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9 May 2005

Volume 86, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 86, 191102 (2005); http://dx.doi.org/10.1063/1.1922084 (3 pages)

Nir Dahan, Avi Niv, Gabriel Biener, Vladimir Kleiner, and Erez Hasman
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Optical properties of highly ordered AlN nanowire arrays grown on sapphire substrate

Qing Zhao, Hongzhou Zhang, Xiangyu Xu, Zhe Wang, Jun Xu, Dapeng Yu, Guohua Li, and Fuhai Su

Appl. Phys. Lett. 86, 193101 (2005); http://dx.doi.org/10.1063/1.1922577 (3 pages) | Cited 38 times

Online Publication Date: 2 May 2005

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Highly ordered AlN nanowire arrays were synthesized via a simple physical vapor deposition method on sapphire substrate. The nanowires have an extremely sharp tip <10 nm, with the average length around 3 μm. Raman spectroscopy analysis on the AlN nanowire arrays revealed that the lifetime of the phonons is shorter than that in bulk AlN. The transmission spectra of the AlN nanowires showed a blueshift ∼ 0.27 eV at the absorption edge with that of the bulk AlN, which is closely related to the small size of the nanowires.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
78.40.Fy Semiconductors

Nanoscale friction mapping

Nikhil S. Tambe and Bharat Bhushan

Appl. Phys. Lett. 86, 193102 (2005); http://dx.doi.org/10.1063/1.1923179 (3 pages)

Online Publication Date: 2 May 2005

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Contrary to classical friction laws postulated by Amontons and Coulomb centuries ago, nanoscale friction force is found to be strongly dependent on the normal load and sliding velocity. Many materials, coatings, and lubricants that have wide applications in micro/nanoelectromechanical systems show reversals in friction behavior corresponding to transitions between different friction mechanisms. We have developed a contour map to provide a fundamental insight into the normal load and sliding velocity dependence of friction force and thus help identify and classify dominant friction mechanisms.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Role of phonon scattering in carbon nanotube field-effect transistors

Jing Guo and Mark Lundstrom

Appl. Phys. Lett. 86, 193103 (2005); http://dx.doi.org/10.1063/1.1923183 (3 pages) | Cited 35 times

Online Publication Date: 2 May 2005

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The role of phonon scattering in carbon nanotube field-effect transistors (CNTFETs) is explored by solving the Boltzmann transport equation using the Monte Carlo method. The results show that elastic scattering in a short-channel CNTFET has a small effect on the source-drain current due to the long elastic mean-free path (mfp) ( ∼ 1 μm). If elastic scattering with a short mfp were to exist in a CNTFET, the on current would be severely degraded due to the one-dimensional channel geometry. At high drain bias, optical phonon scattering, which has a much shorter mfp ( ∼ 10 nm), is expected to dominate, even in a short-channel CNTFET. We find, however, that inelastic optical scattering has a small effect in CNTFETs under modest gate bias.
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85.30.Tv Field effect devices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.22.Lp Collective excitations
81.07.De Nanotubes

Role of surface-to-volume ratio of metal nanoparticles in optical properties of Cu:Al2O3 nanocomposite films

J. Requejo-Isidro, R. del Coso, J. Solis, J. Gonzalo, and C. N. Afonso

Appl. Phys. Lett. 86, 193104 (2005); http://dx.doi.org/10.1063/1.1923198 (3 pages) | Cited 3 times

Online Publication Date: 2 May 2005

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We report on the role of the surface-to-volume ratio of Cu nanoparticles (NPs) both in the linear and nonlinear optical properties of Cu:Al2O3 nanocomposite films. The results show that when the shape of the NPs deviates sufficiently from that of a sphere, the increase of the fraction of metal atoms present at the surface (NS) with respect to the total amount of atoms (NT) in the NP leads to a substantial reduction of the enhancement of the local field. As a consequence, for NS/NT values above a certain threshold ( ≈ 0.4–0.5), the surface–plasma resonance is smeared out and the nonlinear optical response of the nanocomposite film becomes very weak and independent of the dimensions of the NPs or their volume fraction in the matrix.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Sq Composite materials
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
81.15.Fg Pulsed laser ablation deposition

