In situ measurements of the axial expansion of palladium microdisks during hydrogen exposure using diffraction phase microscopy

PDF Link

We measured the height of Pd microdisks during H2 exposure using epi-illumination diffraction phase microscopy, a quantitative phase imaging technique for capturing nanoscale dynamics in situ. From these microdisk height measurements, we extracted the axial expansion coefficient as a function of H2 concentration as well as image sequences that show the instantaneous rate of axial expansion in a spatially and temporally resolved manner. Quantifying these two parameters is important in modeling Pd-based H2 sensors. For H2 concentrations below 0.5%, i.e. an order of magnitude below the lower explosive limit, the axial expansion coefficient followed the Freundlich distribution: Δh(c) = 1.28 c0.51 where Δh is the percentage change in height of the Pd microdisk and c is the percent concentration of H2 in N2. The fit agrees well with the anticipated square root dependence for diatomic gas.

Tae Woo Kim Graduate Research Assistant Electrical and Computer Engineering Quantitative Light Imaging Laboratory 4053 Beckman Institute University of Illinois, Urbana-Champaign