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- Augulis, R, et al.
(författare)
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Atomic force microscopy of self-assembled nanostructures of TPPS4 on SAM substrates
- 2004
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Ingår i: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 97-98, s. 195-200
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of organic molecules on solid surfaces is one of the fundamental processes for the development of molecular-based nanodevices. Here we focus on the adsorption and ordering of the TPPS4-based J-aggregates on silicon and gold as well as on self-assembled monolayer (SAM) surfaces. The SAMs used for the experiments were based on the chemisorption of thiol containing compounds onto gold. Long omega-substituted alkanethiols are spontaneously assembled on gold to form highly ordered and densely packed layers with controllable chemical and physical properties. TPPS4 J-aggregates were dispersed on SAM surfaces, and on plain gold and silicon substrates for comparison. The dimensions of aggregates, measured by means of atomic force microscopy, varied depending on the type of substrate. Long stripe-like aggregates were flattened on the substrate surface, and the height and width of aggregates highly correlated with the polarity of surface groups. For example, the J-aggregates were narrower on hydrophobic substrates (with non-polar groups) and wider on hydrophilic substrates (with polar groups). These observations support the hypothesis, that TPPS4 forms,soft" cylindrical aggregates, that appear flattened on the substrate.
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- Rotomskis, R, et al.
(författare)
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Hierarchical structure of TPPS4 J-aggregates on substrate revealed by atomic force microscopy
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:9, s. 2833-2838
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Tidskriftsartikel (refereegranskat)abstract
- The spatial structure of the J-aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS4) formed in acidic aqueous solutions and coated on silicon substrates was analyzed by means of atomic force microscopy (AFM). The AFM experiments indicate the presence of the stripelike J-aggregate structures on the surface. The size of the individual stripes ranged from 4.5 x 40 x 200 to 4.5 x 40 x 1000 nm(3) (height x width x length). The length of the stripelike structures varied, whereas stripe width and thickness remained unchanged. The stripes stacked into larger domains, "fibers", containing typically 2-20 stripes aligned parallel with a longitudinal shift with respect to each other. The size of individual stripes remained the same when interacting side-by-side in fibers. At lower magnification it is clearly seen that fibers form a network-like structure. The J-aggregates assemble into large (up to several millimeters) bushlike structures. It takes several weeks to form such structures in acidic aqueous solutions. On the basis of our experimental findings, it is also suggested that the stripes consist of rings that form nanotube-like TPPS4 J-aggregates, which are flattened as a result of attractive interactions with the substrate.
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