Fixed-polarizer ellipsometry: a simple technique to measure the thickness of very thin films, B. Trotter, G. Moddel, R. Ostroff, and G. R. Bogart, Opt. Engr., 38 , 902

Fixed-polarizer ellipsometry: a simple technique to measure the thickness of very thin films, B. Trotter, G. Moddel, R. Ostroff, and G. R. Bogart, Opt. Engr., 38 , 902
Fixed-polarizer ellipsometry: a simple technique
to measure the thickness of very thin films
Brian Trotter
Garret Moddel
University of Colorado
Electrical & Computer Engineering
Department
Campus Box 0425
Boulder, Colorado 80309-0425
E-mail: [email protected]
Rachel Ostroff
Gregory R. Bogart
BioStar, Incorporated
6655 Lookout Road
Boulder, Colorado 80301
Abstract. The fixed-polarizer ellipsometer measures thickness of thin
films. It is simple, inexpensive, and provides a linear response over a
range of 800 Å. We develop a matrix formulation to describe the optical
characteristics of the instrument and apply it to the case of a single thin
film on a substrate. Excellent agreement is found between experimental
and simulated results. Applying the instrument to optical immunoassay,
we show that its sensitivity can extend to 4 pg/ml, depending upon the
analyte. This compares favorably with commercially available manual
and automated immunoassay systems. The fixed-polarizer ellipsometer
appears to be well-suited for use in laboratory and production environments. © 1999 Society of Photo-Optical Instrumentation Engineers.
[S0091-3286(99)02205-9]
Subject terms: ellipsometry; thin films; optical immunoassay; optical measurements; thickness measurement.
Paper 980007 received Jan. 12, 1998; revised manuscript received May 26,
1998, and Nov. 15, 1998; accepted for publication Dec. 15, 1998.
1 Introduction
Ellipsometry provides a powerful method to measure the
thickness of thin transparent films. The measurement is
based on the difference between reflection coefficients and
phase delays of light having polarizations parallel versus
perpendicular to the plane of incidence. Conventional
ellipsometers1,2 incorporate two polarizers and a quarterwave plate, at least one of which is rotating. These instruments can accurately measure film thicknesses in the angstrom range and below.
Another type of ellipsometer, the comparison
ellipsometer,3 has no moving parts. It is designed such that
light reflects first off a surface coated with a film of unknown thickness and then off a reference film. The reference film consists of a wedge of material having the same
optical properties as those of the unknown film, but with
varying thickness. A dark extinction line appears where the
two thicknesses are the same. This approach provides the
ability to view an area rather than a single point, but yields
accurate thickness measurements only of films of known
optical properties.
We present an even simpler instrument for accurately
measuring the thickness of very thin films. The instrument
incorporates one or two fixed-position polarizers in addition to the light source and detector. It is simpler and faster
to use than a standard ellipsometer, requiring only one intensity measurement to determine the film thickness. Different substrates and films are easily accommodated by
changing the polarizer and analyzer angles and the calibration curve. An instrument that has a similar configuration,
but is restricted to operating close to the Brewster angle,
was applied by Arwin and Lundström to quantify immunological reactions.4
In this paper we apply optical theory to describe the
operation of the fixed-polarizer ellipsometer. The determination of single- or multi-layer transparent film thickness is
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Opt. Eng. 38(5) 902–907 (May 1999)
0091-3286/99/$10.00
first modeled then compared to experimental results. Examples of the application of the fixed-polarizer ellipsometer
to immunological reaction measurement are given and
compared to other immunoassay techniques.
2
Optical Theory
2.1 Polarization States and Reflection Coefficients
When light is incident on a flat sample at a nonperpendicular angle, the directions of propagation for the
incident and reflected beam together define a plane. This
plane of incidence is the plane in which we analyze the
problem. Our goal is to analyze the change in polarization
state, including amplitude and phase, of the reflected beam
to determine the thickness of a thin film on the reflecting
substrate. There are two independent linear polarization
states of the incident light. The electric field of the light can
either be in the plane of incidence ~p-polarized, also called
TM-polarized! or it can be perpendicular to it ~s-polarized,
also called TE-polarized!. Any linear state of polarization
can be expressed as a combination of these two states, provided they are in phase. If there is a difference between the
phases of these two states, the light is described as being
elliptically or circularly polarized, because the electric field
vector follows an elliptical or circular spiral as the light ray
propagates.5
Due to differences in the coupling of the two polarizations to the medium of the sample, the amplitude and phase
of reflected light is different for light in the two polarization
states. The reflection coefficients for the amplitude are
given in Eqs. ~1a! and ~1b! for waves respectively parallel
and perpendicular to the plane of incidence.
p
r 12
5
n 2 cos u 1 2n 1 cos u 2
n 2 cos u 1 1n 1 cos u 2
~1a!
