Figure 1: The 2D membrane PnC device.

(a) Schematic representation of a perforated membrane PnC geometry with a square array of circular holes, fabricated by e-beam lithography. The central region has a heater, which emits thermal phonons into the PnC structure. (b) A false colour scanning electron micrograph (s.e.m.) of the central region of the larger period a=2425, nm PnC sample. The blue (Al) and yellow (Cu) lines are the metallic wiring which form the heater and thermometer elements at the centre of the PnC. The shorter period sample has the same wiring locations and dimensions. The full size of the perforated membrane is 100 μm × 100 μm. (c) A scanning electron micrograph of a region of the shorter period sample (black areas, empty space, grey areas SiN membrane), showing the unit cell size 970 nm × 970 nm and the width of the narrowest region ~60 nm. The sidewalls have a slight angle so that the bottom end of the hole is slightly smaller. Scale bar has length 200 nm. (d) A false colour s.e.m. of the heater/thermometer structure, consisting of a Cu normal metal wire (yellow) sandwiched between two normal metal-insulator-superconductor (NIS) tunnel junctions, connected to the measurement circuit by superconducting Al leads (blue).