We have studied the origin of excess noise in superconducting transition-edge sensors (TES) with several different detector designs. We show that most of the observed noise and complex impedance features can be explained by a thermal model consisting of three bodies. We suggest that one of the thermal blocks and the corresponding thermal fluctuation noise arises due to the high-frequency thermal decoupling of the normal and superconducting phase regions inside the TES film. Our results are also consistent with the prediction that in thin bilayer proximitized superconductors, the jump in heat capacity at the critical temperature is smaller than the universal BCS theory result.
In this paper we present a new measurement setup, where a transitionedge
sensor detector array is used to detect X-rays in particle induced X-ray
emission measurements with a 2 MeV proton beam. Transition-edge sensors offer
orders of magnitude improvement in energy resolution compared to conventional
silicon or germanium detectors, making it possible to recognize spectral lines
in materials analysis that have previously been impossible to resolve, and to
get chemical information from the elements. Our sensors are cooled to the
operation temperature (65 mK) with a cryogen-free adiabatic demagnetization
refrigerator, which houses a specially designed X-ray snout that has a vacuum
tight window to couple in the radiation. For the best pixel, the measured
instrumental energy resolution was 3.06 eV full width at half maximum at 5.9
keV.We discuss the current status of the project, benefits of transition-edge
sensors when used in particle induced X-ray emission spectroscopy, and the
results from the first measurements.Comment: 6 pages, 3 figure, LTD-15 proceeding
The so-called excess noise limits the energy resolution of transition-edge sensor (TES) detectors, and its physical origin has been unclear, with many competing models proposed. Here we present the noise and impedance data analysis of a rectangular X-ray Ti/Au TES fabricated at SRON. To account for all the major features in the impedance and noise data simultaneously, we have used a thermal model consisting of three blocks of heat capacities, whereas a two-block model is clearly insufficient. The implication is that, for these detectors, the excess noise is simply thermal fluctuation noise of the internal parts of the device. Equations for the impedance and noise for a three-block model are also given.
Nondestructive analysis (NDA) based on x-ray emission is widely used, for example, in the semiconductor and concrete industries. Here, we demonstrate significant quantitative and qualitative improvements in broadband x-ray NDA by combining particle-induced emission with detection based on superconducting microcalorimeter arrays. We show that the technique offers great promise in the elemental analysis of thin-film and bulk samples, especially in the difficult cases where tens of different elements with nearly overlapping emission lines have to be identified down to trace concentrations. We demonstrate the efficiency and resolving capabilities by spectroscopy of several complex multielement samples in the energy range 1-10 keV, some of which have a trace amount of impurities not detectable with standard silicon drift detectors. The ability to distinguish the chemical environment of an element is also demonstrated by measuring the intensity differences and chemical shifts of the characteristics x-ray peaks of titanium compounds. In particular, we report measurements of the Kα=Kβ intensity ratio of thin films of TiN and measurements of Ti Kα satellite peak intensities in various Ti thin-film compounds. We also assess the detection limits of the technique, comment on detection limits possible in the future, and discuss possible applications.
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