e combination of nanomaterial graphene quantum dots (GQDs) with magnetic nanoparticles offers a unique set of optical and magnetic properties for future energy and medical applications. We report on the synthesis and engineering of GQDs and iron oxide (Fe 3 O 4 ) nanocomposites (NCs) by using a pulsed laser discharge technique. High-resolution transmission electron microscopy (HRTEM) images showed a high yield of pure GQDs with 2-10 nm diameter. e hexagonal structures and lattice fringes associated with the C-C bond in GQDs were clearly identifiable. e structural and optical changes in GQDs and GQDsFe 3 O 4 NC samples induced by UV light were investigated by the absorption and emission spectroscopy over the deep UV-visible spectral range. e photoluminescence spectra have shown subband π→π * transitions in GQDs-Fe 3 O 4 NC. Magnetic properties of the GQDs-Fe 3 O 4 NC samples have shown room temperature ferromagnetism induced by pure Fe 3 O 4 nanoparticles and from the substantial spin polarized edges of GQD nanoparticles. It is concluded that the observed optical and magnetic properties could be further tailored in the studied nanocomposites for prospective medical applications.

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Various types of 2D/2D prototype devices based on graphene (G) and boron nitride nanosheets (BNNS) were fabricated to study the charge tunneling phenomenon pertinent to vertical transistors for digital and high frequency electronics. Specifically, G/BNNS/metal, G/SiO2, and G/BNNS/SiO2 heterostructures were investigated under direct current (DC-bias) conditions at room temperature. Bilayer graphene and BNNS were grown separately and transferred subsequently onto the substrates to fabricate 2D device architectures. High-resolution transmission electron microscopy confirmed the bilayer graphene structure and few layer BNNS sheets having a hexagonal B3-N3 lattice. The current vs voltage I(V) data for the G/BNNS/Metal devices show Schottky barrier characteristics with very low forward voltage drop, Fowler-Nordheim behavior, and 10−4 Ω/sq. sheet resistance. This result is ascribed to the combination of fast electron transport within graphene grains and out-of-plane tunneling in BNNS that circumvents grain boundary resistance. A theoretical model based on electron tunneling is used to qualitatively describe the behavior of the 2D G/BNNS/metal devices.

In this paper, the authors report the device instability of solution based ZnO thin film transistors by studying the time-evolution of electrical characteristics during electrical stressing and subsequent relaxation. A systematic comparison between ambient and vacuum conditions was carried out to investigate the effect of adsorption of oxygen and water molecules, which leads to the creation of defects in the channel layer. The observed subthreshold swing and change in field effect mobility under gate bias stressing have supported the fact that oxygen and moisture directly affect the threshold voltage shift. The authors have presented the comprehensive analysis of device relaxation under both ambient and vacuum conditions to further confirm the defect creation and charge trapping/detrapping process since it has not been reported before. It was hypothesized that chemisorbed molecules form acceptorlike traps and can diffuse into the ZnO thin film through the void on the grain boundary, being relocated even near the semiconductor/dielectric interface. The stretched exponential and power law model fitting reinforce the conclusion of defect creation by oxygen and moisture adsorption on the active layer.

Solution-based bottom-gate zinc oxide thin film transistors (TFTs) were fabricated, remaining functional and demonstrating stability under extreme gamma irradiation conditions. Unpassivated TFTs were fabricated on samples with different number of ZnO layers grown via sol-gel spin coating technique. The devices were characterized before and after exposure to a cumulative dose of 220 MRad (air) of gamma irradiation. Atomic force microscopy (AFM), x-ray diffraction (XRD), and photoluminescence (PL) were employed to characterize the TFT active layers. Thickness measurements and optical images suggest the removal of the channel surface, conceivably due to cumulative effect of displacement damage near the ZnO surface. Device electrical characteristics were extracted from current-voltage measurements. The impact of displacement damage on the degradation/enhancement of device characteristics as a consequence of surface/bulk effects is discussed.