ABSTRACT
Crystalline inverted membranes of the nonvolatile surfactant sodium dodecylsulfate are found on solid surfaces after electrospray ion beam deposition (ES-IBD) of large SDS clusters in vacuum. This demonstrates the equivalence of ES-IBD to conventional molecular beam epitaxy.
Subject(s)
Membranes, Artificial , Crystallization , Graphite/chemistry , Hydrophobic and Hydrophilic Interactions , Ions/chemistry , Microscopy, Atomic Force , Sodium Dodecyl Sulfate/chemistry , Surface Properties , VacuumABSTRACT
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.
Subject(s)
Cytochromes c/metabolism , Cytochromes c/chemistry , Microscopy, Scanning Probe , Protein Folding , Spectrometry, Mass, Electrospray IonizationABSTRACT
The high intrinsic spin and long spin relaxation time of manganese-12-acetate (Mn(12)) 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 Mn(12) 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 Mn(12) molecules retain their intrinsic spin on a well chosen solid support.
Subject(s)
Acetates/chemistry , Magnets , Manganese/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Macromolecular Substances/chemistry , Magnetic Fields , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
The ion beam deposition (IBD) of rhodamine dye molecules on solid surfaces in high vacuum is explored in order to characterize the possibility of fabricating molecular coatings or nanostructures from nonvolatile molecules. Molecular ion beams with a well-defined composition are deposited on silicon oxide surfaces with a controlled kinetic energy. Photoluminescence spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are employed in order to characterize the sample with respect to coverage, homogeneity, and the fraction of intact landed ions (soft-landing ratio). We find that homogeneous rhodamine films of defined composition can be produced at energies of 2-100 eV. The coverage is found to be proportional to the ion dose. Soft-landing is observed for energies up to 35 eV.
