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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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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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Chip-scale atomic magnetometer

Peter D. D. Schwindt, Svenja Knappe, Vishal Shah, Leo Hollberg, John Kitching, Li-Anne Liew, and John Moreland

Appl. Phys. Lett. 85, 6409 (2004); http://dx.doi.org/10.1063/1.1839274 (3 pages) | Cited 94 times

Online Publication Date: 17 December 2004

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Using the techniques of microelectromechanical systems, we have constructed a small low-power magnetic sensor based on alkali atoms. We use a coherent population trapping resonance to probe the interaction of the atoms’ magnetic moment with a magnetic field, and we detect changes in the magnetic flux density with a sensitivity of 50 pT Hz−1∕2 at 10 Hz. The magnetic sensor has a size of 12 mm3 and dissipates 195 mW of power. Further improvements in size, power dissipation, and magnetic field sensitivity are immediately foreseeable, and such a device could provide a hand-held battery-operated magnetometer with an atom shot-noise limited sensitivity of 0.05 pT Hz−1∕2.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.55.Ge Magnetometers for magnetic field measurements
85.75.Ss Magnetic field sensors using spin polarized transport
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Effects of intrinsic layer thickness on solar cell parameters of organic p‐i‐n heterojunction photovoltaic cells

Tetsuya Taima, Masayuki Chikamatsu, Yuji Yoshida, Kazuhiro Saito, and Kiyoshi Yase

Appl. Phys. Lett. 85, 6412 (2004); http://dx.doi.org/10.1063/1.1841479 (3 pages) | Cited 28 times

Online Publication Date: 17 December 2004

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We fabricated organic p‐i‐n heterojunction photovoltaic cells of a zinc phthalocyanine (ZnPc)∕1:1 codeposition (ZnPc:C60)∕C60 structure. We investigated the effects of the intrinsic (i-) layer thickness on the photovoltaic properties. The thickness was changed from 0 nm (=p‐n heterojunction) to 50 nm (=all i-layer) with the total thickness of 50 nm. While the short-circuit photocurrent increased with increasing the thickness, the fill factor showed the opposite tendency. Therefore, the power conversion efficiency showed a maximum (1.5%) at the thickness of 10 nm under air mass 1.5 global solar conditions. Device simulation based on idealized equivalent circuit of a solar cell demonstrates that the i-layer thickness is concerned in the series resistance of the cells.
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84.60.Jt Photoelectric conversion
85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects

High-pressure deuterium annealing for improving the reliability characteristics of silicon–oxide–nitride–oxide–silicon nonvolatile memory devices

Sangmoo Choi, Man Jang, Hokyung Park, Hyunsang Hwang, Sanghun Jeon, Juhyung Kim, and Chungwoo Kim

Appl. Phys. Lett. 85, 6415 (2004); http://dx.doi.org/10.1063/1.1842363 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2004

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We report the effects of high-pressure deuterium postmetallization annealing on the reliability characteristics of silicon–oxide–nitride–oxide–silicon nonvolatile memory devices. Compared with the control samples annealed in a conventional forming gas ambient (H2∕N2=4% ∕ 96%), the samples annealed in a high-pressure (10 atm) pure deuterium ambient show improved endurance and retention characteristics without the degradation of program/erase (P/E) speed. In addition, the high-pressure deuterium-annealed samples show a significantly reduced charge loss rate for the electron-stored state and the hole-stored state, before and after the P/E cycles. The improved reliability of the high-pressure deuterium-annealed samples can be explained by the significantly decreased interface trap density and the large kinetic isotope effect of deuterium, which reduces the generation of the interface trap density under the stress of the P/E cycles.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
73.40.Ty Semiconductor-insulator-semiconductor structures
61.72.Cc Kinetics of defect formation and annealing
85.40.Ls Metallization, contacts, interconnects; device isolation
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Protein patterning by micromachined silicon embossing on polymer surfaces

D. Goustouridis, K. Misiakos, P. S. Petrou, and S. E. Kakabakos

Appl. Phys. Lett. 85, 6418 (2004); http://dx.doi.org/10.1063/1.1841458 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2004

