Variations in the superconducting transition temperature with changes in thickness for FeSe0.8Te0.2 samples on various substrates. (a–c) The T dependences of RS (normalized to the RS value at 100 K, RS(100 K)) for LAO, CaF2 and STO samples, respectively, subjected to electrochemical etching at VG = 5 V. (d) The thickness dependences of Tconset for the three samples. Filled symbols correspond to the data shown in (a–c), for which the thickness was estimated from QF. Open symbols correspond to other samples whose thicknesses after etching were directly measured via TEM, as shown in Fig. 4.