title: Preparation and characterization of dense films of poly(amidoamine) dendrimers on indium tin oxide.
abstract: Indium tin oxide (ITO) substrates were modified with a layer of poly(amidoamine) (PAMAM) dendrimers to change their surface properties and, in particular, the substrates' work function. The functionalization procedure involved the electrostatic adsorption of positively charged PAMAM dendrimers of generation five onto negatively polarized ITO surfaces. Three different PAMAM dendrimers were used: PAMAM-NH2 and PAMAM-OH with terminal amine and hydroxyl groups, respectively, as well as Q-PAMAM-NH2, which had been prepared from PAMAM-NH2 by quaternization of the dendrimer's terminal and internal amine groups with methyl iodide. The resulting organic films were analyzed by contact angle goniometry, X-ray photoelectron spectroscopy, ellipsometry, and Kelvin probe force microscopy to confirm the presence of a dense layer. A Langmuir isotherm was derived from surface densities of fluorescence-labeled PAMAM-NH2 dendrimers from which we deduced an equilibrium binding constant, K(eq), of (1.3 +/- 0.3) x 10(5) M(-1). Kelvin probe measurements of the contact potential difference revealed a high reduction of the work function from 4.9 eV for bare ITO to 4.3 eV for ITO with a dense film of PAMAM-NH2 of generation five. PAMAM-OH and Q-PAMAM-NH2 resulted in slightly smaller work function changes. This study illustrates that the work function of ITO can be tuned by adlayers composed of PAMAM dendrimers.
authors.affiliation: Center for Biomedical Nanotechnology, Upper Austrian Research GmbH, A-4020 Linz, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Schlapak
authors.forename: David
authors.initials: D
authors.lastname: Armitage
authors.forename: Nadia
authors.initials: N
authors.lastname: Saucedo-Zeni
authors.forename: Gianluca
authors.initials: G
authors.lastname: Latini
authors.forename: Hermann J
authors.initials: HJ
authors.lastname: Gruber
authors.forename: Patrick
authors.initials: P
authors.lastname: Mesquida
authors.forename: Yulia
authors.initials: Y
authors.lastname: Samotskaya
authors.forename: Michael
authors.initials: M
authors.lastname: Hohage
authors.forename: Franco
authors.initials: F
authors.lastname: Cacialli
authors.forename: Stefan
authors.initials: S
authors.lastname: Howorka
mesh_terms: D000588:Amines / Q000737:chemistry; D050091:Dendrimers / Q000737:chemistry*; D004583:Electrons; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D009757:Nylons / Q000737:chemistry*; D010777:Photochemistry; D013053:Spectrophotometry; D013499:Surface Properties; D017971:Tin Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014965:X-Rays
chemical_list: D000588:Amines; D050091:Dendrimers; D009757:Nylons; C520550:PAMAM-G4; D017971:Tin Compounds; D014867:Water; C109984:indium tin oxide