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5 Sep 2005

Volume 87, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 87, 101107 (2005); http://dx.doi.org/10.1063/1.2039987 (3 pages)

A. David, C. Meier, R. Sharma, F. S. Diana, S. P. DenBaars, E. Hu, S. Nakamura, C. Weisbuch, and H. Benisty
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Faster H recovery in Pd nanoparticle layer based Gd switchable mirrors: Size-induced geometric and electronic effects

I. Aruna, B. R. Mehta, and L. K. Malhotra

Appl. Phys. Lett. 87, 103101 (2005); http://dx.doi.org/10.1063/1.2035322 (3 pages) | Cited 16 times

Online Publication Date: 29 August 2005

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An investigation of the effect of the nanoparticle size in the Pd overlayer on the hydrogen-induced changes in the Gd switchable mirrors is reported in the present study. Deposition of a 10 nm thick Pd overlayer consisting of nanoparticles of 9 nm size results in a large increase in optical and electrical contrast and a substantial decrease in response and recovery time in Gd switchable mirrors. This study shows that a uniformly-deposited nanoparticle catalytic layer is important for improving H recovery. These results have been explained in terms of the size-induced increase in surface area, lattice contraction, and shift of Pd d-band centroid. The results of the present study, specifically the observation of decrease in recovery time has important implications for hydrogen sensor, storage, and switching applications.
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61.46.-w Structure of nanoscale materials
42.79.Bh Lenses, prisms and mirrors
81.07.Bc Nanocrystalline materials
72.30.+q High-frequency effects; plasma effects
82.45.Jn Surface structure, reactivity and catalysis
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.63.Bd Nanocrystalline materials

Design of two-dimensional/three-dimensional composite porous alumina by colloidal crystal templating and subsequent anodization

Hidetaka Asoh and Sachiko Ono

Appl. Phys. Lett. 87, 103102 (2005); http://dx.doi.org/10.1063/1.2037199 (3 pages) | Cited 5 times

Online Publication Date: 29 August 2005

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The unique two-dimensional/three-dimensional composite porous alumina structure, which consisted of the outer inverse opal structure and the inner parallel channel array structure formed on an Al substrate, has been fabricated using a combination process involving colloidal crystal templating and subsequent multistep anodization. The pore periodicity and film thickness of the sophisticated porous structure presented here can be easily controlled by changing the diameter of spherical colloidal particles used as templates and adjusting the anodization conditions, such as voltage and time. The resulting porous materials can potentially find applications as catalytic supports, separation media, optical devices, and sensors.
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81.05.Rm Porous materials; granular materials
68.55.-a Thin film structure and morphology
82.45.Cc Anodic films
82.70.Dd Colloids
61.43.Gt Powders, porous materials

Low-temperature high-resolution magnetic force microscopy using a quartz tuning fork

Yongho Seo, Paul Cadden-Zimansky, and Venkat Chandrasekhar

Appl. Phys. Lett. 87, 103103 (2005); http://dx.doi.org/10.1063/1.2037852 (3 pages) | Cited 13 times

Online Publication Date: 29 August 2005

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We have developed a low-temperature high resolution magnetic force microscope (MFM) using a quartz tuning fork that can operate in a magnetic field. A tuning fork with a spring constant of 1300 N/m mounted with a commercial MFM cantilever tip was used. We have obtained high-resolution images of the stray magnetic fields exerted from grains with a spatial resolution of 15 nm and force resolution of 2 pN at 4.2 K. Tuning fork-based magnetic force microscopes have the potential to be used at millikelvin temperatures due to their low power dissipation and high force sensitivity.
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07.79.Pk Magnetic force microscopes

Nonlinear current-voltage curves of gold quantum point contacts

M. Yoshida, Y. Oshima, and K. Takayanagi

Appl. Phys. Lett. 87, 103104 (2005); http://dx.doi.org/10.1063/1.2037874 (3 pages) | Cited 9 times

Online Publication Date: 29 August 2005

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Nonlinear current-voltage (I‐V) curves of gold quantum point contacts (QPC) were investigated using a transmission electron microscope–scanning tunneling microscope system. The I‐V curves were measured by sweeping the bias voltage from 0 to 0.3 V at room temperature under ultrahigh vacuum. The results revealed that when the QPC formed a short nanowire, a nonlinear I‐V curve was observed, while a long nanowire produced a linear I‐V curve. The nonlinear I‐V curves were found to be caused by a nanowire thickening that occurred during increases of the bias voltage. This thickening resulted from a shortened distance between electrodes.
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73.63.Rt Nanoscale contacts
73.63.Nm Quantum wires

