A two-component self-assembly process that results in three different compositional phases is observed and explained. Solutions containing various molar ratios of cobalt octaethylporphyrin (CoOEP) and coronene in phenyloctane were brought into contact with a clean Au(111) surface. At no relative concentration was coexistence of the CoOEP and coronene phase observed. Rather, at intermediate concentrations a new 1−1 surface structure (1 coronene to 1 CoOEP) is formed with sharp compositional boundaries. This behavior is unusual in that only weak van der Waals forces, slight variations in surface charge exchange, and steric effects stabilize the 1−1 structure and that it occurs where the solution concentration ratio is an order of magnitude different than the surface concentration. The nature of this 1−1 structure and the transitions between the three phases (pure CoOEP, 1−1, and pure coronene) were studied by variable temperature STM and by density functional theory (DFT). Adsorption energies for CoOEP and coronene, both in their separate phases, and in the 1−1 structure were determined by DFT. The desorption energy into vacuum of CoOEP was found to be ∼1.8 times that of coronene, and the desorption energy of each component in the 1−1 composition was found to be greater than in the corresponding pure monolayer. Measured by energy per nm 2 , pure CoOEP is predicted to be the most strongly adsorbed, coronene is predicted to be the least strongly adsorbed, and the 1−1 structure holds an intermediate position. By heating the sample to 50°C it is possible to observe the transformation of the kinetically stabilized 1−1 structure into the pure CoOEP monolayer under the same solution from which it is formed at 22°C. The existence of these three surface structures is shown to be a kinetic phenomenon rather than due to thermodynamics. We attribute the existence of the three structures at various growth concentrations to changes in nucleation and growth rate with relative impingement rates of each component. A critical element is the fact that one component (CoOEP) is irreversibly adsorbed. The new 1−1 structure is found to have lattice constants of A = (1.73 ± 0.04) nm, B = (1.56 ± 0.04) nm, and α = 90°± 2°and appears to be commensurate with the Au(111) surface.

For the first time, accurate quantitative data on the temperature evolution of a surface monolayer formed at the solution solid interface are reported. In addition, a detailed analysis is provided of the structures of three different monolayers formed when coronene in heptanoic acid is in contact with Au(111). All three monolayer structures are well-defined epitaxial structures that are extremely stable for temperature variations between 0 and 60 °C. At high concentrations, a dense hexagonal structure with molecular separation of 1.19 ± 0.04 nm is observed. At reduced concentration, the most often observed structure is an open hexagonal epitaxial structure with one molecule per unit cell and a molecular separation of 1.45 ± 0.04 nm. This structure is stabilized by solvent molecule adsorption. If the dense phase is exposed to pure solvent, or occasionally with low concentration direct adsorption, then a different hexagonal phase is formed with three molecules per unit cell but exactly the same density (lattice length of 2.46 ± 0.04 nm). Under some conditions, all three phases can be simultaneously present. It is notable that even when the least stable triangular phase is present on a large fraction of the surface, the low-density hexagonal phase is often observed decorating the reconstruction lines. The energy difference between the two low density phases is due to surface–solvent and coronene-adsorbed solvent interactions as the coronene–gold interactions in the two phases are essentially the same. The barrier to thermal conversion between the two low density phases must be several kT or greater than 2 kcal/mol.

We present the spatially resolved modification of the topography and electronic properties of monolayer graphene by a low dosage of atomic oxygen on the nanometer scale. Using the combination of an ultrahigh-vacuum scanning tunneling microscope and a gas beam of oxygen atoms, we show that the surface O-atoms, even at a low coverage of O/C = ∼1/150, serve as p-type dopants that leads to site-dependent partial and full graphene band modifications up to a gap of a few hundred millielectronvolts. The degree of modification and the number of O-atom-induced charge-holes per area are inversely proportional to the distance between the measuring position and the location of the nearest adsorbate. However, the number of holes contributed per oxygen atom is found to be a site-independent constant of 0.15 ± 0.05. For a small population of adsorbates taller than 4 Å, the graphene energy bands are no longer resolved; instead, our tunneling spectra show very spatially localized but highly dense states over a wide potential range, which indicates a sole tunneling contribution from the tall stacks of the electron-rich O-atoms and a complete decoupling from the graphene bands.

We present a new solution-solid (SS) interface scanning tunneling microscope design that enables imaging at high temperatures with low thermal drift and with volatile solvents. In this new design, distinct from the conventional designs, the entire microscope is surrounded in a controlled-temperature and controlled-atmosphere chamber. This allows users to take measurements at high temperatures while minimizing thermal drift. By incorporating an open solution reservoir in the chamber, solvent evaporation from the sample is minimized; allowing users to use volatile solvents for temperature dependent studies at high temperatures. The new design enables the user to image at the SS interface with some volatile solvents for long periods of time (>24 h). An increase in the nonlinearity of the piezoelectric scanner in the lateral direction as a function of temperature is addressed. A temperature dependent study of cobalt(II) octaethylporphyrin (CoOEP) at the toluene/Au(111) interface has been performed with this instrument. It is demonstrated that the lattice parameters remain constant within experimental error from 24 °C to 75 °C. Similar quality images were obtained over the entire temperature range. We report the unit cell of CoOEP at the toluene/Au(111) interface (based on two molecules per unit cell) to be A = (1.36 ± 0.04) nm, B = (2.51 ± 0.04) nm, and α = 97° ± 2°.

We describe an example of a piecewise gas chamber that can be customized to incorporate a low flux of gas-phase radicals with an existing surface analysis chamber for in situ and stepwise gas-surface interaction experiments without any constraint in orientation. The piecewise nature of this gas chamber provides complete angular freedom and easy alignment and does not require any modification of the existing surface analysis chamber. In addition, the entire gas-surface system is readily differentially pumped with the surface chamber kept under ultra-high-vacuum during the gas-surface measurements. This new design also allows not only straightforward reconstruction to accommodate the orientation of different surface chambers but also for the addition of other desired features, such as an additional pump to the current configuration. Stepwise interaction between atomic oxygen and a highly ordered pyrolytic graphite surface was chosen to test the effectiveness of this design, and the site-dependent O-atom chemisorption and clustering on the graphite surface were resolved by a scanning tunneling microscope in the nm-scale. X-ray photoelectron spectroscopy was used to further confirm the identity of the chemisorbed species on the graphite surface as oxygen.