| Research Abstract |
1.To investigate the formation, geometrical and electronic structures, and the properties of monolayers comprising reactive molecules or networked carbon atoms laid flat on solid surfaces as well as the piled-up layers, we have developed a low-temperature scanning tunneling microscope which can be connected to our photo-and Penning electron spectrometer. We have obtained the following conclusions on the monolayers of alkadiyne or sashlike polydiacetylene (PD), atomic sash (AS) prepared on graphite (0001) surfaces. In a monomer monolayer prepared by evaporation onto a substrate held at room temperature, molecules form large (1000Å) domains with column structure although they are, liable to be desorbed, while they provide small ones at low temperature. When a monolayer prepared at 150 K is annealed at 220 K, molecules obtain suitable mobility for monolayer polymerization, loosing the column structure. when irradiated with UV light at 220 K, the molecules are transformed into AS-I in a lo
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w temperature phase having raised" PD chains orthogonal to alkyl chains with gauche conformation at f3-y methylenes. Heating the AS-I to room temperature yields A S-II in a high temperature phase ; the alkyl and PD chains intersect at ca. 70゜ and are maintained in a common plane.On cooling, the AS-II is transformed back to the AS-I. Furthermore, there are two kinds 'of AS-II with different molecule-substrate commensurations. In addition, the phase transition and deformation of a single PD chain can be induced by an STM tip.
2.We carried out infrared reflection absorption spectroscopy for alkadiyne on Au(111) and found that all-trans molecules are laid flat with a column structure as in a vapor-deposited monolayer on graphite if the monolayer is prepared by adsorption from a solution. Transformation to AS is now under investgation.
3.We have developed a program to synthesize the Penning ionization electron spectra of solid phase molecules theoretically for expected molecular orientation and arrangement. The flat-on and tilted-on orientation were verified for the mono-and multilayers of long chain molecules on graphite, respectively, by comparing the synthesized and observed spectra. Less
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