(a) A temperature profile for the insulated chip from COMSOL simulations. (b) An x–y axis slice through the heater-well area and (c) temperature as a function of distance from the heater-chip surface. The simulations were carried out outside the transmission electron microscope using He gas and a mass flow of 2.64 × 10−9 kg s−1. The ambient temperature was 20°C. A range of temperatures for the heater including 20, 200, 400 and 700°C are compared.