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1.
Dalton Trans ; 41(15): 4445-50, 2012 Apr 21.
Article in English | MEDLINE | ID: mdl-22344390

ABSTRACT

Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H(2)O)(2+) and Cr(CN)(6)(3-) (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process.

2.
Dalton Trans ; 41(5): 1582-90, 2012 Feb 07.
Article in English | MEDLINE | ID: mdl-22159371

ABSTRACT

Controlling the elaboration of Coordination Networks (CoNet) on surfaces at the nanoscale remains a challenge. One suitable technique is the Sequential Growth in Solution (SGS), which has the advantage to be simple, cheap and fast. We addressed two issues in this article: i) the controlled synthesis of ultra thin films of CoNet (thickness lower than 10 nm), and ii) the investigation of the influence of the precursors' concentration on the growth process. Si(100) was used because it is possible to prepare atomically flat Si-H surfaces, which is necessary for the growth of ultrathin films. We used, as a model system, the sequential reactions of K(4)[Fe(II)(CN)(6)] and [Ni(II)(H(2)O)(6)]Cl(2) that occur by the substitution of the water molecules in the coordination sphere of Ni(II) by the nitrogen atoms of ferrocyanide. We demonstrated that the nature of the deposited film depends mainly on the relative concentration of the anchoring sites versus the precursors' solution. Attenuated Total Reflection Fourier Transformed Infra Red (ATR-FTIR), X-ray reflectivity, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the steps of the growth process.

3.
Langmuir ; 27(8): 4397-402, 2011 Apr 19.
Article in English | MEDLINE | ID: mdl-21413746

ABSTRACT

Homogeneous two-dimensional structures of CeVO(4) nanowires (NWs) deposited on silicon substrates are obtained by means of the bubble deposition method (BDM). Surface wettability (i.e., surface energy) and film ripening (i.e., film thickness) are two major parameters in nanoparticle confinement and deposition. As the presence of surfactant could be detrimental to applications, a washing treatment is developed without CeVO(4) chemical changes or NW film modifications. Careful investigations of the film topography are carried out by atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) is used to check the chemical composition of the film at different stages. Finally, samples made by BDM are compared to those made by dip-coating method, demonstrating the higher efficiency of the BDM in providing large areas of well-organized and dense CeVO(4) monolayer.

4.
Chem Commun (Camb) ; 46(24): 4327-9, 2010 Jun 28.
Article in English | MEDLINE | ID: mdl-20461273

ABSTRACT

Isolated nanometric objects of the nickel-iron cyanide-bridged coordination network are obtained by a sequential growth on "molecular seeds" anchored on Si(100) surfaces. Control of the density and the size of the nano-objects is achieved by imposing a growth process without side nucleation.

5.
J Phys Chem A ; 114(22): 6394-400, 2010 Jun 10.
Article in English | MEDLINE | ID: mdl-20476779

ABSTRACT

Absorption spectrum of derived Dawson sandwich polyoxometalates (POM) [M(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](n-) with n = 16 for M = Zn(II), Ni(II), and n = 12 for M = Fe(III) have been extended in the visible range forming electrostatic complexes with a chromophore, the zinc tetracationic porphyrin [ZnTMePyP](4+). Formation of such complexes was followed by steady-state absorption and luminescence spectroscopies. The electrostatic complexation gives in all cases a strong, neutral, and nonluminescent complex. A charge transfer between the two units was shown by transient absorption spectroscopy. Upon a visible excitation of the porphyrin subunit, an electron transfer from the porphyrin to the POM occurs and imparts it a catalytic activity. This has been demonstrated studying a model reaction such as the reduction of silver cations leading to nanoparticles. In all cases, the reduction of the silver cations takes place. We showed that the catalytic activity depends of the nature of the metal of the tetraoxometallic central cluster of the Dawson sandwich POM.

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