We have studied structural and superconducting properties of MgB 2 thin films doped with carbon during the hybrid physical-chemical vapor deposition process. A carbon-containing metalorganic precursor bis(methylcyclopentadienyl)magnesium was added to the carrier gas to achieve carbon doping. As the amount of carbon in the film increases, the resistivity increases, T c decreases, and the upper critical field increases dramatically as compared to clean films. The selffield J c in the carbon doped film is lower than that in the clean film, but J c remains relatively high to much higher magnetic fields, indicating stronger pinning. Structurally, the doped films are textured with columnar nano-grains and highly resistive amorphous areas at the grain boundaries. The carbon doping approach can be used to produce MgB 2 materials for high magnetic-field applications. a)Electronic address: avp11@psu.edu

We report a large normal-state magnetoresistance with temperature-dependent anisotropy in very clean epitaxial MgB2 thin films (residual resistivity much smaller than 1 microOmega cm) grown by hybrid physical-chemical vapor deposition. The magnetoresistance shows a complex dependence on the orientation of the applied magnetic field, with a large magnetoresistance (Delta(rho)/(rho)0=136%) observed for the field H perpendicular ab plane. The angular dependence changes dramatically as the temperature is increased, and at high temperatures the magnetoresistance maximum changes to H||ab. We attribute the large magnetoresistance and the evolution of its angular dependence with temperature to the multiple bands with different Fermi surface topology in MgB2 and the relative scattering rates of the sigma and pi bands, which vary with temperature due to stronger electron-phonon coupling for the sigma bands.

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We report on structural and superconducting properties of round MgB2 coated-conductor fibers deposited by hybrid physical-chemical vapor deposition on SiC fibers. The coating is polycrystalline and composed of elongated crystallites with dimensions less than 1μm in length and 0.2μm in width. The pure MgB2 fiber shows a zero-resistance Tc of 39.3 K. The carbon-alloyed fibers show a high upper critical field of 55 T at 1.5 K and a high irreversibility field of 40 T at 1.5 K. The result demonstrates great potential of MgB2 coated conductors for superconducting magnets.

We present a microstereolithographic technique that enables the manufacturing of polymeric components for microelectromechanical systems. Model microstructures were fabricated in the form of end-supported microbeams (10 μm in diameter), in order to characterize the mechanical properties of the produced structures at the micron scale. The flexural modulus of these microbeams was measured by atomic force microscopy, using cantilevers with attached metal spheres, and employed in a three-point bending geometry. Postfabrication treatment of the microstructures allows for the tailoring of their stiffness.

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Ferroelectric thin films of lead zirconate titanate (PZT) of the morphotropic phase boundary composition have been fabricated for application to a new family of flexure-wave piezoelectric micromotors that are characterized by low speed and high torque. The high relative dielectric constant (1300) and breakdown strength (1 MV/cm) of the films lead to high stored energy densities. The piezoelectric coefficients d33 and d 3~ were measured to be 220 pC/N and -88 pC/N respectively; the electromechanical coupling factors calculated thereupon were k33=0.49, k31=0.22, and kp=0.32. The development of the piezoelectric ultrasonic nucromotors from the PZT thin films, and the architecture of the stator structure are described. Nonoptimiwi prototype micromotors show rotational velocities of 100-300 rpm, and net normalized torques in the pN-m/vz range.

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