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16 Oct 2006

Volume 89, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 164101 (2006); http://dx.doi.org/10.1063/1.2362602 (3 pages)

Yen-Wen Lu and Chang-Jin(CJ) Kim
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Nanowire-based multiple quantum dot memory

Henrik A. Nilsson, Claes Thelander, Linus E. Fröberg, Jakob B. Wagner, and Lars Samuelson

Appl. Phys. Lett. 89, 163101 (2006); http://dx.doi.org/10.1063/1.2362594 (3 pages) | Cited 18 times

Online Publication Date: 16 October 2006

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The authors propose and demonstrate an alternative memory concept in which a storage island is connected to a nanowire containing a stack of nine InAs quantum dots, each separated by thin InP tunnel barriers. Transport through the quantum dot structure is suppressed for a particular biasing window due to misalignment of the energy levels. This leads to hysteresis in the charging/discharging of the storage island. The memory operates for temperatures up to around 150 K and has write times down to at least 15 ns. A comparison is made to a nanowire memory based on a single, thick InP barrier.
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84.30.Sk Pulse and digital circuits
85.30.De Semiconductor-device characterization, design, and modeling

Tunable room temperature low-field spin polarized tunneling magnetoresistance of La0.7Sr0.3MnO3 nanoparticles

P. Dey and T. K. Nath

Appl. Phys. Lett. 89, 163102 (2006); http://dx.doi.org/10.1063/1.2362595 (3 pages) | Cited 14 times

Online Publication Date: 16 October 2006

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The authors have studied low-field spin polarized tunneling magnetoresistance (LFMR) at room temperature of a series of nanocrystalline La0.67Sr0.33MnO3 samples having average crystallite size (ϕ) from 14 to 150 nm. Interestingly with decrease in ϕ, LFMR enhances up to a critical ϕ of 28 nm, beyond which LFMR starts decreasing, indicating a pronounced crossover of LFMR value (LFMRmax ∼ 1.67%) with decrease in ϕ. Magnetization versus magnetic field study at room temperature reveals that with decrease in ϕ LFMR increases untill the nanoparticles remain magnetically multidomain (MD), but as soon as it falls in the single domain (SD) regime, LFMR immediately starts diminishing. Their study explores the fact that for MD nanoparticles room temperature LFMR is decided only by surface spin susceptibility (χb), whereas for SD nanoparticles LFMR arises as a result of a sensitive balance between χb and thermal effect.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Lx Magnetic oxides
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Distance dependent interaction as the limiting factor for Si nanocluster to Er energy transfer in silica

B. Garrido, C. García, P. Pellegrino, D. Navarro-Urrios, N. Daldosso, L. Pavesi, F. Gourbilleau, and R. Rizk

Appl. Phys. Lett. 89, 163103 (2006); http://dx.doi.org/10.1063/1.2362600 (3 pages) | Cited 28 times

Online Publication Date: 16 October 2006

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Si excess, Er content, and processing parameters have been optimized in a series of cosputtered oxide layers for maximizing Er emission and lifetime. The amount of excited Er as a function of the incident photon flux has been quantified for resonant (488 nm) and nonresonant (476 nm) excitations. Results show that a maximum of 3.5% of Er ions is excitable through the Si nanoclusters (Si-nc). This low value cannot be explained only by cooperative upconversion and/or excited state absorption. A short range (0.5 nm) distance dependent interaction model is developed that accounts for this low Er population inversion. The model points to the low density of Si-nc [(3–5)×1017 cm−3] as the ultimate limiting step for indirect Er excitation in this system.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials

Phonon transport through a three-dimensional abrupt junction

Wen-Xia Li, Tianyu Liu, and Changlong Liu

Appl. Phys. Lett. 89, 163104 (2006); http://dx.doi.org/10.1063/1.2362970 (3 pages) | Cited 10 times

Online Publication Date: 16 October 2006

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By using the scattering matrix method, the authors investigate the transmission coefficient and thermal conductance of acoustic phonon through a three-dimensional abrupt junction at low temperatures. It is found that the transmission coefficient of long-wavelength phonon strongly depends on the geometrical parameters of the structure as the incident frequency ω→0, and there exist some dips in the transmission spectrum with an increase of incident frequency ω. In the meantime, as the temperature T→0, the thermal conductance is strongly influenced by the abrupt junction structure. These results are not in agreement with previous theoretical studies for the case of two-dimensional structure and can be used as a guideline for the thermal management of the various nanostructures.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Two-color upconversion in rare-earth-ion-doped ZrO2 nanocrystals

