Hydroquinone (HQ) adlayers were formed on Pt(111) in HF solution and in a vacuum. By using scanning tunneling microscopy (STM) in solution, it was revealed that HQ formed an ordered structure on Pt(111) with a strong attractive interaction between two adjacent hydroxyl groups in neighboring HQ molecules. After the sample was transferred into a vacuum, low-energy electron diffraction (LEED) measurement was performed, which showed that the (2.56 x 2.56)R16 degrees incommensurate structure of the HQ adlayer was formed in solution. The HQ adlayer on Pt(111) was formed also by vapor deposition, and the identical (2.56 x 2.56)R16 degrees adlayer structure was found by LEED and STM in a vacuum.

Hydroquinone ͑HQ͒ adlayers were formed on Rh͑111͒ in HF solution and in vacuum. Cyclic voltammetry showed that HQ adsorbed on Rh͑111͒ does not undergo redox reactions on the surface. In situ scanning tunneling microscopy revealed that HQ formed a (ͱ7 ϫ ͱ7)R19.1°structure on Rh͑111͒. A strong interaction was seen between two adjacent hydroxyl groups of neighboring HQ molecules. After the sample was transferred into vacuum, low-energy electron diffraction measurement was performed, which showed that the (ͱ7 ϫ ͱ7)R19.1°structure of the HQ adlayer remained unchanged even in vacuum. The HQ adlayer formed on Rh͑111͒ by vapor deposition was found to have the same structure as that observed in solution. Interestingly, the adlayer structure of HQ on Rh͑111͒ was almost identical to that previously reported on Pt͑111͒, ͑2.56 ϫ 2.56͒P16°, despite the difference in the lattice constants of those metal surfaces.

Structure of the adlayer of p-xylene on Rh(111) in HF solution was investigated by the complementary use of in situ scanning tunneling microscopy (STM) and ex situ low-energy electron diffraction (LEED). In situ STM images revealed that p-xylene molecules lie flat on the Rh(111) surface, forming a highly ordered adlayer with a c(2 3 × 4)rect structure. High-resolution imaging revealed not only the packing arrangement but also the internal structure of each molecule. Two methyl functional groups at the para position of benzene were clearly discerned. The adlayer structure obtained by LEED was consistent with that determined by in situ STM.