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New measurements of the angular distributions of effusive gas beams emanating from two collimating tube sources are presented. These sources are a single tube of aspect ratio 25 and a multi-capillary array of aspect ratio 100. The data were collected for a wide variety of gases (He, Ne, Ar, Kr, Xe, H2, N2, CO2 and C2H2) over a broad range of driving pressures. The profiles were obtained by rotating the ionization gauge gas detector about the centre of the exit of the tube. The data were acquired as a function of the gas flow rate and pressure in the source line. Comparisons of the present measurements with other experimental work and models are made.

Artificial Au atomic chains with individual Pd impurities were assembled from single metal atoms with a scanning tunneling microscope on a NiAl(110) surface. Scanning tunneling spectroscopy (STS) revealed an electronic resonance 2.15 eV above the Fermi energy localized within 4 A of single Pd atom impurities and two electronic resonances 2.25 eV and 2.95 eV above the Fermi energy localized within 8 A of Pd dimer impurities. The emergence of these localized resonances was studied by STS at each stage of the atom-by-atom assembly. Additionally, conductance images of the chains revealed delocalized electronic density oscillations in the pure Au segments of the chains.

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