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23 Jul 2012

Volume 101, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 043101 (2012); http://dx.doi.org/10.1063/1.4737152 (4 pages)

Toshiaki Tanigaki, Yoshikatsu Inada, Shinji Aizawa, Takahiro Suzuki, Hyun Soon Park, Tsuyoshi Matsuda, Akira Taniyama, Daisuke Shindo, and Akira Tonomura
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Split-illumination electron holography

Toshiaki Tanigaki, Yoshikatsu Inada, Shinji Aizawa, Takahiro Suzuki, Hyun Soon Park, Tsuyoshi Matsuda, Akira Taniyama, Daisuke Shindo, and Akira Tonomura

Appl. Phys. Lett. 101, 043101 (2012); http://dx.doi.org/10.1063/1.4737152 (4 pages)

Online Publication Date: 23 July 2012

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We developed a split-illumination electron holography that uses an electron biprism in the illuminating system and two biprisms (applicable to one biprism) in the imaging system, enabling holographic interference micrographs of regions far from the sample edge to be obtained. Using a condenser biprism, we split an electron wave into two coherent electron waves: one wave is to illuminate an observation area far from the sample edge in the sample plane and the other wave to pass through a vacuum space outside the sample. The split-illumination holography has the potential to greatly expand the breadth of applications of electron holography.
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42.40.-i Holography
42.79.Bh Lenses, prisms and mirrors
41.85.-p Beam optics

Lithium niobate nanoparticulate clad on the core of single mode optical fiber for temperature and magnetic field sensing

Ch. N. Rao, Anoopam Bharadwaj, Suwarna Datar, and S. N. Kale

Appl. Phys. Lett. 101, 043102 (2012); http://dx.doi.org/10.1063/1.4738884 (4 pages)

Online Publication Date: 23 July 2012

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Lithium niobate with large non-linear optical coefficient and birefringence finds applications as varied optical devices. Nanoparticulate, polycrystalline LiNbO3 was synthesised and deposited on the core of the single-mode optical fiber and evaluated for their temperature and magnetic field sensing using C-band source. Temperature sensing was 30 pm/ °C with improved core-clad coupling at higher temperature. The magnetic field (0-30 mT) response was 131 pm/mT, with large hysteresis. The results have been correlated with the manipulation of core-clad modes due to strain induced in the core-deposited film and introduction of cation vacancies, resulting in induced ferromagnetism; thereby resulting in changed refractive index.
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42.81.Pa Sensors, gyros
42.25.Lc Birefringence
42.79.-e Optical elements, devices, and systems
42.81.Bm Fabrication, cladding, and splicing
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Small-signal amplifier based on single-layer MoS2

Branimir Radisavljevic, Michael B. Whitwick, and Andras Kis

Appl. Phys. Lett. 101, 043103 (2012); http://dx.doi.org/10.1063/1.4738986 (4 pages) | Cited 8 times

Online Publication Date: 23 July 2012

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In this letter we demonstrate the operation of an analog small-signal amplifier based on single-layer MoS2, a semiconducting analogue of graphene. Our device consists of two transistors integrated on the same piece of single-layer MoS2. The high intrinsic band gap of 1.8 eV allows MoS2-based amplifiers to operate with a room temperature gain of 4. The amplifier operation is demonstrated for the frequencies of input signal up to 2 kHz preserving the gain higher than 1. Our work shows that MoS2 can effectively amplify signals and that it could be used for advanced analog circuits based on two-dimensional materials.
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84.30.Le Amplifiers

Noise sensitivity of a mass detection method using vibration modes of coupled microcantilever arrays

Teresa J. Ryan, John A. Judge, Joseph F. Vignola, and Aldo A. Glean

Appl. Phys. Lett. 101, 043104 (2012); http://dx.doi.org/10.1063/1.4737636 (4 pages)

Online Publication Date: 23 July 2012

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Numerical simulation is used to explore the sensitivity to measurement noise of a mass detection approach that uses eigenmodes of an array of nominally identical micro- or nanomechanical resonators. The mode shapes are perturbed to simulate measurement noise, and resulting errors in identifying variations in mass are quantified as a function of array size, coupling strength, and level of mass variation. Sensitivity to measurement noise is low for lightly coupled arrays of nearly identical elements and increases when mass variation causes significant mode localization. For any mass variation level, an optimal combination of array size and coupling strength minimizes noise sensitivity.
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07.10.Cm Micromechanical devices and systems
02.10.Ud Linear algebra

