Scott K. McCall

Chemical vapor discrimination using a compact and low-power array of piezoresistive microcantilevers

A compact and low-power microcantilever-based sensor array has been developed and used to detect various chemical vapor analytes. In contrast to earlier micro-electro-mechanical systems (MEMS) array sensors, this device uses the static deflection of piezoresistive cantilevers due to the swelling of glassy polyolefin coatings during sorption of chemical vapors. To maximize the sensor response to a variety of chemical analytes, the polymers are selected based on their Hildebrand solubility parameters to span a wide range of chemical properties. We utilize a novel microcontact spotting method to reproducibly coat a single side of each cantilever in the array with the polymers. To demonstrate the utility of the sensor array we have reproducibly detected 11 chemical vapors, representing a breadth of chemical properties, in real time and over a wide range of vapor concentrations. We also report the detection of the chemical warfare agents (CWAs) VX and sulfur mustard (HD), representing the first published report of CWA vapor detection by a polymer-based, cantilever sensor array. Comparisons of the theoretical polymer/vapor partition coefficient to the experimental cantilever deflection responses show that, while general trends can be reasonably predicted, a simple linear relationship does not exist.

Evidence for Ligand-Induced Paramagnetism in CdSe Quantum Dots

We report evidence that paramagnetism in CdSe QDs can be induced via manipulation of the surface chemistry. Using SQUID magnetometry and X-ray absorption spectroscopy, we demonstrate that the paramagnetic behavior of the CdSe QDs can be varied by changing the ligand end-group functionality of the passivating layer. Contrary to previous reports, no evidence for ferromagnetism was observed. The results suggest that the paramagnetism is induced via pi back-bonding between Cd 4d orbtials and ligands with empty pi* orbitals.

Enhanced magnetic refrigeration capacity in phase separated manganites

Multiple phase transitions and magnetic phase coexistence lead to a negative magnetocaloric effect in a wide temperature range of ∼10–250 K in La0.215Pr0.41Ca0.375MnO3. A large fraction of the magnetocaloric effect originates from the low temperature phase separated state, which is composed of coexisting, magnetic field dependent charge ordered, and ferromagnetic regions. While the maximum isothermal entropy change is modest, the persistence of the field-dependent phase separated state over a ∼240 K temperature span yields a refrigeration capacity of ∼3.2 J/cm3. Materials with magnetic field dependent phase separation can therefore be used to improve regenerative magnetic refrigerators.

Magnetization and magnetotransport of LBaCo2O5.5(L=Gd, Eu) single crystals

The magnetization, resistivity, and magnetoresistance (MR) of single crystals of

An analytic model of thermal drift in piezoresistive microcantilever sensors

\mathrm{Gd}\mathrm{Ba}{\mathrm{Co}}_{2}{\mathrm{O}}_{5.5}

Gd5Si2Ge2 composite for magnetostrictive actuator applications

and

High performance aluminum–cerium alloys for high-temperature applications

\mathrm{Eu}\mathrm{Ba}{\mathrm{Co}}_{2}{\mathrm{O}}_{5.5}

Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ -Pu

are measured over a wide range of dc magnetic fields (up to

Casting Characteristics of High Cerium Content Aluminum Alloys

30\phantom{\rule{0.3em}{0ex}}\mathrm{T}

Characterization of Near Net-Shape Castable Rare Earth Modified Aluminum Alloys for High Temperature Application

) and temperature. In