SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing (ERC)

                                                          **  Bringing Sustainability to Semiconductor Manufacturing **

A multi-university research center leading the way to environmentally friendly semiconductor manufacturing, sponsored by the Semiconductor Research Corporation's Global Research Collaboration (GRC) Research Program



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- 2012 -
Jan. 12, 2012 No TeleSeminar--Holiday Schedule
Jan. 26 Host: Ara Philipossian, Chemical & Environmental Engineering, University of Arizona
Presented by:  Yun Zhuang, Chemical & Environmental Engineering, University of Arizona
Topic title
Tribological, Thermal and Kinetic Attributes of 300 vs. 450 mm Chemical Mechanical Planarization Processes
An existing 300 mm CMP tool has been modified to polish 450 mm wafers in order to demonstrate experimentally whether any differences exist in the tribological and thermal characteristics of the two processes, and from that, to infer whether one can expect any removal rate differences between the two systems. Results suggest that, within the ranges of parameter investigated, the two systems behave similarly in terms of their coefficients of friction and lubrication regimes. Additionally, it is shown that the 450 mm process, once adjusted for its platen velocity, runs only slightly warmer (by 1 – 2 °C) than its 300 mm counterpart. Experimental data, coupled with copper removal rate simulations show that the wafer surface reaction temperature of the 450 mm process is slightly higher (by 2 – 3 °C) than the 300 mm process. Consequently, simulated copper removal rates for the 450 mm process are higher (by 8 – 31%) than those for the 300 mm process depending on the polishing conditions. The above results indicate that when current 300 mm CMP processes are scaled up to 450 mm, tribological and thermal effects dictate material removal rates thereby somewhat complicating direct recipe transfers by IC makers.  (PDF) (Video)
Feb. 9 Host: Anthony Muscat, Chemical & Environmental Engineering, University of Arizona
Presented by:  Shawn Miller, Chemical & Environmental Engineering, University of Arizona
Topic title:  "
Low-ESH-impact Gate Stack Fabrication by Selective Surface Chemistry"
Abstract An additive processing approach where device layers selectively deposited on a surface to build a device from the bottom up can reduce the number of fabrication steps, reduce energy, reduce waste, and improve industrial process flows. On the front end of CMOS device fabrication, one application is to deposit a high-k dielectric film selectively on exposed gate channel areas relative to the surrounding masked regions. This presentation reports a study on the use of patterned hydrophobic, self assembled monolayers (SAMs) to spatially control the growth of high-k dielectric films deposited by atomic layer deposition (ALD). In this study, formation and patterning of a high quality octadecyltrichlorosilane (OTS) SAM have been used to control selective deposition of TiO2 from TiCl4 water ALD process.  (PDF)
Feb. 23 Host:  Farhang Shadman, Chemical & Environmental Engineering, University of Arizona
Presented by:  Manish Keswani, Materials Science and Engineering, University of Arizona
Topic title
"Use of Sonoluminescence and Sono-Electrochemistry Based Techniques for Fundamental Investigations of Acoustic Cavitation for Megasonic Cleaning Applications"
Abstract Megasonic assisted wet cleaning has been of interest to the semiconductor industry due to its effectiveness in removing particulate contaminants from silicon wafer surfaces. There has been a significant interest in understanding the phenomena of cavitation and acoustic streaming, which are known to play an important role in particle removal during megasonic cleaning. The different variables that can affect cavitation include sound field parameters (frequency, power density and percent duty cycle) and solution parameters (dissolved gas content, additives such as surfactants, liquid temperature etc). In the present work, the effect of various dissolved gases (Ar, N2 and CO2) and non ionic surfactants (Triton X-100 and NCW-1002) on cavitation in acoustically (~ 1 MHz frequency) irradiated aqueous solutions has been demonstrated through sonoluminescence and sono-electrochemistry based techniques.  In the first part of the presentation, role of dissolved gases in de-ionized water on sonoluminescence at various transducer power densities and percent duty cycle will be discussed. The second part of the presentation will include characterization of transient cavities in megasonic irradiated aqueous solutions containing either dissolved gases or non-ionic surfactants using micro-electrode based high resolution electrochemical techniques.
