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27 Dec 2004

Volume 85, Issue 26, pp. 6323-6432

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 6409 (2004); http://dx.doi.org/10.1063/1.1839274 (3 pages)

Peter D. D. Schwindt, Svenja Knappe, Vishal Shah, Leo Hollberg, John Kitching, Li-Anne Liew, and John Moreland
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Shapes of InAs quantum dots on InGaAs∕InP

Heedon Hwang, Sukho Yoon, Hyeok Kwon, Euijoon Yoon, Hong-Seung Kim, Jeong Yong Lee, and Benjamin Cho

Appl. Phys. Lett. 85, 6383 (2004); http://dx.doi.org/10.1063/1.1840123 (3 pages) | Cited 15 times

Online Publication Date: 17 December 2004

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InAs self-assembled quantum dots were grown on InGaAs lattice-matched on InP by metalorganic chemical vapor deposition. The facet formation on the dot was investigated by atomic force microscopy and transmission electron microscopy. The {136}-faceted InAs dots were elongated along either [1math0] or [math10] to form parallelogram-shaped islands analogous to hut cluster formation in SiGe∕Si quantum dots. Some parallelogram dots also exhibited {110} faceting, presumably on undergoing a shape transition toward dots with facets of higher symmetry.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)

Nanoscale chemical sensor based on organic thin-film transistors

Liang Wang, Daniel Fine, and Ananth Dodabalapur

Appl. Phys. Lett. 85, 6386 (2004); http://dx.doi.org/10.1063/1.1842364 (3 pages) | Cited 45 times

Online Publication Date: 17 December 2004

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Nanoscale organic thin-film transistors were fabricated to investigate their chemical sensing properties. The use of a four-terminal geometry ensures that the sensor active area is truly nanoscale, and eliminates undesirable spreading currents. The sensor response was markedly different in nanoscale sensors compared to large-area sensors for the same analyte–semiconductor combination. The chemical sensing mechanisms in both microscale and nanoscale transistors are briefly discussed.
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85.30.Tv Field effect devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Oxygen sensing characteristics of individual ZnO nanowire transistors

Q. H. Li, Y. X. Liang, Q. Wan, and T. H. Wang

Appl. Phys. Lett. 85, 6389 (2004); http://dx.doi.org/10.1063/1.1840116 (3 pages) | Cited 125 times

Online Publication Date: 17 December 2004

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Individual ZnO nanowire transistors are fabricated, and their sensing properties are investigated. The transistors show a carrier density of 2300 μm−1 and mobility up to 6.4 cm2∕V s, which are obtained from the ISD−VG curves. The threshold voltage shifts in the positive direction and the source-drain current decreases as ambient oxygen concentration increases. However, the opposite occurs when the transistors are under illumination. Surface adsorbates on the ZnO nanowires affect both the mobility and the carrier density. Our data are helpful in understanding the sensing mechanism of the gas sensors.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
72.20.Fr Low-field transport and mobility; piezoresistance
68.43.Mn Adsorption kinetics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials

Electrical probe storage using Joule heating in phase change media

S. Gidon, O. Lemonnier, B. Rolland, O. Bichet, C. Dressler, and Y. Samson

Appl. Phys. Lett. 85, 6392 (2004); http://dx.doi.org/10.1063/1.1834718 (3 pages) | Cited 48 times

Online Publication Date: 17 December 2004

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We demonstrate the feasibility of ultrahigh-density probe recording in chalcogenide-based phase change media. The multilayer medium has been optimized with respect to electrical, thermal, and tribological requirements. Design of the multilayer takes into account the nonlinear dependence of the electrical properties of the phase change layer with respect to both electrical field and temperature. Memory dots as small as 15 nm have been written and read repeatably. Data storage density of greater than Tbit∕in.2 density has been successfully achieved.
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42.79.Vb Optical storage systems, optical disks
64.70.K- Solid-solid transitions
72.80.Ng Disordered solids
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

CdSe self-assembled quantum dots with ZnCdMgSe barriers emitting throughout the visible spectrum

M. Noemi Perez-Paz, Xuecong Zhou, Martin Muñoz, Hong Lu, Mohammad Sohel, Maria C. Tamargo, Fleumingue Jean-Mary, and Daniel L. Akins

Appl. Phys. Lett. 85, 6395 (2004); http://dx.doi.org/10.1063/1.1834993 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2004

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Self-assembled quantum dots of CdSe with ZnCdMgSe barriers have been grown by molecular beam epitaxy on InP substrates. The optical and microstructural properties were investigated using photoluminescence (PL) and atomic force microscopy (AFM) measurements. Control and reproducibility of the quantum dot (QD) size leading to light emission throughout the entire visible spectrum range has been obtained by varying the CdSe deposition time. Longer CdSe deposition times result in a redshift of the PL peaks as a consequence of an increase of QD size. AFM studies demonstrate the presence of QDs in uncapped structures. A comparison of this QD system with CdSe∕ZnSe shows that not only the strain but also the chemical properties of the system play an important role in QD formation.
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81.07.Ta Quantum dots
81.05.Dz II-VI semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
68.37.Ps Atomic force microscopy (AFM)