Germanium nanowire growth controlled by surface diffusion effects

Jan Schmidtbauer, Roman Bansen, Robert Heimburger, Thomas Teubner, Torsten Boeck, and Roberto Fornari

Appl. Phys. Lett. 101, 043105 (2012); http://dx.doi.org/10.1063/1.4737004 (4 pages)

Online Publication Date: 23 July 2012

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Germanium nanowires (NWs) were grown onto Ge(111) substrates by the vapor-liquid-solid process using gold droplets. The growth was carried out in a molecular beam epitaxy chamber at substrate temperatures between 370 °C and 510 °C. The resulting nanowire growth rate turns out to be highly dependent on the substrate temperature exhibiting the maximum at T = 430 °C. The temperature dependence of growth rate can be attributed to surface diffusion both along the substrate and nanowire sidewalls. Analyzing the diffusive material transport yields a diffusion length of 126 nm at a substrate temperature of 430 °C.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Gf Nanowires
68.35.Fx Diffusion; interface formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Autonomic restoration of electrical conductivity using polymer-stabilized carbon nanotube and graphene microcapsules

Susan A. Odom, Timothy P. Tyler, Mary M. Caruso, Joshua A. Ritchey, Matthew V. Schulmerich, Scott J. Robinson, Rohit Bhargava, Nancy R. Sottos, Scott R. White, Mark C. Hersam, and Jeffrey S. Moore

Appl. Phys. Lett. 101, 043106 (2012); http://dx.doi.org/10.1063/1.4737935 (5 pages) | Cited 2 times

Online Publication Date: 23 July 2012

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We report the use of microcapsules containing suspensions of polymer-stabilized carbon nanotubes and/or graphene flakes for the autonomic restoration of conductivity in fractured gold lines. Multilayered samples were prepared in which microcapsules were embedded in layers of epoxy above and below a glass slide patterned with gold lines. Upon sample fracture, conductivity was lost as a crack formed in the gold line. Simultaneous release of carbon nanotubes and/or graphene suspensions from capsule cores restored conductivity in minutes. We suggest a healing mechanism in which the released carbon nanomaterials bridge gaps in the gold lines.
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73.63.-b Electronic transport in nanoscale materials and structures
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
82.70.Kj Emulsions and suspensions
62.20.mt Cracks
68.35.Gy Mechanical properties; surface strains
73.21.Ac Multilayers

High-frequency gate manipulation of a bilayer graphene quantum dot

S. Dröscher, J. Güttinger, T. Mathis, B. Batlogg, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 101, 043107 (2012); http://dx.doi.org/10.1063/1.4737937 (4 pages) | Cited 2 times

Online Publication Date: 23 July 2012

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We report transport data obtained for a double-gated bilayer graphene quantum dot. In Coulomb blockade measurements, the gate dielectric Cytop™ is found to provide remarkable electronic stability even at cryogenic temperatures. Moreover, we demonstrate gate manipulation with square shaped voltage pulses at frequencies up to 100 MHz and show that the signal amplitude is not affected by the presence of the capacitively coupled back gate.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots
72.30.+q High-frequency effects; plasma effects

Emergence of giant magnetic anisotropy in freestanding Au/Co nanowires

K. M. Tsysar, D. I. Bazhanov, E. M. Smelova, and A. M. Saletsky

Appl. Phys. Lett. 101, 043108 (2012); http://dx.doi.org/10.1063/1.4738767 (4 pages)

Online Publication Date: 24 July 2012

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The emergence of giant magnetic anisotropy was found in evenly mixed Au/Co nanowires. First principles molecular dynamics calculations revealed the large values of magnetic anisotropy energy of about ∼130 meV per Co atom in Au/Co nanowires. It was established that the emergence of giant magnetic anisotropy is due to (dxy,dx2) band splitting caused by the strong spin-orbit interaction between gold and cobalt atoms in the wire. It is also shown that the energy of the magnetic anisotropy depends strongly on the geometry and composition of the wire.
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75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
64.75.Ef Mixing
75.75.-c Magnetic properties of nanostructures
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Sub-wavelength surface gratings for light redirection in transparent substrates