Mar. 8 No TeleSeminar-- Annual Review Meeting Preparation
Mar. 22 No TeleSeminar-- Annual Review Meeting
April 5 No TeleSeminar-- Post-Annual Review Meeting
April 19 Host: Farhang Shadman, Chemical & Environmental Engineering, University of Arizona
Presented by:  Hao Wang, Chemical & Environmental Engineering, University of Arizona
Topic title:  "
Effect of Particle Size on the Adsorption and Desorption Properties of Oxide Nanoparticles"
Using water molecules as a model adsorbing compound, the effect of particle size on the adsorption and desorption properties of porous oxide nanoparticles (NPs) was investigated.   The experiments were conducted using silica, hafnia and ceria NPs at
25C, 55C, 80C and 105C.  The moisture concentration on the surface of NPs was measured by monitoring the FTIR (Fourier Transform Infra-Red) spectra peaks corresponding to the stretching vibration of water molecules. A transient multilayer porous adsorption and desorption model was developed to represent the fundamental steps in the process. The model included the effect of NP surface properties, size, and porosity. The thermal stability of adsorbed species and the strength of bonding to the surface were evaluated by determining the activation energies of various steps. The results indicate that the surface interaction parameters are both temperature and particle size dependent. NPs with smaller size have a higher saturated surface concentration and a slower response to purge and desorption; this means that they attract more contaminants and retain them more strongly. As temperature decreases, NPs exhibit a higher saturated moisture concentration and are more prone to the adsorption of moisture and similar contaminants. Factors contributing to the environmental and health impact of NPs (extent of surface coverage, capacity, and activation energies of retention) are also evaluated and discussed.  (PDF)
May 3 Host: Farhang Shadman, Chemical & Environmental Engineering
Presented by: David Blackford, President, Fluid Measurement Technologies, Inc.
Topic title:  "
ITRS, SEMI and ASTM Guidelines for Semiconductor Ultrapure Water (UPW)Production and the Consequences for UPW Particle Metrology"
Recent committee activity by ITRS and SEMI has led to a major revision of the guidelines for UPW used to manufacture semiconductors. Based on input from worldwide contributors water specification guidelines now reflect a more logical approach to acceptable levels of contamination in UPW. For the first ITRS, SEMI and ASTM are actively seeking a common set of UPW guidelines rather than pursuing individual agendas. The new guidelines will be presented as part of this seminar.
The inability to detect nanometer-sized particles in UPW in near real-time is posing a serious threat to our ability to manufacture semiconductors as line-widths continue to shrink. The gulf between the size of particles the semiconductor industry needs to monitor (courtesy of ITRS) and the detection capability of Optical Particles Counters has reached crisis dimensions and is growing. A
SEMI task force is proposing a new stop-gap method to validate the performance of final filters between 5-15nm. Initial results of validated filters will be presented together with a discussion of the difficulties of designing such a filter validation guideline.  (PDF)
May 17 Host:  Paul Westerhoff, Civil, Environmental and Sustainable Engineering Program, School of Sustainable Engineering and The Built Environment, Ira A. Fulton Schools of Engineering, Arizona State University
Presented by
*** Paul Westerhoff, Civil, Environmental and Sustainable Engineering Program, School of Sustainable Engineering and The Built Environment
*** James Ranville, Department of Chemistry and Geochemistry, Colorado School of Mines
Topic title:  "Interaction of Nanomaterials with Wastewater Biomass and Their Detection in Water"  (
Paul Westerhoff, James Ranville, Pierre Herckes, Sung Lee)
