Significance: Performance improvements in microfluidic systems depend on accurate measurement and fluid control on the micro- and nanoscales. New applications are continuously leading to lower volumetric flow rates.
Aim: We focus on improving an optofluidic system for measuring and calibrating microflows to the sub-nanoliter per minute range.
Approach: Measurements rely on an optofluidic system that delivers excitation light and records fluorescence in a precise interrogation region of a microfluidic channel. Exploiting a scaling relationship between the flow rate and fluorescence emission after photobleaching, the system enables real-time determination of flow rates.
Results: Here, we demonstrate improved calibration of a flow controller to 1% uncertainty. Further, the resolution of the optofluidic flow meter improved to less than 1 nL / min with 5% uncertainty using a molecule with a 14-fold smaller diffusion coefficient than our previous report.
Conclusions: We demonstrate new capabilities in sub-nanoliter per minute flow control and measurement that are generalizable to cutting-edge light-material interaction and molecular diffusion for chemical and biomedical industries.
Performance improvements in microfluidic systems depend on accurate measurement and control of fluids on the micro- and nanoscale, and new applications are continuously moving the needle to lower volumetric flow rates. This work focuses on improving an optofluidic system for the measurement and calibration of microflows to the sub-nanoliter per minute range. The experimental measurements rely on an optofluidic system that delivers excitation light and records fluorescence in a precise interrogation region of a microfluidic channel. Using a scaling relationship between flow rate and the fluorescence emission after photobleaching, the system enables real-time determination of flow rates. Here we demonstrate improved calibration of a flow controller to 1 % uncertainty and improved resolution of the optofluidic flow meter to less than 1 nL/min using molecules with lower diffusion coefficients.
KEYWORDS: Interfaces, Polymers, Systems modeling, Standards development, Physics, Condensed matter, Directed self assembly, Line edge roughness, Lithography, Monte Carlo methods
Using the Leibler-Ohta-Kawasaki (LOK) phase-field model of block copolymers (BCPs), we characterize how a chemoepitaxial template with parallel lines of arbitrary width affects the BCP microdomain shape. We apply boundary conditions that account for the interactions of the polymers with the templated substrate and a neutral top-coat. We derive formulas for the monomer density and the microdomain interface profile of periodic, lamellar BCP melts whose template lines are wider or narrower than the bulk microdomain width. For such systems, our analysis (i) shows that mass conservation causes the microdomain interfaces to oscillate about their bulk positions and (ii) determines the length scale λ over which these oscillations decay away from the substrate.
Block copolymers oer an appealing alternative to current lithographic techniques with regard to fabrication of the next generation micro-processors. However, if copolymers are to be useful on an industrial manufacturing scale, they must meet or exceed lithography specications for placement and line edge roughness (LER) of resist features. Here we discuss a eld theoretic approach to modeling the LER of lamellar microdomain interfaces in a strongly segregated block copolymer system; specically, we derive a formula for the LER as a functions of the Flory Huggins parameter and the index of polymerization N. Our model is based on the Leibler-Ohta-Kawasaki energy functional. We consider a system with a nite number of phase separated microdomains and also show how the LER depends on distance of the microdomain interface from the system boundary. Our results suggest that in order to meet target LER goals at the 15 nm, 11 nm, and 6 nm nodes, must be increased by a factor of at least 5 above currently attainable values.
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