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Undoped n-GaN grown by two different metallorganic chemical vapor deposition (MOCVD) techniques, standard MOCVD and epitaxial lateral overgrowth, and Mg-doped p-GaN prepared by hydride vapor phase epitaxy and molecular beam epitaxy were irradiated with fast reactor neutrons to the high fluence of 1018 cm−2. In such heavily irradiated samples the Fermi level is shown to be pinned in a narrow interval of Ec−(0.8−0.95) eV, irrespective of the starting sample properties. The Fermi level pinning position correlates with the measured Schottky barrier height in n-type GaN. The results are interpreted from the standpoint of the existence of the charge neutrality level in heavily disordered material. Based on published theoretical calculations and on deep level transient spectroscopy (measurements and lattice parameter measurements in irradiated material), it is proposed that the Fermi level could be pinned between the gallium-interstitial-related deep donors near Ec−0.8 eV and nitrogen-interstitial-related acceptors near Ec−0.9 eV

Composite films and aerogels of polyvinylpyrrolidone/cellulose nanocrystals (PVP/CNC) were prepared by solution casting and freeze-drying, respectively. Investigations into the PVP/CNC composite films and aerogels over a wide composition range were conducted. Thermal stability, morphology, and the resulting reinforcing effect on the PVP matrix were explored. FTIR, TGA, DSC, X-ray diffraction, SEM, and tensile testing were used to examine the properties of the composites. It was revealed PVP-assisted CNC self-assembly that produces uniform CNC aggregates with a high aspect ratio (length/width). A possible model of the PVP-assisted CNC self-assembly has been considered. Dispersibility of the composite aerogels in water and some organic solvents was studied. It was shown that dispersing the composite aerogels in water resulted in stable colloidal suspensions. CNC particles size in the redispersed aqueous suspensions was near similar to the CNC particles size in never-dried CNC aqueous suspensions.

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Electrical properties, admittance, and microcathodoluminescence spectra are compared for p-GaN samples grown by hydride vapor phase epitaxy ͑HVPE͒ and by molecular beam epitaxy ͑MBE͒. The former are characterized by a high 300 K hole concentration and a weak temperature dependence of conductivity. The latter samples show strongly temperature-activated conductivity due to ionization of Mg acceptors. The main effects of neutron irradiation were similar for the p-HVPE and the p-MBE materials: a compensation of p-type conductivity starting with neutron fluences exceeding 2 ϫ 10 16 cm −2 and conversion to high resistivity n type with the Fermi level pinned near E c -͑0.8-0.9͒ eV after irradiation with high doses of 10 18 cm −2 . For the heavily neutron irradiated p-HVPE samples, a strong increase was observed in the c-lattice parameter which indicates an important role for interstitial-type defects.

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Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (αME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO3 particles. Developed strategies allow us to increase the αME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe2O4 nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures.