High resolution tunnel junction extreme ultraviolet detectors limited by quasiparticle counting statistics

Abstract

Superconducting tunnel junctions (STJs) can be used as high-resolution high-count rate photon detectors. They are based on the measurement of the excess quasiparticle tunneling current caused by the absorption of a photon i n one of the junction electrodes. We have fabricated Nb-Al-AlOx-AQ-Nb tunnel junction detectors with different sizes and characterized them in sychrotron experiments. We present a study of the detector performance in the energy band between 5 0 and 1000 eV. For photon energies below 70 e V , the intrinsic device resolution of the best STJ devices agrees with the theoretical limit set by the statistics of the charge generation and tunneling processes.

A superconducting detector endstation for high-resolution energy-dispersive SR-XRF

“…3). On the other hand, the resolution is less than that of nominally identical STJ detectors mounted in the center of an ADR, rather than at the end of a cold finger within 2.5 cm of a room temperature sample [4,6]. This discrepancy may be due to excess noise caused by IR radiation, or due to insufficient shielding of external magnetic fields The UHV chamber vacuum was in the low 10 À9 mbar range, and no signs of gas freeze-out on the IR blocking windows have been observed.…”

“…We have developed Nb-Al-AlOx-Al-Nb STJ detectors and operated them in an adiabatic demagnetization refrigerator (ADR) in SR-XRF applications [6,7]. Our STJ detectors have achieved an energy resolution between 1.7 and 8.9 eV FWHM at 50 eV-1 keV, and they have been successfully operated at count rates above 10,000 counts/s [4,6].…”

“…Cryogenic detectors for the photon energy range between 0.1 and 6 keV fall into two groups: microcalorimeters, which offer very high energy resolution between 2 and 5 eV FWHM at the expense of low count rate around 500 counts/s [2,3], and superconducting tunnel junctions (STJs), which offer somewhat poorer resolution between 2 and 13 eV FWHM but can be operated at an order of magnitude higher count rates [4][5][6].…”

X-ray spectroscopy of ion-surface interactions using superconducting tunnel junctions

“…A room temperature FET-based preamplifier measures the excess tunneling current produced by an X-ray in the detector. We have measured an energy resolution as low as 1.7 eV at 70 eV and 8.9 eV at 1 keV using 70 µm × 70 µm STJ detector [6]. However, here we have used a 141 µm × 141 µm device with a resolution of 12-14 eV at 525 eV, trading off energy resolution for increased detector area.…”

Diffusion-engineered single-photon spectrometer for UV/visible detection

“…The collected charge is then Q ¼ pQ 0 : Backtunneling can be achieved by confinement of the quasiparticles near the tunnel barrier by a higher gap superconductor (Ta [1,2] or Nb [3] confines quasiparticles in Al), or by slowing down the diffusion away of the quasiparticles. It is this latter approach that we introduce in this work, for use with lateral structure devices.…”