First results from Mo/Au transition-edge sensor X-ray calorimeters

Superconducting bilayers made of thin films of molybdenum and gold show promise as robust transition-edge sensor (TES) thermometers for calorimeters. We present our first X-ray results from experiments with Mo/Au TES calorimeters on silicon-nitride membranes. These results include analysis of the signal pulse shape and noise as functions of the bias point, which is varied through changing the bias voltage for operation at different places within the superconducting transition and changing the heat sink temperature relative to the transition temperature. Ultimately, we determined that the performance of our devices is limited by the slew rate of the SQUID amplifier used to measure the change in current, which restricts the choice of bias. The amplifier must be replaced before further device characterization and optimization can proceed.