LAUSR

Abstract A molecular adlayer of biphenyl was vapor deposited amorphously onto a single crystal of cryogenically cooled Al2O3. The biphenyl conformer at deposition was determined to be non-planar with a fluorescence λmax ~320 nm. At 161 K biphenyl underwent a disorder-to-order transition which was a planar conformation analogous to the solid crystal with a fluorescence λmax ~345 nm and characterized by a lower fluorescence intensity due to energy transfer. To demonstrate homoepitaxy, a molecular adlayer of biphenyl was vapor deposited and annealed above the disorder-to-order transition temperature. The thinnest adlayer for epitaxial ordering was 35 ML, monolayers, and epitaxy was achieved up to 5000 ML. Heteroepitaxy was demonstrated with p-xylene substrate with biphenyl overlayer. In addition the passage of the xylene through the biphenyl overlayer increased the density of crystalline defect sites and resulted in enhanced fluorescence intensity.