Concepts for chemical state analysis at constant probing depth by lab-based XPS/HAXPES combining soft and hard X-ray sources

The greater information depth provided in hard X-ray photoelectron spectroscopy (HAXPES) enables nondestructive analyses of the chemistry and electronic structure of buried interfaces. Moreover, for industrially relevant elements like Al, Si, and Ti, the combined access to the Al 1s, Si 1s, or Ti 1s photoelectron line and its associated Al KLL, Si KLL, or Ti KLL Auger transition, as required for local chemical state analysis on the basis of the Auger parameter, is only possible with hard X-rays. Until now, such photoemission studies were only possible at synchrotron facilities. Recently, however, the first commercial XPS/HAXPES systems, equipped with both soft and hard X-ray sources, have entered the market, providing unique opportunities for monitoring the local chemical state of all constituent ions in functional oxides at different probing depths, in a routine laboratory environment. Bulk-sensitive shallow core levels can be excited using either the hard or soft X-ray source, whereas more surface-sensitive deep core-level photoelectron lines and associated Auger transitions can be measured using the hard X-ray source. As demonstrated for thin Al₂O₃, SiO₂, and TiO₂ films, the local chemical state of the constituting ions in the oxide may even be probed at near-constant probing depth by careful selection of sets of photoelectron and Auger lines, as excited with the combined soft and hard X-ray sources. We highlight the potential of lab-based HAXPES for the research on functional oxides and also discuss relevant technical details regarding the calibration of the kinetic binding energy scale.     

Absence of site percolation at criticality in

In this note we consider site percolation on a two dimensional sandwich of thickness two, the graph . We prove that there is no percolation at the critical point. The same arguments are valid for a sandwich of thickness three with periodic boundary conditions. It remains an open problem to extend this result to other sandwiches. “Note added in proof: This extension has recently been accomplished in arXiv 1401.7130.” © 2014 Wiley Periodicals, Inc. Random Struct. Alg., 47, 328–340, 2015     

Optimization-based heuristics for underground mine scheduling

Underground mine production scheduling possesses mathematical structure similar to and yields many of the same challenges as general scheduling problems. That is, binary variables represent the time at which various activities are scheduled. Typical objectives seek to minimize costs or some measure of production time, or to maximize net present value; two principal types of constraints exist: (i) resource constraints and (ii) precedence constraints. In our setting, we maximize “discounted metal production” for the remaining life of an underground lead and zinc mine that uses three different underground methods to extract the ore. Resource constraints limit the grade, tonnage, and backfill paste (used for structural stability) in each time period, while precedence constraints enforce the sequence in which extraction (and backfill) is performed in accordance with the underground mining methods used. We tailor exact and heuristic approaches to reduce model size, and develop an optimization-based decomposition heuristic; both of these methods transform a computationally intractable problem to one for which we obtain solutions in seconds, or, at most, hours for problem instances based on data sets from the Lisheen mine near Thurles, Ireland.     

Magnetic trapping of silver and copper, and anomalous spin relaxation in the ag-he system

We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer-gas cooling. Up to 3 x 10{12} Cu atoms and 4 x 10{13} Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are >or=10{6}, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag-3He collision rate varies as T;{5.8+/-0.4}. We find that this temperature dependence is inconsistent with the behavior predicted for relaxation arising from the spin-rotation interaction, and conclude that the Ag-3He system displays anomalous collisional behavior in the multiple-partial wave regime. Gold (Au) was ablated into 3He buffer gas, however, atomic Au lifetimes were observed to be too short to permit trapping.     

Mao based catalysts for syndiotactic polystyrene (sPS)

Several non-metallocene (Ti, Zr) and substituted mono-Cp titanium metallocenes have been tested in the presence of methylalumoxane (MAO) as catalyst for syndiospecific polymerization of styrene. Effect of substitutions on the titanium and Cp ligand, molar ratio of Al/Ti, TMA and temperature on activity, Mwt. and % sPS were studied. CpTi(OiPr)₃ gives a less active catalyst than Cp*Ti(OiPr)₃ and the resulting sPS is less stereoregular and of lower molecular weight.     

Recent advances in ferroelectric polymers

In the Polymer Electroprocessing Laboratory at Rutgers University, we have discovered that the odd-numbered nylons constitute the second known class of ferroelectric polymers^1–3, and that polarized films exhibit piezoelectric properties similar to poly(vinylidene fluoride) (PVF₂) and copolymers of PVF₂ and trifluoroethylene (PVF₂/PVF₃). A study of a series of these polymers including nylon 11, nylon 9, nylon 7 and nylon 5 showed that the remanent polarization produced in quenched, cold-drawn films was a linear function of polymer dipole density⁴. The highest remanent polarization produced was that of nylon 5, the value attained (P₁=125mC/m²) being approximately 2.5 times that of PVF₂. We also discovered that (unlike PVF₂ or PVF₂/PVF₃) the remanent polarization could be stabilized to elevated temperatures (close to the polymer melting point). For nylon 5, the remanent polarization and piezoelectric response was stable to over 250°C⁵. We showed that the hydrogen-bonded sheet structure in nylon 11 for quenched cold-drawn films was parallel to the plane of the film, and that after application of high electric fields the hydrogen-bonded sheet structure was rotated 90° to an orientation perpendicular to the plane of the film³. A detailed X-ray diffraction study of the effects of humidity and electroprocessing on the switching behavior of nylon 5, nylon 7 and nylon 11 films was carried out⁵. The piezoelectric and pyroelectric response⁶ of these films was also determined. The different switching mechanisms observed and the measured piezoelectric and pyroelectric properties will be presented and discussed.