Asymmetric fluid-structure dynamics in nanoscale imprint lithography

hardware systems are for stream-to-disk or RAM buffer operations. For in situsampling, or in this case, when time stamps of the corresponding encoder, forcesensor, and spectral data are required, the data cannot be streamed to the RAMbuffer for post-processing. LabVIEW limited the sampling frequency. Inoptimizing the software for speed, there was a trade-off between speed,robustness, and memory usage. The spectrometer CCD array has 2048 pixels andthe LabVIEW software drivers provided by Ocean Optics ® output the entiredata array. If the amount of memory allocated to store this array is large, thislimits the speed at which the spectral data can be sampled. Therefore, data wascollected for up to 2 seconds. This resulted in a sampling frequency of 13 Hz,which is adequate to see trends in the motion profile. This sampling frequency isan example for this particular embodiment and is not a limitation of theprocessing capability for in situ gap sensing. An implementation in C/C++ orother high level language would yield vastly improved processing speed.Figure 6.3 shows a screenshot of the current implementation inLabVIEW. Notice that the two charts, on the left of Figure 6.3, displaying anFFT of the signal are exemplary. Removing the periodic information contained inthe reference signal was initially difficult since measuring reflectivity datathrough quartz was not performed in dissolution rate monitoring. This problemwas overcome by recognizing that when the template is far away from thesubstrate, a reference signal can be taken because there is no interference at largegaps. This distance still needs to be quantified, however, this is a signalprocessing issue. Some discussion of the signal processing issues will beprovided later in section 6.4 of this chapter.81