Volume 106, Issue 12, 15 December 2009
Index of content:
106(2009); http://dx.doi.org/10.1063/1.3271140View Description Hide Description
Studies on magnetoelectric (ME) coupling in a semiring of lead zirconate titanate(PZT) with a Terfenol-D insert reveal strong ME coupling at low frequencies and two orders of magnitude enhancement in the strength at resonance associated with a unique bending mode in PZT. A model is discussed for the resonance ME coupling that arises from radial and shearing displacements and theoretical estimates are in excellent agreement with the data. The model also predicts weak ME coupling in a full ring of PZT with Terfenol-D insert in agreement with the experiment. The results are of importance for ME composite based magnetic field sensors.
106(2009); http://dx.doi.org/10.1063/1.3267151View Description Hide Description
The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growthtemperature. Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth.
106(2009); http://dx.doi.org/10.1063/1.3272027View Description Hide Description
First results of numerical and physical experiments for the ring waveguideresonator on surface acoustic waves are presented. The structure consists of a goldinterdigital transducer in the form of a ring placed on the cut of aluminum nitride crystal. Excitation of radial modes is investigated. The electrical admittance frequency dependence of such resonator does not have sidelobes. A high quality factor is achievable.
106(2009); http://dx.doi.org/10.1063/1.3273477View Description Hide Description
Strong upconversion green luminescence was observed in and codoped ferroelectric thin films. The thin films were prepared on fused silica and substrates by chemical solution deposition method. There are two strong green emission bands centered at 524 and 545 nm and a weak red emission band centered at 667 nm in the upconversion luminescence spectra pumped by 980 nm at room temperature. They correspond to the radiative relaxation of from , , and levels to the ground level , respectively. thin films exhibit higher green emission intensity by a factor of about 30 compared with thin films. The upconversion emission mechanism of the thin films has been discussed. In addition, ferroelectric thin films on substrates also show well-defined hysteresis loops with a remnant polarization of . This study opens the possibility of constructing new integrated photoluminescent ferroelectric thin film devices.
106(2009); http://dx.doi.org/10.1063/1.3272035View Description Hide Description
In this paper, the photoexcitation response of high mobility -type organic field-effect transistors is analyzed. White light exposure of -dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) transistors is demonstrated to promote the occurrence of metastable conductance states with very long retention times, similar to what has been previously reported for -type compounds. Even in the absence of a gate-source voltage , the complete recovery of the initial electrical condition can take up to 20 days. However, the initial state restoring is electrically controllable by the application of a positive . These effects suggest that PTCDI-C8H is an interesting -type material for the development of light-sensitive organic circuitry.