Excess Heat Capacity in Mo/Au Transition Edge Sensor Bolometric Detectors

Area of Science:

• Astrophysics
• Materials Science
• Detector Physics

Background:

• Transition Edge Sensors (TES) are crucial bolometric detectors for high-resolution spectroscopy.
• Mo/Au bilayer TES detectors for the HIRMES instrument showed unexpected, slow thermal response times.
• This anomalous behavior was linked to excess heat capacity beyond bulk material properties.

Purpose of the Study:

• Investigate the origin of the secondary, slow thermalization time constant in Mo/Au bilayer TES detectors.
• Determine the cause of the excess heat capacity affecting detector response.
• Optimize TES detector performance by mitigating the anomalous time constant.

Main Methods:

• Fabrication and characterization of Mo/Au bilayer TES detectors for HIRMES.
• Utilized laser ablation to modify silicon membranes and analyze its effect on detector response.
• Employed glancing incidence x-ray diffraction (GIXRD) to identify material phases.
• Quantified molybdenum concentration using secondary ion mass spectroscopy (SIMS).

Main Results:

• Mo/Au bilayer TES detectors exhibited two distinct thermal response timescales.
• Laser ablation of silicon membranes reduced the contribution of the secondary, slower time constant.
• GIXRD revealed the presence of molybdenum silicides at the silicon interface.
• SIMS analysis indicated excess molybdenum concentration, correlating with the observed excess heat capacity.

Conclusions:

• The anomalous slow thermal response in Mo/Au bilayer TES detectors is attributed to the formation of molybdenum silicides.
• Excess heat capacity from these silicides significantly impacts detector time constants.
• Material processing and characterization are key to understanding and improving TES detector performance for applications like HIRMES.