Stress-driven formation of Si nanowires

S. M. Prokes and Stephen Arnold

Appl. Phys. Lett. 86, 193105 (2005); http://dx.doi.org/10.1063/1.1925756 (3 pages) | Cited 11 times

Online Publication Date: 3 May 2005

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We present an alternate mechanism for the growth of Si nanowires directly from a silicon substrate, without the use of a metal catalyst, silicon vapor or chemical vapor deposition (CVD) gasses. Since the silicon wires grow directly from the silicon substrate, they do not need to be manipulated or aligned for subsequent applications. Wires in the 20–50 nm diameter range with lengths over 80 μm can be easily grown by this technique. The critical parameters in the growth of these nanowires are the surface treatment and the carrier gas used. A model is proposed involving stress-driven wire growth, which is enhanced by surface Si atom diffusion due to the presence of hydrogen gas.
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81.05.Cy Elemental semiconductors
81.07.Vb Quantum wires
68.47.Fg Semiconductor surfaces
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
68.35.Fx Diffusion; interface formation
81.65.-b Surface treatments

CdSe nanocrystal quantum-dot memory

M. D. Fischbein and M. Drndic

Appl. Phys. Lett. 86, 193106 (2005); http://dx.doi.org/10.1063/1.1923189 (3 pages) | Cited 44 times

Online Publication Date: 3 May 2005

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Memory effects in the electronic transport in CdSe nanocrystal (NC) quantum-dot arrays have been observed and characterized. Conduction through a NC array can be reduced with a negative voltage and then restored with a positive voltage. Light can also be used to restore or even increase the NC array conduction. We have studied the switching of the conduction in CdSe NC arrays and found the behavior to be highly sensitive to the value and duration of the laser and voltage pulses.
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81.07.Ta Quantum dots
81.07.Bc Nanocrystalline materials

An ultrasmall amplitude operation of dynamic force microscopy with second flexural mode

Shigeki Kawai, Shin-ichi Kitamura, Dai Kobayashi, Sakae Meguro, and Hideki Kawakatsu

Appl. Phys. Lett. 86, 193107 (2005); http://dx.doi.org/10.1063/1.1923200 (3 pages) | Cited 33 times

Online Publication Date: 3 May 2005

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Selective detection of short-range interaction forces was carried out with the second flexural mode of a commercially available dynamic mode cantilever. A higher mode has a higher spring constant and a lower mechanical quality factor, which are suitable for the small amplitude operation in dynamic force microscopy. With 0.70 Å amplitude of the second flexural mode, atomically resolved constant frequency shift images of the Si(111)−7×7 reconstructed surface were obtained. The ultrasmall amplitude operation enabled imaging with high stability, due to the detection of the interaction force gradients at relatively long distances from the sample surface, and is an effective way to observe reactive surfaces while avoiding modifications and damaging of the tip and the sample.
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82.80.-d Chemical analysis and related physical methods of analysis

True molecular resolution in liquid by frequency-modulation atomic force microscopy

Takeshi Fukuma, Kei Kobayashi, Kazumi Matsushige, and Hirofumi Yamada

Appl. Phys. Lett. 86, 193108 (2005); http://dx.doi.org/10.1063/1.1925780 (3 pages) | Cited 45 times

Online Publication Date: 4 May 2005

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The increasing attention directed towards nanobiological science requires high-resolution imaging tools for the liquid environment. We have been successful in recording molecular-resolution images of polydiacetylene in water with the frequency-modulation atomic force microscopy (FM-AFM). With the oscillation amplitude of a force-sensing cantilever reduced to 0.20 nm, we were able to overcome the large frequency noise due to the low Q-factor of cantilever resonance in water. We have obtained vertical and lateral resolutions of 10 pm and 250 pm, respectively. This method enables nondestructive imaging of soft biological samples with a load force on the order of 1 pN.
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87.64.Dz Scanning tunneling and atomic force microscopy
87.15.-v Biomolecules: structure and physical properties
81.70.Fy Nondestructive testing: optical methods

