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2012 - |
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Jan. 12,
2012 |
No
TeleSeminar--Holiday Schedule |
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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
Abstract:
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"
Abstract:
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
25 C,
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"
Abstract:
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)
Abstract:
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"
Abstract:
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"
Abstract:
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“
Abstract:
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"
Abstract:
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.
Host:
Manish Keswani, Materials Science and Engineering, University of Arizona
Presented by: Dr. Khaled Ahmed, Applied Materials
Topic title: "Nanoscale CMOS Contacts: Science and
Technology"
Abstract:
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"
Abstract:
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"
Abstract:
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"
Abstract:
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"
Abstract:
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"
Abstract:
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"
Abstract:
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 |
Host:
Paul 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”
Abstract:
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 |
|
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Jan. 10,
2013 |
No
TeleSeminar--Holiday Schedule |
|
Jan. 24 |
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Feb. 7 |
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Feb. 21 |
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March 7 |
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March 21 |
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April 4 |
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April 18 |
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May 2 |
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