Cryogenically cold nanowire devices, originally employed as superconducting single photon detectors (SSPD), have recently been proposed as detectors for massive particles with kinetic energies in the range 10–20 keV.

In commercial mass spectrometers the detection of molecular ions still almost exclusively relies on secondary electron generation and amplification, but superconducting nanowires could offer a superior solution, based on the argument that an impacting particle only needs to break a certain number of cooper pairs to render the wire normal-conducting. This process depends on the particle energy rather than its velocity, as is the case in secondary electron emission, which falls with increasing mass at a given energy.

Now, using a NbN nanowire chip fabricated by SSPD pioneers including Gregory Gol'tsman at Moscow Pedagogical University, the Vienna team featuring Markus Arndt and Michele Sclafani has quantified the true sensitivity of such cryogenic devices at low ion energy.

Contrary to the common wisdom that high quantum efficiency should be routinely achieved, the Austrian-Russian collaboration found that the detection efficiency is sensitive to the surface conditions of the chip, in particular to the accumulation of dilute adsorbates on exposure of the surface to the residual gas in high vacuum.

The group has quantified the effective detection probability as a function of the impact energy and the researchers find that it typically varies between 10–2 and 100% at energies between 200 and 1000 eV.

This experimentally determined high-energy dependence of the SSPD detection process at low energies opens a new window to the investigation of optical spectroscopy with single photons and single nanoparticles: even a single UV photon is expected to alter the SSPD response to the heated nanoparticle, if the molecule is able to convert the additional internal energy into electronic excitations upon impact on the chip. More directly, a nanoparticle isolated in a liquid helium droplet will change the mass and kinetic energy of its host on absorption of a single photon to a degree that the change in the kinetic energy of the droplet should become visible as a change in the SSPD count rate.

Further information can be found in the journal Nanotechnology.