© 1999 Society of Photo-Optical Instrumentation Engineers
Trotter et al.: Fixed-polarizer ellipsometry: . . .
r tot 5
b5
Fig. 1 Fixed-position ellipsometer configuration. The source can be
a laser, laser diode, or filtered white light source. The instrument
arm angle is f. Inset: multiple reflections for a single film.
r 121r 23e 22i b
,
11r 12r 23e 22i b
2 p n 2 d cos u 2
,
l
~2a!
~2b!
where medium 1 is the air, 2 is the film, and 3 is the substrate; r 12 and r 23 are the amplitude reflection coefficients
at each interface; b is the phase delay that results from the
film; d is the thickness of the film; and u 2 is the angle of
the light beam in the film with respect to the surface normal. There are two values for r tot , corresponding to the
two polarization states and two sets of reflection coefficients.
These reflection coefficients are complex numbers. This
results from the wave nature of light and is a shorthand
notation for both the magnitude and the phase of the
electro-magnetic wave. The instrument measures light intensity, and we are therefore concerned with the reflection
coefficient for intensity. The intensity reflection coefficient,
also called the reflectivity, is the square of the amplitude
reflection coefficient, u r u 2 .
Fixed-Polarizer Ellipsometer
The fixed-polarizer ellipsometer uses the variation in reflection coefficient with film thickness @affecting b in Eq.
~2b!# and the difference between reflection coefficients for
the two polarizations @r s vs. r p from Eqs. ~1a!, ~1b!, and
~2a!# to determine the thickness of a thin film. This is done
in a manner similar to conventional ellipsometry with two
key differences: ~1! the fixed-polarizer ellipsometer uses no
quarter-wave plate and thus can be used with monochromatic light sources of any wavelength without changing
components; and ~2! the polarizers in the fixed-polarizer
ellipsometer are fixed, as opposed to the rotating polarizers
found in conventional ellipsometers. ~For more on conventional ellipsometers, see the excellent book by Tompkins,1
and the classic work on ellipsometry by Azzam and
Bashara.2!
Figure 1 is a schematic of the fixed-polarizer ellipsometer. The input polarizer is referred to as the ‘‘polarizer,’’
while the output polarizer is called the ‘‘analyzer.’’ Both
are linear polarizers which can be rotated about the beam
axis. Once adjusted, they remain fixed throughout the measurement. The instrument arm angle is f, which is equal to
u 1 in Eqs. ~1a! and ~1b!.
Light incident on the sample is linearly polarized. After
reflection it has, in the general case, some degree of ellipticity. For a bare silicon substrate this ellipticity is very
small, and the light is very close to being linearly polarized.
The analyzer is oriented such that most of the light is
blocked. The remaining light enters the detector and produces a photocurrent which is proportional to the intensity.
The photocurrent is usually transformed into a voltage by a
transimpedance amplifier.
When a film is first grown on the silicon substrate the
ellipticity increases with thickness, the axes of the ellipticity rotate, and the fraction of reflected light passing through
the analyzer increases. This increase in output intensity
continues until an axis of the ellipse passes the analyzer
angle or until the film reaches a thickness of
2.3
r s125
n 1 cos u 1 2n 2 cos u 2
.
n 1 cos u 1 1n 2 cos u 2
~1b!
The indices of refraction of the media above and below the
interface are n 1 and n 2 , respectively, and u 1 and u 2 are the
respective angles between a normal to the interface and the
light beam for the incident and transmitted light. These
angles are found using Snell’s law: n 1 sin(u1)
5 n2 sin(u2).
Layered Films
The fixed-polarizer ellipsometer provides a measurement of
the thickness of a film on a substrate that has a different
refractive index from that of the film. While the formulas
given above work for a single reflection, one must also take
into account multiple reflections among the interfaces of
the layer. This multiple reflection condition is depicted in
the inset of Fig. 1.