G. Y. Chen, Y. G. Zhang, G. Somesfalean, Z. G. Zhang, Q. Sun, and F. P. Wang

Appl. Phys. Lett. 89, 163105 (2006); http://dx.doi.org/10.1063/1.2363146 (3 pages) | Cited 54 times

Online Publication Date: 16 October 2006

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To develop fluorescent labels for multicolor imaging, rare-earth-ion-doped ZrO2 nanocrystals were prepared by a complex precursor method. Laser excitation of 976 nm induced single fluorescent bands of green and red upconversion (UC) in ZrO2:Er3+ and ZrO2:Er3++Yb3+ nanocrystals, respectively. A suppression ratio (SR) parameter was introduced, defined as the UC intensity ratio of the main band to all the other detected impurity bands, and SR values in the order of 10–100 were experimentally obtained, demonstrating the excellent monochromaticity of the UC labels. Thus, the two-color UC labels obtained are potentially ideal to be used for biological multicolor imaging.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Photoelectrochemical water splitting at titanium dioxide nanotubes coated with tungsten trioxide

Jong Hyeok Park, O Ok Park, and Sungwook Kim

Appl. Phys. Lett. 89, 163106 (2006); http://dx.doi.org/10.1063/1.2357878 (3 pages) | Cited 39 times

Online Publication Date: 16 October 2006

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The photocatalytic splitting of water into hydrogen and oxygen using solar light is a potentially clean and renewable source for hydrogen fuel. Titanium oxide nanotubes coated with tungsten oxide were prepared to harvest more solar light for the first time and characterized their water splitting efficiency. The tungsten trioxide coatings significantly enhanced the visible spectrum absorption of the titanium dioxide nanotube array, as well as their solar-spectrum induced photocurrents. For the sample, upon white light illumination at 150 mW/cm2, hydrogen gas generated at the overall conversion efficiency of 0.87%.
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82.45.Yz Nanostructured materials in electrochemistry
82.50.-m Photochemistry
82.45.Jn Surface structure, reactivity and catalysis
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.63.Fg Nanotubes
82.45.Hk Electrolysis

Visible light emission from single layer Si nanodots fabricated by laser irradiation method

Zhanhong Cen, Jun Xu, Yansong Liu, Wei Li, Ling Xu, Zhongyuan Ma, Xinfan Huang, and Kunji Chen

Appl. Phys. Lett. 89, 163107 (2006); http://dx.doi.org/10.1063/1.2362577 (3 pages) | Cited 16 times

Online Publication Date: 17 October 2006

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A single layer of dense (>1011 cm−2) Si nanodots on an insulating a-SiN layer was fabricated by the method combining the laser irradiation on the ultrathin amorphous Si films and subsequent thermal annealing. Raman scattering spectroscopy, planar and cross-section transmission electron microscopy were employed to characterize the formation of Si nanodots. It was found that the size of formed Si nanodots is strongly influenced by the initial amorphous Si film thickness. Visible light emission was observed from the obtained Si nanodots at room temperature and the luminescence peak is varied from 660 to 725 nm with increasing the amorphous Si film thickness. The variable luminescence can be attributed to the interface state assisted radiative recombination rather than the quantum size effect.
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78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
73.21.La Quantum dots
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Noncontact tuning fork position sensing for hollow-pyramid near-field cantilevered probes

A. Ambrosio, E. Cefalì, S. Spadaro, S. Patanè, M. Allegrini, D. Albert, and E. Oesterschulze

Appl. Phys. Lett. 89, 163108 (2006); http://dx.doi.org/10.1063/1.2362588 (3 pages) | Cited 3 times

Online Publication Date: 17 October 2006

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We demonstrate that tuning fork sensing provides a stable, noncontact mode of operation when applied to near-field optical microscopy employing cantilevered probes. Detrimental damping effects that have so far limited the practical use of these otherwise very advantageous probes are totally overcome. We validate our tuning fork setup featuring hollow-pyramid probes by an optical nanolithography application.
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07.79.Fc Near-field scanning optical microscopes

Instabilities of switching processes in synthetic antiferromagnets

A. N. Bogdanov and U. K. Rößler

Appl. Phys. Lett. 89, 163109 (2006); http://dx.doi.org/10.1063/1.2363177 (3 pages) | Cited 5 times

