CoPt 3 nanoparticles adsorbed on SiO 2 : A GISAXS and SEM study
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CoPt3 nanoparticles adsorbed on SiO2 : a GISAXS and SEM study Jan I. Flege1 , Thomas Schmidt1, Gabriela Alexe1, Torben Clausen1 , Sigrid Bernstorff2 , Igor Randjelovic3, Vesna Aleksandrovic3, Andreas Kornowski3, Horst Weller3 and Jens Falta1 1 Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee, 28359 Bremen, Germany 2 Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza / Trieste, Italy 3 Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany ABSTRACT Ultra-thin CoPt3 nanoparticle films have been prepared on SiO2 surfaces using a Langmuir-Blodgett (LB) deposition technique. The structural properties of the overlayers have been investigated by grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution scanning electron microscopy (SEM) for the first time. Self-assembly of the nanoparticles is found and with GISAXS an average particle-particle distance of (8.23 ± 0.06) nm is determined, in good agreement with the SEM results. A particle correlation length of (22.3 ± 1.2) nm was derived which is shown to be independent of the surface coverage. The latter quantity may be controlled by choice of a suitable retraction speed during the LB step.
INTRODUCTION The preparation of ordered arrays of nanoparticles has attracted a tremendously increasing interest in the last years due to their wide range of potential applications e. g. in opto-electronics, ultra-dense magnetic storage devices and catalysis [1]. In this respect, the “bottom-up” concept of two-dimensional self-assembly of ex-situ prepared quantum dots from colloidal solutions with well-defined electronic properties is very promising for industrial use. In comparison to the alternative “top-down” approach which comprises a lithographic patterning process in which the required lateral resolution has to be enhanced to the near-atomic scale, using self-organization would allow the manufacturing of highly-integrated devices at reasonable costs. However, for an efficient and optimized fabrication of dense nanoparticle films a thorough structural characterization of the prepared overlayers as function of the parameters governing the preparation process is necessary. Here, we present a first grazing incidence small-angle x-ray scattering (GISAXS) study of CoPt3 nanoparticles of about 5 nm in diameter which have been adsorbed on silicon wafers covered by native SiO2 buffer layers using Langmuir-Blodgett techniques. Additionally, micro and mesoscale features of the film morphology have been investigated in real space with scanning electron microscopy (SEM).
EXPERIMENTAL DETAILS Preceding the deposition of CoPt3 nanoparticle films on native SiO2 , the nanoparticles were synthesized via the simultaneous reduction of Pt(acac)2 and thermal decomposition of Co2 (CO)8
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in a high-boiling coordinating solvent mixture of hexadecylamine-diphenyl ether, as described elsewhere [2, 3]. For a given set of preparational parameters, this procedure results in the formation of monodisp
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