The multiple reflections from this film are accounted for
using a matrix formulation of the reflection equations. For
multi-layer films, the matrix formulation models the multiple interfaces, with each layer and each interface between
layers corresponding to a matrix. Interfaces which are
rough can be modeled using an effective medium
approximation.6–8 These matrices are then multiplied together to find the overall reflection coefficient. Each of the
two polarization states of the system requires a separate
matrix which is used to find the reflection coefficient for
that polarization. The matrices and examples of their use
can be found in the literature.9
In this paper we analyze a single film on an opaque
substrate. When dealing with such a system, the matrix
technique simplifies to the following equation
2.2
Optical Engineering, Vol. 38 No. 5, May 1999
903
Trotter et al.: Fixed-polarizer ellipsometry: . . .
Fig. 2 Comparison of simulated (line) and experimental (points) results for a siloxane film. The wavelength is 670 nm, the refractive
index of the film is 1.41, the polarizer angle ( u p ) is 10°, the analyzer
angle ( u a ) is 50°, and the instrument arm angle (f) is 65°.
range of accuracy works well for our current immunoassay
technology, future work in this or other areas may require
accuracy in a different range.
Changing this region of sensitivity can be accomplished,
but this requires complicating the system. The lack of sensitivity outside of this thickness region arises due to the
elliptical polarization of the reflected light, which cannot be
readily blocked by a linear polarizer. This ellipticity reduces the contrast between different thickness levels and
thus reduces the sensitivity of the reading. If a quarter-wave
plate is added to remove this ellipticity, however, the region of sensitivity can be moved to any thickness of interest. Addition of a quarter wave plate changes the physical
setup to that used in most conventional ellipsometers which
incorporate a rotating polarizer.
2.5 Calibration
(l cos(u2))/(4n2). In the former case, the transmitted intensity falls slightly because less of the elliptically polarized
light goes through the polarizer, i.e., the component of polarization along the polarizer is falling as the ellipse axis
rotates away. In the latter case, the effect of the film starts
to cancel itself and the ellipticity of the light returns towards its original state. By the time the thickness has
reached (l cos(u2))/(2n2), the film is optically invisible and
the sample looks like a clean substrate. Thus the transmitted intensity is periodic with thickness.
We now describe mathematically this transmitted light
intensity. The intensity at the detector can be expressed as
I out5I inu r tot,p cos~ u p ! cos~ u a ! 1r tot,s sin~ u p ! sin~ u a ! u 2
~3!
where I in is the source intensity and u p and u a are the
respective polarizer and analyzer angles with respect to the
p-polarization axis.
In a conventional ellipsometer the polarizer and analyzer
must be rotated to determine a film thickness. The fixedpolarizer ellipsometer, however, is constrained such that a
single intensity measurement with fixed polarizers is sufficient to provide the thickness of a deposited film to a high
degree of accuracy. A simulation of the fixed-polarizer ellipsometer was made using the software program
Mathematica.10 The results are shown in Fig. 2. This simulation incorporated values for our particular experimental
system, described below. ~Numerical values for a given experiment are given in the corresponding figure caption.!
The measurement of other common materials, e.g., organic
films, silicon nitride, and indium tin oxide, can be measured
using this technique. The magnitude and period of the
curve change with a change of the instrument angles ~f, u p
and u a ) and the refractive index of the film.
2.4 Region of Sensitivity
The variation of ellipticity with film thickness is not linear,
and hence the output of our instrument exhibits regions of
high and of low sensitivity, consistent with the discussion
preceding Eq. ~3!. The measurement is most accurate where
the variation of intensity with film thickness is the greatest.
This corresponds to the region where the slope is highest in
Fig. 2. From the figure, we can see that the measurement is
most accurate in the range of 150 to 950 Å. While this
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Optical Engineering, Vol. 38 No. 5, May 1999
The instrument angles ~f, u p and u a ) are chosen through a
trade-off of competing criteria, including sensitivity, dynamic range, and background signal. For a given polarizer
angle there is a range of analyzer angles that yield closeto-optimal results. Our instrument angles were chosen experimentally to minimize the background signal while
maintaining the dynamic range.
Before use, the fixed-polarizer ellipsometer must be calibrated to determine the thickness as a function of detector
output. In principle, this could be accomplished by careful
measurement of polarizer transmissivity and input beam intensity, taking into account the photodetector and amplifier
characteristics. We have taken the simpler approach of running a series of thickness standards through the instrument
to calibrate it. To measure films of unknown thickness, first
the substrate ~which can include thin films onto which the
coating of unknown thickness is deposited! is pre-read.
