No abstract

GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30–40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the ‘‘anode’’ plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al2O3 at 600–800 °C. The films were investigated by photoluminescence, cathodoluminescence, x-ray diffraction, Rutherford backscattering, and particle-induced x-ray emission. The film with the highest structural quality had a rocking curve width of 5 arcmin, the lowest reported value for MBE growth to date.

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The molecular structure of the hydrocarbon 5,6;11,12-di-o-phenylenetetracene (DOPT), its material characterization and evaluation of electronic properties is reported for the first time.Asingle-crystal X-rays tudy reveals two different motifs of intramolecular overlap with herringbonetype arrangement displaying either face-to-edge or co-facial face-to-face packing depicting intensive p-p interactions. Density functional theory (DFT) calculations underpin that afavorable electronic transport mechanism occurs by acharge hopping process due to a p-bond overlap in the DOPT polymorph with co-facial arene orientation. The performance of polycrystalline DOPT films as active organic semiconducting layer in as tate-of-the-art organic field effect transistor (OFET) device was evaluated and proves to be film thickness dependent. For4 0nml ayer thickness it displays as aturation hole mobility (m hole)o fu pt o0 .01 cm 2 V À1 s À1 and an on/offratio (I on /I off)o f1.5 10 3 .