Thomas Buß, Cameron L. C. Smith, Mads Brøkner Christiansen, Rodolphe Marie, and Anders Kristensen

Appl. Phys. Lett. 101, 043109 (2012); http://dx.doi.org/10.1063/1.4738777 (4 pages) | Cited 1 time

Online Publication Date: 24 July 2012

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We demonstrate sub-wavelength grating couplers patterned on glass surfaces which are designed to convert incident free-space radiation into guided modes along the glass material. The devices are fabricated by nanoimprint lithography and the measured optical performance is compared to a simple model based on diffraction and ray-optics, and complemented by numerical simulations. We show that our approach is suitable for redirecting and guiding light over a broad range of incident angles and wavelengths in transparent substrates. The technique has potential applications for solar harvesting in window panes and display applications with minimal influence on vision quality.
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42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques

Multi-scale graphene patterns on arbitrary substrates via laser-assisted transfer-printing process

J. B. Park, J.-H. Yoo, and C. P. Grigoropoulos

Appl. Phys. Lett. 101, 043110 (2012); http://dx.doi.org/10.1063/1.4738883 (4 pages) | Cited 1 time

Online Publication Date: 24 July 2012

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A laser-assisted transfer-printing process is developed for multi-scale graphene patterns on arbitrary substrates using femtosecond laser scanning on a graphene/metal substrate and transfer techniques without using multi-step patterning processes. The short pulse nature of a femtosecond laser on a graphene/copper sheet enables fabrication of high-resolution graphene patterns. Thanks to the scale up, fast, direct writing, multi-scale with high resolution, and reliable process characteristics, it can be an alternative pathway to the multi-step photolithography methods for printing arbitrary graphene patterns on desired substrates. We also demonstrate transparent strain devices without expensive photomasks and multi-step patterning process.
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81.16.Rf Micro- and nanoscale pattern formation
78.47.J- Ultrafast spectroscopy (<1 psec)
81.05.ue Graphene
81.16.Nd Micro- and nanolithography

Spontaneously intermixed Al-Mg barriers enable corrosion-resistant Mg/SiC multilayer coatings

Regina Soufli, Mónica Fernández-Perea, Sherry L. Baker, Jeff C. Robinson, Jennifer Alameda, and Christopher C. Walton

Appl. Phys. Lett. 101, 043111 (2012); http://dx.doi.org/10.1063/1.4737649 (5 pages) | Cited 2 times

Online Publication Date: 24 July 2012

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Magnesium/silicon carbide (Mg/SiC) has the potential to be the best-performing reflective multilayer coating in the 25–80 nm wavelength region but suffers from Mg-related corrosion, an insidious problem which completely degrades reflectance. We have elucidated the origins and mechanisms of corrosion propagation within Mg/SiC multilayers. Based on our findings, we have demonstrated an efficient and simple-to-implement corrosion barrier for Mg/SiC multilayers. The barrier consists of nanometer-scale Mg and Al layers that intermix spontaneously to form a partially amorphous Al-Mg layer and is shown to prevent atmospheric corrosion while maintaining the unique combination of favorable Mg/SiC reflective properties.
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81.65.Kn Corrosion protection
64.75.Ef Mixing
68.65.Ac Multilayers
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Thermal transport in grain boundary of graphene by non-equilibrium Green’s function approach

Yang Lu and Jing Guo

Appl. Phys. Lett. 101, 043112 (2012); http://dx.doi.org/10.1063/1.4737653 (5 pages) | Cited 2 times

Online Publication Date: 24 July 2012

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A method of combining lattice dynamics through the Brenner potential [D. W. Brenner et al., J. Phys.: Condens. Matter 14, 783 (2002)] with phonon transport through non-equilibrium Green’s function approach is applied to calculate the thermal conductance of graphene grain boundaries. The results show that all types of grain boundaries offer excellent thermal conductivity, in contrast to electronic transport which is structure-dependent. Zigzag-oriented symmetric grain boundaries present the highest thermal conductance, with weak dependence on the crystal alignment angle of graphene domains. The thermal conductance of grain boundaries increases while thermal ballisticity decreases with temperature. The out-of-plane mode is dominant in thermal conductivity of graphene grain boundaries.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.48.Gh Structure of graphene
61.72.Mm Grain and twin boundaries

