Properties of tunnel junctions with alumina barrier

Tunnel junctions formed of base aluminum electrode, which is oxidized and doped by a substance under investigation, are used in inelastic electron tunneling spectroscopy (IETS). The resistance of the samples is strongly dependent on the thickness of the tunnel barrier and must be in the interval 100 Ω – 1 kΩ to obtain low-noise spectra with sufficient resolution. Measurement of IETS spectra is performed in liquid helium; multiple samples are always measured simultaneously. Preparation of one group of samples takes approximately 4 days. Therefore it is necessary to store some junctions without significant change of their resistance for 4–5 days before the measurement. It was found that storing of the samples in standard laboratory conditions (23 °C, 55 % RH) causes change of their resistance, which depends on the dopant of the junction (measured substance). Various methods of storage and various types of protective coatings were tested for storage of tunnel samples. It was found that the best way is storage in a dry desiccator.