Growth process of close-packed aligned carbon nanotubes on SiC

M. Kusunoki, C. Honjo, T. Suzuki, and T. Hirayama

Appl. Phys. Lett. 87, 103105 (2005); http://dx.doi.org/10.1063/1.2037848 (3 pages) | Cited 11 times

Online Publication Date: 29 August 2005

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Densely aligned carbon nanotubes (CNTs) by surface decomposition of SiC (000math) C-face in vacuum were observed by plan-view transmission electron microscopy. It was found that the wall number of CNTs was directly proportional to the diameter of CNTs. Comparing with the theoretical calculation, it was revealed that all of the carbon atoms remained on the surface after the selective evaporation of Si atoms by decomposition of each monolayer of SiC (000math), and then constructed the CNT walls with the minimum diffusion distance at the interface.
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81.07.De Nanotubes
68.35.Fx Diffusion; interface formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.46.-w Structure of nanoscale materials

Packing-induced electronic structure changes in bundled single-wall carbon nanotubes

P. Castrucci, M. Scarselli, M. De Crescenzi, M. Diociaiuti, P. Chistolini, M. A. El Khakani, and F. Rosei

Appl. Phys. Lett. 87, 103106 (2005); http://dx.doi.org/10.1063/1.2039989 (3 pages) | Cited 8 times

Online Publication Date: 30 August 2005

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The electronic structure of free-standing parallel and braided bundles of single-wall carbon nanotubes ( ∼ 1.2 nm diameter) was probed by transmission electron microscopy and electron energy loss spectroscopy. The observed dramatic changes in the carbon K(1s) near-edge structures are attributed to the tubes’ structural packing in bundles which consequently alters their electronic structure. The π*- and the σ*-states are shown to be strongly affected by the way the tubes are packed in the bundles (i.e., parallel, braided, turned, or twisted).
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73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials
79.20.Uv Electron energy loss spectroscopy

Fundamental optical recombination in pentacene clusters and ultrathin films

Rui He, Nancy G. Tassi, Graciela B. Blanchet, and Aron Pinczuk

Appl. Phys. Lett. 87, 103107 (2005); http://dx.doi.org/10.1063/1.2040011 (3 pages) | Cited 14 times

Online Publication Date: 30 August 2005

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Photoluminescence spectra of pentacene clusters and films of few monolayers in thickness reveal two fundamental excitations that are assigned to the Davydov doublets of the lowest singlet exciton. While the energy splittings of the doublets have minor dependence on cluster thickness, their bandwidths become narrower as the pentacene clusters grow larger and into continuous ultrathin films. The marked similarity of these Davydov doublets to those in optical absorption spectra of thicker pentacene films and crystals suggests a similarity in molecular arrangements. Luminescence of self-trapped excitons is quenched in the few monolayer clusters and ultrathin films.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
78.66.Li Other semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Libraries of cluster-assembled titania films for chemical sensing

T. Mazza, E. Barborini, I. N. Kholmanov, P. Piseri, G. Bongiorno, S. Vinati, P. Milani, C. Ducati, D. Cattaneo, A. Li Bassi, C. E. Bottani, A. M. Taurino, and P. Siciliano

Appl. Phys. Lett. 87, 103108 (2005); http://dx.doi.org/10.1063/1.2035874 (3 pages) | Cited 19 times

Online Publication Date: 30 August 2005

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We report the fabrication of libraries of nanostructured TiO2 films with a gradient in nanoparticle crystalline phase and dimensions. By supersonic cluster beam deposition it is possible to produce rutile nanoparticles with a diameter smaller than 10 nm and to spread them into a co-deposited amorphous titania matrix. Upon thermal annealing rutile nanocrystals act as growth seeds of a film with a spatially controlled rutile/anatase ratio. Films with controlled crystalline phase variation have been deposited on micropatterned substrate to produce arrays of chemoresistive sensors of volatile organic compounds. Devices with different nanocrystalline structures and performances are obtained by a simple one-step thermal treatment after deposition.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Shell buckling of individual multiwalled carbon nanotubes using nanoindentation

J. F. Waters, P. R. Guduru, M. Jouzi, J. M. Xu, T. Hanlon, and S. Suresh

Appl. Phys. Lett. 87, 103109 (2005); http://dx.doi.org/10.1063/1.2012530 (3 pages) | Cited 30 times

