A numerical algorithm is described
that accurately locates and calculates the area beneath peaks from
real mass spectral data using only reproducible mathematical operations
and no user-selected parameters. Such a fully automated algorithm
was required for rapid and repeatable processing of mass spectral
data containing hundreds of peaks. By working without any user input
it both saves operator time and eliminates operator bias. The first
criterion is desirable when processing large amounts of data (for
example in proteomics research). The second criterion is necessary
to the Polymer Division's goal of creating an absolute molecular mass
distribution synthetic polymer Standard Reference Material where operator
bias in the data analysis cannot be tolerated.
The microelectronics industry
is testing a wide variety of porous low-dielectric constant ("low-k")
materials for future use in integrated circuits. To understand low-k
thin film properties, a quantitative analysis of pore size distribution
is vital. The Electronics Materials group has developed a new approach
to this challenging problem based on a small angle neutron scattering
(SANS) porosimetry technique. The new technique quantifies pore size
distribution and reveals subtle material characteristics inaccessible
to other measurement techniques.
The continued reduction in
pattern sizes throughout the semiconductor industry will soon require
new metrologies capable of high throughput non-destructive measurements
of dense, high aspect ratio patterns with subnanometer resolution.
In collaboration with industrial partners, we are developing a metrology
based on Small Angle X-ray Scattering (SAXS) to quickly, quantitatively,
and non-destructively measure the smallest, or "critical",
dimensions expected in the next two technology nodes with subnanometer
precision. Quantities of interest include critical dimension, pattern
sidewall angle, statistical deviations across large areas, and quantitative
measures of pattern sidewall roughness. These efforts are driving
toward the specification of a laboratory scale device capable of providing
pattern dimensions during routine tests of fabrication processes.
As technology continues to
strive towards smaller, thinner, and lighter devices, more stringent
demands are being placed on polymer films as diffusion barriers, dielectric
coatings, electronic packaging, etc. The material properties of thin
films can be drastically different from that of the bulk material.
Therefore, there is a growing need for testing platforms that allow
for rapid determination of the mechanical properties of thin polymer
films/coatings. We demonstrate here a novel measurement technique
that yields the elastic modulus of supported polymer films in a rapid
and quantitative manner without the need for expensive equipment or
material-specific modeling.
Novel composites engineered
from polymers and carbon nanotubes offer the promise of plastics with
enhanced thermal, electronic, and mechanical properties, but the ability
to control and quantify particle dispersion in such materials is an
unresolved issue of fundamental importance. Of particular interest
is how processing flows influence tube dispersion and orientation.
We are developing metrologies and methods that directly address the
fundamental nature of elastic flow instabilities in polymer-dispersed
carbon nanotubes, enabling better control of dispersion during flow
processing of melts and suspensions.
Non-destructive, in vitro evaluation
of tissue engineered medical products (TEMPs) will shorten their development
time. Imaging techniques such as collinear optical coherence and confocal
fluorescence microscopies are being used to address the challenges
of imaging these systems. An equally important component of the work
is the image quantification as a vehicle to evaluate the voluminous
imaging data.
Polyolefins, primarily polyethylene
and polypropylene, comprise the largest share of the U.S. market for
polymers. Demand for the newer metallocene polyolefins is expected
to grow 20 percent per year through 2006. The Polymers Division develops
a variety of measurement tools and concepts to meet the broad needs
of this diverse industry. Below, the program is broken down into four
interrelated components: molecular characterization, microscopic structure,
processing, and physical properties. Each component addresses the
needs of different industrial segments, but together they provide
a backbone for continued growth. While each component has focused
on polyolefins, there is a broader applicability of the research.
Microscale processing is an emerging
technology with unique challenges and applications in polymer processing
and microfluidics industries, but the physics of processing emulsions
when the drop size is comparable to a sample dimension is poorly understood.
We are developing predictive models as we measure the effect of confinement
and flow on the distribution and morphology of one component in another.
Pore size distributions in low-k dielectric thin films from X-ray
porosimetry
NIST is working to provide the
semiconductor industry with detailed information on the nanoscopic
pore size distribution of porous thin films destined as low-k dielectric
materials for the next generation of integrated circuits. The electronics
industry has chosen the introduction of nanometer scale pores into
interlayer dielectric films as the method of lowering the effective
dielectric constant. While these modifications change the dielectric
constant favorably, other important parameters such as physical strength
and barrier properties will also change, often in an unfavorable way.
A new method has been developed to calculate the pore size distribution
from x-ray reflectivity measurements on thin films in a controlled
environment of solvent vapor.
Direct Measurement of the Reaction Front in Chemically Amplified
Photoresists
The continual device performance
increases by the semiconductor industry has been largely driven by
the fabrication of smaller structures with lithography. As feature
sizes approach sub-100 nm, the photolithographic process must be controlled
with tolerances of (2 to 5) nm, dimensions comparable to the molecular
size of the polymer chains in the photoresist imaging material. New
experimental methods are needed to measure transport and materials
science phenomena over nanometer length scales to provide critically
needed data for the understanding, design, and control of new lithographic
materials and processes. In collaboration with IBM and the University
of Texas, we directly measured the spatial evolution of a reaction
front, within a photoresist, with nanometer resolution using neutron
and x-ray reflectometry and a deuterium-labeled photoresist polymer.
Tissue engineering represents
a new paradigm in medicine by seeking to regenerate missing or damaged
tissue. Developing, manufacturing, and regulating tissue engineered
medical products require proving the safety and efficacy of these
complex devices. This presents a significant measurement challenge
involving qualification of materials, cells, and delivery methods.
The NIST Combinatorial Methods
Center (NCMC) was formally established in January 2002 to provide
information and expertise on combinatorial methods to a wide range
of industrial, academic and government institutions interested in
acquiring combinatorial and high-throughput capabilities suited for
materials research. The NCMC functions through two complimentary efforts.
