Quenched growth of nanostructured lead thin films on insulating substrates

Lead island films were obtained via vacuum vapor deposition on glass and ceramic substrates at 80 K. Electrical conductance was measured during vapor condensation and further annealing of the film up to room temperature. The resistance behavior during film formation and atomic force microscopy of annealed films were used as information sources about their structure. A model for the quenched growth, based on ballistic aggregation theory, was proposed. The nanostructure, responsible for chemiresistive properties of thin lead films and the mechanism of sensor response are discussed.Comment: 2 figures; accepted to Thin Solid Film

Early stage morphology of quench condensed Ag, Pb and Pb/Ag hybrid films

Scanning Tunneling Microscopy (STM) has been used to study the morphology of Ag, Pb and Pb/Ag bilayer films fabricated by quench condensation of the elements onto cold (T=77K), inert and atomically flat Highly Oriented Pyrolytic Graphite (HOPG) substrates. All films are thinner than 10 nm and show a granular structure that is consistent with earlier studies of QC films. The average lateral diameter, $\bar {2r}$, of the Ag grains, however, depends on whether the Ag is deposited directly on HOPG ($\bar {2r}$ = 13 nm) or on a Pb film consisting of a single layer of Pb grains ($\bar {2r}$ = 26.8 nm). In addition, the critical thickness for electrical conduction ($d_{G}$) of Pb/Ag films on inert glass substrates is substantially larger than for pure Ag films. These results are evidence that the structure of the underlying substrate exerts an influence on the size of the grains in QC films. We propose a qualitative explanation for this previously unencountered phenomenon.Comment: 11 pages, 3 figures and one tabl

Plasmonic fluorescence enhancement of DBMBF2 monomers and DBMBF2-toluene exciplexes using al-hole arrays

The optical properties of aluminum hole arrays fabricated via colloidal lithography were investigated. By tuning the hole diameter and hole spacing independently, their influence on the Bloch wave-surface plasmon polariton (BW-SPP) and localized surface plasmon resonances resonances (LSPR) could be identified. The aluminum hole arrays were used to enhance the fluorescence of a dibenzoylmethanatoboron difluoride (DBMBF2) dye. The dye exhibits the advantageous property of forming an exciplex with aromatic compounds. The interaction of DBMBF2 monomer fluorescence and DBMBF 2-toluene exciplexes with Al hole arrays is studied. Furthermore, the respective roles of the BW-SPPs and LSPRs were studied through tuning of the plasmon resonances from the UV excitation wavelength (λext = 385 nm) through the visible emission range (400-550 nm). Monomer emission was predominately enhanced by BW-SPPs while exciplex emission showed a contribution from both BW-SPPs and LSPRs. Fluorescence enhancement of 3.8 was observed for DBMBF2-toluene exciplex emission from 26 nm thick polymer films. Aluminum hole arrays are shown to be attractive structures for fluorescence enhancing applications with excitation in the UV and stable oxide coatings. © 2014 American Chemical Society