Surfaces and Interfaces at the nanoscale

We are studying organic/inorganic and inorganic/inorganic interfaces involving surfaces of bulk systems, molecular assemblies and nanoparticles. Our main goal is to provide a description of physical and chemical properties of nanostructured materials in realistic environments, directly comparable with experiment.

  • Structural and electronic properties of self-assembled monolayers on gold
  • Crystallized, thiol-protected gold nanoparticles
  • Si nanoparticles embedded in amorphous matrices
  • Group IV and chalcogenides nanoparticles

PDI/Au(111)
Structural and electronic properties of isocynide molecules on Au (111). (a) Molecular transport devices based on aromatic SAMs . STM image (c) of herringbone structure of PDI SAMs as shown in (b)

Understanding the electronic and transport properties of metal/self-assembled monolayer (SAM) interfaces is key to control charge carrier mobility and charge injection, which are important parameters determining the performance of organic electronic devices. We have studied in detail isocynide SAMs on gold with the goal of unraveling the electronic properties of the interface, and interpreting recent experiments. By combing many-body perturbation theory (GW) and a surface polarization model, we go beyond conventional DFT and provide an accurate picture of energy level alignment at the interface [1,2].


Au102MBA44

Geometry (a), isosurface of Highest Occupied Molecular Orbital (HOMO) (b) and Wannier center distribution (c) of Au102(MBA)44

We have carried out first-principles calculations of the electronic and bonding properties of the newly crystallized gold nanoparticle structure Au102(MBA)44. Using optimized ab-initio codes and algorithms and high performance computers, we could optimize the structure and investigate the properties of exactly the same system explored experimentally, including in our calculations the 1596 atoms of the full unit cell (6924 valence electrons) [3].


Si nanocluster

Structural model of a 1 nm Si cluster (red spheres) embedded in an amorphous Silicon nitride matrix, as obtained by classical MD, in which the precipitation process is simulated using forward-flux techniques. Yellow and blue spheres denote Si and N atoms in the matrix, respectively.

Si nano crystals are promising materials for photonic applications, yet the origin of their photoluminescence, observed experimentally, remains elusive. Si nano crystals obtained by Chemical Vapor Deposition (VD) or Physical VD are embedded in amorphous media such as amorphous Si-rich nitride or oxide films. To understand the opto-electronic properties of such composite systems, we are investigating both their atomic and electronic structures, by employing a combination of classical and ab-initio molecular dynamics simulations.


References

  1. "Microscopic Characterization of the Interface between Aromatic Isocyanides and Au(111): a First-Principles Investigation", Y. Li, D. Lu, S. A. Swanson, J. C. Scott and G. Galli, J. Phys. Chem. C, 112, 6413 (2008).
  2. "Calculation of Quasi-Particle Energies of Aromatic Self-Assembled Monolayers on Au(111)", Y. Li, D. Lu and G. Galli, J. Comp. Theor. Chem, 5, 881 (2009)
  3. "Electronic Structure of Thiol-Covered Gold Nanoparticles: Au102(MBA)44", Y. Li, G. Galli and F. Gygi, ACS Nano, 2, 1896 (2008).