1 research outputs found
Coverage-Dependent Disorder-to-Order Phase Transformation of a Uracil Derivative on Ag(111)
The
self-organization of an angular bisÂ(uracil-ethynyl) benzene
derivative is investigated on Ag(111) by means of scanning tunneling
microscopy (STM) under ultrahigh vacuum (UHV) conditions. It is foundî—¸starting
at low submonolayer coverageî—¸that upon increasing the molecular
coverage a disorder-to-order phase transformation occurs. Specifically,
at low and intermediate molecular coverage a glassy phase consisting
of one-dimensional (1D) chains and 2D aggregates is observed, while
close to a first complete molecular layer, a well-ordered 2D close-packed
phase is revealed. The main driving forces responsible for the structure
formation are (i) the high self-complementarity of the uracil (<b>U</b>) moiety, resulting in <b>U</b>–<b>U</b> homopairs through 2-fold CO···H–N
H-bonds and (ii) the steric hindrance induced in the system by the
alkyl chains. The delicate balance between the molecule–molecule
and the molecule–substrate interactions leads to a complex
phase behavior of the uracil derivative at the solid–vacuum
interface. On the basis of this detailed study, we present a qualitative
understanding of the peculiar phase behavior of the system