Online Publication Date: 17 October 2006

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It is shown that magnetic states and field-driven reorientation transitions in synthetic antiferromagnets crucially depend on contributions of higher-order anisotropies. A phenomenological macrospin model is derived to describe the magnetic states of two antiferromagnetically coupled magnetic thin-film elements. The calculated phase diagrams show that magnetic states with out-of-plane magnetization, symmetric escaped spin-flop phases, exist in a broad range of the applied magnetic field. Due to the formation of such states and concomitant multidomain patterns, the switching processes in toggle magnetic random access memory devices can radically deviate from predictions within oversimplified models.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ordered arrays of Ag nanoparticles grown by constrained self-organization

Pradeep Sharma, C. Y. Liu, Chen-Feng Hsu, N. W. Liu, and Y. L. Wang

Appl. Phys. Lett. 89, 163110 (2006); http://dx.doi.org/10.1063/1.2355475 (3 pages) | Cited 12 times

Online Publication Date: 17 October 2006

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In a postdeposition annealing process, the Ag deposited at low temperature on a Si(100) substrate aggregates to regions that have been exposed to adequate dose of energetic ions. By patterning an array of such aggregation centers on the substrate, using a 50 keV focused Ga+ ion beam, the migration of Ag on the patterned area during the subsequent annealing is constrained and ordered arrays of Ag nanoparticles with uniform size distribution are formed spontaneously. The mechanism and the optimum conditions for constraining the self-organization of Ag on Si by focused-ion-beam patterning are discussed.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Rf Micro- and nanoscale pattern formation
81.40.Gh Other heat and thermomechanical treatments

High-conductance states of single benzenedithiol molecules

Makusu Tsutsui, Yumi Teramae, Shu Kurokawa, and Akira Sakai

Appl. Phys. Lett. 89, 163111 (2006); http://dx.doi.org/10.1063/1.2363995 (3 pages) | Cited 43 times

Online Publication Date: 17 October 2006

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Conductance of single 1,4-benzenedithiol (BDT) molecules is investigated in a wide range (0–0.3)G0, exploiting mechanically controllable break junction technique. The authors observed a series of clear conductance steps both in low- ( ∼ 0.01G0) and high-conductance ( ∼ 0.1G0) regimes and corresponding two sets of peak structures in the conductance histograms. The two distinct conductance states are attributable to different Au–S bonding configurations of Au∕BDT∕Au junctions. The high-bias measurements reveal that the high-conductance state of single BDT molecules is stable up to 1.6 V and prospective for molecular device applications.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
73.40.Ns Metal-nonmetal contacts

Multiple reference Fourier transform holography with soft x rays

W. F. Schlotter, R. Rick, K. Chen, A. Scherz, J. Stöhr, J. Lüning, S. Eisebitt, Ch. Günther, W. Eberhardt, O. Hellwig, and I. McNulty

Appl. Phys. Lett. 89, 163112 (2006); http://dx.doi.org/10.1063/1.2364259 (3 pages) | Cited 39 times

Online Publication Date: 17 October 2006

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The authors demonstrate multiple reference source Fourier transform holography with soft x rays. This technique extends the detection limit of high resolution lensless imaging by introducing spatial multiplexing to coherent x-ray scattering. In this way, image quality is improved without increasing the radiation exposure to the sample. This technique is especially relevant for recording static images of radiation sensitive samples and for studying spatial dynamics with pulsed light sources. Applying their technique in the weak illumination limit they image a nanoscale test object by detecting ∼ 2500 photons. The observed enhancement in the signal-to-noise ratio of the image follows the square root of the number of reference sources.
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42.40.-i Holography
42.30.Kq Fourier optics
07.85.-m X- and γ-ray instruments
42.30.Va Image forming and processing

Fabrication of sub-50 nm (La,Ba)MnO3 ferromagnetic nanochannels by atomic force microscopy lithography and their electrical properties

Motoyuki Hirooka, Yoshihiko Yanagisawa, Teruo Kanki, Hidekazu Tanaka, and Tomoji Kawai

Appl. Phys. Lett. 89, 163113 (2006); http://dx.doi.org/10.1063/1.2360208 (3 pages) | Cited 8 times

