Capacitance has been used as a non-destructive measure of root system size for 30 years. The equipment required is cheap and simple to apply in both field and laboratory. Good linear correlations have been reported between capacitance and root mass. A model by F. N. Dalton, predicting a linear relationship between these two variables, has become accepted widely. This model was tested for barley (Hordeum vulgare) grown hydroponically using treatments that included: raising roots out of solution, cutting roots at positions below the solution surface, and varying the distance between plant electrode and the solution surface. Although good linear correlations were found between capacitance and mass for whole root systems, when roots were raised out of solution capacitances were not linearly related to submerged root mass. Excision of roots in the solution had negligible effect on the measured capacitance. These latter observations conflict with Dalton’s model. Capacitance correlated linearly with the sum of root cross-sectional areas at the solution surface and inversely with distance between plant electrode and solution surface. A new model for capacitance is proposed that is consistent with these observations.
The results were consistent with the new physical interpretation of plant capacitance. Substrate capacitance and plant capacitance combine according to standard physical laws. For plants growing in wet substrate, the capacitance measured is largely determined by the tissue between the surface of the substrate and the electrode attached to the plant. Whilst the measured capacitance can, in some circumstances, be correlated with root mass, it is not a direct assay of root mass.
In this paper we describe the development of a chrome dry etch process on a new type of mask etch tool. One crucial goal was to minimize the CD etch bias. To meet this goal, a procedure for the direct characterization of CD etch bias was developed. The common methods for measuring the CD etch bias as resist-to-chrome CD difference, such as confocal optical microscope or SEM measurement, only give correct results, if the sidewalls are identical to the calibration standard. This is normally not the case as, due to the differing step height of resist and chrome, and the fact that during process development, in particular, the sidewall shapes and angles can vary significantly. Thus, it is very important to use a CD measurement method which takes the sidewall shapes (slope, foot) into account. One novel method is the use of a Scanning Nano Profiler (SNP) which was derived from the AFM principle. In contrast to AFM the use of a special high aspect ratio tip with 90° sidewall angle, in combination with pixelwise scanning of the substrate surface, provides information about the true sidewall shape and CD.
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