23,415 research outputs found
Calibration of shielded microwave probes using bulk dielectrics
A stripline-type near-field microwave probe is microfabricated for microwave
impedance microscopy. Unlike the poorly shielded coplanar probe that senses the
sample tens of microns away, the stripline structure removes the stray fields
from the cantilever body and localizes the interaction only around the
focused-ion beam deposited Pt tip. The approaching curve of an oscillating tip
toward bulk dielectrics can be quantitatively simulated and fitted to the
finite-element analysis result. The peak signal of the approaching curve is a
measure of the sample dielectric constant and can be used to study unknown bulk
materials.Comment: 10 pages, 3 figure
Octet baryon magnetic moments from QCD sum rules
A comprehensive study is made for the magnetic moments of octet baryons in
the method of QCD sum rules. A complete set of QCD sum rules is derived using
the external field method and generalized interpolating fields. For each
member, three sum rules are constructed from three independent tensor
structures. They are analyzed in conjunction with the corresponding mass sum
rules. The performance of each of the sum rules is examined using the criteria
of OPE convergence and ground-state dominance, along with the role of the
transitions in intermediate states. Individual contributions from the u, d and
s quarks are isolated and their implications in the underlying dynamics are
explored. Valid sum rules are identified and their predictions are obtained.
The results are compared with experiment and previous calculations.Comment: 21 pages, 11 figures, 6 figures; added a reference, minor change in
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Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope
We present a detailed modeling and characterization of our scalable microwave
nanoprobe, which is a micro-fabricated cantilever-based scanning microwave
probe with separated excitation and sensing electrodes. Using finite-element
analysis, the tip-sample interaction is modeled as small impedance changes
between the tip electrode and the ground at our working frequencies near 1GHz.
The equivalent lumped elements of the cantilever can be determined by
transmission line simulation of the matching network, which routes the
cantilever signals to 50 Ohm feed lines. In the microwave electronics, the
background common-mode signal is cancelled before the amplifier stage so that
high sensitivity (below 1 atto-Farad capacitance changes) is obtained.
Experimental characterization of the microwave probes was performed on
ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or
topographical signals can be realized using different reflection modes of the
probe.Comment: 7 figure
N to transition amplitudes from QCD sum rules
We present a calculation of the N to electromagnetic transition
amplitudes using the method of QCD sum rules. A complete set of QCD sum rules
are derived for the entire family of transitions from the baryon octet to
decuplet. They are analyzed in conjunction with the corresponding mass sum
rules using a Monte-Carlo-based analysis procedure. The performance of each of
the sum rules is examined using the criteria of OPE convergence and
ground-state dominance, along with the role of the transitions in intermediate
states. Individual contributions from the u, d and s quarks are isolated and
their implications in the underlying dynamics are explored. Valid sum rules are
identified and their predictions are obtained. The results are compared with
experiment and other calculations.Comment: 18 pages, 8 figures, 7 tables. Updated references and Fig. 7 and Fig.
Transition magnetic moment of in QCD sum rules
The transition magnetic moment is computed in the
QCD sum rules approach. Three independent tensor structures are derived in the
external field method using generalized interpolating fields. They are analyzed
together with the and mass sum rules using a
Monte-Carlo-based analysis, with attention to OPE convergence, ground-state
dominance, and the role of the transitions in the intermediate states.
Relations between sum rules for magnetic moments of and
and sum rules for transition magnetic moment of are
also examined. Our best prediction for the transition magnetic moment is
. A comparison is made with other
calculations in the literature.Comment: 9 pages, 4 figures, 2 tables. Typos correcte
Synthesis of Zinc Carbonate Hydroxide Nanoparticles Using Microemulsion Process
In order to control the particle size and morphology, zinc carbonate hydroxide Zn5(CO3)2(OH)6 nanoparticles have been synthesized using a reverse microemulsion technique. The pseudo-ternary phase diagrams of the two microemulsion systems, prepared using CTAB/1-butanol/n-octane/aqueous phase system with the aqueous phase comprised of either zinc nitrate (Zn(NO3)2) or sodium carbonate (Na2CO3), were experimentally constructed. The nanoparticles synthesized by mixing of the two emulsion systems were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The nanoparticles were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Several important experimental parameters have been investigated for the ability to control particle size and morphology as the function of water/surfactant molar ratio (ω), water/oil molar ratio (S) and the initial concentration of reactants in the aqueous phase. Results indicate that ω values have the ability to affect the particle size and levels of aggregation, while S values had no apparent effect. In addition, the initial concentration of reactants in the aqueous phase was considered to be an important parameter as raising its values from 0.1M to 0.5M produced an unknown phase of zinc carbonate, exhibiting larger particle size with a unique flake like morphology
Microwave imaging of mesoscopic percolating network in a manganite thin film
Many unusual behaviors in complex oxides are deeply associated with the
spontaneous emergence of microscopic phase separation. Depending on the
underlying mechanism, the competing phases can form ordered or random patterns
at vastly different length scales. Using a microwave impedance microscope, we
observed an orientation-ordered percolating network in strained Nd0.5Sr0.5MnO3
thin films with a large period of 100 nm. The filamentary metallic domains
align preferentially along certain crystal axes of the substrate, suggesting
the anisotropic elastic strain as the key interaction in this system. The local
impedance maps provide microscopic electrical information of the hysteretic
behavior in strained thin film manganites, suggesting close connection between
the glassy order and the colossal magnetoresistance effects at low
temperatures.Comment: 4 pages,4 figure
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