Heat conduction in carbon nanotube materials: Strong effect of intrinsic thermal conductivity of carbon nanotubes

Alexey N. Volkov and Leonid V. Zhigilei

Appl. Phys. Lett. 101, 043113 (2012); http://dx.doi.org/10.1063/1.4737903 (5 pages) | Cited 2 times

Online Publication Date: 24 July 2012

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Computational study of thermal conductivity of interconnected networks of bundles in carbon nanotube (CNT) films reveals a strong effect of the finite thermal conductivity kT of individual nanotubes on the conductivity k of the CNT materials. The physical origin of this effect is explained in a theoretical analysis of systems composed of straight randomly dispersed CNTs. An analytical equation for quantitative description of the effect of finite kT on the value of k is obtained and adopted for continuous networks of bundles characteristic of CNT films and buckypaper. Contrary to the common assumption of the dominant effect of the contact conductance, the contribution of the finite kT is found to control the value of k at material densities and CNT lengths typical for real materials.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.55.aj Insulators
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

The influence of phonon scatterings on the thermal conductivity of SiGe nanowires

Liang Yin, Eun Kyung Lee, Jong Woon Lee, Dongmok Whang, Byoung Lyong Choi, and Choongho Yu

Appl. Phys. Lett. 101, 043114 (2012); http://dx.doi.org/10.1063/1.4737909 (4 pages) | Cited 2 times

Online Publication Date: 24 July 2012

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The thermal conductivities of SiGe alloy nanowires with different Ge concentrations and diameters were measured at 60–450 K, and all the nanowires for the measurements were characterized by electron microscopies for accurately determining dimensions and atomic concentrations. With 37–63 at. % Ge concentrations and 44–60 nm diameters, their thermal conductivities approached to the minimum thermal conductivity of SiGe alloys due to strong phonon scatterings. This may suggest these parameters are sufficient to result in the smallest achievable thermal conductivity with SiGe in practice. A parallel resistor model was employed to investigate the influence of silicon oxide layers on their thermal conductivities.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
63.22.Gh Nanotubes and nanowires

High efficiency ultraviolet emission from AlxGa1−xN core-shell nanowire heterostructures grown on Si (111) by molecular beam epitaxy

Q. Wang, H. P. T. Nguyen, K. Cui, and Z. Mi

Appl. Phys. Lett. 101, 043115 (2012); http://dx.doi.org/10.1063/1.4738983 (4 pages) | Cited 1 time

Online Publication Date: 25 July 2012

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High crystalline quality, vertically aligned AlxGa1−xN nanowire heterostructures are grown on GaN nanowire templates on Si (111) substrates by plasma-assisted molecular beam epitaxy. The nanowires exhibit unique core-shell structures, with enhanced Al compositions in the near-surface region. The emission wavelength can be varied across nearly the entire ultraviolet A (∼3.10–3.94 eV) and B (∼3.94–4.43 eV) spectral range by controlling the Al compositions. Such nanowire structures can exhibit extremely high internal quantum efficiency (up to ∼58%) at room-temperature, which is attributed to the superior carrier confinement offered by the core-shell structures and to the use of defect-free GaN nanowire templates.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.67.Uh Nanowires
81.07.Gf Nanowires
78.40.Fy Semiconductors

High compositional homogeneity in In-rich InGaAs nanowire arrays on nanoimprinted SiO2/Si (111)

S. Hertenberger, S. Funk, K. Vizbaras, A. Yadav, D. Rudolph, J. Becker, S. Bolte, M. Döblinger, M. Bichler, G. Scarpa, P. Lugli, I. Zardo, J. J. Finley, M.-C. Amann, G. Abstreiter, et al.