Engineered nanomaterials have and will continue to be discharged to sewers from industry, private residence and other commercial activities.  First, this presentation explores these sources and to what extent engineered nanomaterials are removed at municipal wastewater treatment plants (WTPs).  Treated effluent from WTPs enters our rivers and lakes, while biosolids are land applied, landfilled or incinerated.  Second, we explore potential analytical methods to quantify and size engineered nanomaterials at environmentally relevant concentrations in water, such as that being discharged by industry to sewers or effluent from WTPs.  This includes a brief description of a few analytical methods and then in-depth description of Single Particle ICP-MS for quantification of engineered nanomaterials, including those relevant to the semi-conductor industry.  (PDF)
May 31 Host:  Shyam Aravamudhan, Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University
Presented by:  Christie M. Sayes, Ph.D., Program Manager, Nanotoxicology & Nanopharmacology, RTI International
Topic title:  "
Contemporary Issues in Nanotoxicology: Continuing to Relate Material Properties to Biological Responses"
Nanotechnology is most commonly driven by the increasing importance of very small particles in a variety of applications. These applications mainly reside in technologies stemming from the electronic or optical sensing approaches. With the advent of surface functionalization on very small particulates, however, gave way to the birth of nanomedicine and nanotoxicology. Our research continues to investigate the interface between the hydrophobic nature of inorganic nanostructures and the hydrophilic nature of biology. As part of the R&D in biological applications, we also study the unintended implications of engineered nanomaterials. Particles are carefully selected in groups of similar physicochemical properties, characterized as they transform over time, and exposed to mammalian and bacterial systems. Properties such as particle size, surface charge, and chemical composition are related to specific pathway-specific biological responses such as apoptotic, oxidative stress, or other immune or inflammatory events. Results of these studies provide insights on how engineered nanomaterial features influence cellular responses and thereby outline possible approaches for developing and applying predictive models for biological responses caused by exposure to nanomaterials.  (PDF)
June 14 Host:  Ara Philipossian, Chemical and Environmental Engineering, University of Arizona  
Presentation by:  Matthew Smalley, CMP Process Development Engineer, College of Nanoscale Science and Engineering, University at Albany
Topic title:  "
Chemical Mechanical Polishing to Create Pure Ge-filled Trenches within Silicon Dioxide"
Recent advances in on-chip optical interconnect propose using waveguides consisting of silicon-germanium (SiGe) or pure germanium (Ge) material confined within an oxide (SiO2) dielectric.  Pure Ge can be grown selectively within deep trenches, with some similarities to a damascene process.  New process flow is required which must result in filled trenches with a planar top surface.  The approach taken was to grow epitaxial Ge on patterned oxide trenches above a standard silicon substrate; followed by a chemical mechanical polish (CMP) to remove extra material above the trench top, and flatten the waveguide surface. This approach gives rise to a new set of problems not observed in a typical front end of line or back end of line CMP process.  One such problem observed and requiring solution is the “reverse” topography introduced by the nature of bottom up epitaxial growth.  It is also known that the Ge surface can easily be corroded or pitted during polish through chemical attack by a typical metal CMP slurry which uses a significant amount of hydrogen peroxide (H2O2) oxidizer.  In this work, initial process optimization is performed using test structures on 300mm wafers to facilitate delivery of planar Ge filled trenches using a CMP slurry with a low oxidizer concentration.  Consideration is given to the required balance of Ge and oxide rates, selectivity, and gross defectivity – measured using profilometry, scanning electron microscope imaging, atomic force microscopy, and optical inspection.  (PDF)
June 28 Host:  Jane Chang, Chemical and Biomolecular Engineering, University of California-Los Angeles
Presented by:  Jane Chang, Chemical and Biomolecular Engineering, University of California-Los Angeles
Topic title:  “Assessment of non-PFC chemistries for through-silicon via etch“
