Grafting Crown Ether Alkali Host-Guest Complexes at Surfaces by Electrospray Ion Beam Deposition

The functionalization of surfaces with host guest compounds is promising for many applications, yet often limited by constraints such as the volatility of the functional compound or the lack of binding to the surface. We use electrospray ion beam deposition (ES-MD) on surfaces in ultrahigh vacuum as a novel approach to modify an atomically defined copper surface with preformed dibenzo-24-crown-8-alkali complexes, in which the central ion (H+, Na+, or Cs+) can be exchanged in the electrospray solution. In situ scanning tunneling microscopy maps the single alkali ion complexes as an oval protrusion with a four-lobe submolecular structure immobilized at the surface. Density functional theory calculations confirm that the crown ether is bound to the surface via the central alkali ion within its cavity, indicating that the properties of the molecular complex are retained after deposition

A Close Look at Proteins: Submolecular Resolution of Two- and Three-Dimensionally Folded Cytochrome c at Surfaces

Imaging of individual protein molecules at the single amino acid level has so far not been possible due to the incompatibility of proteins with the vacuum environment necessary for high-resolution scanning probe microscopy. Here we demonstrate electrospray ion beam deposition of selectively folded and unfolded cytochrome c protein ions on atomically defined solid surfaces in ultrahigh vacuum (10^–10 mbar) and achieve unprecedented resolution with scanning tunneling microscopy. On the surface folded proteins are found to retain their three-dimensional structure. Unfolded proteins are observed as extended polymer strands displaying submolecular features with resolution at the amino acid level. On weakly interacting surfaces, unfolded proteins refold into flat, irregular patches composed of individual molecules. This suggests the possibility of two-dimensionally confined folding of peptides of an appropriate sequence into regular two-dimensional structures as a new approach toward functional molecular surface coatings

The Quantum Magnetism of Individual Manganese-12-Acetate Molecular Magnets Anchored at Surfaces

The high intrinsic spin and long spin relaxation time of manganese-12-acetate (Mn₁₂) makes it an archetypical single molecular magnet. While these characteristics have been measured on bulk samples, questions remain whether the magnetic properties replicate themselves in surface supported isolated molecules, a prerequisite for any application. Here we demonstrate that electrospray ion beam deposition facilitates grafting of intact Mn₁₂ molecules on metal as well as ultrathin insulating surfaces enabling submolecular resolution imaging by scanning tunneling microscopy. Using scanning tunneling spectroscopy we detect spin excitations from the magnetic ground state of the molecule at an ultrathin boron nitride decoupling layer. Our results are supported by density functional theory based calculations and establish that individual Mn₁₂ molecules retain their intrinsic spin on a well chosen solid support