We present the application of ellipsometry to the phase measurement of surface plasmon resonance (SPR) in
biomolecular detection. In this work, the experimental setup for the SPR sensor was based on a custom-built rotating
analyzer ellipsometer, which was equipped with a SPR cell and a microfluidic system. We investigate the sensitivity of
SPR sensor which is dependent on the thickness and roughness of metal film, alignment of optical system, and stability
of microfluidics. In the drug discovery process, to directly monitor the interaction of small molecule-protein, it is
necessary to design a high-sensitivity SPR sensor with a sensitivity of greater than 1 pg/mm2. Our sensor demonstrates a
much better sensitivity in comparison to other SPR sensors based on reflectometry or phase measurements. The results of
calibration indicate that the phase change, δ▵, had an almost linear response to the concentration of ethanol in the
double-distilled water solutions. A quantitative analysis of refractive index variation was possible using the results of the
ellipsometric model fits for the multilayered thin film on the gold film. Thus, this method is applicable not only to sensor
applications, such as affinity biosensors, but also to highly sensitive kinetics for drug discovery. In this paper, we
demonstrate how a custom-built rotating analyzer ellipsometer in the SPR condition can be used to directly obtain the
interactions and binding kinetics of analytes (biotins, peptides) with immobilized ligand (streptavidin, antibody). We
achieved a detection limit of lower than 1.0 x10-7 RIU, which is the equivalent of 0.1 pg/mm2.
We present the application of ellipsometry to the phase measurement of surface plasmon resonance (SPR) in biomolecular detection. In this configuration, the phase measurement gives a large enhancement of detection sensitivity in comparison to traditional SPR techniques. In this work, the experimental setup for SPR ellipsometry is based on both custom-built rotating analyzer ellipsometer and an imaging ellipsometer which are equipped with a SPR-cell and a flow system, respectively. We investigate the adequate thickness of the gold layer used for SPR cell and the resolution of the phase detection using two ellipsometric methods under the SPR condition. The rotating analyzer method yields higher sensitivity sufficient to detect changes in the effective thickness of biomolecular layers of less than 1 pm. In comparison to conventional SPR the simultaneous measurement of ellipsometric parameters, Δ and ψ, yields more information
which is useful for quantitative analysis based on fitting theoretical solutions to experimental results.
We present imaging ellipsometry technique for kinetic measurement of bimolecular interactions with high sensitivity. When combined with surface plasmon resonance (SPR) effects, the ellipsometry becomes powerful technique for analyzing adsorption and desorption of biomolecules on gold layer based sensor chip surfaces. Because ellipsometric measurement gives ellipsometric parameters, namely Δ, that is very sensitive to surface layer changes. The SPR combined ellipsometry is realized by Kretschmann configuration SPR cell comprising with about 30-nm-thick gold film deposited on top of glass slides, SF10 glass prism, and flow injection system. We used nulling type of imagining ellipsometer to acquire two dimensional ellipsometric parameters with spatial resolution down to one micrometer. We present results of kinetic measurements of biotin-streptavidin interactions for custom-built sensor chip.
Ellipsometry is known as high precision metrology for thin film thickness measurements with sub-angstrom resolution. In ellipsometric measurements it does not measure film thickness or optical constants directly. It measures ellipsometric parameters, ψ and Δ, namely, defined as the ratio of reflection coefficients for p- and s-polarized light. Generally in rotating component ellipsometry, light intensity values at more than 256 angular positions of polarizer or analyzer with discrete Fourier transform methods are used to evaluate Fourier coefficients, which can be calculated to ellipsometric parameters explicitly. Using this scheme it is well suited in single point measuring ellipsometry, but it degrades measurement speed in imaging ellipsometry. In imaging ellipsometry due to the limitation in CCD detection speed, rotating components must move stepwisely, so more discrete positions of polarizer or analyzer takes more measurement time dramatically. So we propose four frame method which can be easily substituted for conventional discrete Fourier transform methods. Four frame method can save measurement time, but natively intensity measurements at only four angular positions can cause erroneous results in Fourier coefficients compared with that of discrete Fourier transform method. In the four frame method, many repetitive measurements for light intensity at each angular position can solve these shortcomings. That is, conceptually to reduce random noise in ellipsometric measurements, conventional discrete Fourier transform method uses spatial averaging technique, but four frame method uses temporal averaging technique. In our experiments we could get more than ten times fast measurements with four frame method.
The ellipsometry is known as high precision metrology for thin film thickness measurements and its optical properties by measuring ellipsometric parameters, ψ and Δ, defined as amplitude and phase values of the ratio of Fourier reflection coefficients for p- and s-polarized light. With conventional ellipsometers, we can get average values of ellipsometric parameters in the region of interest determined by spot size of measurement beam. However, we can expand the measurement scheme to two dimensional spectral imaging with additional imaging spectrograph compatible to the structure of ellipsometer. That is, we can simultaneously get spatial and spectroscopic ellipsometric parameters using two dimensional imaging detectors. Using this type of ellipsometers, polarization state dependent response of imaging spectrograph must be considered carefully during azimuth calibration procedures as well as ellipsometric parameters measurement. In this paper, we suggest Jones calculus model for ellipsometer with considering dichroic response in spectrograph and background signal levels in detector. And we show experimental calibration results comparison with that of simulation using suggested Jones calculus model.
We investigated the optical properties of titanium dioxide (TiO2) thin films which were deposited by ion beam assisted deposition (IAD) method on crystalline silicon and acrylic substrates. TiO2 thin films were grown by different growing conditions which are used the conditions of vacuum pressure, and deposition rate. The controlled vacuum pressure were 3 x 10-5Torr and 3 x 10-6 Torr, and the deposition rate was controlled to 0.35 nm/second, 0.20 nm/second, and 0.12 nm/second. Measurements of spectroscopic ellipsometry were performed in the spectral range between 0.76 eV and 8.7 eV with 0.02 eV steps and at the angle of incidence of 75°. We determined the complex refractive index and thickness of TiO2 thin films using the optical model which is included the Tauc-Lorentz dispersion equation and compared the relations between the optical properties and deposition rate or vacuum pressure variation. The optical band gaps of TiO2 thin films are around 3.42 eV.
We have developed an in-situ single wavelength ellipsometer applicable to a vacuum sputter to monitor ellipsometric parameters during thin film deposition. The translation and tilting stages in the polarizer and analyzer make it easy to adjust optical axis and the angle of incidence. To calibrate inherent offset in the azimuth axis of the polarizer and analyzer, regression and residual calibration procedures are conducted. This work also includes the measurement results of the silver target deposition on the alloy, made of chrome and nickel, and silicon wafers. The manufactured ellipsometer will be used to investigate optical properties of the thin film and substrate in the vacuum state with various temperature ranges.
This paper describes a newly designed multipoint process monitoring system based on an acousto-optic tunable filter. In order to prove the feasibility of the suggested multipoint monitoring system for use in the NIR spectral region, some experiments were carried out in the visible range. The multipoint process monitoring system consists of an AOTF device for wavelength selecting, a CCD imaging sensor, and a specially designed in-line type of optical fiber probe. Unlike an FTS (Fourier Transform Spectrometry) based monitoring system, an AOTF has no moving parts, and it can be rapidly tuned to any wavelength in its operating range within microseconds. Thus, the AOTF is advantageous in terms of faster spectral imaging capability and rigidity required for industrial monitoring environment. Also, Fourier Transform Spectrometry experiments were conducted for comparison with the AOTF based monitoring system. In the current feasibility evaluation, an enhanced optical fiber probe with 3 monitoring points was used. However, the number of monitoring points can be easily expanded to dozens more points as required.