  Through-silicon-via etch (TSV) is at the core of 3-D integration, which yields higher performance than conventional 2-D wiring systems, and has been demonstrated with various gases such as SF6 and perfluorocarbon (PFC), which are high global warming potential (GWP) greenhouse gases, making their increased usage undesirable.  In this talk, a thermodynamics approach is used to assess and select other viable etch chemistries for TSV that are non-PFC, in an effort to reduce the usage of PFC gases and minimize their environmental impact.  A systematic study is based on the assessment of various halogen-based gases, utilizing a volatility diagram where the partial pressure of the etch products are determined as a function of the etchant pressure at various temperatures.  This functional relation can be determined from the thermodynamic equilibrium between the surface and gas-phase species, by considering the standard Gibbs free energy and the equilibrium constant.   (PDF)  (PDF-save 2)
July 12 Host:  Kai Loon Chen, Geography and Environmental Engineering, Johns Hopkins University
Presented by Kai Loon Chen, Johns Hopkins University
Topic title:  "
Fate and Transport of Multiwalled Carbon Nanotubes in Aquatic Systems"
Carbon nanotubes (CNTs) are increasingly used in commercial and industrial applications because of their unique mechanical and electronic properties.  With CNT-containing products already available in the market, it is inevitable that some CNTs will be released into natural aquatic systems (e.g., lakes, rivers, and groundwater), as well as engineered aquatic systems (e.g., water treatment plants).  To better predict the fate and transport of CNTs in these systems, the aggregation and deposition kinetics of multiwalled CNTs (MWNTs) in aqueous solutions are investigated.  Two batches of MWNTs with different degrees of surface oxidation are prepared in order to compare the effects of surface chemistry on nanotube aggregation and deposition kinetics.  The distributions of oxygen-containing surface functional groups for the lowly oxidized and highly oxidized MWNTs (LO-MWNTs and HO-MWNTs, respectively) are determined using X-ray photoelectron spectroscopy in conjunction with vapor phase chemical derivatization.  Aggregation and deposition kinetics of the MWNTs are monitored over a broad range of monovalent and divalent electrolyte concentrations using time-resolved dynamic light scattering and a quartz crystal microbalance, respectively.  HO-MWNTs are found to be more stable to aggregration and deposition than LO-MWNTs in the presence of NaCl.  However, in the presence of CaCl2, the stability profiles of both MWNTs are comparable.  Additionally, the deposited MWNTs can be released from silica surfaces when they are rinsed with low ionic strength solutions, indicating that the deposition of MWNTs is not always irreversible. (PDF)
July 26 Host:  Rockford Draper, Department of Molecular & Cell Biology and Department of Chemistry, University of Texas/Dallas
Presented by:  R. J. K. Udayana Rantunga  and  Ru-Hung Wang, Department of Chemistry, University of Texas/Dallas
Topic title:  “Pluronics and CNTs: Modeling and Toxicity”
Abstract:  The aggregation of carbon nanotubes (CNTs) is an impediment in developing applications for these unique molecules and investigating their inherent toxicity towards biological systems. Pluronic tri-block copolymers are among the most commonly used non-covalent dispersal agents in use. These non-ionic molecules are known to provide robust dispersions, although the factors governing their effectiveness are not well established. Furthermore, reports on the toxicity of Pluronic:CNT composites give conflicting accounts. He we present computer simulation and experimental studies on Pluronic:CNT composite structures, aimed at further understanding (1) the mechanism of Pluronic dispersion of CNTs, (2) the interaction of Pluronic:CNT composites with biological cells, and (3) reported Pluronic toxicity. We find that the hydrophilic:hydrophobic balance of the polymer species, as well as the concentration of polymer loading has a large impact on the behavior of composite structure. We also find that the conditions used in the preparation of these dispersions can significantly impact reported toxicity data. (PDF)
Aug. 9 CANCELLED:  Due to an unexpected scheduling conflict, today's TeleSeminar has been cancelled.  Please join us on August 23rd for the next SRC ERC TeleSeminar.  