Online Publication Date: 18 October 2006

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The technique of atomic force microscope nanolithography was used to construct robust nano-structures with atomically flat surface of ferromagnetic perovskite manganites down to 30 nm in size over 5 μm long. The resulting (La,Ba)MnO3 nanochannel possessed no lithographic damage and exhibited bulklike room temperature ferromagnetism down to 30 nm beyond electrical phase separation picture. High-quality ferromagnetic oxide nanostructures allow to instigate intrinsic nanoscale electrical transport properties of these materials and to construct high-performance and novel spin electronics devices.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Nd Micro- and nanolithography
81.16.Ta Atom manipulation
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
73.63.Bd Nanocrystalline materials

Controlled two-dimensional coated nanostructures for bulk thermoelectric composites

B. Zhang, J. He, X. Ji, Terry M. Tritt, and Amar Kumbhar

Appl. Phys. Lett. 89, 163114 (2006); http://dx.doi.org/10.1063/1.2363954 (3 pages) | Cited 12 times

Online Publication Date: 18 October 2006

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The authors demonstrate herein a new route to introduce two-dimensional nanostructures into a bulk thermoelectric material using a hydrothermal coating technique. A very thin Pb0.75Sn0.25Se crystalline layer (typically about 30 nm) is fabricated onto the surfaces of micron-sized Pb0.75Sn0.25Te seed particles. Compared to the conventional preparation of the nanocomposite thermoelectric materials, the salient advantage of this “coating” technique is that the authors are able to achieve a more homogenous dispersion of the nanostructures, which should subsequently result in more desirable effects on both the thermal and electrical transports via the direct control of the intergrain boundary.
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81.05.Hd Other semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
72.20.Pa Thermoelectric and thermomagnetic effects
73.63.-b Electronic transport in nanoscale materials and structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Internanotube friction

Sen-Hong Syue, Sheng-Yi Lu, Wen-Kuang Hsu, and Han-Chang Shih

Appl. Phys. Lett. 89, 163115 (2006); http://dx.doi.org/10.1063/1.2369721 (3 pages) | Cited 8 times

Online Publication Date: 18 October 2006

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Field induced displacement of carbon nanotubes is detected within a bundle and intertube friction is calculated via cohesive energy and electromagnetic formula. Tube-tube friction is found to be 1.4×10−4 N which is five orders of magnitude greater than value obtained between adjacent layers within a nanotube.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
61.46.Fg Nanotubes

Enhanced low-temperature protonic conductivity in fully dense nanometric cubic zirconia

Umberto Anselmi-Tamburini, Filippo Maglia, Gaetano Chiodelli, Pietro Riello, Stefania Bucella, and Zuhair A. Munir

Appl. Phys. Lett. 89, 163116 (2006); http://dx.doi.org/10.1063/1.2360934 (3 pages) | Cited 19 times

Online Publication Date: 18 October 2006

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The authors report on the consolidation of nanostructured bulk cubic zirconia with a grain size of about 15 nm and a relative density greater than 98%. This material exhibits a change in the conduction mechanism with considerable protonic conductivity when exposed to moisture. The marked reduction of the resistivity of zirconia at low temperatures brings it to a level comparable to that typical of other protonic conductors, but with the advantage of superior mechanical and chemical stabilities.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.46.Hk Nanocrystals
73.63.Bd Nanocrystalline materials

Nanopatterning of multiferroic BiFeO3 using “soft” electron beam lithography

Tao Sun, Zixiao Pan, Vinayak P. Dravid, Zhaoyu Wang, Min-Feng Yu, and Jin Wang

Appl. Phys. Lett. 89, 163117 (2006); http://dx.doi.org/10.1063/1.2364117 (3 pages) | Cited 11 times

Online Publication Date: 18 October 2006

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The authors report fabrication of multiferroic BiFeO3 (BFO) by the soft electron beam lithography technique. BiFeO3 nanopatterns with less than 100 nm characteristic dimension are fabricated from its liquid-phase precursor on diverse substrates. The chemical constituents and phase purity are characterized by transmission electron microscopy. The ferroelectric behavior is confirmed by piezoresponse force microscopy. A saturation magnetization of about 10 emu/cm3 is observed, demonstrating the multiferroic characteristic of the BFO nanopatterns. Furthermore, the BFO nanolines pattened on SrTiO3 substrate exhibit a bamboolike structure, which can serve as an excellent model system for investigating the contribution of grain boundaries to the leakage current.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Size-dependent modifications of the Raman spectrum of rutile TiO2

Varghese Swamy, Barry C. Muddle, and Qing Dai

Appl. Phys. Lett. 89, 163118 (2006); http://dx.doi.org/10.1063/1.2364123 (3 pages) | Cited 36 times

