MONOLAYER STRUCTURES OF CARBON-MONOXIDE ADSORBED ON SODIUM-CHLORIDE - A HELIUM ATOM DIFFRACTION STUDY

Helium atom diffraction from an ordered monolayer CO on the NaCl(001) plane is reported for the first time. In the temperature range between 25 and 53 K the adsorbate is commensurate to the substrate. At a sample temperature of 45 K a (1×1) structure is formed, in agreement with conclusions drawn from infrared spectroscopy. At T≤30 K the adsorbate lattice forms a superstructure having (2×1) symmetry, the unit cell containing two molecules and a glide plane. In this structure the CO molecules are tilted away from the normal, as evidenced by infrared spectroscopy. As a final remark we want to point out that the interplay of two nondestructive methods, helium atom diffraction and infrared spectroscopy, can widen our knowledge of adsorption on insulator surfaces significantly. © 1991 American Institute of Physics.