Then the film which coats the pre-read substrate is measured. Comparing the pre-reading to the film measurement
provides a very accurate measurement of thickness change.
We consider the effects of variations in the instrument
angles on the measured thickness. For a 750 Å thick film
having a refractive index of 1.4, the measured thickness
changes by ; 0.3% per degree variation in u p , ; 3% per
degree variation in u a and 6% per degree variation in f.
This assumes no pre-reading. When there is a pre-reading,
the closer the thickness of the pre-read substrate is to that
of the coated substrate, the smaller the error. We have
found that it is not difficult to achieve sufficient precision in
the instrument angles to produce highly repeatable measurements. We note that the measurement is least tolerant
to variations in f, and therefore the instrument arms should
be fixed rigidly.
3
Examples
3.1 Siloxane Polymer Film
We have made a series of thickness standards in order to
calibrate the fixed-polarizer ellipsometer. These standards
consist of a siloxane polymer film spun onto a silicon wafer
and baked. These films vary in thickness from 23 Å to 1570
Å and have an index of 1.41 as determined by a Gaertner
ellipsometer.11 The silicon wafer has an index of 3.821
Trotter et al.: Fixed-polarizer ellipsometry: . . .
Fig. 3 Comparison of simulated (line) and experimental (points) results, for a siloxane film. The wavelength is 670 nm, the refractive
index is 1.41, the polarizer angle ( u p ) is 2 25°, the analyzer angle
( u a ) is 80°, and the instrument arm angle (f) is 55°.
10.014i for l 5 670 nm. The index of silicon is complex because it is absorptive at this measurement wavelength.
12
Thickness Standards
The thickness standards described above have been measured using both our fixed-polarizer ellipsometer and a
standard ellipsometer.11 In the current working version of
the fixed-polarizer ellipsometer, the intensity-readout scale
is arbitrary but the response of the detector is linear with
intensity in the thickness region of interest. To scale the
normalized intensities found in the theory to the arbitrary
units of the fixed-polarizer ellipsometer, we normalize
around a given point.
We have modeled the expected response of the fixedpolarizer ellipsometer for two different sets of polarizer orientations. The first case involved setting u p and then u a
manually so as to minimize the output intensity for a filmfree substrate. The results, shown in Fig. 2, show close
agreement between theory and experiment. For the second
case, u p and u a are chosen to maximize background intensity for a film-free substrate. As can be seen in Fig. 3, this
arrangement allows us to reverse the trend in our readings
such that increasing thickness yields decreasing intensity.
3.2
4
Application to Immunoassay
Two examples of the application of the fixed-polarizer to
immunoassay are described below. In both examples, specific antibody molecules are coated onto the silicon wafer.
The surface is then pre-read, as described above, to determine a baseline reading. When a sample containing the
specific analyte is placed onto the test surface, binding occurs between the analyte ~antigen! and the immobilized antibody, causing an increase in thickness of the molecular
thin film. The thickness increase over the baseline reading
is measured by the fixed-polarizer ellipsometer. If antigen
is not present in the sample, no binding takes place and the
baseline reading is maintained.
Hepatitis B Surface Antigen (HBsAg)
The HBsAg assay is a 30-minute, room-temperature immunoassay. Dilutions of HBsAg in plasma ranging from 0.1
4.1
ng/ml to 10 ng/ml were incubated on the antibody coated
surfaces for 15 minutes. The surface was washed and
monoclonal antibody to HBsAg labeled with horse-radish
peroxidase ~HRP! was incubated on the surface for 5 minutes. The surface was washed and a precipitating HRP substrate was incubated on the surface for 10 minutes. The
surface was washed and air dried, and the results were measured by the fixed-polarizer ellipsometer. The 0.1 ng/ml
specimen gave a signal that was 10 fold above that of the
negative control. The detection limit calculated as 3 standard deviations above the mean negative control reading
results in a theoretical cutoff for this assay of 4 pg/ml.
However, the clinical sensitivity of this assay must be validated by analyzing negative samples and a range of lowlevel positive clinical samples.