:  Manish Keswani, Materials Science and Engineering, University of Arizona
Presented by:  Dr. Khaled Ahmed, Applied Materials

Topic title:  "Nanoscale CMOS Contacts: Science and Technology"

Switching speed in advanced CMOS transistors has become limited by the increasing parasitic resistance, which is dominated by the always shrinking source/drain contact area (<50nm). The solution to this pain is to reduce specific contact resistivity. Resistivity of 8E-9 ohm-cm2 has already been achieved in 32nm CMOS. Smaller values will be needed as contact area shrinks for future CMOS nodes. In this talk we discuss specific contact resistivity targets and how to achieve these aggressive targets using new contact architectures and equipment platforms. Also discussed are the challenges that result from changing the channel material from silicon to germanium and/or III-V, which also demands new source/drain materials and appropriate contact architectures. 
Aug. 23 Host:  Farhang Shadman, Chemical and Environmental Engineering, University of Arizona
Presented by
C. R. Helms, Professor, Electrical Engineering & Founding Director, Institute for Intelligent Energy Systems, University of Texas-Dallas; Professor Emeritus, Stanford University
Topic title:  "
New Paradigms in Energy Production – Texas Style"
Energy use in semiconductor manufacturing continues to increase year by year and projections for future generations of devices indicate this increase will continue and even accelerate in the future.  Thus, low cost, reliable energy, and effective energy strategies will continue to be important. 
     Interest in renewable energy sources has also mushroomed over the last few decades.  The holy grail, of course, is clean energy that does not produce (any) by products, and does not depend on the depletion of any natural resource.  More recently, there has been an increasing focus on reducing the use of carbon as an energy source altogether. 
     It is clear that the major impediment to the large scale implementation of renewables, especially in the US, is economic.  In Texas, for example, with electric rates at or below $0.10/KWatt-hr and with best-case costs for solar or wind at more than double that, the economics are hard to justify.  Most renewables, such as wind and solar also require large capacity energy storage systems.   
     This presentation will focus on the underlying issues leading to the current situation, especially in Texas.  We will then provide some predictions of what the future will bring, in terms of energy costs, sources for energy, and research needed.  Natural gas will be highlighted for its role in Texas as well as for the remainder of the US.  The presentation will focus mainly on electric power, but will show how the same developments in electric power generation will also impact energy production for the transportation sector.  (PDF)
Sept. 6 Host Shyam Aravamudhan,Assistant Professor of Nanoengineering, Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University and The University of North Carolina at Greensboro
Presented by
Eric Blough, Ph.D., Dept. of Pharmaceutical Sciences and Research, Center for Diagnostic Nanosystems, School of Pharmacy, Marshall University, Huntington, WV
Topic title:  "
Exposure to cerium oxide nanoparticles is associated with activation of MAPK signaling and apoptosis in the rat lungs"
Whether exposure to cerium oxide (CeO2) nanoparticles causes alterations in events associated with oxidative stress and apoptosis in rat lung has not been investigated. Male Sprague-Dawley rats were instilled with either vehicle (saline) or CeO2 nanoparticles at a dosage of 7.0 mg/kg and euthanized 1, 3, 14, 28, 56 or 90 days post exposure. Compared to age-matched control animals, exposure to CeO2 nanoparticles increased lung weight to body weight significantly (P<0.05). Furthermore changes in weights were associated with the cerium accumulation in the lungs, elevations in serum inflammatory markers, an increased Bax to Bcl-2 ratio, elevated cleaved caspase-3 protein levels, increased phosphorylation of p38-MAPK and diminished phosphorylation of ERK1/2-MAPK (P<0.05).  Taken together, these data suggest that exposure to CeO2 nanoparticles is associated with lung oxidative stress and cellular apoptosis. Supported by DOE Grant #DE-PS02-09ER-01 to ERB.  (PDF)
Sept. 20 Host:  Ara Philipossian, Chemical and Environmental Engineering, University of Arizona 
Presented by:  Yun Zhuang, Chemical and Environmental Engineering, University of Arizona
Topic title:
Aggressive Diamond Characterization and Wear Analysis during Chemical Mechanical Planarization"
