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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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Vertical quantum dot with a vertically coupled charge detector

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha

Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages) | Cited 2 times

Online Publication Date: 22 January 2008

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We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to the electrostatic coupling to the dot. The charge state of the vertical dot was detected, starting from zero electrons. The sensitivity of the charge detector was comparable to that previously reported for lateral dots with nearby quantum point contacts.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
06.30.Ka Basic electromagnetic quantities

Measuring the electrical characteristics of individual junctions in the SnO2 capped ZnO nanowire arrays on Zn substrate

Y. Liu, S. Wang, Z. Y. Zhang, L.-M. Peng, L. Shi, and Quan Li

Appl. Phys. Lett. 92, 033102 (2008); http://dx.doi.org/10.1063/1.2837060 (3 pages) | Cited 4 times

Online Publication Date: 23 January 2008

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Direct measurements on electrical characteristics have been carried out in situ inside a scanning electron microscope using a multiple nanoprobe system on individual SnO2 capped ZnO nanowires (NWs) within a NW film on a Zn substrate. It is shown that while good Ohmic contacts can be made at Zn–ZnO NW and ZnO NW–SnO2 cap (when heavily doped with Zn) junctions, the overall I-V characteristics of the Zn–ZnO–SnO2 junction system differ significantly among different NWs, suggesting doping inhomogeneity in the NW film.
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73.63.Nm Quantum wires
72.80.Ey III-V and II-VI semiconductors

Magnetic molecules made of nitrogen or boron-doped fullerenes

Chih-Kai Yang

Appl. Phys. Lett. 92, 033103 (2008); http://dx.doi.org/10.1063/1.2837182 (3 pages) | Cited 5 times

Online Publication Date: 23 January 2008

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By using density functional theory, we investigate the electronic structure of a fullerene C60 molecule doped with a nitrogen atom on its surface. We find that the impurity is strongly bonded to the carbon cage and the C60N molecule has a large magnetic moment of 3.00μB. We also study the adsorption of a boron atom on the fullerene. The bonding is not as strong but still provides a fairly stable structure. Most importantly, the C60B molecule possesses a magnetic moment of 0.99μB. Both molecular magnets should be useful for the application in magnetic detection, quantum information, and spintronics.
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75.50.Xx Molecular magnets
75.30.Cr Saturation moments and magnetic susceptibilities
71.20.Tx Fullerenes and related materials; intercalation compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.43.Mn Adsorption kinetics

Critical clearance and lubricant instability at the head-disk interface of a disk drive

Rohit P. Ambekar, David B. Bogy, Qing Dai, and Bruno Marchon

Appl. Phys. Lett. 92, 033104 (2008); http://dx.doi.org/10.1063/1.2837187 (3 pages) | Cited 19 times

Online Publication Date: 23 January 2008

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We report experimental data that suggest the existence of a critical clearance between the flying head and the disk in a hard disk drive, below which significant lubricant transfer from the disk to the slider takes place. This phenomenon is interpreted as originating from dewetting instabilities brought about by molecular interactions with the slider. A model that reproduces the onset of instability is presented.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Terahertz detection in single wall carbon nanotubes

K. Fu, R. Zannoni, C. Chan, S. H. Adams, J. Nicholson, E. Polizzi, and K. S. Yngvesson

Appl. Phys. Lett. 92, 033105 (2008); http://dx.doi.org/10.1063/1.2837188 (3 pages) | Cited 15 times

Online Publication Date: 23 January 2008

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It is reported that terahertz radiation from 0.69 to 2.54 THz has been sensitively detected in a device consisting of bundles of carbon nanotubes containing single wall metallic carbon nanotubes, quasioptically coupled through a lithographically fabricated antenna, and a silicon lens. The measured data are consistent with a bolometric detection process in the metallic tubes and the devices show promise for operation well above 4.2 K.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Enhanced optical nonlinearity of surfactant-capped CdS quantum dots embedded in an optically transparent polystyrene thin film

Y. Gao, A. Tonizzo, A. Walser, M. Potasek, and R. Dorsinville

Appl. Phys. Lett. 92, 033106 (2008); http://dx.doi.org/10.1063/1.2833689 (3 pages) | Cited 12 times

Online Publication Date: 24 January 2008

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Nanocomposites of surfactant-capped CdS quantum dots embedded in polystyrene thin film have been prepared and characterized by z-scan measurements. Large values of the two- and three-photon absorption coefficients were observed at 532 nm (252 cm/GW) and 1064 nm (160 cm3/GW2). The cross sections of absorption were ∼ 1×10−44 cm4 s/photon (532 nm) and 8×10−73 cm6 s2/photon2 (1064 nm). These results are among the highest values of nonlinear absorption reported and orders of magnitude larger than CdS quantum dots capped by inorganic materials or in other matrix material. The high multiphoton absorption suggests that this class of materials is extremely promising for optical applications.
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78.67.Hc Quantum dots
42.65.-k Nonlinear optics

