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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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Transformation of diamond nanoparticles into onion-like carbon by electron irradiation studied directly inside an ultrahigh-vacuum transmission electron microscope

J. Hiraki, H. Mori, E. Taguchi, H. Yasuda, H. Kinoshita, and N. Ohmae

Appl. Phys. Lett. 86, 223101 (2005); http://dx.doi.org/10.1063/1.1935047 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2005

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In situ observation of the transformation of diamond nanoparticles (DNP) into onion-like carbon (OLC) was made during electron-beam irradiation inside an ultrahigh-vacuum transmission electron microscope at 300 kV with 8.5×1023 e/m2. 5 nm DNP changed into OLC within about 10 min of irradiation, while 20 nm DNP did not change to OLC but to graphite. Therefore, the size effect is critical to the formation of OLC. The mechanism of formation of OLC from DNP is discussed.
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61.80.Fe Electron and positron radiation effects
61.82.Rx Nanocrystalline materials
64.70.K- Solid-solid transitions
61.46.-w Structure of nanoscale materials

Nucleation of β‐FeSi2 nanostructures at pinned step bunches on the Si(111) surface

R. P. Brady, A. S. Sharma, R. L. Giblet, R. J. Cottier, T. D. Golding, and J. M. Perez

Appl. Phys. Lett. 86, 223102 (2005); http://dx.doi.org/10.1063/1.1940128 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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We report the preferential nucleation and synthesis of β‐FeSi2 nanostructures at pinned step bunches on the Si(111) surface. The nanostructures are synthesized by depositing Fe on Si at room temperature and subsequent annealing. The surface topography is studied using scanning tunneling microscopy and atomic force microscopy. The size, shape and orientation of the nanostructures indicate that the phase is the semiconducting β‐FeSi2 phase.
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81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Spatially resolved cathodoluminescence of GaN nanostructures fabricated by photoelectrochemical etching

C. Díaz-Guerra, J. Piqueras, V. Popa, A. Cojocaru, and I. M. Tiginyanu

Appl. Phys. Lett. 86, 223103 (2005); http://dx.doi.org/10.1063/1.1940734 (3 pages) | Cited 8 times

Online Publication Date: 24 May 2005

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The emission properties of GaN nanostructures created by photoelectrochemical etching have been investigated by cathodoluminescence (CL) in the scanning electron microscope. Columnar structures with diameters of 150–250 nm formed near the surface of the as-grown GaN layers branch into nanowires with diameters of 20–60 nm, while islands with coral-like relief were observed at the bottom of the etched areas. CL emission of the observed nanostructures is dominated by free electron to acceptor transitions. Local CL spectra provide direct evidence of the existence of either compressive or tensile stress in different nanostructures. No free exciton luminescence was observed in GaN nanowires, supporting their relation to threading dislocations.
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81.05.Ea III-V semiconductors
81.07.Vb Quantum wires
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.65.Cf Surface cleaning, etching, patterning
82.45.-h Electrochemistry and electrophoresis
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires

Highly sensitive optical response of optical fiber long period gratings to nanometer-thick ionic self-assembled multilayers

Zhiyong Wang, J. R. Heflin, Rogers H. Stolen, and Siddharth Ramachandran

Appl. Phys. Lett. 86, 223104 (2005); http://dx.doi.org/10.1063/1.1940735 (3 pages) | Cited 22 times

Online Publication Date: 24 May 2005

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Ionic self-assembled multilayers deposited on long period fiber gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Fine control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition technique for fine-tuning grating properties. In addition a variety of biological and chemical sensing agents can easily be incorporated into these films, which makes this an attractive platform for realization of high-performance LPG-based sensors.
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42.81.Wg Other fiber-optical devices
81.07.Bc Nanocrystalline materials
42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.16.Dn Self-assembly

Dynamic range of nanotube- and nanowire-based electromechanical systems

H. W. Ch. Postma, I. Kozinsky, A. Husain, and M. L. Roukes

Appl. Phys. Lett. 86, 223105 (2005); http://dx.doi.org/10.1063/1.1929098 (3 pages) | Cited 20 times

Online Publication Date: 25 May 2005

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Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [∝dmath] of the dynamic range on aspect ratio.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Ultraviolet lasing and time-resolved photoluminescence of well-aligned ZnO nanorod arrays

Xinhai Han, Guanzhong Wang, Qingtao Wang, Li Cao, Ruibin Liu, Bingsuo Zou, and J. G. Hou

Appl. Phys. Lett. 86, 223106 (2005); http://dx.doi.org/10.1063/1.1941477 (3 pages) | Cited 46 times