In this study, a 3M A3700 diamond disc was used to condition a Cabot Microelectronics Corporation D100 pad for a total of 30 hours. Its aggressive diamonds and the furrow surface area evolution were analyzed on a pad substitute material (i.e. polycarbonate sheets). Results showed that the top 20 aggressive diamonds identified during the 30-hour polishing tests accounted for more than 75% of the total furrow surface area, confirming that they are the dominant working diamonds in pad conditioning. Results also showed that the original top 20 aggressive diamonds identified before wafer polishing experienced wear after the first 15 hours of polishing, indicated by the significant decrease (47%) in their furrow surface area. Seven new aggressive diamonds were “born” and they made a significant contribution (34% and 26% for Orientation 1 and 7, respectively) to the total furrow surface area. On the other hand, the furrow surface area generated by the new top 20 aggressive diamonds identified after the first 15-hour polishing was significantly lower (by 20%) than the original top 20 aggressive diamonds, leading to the loss of disc aggressiveness. In comparison, the disc aggressiveness was maintained after the second 15-hour wafer polishing as the furrow surface area of these new top 20 aggressive diamonds did not change significantly. The above results showed a general trend for a conventional diamond disc during its early life: the disc initially loses its aggressiveness due to wear of its original aggressive diamonds; as the original aggressive diamonds wear out, new aggressive diamonds are “born”, but these new aggressive diamonds are less aggressive than the original aggressive diamonds; the disc aggressiveness can be maintained if these new aggressive diamonds withstand further wear. (PDF) 
Oct. 4 Host:  Jane Chang, Chemical and Biomolecular Engineering, University of California,Los Angeles
Presented by
Kun-Chieh Chen, Nathan Marchack, and Jane P. Chang, University of California, Los Angeles
Topic title
"Selection of non-PFC chemistries for through-silicon via etch"
The continued extension of Moore’s Law, which dictates that the density of integrated circuit (IC) devices doubles every two years, presents formidable challenges in realizing complex and three-dimensional interconnect structures. Through-silicon-via etch (TSV) is at the core of 3-D integration, which yields higher performance than conventional 2-D wiring systems, and has been demonstrated with Bosch deep reactive ion etching (DRIE), cryogenic DRIE, laser drilling, and wet etching. In order to achieve the desired and continuously increasing aspect ratio (AR) of the features required for the device integration, DRIE is the preferred method for TSV for the attainable vertical sidewalls and high AR. Unfortunately, the primary gases used in DRIE for TSV are SF6 and perfluorocarbon (PFC) gases, which are high global warming potential (GWP) greenhouse gases, making their increased usage undesirable.
In this work, a thermodynamics approach is used to assess and select other viable etch chemistries for TSV that are non-PFC, in an effort to reduce the usage of PFC gases and minimize their environmental impact.  A systematic study is based on the assessment of various halogen-based gases, utilizing a volatility diagram where the partial pressure of the etch products are determined as a function of the etchant pressure at various temperatures.  This functional relation can be determined from the thermodynamic equilibrium between the surface and gas-phase species, by considering the standard Gibbs free energy and the equilibrium constant. A careful control of the etchant partial pressure near the isomolar point, where the partial pressure of the volatile species would reach that of the equilibrium value, has been shown to be necessary to control the formation of volatile species [1].  Amongst various candidates, NF3, a non-PFC gas with greenhouse rating only 1ppt in atmosphere, appears promising. From the thermodynamics analysis, the generation of fluorine atom from SF6 and NF3 is comparable, however, NF3 is much more able to form more SiF4, the volatile etch product, than SF6. While this is promising, another significant reaction product from NF3 is Si3N4, which is non-volatile. The addition of a second chemical such as O2 can necessitate its subsequent removal, through the formation of volatile products such as nitrogen oxides (NxOy). In addition, NF3 is also capable of removing SiO2 which is unintentionally formed during reaction with O2.  This work will highlight the analysis to design a NF3/O2 process (sequential exposure versus mixture) that yields comparable etch results compared to that achieved by SF6, thereby offering a viable alternate for TSV etch.  (PDF)
Oct. 18 Host Paul Westerhoff, Associate Dean for Research, Ira A. Fulton Schools of Engineering, and Professor, School of Sustainable Engineering and The Built Environment, Arizona State University
Presented by:  Paul Westerhoff, Arizona State University
Topic title: 
"Detection of carbon nanotubes in environmental and biological matrices using programmed thermal analysis"