Optoelectronic characteristics of single CdS nanobelts

Q. H. Li, T. Gao, and T. H. Wang

Appl. Phys. Lett. 86, 193109 (2005); http://dx.doi.org/10.1063/1.1923186 (3 pages) | Cited 23 times

Online Publication Date: 4 May 2005

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Optoelectronic properties of single CdS nanobelts are investigated by performing transport measurements with different laser ON/OFF circles. The current increases linearly with the bias voltage in the dark, and superlinearly under illumination. The superlinear increase can be related to the enhanced mobility due to the partial release of surface adsorbates under illumination. The current jumps up by five orders of magnitude upon turning on the laser with an intensity of 0.3 W/cm2 within 91 ms and decreases by five orders 6 ms just after turning off the laser. The high sensitivity and fast response in the visible range indicate potential applications of CdS nanobelts in realizing optoelectronic switches.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
61.82.Rx Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.43.Mn Adsorption kinetics
72.20.Fr Low-field transport and mobility; piezoresistance

Diffraction element assisted lithography: Pattern control for photonic crystal fabrication

Cheng Lu, X. K. Hu, I. V. Mitchell, and R. H. Lipson

Appl. Phys. Lett. 86, 193110 (2005); http://dx.doi.org/10.1063/1.1924894 (3 pages) | Cited 6 times

Online Publication Date: 4 May 2005

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Near-field diffraction element assisted lithography or DEAL has been used to fabricate two-dimensional lattice patterns in a photoresist. Specifically, a diffraction element was used to prepattern the coherent output of a laser prior to its capture in a photoresist. The pattern symmetry and spacing can be readily modified with the same experimental arrangement since the near-field diffraction pattern strongly depends on the nature of the diffractive element and the distance between the element and the photoresist. The patterns that are formed can serve as masks for patterning high index materials to create photonic band gap crystals. Alternatively, they have the potential to behave as two-dimensional photonic band gap arrays provided the polymer used exhibits a large enough index contrast.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.25.Fx Diffraction and scattering
71.20.Rv Polymers and organic compounds
42.70.Qs Photonic bandgap materials

Self-assembled growth and enhanced blue emission of SiOxNy-capped silicon nanowire arrays

T. Qiu, X. L. Wu, G. J. Wan, Y. F. Mei, G. G. Siu, and Paul K. Chu

Appl. Phys. Lett. 86, 193111 (2005); http://dx.doi.org/10.1063/1.1929069 (3 pages) | Cited 14 times

Online Publication Date: 5 May 2005

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Unique structured SiOxNy-capped Si nanowire arrays were fabricated via electroless metal deposition on α-SiOxNy-covered Si wafer in ionic silver HF solution through selective chemical etching. A self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation process are associated with the formation of the SiOxNy-capped Si nanowire arrays. An enhanced blue photoluminescence band has been recorded. Emission and excitation spectral analyses suggest that generation of photoexcited carriers takes place mainly in the quantum confined Si nanowires, whereas their radiative recombination occurs in the Si–N binding states of SiOxNy nanocaps.
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81.07.Vb Quantum wires
81.16.Dn Self-assembly
81.15.Pq Electrodeposition, electroplating
68.55.A- Nucleation and growth
81.65.Cf Surface cleaning, etching, patterning
78.55.Ap Elemental semiconductors
66.30.-h Diffusion in solids
68.47.Fg Semiconductor surfaces

Focused-ion-beam platinum nanopatterning for GaN nanowires: Ohmic contacts and patterned growth

C. Y. Nam, J. Y. Kim, and J. E. Fischer

Appl. Phys. Lett. 86, 193112 (2005); http://dx.doi.org/10.1063/1.1925775 (3 pages) | Cited 28 times

