The magnetic-induced dielectric responses of BiFeO3 (BFO) thin films were measured at the X -band microwave frequency ranged from 7 to 12.5 GHz. The measurement was given initially by a high-precision cavity microwave...
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A series of demonstrations and laboratory exercises have been developed to teach fundamental concepts in the thermal and fluid sciences of the undergraduate engineering curriculum. This material is part of an educatio...
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We have been developing a new approach to layered hybrid (inorganic/organic) photovoltaic materials for fabrication by Roll-to-Roll (R2R) manufacturing. In this report, we combine the low cost and processability of or...
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We have been developing a new approach to layered hybrid (inorganic/organic) photovoltaic materials for fabrication by Roll-to-Roll (R2R) manufacturing. In this report, we combine the low cost and processability of organic electrically conducting polymers with the efficiency of dye sensitized titanium dioxide, semi-conductor quantum dots (CdSe) self-assembled on layered clay materials (Laponite) onto indium tin oxide coated flexible polyethylene terephthalate (PET) substrates. We have shown electron transfer, guest-guest and host-guest interactions, charge separation, spectral line broadening, and quenching of fluorescence signals which indicate electronic coupling of the dye [Ru(bpy)3]2+ on a CdSe nanocrystal and titanium dioxide nanoparticles. Scanning electron microscopy and atomic force microscopy demonstrate successful nanoparticle formation and thin film self-assembly, as well as surface morphology and polymer thickness.
The formation and dynamics of spatially extended compositional domains in multicomponent lipid membranes both in vivo and in vitro lie at the heart of many important biological and biophysical phenomena. While the the...
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The formation and dynamics of spatially extended compositional domains in multicomponent lipid membranes both in vivo and in vitro lie at the heart of many important biological and biophysical phenomena. While the thermodynamic basis for domain formation has been explored extensively in the past, the roles of membrane and exterior fluid hydrodynamics on domain formation kinetics have received less attention. A case in point is the impact of hydrodynamics on the dynamics of compositional heterogeneities in lipid membranes in the vicinity of a critical point. In this Rapid Communication it is argued that the asymptotic dynamic behavior of a lipid membrane system in the vicinity of a critical point is strongly influenced by hydrodynamic interactions. More specifically, a mode-coupling argument is developed which predicts a scaling behavior of lipid transport coefficients near the critical point for both symmetric and asymmetric bilayers immersed in a bulk fluid.
We present an improved methodology for a thermal transient method enabling simultaneous measurement of thermal conductivity and specific heat of nanoscale structures with one-dimensional heat flow. The temporal respon...
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We present an improved methodology for a thermal transient method enabling simultaneous measurement of thermal conductivity and specific heat of nanoscale structures with one-dimensional heat flow. The temporal response of a sample to finite duration heat pulse inputs for both short (1 ns) and long (5μs) pulses is analyzed and exploited to deduce the thermal properties. Excellent agreement has been obtained between the recovered physical parameters and computational simulations.
We report on the measurement of the thermal conductivity of Si/Si0.8Ge0.2 multilayers on Si substrates through a variation of the 3? method. We exploit the frequency dependent variation of the thermal wave, through in...
We report on the measurement of the thermal conductivity of Si/Si0.8Ge0.2 multilayers on Si substrates through a variation of the 3? method. We exploit the frequency dependent variation of the thermal wave, through invoking the thermal penetration depth (TPD), which is inversely proportional to the frequency. Consequently, spectral measurements covering decades of frequency were used to finely probe the substrate and the overlying Si and Si0.8Ge0.2 thin film layers. Both in-phase and out-of phase measurements yielded comparable values of the thermal conductivity in the range of 3-5 W/mK, much lower than the reported bulk values. Our results provide proof of the potential of multilayered media to be used for reduced thermal conductance applications such as thermoelectrics, heat insulation etc.
A thermodynamic model was developed to understand the role of charge compensation at the interlayer interfaces in compositionally graded monodomain ferroelectric multilayers. The polarization mismatch between the ferr...
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A thermodynamic model was developed to understand the role of charge compensation at the interlayer interfaces in compositionally graded monodomain ferroelectric multilayers. The polarization mismatch between the ferroelectric layers generates depoling fields with the polarization in each layer varying from its bulk uncoupled value as to adapt to the electrical boundary conditions. By treating the strength of the electrostatic field as a phenomenological parameter, it is shown that if there are localized charges to compensate for the polarization mismatch and relax the depolarization fields, ferroelectric layers behave independently of each other and exhibit a dielectric response that can be described as the sum of their corresponding intrinsic uncoupled dielectric properties. For perfectly insulating heterostructures with no localized charges, the depolarization field is minimized by lowering the polarization difference between layers, yielding a ferroelectric multilayer that behaves as if it were a single ferroelectric material. There exists an optimum value of coupling strength at which average polarization of the multilayer is maximized. Furthermore, ferroelectric multilayers may display a colossal dielectric response dependant upon the interlayer electrostatic interactions.
LaBO3 (B=Mn, Fe, Co, and Ni) perovskites form a family of materials of significant interest for cathodes of solid oxide fuel cells (SOFCs). In this paper ab initio methods are used to study both bulk and surface prope...
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LaBO3 (B=Mn, Fe, Co, and Ni) perovskites form a family of materials of significant interest for cathodes of solid oxide fuel cells (SOFCs). In this paper ab initio methods are used to study both bulk and surface properties of relevance for SOFCs, including vacancy formation and oxygen binding energies. A thermodynamic approach and the density functional theory plus U method are combined to obtain energies relevant for SOFC conditions (T≈800 °C, PO2≈0.2 atm). The impact of varying Ueff (Ueff=U−J) on energy and electronic structure is explored in detail and it is shown that optimal Ueff values yield significantly better agreement with experimental energies than Ueff=0 (which corresponds to the standard generalized gradient approximation). LaBO3 oxygen vacancy formation energies are predicted to be in the order Fe>Mn>Co>Ni (where the largest implies most difficult to form a vacancy). It is shown that (001) BO2 terminated surfaces have 1–2 eV lower vacancy formation energies and therefore far higher vacancy concentrations than the bulk. The stable surface species at low temperature are predicted to be the superoxide O2− for B=Mn, Fe, Co and a peroxide O22− with a surface oxygen for B=Ni. Entropy effects are predicted to stabilize the monomer oxygen surface state for all B cations at higher temperatures. Overall oxygen coverage of the (001) BO2 surface is predicted to be quite low at SOFC operating conditions. These results will aid in understanding the oxygen reduction reaction on perovskite SOFC cathodes.
In this work we report on structural and optical properties of ZnO-MgO alloys. The alloys were synthesized using the combustion and co-precipitation methods, forming solid solutions of ZnO powders with MgO. SEM measur...
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ISBN:
(纸本)9781615673056
In this work we report on structural and optical properties of ZnO-MgO alloys. The alloys were synthesized using the combustion and co-precipitation methods, forming solid solutions of ZnO powders with MgO. SEM measurements show that the powders have sizes on the order of tens of nanometers, and XRD measurements indícate that the compounds produced are solid solutions of MgO in the ZnO lattice. The bandgaps of these solid solutions, as determined from reflectance measurements, increase with increasing MgO concentration. The luminescence measurements show emission from the bound exciton and from defects in the lattice. The excitonic emission shifts te higher energies as the MgO concentration increases.
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