Carbon nanotubes (CNTs) may be used in the semi-conductor manufacturing sector. This presentation will describe advances our team has made in analyzing a wide array of single and multi-wall CNTs in water and biological tissues down to 3 micro-grams of CNT mass.  This work supports ecotoxicity testing, but established a method to understand exposure (I.e., dose metrics).  It will support release studies from commercial products, and help assess workplace exposure.  [Paul Westerhoff, Kyle Doudrick, Pierre Herckes]  (PDF)
Nov. 1 Host:  Kai Loon Chen, Department of Geography and Environmental Engineering, Johns Hopkins University
Presented by:  Peng Yi,
Department of Geography and Environmental Engineering, Johns Hopkins University
Topic title
"Interaction of Multiwalled Carbon Nanotubes with Model Cell Membranes: A QCM-D Study"
Carbon nanotubes (CNTs) are widely used in consumer products and industrial and research applications because of their unique mechanical, chemical, and electronic properties.  Recently, several studies have shown that CNTs can exhibit toxic effects on bacterial and mammalian cells.  One of the proposed mechanisms for the cytotoxicity of CNTs is that the nanotubes can damage cell membranes and result in the inactivation of the cells.  In order to better understand the interaction between CNTs and cell membranes, the adsorption and desorption of multiwalled CNTs (MWNTs) on model cell membranes is investigated in solution chemistries that are relevant to environmental and biological systems using a quartz crystal microbalance with dissipation monitoring (QCM-D).
            In this study, supported lipid bilayers (SLBs) comprising 1, 2‒dioleoyl‒sn‒glycero‒3‒phosphocholine (DOPC) are employed as model cell membranes.  DOPC unilamellar liposomes are first produced by extruding a DOPC suspension through a membrane with a pore size of 50 nm.  When the liposomes are deposited on a silica-coated crystal in the QCM-D, they collapse to form a SLB on the crystal.  MWNTs are subsequently deposited on the SLB over a range of CaCl2 concentrations at pH 7.3.  The attachment efficiencies are obtained by normalizing the deposition rates of MWNTs on SLBs to the favorable deposition rates on silica surfaces that have been modified with positively charged poly-L-lysine.  The deposition kinetics of MWNTs on SLBs increases with increasing CaCl2 concentrations due to the neutralization of charges on the nanotubes and SLBs.  At CaCl2 concentrations above 1 mM, the MWNTs undergo favorable deposition on the SLBs.  In addition, release experiments are conducted by rinsing the deposited MWNTs with solutions of low electrolyte concentrations.  Our results show that some of the deposited MWNTs can be released from the SLBs when the solution CaCl2 concentration is decreased from 3 mM to 1 µM.  Similar deposition and release experiments will be conducted in the presence of NaCl.  The effect of solution pH on the deposition and release behavior of MWNTs on SLBs will also be investigated.   (PDF)
Nov. 15 HostPaul Pantano, Associate Professor of Analytical Chemistry, The University of Texas at Dallas
Presented by:  Angela R. Hight Walker, Ph.D., Senior Scientist, Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology
Topic title:  “Physicochemical Characterization of Engineered Nanoparticles: The Measurands that Influence Nano EHS”
:   There is general consensus that toxicology assessment of engineered nanoparticles (NPs) is hampered by a lack of reproducibility.  In general, there is a dearth of comparable and validated outcomes, even though substantial time and resources have been devoted to the cause.  One reason is the lack of thorough characterization of the NPs under study, i.e. are we testing the same NP or not?  As batch-to-batch and company-to-company variability is significant at the nanoscale, this question must be asked.  This issue, combined with the recent nano definition adopted within the EU which cannot be realized with current metrology, has the focus once again on the measurement science community.  Work ongoing within the standards organization of ISO/TC 229-Nanotechnology strives to establish guidance on the physicochemical characterization necessary to forge a path towards validation.  This work is collaborative with many other groups that have also proposed a minimum set of measurements necessary, such as OECD and MinChar.  Through a consensus process, these parameters have been assigned measurands — the quantity that is intended be measured — to aid the toxicologists and ultimately reach comparability between studies.  These measurands have also been assigned measurement methods and appropriate caveats to consider when working in the nano regime.  NIST is incorporating these terms, measurands and measurement method into our Nano EHS program and looking to establish metrological collaborations to reduce measurement uncertainty and increase comparability of toxicological studies in order to rigorously establish connections between physicochemical properties and toxicological response.
