Novel Growth of Naphthalene Overlayer on Cu(111) Studied by STM, LEED, and 2PPE

Abstract

Adsorbed structures of naphthalene on Cu(111) have been studied using low temperature scanning tunneling microscope (LT-STM) and low energy electron diffraction (LEED). Starting from single molecules, three kinds of long-range ordered superstructures, ( 5 3 × 5 3)R30°, (2 3 × 3)rect-1C 10 H 8 , and ( -4 1 1 -4 ) are observed depending on the molecular concentrations and the substrate temperatures during molecular adsorption.One of the self-assembled ordered phases with a (5 3 × 5 3) R30°periodicity is chiral in adsorptioninduced arrangement though a single naphthalene molecule itself has no inherent chirality. In STM images, isolated single molecules appear as depressions whereas the molecules are seen as protrusions in self-assembled layers. Coverage dependent two-photon photoemission (2PPE) spectra show that the adsorption-induced occupied states is formed at around Cu 3d bands, and this results in the enhanced tunneling of occupied state images in assembled layers.

Adsorption structures and energetics of molecules on metal surfaces: Bridging experiment and theory

“…The average C-Ag vertical adsorption distance is 2.99Å at an adsorption energy of 1.22 eV. D. Naphthalene on Cu (111) Experimental Data Np on Cu(111) shows a variety of overlayer structures that are both commensurate and incommensurate, the latter giving rise to Moiré patterns 185,186 . The overlayer structures are all nonprimitive structures in surface area between (4x3),(5x3), and larger superstructures.…”

SAMPLE: Surface structure search enabled by coarse graining and statistical learning

“…The commensurate polymorphs of naphthalene on Cu(111), that were found in experiment, exhibit coverages of 1.19 N ads nm −2 to 1.48 N ads nm −2 (15 to 12 primitive substrate unit cell areas A PUC per naphthalene molecule) and have between 1 and 6 flat lying molecules per unit cell [34,35]. For our structure prediction, we therefore select a slightly larger coverage range of 1.19 to 1.98 N ads nm −2 (15 A PUC to 9 A PUC per naphthalene molecule) with 1 to 6 molecules per unit cell.…”

“…Beyond that, evaluating the prediction results with ab initio thermodynamics provides further insight into a system's polymorphism. Table 3: Ranking of the experimental phases in out prediction: ∆E is the energy difference between experimental phases and lowest energy configuration of similar coverage, experimental figures modified with permission from [34,35] We demonstrate these capabilities using the example of naphthalene on Cu(111) and show SAMPLE's ability to efficiently predict adsorption and Gibbs free energies of millions of possible commensurate configurations of molecules on surfaces. Moreover, the comparison with experiment demonstrates SAMPLE's predictive power, since all experimental polymorphs rank within the numerical DFT uncertainty compared to the best prediction.…”

“…Throughout the text, we illustrate the procedure on the example of naphthalene on Cu(111). Naphthalene is a small organic molecule, which forms a number of commensurate structures on the Cu(111) substrate depending on the preparation conditions [34,35]. Hence, it is an ideal test system to demonstrate the capabilities of SAMPLE.…”

Temperature and Coverage Dependent Quasi-reversible Two-photon Photoemission of 1-phenyl-1-propyne on Cu(111)

“…8 One may argue that although the change in UPS is not significant as 2PPE, there is a slight spectral change (marked by arrows) in the HOMO position between 0.0 and 5.0 eV (7× expanded spectra). This could be related with a slight change in chemical interaction between PP and Cu d-band, 12 consequently leading a dramatic change in 2PPE.…”