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.
Observation of the enhanced infrared absorption of p-nitrobenzoate on Ag island films with an ATR technique
By the use of an ATR technique we have found that the infrared absorption of p-nitrobenzoate, formed on Ag island film about 5 nm thick, is enhanced by a factor of the order of 10. Only vibrational modes involving a change in the dipole moment of the benzoate ion perpendicular to the macroscopic Ag surface are enhanced by p-polarized radiation alone, indicating the electric field of the evanescent wave polarized perpendicular to the Ag surface plays a dominant role in the infrared excitation process. A monolayer of stearic acid deposited on a Ag underlayer 5nm thick gave another example of the enhancement. Although the mechanism of enhancement is not fully elucidated, the existing model based on the collective electron resonances of Ag islands is not applicable to the present case, since it predicts the electron resonance can be excited irrespective of polarization state of infrared beam.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.