Speaker bio
:  Dr. Angela Hight Walker came to NIST in 1994 as a National Research Council Postdoctoral Fellow and was hired as a staff member in 1996.  She is now a Senior Scientist in the Semiconductor and Dimensional Metrology Division.  Her group’s present research focuses on understanding the underlying chemistry and physics of nanomaterials, including noble and transition metallic nanoparticles, carbon nanotubes, and graphene.  While the tool of choice is Raman spectroscopy, they use a suite of measurement methods to characterize the physicochemical properties of nanomaterials that enable key applications, such as electronics and medicine, as well as predict their impact on the Environmental Health and Safety.  Angela is actively involved in standard activities regarding nanotechnology.  Under ISO/TC 229, she chairs the US Technical Advisory Group for Working Group 2: Measurement and Characterization.  (PPT)
Nov. 29 Host:  Farhang Shadman, Chemical and Environmental Engineering, University of Arizona
Presented by:  Roy Dittler, Chemical and Environmental Engineering, University of Arizona
Topic title:  “Reducing Ultra-High-Purity (UHP) Gas Consumption by Characterization of Trace Contaminant Kinetic and Transport Behavior in UHP Fab Environments”
Abstract:   A combination of experimental investigation and process simulations was used to analyze the effect of various operational parameters on the extent of impurity back diffusion into the UHP gas systems. The results were then used to determine lateral venting designs and operational conditions to minimize back diffusion, UHP gas consumption, operating costs, and lost operation time due to contamination.

                The process model developed included various modes of impurity transport; the predicted results were in good agreement with the experimental data. Surface diffusion was a key mechanism of moisture transport into the lateral and it had a considerable impact on moisture levels seen in the UHP gas. At times, dispersion played a strong role in the transport of moisture into the lateral; especially in large diameter piping. Convection was the mechanism for moisture removal; however, relatively high Reynolds and Peclet numbers were needed to allow convection to overcome dispersion and surface diffusion.  Guidelines and critical values for Reynolds and Peclet numbers were identified for reducing back diffusion to the point where operating purity requirements were met while minimizing UHP gas usage. These guidelines allowed the determination of; lateral lengths, lateral diameters, flow rates, and operating pressures. Parametric studies on key operational parameters were performed with the process simulator and are presented.
                More recently, the process model has been adapted predict the transport of contaminants from multiple sources; more specifically, multiple venting laterals with restrictive flow orifices (RFOs) at the lateral/atmosphere interface. Preliminary results show that decreasing RFO diameter decreases the back diffusion of impurities into the UHP supply system. As expected, results showed that multiple sources of back diffusion have a compounding effect.  (PDF)
Dec. 13 Host Alex Tropsha, Division of Medicinal Chemistry and Natural Products, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill
Presented by:  Amy Wang, National Center for Computational Toxicology, U.S. Environmental Protection Agency
Topic title
:  "Toward Predicting Nanomaterial Biological Effects -- ToxCast Nano Data as an Example"  (PPT)
Dec. 27 No TeleSeminar--Holiday Schedule
Jan. 10, 2013 No TeleSeminar--Holiday Schedule
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