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The presented work is dedicated to the study and comparison of scintillating properties of zinc oxide samples prepared in different morphologies: whiskers, nanowalls, multipods, and ceramics. It was shown that total transmittance, photo- and radioluminescence spectra, and radioluminescence kinetics can vary significantly depending on sample structure and preparation conditions. The highest total transmittance was registered for ZnO ceramics (>50% at 0.5 mm thickness). Differences in the transmittance of whiskers, nanowalls, and multipods can be attributed to their shape and thickness which affects the amount of light refraction and scattering. The study of radioluminescence demonstrated that all samples, except undoped ceramics and air annealed whiskers, have predominantly fast luminescence with a decay time <1 ns. High transmittance of ceramics opens the way for their use in the registration of high energy X-ray and gamma radiation, where a large volume of scintillators is required. In cases, where large scintillator thickness is not a necessity, one may prefer to use other ZnO structures, such as ensembles of whiskers and nanowalls. Studies of near-band-edge luminescence components at low temperatures showed that the structure is quite similar in all samples except Ga doped ceramics.

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We have studied luminescent properties of a ZnO whisker array, a promising crystalline material for scintillation detectors, capable of ensuring a fast and strong response and a short afterglow time. Measurements have been performed under X-ray and UV optical excitation. We present a comparative analysis of spectral features of the near-band-edge emission of the whisker array at low (∼80 K) and room temperatures in relation to the excitation method.

High current density field emission from arrays of carbon nanotubes and diamond-clad Si tips Demonstration of Li-based alloy coatings as low-voltage stable electron-emission surfaces for field-emission devices J. Appl. Phys. 85, 8405 (1999); 10.1063/1.370688 Model calculations of internal field emission and J-V characteristics of a composite n -Si and N-diamond cold cathode sourceWe have investigated the suitability of nanodiamond ͑ND͒ and AlN coated Si tip arrays for cold cathodes by means of a field emission scanning microscope combined with scanning electron microscopy. The ND coated tips required an average extraction voltage U(10 nA) of 360 V for 10 m electrode distance and yielded stable emission up to currents of 10-50 A. The rather nonuniform emission distribution of the arrays (80 VϽU(10 nA)Ͻ1800 V) was correlated with the varying morphology of the ND tips. Field-enhancing nanoprotrusions were observed at the apex of the strongest emitters. The AlN coated tips showed strong activation effects at emission currents below 10 nA or after annealing at 250°C resulting in an average U(10 nA) of 410 V, improved lateral emission uniformity (150 VϽU(10 nA)Ͻ600 V), and stable currents up to 1-10 A. Direct high current processing of such emitters led to a partial destruction of the apex. Different field emission mechanism will be discussed for ND and AlN coatings.

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