Fig. 4.
(a) (x,y)-averaged electrostatic energy of an electron across monolayers for 3, 6, and 15 repeat units aligned at the “left” vacuum energy, VLleft. The step in energy across the layer, ΔEvac, is indicated by vertical black arrows. The light gray inclined lines serve as a guide to the eye to illustrate the net potential gradients across the respective SAMs (note that when “drawing” those lines the potential in the region of the terminal ring has not been considered as that ring is subject to a qualitatively different bonding environment). (b) Evolution of the molecular dipole moment of oligopyrimidinethiol molecules (orange (light gray in b/w) stars) and SAMs (green (dark gray in b/w) rectangles) with increasing number of pyrimidine units; note that the scales differ by a factor of 10. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)