Online Publication Date: 25 May 2005

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Well-aligned ZnO nanorod arrays were synthesized by thermal evaporation of ZnO powder on ZnO thin films. The nanorods are almost the same length of 5.5 μm and well-oriented perpendicular to the substrates. The time-integrated and time-resolved photoluminescence spectra of the nanorod arrays revealed the existence of laser action with the excitation threshold of 130 μJ/cm2 and emission lifetime of less than 30 ps. At the excitation fluence a little below threshold, the decay fits well to a biexponential function with a fast component ( ∼ 80 ps) and a slower component ( ∼ 360 ps).
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors

Infrared absorption study of hydrogen incorporation in thick nanocrystalline diamond films

C. J. Tang, A. J. Neves, and M. C. Carmo

Appl. Phys. Lett. 86, 223107 (2005); http://dx.doi.org/10.1063/1.1941457 (3 pages) | Cited 11 times

Online Publication Date: 25 May 2005

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We present an infrared (IR) optical absorbance study of hydrogen incorporation in nanocrystalline diamond films. The thick nanocrystalline diamond films were synthesized by microwave plasma-assisted chemical vapor deposition and a high growth rate about 3.0 μm/h was achieved. The morphology, phase quality, and hydrogen incorporation were assessed by means of scanning electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Large amount of hydrogen bonded to nanocrystalline diamond is clearly evidenced by the huge CH stretching band in the FTIR spectrum. The mechanism of hydrogen incorporation is discussed in light of the growth mechanism of nanocrystalline diamond. This suggests the potential of nanocrystalline diamond for IR electro-optical device applications.
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78.30.Hv Other nonmetallic inorganics
81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
78.66.-w Optical properties of specific thin films
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Metallic–nonmetallic transition on the conductivity temperature dependence of multiwall carbon nanotubes

Yong Sun, Tatsuro Miyasato, Kenta Kirimoto, and Michiko Kusunoki

Appl. Phys. Lett. 86, 223108 (2005); http://dx.doi.org/10.1063/1.1927696 (3 pages) | Cited 5 times

Online Publication Date: 25 May 2005

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We applied a noncontacting surface acoustic wave technique to measure the conductivity of aligned multiwall carbon nanotube films. By changing intensities of the parallel and perpendicular electric field components at the surface of the film sample, we observed different temperature dependencies of the conductivity. It was found that the temperature dependence of the conductivity parallel to the tube axis is comparable to that of a single-wall carbon nanotube, namely, there is a metallic–nonmetallic transition at temperature of 280 K. On the other hand, the temperature dependence of the conductivity perpendicular to the tube axis is similar to that of a graphene sheet.
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73.63.Fg Nanotubes
81.07.De Nanotubes
72.60.+g Mixed conductivity and conductivity transitions
68.35.Iv Acoustical properties

Unidirectional self-assembling of SiGe Stranski-Krastanow islands on Si(113)

M. Hanke, T. Boeck, A.-K. Gerlitzke, F. Syrowatka, and F. Heyroth

Appl. Phys. Lett. 86, 223109 (2005); http://dx.doi.org/10.1063/1.1943490 (3 pages) | Cited 4 times

Online Publication Date: 26 May 2005

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We report on a dedicated two-step liquid phase epitaxy (LPE) experiment yielding ensembles of SiGe/Si(113) nanoscale islands with unidirectional ordering along the [math10] direction. Initial homoepitaxy of silicon on a polished Si(113) wafer from an indium solution at 930 °C results in a highly regular pattern consisting of (111) and (116) facets. For the subsequent heteroepitaxy with SiGe the solvent has been exchanged for bismuth since it enables an LPE process at considerably lower temperatures around 590 °C, and thus preserves the initial template which strictly enforces the linear self-assembling of SiGe islands. However, with respect to the initial grooves the established island–island correlation length perpendicular to them has been increased by a factor of about 1.6 indicating that not every groove acts as a nucleation place. This can be explained by finite element calculations on the three-dimensional deformation field which proves energetically favorable nucleation sites in the island vicinity within and infavorable places in adjacent rows.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Effects of thin GaAs insertion layer on InAs/(InGaAs)/InP(001) quantum dots grown by metalorganic chemical vapor deposition

Kwangmin Park, Pilkyung Moon, Eungjin Ahn, Sukwon Hong, Euijoon Yoon, Jeong Won Yoon, Hyeonsik Cheong, and Jean-Pierre Leburton

Appl. Phys. Lett. 86, 223110 (2005); http://dx.doi.org/10.1063/1.1943494 (3 pages) | Cited 5 times

