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Improvement of Energy Linearity in Kinetic Energy Measurement with Superconducting Detectors for TOF-MS Yiner Chen, Masahiro Ukibe, and Masataka Ohkubo National Institute of Advanced Industrial Science and Technology (AIST), Umezono, Tsukuba, Ibaraki 305-8568, Japan ✰ Cryogenic Nb-based proximized STJ detectors with 100 elements of 200×200 μm 2 was fabricated successfully. ✰ The STJ elements show good tunnel junction performance at 0.3K (extremely low leakage current ~ a few nA). ✰ The kinetic energy spectrum of TOF-MS experiment for polystyrene of 100KDa proved that the detector has a 100% detection efficiency independent on molecular weight up to 2MDa. ✰ Energy non-linearity has been observed. The fabrication to obtain a good energy linearity is under progress. Conclusions MP09-171 (1). Fabrication of large-array cryogenic tunnel junction (STJ) detectors by photolithographic techniques, DC magnetron sputtering, reaction ion etching (RIE), and wet-etching processes. (2). Good tunnel junction property. (3). 100% detection efficiency independent on molecular weight. Overview (1). STJ detectors have a faster time resolution of a few 10 ns, which is advantageous for a high mass resolution, than other cryogenic detectors such as calorimeters of which time resolution is about 1 μs. (2). Problem of STJ detectors to be solved is small active area (currently<200μm). In this study, array of one-hundred STJ elements with a size of 200×200 μm 2 have been fabricated and tested. (3). Advantage for TOF-MS comes from 100% detection efficiency for a wide mass range, no noise, and kinetic energy measurement. Introduction UV laser 17.5kV high voltage Analyte in matrix field free region STJ detector + ion Scheme of STJ detector structure Experimental Methods photolithographic equipment sputtering apparatus with six targets cryostat apparatus Experimental Results Kinetic energy spectrum of TOF-MS experiment for polystyrene of 100kDa -8 -6 -4 -2 0 2 4 6 8 -0.4 -0.2 0 0.2 0.4 V [mV] I [nA] Image of Nb-based STJ array with 100 elements of 200×200 μm 2 enlarged Bottom (Nb) Upper (Nb) Nb/Al/AlOx/Al/Nb Substrate(Si) Isolation (SiO 2 ) k Da/z k Da/z Mass spectrum of BSA(66.4kDa) k Da/z 1cm I-V curve at 0.3K I-V curves at different temperatures Mass vs. kinetic energy plot k Da/z Kinetic energy spectrum of BSA + (17.5 keV) and BSA ++ (35keV) Non-linearity should be improved molecular impact ✰ Normal resistance R N : ~0.4 Ω; Quality factor (R d /R N ): ~10 6 at 0.3K. ✰ 25% elements have good superconducting performance. 100% detection efficiency (independent on molecular weight)
