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21 Feb 2013

Volume 113, Issue 7, Articles (07xxxx)

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J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt
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back to top Nanoscale Science and Design

Scale-and shape-dependent transport property of nanoporous materials

Sangil Hyun and Eunhae Koo

J. Appl. Phys. 113, 074301 (2013); http://dx.doi.org/10.1063/1.4790570 (7 pages)

Online Publication Date: 15 February 2013

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A cellular material was proposed as an ideal candidate for multifunctional material achieving various optimal properties in many length scales. The superior performances on mechanical, thermal, electrical, and fluidic properties have been explored in analytic, numerical, and experimental studies. Since the cellular materials have wide range of potential applications in microscopic devices, characterization in small length scale gains more attentions recently. For this assessment, the atomistic approach as well as continuum approach becomes crucial to characterize its performance in multiscales. One of the key multifunctional features of the nanoporous microstructures would be high fluidic performance. Some studies investigated macroscopic transport properties, but less has been done to address the scale- and shape-dependent transport properties for their microscopic fluidics applications. In this study, we investigated complex flow patterns and transport properties of porous structures in microscopic scales. To address the geometry-dependent transport properties, a non-equilibrium molecular dynamics was employed in the atomistic scale. Various flow channels in the porous materials were introduced to address the size and shape effect of the flow patterns in small length scales.
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47.56.+r Flows through porous media
47.61.-k Micro- and nano- scale flow phenomena
47.85.Np Fluidics
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Gt Powders, porous materials

Investigating the origin of intense photoluminescence in Si capping layer on Ge1−xSnx nanodots by transmission electron microscopy

Jun Kikkawa, Yoshiaki Nakamura, Norihito Fujinoki, and Masakazu Ichikawa

J. Appl. Phys. 113, 074302 (2013); http://dx.doi.org/10.1063/1.4792647 (6 pages)

Online Publication Date: 15 February 2013

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The authors investigated the annealing effects on atomic structures and elemental compositions in a stacking structure, Si capping layer on Ge1−xSnx nanodots on Si substrate covered with ultrathin SiO2 film, to clarify the origin of intense photoluminescence at ∼0.8 eV from the structure, using transmission electron microscopy. After the annealing, it was found that decay of Ge1−xSnx nanodots, formation of SiOx precipitates embedded in Si-rich Si1−xGex layer at the Si cap/Si substrate interface, formation of SnO2 nanoparticles on the oxidized surface of the Si capping layer, and morphological change of dislocations in the Si capping layer occur. Reaction products that appear as a result of the movement of dislocations can be related to the origin of intense photoluminescence.
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78.55.-m Photoluminescence, properties and materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Gh Other heat and thermomechanical treatments

Probing confined acoustic phonons in free standing small gold nanoparticles

Venu Mankad, Prafulla K. Jha, and T. R. Ravindran

J. Appl. Phys. 113, 074303 (2013); http://dx.doi.org/10.1063/1.4792654 (7 pages)

Online Publication Date: 20 February 2013

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Polarized and depolarized spectra from gold (Au) nanoparticles of different sizes are investigated in the small size range, between 3 and 7 nm, using low frequency Raman spectroscopy. Acoustic vibrations of the free-standing Au nanoparticles are demonstrated with frequencies ranging from 5 to 35 cm−1, opening the way to the development of the acoustic resonators. A blue shift in the phonon peaks along with the broadening is observed with a decrease in particle size. Comparison of the measured frequencies with vibrational dynamics calculation and an examination as from the transmission electron microscopy results ascertain that the low frequency phonon modes are due to acoustic phonon quantization. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar (l = 2) vibrations of the spheroidal mode due to plasmon mediated acoustic vibrations in Au nanoparticles.
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81.05.Bx Metals, semimetals, and alloys
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Er Solid metals and alloys
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Hot-spot detection and calibration of a scanning thermal probe with a noise thermometry gold wire sample

Angelo Gaitas, Steven Wolgast, Elizabeth Covington, and Cagliyan Kurdak

J. Appl. Phys. 113, 074304 (2013); http://dx.doi.org/10.1063/1.4792656 (6 pages)

Online Publication Date: 20 February 2013

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Measuring the temperature profile of a nanoscale sample using scanning thermal microscopy is challenging due to a scanning probe's non-uniform heating. In order to address this challenge, we have developed a calibration sample consisting of a 1-μm wide gold wire, which can be heated electrically by a small bias current. The Joule heating in the calibration sample wire is characterized using noise thermometry. A thermal probe was scanned in contact over the gold wire and measured temperature changes as small as 0.4 K, corresponding to 17 ppm changes in probe resistance. The non-uniformity of the probe's temperature profile during a typical scan necessitated the introduction of a temperature conversion factor, η, which is defined as the ratio of the average temperature change of the probe with respect to the temperature change of the substrate. The conversion factor was calculated to be 0.035 ± 0.007. Finite element analysis simulations indicate a strong correlation between thermal probe sensitivity and probe tip curvature, suggesting that the sensitivity of the thermal probe can be improved by increasing the probe tip curvature, though at the expense of the spatial resolution provided by sharper tips. Simulations also indicate that a bow-tie metallization design could yield an additional 5- to 7-fold increase in sensitivity.
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07.20.Dt Thermometers
07.79.-v Scanning probe microscopes and components

Imbibition of polystyrene melts in aligned carbon nanotube arrays

Marina Khaneft, Bernd Stühn, Jörg Engstler, Hermann Tempel, Jörg J. Schneider, Tobias Pirzer, and Thorsten Hugel

J. Appl. Phys. 113, 074305 (2013); http://dx.doi.org/10.1063/1.4793087 (10 pages)

Online Publication Date: 21 February 2013

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We analyze the polymer filling mechanism in composites containing highly ordered and vertically aligned carbon nanotube (CNT) arrays. CNTs are obtained by a template assisted chemical vapor deposition (CVD) method. Different forms of the arrays are studied with one or two carbon layers on top and bottom surface of the array, or freestanding CNTs. Investigation is done by small-angle X-ray scattering (SAXS) in combination with electron microscopy (TEM and SEM) and atomic force microscopy. Tubes are of 40 μm length and 40/90 nm diameter. The original order of the template is only locally preserved in the CNT array. Imbibition of polymer is achieved in the inside of CNTs as well as in between. It modifies the local order of the tubes. We compare structural changes of CNT arrays caused by polymer infiltration. Filling kinetics is followed with time-resolved SAXS. We find two well separated processes that are related to the formation of a precursor film and subsequent partial completion of the imbibition process.
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81.07.De Nanotubes
47.56.+r Flows through porous media
78.70.Ck X-ray scattering
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