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19 Mar 2007

Volume 90, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages)

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg
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High-symmetry ZnS hepta- and tetrapods composed of assembled ZnS nanowire arrays

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg

Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages) | Cited 32 times

Online Publication Date: 19 March 2007

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Sixfold symmetry heptapodlike and threefold symmetry tetrapodlike ZnS structures have been fabricated by thermal evaporation of a ZnS and SiO mixture source in N2 at 1300 °C. Both the heptapods and tetrapods have been formed by the self-assembly of ZnS nanowires with the preferred (0001) orientations. Structures and morphologies of the obtained heptapods and tetrapods are thoroughly studied using x-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Room-temperature photoluminescence spectra taken from the nanostructures show a strong green emission centered at 550 nm.
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68.65.La Quantum wires (patterned in quantum wells)
81.16.Dn Self-assembly
78.67.Lt Quantum wires
78.55.Et II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Winding of single-walled carbon nanotube ropes: An effective load transfer

Tung-Wen Cheng and Wen-Kuang Hsu

Appl. Phys. Lett. 90, 123102 (2007); http://dx.doi.org/10.1063/1.2714282 (3 pages) | Cited 3 times

Online Publication Date: 19 March 2007

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The strength of single-walled carbon nanotube ropes is enhanced by a factor of 6 via a winding procedure. A stepwise structure seen at a load-strain profile is explained based on an intermittent fracture mechanism.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.M- Structural failure of materials
62.20.D- Elasticity
61.46.Fg Nanotubes

Aligned AlN nanowires and microrods by self-patterning

G. R. Yazdi, M. Syväjärvi, and R. Yakimova

Appl. Phys. Lett. 90, 123103 (2007); http://dx.doi.org/10.1063/1.2715129 (3 pages) | Cited 6 times

Online Publication Date: 19 March 2007

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Self-patterned AlN microrods and nanowires were grown on 4H-SiC substrate by a physical vapor transport method. AlN hexagonal pyramids were found to be nucleation sites for the evolution of the observed morphological forms. The average diameter and length of the nanowires are about 200 nm and 90 μm, respectively. The density of microrods corresponds to the concentration of the pyramids, while the nanowires are less compact. Low-temperature cathodoluminescence spectra of microrods show band gap emission of AlN at 208 nm, which confirms that they are AlN single crystals. A formation mechanism of the AlN structures is suggested.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.Hk Nanocrystals
78.67.Lt Quantum wires
78.60.Hk Cathodoluminescence, ionoluminescence

Nanoscale x-ray magnetic circular dichroism probing of electric-field-induced magnetic switching in multiferroic nanostructures

T. Zhao, A. Scholl, F. Zavaliche, H. Zheng, M. Barry, A. Doran, K. Lee, M. P. Cruz, and R. Ramesh

Appl. Phys. Lett. 90, 123104 (2007); http://dx.doi.org/10.1063/1.2714201 (3 pages) | Cited 6 times

Online Publication Date: 20 March 2007

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The magnetic structure as well as its response to an external electric field were studied in ferrimagnetic CoFe2O4 nanopillars embedded in an epitaxial ferroelectric BiFeO3 film using photoemission electron microscopy and x-ray magnetic circular dichroism. Magnetic switching was observed in both Co and Fe magnetic sublattices after application of an electric field. About 50% of the CoFe2O4 nanopillars were measured to switch their magnetization with the electric field, implying an elastic-mediated electric-field-induced magnetic anisotropy change.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
78.20.Ls Magneto-optical effects
79.60.Dp Adsorbed layers and thin films
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Chip cooling with integrated carbon nanotube microfin architectures

K. Kordás, G. Tóth, P. Moilanen, M. Kumpumäki, J. Vähäkangas, A. Uusimäki, R. Vajtai, and P. M. Ajayan

Appl. Phys. Lett. 90, 123105 (2007); http://dx.doi.org/10.1063/1.2714281 (3 pages) | Cited 62 times

Online Publication Date: 20 March 2007

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Efficient cooling of silicon chips using microfin structures made of aligned multiwalled carbon nanotube arrays is achieved. The tiny cooling elements mounted on the back side of the chips enable power dissipation from the heated chips on the level of modern electronics demands. The nanotube fins are mechanically superior compared to other materials being ten times lighter, flexible, and stiff at the same time. These properties accompanied with the relative simplicity of the fabrication makes the nanotube structures strong candidates for future on-chip thermal management applications.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Near field distribution in two dimensionally arrayed gold nanoparticles on platinum substrate

