Abstract
We report the fabrication and evaluation of the Cu/Bi bilayer absorber with electrodeposition. We designed the Cu/Bi absorber to satisfy the requirements for scanning transmission electron microscope (STEM). The residual resistivity ratios of films of Cu and Bi with electrodeposition was \({5.91\pm 0.49}\) and \({2.06\pm 0.33}\), respectively; these values are sufficient for the requirements of STEM. We found that the Cu/Bi bilayer absorber TES microcalorimeter experienced a pulse-shape variation and we considered that these variations were caused by the quality of the contact surface between the absorber and TES. In addition, we examined the structure of the absorber using focus ion beam analysis and STEM. The results suggest that an oxidation between the Cu and seed layer, in which the layer is an electrode for electrodeposition, yielded variations. Moreover, thermal simulation suggests that the thermal conduction between the absorber and TES caused variations. The results of this study will improve the process of Bi electrodeposition.
Highlights
In microcalorimeters used for astronomical applications, high spatial coverage is essential because the number of photons is limited and invaluable
We used the dilution refrigerator, which has a lowest temperature of ∼50 mK in ISAS/JAXA, set to the cold stage made from Cu in a dilution refrigerator, and placed the TES chip on this cold stage. 55Fe isotopes were mounted above the TES chip as X-ray sources
The bath temperature was set to 230 mK, with a TES bias current of 1110 μA
Summary
In microcalorimeters used for astronomical applications, high spatial coverage is essential because the number of photons is limited and invaluable. An example are so-called mushroom-shape absorbers that cover the dead space between pixels. We require relatively large (∼0.5 mm2) pixels, as this degrades the energy resolution because of an increase in heat capacity and the pulse shape having X-ray absorption position dependence. Bi is the ideal material due to its low specific heat capacity and high X-ray stopping power. We developed the Bi absorber using vapor deposition, which has low heat conductance, but has a pulse-to-pulse variation of decay time constant [1]. Due to its low heat conductance, the Bi absorber might produce pulse shape variations. To improve the thermal conductivity, it was used with a high-thermal conductance material such as Cu. we developed the Cu absorber with electrodeposition. We fabricated a bilayer absorber of Bi and Cu using the electrodeposition process
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