Appl. Phys. Lett. 101, 043116 (2012); http://dx.doi.org/10.1063/1.4738769 (5 pages) | Cited 6 times

Online Publication Date: 26 July 2012

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We report improved homogeneity control of composition-tuned In1−xGaxAs (x < 0.4) nanowire (NW) arrays grown by catalyst-free molecular beam epitaxy (MBE) on nanoimprinted SiO2/Si (111) substrates. Using very high As/(Ga+In) ratios at growth temperatures of 550 °C enabled uniform incorporation of the respective group-III elements (In,Ga) over the investigated composition range, confirmed by high-resolution x-ray diffraction (HRXRD) and energy dispersive x-ray spectroscopy. Low-temperature (20 K) photoluminescence of these In-rich In1−xGaxAs NW ensembles reveal state-of-the-art linewidths of ∼29–33 meV. These are independent of Ga content, suggesting an overall low degree of phase separation. In contrast, self-assembled, non-periodic In1−xGaxAs NW arrays show larger inhomogeneity with increased peakwidths in 2θ−ω HRXRD scans as well as broadened Raman modes. These results demonstrate the excellent potential of site-selective MBE growth of high-periodicity non-tapered In1−xGaxAs NW arrays with low size and composition dispersion for optimized device integration on Si.
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81.16.Dn Self-assembly
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Patterned substrates to facilitate long-range ordering in the formation of nanoparticle monolayers by electrophoretic deposition

Alex J. Krejci, Jyotirmoy Mandal, and James H. Dickerson

Appl. Phys. Lett. 101, 043117 (2012); http://dx.doi.org/10.1063/1.4738988 (4 pages) | Cited 2 times

Online Publication Date: 26 July 2012

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Nanoparticle submonolayer and monolayer films were deposited using electrophoretic deposition onto silicon substrates that were patterned with arrays of hexagonally ordered polymeric structural elements. Line structures of four different lengths were fabricated on the substrates by electron-beam lithography. Scanning electron microscopy, used to analyze the deposited nanoparticle films, confirmed that the particles tended to align along the faceted edges of these structures. Such phenomena appeared to promote correlations among the nanoparticles that facilitated ordered arrangements within the monolayers and sub-monolayers.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
82.45.Qr Electrodeposition and electrodissolution
68.55.aj Insulators
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.15.Pq Electrodeposition, electroplating

Nanoscale fluorescence imaging with quantum dot near-field electroluminescence

Kazunori Hoshino, Ashwini Gopal, Micah S. Glaz, David A. Vanden Bout, and Xiaojing Zhang

Appl. Phys. Lett. 101, 043118 (2012); http://dx.doi.org/10.1063/1.4739235 (4 pages) | Cited 1 time

Online Publication Date: 26 July 2012

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We demonstrate near-field fluorescence excitation and imaging with a quantum dot (QD) light emitting diode (QDLED) integrated at the tip of a scanning probe. The tip-embedded QDLED is employed in a near-field scanning optical microscopy setup to directly excite a secondary colloidal QD sample. Electrically pumped QDs enable multi-color, self-illuminating probes with no conventional optics needed for light coupling. Monolayer QDs stamped at the very tip of a micromachined silicon probe facilitates precise position control of the ultra-thin (10–15 nm) light source. Sensitivity of fluorescence intensity to the QDLED–QD sample distance was measured down to 50 nm order, demonstrating spatially resolved imaging.
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78.60.Fi Electroluminescence
78.67.Hc Quantum dots
85.60.Jb Light-emitting devices
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors

Electrically pumped lasing from single ZnO micro/nanowire and poly(3,4-ethylenedioxythiophene):poly(styrenexulfonate) hybrid heterostructures

Qi Zhang, Junjie Qi, Xin Li, Fang Yi, Zengze Wang, and Yue Zhang

Appl. Phys. Lett. 101, 043119 (2012); http://dx.doi.org/10.1063/1.4739430 (5 pages)

Online Publication Date: 26 July 2012

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We report electrically driven ultraviolet lasing by electrical injection in a single ZnO micro/nanowire. Heterojunctions were fabricated by contacting poly(3,4-ethylenedioxythiophene): poly(styrenexulfonate) (PEDOT:PSS) with one end of a single ZnO wire. At an excitation injection of ∼1 A/cm2, the electroluminescence spectrum showed a near-ultraviolet lasing action. This phenomenon was understood based on whispering-gallery mode, which results from trajectories that traverse a polygonal cross-section near the edges of the cylinder. The reduction of some modes was associated with the surface states or defects and the resonance below the intrinsic exciton emission of ZnO is related to electron accumulation at the polymer/ZnO interface.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.60.Fi Electroluminescence
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Optimum drift velocity for single molecule fluorescence bursts in micro/nano-fluidic channels