Imaging using lateral bending modes of atomic force microscope cantilevers

A. Caron, U. Rabe, M. Reinstädtler, J. A. Turner, and W. Arnold

Appl. Phys. Lett. 85, 6398 (2004); http://dx.doi.org/10.1063/1.1833553 (3 pages) | Cited 12 times

Online Publication Date: 17 December 2004

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Using scanning probe techniques, surface properties such as shear stiffness and friction can be measured with a resolution in the nanometer range. The torsional deflection or buckling of atomic force microscope cantilevers has previously been used in order to measure the lateral forces acting on the tip. This letter shows that the flexural vibration modes of cantilevers oscillating in their width direction parallel to the sample surface can also be used for imaging. These lateral cantilever modes exhibit vertical deflection amplitudes if the cantilever is asymmetric in thickness direction, e.g., by a trapezoidal cross section.
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07.79.Lh Atomic force microscopes
46.35.+z Viscoelasticity, plasticity, viscoplasticity
46.32.+x Static buckling and instability
46.25.-y Static elasticity
46.55.+d Tribology and mechanical contacts
46.40.Ff Resonance, damping, and dynamic stability

Ge dot organization on Si substrates patterned by focused ion beam

A. Karmous, A. Cuenat, A. Ronda, I. Berbezier, S. Atha, and R. Hull

Appl. Phys. Lett. 85, 6401 (2004); http://dx.doi.org/10.1063/1.1828597 (3 pages) | Cited 20 times

Online Publication Date: 17 December 2004

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One of the major challenges for the reliable use of self-organization phenomena for device applications is to accurately position quantum dots on the surface. A promising way to get ordered dots is to use prepatterned substrates. We show that a combination of focused ion beam (FIB) prepatterned Si(001) substrates and self-assembled Ge quantum dots (QDs) leads to the precise placement of QDs. The technological advantages of this method are to control the Ge dots size and location, and to scale down the interdots distance to ∼20 nm. Regarding more fundamental aspects, the accurate control of nanopatterns characteristics allows us to investigate the influence of various experimental parameters on QDs formation. The process proposed consists mainly of three steps: (1) FIB nanopatterning; (2) ex situ cleaning of the FIB-patterned substrate in order to fully remove the Ga contamination before introduction into the molecular beam epitaxy (MBE) chamber; and (3) Ge deposition by solid source MBE. After optimization of the growth parameters, nicely ordered dense arrays of homogeneous QDs are obtained. QDs are organized on the edges of the FIB holes at high temperature or inside the holes at lower temperature. We suggest that two different mechanisms of Ge dots formation are responsible of these results: kinetically limited nucleation at low temperature and stress driven nucleation at higher temperature.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Gate-induced crossover from unconventional metals to Fermi liquids in multiwalled carbon nanotubes

Takayoshi Kanbara, Tatsuya Iwasa, Kazuhito Tsukagoshi, Yoshinobu Aoyagi, and Yoshihiro Iwasa

Appl. Phys. Lett. 85, 6404 (2004); http://dx.doi.org/10.1063/1.1842373 (3 pages) | Cited 6 times

Online Publication Date: 17 December 2004

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We observed an ambipolar behavior in multiwalled carbon nanotubes in a backgate configuration, which allowed us to perform systematic inspection of the low-temperature transport properties against gate voltage. The results revealed that a power-law temperature-dependent conductance, which is a sign of an unconventional metallic state, disappears when a high gate voltage is applied, and conductance becomes temperature independent, indicating a normal Fermi liquid state. This demonstrates a field effect tuning of electronic states in nanoscaled materials.
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73.63.Fg Nanotubes
85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Photoluminescence of GaAs nanowhiskers grown on Si substrate

V. Khorenko, I. Regolin, S. Neumann, W. Prost, F.-J. Tegude, and H. Wiggers

Appl. Phys. Lett. 85, 6407 (2004); http://dx.doi.org/10.1063/1.1841475 (2 pages) | Cited 14 times

Online Publication Date: 17 December 2004

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GaAs nanowhiskers were grown by metalorganic vapor-phase epitaxy on (111) Si substrates using the vapor-liquid-solid growth mode. The diameter of the nanowhiskers was defined by polydisperse catalytic Au nanoparticles in the range from 5 to 100 nm deposited on the Si substrate from the liquid phase. The low-temperature photoluminescence spectra exhibit a series of unresolved exciton-related transitions shifted to a shorter wavelength due to the quantization effects. Despite some structure defects, relatively high photoluminescence intensity and its linear dependence on the excitation power without saturation confirms the good material quality of fabricated GaAs nanowhiskers.
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81.07.Wx Nanopowders
81.05.Ea III-V semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Cr III-V semiconductors
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.22.Lp Collective excitations
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