21 research outputs found
Optical-based spectroscopic methods for measuring chemical, optical, and physical properties of thin polymer waveguide films
Non-destructive optical-based spectroscopic methods are needed for analyzing “real world” devices that consist of thin polymer waveguide films. Many applications (e.g., sensors, microelectronics, optics, and biomedical applications, etc.) utilize thin polymer waveguide films, and non-destructive characterization methods based on Fourier transform (FT)-plasmon waveguide spectroscopy (PWR) and scanning angle (SA) Raman spectroscopy are used to extract optical, physical, and chemical properties simultaneously.
The FT-PWR method measures reflected light at polymer waveguide interface as both the incident frequency (wavelength) and incident angle are scanned. This method uses p- and s-polarized light to simultaneously extract the polymer waveguide thickness and apparent anisotropic indices of refraction. Polystyrene waveguide films ranging from 360 to 800 nm are used to demonstrate the method and it has an average 0.4% relative error when compared to profilometry and atomic force microscopy measurements.
SA Raman spectroscopy is used to measure mixed waveguide polymer films consisting of polystyrene-block-poly(methyl methacrylate) and homopolymer poly(methyl methacrylate) (PS-b-PMMA:PMMA), and poly(2-vinylnapthalene)-block-poly(methyl methacrylate) (P2VN-b-PMMA). PMMA homopolymer is added to the PS-b-PMMA solutions to vary the chemical composition. The chemical composition of each mixed film is quantified (SA Raman peak amplitude ratios) and averaged over all incident angles and is termed the Raman amplitude ratio (rps). This parameter is used to calculate the refractive index of each mixed waveguide polymer film. The refractive index is an input parameter for sum square electric field (SSEF) calculations, which are used to model SA Raman spectra as a function of incident angle to extract the film thickness. The mixed polymer waveguide film thicknesses ranged from 495 to 971 nm, and the SA Raman spectroscopy method has an average 5% difference between the values determined by profilometry.
The SA Raman spectroscopy method developed for mixed polymer waveguide films is used to measure the chemical composition and extract interface locations in bilayer and trilayer films consisting of PMMA/PS or PMMA/PS/PMMA, respectively. The rps value is averaged over angle ranges corresponding to waveguide mode 0 and waveguide mode 1 for the bilayer and trilayer films, respectively. Six multilayer films are analyzed and their total thicknesses range from 330 to 1260 nm. Iterative SSEF calculations are used to model the SA Raman spectra as a function of incident angle, and the best fit to the experimental data is used to extract the total thickness and interface location(s). The method has an axial spatial resolution of 7 to 80 nm and provides comparable values to films measured by profilometry with an average 8% and 7% difference for the bilayer and trilayer films, respectively
Extracting interface locations in multilayer polymer waveguide films using scanning angle Raman spectroscopy
There is an increasing demand for nondestructive in situ techniques that measure chemical content, total thickness, and interface locations for multilayer polymer films, and scanning angle (SA) Raman spectroscopy in combination with appropriate data models can provide this information. A SA Raman spectroscopy method was developed to measure the chemical composition of multilayer polymer waveguide films and to extract the location of buried interfaces between polymer layers with 7- to 80-nm axial spatial resolution. The SA Raman method acquires Raman spectra as the incident angle of light upon a prism-coupled thin film is scanned. Six multilayer films consisting of poly(methyl methacrylate)/polystyrene or poly(methyl methacrylate)/polystyrene/poly(methyl methacrylate) were prepared with total thicknesses ranging from 330 to 1,260 nm. The interface locations were varied by altering the individual layer thicknesses between 140 and 680 nm. The Raman amplitude ratio of the 1,605-cm−1 peak for polystyrene and 812-cm−1 peak for poly(methyl methacrylate) was used in calculations of the electric field intensity within the polymer layers to model the SA Raman data and extract the total thickness and interface locations. There is an average 8% and 7% difference in the measured thickness between the SA Raman and profilometry measurements for bilayer and trilayer films, respectively
Design and Demonstration of a New Small-Scale Jet Noise Experiment
A facility capable of acoustic and velocity field measurements of high-speed jets has
recently been built and tested. The anechoic chamber that houses the jet has a 2.1 m
× 2.3 m × 2.5 m wedge tip to wedge tip working volume. We aim to demonstrate that
useful experiments can be performed in such a relatively small facility for a substantially
lower cost than in larger facility. Rapid prototyping allows for quick manufacturing of both
simple and complex geometry nozzles. Sideline and 30° downstream acoustic measurements
between 400 Hz and 100 kHz agree well with accepted results. Likewise, nozzle exit-plane
data obtained using particle image velocimetry are in good agreement with other studies
Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination
Assumption without representation: the unacknowledged abstraction from communities and social goods
We have not clearly acknowledged the abstraction from unpriceable “social goods” (derived from
communities) which, different from private and public goods, simply disappear if it is attempted to
market them. Separability from markets and economics has not been argued, much less established.
