Stability of radical-functionalized gold surfaces by self-assembly and on-surface chemistry

We have investigated the radical functionalization of gold surfaces with a derivative of the perchlorotriphenylmethyl (PTM) radical using two methods: by chemisorption from the radical solution and by on-surface chemical derivation from a precursor. We have investigated the obtained self-assembled monolayers by photon-energy dependent X-ray photoelectron spectroscopy. Our results show that the molecules were successfully anchored on the surfaces. We have used a robust method that can be applied to a variety of materials to assess the stability of the functionalized interface. The monolayers are characterized by air and X-ray beam stability unprecedented for films of organic radicals. Over very long X-ray beam exposure we observed a dynamic nature of the radical-Au complex. The results clearly indicate that (mono)layers of PTM radical derivatives have the necessary stability to withstand device applications.

Island shape and electronic structure in diindenoperylene thin films deposited on Au(110) single crystals

We have investigated diindenoperylene (DIP) thin films deposited on Au(110) single crystals, by using a multi-technique approach based on X-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, atomic force microscopy (AFM) and photoemission electron microscopy (PEEM). DIP molecules are physisorbed on gold, with image-charge screening playing the major role as an interface phenomenon. DIP thin films show Stranski-Krastanov growth mode and the structural herringbone arrangement mimics the arrangement found in DIP single crystals. These results are common with the (100) and (111) gold substrate geometries. On the contrary, the island aggregation is substrate geometry-dependent. This paves the way to exploit the degree of anisotropy in different lattice geometries as a tool for molecular patterning of inorganic surfaces, keeping the electronic structure preserved.

Chemisorption, morphology, and structure of a n-type perylene diimide derivative at the interface with gold: influence on devices from thin films to single molecules

We have investigated thin films of a perylene diimide derivative with a cyano-functionalized core (PDI-8CN2) deposited on Au(111) single crystals from the monolayer to the multilayer regime. We found that PDI-8CN2 is chemisorbed on gold. The molecules experience a thickness-dependent reorientation, and a 2D growth mode with molecular stepped terraces is achieved adopting low deposition rates. The obtained results are discussed in terms of their impact on field effect devices, also clarifying why the use of substrate/contact treatments, decoupling PDI-8CN2 molecules from the substrate/contacts, is beneficial for such devices. Our results also suggest that perylene diimide derivatives with CN bay-functionalization are very promising candidates for single-molecule electronic devices.

Structure formation in diindenoperylene thin films on copper(111)

First-principles calculations were combined with scanning tunneling microscopy (STM) measurements to analyze the adsorption of diindenoperylene (DIP) molecules on Cu(111) surfaces.

Paramagnetic nitronyl nitroxide radicals on Al2O3(11-20) single crystals: nanoscale assembly, morphology, electronic structure, and paramagnetic character toward future applications

Aiming at future technological applications, we describe the interface and the thin film processes of a pyrene-substituted nitronyl nitroxide radical deposited on Al2O3(11-20) single crystals. Electronic properties, chemical environment at the interface, and morphology of the thin films have been investigated by a multitechnique approach. Spectroscopic and morphologic analyses indicate a Stranski-Krastanov growth mode and weak physisorption of the molecules on the surface. The deposition does not affect the paramagnetic character of the molecules. The results presented in this paper show not only that the investigated system is a promising candidate as a model for understanding thin film processes in purely organic-based magnets, but its characteristics are worth its future use in electronics, because the radical character of the molecules is completely preserved in the thin films.