TaS2 (and TaSe2) exhibit an electronic phase transition from a normal into a condensed state which is called the Charge Density Wave (CDW) state. The transition is caused by an electron-phonon coupling. STM images of TaS2 show a triangular atomic lattice (a0=0.33 nm) with a superimposed CDW lattice of about 3.5 a0. The CDW lattice is rotated 11° with respect to the atomic lattice.
11 x 11 nm2 image; z-range 0.8 nm
To observe the CDW we typically use parameters of 2-3 nA tunneling current and 10-20 mV gap voltage. The atomic lattice can be seen simultaneously when the current is increased to higher values (30 - 40 nA).
6 x 6 nm2 image; z-range 0.8 nm