Density-functional study of Cu atoms, monolayers, and coadsorbates on polar ZnO surfaces

The structure and electronic properties of single Cu atoms, copper monolayers and thin copper films on the polar oxygen and zinc terminated surfaces of ZnO are studied using periodic density-functional calculations. We find that the binding energy of Cu atoms sensitively depends on how charge neutrality of the polar surfaces is achieved. Bonding is very strong if the surfaces are stabilized by an electronic mechanism which leads to partially filled surface bands. As soon as the surface bands are filled (either by partial Cu coverage, by coadsorbates, or by the formation of defects), the binding energy decreases significantly. In this case, values very similar to those found for nonpolar surfaces and for copper on finite ZnO clusters are obtained. Possible implications of these observations concerning the growth mode of copper on polar ZnO surfaces and their importance in catalysis are discussed.Comment: 6 pages with 2 postscript figures embedded. Uses REVTEX and epsf macro

Selective Ionization of Group I Elements from Laser Ablated Plumes of Rb Ga Sb, K3Ga3As4, and K4In4As6

Experimental results are reported on the I-III-V Zintl compounds Rb·Ga·Sb, K3Ga3As4, and K4In4As6 with respect to laser ablation and subsequent laser ionization/removal processes. The approach takes advantage of the low ionization potentials of the group I elements to achieve selectivity and exert a measure of control over neutral mixtures. A 308 nm laser pulse is used to ablate a I-III-V Zintl compound, while a second laser is used to selectively ionize the ejected species within the extraction region of a time-of-flight mass spectrometer. With the second laser operating at 248 nm (in the case of Rb·Ga·Sb) and at 266 nm (in the case of K3Ga3As4 and K4In4As6), selective gas-phase ionization and removal of the group I elements is clearly demonstrated

MEASURING THE NUCLEAR HYPERFINE POPULATIONS IN THE GROUND ELECTRONIC STATE OF ATOMIC HYDROGEN USING VELOCITY-ALIGNED DOPPLER SPECTROSCOPY

Author Institution: Department of Chemistry, Tulane UniversityA variation on the technique of velocity-aligned Doppler spectroscopy has been used to measure the relative populations in the F=0 and F=1 nuclear hyperfine levels in the ground electronic state of atomic hydrogen produced in the 193 nm photolysis of HBr. This technique provides an unambiguous correlation between the H atom state distributions and the spin-orbit states of the counter fragment, i.e. Br($^{2}P_{3/2}$) and Br($^{2}P_{1/2}$). H atom state distributions are monitored by observing the (1+1) two-color multiphoton ionization spectrum exciting through the Lyman-$\alpha$ transition. Effects of small Stark fields on the observed spectra will be discussed

The Masses of Supernova Remnant Progenitors in NGC 6946

We constrained the progenitor masses for 169 supernova remnants (SNRs), eight historically observed supernovae (SNe), and the black hole formation candidate in NGC 6946, finding that they are consistent with originating from a standard initial mass function. Additionally, there were 16 remnants that showed no sign of nearby star formation consistent with a core-collapse SN, making them good Type Ia candidates. Using Hubble Space Telescope broadband imaging, we measured the stellar photometry of ACS/WFC fields in the F435W, F555W, F606W, and F814W filters, as well as WFC3/UVIS fields in F438W, F606W, and F814W. We then fitted this photometry with stellar evolutionary models to determine the ages of the young populations present at the positions of the SNRs and SNe. We then inferred a progenitor mass probability distribution from the fitted age distribution. For 37 SNRs, we tested how different filter combinations affected the inferred masses. We find that filters sensitive to Hα, [N ii], and [S ii] gas emission can bias mass estimates for remnants that rely on our technique. Using a Kolmogorov-Smirnov test analysis on our most reliable measurements, we find that the progenitor mass distribution is well matched by a power-law index of -2.6-0.6+0.5, which is consistent with a standard initial mass function. © 2021. The American Astronomical Society. All rights reserved..Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]