Online Publication Date: 26 May 2005

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We studied the influence of a thin GaAs insertion layer (5–10 monolayers) on the optical properties of InAs QDs grown by metalorganic chemical vapor deposition. The insertion of a 10 monolayer (ML) thick GaAs layer on the InAs QDs led to significant photoluminescence blueshifts of 54 and 111 meV when they were grown on InGaAs and InP, respectively. In addition, a narrowing of full width at half maximum was observed when the thicker GaAs insertion layers and higher overgrowth temperature for the top capping layer were used. These results can be applied for tuning the emission wavelength around 1.55 μm for optical fiber communication.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Exploring extreme particle density and size for blue photoluminescence from as-deposited amorphous Si-in-SiNx films

Cheng Liu, Chaorong Li, Ailing Ji, Libo Ma, Yongqian Wang, and Zexian Cao

Appl. Phys. Lett. 86, 223111 (2005); http://dx.doi.org/10.1063/1.1943499 (3 pages) | Cited 12 times

Online Publication Date: 26 May 2005

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The number density of silicon particles in a silicon compound matrix that are smaller than 3.0 nm is subject to a few restrictive factors. We report the growth of amorphous Si-in-SiNx thin films containing small particles (down to 2.2 nm) of a density over 1.4×1013/cm2, as determined from transmission electron microscopic graphs. Intense blue photoluminescence centered at 440 nm could be measured in such as-deposited films, and the external quantum efficiency was estimated to be at the 0.1–1.0 % level by comparing against that from a high-quality GaN sample. Rapid annealing for two minutes at 500 °C induced only slight enhancement of photoluminescence intensity. Further effort to increase the particle density led to particle conglomeration, and continued reduction of particle size endangers the survival of nanoparticles in matrix material. Clues for a more realistic mechanism are discussed based on the correlation of photoluminescence features to the microstructure of the films.
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81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
78.55.Qr Amorphous materials; glasses and other disordered solids
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.47.Fg Semiconductor surfaces
61.43.Dq Amorphous semiconductors, metals, and alloys
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)
78.40.Fy Semiconductors

Dynamics of coupled vortices in layered magnetic nanodots

K. Yu. Guslienko, K. S. Buchanan, S. D. Bader, and V. Novosad

Appl. Phys. Lett. 86, 223112 (2005); http://dx.doi.org/10.1063/1.1929078 (3 pages) | Cited 21 times

Online Publication Date: 26 May 2005

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The spin dynamics are calculated for a model system consisting of two ferromagnetic (F) cylindrical dots, each with a magnetic vortex ground state, are separated by a nonmagnetic spacer (N). The effects of interlayer magnetostatic interactions on the vortex dynamics were explored by applying the equations of motion for the vortex core positions. For trilayer F/N/F dots with opposite chiralities and the same core polarizations two eigenmodes are predicted. One mode is in the sub-GHz range for submicron dot diameters and corresponds to quasicircular rotation of the cores about the dot center. A second mode in the MHz range corresponds to a small amplitude rotation of the mean core position.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Controllable p and n doping of single-walled carbon nanotubes by encapsulation of organic molecules and fullerene: A theoretical investigation

WanZhen Liang, Jinlong Yang, and Jin Sun

Appl. Phys. Lett. 86, 223113 (2005); http://dx.doi.org/10.1063/1.1941476 (3 pages) | Cited 5 times

Online Publication Date: 26 May 2005

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We report theoretical investigations on the changes in optical and electronic properties of single-walled carbon nanotubes (SWNTs) induced by chemical doping with organic molecules or fullerene C60. It is found that doping alters the electronic and optical properties of parent SWNTs and both p- and n-type doping can be realized on SWNTs by encapsulating organic molecules which have large electron affinities or small ionization energies. The doping-induced optical features and additions of donor∕acceptor states to the density of states provide compelling evidence that the standard rigid-band model breaks down and the band-structure changes play an important role on the solid state properties of doped SWNTs.
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71.20.Tx Fullerenes and related materials; intercalation compounds
78.67.Ch Nanotubes
71.55.Ht Other nonmetals

Field emission properties of macroscopic single-walled carbon nanotube strands

Chang Liu, Yu Tong, Hui-Ming Cheng, Dmitri Golberg, and Yoshio Bando

Appl. Phys. Lett. 86, 223114 (2005); http://dx.doi.org/10.1063/1.1944229 (3 pages) | Cited 17 times

Online Publication Date: 27 May 2005

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Centimeter-long strands of well-aligned single-walled carbon nanotubes (SWNT) synthesized by a hydrogen–argon arc discharge method were employed for the investigation of their field emission properties. These macroscopically long aligned SWNT strands showed advantages of low turn on electric field, high current density, good emission stability, and easy manipulation over the disoriented SWNT samples. The field enhancement factor of the strand is basically linearly proportional to its macro aspect ratio when the microstructure of the emission tip is kept unchanged. The present SWNT strands can be valuable candidates for the applications as electron-emitting sources in various electronic devices.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes
52.77.-j Plasma applications
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