1) A research program geared towards the development of techniques
and instrumentation for the fabrication and analysis of novel combinatorial
libraries. This research centers on novel gradient combi methods,
where the NCMC has recognized expertise. 2) An outreach program designed
to gauge industrial needs in combi research and effectively disseminate
data, instrumentation design, best practices and protocols, and other
information relevant to combi techniques.
Off-Shore Oil Industry Benefits From New Tools for Design of Composite
Structures
The off-shore oil industry needs
the light weight of composite structures if it is to retrieve the
vast supply of oil that exists in deep water deposits. In the last
five years, fabricators have make composite components such as drilling
and production risers, but their light weight can magnify problems
such as harmful vibrations induced by waves and currents. A joint
program between NIST and the University of Houston has provided the
first tools that allow industry to simultaneously optimize material
selection and structural design to control unwanted vibrations in
drilling and production risers. The basic material property data are
generated by NIST and used in a computer model developed by the University
of Houston to predict vortex-induced vibrations so the effects of
changes in material and design can be determined.
Fluorescence Based Temperature Measurements Impact Industrial
Polymer Processing
Temperature is the most important
parameter for controlling and modeling polymer processing. It plays
a fundamental role in determining flow characteristics, degradation
phenomenon, phase transitions, and morphology of the final product.
Accurate measurements of resin temperature are not obtained using
conventional methods such as thermocouples because such devices are
unduly influenced by the large thermal mass of the processing machine.
Resin and machine temperatures are never the same because the viscous
resin dissipates energy during flow causing its temperature to increase
significantly, sometimes approaching the degradation threshold. Our
method to measure the true resin temperature is based on fluorescence
spectroscopy. The technique has implications for materials testing,
for development of processing strategies and for process control.
New tools in the battle against the “sharkskin” instability in
polymer extrusion
The throughput of widely used polyolefins
is limited by a processing defect known as “sharkskin,” which is a
flow instability that causes an undesirable surface roughness on the
extruded polymer. Polymer processing additives (PPAs) are commonly
used to eliminate sharkskin, and hence are an enabling technology
for the polyolefin industry. However, the mechanism by which they
work is unclear, hindering development of next generation additives.
We developed a capillary rheo-optics technique to visualize how PPAs
eliminate sharkskin. We successfully monitored the coating of the
PPA onto the internal surface of the capillary die wall and also measured
extraordinary levels of slippage between the PPA and the polyolefin.
These results provide the first quantitative measurement tools with
which to gauge PPA performance.
Polymer Reference Materials for Calibration of Instruments and
for Benchmarking
Standard reference materials and
reference materials are issued to address needs of the producers,
processors and users of polymers for calibration and for performance
evaluation of instruments used in the control of the synthesis and
processing of polymers as well as benchmarks for comparisons of measurement
methods and development of new materials. Recently produced standard
reference materials include polyethylene of narrow mass distribution
certified for mass average molecular mass and intrinsic viscosity
and a nonlinear fluid standard for rheological measurements. In addition,
the first reference biomaterial, an orthopedic grade ultrahigh molecular
weight polyethylene, was issued for use in development of improved
test methods for wear and as a benchmark for development of improved
materials. 40 50 DRI Signal
Nitric Acid-Modified N-Phenyliminodiacetic Acid – A Total Self-etching
Primer for Bonding to Tooth Structure
Dental manufacturers and practicing
dentists need stable, simplified, self-etching primers that will simultaneously
condition both dentin and enamel surfaces and also mediate effective
bonding to these mineralized tissues. Such self-etching primers will
overcome many of the problems of current dental adhesives, promote
conservative dentistry and benefit the general public.
Combinatorial Measurements of Phase Separation and Dewetting in
Polymer Films
An understanding of the stability
and homogeneity of thin polymer films on solid substrates has technological
and scientific importance in applications ranging from coatings, dielectric
layers, and lubricant surfaces to fundamental studies of polymer thin
films. Dewetting and phase separation are two important and commonly
occurring phenomena that can be used to control the morphology, topography
and chemical composition heterogeneity of polymeric surfaces. These
phenomena are influenced by a large number of factors that include
both material properties as well as process variables, leading to
a multidimensional parameter space that is difficult to explore by
conventional experimental and analysis methods. The power of combinatorial
methods for mapping out phase separation and dewetting in polymer
thin films is demonstrated here.
Structure and Property Measurements of Porous Low-k Dielectric
Thin Films
Low-k interlayer dielectric materials
have been identified by the microelectronics industry as a critical
factor to enable deep submicron technology for the continued improvement
of integrated circuits. NIST is working to provide the semiconductor
industry with unique on-wafer measurements of the physical and structural
properties of porous thin films important to their use as low-k dielectric
materials. We have developed a novel methodology utilizing several
complementary experimental techniques to measure the average pore
size, porosity, pore connectivity, film thickness, matrix material
density, coefficient of thermal expansion, moisture uptake, and film
composition of several classes of candidate porous thin film materials.
Polymer composite dielectrics enable development of embedded decoupling
capacitance technology for high speed electronics
Increased signal speed within electronic
circuits can be achieved by creating an efficient local power supply
for charging fast processors and switching devices. Current technologies
utilize surface mount discrete capacitors, which become ineffective
at frequencies approaching 1 GHz. Our effort focused on embedded capacitance
layers made of polymer composite films to effectively eliminate the
switching noise. We have developed a specialized test vehicle design
and invented a new testing procedure to verify the efficiency of embedded
capacitance on circuit boards and to measure the broad-band dielectric
permittivity of new materials at functional frequencies from 100 MHz
to 10 GHz.
NIST Material
Science & Engineering Laboratory - Polymers Division