Online Publication Date: 18 October 2006

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Crystallite-size-dependent variations in the Raman spectrum of rutile TiO2 have been characterized and compared with those of the well-investigated rutile SnO2. For an average crystallite size below ∼ 25 nm, the Raman spectrum of rutile TiO2 nanocrystals displays an additional low-frequency, possibly surface vibrational, mode at ∼ 105 cm−1. The disorder-activated, high-frequency surface modes seen in the Raman spectrum of rutile SnO2 nanocrystals are absent. The Eg and A1g vibrational modes of rutile TiO2 show systematic redshifts, broadening, and intensity reductions with decreasing crystallite size, which are consistent with phonon confinement behavior. A phonon confinement model provides reasonable crystallite size quantification, as in the case of rutile SnO2 and RuO2.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Hk Nanocrystals
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.30.Hv Other nonmetallic inorganics
68.35.Ja Surface and interface dynamics and vibrations

Magnetic field sensing scheme using CoFeB/MgO/CoFeB tunneling junction with superparamagnetic CoFeB layer

Youngman Jang, Chunghee Nam, J. Y. Kim, B. K. Cho, Y. J. Cho, and T. W. Kim

Appl. Phys. Lett. 89, 163119 (2006); http://dx.doi.org/10.1063/1.2370876 (3 pages) | Cited 20 times

Online Publication Date: 18 October 2006

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The authors investigated the tunneling magnetoresistance (TMR) of CoFeB/MgO/CoFeB tunnel junctions by varying the thickness (tCoFeB) of the top CoFeB layer. Linear and hysteresis-free switching was observed in junctions with tCoFeB ⩽ 10 Å, while normal tunneling behavior occurred for tCoFeB>10 Å. The field sensitivity and the sensing field range were found to be controlled by varying the thickness of the sensing layer. This finding means that the magnetic tunneling junction (MTJ) provides a scheme for magnetic field sensing, which has a simple sensor design and low power consumption. The magnetic properties of the sensing layer with tCoFeB ⩽ 10 Å were found to show the characteristics of superparamagnetism. Although the detailed mechanism of TMR in MTJs with a superparamagnetic layer is not fully understood at present, this phenomenon is observed repeatedly. Therefore, this sensing scheme would be an alternative method for overcoming the problems in magnetic sensors with a crossed magnetization pattern.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Contact transfer of aligned carbon nanotube arrays onto conducting substrates

Ashavani Kumar, Victor L. Pushparaj, Swastik Kar, Omkaram Nalamasu, Pulickel M. Ajayan, and Rajashree Baskaran

Appl. Phys. Lett. 89, 163120 (2006); http://dx.doi.org/10.1063/1.2356899 (3 pages) | Cited 21 times

Online Publication Date: 19 October 2006

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The authors demonstrate the fabrication of different architectures of carbon nanotubes on conducting substrates via contact transfer of nanotubes using low temperature solders. Lithographically patterned multiwalled carbon nanotube arrays grown on silica substrates by chemical vapor deposition methods are transferred onto solder coated substrates. Both negative and positive patterns can be obtained by changing the printing parameters. Good wetting and electrical contacts are confirmed by measuring their field emission properties. This method can be used to construct nanotube structures of different shapes and dimensions over large areas on substrates of choice and could be a feasible process to integrate nanotubes into various devices.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Lk Nanocontacts
68.08.Bc Wetting
79.70.+q Field emission, ionization, evaporation, and desorption

Transport in carbon nanotube p-i-n diodes

Ken Bosnick, Nathan Gabor, and Paul McEuen

Appl. Phys. Lett. 89, 163121 (2006); http://dx.doi.org/10.1063/1.2360895 (3 pages) | Cited 15 times

Online Publication Date: 19 October 2006

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Single-walled carbon nanotube diodes are fabricated in a split-gate geometry with electron (n) and hole (p) regions separated by a central region. With the central region gated p or n type the diodes “leak” at low voltages, likely due to tunneling across the smaller depletion region. With the central region intrinsic, nearly ideal diode behavior is observed. Comparison to theory for a one-dimensional diode yields the band gap of the tube and the transmission coefficient through the junction. In reverse bias, the breakdown voltage depends weakly on temperature and nanotube diameter. Comparisons are made to predictions for Zener tunneling and avalanche breakdown.
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85.30.Kk Junction diodes
85.35.Kt Nanotube devices
72.20.Ht High-field and nonlinear effects

