  Charge density waves (CDW) have been studied at the surface of a cleaved
TTF-TCNQ single crystal using a low temperature scanning tunneling microscope
(STM) under ultra high vacuum (UHV) conditions. All CDW phase transitions of
TTF-TCNQ have been identified. The measurement of the modulation wave vector
along the a direction provides the first evidence for the existence of domains
comprising single plane wave modulated structures in the temperature regime
where the transverse wave vector of the CDW is temperature dependent, as hinted
by the theory more than 20 years ago.
