Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques.

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.

Imidazole-fe interaction in an aqueous chloride medium: effect of cathodic reduction of the native oxide.

The effect of the reduction of the native surface oxide of Fe on the binding of imidazole (as a corrosion inhibitor) with Fe in an aqueous brine solution has been addressed here. The surface interactions and corrosion inhibition efficiency were studied using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). It was shown that imidazole dissolved in brine bonds with the unreduced iron oxide surface via pyrrole-type nitrogen. However, surface interactions with Fe occur via both pyridine-type and pyrrole-type nitrogen atoms when imidazole is added to brine containing a cathodically reduced iron surface. The packing density of imidazole is found to be higher in the latter case with a corresponding increase in the corrosion inhibition efficiency.

The internal energy of CO2 produced by the catalytic oxidation of CH3OH by O2 on polycrystalline platinum.

The dynamics of steady state catalytic methanol oxidation on a polycrystalline Pt surface over a range of surface temperatures and reactant flow conditions were investigated by monitoring the kinetics with mass spectrometry and the internal state distribution of nascent CO(2) with tunable diode laser absorption spectroscopy. The results indicate that CO(2) formation proceeds via three distinct reaction pathways. The first produced CO(2), which is vibrationally excited relative to CO(2) in thermal equilibrium with the surface and shows preferential excitation in the asymmetric stretch. This pathway proceeds via the decomposition of CH(3)OH and the subsequent oxidation of nascent CO adsorbed to Pt in a weakly held precursor state. CO(2) production via this pathway is favored at high surface temperatures and high oxygen coverage. The second forms CO(2), which is vibrationally deactivated relative to CO(2) in thermal equilibrium with the surface and exhibits no preferential excitation among its three nondegenerate vibrational modes or the rotational energy. This pathway involves the decomposition of CH(3)OH and subsequent oxidation of nascent CO adsorbed to Pt in a more strongly held chemisorbed state. CO(2) production via this pathway is favored at low surface temperatures and low oxygen coverage. The third forms CO(2) with preferential excitation in the asymmetric stretch but with less overall vibrational excitation than CO(2) from the first pathway and more vibrational excitation than CO(2) from the second. This third pathway occurs via the complete dehydrogenation of CH(3)OH and subsequent oxidation of nascent CO adsorbed to Pt in a bridged state bound through both ends of the molecule. CO(2) production via this pathway is favored at intermediate surface temperatures and oxygen coverage, conditions which favor overall oxidation to form CO(2).

Analysis of a photographic-vidicon camera method of LEED intensity measurements.

Low-energy electron diffraction (LEED) has great need for a quick and efficient means of making intensity measurements (e.g., in studying reactive surfaces which quickly degrade, and in handling the enormous amounts of data needed for data averaging). The photographic-vidicon camera method fills this need. This paper describes a system and procedure for this method. We have pointed out advantages of this method over other methods of LEED intensity data collection and analysis, and have included comments on the advantages of our experimental system over other systems using this method. General properties of the photographic and vicdicon system are analyzed as well as specific tests done on the method. Estimates of probable error in spot intensity measurements due to numerous effects have been analyzed and I-V curves reduced from raw photographic data are compared. It is hoped that the description, comments, and analysis will facilitate the incorporation of the photographic-vidicon method of LEED analysis into research programs.