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An automated method for creating micron-sized patterns of different proteins is described. Unlike other methods, the process requires no masks, photochemichal reagents, or alignment. The basic tools are a motorized x–y stage, a pneumatic drive, and a micromachined silicon chip with an array of micron scale pyramids. Upon pressing the chip on a plastic slide, inverted pyramids are created on the polymer surface, exposing areas that have no previous coating and can adsorb proteins. The method is suitable for the fast and inexpensive fabrication of dense arrays of different proteins on appropriate substrates.
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87.14.E- Proteins
81.16.Rf Micro- and nanoscale pattern formation
87.15.M- Spectra of biomolecules
81.65.Cf Surface cleaning, etching, patterning
78.55.Kz Solid organic materials

Addressable micropost array for the dielectrophoretic manipulation of particles in fluid

T. P. Hunt, H. Lee, and R. M. Westervelt

Appl. Phys. Lett. 85, 6421 (2004); http://dx.doi.org/10.1063/1.1840109 (3 pages) | Cited 18 times

Online Publication Date: 17 December 2004

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A microfluidic device has been developed to trap and position neutral particles using dielectrophoresis. An array of microscale post shaped electrodes provides an inhomogeneous electric field. The voltage on each electrode can be independently controlled by a computer to trap and move particles in fluid above the micropost electrodes. Yeast cells and polystyrene spheres were trapped and moved, demonstrating both positive and negative dielectrophoresis.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.15.Tt Electrophoresis
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Nanoparticle-based microelectromechanical systems fabricated on plastic

Eric J. Wilhelm, Brian T. Neltner, and Joseph M. Jacobson

Appl. Phys. Lett. 85, 6424 (2004); http://dx.doi.org/10.1063/1.1842356 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2004

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In this letter, we demonstrate the additive fabrication of electrostatic actuators on polyimide plastic by offset liquid embossing. They are formed by printing a nanoparticle colloid of gold on a polyimide substrate and then under-etching the polyimide through patterned etch holes. Residual stresses in the released gold films cause the films to bend away from the substrate. These films can then be electrostatically attracted toward the substrate and used to modulate light. The actuators range in size from 45 to 100 μm and are controlled by electric fields of approximately 2 V∕μm, allowing switching at several hundred cycles per second.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
68.60.Bs Mechanical and acoustical properties

Chemical depth profile of passive oxide on stainless steel

D. H. Kim, H. H. Lee, S. S. Kim, H. C. Kang, D. Y. Noh, H. Kim, and S. K. Sinha

Appl. Phys. Lett. 85, 6427 (2004); http://dx.doi.org/10.1063/1.1842362 (3 pages) | Cited 5 times

Online Publication Date: 17 December 2004

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The chemical depth profile of the passive oxides formed on a stainless-steel surface (type 430, Fe–16.3%Cr) in pH 8.4 borate solution was obtained quantitatively by in situ anomalous x-ray reflectivity. The passive film consists of a Cr oxide inner layer and a Fe∕Cr oxide outer layer. The absence of Fe oxide underneath Cr oxide indicates that Cr oxide provides the passivity in stainless steel by inhibiting oxygen anion diffusion. The oxide grows by limited metallic cation transfer. The passivity breaks down in transpassive regime due to the oxidation of the Cr oxide to a soluble oxide.
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81.05.Bx Metals, semimetals, and alloys
81.65.Rv Passivation
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
81.65.Mq Oxidation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.80.Fk Electrochemical methods

Sensitivity reduction mechanisms in amorphous selenium photoconductive x-ray image detectors

M. Yunus, M. Zahangir Kabir, and S. O. Kasap

Appl. Phys. Lett. 85, 6430 (2004); http://dx.doi.org/10.1063/1.1841474 (3 pages) | Cited 10 times

Online Publication Date: 17 December 2004

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Sensitivity reduction in amorphous Se-based photoconductive x-ray image detectors due to previous exposures is studied by Monte Carlo simulation. Collected charge, hence x-ray sensitivity, is calculated by considering deep carrier trapping, taking into account the effects of trap filling, recombination between trapped and drifting carriers and the generation of x-ray induced new deep trap centers. Space charge effects on the electric field, and hence, the effects of electric field on electron hole pair generation and charge transport are also considered. The comparison of the model with the experimental data reveals that the recombination between trapped and oppositely charged drifting carriers and x-ray induced new deep trap centers are mainly responsible for the sensitivity reduction in biased a-Se-based x-ray detectors.
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07.85.-m X- and γ-ray instruments
87.59.-e X-ray imaging
71.55.Jv Disordered structures; amorphous and glassy solids
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