Nikolay Nedyalkov, Tetsuo Sakai, Tomoya Miyanishi, and Minoru Obara

Appl. Phys. Lett. 90, 123106 (2007); http://dx.doi.org/10.1063/1.2715103 (3 pages) | Cited 12 times

Online Publication Date: 20 March 2007

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Theoretical and experimental results for near field properties in the vicinity of two dimensionally aligned gold nanoparticles are presented. The numerical analysis is based on finite difference time domain simulation code. The simulated system consists of gold particles with a radius of 100 nm, deposited on platinum substrate. The near field distribution on the substrate surface and its magnitude are found to depend on the interparticle distance. The experimental results obtained confirm the theoretical findings and demonstrate that the produced near field can result in a permanent substrate surface nanomodification and selective nanoparticle removal.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.47.De Metallic surfaces
81.07.Bc Nanocrystalline materials

Three-dimensional carbon nanowall structures

Alfred T. H. Chuang, John Robertson, Bojan O. Boskovic, and Krzysztof K. K. Koziol

Appl. Phys. Lett. 90, 123107 (2007); http://dx.doi.org/10.1063/1.2715441 (3 pages) | Cited 21 times

Online Publication Date: 20 March 2007

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The authors report the growth of carbon nanowalls in freestanding, three-dimensional aggregates by microwave plasma-enhanced chemical vapor deposition. Carbon nanowalls extrude from plasma sites into three-dimensional space. The growth is catalyst-free and not limited by nucleating surfaces. The growth mechanism is discussed and compared with similar carbon nanomaterials. High surface area of as-grown carbon nanowalls indicates a potential for electrochemical applications. Field emission measurements show a low field turn-on and long-term stability. The results establish a scalable production method and possible applications using field emission or high surface area.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.-w Structure of nanoscale materials
82.45.Yz Nanostructured materials in electrochemistry
79.70.+q Field emission, ionization, evaporation, and desorption

Crystalline ZnO with an enhanced surface area obtained by nanocasting

T. Waitz, M. Tiemann, P. J. Klar, J. Sann, J. Stehr, and B. K. Meyer

Appl. Phys. Lett. 90, 123108 (2007); http://dx.doi.org/10.1063/1.2713872 (3 pages) | Cited 17 times

Online Publication Date: 21 March 2007

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The authors report the synthesis of nanoporous ZnO, which exhibits a periodically ordered, uniform pore system with crystalline pore walls. The crystalline structure is investigated by x-ray diffraction, transmission electron microscopy, and selected area electron diffraction. The large specific surface area and the uniformity of the pore system are confirmed by nitrogen physisorption. Raman spectroscopy along with low-temperature photoluminescence measurements confirms the high degree of crystallinity and gives insight into defects participating in the radiative recombination processes.
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81.05.Dz II-VI semiconductors
81.30.Fb Solidification
61.66.Fn Inorganic compounds
78.55.Et II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)
78.30.Fs III-V and II-VI semiconductors

Infrared lasing in InN nanobelts

Ming-Shien Hu, Geng-Ming Hsu, Kuei-Hsien Chen, Chia-Ju Yu, Hsu-Cheng Hsu, Li-Chyong Chen, Jih-Shang Hwang, Lu-Sheng Hong, and Yang-Fang Chen

Appl. Phys. Lett. 90, 123109 (2007); http://dx.doi.org/10.1063/1.2714291 (3 pages) | Cited 16 times

Online Publication Date: 21 March 2007

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Infrared lasing from single-crystalline InN nanobelts grown by metal organic chemical vapor deposition was demonstrated. Transmission electron microscopy studies revealed that the InN nanobelts of rectangular cross section grew along [110] direction and were enclosed by ±(001) and ±(1math0) planes. The infrared lasing action was observed at 20 K in the InN nanobelts grown on an amorphous silicon nitride coated silicon substrate by continuous wave laser pumping.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.45.+h Stimulated emission
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Self-assembled periodic nanoporous network in multifunctional ZrO2–CeO2–(La0.8Sr0.2)MnO3 composites

Vaneet Sharma, Jiechao Jiang, Maria Hossu, Ali R. Koymen, and Shashank Priya

Appl. Phys. Lett. 90, 123110 (2007); http://dx.doi.org/10.1063/1.2715111 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2007

