Phase Transition Thermometers Research Articles

Raman spectroscopy and XPS study of the thermal decomposition of Mg‐hornblende into augite

AbstractThe breaking and reorganization of chemical bonds during the transformation of amphiboles to pyroxenes are obscure due to similar structures and seemingly stable tetrahedrons. A systematic heating experiment was carried out on amphibolites at medium and high temperatures (600–1180°C) to explore the transformation mechanism of double‐chain silicate minerals (amphiboles) to single‐chain silicate minerals (pyroxenes). It was found that the morphology of Mg‐hornblende changed significantly at 1050°C. Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS) revealed that a large amount of electron transfer promoted H+ escape during Fe2+ oxidation to Fe3+. Meanwhile, the decrease of ANa, AK, and TAl shortens the distance between the two tetrahedrons and breaks the O‐Si‐O bond connecting the tetrahedron and octahedron M4. Electron transfer between the octahedral and tetrahedral sites occurs at approximately 600°C. At ~900°C, a part of the Ca‐O electrons was transferred to the Ca‐O‐Si. Finally, the O‐Si‐O bond break caused Ca in M4 to move into cavity A‐site to form augite together with Si‐O‐Si at the site of T1‐T1, which behaves accordingly, the number of electrons lost by Ca‐O is similar to that gained by Si‐O‐Si at 1050–1100°C. This study provides direct evidence of Raman spectroscopy and XPS to reveal the phase transformation mechanism and establish phase transition thermometers of amphiboles to pyroxenes.

The CRESST dark matter search

The aim of CRESST ( Cryogenic Rare Event Search with Superconducting Thermometers) is to search for particle dark matter via elastic scattering off nuclei. The experiment is located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and it uses low-background cryogenic detectors with superconducting phase-transition thermometers for the direct detection of WIMP–nucleus scattering events.

Waveform Analysis of Bilayer Iridium/Gold Superconducting Transition Edge Sensor Microcalorimeter

We are developing high energy resolution X-ray microcalorimeters based on iridium and gold (Ir/Au) phase transition thermometers. Here we analyze the signal behavior of a 200×200 µm2 Ir/Au transition edge sensor (TES) with iridium and gold having the thicknesses of 100 and 25 nm, respectively. The energy resolution of this device was 15.4 eV full width at half maximum (FWHM) at 5.9 keV X-ray energy. For operation at bias resistances lower than 140 mΩ, we observed two distinct decay components, a slow component followed by a very fast component, which is thought to be due to the variation of current distribution inside the TES. However, taking into consideration the nonlinearity associated with the slow component, a very fast signal response makes the operation of this device promising at low-resistance bias points.

Application of the Neganov–Luke effect to low-threshold light detectors

Simultaneous measurement of a temperature signal and scintillation light of a CaWO 4 crystal can be used for background rejection in cryogenic dark matter experiments. In our case the light is measured with a cryogenic detector that consists of a silicon absorber with a superconducting phase transition thermometer. Due to the Neganov–Luke effect the thermal signal is enhanced when a voltage is applied to the silicon absorber. First results with the application of this effect to our low-threshold light detectors will be discussed in this paper.

CRESST cryogenic dark matter search

The CRESST Phase II experiment at Gran Sasso is using 300 g scintillating CaWO 4 crystals as absorbers for direct WIMP (weakly interactive massive particles) detection. The phonon signal in the CaWO 4 crystal is registered in coincidence with the light signal, which is measured with a separate cryogenic light detector. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers (W-SPTs). As a result an active discrimination of the electron recoils against nuclear recoils is achieved. Results on the properties of the detector modules and on the WIMP sensitivity are presented.

CRESST-II: dark matter search with scintillating absorbers

In the CRESST-II experiment, scintillating CaWO4 crystals are used as absorbers for direct WIMP (weakly interacting massive particles) detection. Nuclear recoils can be discriminated against electron recoils by measuring phonons and scintillation light simultaneously. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers (W-SPTs). Results on the sensitivity of the phonon and the light channel, radiopurity, the scintillation properties of CaWO4, and on the WIMP sensitivity are presented.

