. Phys. Lett. 90, 053112 (2007); http://dx.doi.org/10.1063/1.2437056 (3 pages) | Cited 14 times

Online Publication Date: 2 February 2007

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Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20–50 nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650 to 1015 °C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850 °C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials

Improving sensitivity in electrostatic force detection utilizing cantilever with tailored resonance modes

Kenjiro Kimura, Kei Kobayashi, Kazumi Matsushige, and Hirofumi Yamada

Appl. Phys. Lett. 90, 053113 (2007); http://dx.doi.org/10.1063/1.2433761 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2007

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In order to increase the sensitivity of potential or capacitance measurement in Kelvin probe force microscopy or scanning capacitance force microscopy, the frequency of alternating electric field applied between the tip and the sample is tuned close to the mechanical resonance frequencies of the cantilever. The authors have designed a cantilever with a tailored resonance modes suitable for these measurements. The ratio of the first and the second resonance frequencies is optimized by the finite element method. Furthermore, they modified a commercially available cantilever according to the calculation. The performance of the modified cantilever was demonstrated in the scanning capacitance force microscopy measurement.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
02.70.Dh Finite-element and Galerkin methods

Magnetic properties of strained single-walled carbon nanotubes

Zhuhua Zhang and Wanlin Guo

Appl. Phys. Lett. 90, 053114 (2007); http://dx.doi.org/10.1063/1.2450644 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2007

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Strong effects of uniaxial and torsional strains on the magnetic properties of single-walled carbon nanotubes have been investigated by tight binding calculations and the Green function analyses. The strain-induced peaks of susceptibility are found in the carbon nanotubes, and paramagnetic-diamagnetic transition takes place at certain strains. The critical magnetic flux for semiconductor-metal transition changes linearly with strains depending on the chiralities of the tubes, mainly due to the tuning of the Van Hove singularities by the coupling of strains and magnetic flux. The positive and negative strain effects are asymmetrical in chiral tubes.
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75.20.Ck Nonmetals
71.30.+h Metal-insulator transitions and other electronic transitions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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