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CRITICAL TEMPERATURE IN ALUMINUM FILMS
Even back in 1938 an increase of the superconducting critical temperature with a reduction of
an Al film thickness was observed, while some other superconductors exhibit an opposite
dependence[1,2]. Despite the long history of studying, the nature of this size-effect is still
disputable. Presumably, origin of that effect is attributed to amorphous phase, impurities or
other essential inhomogeneities in crystal structure of the samples[3]. Anyway, it has been
investigated mainly with highly disordered films, but virtually unexplored for ultrathin
monocrystalline structures. Besides, there was no strict control of purity and structure of
samples.
There is hypothesis that if you take pure monocrystal film of any thickness there will not be
difference of superconductive critical temperature from the bulk. However, it is still not
confirmed neither as disproved because of complexity of fabrication and quality control. Our
colleges from Greece manufactured samples of different thickness (from 10 to 100nm), using
molecular beam epitaxy method. We control their structure with atomic -force and scanning
electron Microscopy(AFM, SEM) and angle-resolved photoemission spectroscopy (ARPES).
We have performed investigation of thickness dependence of critical temperature in atomic
pure monocrystal aluminum films. All measurements was set in He-3 based cryo-insert, which
is capable to obtain temperature down to 300 mK. To improve accuracy of temperature
measurements our thermometers was additionally calibrated by reference point of
superconducting transition in bulk aluminum samples. To avoid influence of noises setup was
equipped with EMS- filters.