We describe here the initial bonding geometry and decomposition mechan
ism of HNO3 on Ge(100). A combination of high-resolution electron ener
gy loss spectroscopy, Auger electron spectroscopy, and temperature pro
grammed desorption experiments have been used to shed light on the det
ails of this complex but technologically important system. It was foun
d that HNO3 adsorbs molecularly at 190 K in a predominantly bidentate
bonding configuration. When the substrate is warmed to 425 K, the mole
cule decomposes. In a process that involves two adjacent HNO3 adsorbat
es, H2O and NO desorb while O remains on the surface. Further heating
above 600 K causes the O to desorb as GeO.