EVIDENCE FOR THE ADSORPTION OF ORIENTED NIDO-R2C2B4H6 CARBORANE CLUSTER MOLECULES ON SI(111) SURFACES

Angle-resolved photoemission has provided clear evidence that the initial adsorption of the small heteroborane cluster molecule nido-2,3-diethyl-2,3-dicarbahexaborane(8), (C2H5)2C2B4H6, on Si(111) surfaces at 90 K occurs with partial dissociation of the cluster and results in the loss of ethyl groups (C2H5) from the molecule. The C2B4H6 carborane fragment adsorbs molecularly on the Si(111) surface with the basal C2B3 plane of the cage parallel with the Si(111) surface normal. The complete assignment of the photoemission features and the molecular orientation of the cage is possible from a comparison of the experimental photoemission results with MNDO semiempirical theoretical calculations on nido-(C2H5)2C2B4H6 and nido-C2B4H8.