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.
Infrared absorption study of CO chemisorption on copper island films
Abstract The infrared absorption spectra of chemisorbed CO at 90 K on copper island films deposited by electron-beam evaporation onto surface-oxidized silicon substrates have been measured at normal incidence of radiation. The integrated absorption intensity of the C–O stretch mode at saturation of CO adsorption depends on both the mass thickness of copper and the substrate temperature during copper deposition. The observed CO absorption features are quite different from those observed on bulk single crystals and thick polycrystalline films. The FE-SEM images reveal that at a given mass thickness the islands are larger when deposited at 296 K than when deposited at 473 K. This difference is reflected in the mass thickness dependence of the absorption intensity; the maximum absorption intensity is obtained at a thickness of 9 nm when deposited at 296 K, whereas the corresponding thickness is 16 nm when deposited at 473 K. A feature common to both films is partial aggregation of the islands. The integrated absorption intensity of the C–O stretch mode observed on the 16 nm film is 5 times larger than that observed on the bulk Cu(1 0 0) surface. This absorption enhancement is attributed to the transverse collective electron resonance of the copper islands.
Modelling Roman suicide? The afterlife of Cato
This paper explores the idea of suicide as, under some circumstances, an act which may legitimately be witnessed, indeed demands to be witnessed, making it a proper subject for literary/artistic representation. For ancient Romans, a suicide might be honourable if it was felt to express the status of its agent as a moral witness. The death of Cato in 46 bce was celebrated in antiquity as the prime example of such a suicide. Cato's death was the subject of a highly successful stage play by Joseph Addison first staged in 1713. Addison's uneasy handling of Cato's death betrays the difficulty of presenting suicide as an inspirational spectacle of virtue in the context of early eighteenth-century Britain, where deliberate self-killing was treated as a crime and an offence against religion.