High detection sensitivity achieved with cryogenic detectors in combination with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.

Cryogenic detectors directly measure the impact energy of any impinging particle independent of its velocity. Thus a very high, mass-independent, detection efficiency is expected from their application in TOF-MS. The cryogenic detector applied here is based on a superconducting phase-transition thermometer and was implemented in a dual reflector time-of-flight mass spectrometer (N-geometry). A dilution series using standard sample preparation procedures shows that the detection limit for insulin (Mr: 5,734) can be decreased by several orders of magnitude, down to 0.5 amol on the MALDI target. Detection limits for rhM-CSF beta (Mr: 49,032) and for polyclonal IgG (Mr: ca 150,000) in the high femtomole and low picomole range, respectively, were established.

Cresst-II: dark matter search with scintillating absorbers

In the CRESST-II experiment, scintillating CaWO4 crystals are used as absorbers for direct weakly interacting massive particles (WIMP) detection. Nuclear recoils can be discriminated against electron recoils by measuring phonons and scintillation light simultaneously. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers. Results on the sensitivity of the phonon and the light channel, radiopurity, the scintillation properties of CaWO4, and on the WIMP sensitivity are presented.

Light detector development for CRESST II

CRESST-II detector modules rely on the ability to actively discriminate electron recoils from nuclear recoils via simultaneous measurement of phonons and scintillation light. The scintillation light produced in each target crystal is detected via an associated calorimeter consisting of a thin silicon wafer read out by a tungsten phase transition thermometer deposited on its surface. About 1% of the energy deposited in CaWO4 is detected as scintillation light; therefore, the sensitivity of the light detector is crucial for the discrimination of electron recoils from nuclear recoils at energies relevant for WIMP searches. We report the detector performance obtained using a thermometer geometry characterized by phonon collectors and a thin film thermal coupling to the heat sink (Fig. 1). This concept allows a high sensitivity by decoupling the area required for the collection of non-thermal phonons and the heat capacity of the sensor. With a 30×30×0.45mm3 light detector, energy thresholds below 5keV referred to energy deposition in CaWO4 have been obtained. Results achieved will be presented and an overview on further possibilities of development will be given.

Dark matter search with CRESST cryogenic detectors

Results of the CRESST experiment at Gran Sasso using 262-g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the Galactic halo. The sapphire detectors are especially sensitive to low-mass WIMPs with spin-dependent interaction and improve on existing limits in this region.

Results of CRESST phase I

Results of the CRESST experiment at Gran Sasso using 262 g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the galactic halo. The sapphire detectors are especially sensitive for low-mass WIMPS with spin-dependent interaction and improve on existing limits in this region.

Cross-sectional TEM study of the microstructure of superconducting X-ray detectors based on thin W–Al layers

The relation between structural and morphological properties and the performance of X-ray detectors have been studied by means of cross-sectional transmission electron microscopy (XTEM) and low temperature electrical measurements. The detectors consist of a strip of an aluminium thin film in contact with superconducting phase transition thermometers based on tungsten films at its both ends. Soft X-ray photons are absorbed in the sapphire substrate underneath the Al film and create high energy phonons. These phonons enter the superconducting film and break up Cooper-pairs into quasiparticles which then diffuse into the W films and create correlated thermal signals in both thermometers. XTEM investigations revealed a polycrystalline structure of the Al films above both the bare sapphire and chemically etched areas of the highly oriented W films, while the Al is single crystalline above the intact W film surface showing an orientational relationship: (2 0 0) Al∥(0 2 0) W∥( 0 1 1 ̄ 2)Al 2O 3 and [0 2 ̄ 2 ] Al∥[2 0 0] W∥[ 1 0 1 ̄ 2 ̄ ] Al 2 O 3 . No remarkable difference in morphology and structure of the layers of the two detector sides was observed. On the other hand, irregular saw-tooth-like interfaces of different profiles of low slope were found between the chemically etched regions of the W sensor films and the overlapping Al diffusion film. The observed strong asymmetry of the correlated signals is attributed to the disturbed quasiparticle propagation through the observed different interface structures of the two detector sides.

