Scanning tunneling microscope images of adenine on Ag(111) recorded at 83 K. Large scale image shows two adenine islands that formed on the center terrace, which nucleated at the bottom of the upper step edge. Inset shows the typical dimerization and defect sites in these films (imaging conditions: , ).
Topography (a) and sequential, concurrently acquired differential conductance images (b)–(d) (area: ) recorded at 83 K of an adenine island [dark in (a), bright in (c)] in between two silver terraces. Decreasing the bias voltage from to −80 mV results in a contrast reversal between the adenine film and the clean silver. (Imaging conditions: , , with , for phase sensitive detection of the first harmonic of the tunneling current with respect to dc bias.)
Differential conductance spectroscopy recorded at 83 K in the center of an adenine domain (blue), the silver substrate (red), and the center of a defect in the overlayer (green). Gap conditions: , . Acquisition parameters: , for phase sensitive detection of the first harmonic of the tunneling current with respect to dc bias.
(a) Topographic image of the region in which the dispersion data were obtained. An adenine domain is bounded by two Ag terraces (bright plateaus in the differential conductance images). [(b)–(f)] Representative differential conductance images of the same location at different bias voltages listed in each image used for wave vector measurements. Note the changes in the interference patterns for the adenine covered region compared to the bare silver terraces (imaging conditions: (a) , , (b)–(d) , , ).
Dispersion curve with the experimentally measured Ag(111) curve (blue) and the experimentally measured adenine dispersion curve (red). Error bars for the wave vector are derived from the measurement uncertainty due primarily to the FFT sampling size of the domains analyzed. Parabolic fits to the data shown confirm the nature of the dispersion as a free-electron type band.
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