Electrostatic clamping with an EUVL mask chuck: Particle issues

Particle and defect issues related to electrostatic chucking with an ultra-planar, pin-structured mask chuck for EUVL application were addressed. By mapping particles/defects on the backside of 8 inch Si-wafers before and after chucking, particle transport from the chuck to the wafer was studied at application relevant electrostatic forces. Particles were detected by analysis of stray light intensities on the wafer side. Investigations were performed under ambient conditions at high chucking voltages on a bipolar chuck. Particle transport from the chuck surface to the wafer surface was mapped and found to concentrate at the pin sites. Successively lower particle counts with increasing number of chucked wafers were observed, indicating a “cleaning effect” on the chuck’s surface induced by the electrostatic chucking procedure. No influence of electric field direction (polarity) on particle count was discernable.     

Impact of Nonuniform Fouling on Operating Temperatures in Heat Exchanger Networks

ABSTRACT

Investigations of fouling in heat exchangers are mainly focused on two factors: commercial impact due to energy losses, and environmental impact manifested through higher CO₂ emissions. The purpose of this paper is to introduce a third factor relating to safety in operations. This paper presents two case studies, one for a hydroprocessing unit with feed/effluent heat exchangers and another for preheat train exchangers installed upstream of the atmospheric furnace in a refinery crude unit. Due to a wide range of process temperatures examined in both case studies, the heat exchangers in the network are subject to various fouling mechanisms. As illustrated in the pictures of actual tube bundles, some of the exchangers within the network are heavily fouled, while the other exchangers operate in nearly clean conditions. Detailed simulations indicate that nonuniform fouling results in heat exchanger operating temperatures that are significantly higher than those predicted by conventional analyses using uniform fouling. Higher than anticipated process fluid temperatures may result in exceeding the threshold limits for certain corrosion mechanisms and/or significantly higher than expected rates of corrosion.     

Determination of Vitamin B12 in meat products by RP-HPLC after enrichment and purification on an immunoaffinity column

A quantitative method for the determination of Vitamin B12 in meat products by RP-HPLC and UV detection was developed and compared to the reference method (microbiological assay, MBA). Vitamin B12 was extracted with 50 mM sodium acetate buffer in the presence of sodium cyanide. For the quantification of total Vitamin B12, it was necessary to release protein-bound Vitamin B12 by pepsin treatment. Cyanocobalamin was detected as total Vitamin B12 after purification and enrichment on an immunoaffinity column. The calibration with five concentrations of Vitamin B12 was linear with a regression coefficient r2 > 0.99. The method was validated at three different concentration levels (5-15 ng/g) with salami showing good recovery rates between 80 and 108% and low relative standard deviations between 1.50 and 7.26% (n = 6). The detection limit was found to be 2 ng/g. The Vitamin B12 levels of 50 meat products measured by the developed procedure were similar or significantly lower than those determined by the MBA.     

Model Studies in Catalysis

We review our approach to model heterogeneous catalysts on the basis of four examples. It is shown that Pd nanoparticles in hydrogenation incorporate hydrogen which turns out to be crucial for the actual hydrogenation step. The second example correlates the structure of vanadia monolayer catalysts with its reactivity in methanol oxidation. Further examples refer to ultrathin oxide film catalysts where the oxide metal interface controls either the charge state of Au particles grown on the film (example 3), and, in the fourth example, the oxide film itself exhibits remarkable CO-oxidation activity which can be traced to a reactive intermediate structure of the ultrathin film.     

Gold supported on thin oxide films: from single atoms to nanoparticles

[Figure: see text]. Historically, people have prized gold for its beauty and the durability that resulted from its chemical inertness. However, even the ancient Romans had noted that finely dispersed gold can give rise to particular optical phenomena. A decade ago, researchers found that highly dispersed gold supported on oxides exhibits high chemical activity in a number of reactions. These chemical and optical properties have recently prompted considerable interest in applications of nanodispersed gold. Despite their broad use, a microscopic understanding of these gold-metal oxide systems lags behind their application. Numerous studies are currently underway to understand why supported nanometer-sized gold particles show catalytic activity and to explore possible applications of their optical properties in photonics and biology. This Account focuses on a microscopic understanding of the gold-substrate interaction and its impact on the properties of the adsorbed gold. Our strategy uses model systems in which gold atoms and clusters are supported on well-ordered thin oxide films grown on metal single crystals. As a result, we can investigate the systems with the rigor of modern surface science techniques while incorporating some of the complexity found in technological applications. We use a variety of different experimental methods, namely, scanning probe techniques (scanning tunneling microscopy and spectroscopy, STM and STS), as well as infrared (IR), temperature-programmed desorption (TPD), and electron paramagnetic resonance (EPR) spectroscopy, to evaluate these interactions and combine these results with theoretical calculations. We examined the properties of supported gold with increasing complexity starting from single gold atoms to one- and two-dimensional clusters and three-dimensional particles. These investigations show that the binding of gold on oxide surfaces depends on the properties of the oxide, which leads to different electronic properties of the Au deposits. Changes in the electronic structure, namely, the charge state of Au atoms and clusters, can be induced by surface defects such as color centers. Interestingly, the film thickness can also serve as a parameter to alter the properties of Au. Thin MgO films (two to three monolayer thickness) stabilize negatively charged Au atoms and two-dimensional Au particles. In three dimensions, the properties of Au particles bigger than 2-3 nm in diameter are largely independent of the support. Smaller three-dimensional particles, however, showed differences based on the supporting oxide. Presumably, the oxide support stabilizes particular atomic configurations, charge states, or electronic properties of the ultrasmall Au aggregates, which are in turn responsible for this distinct chemical behavior.