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This letter reports the structural characteristics of the self-assembled surface nanostructure in the 0.75 wt % (Zr0.88Ce0.12)O2–0.25 wt % (La0.8Sr0.2)MnO3 ceramics. The surface consists of periodic porous network with islandlike structures occurring at the triple boundary junctions. The pores were found to have the diameter in the range of 150–200 nm with the thickness of the porous surface layer of the order of 100 nm. The pore distribution was quasiperiodic with the spacing in the range of 50–150 nm. The formation of the nanoporous network is correlated to the structural transformation occurring in ZrO2 system.
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81.05.Mh Cermets, ceramic and refractory composites
81.05.Rm Porous materials; granular materials
81.16.Dn Self-assembly
61.43.Gt Powders, porous materials

Large magnetoresistance in Co/Ni/Co ferromagnetic single electron transistors

R. S. Liu, H. Pettersson, L. Michalak, C. M. Canali, D. Suyatin, and L. Samuelson

Appl. Phys. Lett. 90, 123111 (2007); http://dx.doi.org/10.1063/1.2714289 (3 pages)

Online Publication Date: 22 March 2007

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The authors report on magnetotransport investigations of nanoscaled ferromagnetic Co/Ni/Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2 K. Magnetotransport measurements carried out at 1.8 K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which the authors interpret in terms of a switching mechanism driven by the shape anisotropy of the central wirelike Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which the authors tentatively attribute to excitation of magnons in the central island.
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85.35.Gv Single electron devices
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Competition and cooperation between lattice-oriented growth and step-templated growth of aligned carbon nanotubes on sapphire

Hiroki Ago, Kenta Imamoto, Naoki Ishigami, Ryota Ohdo, Ken-ichi Ikeda, and Masaharu Tsuji

Appl. Phys. Lett. 90, 123112 (2007); http://dx.doi.org/10.1063/1.2715031 (3 pages) | Cited 16 times

Online Publication Date: 22 March 2007

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The authors study the growth mechanism of single-walled carbon nanotubes (SWNTs) horizontally aligned on A-plane single crystal sapphire (11math0) by making the controlled step/terrace structure. SWNT growth direction was sensitive to the surface geometry of the sapphire, and there was competition between two growth modes, lattice-oriented growth and step-templated growth. On the substrate with single-atomic steps, SWNTs aligned parallel to the [1math00] direction as dominated by the lattice-oriented growth mode, while SWNTs aligned along the step edges when the double-atomic or higher steps were formed. Our findings have potential for the fabrication of designed architecture of SWNTs by combining these two growth modes.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Fg Nanotubes

Flexible conjugated polymer photovoltaic cells with controlled heterojunctions fabricated using nanoimprint lithography

Myung-Su Kim, Jin-Sung Kim, Jae Cheol Cho, Max Shtein, Jinsang Kim, L. Jay Guo, and Jinsang Kim

Appl. Phys. Lett. 90, 123113 (2007); http://dx.doi.org/10.1063/1.2715036 (3 pages) | Cited 73 times

Online Publication Date: 22 March 2007

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The authors describe conjugated polymer-based photovoltaic devices in which the shape and area of the interface between the electron donor and acceptor layers were controllably varied using nanoimprint lithography. The short circuit current is shown to increase with the interfacial area of the heterojunction, without affecting the open circuit voltage. The fill factor and power conversion efficiency are also shown to increase with donor-acceptor interfacial area.
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84.60.Jt Photoelectric conversion

Subnitride and valence band offset at Si3N4/Si interface formed using nitrogen-hydrogen radicals

Masaaki Higuchi, Shigetoshi Sugawa, Eiji Ikenaga, Jiro Ushio, Hiroshi Nohira, Takuya Maruizumi, Akinobu Teramoto, Tadahiro Ohmi, and Takeo Hattori

Appl. Phys. Lett. 90, 123114 (2007); http://dx.doi.org/10.1063/1.2715037 (3 pages) | Cited 7 times

Online Publication Date: 22 March 2007

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The authors measured soft x-ray-excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels, and valence band for nitride films formed on Si(100), Si(111), and Si(110) using nitrogen-hydrogen radicals with the same probing depth. The Si3N4/Si interfaces formed exhibited an almost abrupt compositional transition. Furthermore, the crystal orientation of Si substrate affects the total areal density of subnitrides but not the valence band offset at the Si3N4/Si interface.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Precise replication of antireflective nanostructures from biotemplates

Hongjun Gao, Zhongfan Liu, Jin Zhang, Guoming Zhang, and Guoyong Xie

Appl. Phys. Lett. 90, 123115 (2007); http://dx.doi.org/10.1063/1.2715094 (3 pages) | Cited 6 times

