Devices for Thermal Conductivity Measurements of Electroplated Bi for X-ray TES Absorbers

TL;DR

This paper introduces measurement structures that enable independent thermal conductivity assessment of electroplated Bismuth, crucial for optimizing X-ray TES absorbers, demonstrating its suitability at cryogenic temperatures.

Contribution

It presents novel four-wire resistance measurement structures that isolate Bi's properties from the seed layer, advancing understanding of its thermal behavior at low temperatures.

Findings

Thermal conductivity of electroplated Bi at 3 K is sufficiently high.

Measurement structures effectively separate Bi properties from gold seed layers.

Electroplated Bi is suitable for X-ray TES absorbers at cryogenic temperatures.

Abstract

Electroplated Bismuth (Bi) is commonly used in Transition-Edge Sensors (TESs) for X-rays because of its high stopping power and low heat capacity. Electroplated Bi is usually grown on top of another metal that acts as seed layer, typically gold (Au), making it challenging to extrapolate its thermoelectric properties. In this work, we present four-wire resistance measurement structures that allow us to measure resistance as a function of temperature of electroplated Bi independently of Au. The results show that the thermal conductivity of the Bi at 3 K is high enough to guarantee the correct thermalization of X-ray photons when used as an absorber for TESs.