Effect of disorder in MgB2 thin films

We report on scanning tunneling spectroscopy studies of magnesium diboride (MgB2) thin films grown by different techniques. The films have critical temperatures ranging between 28 and 41 K with very different upper critical fields. We find that the superconducting gap associated with the sigma band decreases almost linearly with decreasing critical temperature while the gap associated with the pi band is only very weakly affected in the range of critical temperatures above 30 K. In the sample with the lowest critical temperature (28 K) we observe a small increase of the pi gap that can only be explained in terms of an increase in the interband scattering. The tunneling data was analyzed in the framework of the two-band model. The magnetic-field-dependent tunneling spectra and the upper critical field measurements of these disordered samples can be consistently explained in terms of an increase of disorder that mostly affects the pi band in samples with reduced critical temperatures

Small signal and power performance of AlGaN/GaN HFETs grown on s.i.SiC

We report on the DC,the mall ignal and the RF power performance of AlGaN/GaN HFET grown on emi in ulating (.i.)SiC ubstrate.DC characterization how a record transconductance of 300mS/mm for a device ith a gatelength of 0.3 µm.Load pull measurements at 10 GHz were performed,indicating output power levels above 4Watts cw for a unpas ivated 1.6mm device.Finally,tandard equivalent circuit parameter are extracted and verified for devices with different gatewidths

Theoretical modeling of edge-controlled growth kinetics and structural engineering of 2D-MoSe2

WOS:000681068200004We introduce the first reactive force field (ReaxFF) for Mo/Se/H interactions, which enables large-scale molecular dynamics simulations of the synthesis, processing, and characterization of 2D-MoSe2 and whose parameters are trained primarily on first-principles energetics data including both periodic and non-periodic calculations. This new potential elucidates the structural transition from metallic to semiconducting phases, the energetics of various defects, and the Se-vacancy migration barrier. A theoretical model developed based on this potential and the Wulff construction also describes an observed morphology evolution of 2D-MoSe2 domains during growth. Since controllable edge-mediated growth kinetics of 2D-MoSe2 are of great interest to the 2D community, we believe that this new ReaxFF potential trained against the edge formation energies of MoSe2 nanoribbons with different Se coverages will be a powerful complementary tool to experimental studies by simulating the edge-growth kinetics of 2D-MoSe2 at high speed and low cost