Enhanced Infrared Absorption of C60 on Thin Evaporated Pd Island Films
Infrared transmission spectra of C 60 * multilayers on thin Pd films deposited onto surface-oxidized Si(100) and hydrogen-terminated Si(111) substrates are reported. In both cases, the spectra in the 1500-1100 cm-' region exhibited bands at 1444, 1429, and 1182 cm-' due, respectively, to the A 8 (2), T 1u (4), and T 1u (3) modes. The appearance of the A 8 (2) mode, which is originally infrared inactive (Raman active), reveals electron transfer from the metal to chemisorbed C 60. Indeed, increasing the thickness of C 60, the A g (2) mode intensity saturated more rapidly than the T 1u (4) and T 1u (3) modes. The originally infrared active T 1u (4) and T 1u (3) modes were enhanced in intensity depending upon the Pd thickness. Actually, while both substrates gave nearly the same magnitude of enhancement, the optimum Pd thickness was smaller on the hydrogen-terminated surface than on the surface-oxidized surface. On the other hand, the A g (2) mode, was less intense on the hydrogen-terminated surface than on the oxidized surface, suggestive of a shortage of chemisorbed C 60 and thus pointing out the importance of the metal film morphology. Indeed, Pd films deposited on the two substrates gave rise to quite different AFM images. We also show that, regardless of the substrate, the A g (2) mode is an order of magnitude smaller than for Ag deposition, though no remarkable intensity differences were observed with respect to the T 1u (4) and T 1u (3) modes.
Nanocarbons in different structural dimensions (0–3D) for phenol adsorption and metal-free catalytic oxidation
Abstract Metal-free nanocarbon materials in different structural dimensions, such as 0D fullerene (C 60 ), 1D single-walled carbon nanotubes (SWCNTs), 2D graphene nanoplate (GNP), 3D hexagonally-ordered mesoporous carbon (CMK-3) and cubically-ordered mesoporous carbon (CMK-8) were investigated for adsorption and catalytic oxidation of phenol in water solutions. A variety of characterisation techniques were used to investigate the properties of the carbon samples. It was found that structural dimension and heat treatment would significantly affect the performance of the nanocarbons in adsorption and catalysis. Both GNP and CMK-3 showed better phenol adsorption with around 40% phenol removal in 500 mL of 20 ppm solutions. The nanocarbons were also used for metal-free activation of peroxymonosulfate (PMS) to produce sulfate radicals for catalytic phenol oxidation. Efficient catalysis was observed on CMK-3, CMK-8 and SWCNTs. Thermal treatment of the nanocarbons at 350 °C in nitrogen was conducted to modulate the crystal- and micro-structures and surface functional groups of the different nanocarbons. Enhancements at 2-fold in adsorption on SWCNTs and 7.5-fold in catalysis on CMK-8 were observed after the heat treatments. Mechanisms of adsorption and catalytic oxidation of phenol were discussed. This study contributes to the development of green materials for sustainable remediation of aqueous organic pollutants.
Simulation study of high power microwave generation by virtual cathode oscillation in coaxial vircator
Summary form only given, as follows. We have numerically simulated the high power microwave generation by virtual cathode oscillation in a coaxial vircator with 3 dimensional PIC code Magic. It is noted that the coaxial vircator has the advantage of an enhancement of power efficiency and gaining of narrow bandwidth frequency. The study is focused on the design of a diode structure for a coaxial vircator suitable for Chundoong IREB pulser (Max. 600 kV, 85 kA, 60 ns). It consists of a center annular cathode, a cylindrical meshed-anode and a reflector. The simulation results showed that the coaxial vircator can indeed be operated at the selected frequency with the narrow bandwidth and the microwave output power strongly depends on the position and geometry of the reflector. From this simulation results we expect that the maximum microwave output power will be obtained by the reflector of 4 cm in width and also 4 cm in distance away from the IREB, where the resonant frequency of microwave from coaxial vircator is simulated to be 6.577 GHz.