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APPLICATION
NOTE ABSTRACTS Abstract:
Colloidal dispersions which contain particles predominantly in the
submicron size range are ideal candidates for particle size analysis
using the combined techniques of dynamic light scattering (DLS) and
single particle optical sensing (SPOS). Our new Accusizer 388 hybrid
instrument system combines results from both of these systems simultaneously,
yielding particle size distribution (PSD) results over a wide size
range with unprecedented resolution. The DLS subsystem provides a
"broad-brush" description of the overall PSD, often using a simple
Gaussian or log-normal shape, where the resolution is limited by the
ensemble nature of DLS, requiring data inversion techniques. The resulting
mean diameter and standard deviation can be used to identify the end
point of the particle manufacturing process (e.g. grinding, homogenization,
emulsion polymerization, etc.). The complementary SPOS subsystem provides
a precise picture of the outlying, large-diameter tail of the primary
particles/aggregates, which often can severely compromise the quality
of the final product associated with the dispersion. Proprietary Autodilution
(Pat.) and specialized data analysis techniques permit the PSD results
from the two subsytems to be coupled quantitatively. Application Note 158 (AN158) Multiangle Sizing of Proteins and Protein Aggregation Abstract:
Proteins prepared using hot and cold methods were sized at 90, 60, and
20 degrees using the Nicomp 380 Dynamic Light Scattering (DLS) Particle
Size Analyzer equipped a multiangle goniometer. This capability was coupled
with a high powered 15 mW laser diode and a high gain avalanche photo-diode
detector providing a gain increase of 12 over the standard Nicomp 380.
Since larger particles scatter relatively more light in the forward direction,
low angle DLS has the potential to provide important information on the
aggregation of proteins and other macromolecules.
Abstract:
Traditionally, blood cells, both red and white, are counted using the
electrozone sensing method. This method measures the increase in resistance
or inversely, the decrease in conductivity across a small aperture when
particles, dispersed in a conductive medium, pass through this aperture.
The magnitude of this response is related to the particle’s volume and
thus its size. While this technique has worked well for years, this paper
demonstrates that particle counting using SPOS (Single Particle Optical
Sensing) in conjunction with Autodilution can size both red and white
blood cells with greater ease of use and less diluent restrictions than
electrozone sensing.
Abstract:
Zeta Potential has been used to gauge the stability of colloidal dispersions.
The basis for this is that zeta potential is proportional to the charge
on the surface of a particle. The larger the zeta potential then, the
stronger the repulsive forces between these particles. Such large repulsive
forces keep diffusing particles from randomly colliding together to form
aggregates. The measurement of zeta potential can be useful in other applications.
In this paper, zeta potential was used to test an instrument that separates
blood into its various fractions. Red blood cells have a larger surface
potential than white blood cells. It was observed that as the concentration
of white blood cells increased in each fraction, the average zeta potential
decreased.
Abstract:
In analyzing the particle size distributions of polymer emulsions, it
is common to employ one of the various light scattering methods. Generally,
they fall into two categories: Static and Dynamic. Static light scattering,
also known as Laser Diffraction, employs the use of spatially arrayed
detectors that record the scattered light patterns as a function of angle.
Dynamic light scattering measures, over a period of time, the amplitude
of the scattered light at one angle. In both techniques, specialized mathematical
algorithms are needed to invert either the scattered light patterns or
scattered light time profiles to arrive at particle size distributions
(PSDs). As a consequence of the ensemble nature of both these light scattering
methods, they are low resolution and low sensitivity techniques and they
can be susceptible to artifacts and instabilities. The data in this paper
demonstrates that the Nicomp algorithm, used only in the Nicomp 380, can
provide accurate and realistic PSDs for emulsion samples which have relatively
wide distributions and would give other light scattering instruments trouble.
Abstract:
Kaolin clay is a naturally occurring mineral used extensively by the paper
industry as filler and as a coating. In its natural state, Kaolin clay
is white in color. It is this whiteness as well as other properties such
a large surface area and good ink retention that makes it an ideal material
for use in the manufacturing of paper. Particle size is extremely important
in the processing of the clay. The clay particles are classified and the
different fractions are used to impart various properties to the paper.
It is also important in the processing of Kaolin clay that impurities
such as sand and mica be removed. The Accusizer 780, with its high sensitivity
and resolution, allows the clay fractions to be more accurately characterized
and out-liers to be more readily detected than can be done with Laser
Diffraction methods.
Abstract:
Chemical Mechanical Polishing (CMP) is an important set of steps in the
production of high-density integrated circuits. And because CMPs are used
during various points in the process for usually short periods of time,
they must be handled extensively and are exposed to many different environments.
New batches must be prepared often, from concentrate kept in storage.
All of these issues impact the stability of the slurries, which in turn
effect the yield levels of chips. What is required is a measurement technique
that is sensitive to low levels of out-of- spec particles, which can be
the result of contamination from handling or aggregation from applied
stress. This technique would need to be used to do quality checks on fresh
material and have the ability to be placed online to monitor the slurry
in-situ. The goal of this paper is demonstrate the utility of Single Particle
Optical Sizing (SPOS) for providing quantitative information about CMP
slurry health.
Abstract:
The semiconductor industry is moving toward smaller line widths and more
layers. One of the most important process considerations that will lead
the way to this higher density chip technology is more sophisticated control
of the planarization steps. The planerization or polishing steps are effected
by the use of colloidally dispersed metal oxide slurries (known as CMPs,
which stands for Chemical-Mechanical Planerization), primarily silica
and alumina, with mean diameters in the 10-200 nm range. These slurries
are applied to spinning polishing pads which rest on the wafers. In the
past, Laser Diffraction was most commonly used to characterize the particle
size distribution of these slurries. It has always been known that these
slurries contain a small volume percentage of particles greater than 1
micron in size. It is believed that these particles can cause scratches
and other defects in the wafer surfaces. This paper will demonstrate that
by virtue of the nature of the measurement, Laser Diffraction is inadequate
to the task of quantitatively determining the concentration of out-of-spec
slurry particles. On the other hand, Single Particle Optical Sizing or SPOS, because it counts particles, will be shown to be an excellent tool
for characterizing CMP slurries.
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