Microwave performance of high-density bulk MgB2

We have performed microwave measurements on superconducting hot-isostatically- pressed (HIPed) bulk MgB2 using a parallel-plate resonator technique. The high density and strength of the HIPed material allowed preparation of samples with mirror-like surfaces for microwave measurements. The microwave surface resistance decreased by about 40% at 20 K when the root-mean-square surface roughness was reduced from 220 nm to 110 nm through surface-polishing and ion-milling. The surface resistance was independent of surface microwave magnetic field at least up to 4 Oe and below 30 K. We attribute this behavior, and the overall low surface resistance (~0.8 mOhms at 10 GHz and 20 K), to the high density of our samples and the absence of weak links between grains

Electrical Conductances and association constants in dilute aqueous NdCl\textsubscript{3} solutions from 298 to 523 K along an isobar of 25 MPa

Electrical measurements were performed in dilute aqueous NdCl3 solutions from 298 to 523 K along the 25 MPa isobar to obtain limiting conductances and association constants. The specific conductance data were estimated using a continuous flow cell and a Markov Chain Monte Carlo (MCMC) correction algorithm. The limiting conductances for the salts in water were derived by regressing the mean spherical approximation (MSA) conductance model and speciation analyses based on the MCMC algorithm and the Deep Earth Water (DEW) model. The limiting conductances derived from the experimental data agree well with a predictive correlation proposed by Smolyakov, Anderko, and Lencka. Only the first association constant between neodymium and chloride could be derived at low temperatures (< 373 K) due to the apparent large statistical uncertainty of the second association constant. Above 373 K, both association constants could be derived and show a reasonable agreement with Migdisov and Williams-Jones and Gammons et al.Comment: 34 pages, 8 figures, to be submitted as an articl

Size-Dependent Silicon Epitaxy at Mesoscale Dimensions

New discoveries on collective processes in materials fabrication and performance are emerging in the mesoscopic size regime between the nanoscale, where atomistic effects dominate, and the macroscale, where bulk-like behavior rules. For semiconductor electronics and photonics, dimensional control of the architecture in this regime is the limiting factor for device performance. Epitaxial crystal growth is the major tool enabling simultaneous control of the dimensions and properties of such architectures. Although size-dependent effects have been studied for many small-scale systems, they have not been reported for the epitaxial growth of Si crystalline surfaces. Here, we show a strong dependence of epitaxial growth rates on size for nano to microscale radial wires and planar stripes. A model for this unexpected size-dependent vapor phase epitaxy behavior at small dimensions suggests that these effects are universal and result from an enhanced surface desorption of the silane (SiH₄) growth precursor near facet edges. Introducing phosphorus or boron dopants during the silicon epitaxy further decreases the growth rates and, for phosphorus, gives rise to a critical layer thickness for single crystalline epitaxial growth. This previously unknown mesoscopic size-dependent growth effect at mesoscopic dimensions points to a new mechanism in vapor phase growth and promises greater control of advanced device geometries