Online Publication Date: 5 May 2005

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Nanopatterned Pt by Ga+ focused ion beam (FIB) decomposition of an organometallic precursor forms low resistance ohmic contacts on 40–70 nm diameter GaN nanowires (NWs) grown by thermal reaction of Ga2O3 and NH3. With no intentional doping, the wires are presumed to be n type. Thus, the linear I‐V behavior is surprising since evaporated Pt usually forms Schottky barriers on n GaN. Ohmic behavior was not obtained for 130–140 diameter wires, even with thicker Pt contacts. A second application of FIB Pt nanopatterning was demonstrated by position-selective growth of GaN NWs on Pt catalyst dots. NW locations and density are defined by the position, size, and thickness of the Pt deposit. Combining these techniques provides a versatile platform for nanostructure research and development.
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81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.40.Ns Metal-nonmetal contacts
81.16.Rf Micro- and nanoscale pattern formation
68.65.La Quantum wires (patterned in quantum wells)
73.30.+y Surface double layers, Schottky barriers, and work functions
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Quantum confinement in Volmer–Weber-type self-assembled ZnO nanocrystals

Tae-Bong Hur, Yoon-Hwae Hwang, and Hyung-Kook Kim

Appl. Phys. Lett. 86, 193113 (2005); http://dx.doi.org/10.1063/1.1921357 (3 pages) | Cited 12 times

Online Publication Date: 5 May 2005

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We have studied the quantum confinement effect on Volmer–Weber-type self-assembled ZnO nanocrystals. Volmer–Weber-type self-assembled ZnO nanocrystals were grown on the Pt(111) substrate by using a rf-magnetron sputtering method and were confirmed by the Auger electron spectroscopy. The free exciton transition energies of 57-, 38-, and 24‐nm-size nanocrystals were found to be roughly 3.298, 3.311, and 3.337 eV, respectively, by photoluminescence measuremnets at room temperature. The blueshift of the photoluminescence peak energy of ZnO nanocrystals of 24 nm in diameter roughly varied by 40 meV compared to bulk ZnO.
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78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
79.20.Fv Electron impact: Auger emission

Optical excitation of nanoelectromechanical oscillators

B. Ilic, S. Krylov, K. Aubin, R. Reichenbach, and H. G. Craighead

Appl. Phys. Lett. 86, 193114 (2005); http://dx.doi.org/10.1063/1.1919395 (3 pages) | Cited 44 times

Online Publication Date: 6 May 2005

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We report a method of optical excitation of nanomechanical cantilever-type oscillators. The periodic driving signal with a controlled modulation amplitude was provided by a 415 nm diode laser, wherein the laser spot was located at some distance away from the clamped end of the cantilever. The measured resonant response of the cantilever was obtained at distances in excess of 160 μm with varying oscillator dimensions. The effectiveness of the driving mode is studied for different combinations of materials, namely Si–SiO2 and Si3N4–SiO2. These observations were considered within the theoretical framework of the mechanism of heat transfer. We show that measurable amplitudes of vibrations can be obtained at temperature changes much less than 1°.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.55.Px Semiconductor lasers; laser diodes

Quantum dot lasers based on a stacked and strain-compensated active region grown by metal-organic chemical vapor deposition

N. Nuntawong, Y. C. Xin, S. Birudavolu, P. S. Wong, S. Huang, C. P. Hains, and D. L. Huffaker

Appl. Phys. Lett. 86, 193115 (2005); http://dx.doi.org/10.1063/1.1926413 (3 pages) | Cited 24 times

Online Publication Date: 6 May 2005

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We demonstrate an InAs/GaAs quantum dot (QD) laser based on a strain-compensated, three-stack active region. Each layer of the stacked QD active region contains a thin GaP (Δao = −3.8%) tensile layer embedded in a GaAs matrix to partially compensate the compressive strain of the InAs (Δao = 7%) QD layer. The optimized GaP thickness is ∼ 4 MLs and results in a 36% reduction of compressive strain in our device structure. Atomic force microscope images, room-temperature photoluminescence, and x-ray diffraction confirm that strain compensation improves both structural and optical device properties. Room-temperature ground state lasing at λ = 1.249 μm, Jth = 550 A/cm2 has been demonstrated.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
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