4.2 Group A Streptococcus (GAS) Antigen
The performance of the fixed-polarizer ellipsometer was
compared to the manual STREP A optical immunoassay
~OIA®! for identification of GAS antigen from patient
throat swabs. The manual STREP A OIA test has consistently been shown to be more sensitive than other rapid test
formats. The assay is also more sensitive than a routine
agar throat culture.13,14 For this comparison, pharyngeal
swabs were collected from symptomatic patients and acid
extracted to release the group A specific antigen. After an
initial reading to establish the baseline value, HRP-labeled
antibody was added to the extraction and the sample was
incubated on the antibody coated surface. After a 3 minute
incubation, the surface was washed and the precipitating
substrate was added for 4 minutes, washed, and then the
surface thickness was measured. Total assay time was 10
minutes.
The results of this study, comprising 107 samples, is
presented in Fig. 4. The purpose of this figure is to show a
comparison of results using the fixed-polarizer ellipsometer
and the manual STREP A optical immunoassay ~OIA®! and
to show the spread of intensity readings and establish a
clinical cutoff for positive/negative sample discrimination.
The cutoff was set at 60 mV for this assay because this
level gave 99% correlation with the manual assay. The data
show that a clear discrimination can be made between the
positive and negative patient population.
5 Discussion
A wide range of different methods to quantify immunoassay results have been developed, from spectrophotometric
determination of colorimetric substrates to sophisticated
biosensors.15 We compare three immunoassay systems, the
Abbott IMx® , electrochemiluminescence, and surface plasmon resonance to the fixed-polarizer ellipsometer. Several
immunoassays are used as a basis for comparison of sensitivity among the different detection platforms.
The IMx system is widely used for commercial immunoassays. Assays conducted on the IMx instrument to
quantify high molecular weight analytes are based on the
Microparticle capture Enzyme ImmunoAssay ~MEIA!.16
MEIA can be formatted in a ‘‘sandwich’’ assay in which
Optical Engineering, Vol. 38 No. 5, May 1999
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Trotter et al.: Fixed-polarizer ellipsometry: . . .
Fig. 4 Comparison of the fixed-polarizer ellipsometer and the
manual STREP A optical immunoassay (OIA® ) for identification of
group A streptococcal antigen in 107 different samples from patient
throat swabs. The open squares were identified as negative by the
manual assay and the filled diamonds as positive. The light intensity, measured using the fixed-polarizer ellipsometer (in mV), is plotted as a function of sample number. The discriminating value between positive and negative samples was chosen to be 60 mV
because this level gave 99% correlation with the manual assay (with
only sample #43 in disagreement).
latex microparticles are covalently coated with capture antibody. A capture complex is formed on the microparticle
in the presence of analyte. An enzyme-labeled antibody
conjugate then forms the second half of the sandwich complex. Microparticles are captured on a glass fiber matrix
and unbound conjugate is washed through. The remaining
conjugate fluoresces in response to excitation from a filtered mercury vapor lamp. The fluorescence intensity is
detected by a photomultiplier tube. The detection limit of
the MEIA technology for measurement of HBsAg is 0.31
ng/ml.17 In comparison, the fixed-polarizer ellipsometer
limit of detection for this analyte is 0.004 ng/ml.
A second detection technology for immunoassay reactions is electrochemiluminescence, developed by IGEN.18
In this system magnetic beads coated with capture antibody
are incubated with the target and conjugate antibody labeled with ruthenium to produce luminescence. The immune complex sandwich is captured onto an electrode surface by a magnetic force, and unbound reagents are washed
away. A voltage is applied between the electrode and a
counterelectrode in the solution, causing an electron transfer reaction which produces light emission from the labeled
molecules. The resulting electrochemiluminescence intensity is measured with an adjacent photomultiplier tube. The
detection limit of this system ranges from 10 pg/ml to 5
ng/ml, depending on the analyte.
Surface plasmon resonance is generated when a light
beam is directed through a medium of sufficiently high refractive index onto a thin film of metal at a critical angle,
which is dependent upon the wavelength of the light and
the characteristics of the thin film. Usually the high refractive index medium is a glass prism. At resonance the light
is absorbed, but for other conditions the light is reflected.
The resonance condition may be shifted by biomolecules
captured close to the metal surface.19,20 Thus the reflected
light intensity varies with the mass and concentration of
adsorbed target molecules in the sample. The detection
limit of surface plasmon resonance is in the ng/ml range
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Optical Engineering, Vol. 38 No. 5, May 1999
when a labeled secondary antibody is used to amplify the
signal.
