Lee; Fridkin, V.M.; Petukhova, N.N.; and Yudin, S.G., "Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)" (2000). Surface structures and a surface structure phase transition are identified that are distinct from the known bulk ferroelectric-paraelectric phase transition of crystalline copolymer films of vinylidene fluoride ͑70%͒ with trifluoroethylene ͑30%͒. The temperature-dependent changes in the surface structure are accompanied by the physical rotation of the polar group ͑CH 2 -CF 2 ͒. These changes in the surface structure are compared to the bulk phase transition. We show that the bulk structural transition, while distinct from the surface, is qualitatively similar in both thick and thin Langmuir-Blodgett-grown films.

We present measurements of longitudinal ultrasonic velocity on single crystals of the heavy-fermion superconductor UPt3. The measurements show clear signatures of second-order phase transitions in the superconducting state, with the velocity anomalies well accounted for by Ginzburg-Landau theory. From these signatures we construct a phase diagram for UPt 3 that reveals all the boundary lines that have been identified as possible phase transitions. We are able to track the phase transition lines to a tetracritical point, located on the upper-critical-field curve, to within the width of the normalsuperconducting transition.PACS numbers: 74.30. Gn, 62.80.+f, 74.70.Tx This Letter presents the first complete phase diagram in the field-temperature plane for the heavy-fermion superconductor UPt3 derived from a single measurement technique. UPt3 has shown a variety of interesting properties in the superconducting state which strongly suggest unconventional superconductivity with a multicomponent order parameter. Power-law temperature dependences of ultrasonic attenuation 1 " 3 and heat capacity 4 have been interpreted in terms of a gap with line or point nodes on the Fermi surface. More convincingly, a series of experiments have revealed the presence of more than one superconducting phase: Initially, ultrasonic-attenuation measurements showed the presence of two superconducting phases depending on the magnetic field; 5 " 7 subsequently, heat-capacity measurements demonstrated the presence of multiple superconducting phases even in zero field. 8,9 A composite phase diagram assembled from different measurements (ultrasonic-attenuation, 5 heat-capacity, 9 and torsional-oscillator data 10 ) on different samples indicates that UPt3 has at least two and possibly three superconducting phases. However, this interpretation relies on data from a variety of measurement techniques on samples with transition temperatures ranging from 420 to 540 mK.Here we present measurements of ultrasonic velocity on two samples of UPt3. Our velocity measurements yield a more complete phase diagram for superconducting UPt3 than has previously been available. Earlier attenuation measurements on one of the samples 7 (sample No. 1) revealed a peak in the attenuation (the 7/FL peak) in field sweeps at constant temperature, as well as a peak (the X peak) in temperature sweeps in low field. From these attenuation studies it was not possible to follow Hf^(T) very close to the upper-critical-field line HdiT).Thus, it was not possible to answer with confidence the basic question of how many phases there are in UPt3. Theoretical proposals for the phase diagram of UPt 3 have been published by several authors. 11 ' 13 Our results bear directly on these theories:The phase diagrams obtained by a single measuring technique on both of the samples studied give strong support for a tetracritical point intersecting the uppercritical-field line, for fields both parallel and perpendicular to the c axis. In addition, the velocity anomalies at both zero-field transitio...

Real-time solid-state neutron detectors have been fabricated from semiconducting boron-carbon alloys, deposited by plasma-enhanced chemical vapor deposition. Single neutrons were detected and signals induced by gamma rays were determined to be insignificant. The source gas closo-1,2-dicarbadodecaborane ͑ortho-carborane͒ was used to fabricate the boron-carbon alloys with only the natural isotopic abundance of 10 B. Devices made of thicker boron-carbon alloy layers enriched in 10 B could lead to increased detection efficiency and active diodes could use the inherent micron scale spatial resolution, increasing the range of possible applications.

We demonstrate unambiguous evidence of the electric field control of magnetic anisotropy in a wedge-shaped Co film of varying thickness. A copolymer ferroelectric of 70% vinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE) overlays the Co wedge, providing a large switchable electric field. As the ferroelectric polarization is switched from up to down, the magnetic anisotropy of the Co films changes by as much as 50%. At the lowest Co thickness the magnetic anisotropy switches from out-of-plane to in-plane as the ferroelectric polarization changes from up to down, enabling us to rotate the magnetization through a large angle at constant magnetic field merely by switching the ferroelectric polarization. The large mismatch in the stiffness coefficients between the polymer ferroelectric and metallic ferromagnet excludes typical magnetoelectric strain coupling; rather, the magnetic changes arise from the large electric field at the ferroelectric/ferromagnet interface.