The movement of electrons across tiny distances between metals
has the power to change the colour of the gap.
Nanophotonics researchers from the University of Cambridge,
Université Paris Sud and Donostia International Physics Centre
discovered that spaces smaller than a nanometre between metals undergo observable
colour changes thanks to the movement of electrons in the
surrounding area -- meaning the scientists could see quantum
mechanical processes in action.
A variety of sub-nanometre distances between nano-sized gold
balls lit by white light were analysed in the study with the light
in the gap initially reddening as the distance decreased below one
nanometre. The colour then shifted towards the blue end of the
spectrum after the point at which electrons could use quantum
tunnelling to jump across the space between metals without them
actually coming into contact (below 0.35 nanometres).
To explain the phenomenon Jeremy Baumberg, leader of the
experimental team at the University of Cambridge, likens the colour
change to "the tension building between a flirtatious couple
staring into each other's eyes. As their faces get closer the
tension mounts, and only a kiss discharges this energy," -- the
nanophotonic kiss in question being a rather chaste one which takes
place without the participants even touching one another.
Matt Hawkeye, from the experimental team at Cambridge,
said: "Lining up the two nano-balls of gold is like closing your
eyes and touching together two needles strapped to the end of your
fingers. It has taken years of practise to get good at
The results of the study contribute valuable data to the field
of nanoplasmonic device engineering -- the creation of tiny
technologies involving plasmonic systems.