Surface polarization enhancement in (Pb0.25Ba0.15Sr0.6)TiO3 nanotubes

Wei Liu, Xiaohua Sun, Hongwei Han, Meiya Li, and Xing-Zhong Zhao

Appl. Phys. Lett. 89, 163122 (2006); http://dx.doi.org/10.1063/1.2364454 (3 pages) | Cited 11 times

Online Publication Date: 20 October 2006

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(Pb0.25Ba0.15Sr0.6)TiO3 (PBST) nanotube arrays were prepared using porous anodic aluminum oxide (AAO) template from PBST sol solution. Electron microscope results showed that uniform length and diameter of PBST nanotubes were obtained and that the diameter and length of PBST nanotubes were dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrated that PBST nanotubes were composed of perovskite nanocrystals. Comparison between nanotube and nanofilm polarization results showed that enhanced polarization existed in PBST nanotubes. A mechanism has been proposed to explain this polarization enhancement effect.
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77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.46.Fg Nanotubes
68.37.Nq Low energy electron microscopy (LEEM)

High-performance, hysteresis-free carbon nanotube field-effect transistors via directed assembly

Stephen A. McGill, Saleem G. Rao, Pradeep Manandhar, Peng Xiong, and Seunghun Hong

Appl. Phys. Lett. 89, 163123 (2006); http://dx.doi.org/10.1063/1.2364461 (3 pages) | Cited 28 times

Online Publication Date: 20 October 2006

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High-performance, single-wall carbon nanotube field-effect transistors (SWCNT-FETs) are fabricated using directed assembly and mass-produced carbon nanotubes (CNTs). These FETs exhibit operating characteristics comparable to state-of-the-art devices, and the process provides a route to large-scale functional CNT circuit assembly that circumvents problems inherent in processes relying on chemical vapor deposition. Furthermore, the integration of hydrophobic self-assembled monolayers in the device structure eliminates the primary source of gating hysteresis in SWCNT-FETs; this leads to hysteresis-free FET operation while exposing unmodified nanotube surfaces to ambient air.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Origin of high oscillator strength in green-emitting InGaN/GaN nanocolumns

Y. Kawakami, S. Suzuki, A. Kaneta, M. Funato, A. Kikuchi, and K. Kishino

Appl. Phys. Lett. 89, 163124 (2006); http://dx.doi.org/10.1063/1.2363958 (3 pages) | Cited 28 times

Online Publication Date: 20 October 2006

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Optical characterization has been performed on an InGaN/GaN nanocolumn structure grown by nitrogen plasma assisted molecular beam epitaxy not only in macroscopic configuration but also in a microscopic one that can be assessed to a single nanocolumn. The photoluminescence (PL) decay monitored at 500 nm is fitted with a double exponential curve, which has lifetimes of 0.67 and 4.33 ns at 13 K. These values are two orders of magnitude smaller than those taken at the same wavelength in conventional InGaN/GaN quantum wells (QWs) grown toward the C orientation. PL detection of each single nanocolumn was achieved using a mechanical lift-off technique. The results indicate that the very broad, macroscopically observed PL spectrum is due to the sum of the sharp PL spectrum from each nanocolumn, the peak energy of which fluctuates. Moreover, unlike conventional QWs, the blueshift of a single nanocolumn is negligibly small under higher photoexcitation. These findings suggest that carrier localization as well as the piezoelectric polarization field is suppressed in InGaN/GaN nanocolumns.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Cr III-V semiconductors
77.22.Ej Polarization and depolarization

In situ studies of semiconductor nanowire growth using optical reflectometry

T. Clement, S. Ingole, S. Ketharanathan, Jeff Drucker, and S. T. Picraux

Appl. Phys. Lett. 89, 163125 (2006); http://dx.doi.org/10.1063/1.2364121 (3 pages) | Cited 14 times

Online Publication Date: 20 October 2006

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The authors report the use of in situ optical reflectometry to determine the incubation time for the onset of growth, mean growth rate, and average length of Si nanowires during chemical vapor deposition vapor-liquid-solid synthesis. Results for the constructive and destructive interferences of 635 nm linearly polarized laser light scattering from growing nanowire layers are compared to simulations. This real time optical reflectance approach is shown to quantitatively determine nanowire growth rates as well as reveal a pressure dependence for the time to nucleate nanowire growth.
Show PACS
68.65.La Quantum wires (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Lt Quantum wires
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