Grand canonical Monte Carlo simulations were performed to identify trends in low-pressure adsorption of a broad range of organic molecules by a set of metal-organic frameworks (MOFs). While previous simulation studies focused on the adsorption of small molecules such as carbon dioxide and methane, we consider more complicated organic molecules relevant to chemical sensing and detection: small aromatics (o-, m-, and p-xylene), polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene), explosives (TNT and RDX), and chemical warfare agents (GA and VM). The framework materials include several Zn-IRMOFs (IRMOFs 1-3, 7, 8), a Cr-MOF (CrMIL-53lp), and a Cu-MOF (HKUST-1). A wide range of loading pressures is examined, extending from 100 ppm to 10 ppb in air, thus spanning the entire range of conditions relevant to chemical sensing for security, environmental, and industrial process monitoring. Our results are validated by comparing calculated adsorption energies with experimental values, where available. Many of the larger organics are significantly adsorbed by the target MOFs at low pressure, which is consistent with the high isosteric heats of adsorption (12 kcal mol(-1)-49 kcal mol(-1)) computed for these analytes. These adsorption energies are significantly large that interference from atmospheric components should not interfere with chemical detection at low pressures. We show that pi-pi stacking interactions are an important contributor to these high heats of adsorption. CrMIL-53lp shows the highest adsorption energy for all analytes, suggesting that this material may be suitable for detection of low-level organics. At higher loading pressures, the Zn-MOFs show a much higher volumetric uptake than either CrMIL-53lp or HKUST-1 for all types of analyte considered here. Within the Zn-IRMOF series, analyte loading is proportional to accessible free volume, and loading decreases with increasing analyte size due to molecular packing effects. Overall, the results demonstrate that atomistic simulation can be used as an efficient first step in the screening of MOFs for detection of large molecules. For example, at the 10 ppb level, all of the Zn-IRMOFs are able to distinguish between TNT and the structurally similar xylenes.

The electrochemical behavior of tungsten during chemical mechanical polishing (CMP) was observed in order to investigate a proposed blanket passivation and abrasion mechanism for tungsten removal. The experiments were performed in a cell that allowed electrochemical measurements to be made during polish. Polish rates were determined from the same samples used in the cell. Alumina-based polish slurries containing potassium iodate, ferric nitrate, or ammonium persulfate were used. DC polarization experiments show no evidence of passive film formation on the tungsten duiing polish. Tungsten oxidation rates measured during polish account for removal rates that are ito 2 orders of magnitude below the measured polish rate. Values of the charge-transfer resistance (measured by ac impedance spectroscopy) during polish are ito 2 orders of magnitude higher than expected from the polish rate, thus corroborating the dc-based data. Polish rates under potentiostatic conditions were also measured. The current required to maintain the metal anodic of the open-circuit potential is well below the current expected from measured polish rates, assuming complete oxidation of the tungsten. The polish rate during cathodic potentiostatic conditions (-0.5 V with regard to the open-circuit potential) was similar to the polish rate at open circuit. We conclude that the formation of a blanket passive layer does not significantly contribute to tungsten removal during CMP. InfroductionChemical mechanical polishing (CMP) is the most effective and now the predominant method for the removal of excess tungsten (W) deposited by nonselective chemical vapor deposition (CVD) for the formation of contacts and vias used in integrated circuit (IC) multilevel interconnects. Figure la depicts the CVD tungsten film and patterned oxide prior to polish. Figure ib depicts the same surface after CMP. The majority of W CMP research to date has focused on empirical cause and effect relationships in which process variables, such as slurry composition, pad type, applied pressures, and platen and carrier speeds, are empirically modeled. These empirical models allow for adequate manufacturing process control; however, they provide little information on the fundamental * Electrochemical Society Active Member.Oxide Fig. 1. The result of a blanket tungsten deposition is shown in the top sketch. The tungsten has been deposited in the vias opened in the inter-level dielectric, but is also present as a blanket film on the surface. The excess tungsten has been polished back to the interlevel dielectric in the bottom sketch.tungsten removal mechanisms that occur during polish. Clearer understanding of the removal mechanism(s) will benefit next-generation designs of slurries and pads and will improve W CMP manufacturing processes.In this work we investigate the role of tungsten oxidation and passive film formation in the mechanism of tungsten removal during CMP, by comparing measurements of the electrochemical behavior of the CVD tungsten film with tungsten removal rates obta...

We conducted experiments to determine the physical processes involved at the inversion point of water-kerosene dispersions. In the course of these experiments, we noted a viscosity maximum at the inversion point. This led to the development of an indirect method for determining the viscosity of concentrated liquid dispersions. Our data were found to be best fit by the dispersion viscosity equation (eq 6). Dispersion viscosity expressed as a function of dispersed-phase volume fraction gives some insight into the structure of the dispersed phase near the inversion point.Liquid-liquid dispersions are used to promote heat and mass transfer in mixer-settler units. The phase inversion behavior of these dispersions is important since the drop size of the dispersed phase and the settling time of the dispersion depend on which of the phases is continuous.

Ion irradiation was used to pattern a region of red-light emitting porous silicon by eliminating visible-light photoluminescence (PL). The PL peak wavelength is approximately 735 nm and shows little dependence on the excitation-light wavelength. The ratio of PL intensities for different excitation wavelengths was shown to be proportional to the ratio of the absorption coefficients. Below saturation, the integrated PL intensity increased linearly with excitation-light power density.

A description of ion-irradiation-induced reduction in the photoluminescence (PL) signal from porous silicon is given and a simple model which is consistent with a nanocrystalline Si structure is presented. Ion irradiation with 250 keV Ne is used to controllably reduce the integrated PL signal by 20% after a fluence of 4*1012 Ne cm-2 and completely eliminate the PL signal after a fluence of 4*1013 Ne cm-2. The use of vacuum and air annealing to recover ion-induced damage is also described, but the high temperatures for annealing cause elimination of the PL signal.