Online Publication Date: 22 March 2007

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The authors report herein a new type of nanonipple structures on the cicada’s eye and the direct structural replication of the complex micro- and nanostructures for potential functional emulation. A two-step direct molding process is developed to replicate these natural micro- and nanostructures using epoxy resin with high fidelity, which demonstrates a general way of fabricating functional nanostructures by direct replication of natural biotemplates via a suitable physicochemical process. Measurements of spectral reflectance showed that this kind of replicated nanostructure has remarkable antireflective property, suggestive of its potential applications to optical devices.
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81.16.-c Methods of micro- and nanofabrication and processing
81.10.Fq Growth from melts; zone melting and refining
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.66.-p Physiological optics

Unusual size dependence of the optical emission gap in small hydrogenated silicon nanoparticles

X. Wang, R. Q. Zhang, S. T. Lee, T. A. Niehaus, and Th. Frauenheim

Appl. Phys. Lett. 90, 123116 (2007); http://dx.doi.org/10.1063/1.2715101 (3 pages) | Cited 16 times

Online Publication Date: 22 March 2007

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It is well known that the electronic and optical absorption gaps of hydrogenated silicon nanoparticles are inversely proportional to the particle size. Here, the authors show that their optical emission gaps are remarkably different and dully dependent on the size for those smaller than 1.5 nm, based on their excited-state calculations of a series of nanoparticles from Si5H12 to Si199H140 using a time-dependent tight-binding density-functional method. It is revealed that this unusual size dependence is due to the strong excited-state structure relaxation in the particle core region that becomes significant when the size decreases.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Mq Elemental semiconductors
71.15.Qe Excited states: methodology
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Mechanism of molecular beam epitaxy growth of GaN nanowires on Si(111)

R. K. Debnath, R. Meijers, T. Richter, T. Stoica, R. Calarco, and H. Lüth

Appl. Phys. Lett. 90, 123117 (2007); http://dx.doi.org/10.1063/1.2715119 (3 pages) | Cited 17 times

Online Publication Date: 22 March 2007

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GaN nanowires have been grown without external catalyst on Si(111) substrates by plasma-assisted molecular beam epitaxy. Nanowire aspect ratios (length/diameter) of about 250 have been achieved. During the initial stage of the growth, there is a nucleation process in which the number of wires increases and the most probable nucleation diameter of about 10 nm has been observed, which slowly increases with deposition time. For deposition time longer than the nucleation stage, the nanowire length as a function of diameter monotonically decreases. This phenomenon can be explained by adatom diffusion on the nanowire lateral surface towards the tip.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
81.07.Vb Quantum wires
81.05.Ea III-V semiconductors

Formation of gold nanoparticles embedded in a polyimide film for nanofloating gate memory

Jung H. Kim, Kwang H. Baek, Chang Kyung Kim, Young Bae Kim, and Chong Seung Yoon

Appl. Phys. Lett. 90, 123118 (2007); http://dx.doi.org/10.1063/1.2716345 (3 pages) | Cited 26 times

Online Publication Date: 23 March 2007

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A monolayer of vertically aligned Au nanoparticles embedded in a dielectric film was fabricated by sandwiching a 3.4-nm-thick Au film between two polyimide (PI) precursor layers. Au formed uniform-sized nanoparticles on the PI precursor and coalesced into 10 nm sized nanoparticles during imidization, forming a well-dispersed monolayer of Au nanoparticles embedded in PI. Capacitance-voltage measurement at 300 K showed that the monolayer of Au nanoparticles functioning as a floating gate in Al/PI/Au nanoparticles/PI/Si metal-insulator-semiconductor-type capacitor exhibited a capacitance hysteresis of 3.4 V at an applied voltage of 6 V. The memory effect can be potentially utilized in next generation flash memories.
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81.07.Bc Nanocrystalline materials
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices
84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Self-organized patterning of molecularly thin liquid polymer films utilizing molecular flow induced by ultraviolet irradiation

Hedong Zhang, Yasunaga Mitsuya, Natsuko Fukuoka, Masashi Imamura, and Kenji Fukuzawa

Appl. Phys. Lett. 90, 123119 (2007); http://dx.doi.org/10.1063/1.2716358 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2007

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A self-organized patterning method for molecularly thin liquid polymer films on solid surfaces has been demonstrated. In contrast to conventional methods that prepattern solid surfaces and then use the patterns as templates for polymer films, this method utilizes self-organization of polymers induced by ultraviolet (UV) radiation through a mask, thereby directly patterning the polymer films and omitting the prepatterning process. Such UV irradiation locally modified the interaction between polymer films and solid surfaces. As a result, molecular flow occurred at the boundary between the irradiated and nonirradiated areas, leading to three-dimensional surface structures.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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