Volume 77, Issue 5, May 2006
Index of content:
77(2006); http://dx.doi.org/10.1063/1.2200764View Description Hide Description
We developed a new method for the measurement of the dynamic birefringence induced by the alternating shear deformation in fluid samples. A quadrupole piezoactuator generates the pure shear deformation in the frequency range from and causes the molecular orientation, or the anisotropic conformation of polymers and molecular associations, which is observed by the optical ellipsometry technique. The spectrum of the shear-induced birefringence observed for the isotropic phase of the liquid crystal-hexyl -cyanobiphenyl (6CB) shows linear dependence on the frequency up to , corroborating the effective band of the experimental system. The sensitivity of the system was demonstrated by the quantitative measurement of the birefringence for the isotropic phase of -pentyl -cyanobiphenyl (5CB). The system was also applied to the aqueous solution of the worm such as micelles and the result shows the relaxation of shear induced birefringence at around , which agrees well with the previous reports.
Molecular beam mass spectrometer equipped with a catalytic wall reactor for in situ studies in high temperature catalysis research77(2006); http://dx.doi.org/10.1063/1.2200872View Description Hide Description
A newly developed apparatus combining a molecular beammass spectrometer and a catalytic wall reactor is described. The setup has been developed for in situ studies of high temperature catalyticreactions, which involve besides surface reactions also gas phase reactions in their mechanism. The goal is to identify gas phase radicals by threshold ionization. A tubular reactor, made from the catalytic material, is positioned in a vacuum chamber. Expansion of the gas through a sampling orifice in the reactor wall into differentially pumped nozzle, skimmer, and collimatorchambers leads to the formation of a molecular beam. A quadrupole mass spectrometer with electron impact ion source designed for molecular beam inlet and threshold ionization measurements is used as the analyzer. The sampling time from nozzle to detector is estimated to be less than . A detection time resolution of up to can be reached. The temperature of the reactor is measured by pyrometry. Besides a detailed description of the setup components and the physical background of the method, this article presents measurements showing the performance of the apparatus. After deriving the shape and width of the energy spread of the ionizing electrons from measurements on and He we estimated the detection limit in threshold ionization measurements using binary mixtures of CO in to be in the range of several hundreds of ppm. Mass spectra and threshold ionization measurements recorded during catalytic partial oxidation of methane at on a Pt catalyst are presented. The detection of radicals is successfully demonstrated.
77(2006); http://dx.doi.org/10.1063/1.2200876View Description Hide Description
We describe the use of stimulated Raman pumping in a molecular beam to perform quantum state resolved gas-surface reactivity measurements for molecules prepared in totally symmetric vibrational states. Vibrational states of homonuclear diatomics as well as totally symmetric vibrations of polyatomic molecules cannot be prepared by direct infrared excitation but are accessible through stimulated Raman pumping by two laser fields when the difference between the incident laser frequencies matches the vibration. We generate a suitable resonant pair of high-energy pump and Stokes laser beams in an injection seeded Raman amplifier filled with the sample gas and equipped with internal gas recirculation. The ability to partially saturate the Raman pumping process in the molecular beam is used to quantify the fraction of vibrationally excited molecules in the irradiated volume, which is needed for quantitative reactivity measurements. We illustrate the method with state resolved reactivity measurements for , prepared in its symmetric C–H stretch vibration on a Ni(100) single crystal surface.
77(2006); http://dx.doi.org/10.1063/1.2202919View Description Hide Description
We describe methodologies for the generation and screening of combinatorial libraries of electrocatalyst materials for fuel cell applications, generated by cosputtering of three elements onto a Si substrate coated with a Ta adhesion underlayer. Screening was carried out via a fluorescence assay as well as by scanning electrochemical microscopy. Whereas the former provided rapid qualitative screening with limited spatial resolution, the latter provided high spatial resolution. The fluorescence screening method was tested on Pt, PtBi, PtPb, and PtRu nanoparticles, while both methods were tested on a film containing a Pt–Bi–Pb ternary composition spread.