Based on the HBsAg test described above, the theoretical sensitivity of the fixed-polarizer ellipsometer, which is
4 pg/ml for this analyte, is significantly higher than that of
commercially available assay systems. The sensitivity of
fluorescence or chemiluminescence systems ranges from
0.15 to 0.3 ng/ml with a time to result of 25 to 60
minutes.17,21 In our GAS test, the high agreement between
the fixed-polarizer ellipsometer and the manual assay implies that this automated assay for identification of GAS
antigen is also more sensitive than routine agar culture
methods. In addition, this assay is complete in approximately 10 minutes while culture results are not available
for 24-48 hours. None of the other technologies appears to
be as sensitive as the fixed-polarizer ellipsometer which has
demonstrated sensitivity in the pg/ml range depending upon
the analyte.
The three alternative technologies described above measure a signal which is generated over a brief period of time
and subsequently decays or disappears. Generation of a thin
film as the positive signal for an optical immunoassay using
the fixed-polarizer ellipsometer creates a permanent result
which can be measured at any time.
6 Conclusions
The main limitation of this measurement technique is that a
prior knowledge of the sample optical constants is required.
The substrate ~including any non-changing layers! must be
well-characterized and the index of the film being grown
must be known. Therefore, the fixed-polarizer ellipsometer
is not useful where these quantities are unknown or cannot
be found through separate means. Fortunately, these values
are often known or measurable even in a research environment.
A more practical application of the fixed-polarizer ellipsometer, however, is in a production environment. As this
system requires none of the rotating components or complex calculations of a standard ellipsometer, it is far less
expensive and easier and faster to use. In a production setting, the substrates and film indices are generally well
known and are within the tolerances imposed by the fixedpolarizer ellipsometer. Different substrates and films can be
accommodated by changing the polarizer and analyzer
angles and calculating, or looking up, a new calibration
curve. This new curve is calculated using the mathematics
above. As the fixed-polarizer ellipsometer must be recalibrated only once for each system being measured, the time
required to retool is minimal.
For biological applications, assays that require sensitivity for a low-concentration range of analyte are suitable
candidates for analysis with the fixed-polarizer ellipsometer. It is well adapted for measuring thin films generated
by molecular binding events, such as immunological reactions, nucleic acid probe detection, and receptor-analyte
binding.
In conclusion, we have demonstrated a working instrument with which to measure thickness and thickness
changes. This fixed-polarizer ellipsometer has a linear response over 800 Å, is simple to calibrate and operate, and
can accommodate different substrates and films easily. It is
inexpensive to manufacture and compact, so that it fits in
diagnostic laboratory or physician office environments.
Trotter et al.: Fixed-polarizer ellipsometry: . . .
Acknowledgments
We gratefully acknowledge early discussions about the
fixed-polarizer ellipsometer with Torbjörn Sandström and
Lars Stiblert.
References
1. H. G. Tompkins, A User’s Guide to Ellipsometry, Academic Press,
Boston ~1993!.
2. R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized
Light, North-Holland, Amsterdam ~1977!.
3. M. Stenberg, T. Sandström, and L. Stiblert, ‘‘A new ellipsometric
method for measurements on surfaces and surface layers,’’ Mater. Sci.
Eng. 42, 65–69 ~1980!.
4. H. Arwin and I. Lundström, ‘‘A reflectance method for quantification
of immunological reactions on surfaces,’’ Anal. Biochem. 145, 106–
112 ~1985!.
5. E. Hecht, Optics, 2nd ed., pp. 270–274, Addison-Wesley, Reading
~1987!.
6. J. C. M. Garnett, Philos. Trans. R. Soc. London, Ser. A 203, 385
~1904!; 205, 237 ~1906!.
7. D. A. G. Bruggeman, Ann. Phys. (Leipzig) 24, 636 ~1935!.
8. Ref. 1, pp. 246–252.
9. P. Yeh, Optical Waves in Layered Media, pp. 102–112, Wiley, New
York ~1988!.
10. Mathematica 3.0, Wolfram Research, Inc., Champaign, Illinois
~1996!.
11. Gaertner, Model # L2W16C.830. Gaertner Scientific Corporation,
Chicago, Illinois.
12. E. D. Palik, Handbook of Optical Constants of Solids, Academic
Press, Orlando, p. 565 ~1985!.
13. R. J. Harbeck, J. Teague, G. R. Crossen, D. M. Maul, and P. L.
Childers, ‘‘Novel, rapid optical immunoassay technique for detection
of group A streptococci from pharyngeal specimens: comparison with
standard culture methods,’’ J. Clin. Microbiol. 31~4!, 839–844
~1993!.