Acknowledging communities would reinforce rather than undermine them, and thus facilitate
the production of social goods. But it would also help economics by facilitating our understanding
of – and response to – financial crises as well as environmental destruction and many social problems,
and by reducing the alienation from economics often felt by students and the public
Fourier Transform-Plasmon Waveguide Spectroscopy: A Nondestructive Multifrequency Method for Simultaneously Determining Polymer Thickness and Apparent Index of Refraction
Fourier transform (FT)-plasmon waveguide
resonance (PWR) spectroscopy
measures light reflectivity at a waveguide interface as the incident
frequency and angle are scanned. Under conditions of total internal
reflection, the reflected light intensity is attenuated when the incident
frequency and angle satisfy conditions for exciting surface plasmon
modes in the metal as well as guided modes within the waveguide. Expanding
upon the concept of two-frequency surface plasmon resonance developed
by Peterlinz and Georgiadis [Opt. Commun. 1996, 130, 260], the apparent index of refraction and the
thickness of a waveguide
can be measured precisely and simultaneously by FT-PWR with an average
percent relative error of 0.4%. Measuring reflectivity for a range
of frequencies extends the analysis to a wide variety of sample compositions
and thicknesses since frequencies with the maximum attenuation can
be selected to optimize the analysis. Additionally, the ability to
measure reflectivity curves with both p- and s-polarized light provides
anisotropic indices of refraction. FT-PWR is demonstrated using polystyrene
waveguides of varying thickness, and the validity of FT-PWR measurements
are verified by comparing the results to data from profilometry and
atomic force microscopy (AFM)
Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination
The
photostability of bulk heterojunction organic photovoltaic films containing
a polymer donor and a fullerene-derivative acceptor was examined using
resonance Raman spectroscopy and controlled laser power densities.
The polymer donors were poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]
(PCDTBT), or poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<i>b</i>]thiophenediyl}) (PTB7). Four sample preparation methods
were studied: (i) thin or (ii) thick films with fast solvent evaporation
under nitrogen, (iii) thick films with slow solvent evaporation under
nitrogen, and (iv) thin films dried under nitrogen followed by thermal
annealing. Polymer order was assessed by monitoring a Raman peak’s
full width at half-maximum and location as a function of illumination
time and laser power densities from 2.5 × 10<sup>3</sup> to 2.5
× 10<sup>5</sup> W cm<sup>–2</sup>. Resonance Raman spectroscopy
measurements show that before prolonged illumination, PCDTBT and PTB7
have the same initial order for all preparation conditions, while
P3HT order improves with slow solvent drying or thermal annealing.
All films exhibited changes to bulk heterojunction structure with
2.5 × 10<sup>5</sup> Wcm<sup>–2</sup> laser illumination
as measured by resonance Raman spectroscopy, and atomic force microscopy
images show evidence of sample heating that affects the polymer over
an area greater than the illumination profile. Photostability data
are important for proper characterization by techniques involving
illumination and the development of devices suitable for real-world
applications