Synthesis and interfacial phenomena in ultra-thin yttria-doped zirconia films grown by alloy oxidation under photon irradiation

Masaru Tsuchiya and Shriram Ramanathan

Appl. Phys. Lett. 92, 033107 (2008); http://dx.doi.org/10.1063/1.2837194 (3 pages) | Cited 3 times

Online Publication Date: 24 January 2008

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We report on synthesis, structural evolution, and high temperature properties of ultrathin yttria-doped-zirconia (YDZ) films grown by alloy oxidation under ultraviolet (UV) irradiation. From high-resolution studies on interfacial layer growth kinetics, we found that oxygen diffusivity maximum in UV-YDZ film is located at higher yttria concentration than that in thermally oxidized films. It is likely that the oxygen-rich nature of UV-grown films enabled by photon irradiation is responsible for the observed differences. The results demonstrate routes for synthesis of oxide films with controlled structure and stoichiometry.
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81.15.Aa Theory and models of film growth
81.65.Mq Oxidation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

The so-called dry laser cleaning governed by humidity at the nanometer scale

D. Grojo, Ph. Delaporte, M. Sentis, O. H. Pakarinen, and A. S. Foster

Appl. Phys. Lett. 92, 033108 (2008); http://dx.doi.org/10.1063/1.2832766 (3 pages) | Cited 5 times

Online Publication Date: 25 January 2008

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Illumination with single nanosecond pulses leads to the detachment of silica particles with 250 nm radii from silicon surfaces. We identify two laser-energy dependent cleaning regimes by time-of-flight particle-scattering diagnostics. For the higher energies, the ejection of particles is produced by nanoscale ablation due to the laser field enhancement at the particle-surface interface. The damage-free regime at lower energy is shown to be governed by the residual water molecules, which are inevitably trapped on the materials. We discuss the great importance that the humidity plays on the cleaning force and on the adhesion in the experiments.
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42.62.-b Laser applications
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Confinement induces both higher free volume and lower molecular mobility in glycerol

Duncan Kilburn, Paul E. Sokol, Victoria García Sakai, and M. Ashraf Alam

Appl. Phys. Lett. 92, 033109 (2008); http://dx.doi.org/10.1063/1.2835903 (3 pages) | Cited 7 times

Online Publication Date: 25 January 2008

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We report measurements of the local free volume and mobility of a glass-forming liquid (glycerol) confined in a mesoporous silica glass. The lower molecular mobility in confinement, measured by neutron scattering spectroscopy, is accompanied by a higher mean free volume size between molecules, measured by positron annihilation lifetime spectroscopy. The confined liquid appears to be perturbed to such an extent that the normally observed free volume/mobility relationship is reversed. This study shows that these effects originate locally at a molecular level.
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61.43.Fs Glasses
34.80.Uv Positron scattering

Photoluminescence thermal quenching in three-dimensional multilayer Si/SiGe nanostructures

E.-K. Lee, L. Tsybeskov, and T. I. Kamins

Appl. Phys. Lett. 92, 033110 (2008); http://dx.doi.org/10.1063/1.2837184 (3 pages) | Cited 6 times

Online Publication Date: 25 January 2008

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We find that in Si/SiGe three-dimensional multilayer nanostructures, photoluminescence intensity as a function of temperature depends on the excitation intensity. The experimental results are explained using a model where electron-hole separation and nonradiative recombination is controlled by a competition between hole tunneling and thermally activated hole diffusion over the valence band energy barriers at Si/SiGe heterointerfaces.
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78.55.Ap Elemental semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.40.Gh Other heat and thermomechanical treatments
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Gk Tunneling
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.Ac Multilayers

Step bunch assisted two dimensional ordering of In0.19Ga0.81As/GaAs quantum dots on vicinal GaAs(001) surfaces

M. Hanke, Zh. M. Wang, Yu. I. Mazur, J. H. Lee, G. J. Salamo, and M. Schmidbauer

Appl. Phys. Lett. 92, 033111 (2008); http://dx.doi.org/10.1063/1.2838453 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2008

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We have investigated the self-organized, step bunch assisted formation of In0.19Ga0.81As/GaAs quantum dots in vertical superlattices consisting of one, four, eight, and ten periods. Samples were grown by molecular beam epitaxy on vicinal 2°A and 2°B GaAs(001) substrates. Those with miscut along the [1math0] (2°B) exclusively show step bunches of an aspect ratio larger than 10 but without the formation of quantum dots. This highly linear pattern is improved during subsequent periods as proved by high resolution x-ray diffraction and grazing incidence diffraction. On the other hand, a miscut along the [110] (2°A) initially causes a crosslike pattern of step bunches, which finally becomes a two-dimensional arrangement of individual quantum dots.
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81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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