Lazar L. Kish, Jun Kameoka, Claes G. Granqvist, and Laszlo B. Kish

Appl. Phys. Lett. 101, 043120 (2012); http://dx.doi.org/10.1063/1.4739471 (3 pages)

Online Publication Date: 26 July 2012

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Photonic burst histograms can be used to identify single protein molecules in micro/nano-fluidic channels provided the width of the histogram is narrow. Photonic shot noise and residence time fluctuations, caused by longitudinal diffusion, are the major sources of the histogram width. This paper is a sequel to an earlier one of ours [L. L. Kish et al., Appl. Phys. Lett. 99, 143121 (2011)] and demonstrates that, for a given diffusion coefficient, an increase of the drift velocity enhances the relative shot noise and decreases the relative residence time fluctuations. This leads to an optimum drift velocity that minimizes the histogram width and maximizes the ability to identify single molecules, which is an important result for applications.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.15.Vv Diffusion
87.15.mq Luminescence
87.80.Ek Mechanical and micromechanical techniques
07.10.Cm Micromechanical devices and systems

Ambipolar operation of hybrid SiC-carbon nanotube based thin film transistors for logic circuits applications

B. Aïssa, M. Nedil, A. H. Esam, N. Tabet, D. Therriault, and F. Rosei

Appl. Phys. Lett. 101, 043121 (2012); http://dx.doi.org/10.1063/1.4739939 (4 pages)

Online Publication Date: 27 July 2012

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We report on the ambipolar operation of back-gated thin film field-effect transistors based on hybrid n-type-SiC/p-type-single-walled carbon nanotube networks made with a simple drop casting process. High-performances such an on/off ratio of 105, on-conductance of 20 μS, and a subthreshold swing of less than 165 mV/decades were obtained. The devices are air-stable and maintained their ambipolar operation characteristics in ambient atmosphere for more than two months. Finally, these hybrid transistors were utilized to demonstrate advanced logic NOR-gates. This could be a fundamental step toward realizing stable operating nanoelectronic devices.
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85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Noble metal nanodisks epitaxially formed on ZnO nanorods and their effect on photoluminescence

Sheng Chu, Jingjian Ren, Dong Yan, Jian Huang, and Jianlin Liu

Appl. Phys. Lett. 101, 043122 (2012); http://dx.doi.org/10.1063/1.4739516 (4 pages)

Online Publication Date: 27 July 2012

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Triangular and hexagonal shaped noble metal (Au, Ag, Pt, Pd) nanodisks were synthesized on the top facets of ZnO nanorods via simple deposition-annealing method. Other metals (Ni, Cu, Cr, Pb, Al) only formed irregular shaped nanostructures on ZnO nanorods. The morphology, elemental composition, as well as growth mechanism of the metal nanodisks/ZnO nanorod composite materials were studied. The localized surface plasmon resonant effects from different metal nanodisks on the photoluminescence of ZnO nanorods were investigated. It was demonstrated that the carriers transfer between the metal nanodisks and ZnO can efficiently manipulate the photoluminescence intensities from the nanorods.
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78.55.-m Photoluminescence, properties and materials
78.68.+m Optical properties of surfaces
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
78.67.Sc Nanoaggregates; nanocomposites
73.22.Lp Collective excitations

Strong photoluminescence from diameter-modulated single-walled carbon nanotubes

M. Mahjouri-Samani, Y. S. Zhou, W. Xiong, Z. Q. Xie, and Y. F. Lu

Appl. Phys. Lett. 101, 043123 (2012); http://dx.doi.org/10.1063/1.4739522 (4 pages)

Online Publication Date: 27 July 2012

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Employing the photoluminescence (PL) properties of the semiconducting single-walled carbon nanotubes (SWNTs) in applications is limited by their low quantum yield. Here, we report a simple method for enhancing the efficiency of PL emission by modulating the diameter and hence the bandgap of semiconducting SWNTs along their axes. The PL enhancement is explained by the exciton energy transfer via exciting SWNT segments of large bandgaps which induces emission from the neighboring segments of small bandgaps. The diameter-modulated SWNTs were grown by periodic modulation of the laser beam, and hence, the temperature in a laser assisted chemical vapor deposition process.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.67.Ch Nanotubes
81.07.De Nanotubes
71.35.-y Excitons and related phenomena
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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