Fast cryodetector and SQUID read-out for mass spectrometry

We report a cryogenic detector with a superconducting phase transition thermometer and SQUID read-out for time of flight (TOF) mass spectrometry of biomolecules. Cryogenic detectors combine 100% detection efficiency independent of the mass of the molecule, an excellent energy resolution and a low threshold. Implementation of the cryogenic detectors into TOF mass spectrometers is expected to improve the efficiency of the detection of large biomolecules. To reach a high time resolution, we have developed two new read-outs based on a double stage SQUID and a cooled amplifier.

Massive cryogenic particle detectors with low energy threshold

We have developed massive cryogenic particle detectors to be used in the CRESST dark matter search. Each detector is made of a sapphire crystal and a tungsten superconducting phase transition thermometer. In this paper, we report on the results obtained with four 262 g detectors, which show energy thresholds as low as 350 eV and good energy resolution at low energies. The shape of the experimental pulses, the linearity of the detector response and the energy dependence of the resolution are discussed.

Quasiparticle diffusion over several mm in cryogenic detectors

The use of quasiparticle diffusion in a superconducting film has the potential to allow an increase in the size of a cryogenic detector without proportional loss of energy resolution. The quasiparticle lifetime and the diffusion constant are critical parameters which have limited this development. Using W superconducting phase transition thermometers as the sensors and a W/Al bilayer as the diffusion film, we have measured quasiparticle diffusion over a distance of 2 mm and deduced a diffusion constant of D=2.5×10 −4 m 2/ s and a quasiparticle lifetime of τ=9.0 ms , which is, to our knowledge, by far the longest ever observed. With Ir/Au thermometers and an Ir/Au/Al diffusion film we found D=4.6×10 −3 m 2/ s and τ=0.43 ms with diffusion over 4 mm , the longest distance observed to date.

Noise and energy resolution of X-ray microcalorimeters

Two type of sensor geometries of voltage-biased X-ray microcalorimeters with a phase-transition thermometer have been built and tested. Both devices show, in addition to the well-known noise sources of thermal fluctuation noise or phonon noise from the heatlink to the bath and Johnson noise from the thermometer resistance, also thermal fluctuation noise from the thermometer itself. In both cases however the measured energy resolution is limited by other sources. The energy resolution of the asymmetric lateral type of sensor, 12 to 15 eV @ 5.9 keV, is limited by a position dependent heatleak of the absorber to the bath. The energy resolution of the symmetric lateral sensor, 6.8+/-0.3 eV FWHM @ 5.9 keV, is limited by excess noise at frequencies below 1000 Hz. The origin of this noise component is unknown so far.

Developing of a fast cryodetector read-out for mass spectrometry

We report on the development of a SQUID read-out for a fast cryogenic detector with superconducting phase transition thermometer. To avoid the usual transformer matching and modulation–demodulation technique we are using a second SQUID to amplify the signal of a first stage input SQUID. A bandwidth of 2 MHz and a slew rate of 2×10 5 Φ 0 s −1 were achieved. The system is developed for the detection of large protein molecules in a time of flight mass spectrometer.

Superconducting phase transition thermometers for X-ray spectroscopy

We report on a first attempt on a cryogenic imaging spectrometer based on sapphire absorber and two superconducting phase transition thermometers. One-dimensional imaging was achieved over a length of 10 mm with a spatial resolution of ≈200 μm and an energy resolution of 216 eV for 5.89 keV X-rays.

Simultaneous measurement of phonons and scintillation light for active background rejection in the CRESST experiment

We report on simultaneous detection of phonons and scintillation light using a cryogenic calorimeter composed of a scintillating CaWO 4 crystal and a separate light detector, both instrumented with a tungsten superconducting phase transition thermometer operating at about 12 mK. Clear discrimination between electron and nuclear recoils was demonstrated by irradiating the detector with electrons, photons and neutrons. The shape of the nuclear recoil energy spectrum induced by the neutrons could be well reproduced by simulations.

The CRESST dark matter experiment: status and perspectives

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO 4 and simultaneous measurement of phonons and scintillation light is in preparation.