14. M. A. Gerber, R. R. Tanz, W. Kabat, E. Dennis, G. L. Bell, E. L.
Kaplan, and S. T. Shulman, ‘‘Optical immunoassay test for group A
b-hemolytic streptococcal pharyngitis,’’ J. Am. Med. Assoc. 277~11!,
899–903 ~1997!.
15. C. L. Morgan, D. J. Newman, and C. P. Price, ‘‘Immunosensors:
technology and opportunities in laboratory medicine,’’ Clin. Chem.
42~2!, 193–209 ~1996!.
16. M. Fiore et al., ‘‘The Abbott IMx automated benchtop immunochemistry analyzer system,’’ Clin. Chem. 34~9!, 1726–1732 ~1988!.
17. J. Smith, G. Osikowicz et al., ‘‘Abbott AxSYM random and continuous access immunoassay system for improved workflow in the clinical
laboratory,’’ Clin. Chem. 39~10!, 2063–2069 ~1993!.
18. H. Yang, J. K. Leland, D. Yost, and R. J. Massey, ‘‘Electrochemilumininescence: a new diagnostic and research tool,’’ Bio/Technology
12, 193–194 ~1994!.
19. B. Liedberg, C. Nylander, and I. Lundström, ‘‘Surface plasmon resonance for gas detection and biosensing,’’ Sens. Actuators 4, 299–304
~1983!.
20. R. Parry, J. K. Deacon, G. A. Robinson, J. J. Skehel, and G. C.
Forrest, ‘‘Surface plasmon resonance immunosensors,’’ in Rapid
Methods & Automation in Microbiology, A. Balows, R. C. Tilton, and
A. Turano, Eds., pp. 641–648, Brixia Academic Press, Brescia
~1988!.
21. O. S. Khalil et al., ‘‘Abbott Prism: a multichannel heterogeneous
chemiluminescence immunoassay analyzer,’’ Clin. Chem. 37~9!,
1540–1547 ~1991!.
Brian Trotter received his bachelor’s degree in applied physics
from Caltech in 1995 and his master’s degree in electrical engineering from University of Colorado at Boulder in 1997 where he carried
out research in phase modulation in thin films. He is currently with
Mobile Storage Technology as a development engineer of test and
production software.
Garret Moddel received his bachelor’s degree in electrical engineering from Stanford
in 1976 and PhD in applied physics from
Harvard in 1981. He worked in a small Silicon Valley start-up for four years developing new silicon-based solar cells before
plunging back into academia at the University of Colorado at Boulder, where he is a
professor in electrical engineering. He is a
fellow of the Optical Society of America.
His group works with new optoelectronic
thin film materials and devices. It pioneered the ferroelectric liquid
crystal optically addressed spatial light modulator which incorporates an amorphous silicon photosensor. Current work involves the
development of other photosensor materials including organic photoconductors for consumer applications and metal-based solar cells.
Rachel Ostroff received a BS degree from
the University of Maryland in 1984, and
graduated from the University of Colorado
Health Sciences Center (UCHSC) with a
PhD in microbiology in 1989. Her thesis
work involved the biochemical investigation
of molecular pathogenesis of Pseudomonas aeruginosa. This work was followed by
an NIH funded postdoctoral fellowship at
UCHSC to study molecular mechanisms of
cell cycle regulation in yeast. Currently Dr.
Ostroff is a technical team leader in the Research and Development
department at BioStar, Inc. She has participated in the development
of a number of rapid infectious disease diagnostic tests using thin
film detection technology and is currently conducting feasibility studies for new infectious disease targets.
Gregory R. Bogart graduated from St.
Cloud State University, Minnesota, in 1984
with a BS degree in chemistry and obtained his doctorate in chemistry from
Colorado State University in 1990. He
worked for BioStar from 1990 to 1997 and
has eight United States Patents covering
various aspects of OIA technology including OIA surface construction, modification,
assay development and detection methodologies. Dr. Bogart currently works for Bell
Laboratories, Lucent Technologies Advanced Lithography Research
Department as part of the SCALPEL Team (a Next Generation Lithography Program). His current interests include photomask construction for SCALPEL (SCattering using Angular Limitation Projection Electron beam Lithography).
Optical Engineering, Vol. 38 No. 5, May 1999
907
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