Online Publication Date: 30 August 2005

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Although the mechanical behavior of carbon nanotubes has been studied extensively in recent years, very few experimental results exist on the shell buckling of nanotubes, despite its fundamental importance in nanotube mechanics and applications. Here we report an experimental technique in which individual multiwalled carbon nanotubes were axially compressed using a nanoindenter and the critical shell-buckling load was measured. The results are compared with predictions of existing continuum theories, which model multiwalled carbon nanotubes as a collection of single-walled shells, interacting through van der Waals forces. The theoretical models significantly underpredict the experimental buckling load.
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81.07.De Nanotubes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Growth habits and defects in ZnO nanowires grown on GaN/sapphire substrates

Igor Levin, Albert Davydov, Babak Nikoobakht, Norman Sanford, and Pavel Mogilevsky

Appl. Phys. Lett. 87, 103110 (2005); http://dx.doi.org/10.1063/1.2041832 (3 pages) | Cited 19 times

Online Publication Date: 31 August 2005

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Growth habits and defects in epitaxial ZnO nanowires grown from Au catalyst on (00.1) GaN/sapphire substrate using the vapor-liquid-solid (VLS) technique were studied using electron microscopy and x-ray diffraction. The results revealed presence of both horizontal (crawling-like) and vertical nanowires having similar orientation relationship to the substrate (00.1)ZnO‖(00.1)GaN, [11.0]ZnO‖[11.0]GaN. The crawling-like growth precedes the vertical growth, and the coalescence and overgrowth of the crawling nanowires produce a highly defective layer which separates the substrate and vertical nanorods. Transmission electron microscopy revealed a high density of planar defects in this interfacial layer. A significant density of stacking faults residing on the (0001) planes was also observed in the shorter vertical nanorods. The crawling nanowires are under residual compressive strain, whereas the vertical nanorods grow strain-free.
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68.65.La Quantum wires (patterned in quantum wells)
61.72.Nn Stacking faults and other planar or extended defects
68.60.Bs Mechanical and acoustical properties
61.46.-w Structure of nanoscale materials

Photonic band gaps in nanowire superlattices

L. Chen and E. Towe

Appl. Phys. Lett. 87, 103111 (2005); http://dx.doi.org/10.1063/1.2041837 (3 pages) | Cited 5 times

Online Publication Date: 31 August 2005

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This paper examines how a complete photonic band gap in a semiconductor nanowire superlattice can be achieved. By choosing the nanowire superlattice periodicity and its radius, a photonic band gap can be localized below the single optical mode cut-off frequency of the nanowire waveguide. We show that Bragg mirrors with near-unity reflectivity as well as high quality factor single defect cavities can be designed in a nanowire even by using dielectric stack materials with a low index contrast.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.82.-m Integrated optics

Electron field emission from a single carbon nanotube: Effects of anode location

R. C. Smith, D. C. Cox, and S. R. P. Silva

Appl. Phys. Lett. 87, 103112 (2005); http://dx.doi.org/10.1063/1.2041824 (3 pages) | Cited 38 times

Online Publication Date: 1 September 2005

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Electron field emission from an isolated carbon nanotube (CNT) was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1–60 μm. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42 V μm−1 at an anode to CNT tip separation of 1 μm, asymptotically, to approach 4 V μm−1 at a separation of 60 μm. It is proposed that at low D, the electric field enhancement factor (β) reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under “far field” conditions, where D>3 h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.63.Fg Nanotubes
61.46.-w Structure of nanoscale materials

Self assembled nanoparticle wires by discontinuous vertical colloidal deposition

J. J. Diao, Jianwei Sun, J. B. Hutchison, and M. E. Reeves

Appl. Phys. Lett. 87, 103113 (2005); http://dx.doi.org/10.1063/1.2042637 (3 pages) | Cited 10 times

Online Publication Date: 2 September 2005

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We report a simple, one-step method for assembling spherical nanoparticles into wires without the need for lithographic templating. It is effective for a variety of conducting and nonconducting nanoparticles and substrates, and the only material requirement is that the nanoparticles be placed in a colloidal suspension that is wettable on the desired substrate. The shape of the meniscus defines the wire’s geometry, and we report the synthesis and physical properties of wires several millimeters long by a few micrometers wide. As we demonstrate here, the technique is fast and easily controlled, and can be used to make integrated nanoparticle wire arrays.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
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