Sequential growth in solution of NiFe Prussian blue coordination network nanolayers on Si(100) surfaces

Long-range electron transport in Prussian blue analog nanocrystals

We report electron transport measurements through nano-scale devices consisting of 1 to 3 Prussian blue analog (PBA) nanocrystals connected between two electrodes. We compare two types of cubic nanocrystals, CsCoIIIFeII (15 nm) and CsNiIICrIII (6 nm), deposited on highly oriented pyrolytic graphite and contacted by conducting-AFM. The measured currents show an exponential dependence with the length of the PBA nano-device (up to 45 nm), with low decay factors β, in the range 0.11-0.18 nm-1 and 0.25-0.34 nm-1 for the CsCoFe and the CsNiCr nanocrystals, respectively. From the theoretical analysis of the current-voltage curve for the nano-scale device made of a single nanoparticle, we deduce that the electron transport is mediated by the localized d bands at around 0.5 eV from the electrode Fermi energy in the two cases. By comparison with previously reported ab initio calculations, we tentatively identify the involved orbitals as the filled Fe(ii)-t2g d band (HOMO) for CsCoFe and the half-filled Ni(ii)-eg d band (SOMO) for CsNiCr. Conductance values measured for multi-nanoparticle nano-scale devices (2 and 3 nanocrystals between the electrodes) are consistent with a multi-step coherent tunneling in the off-resonance regime between adjacent PBAs, a simple model gives a strong coupling (around 0.1-0.25 eV) between the adjacent PBA nanocrystals, mediated by electrostatic interactions.

Tailoring the photoelectrochemistry of catalytic metal-insulator-semiconductor (MIS) photoanodes by a dissolution method

Apart from being key structures of modern microelectronics, metal-insulator-semiconductor (MIS) junctions are highly promising electrodes for artificial leaves, i.e. photoelectrochemical cells that can convert sunlight into energy-rich fuels. Here, we demonstrate that homogeneous Si/SiO_x/Ni MIS junctions, employed as photoanodes, can be functionalized with a redox-active species and simultaneously converted into high-photovoltage inhomogeneous MIS junctions by electrochemical dissolution. We also report on the considerable enhancement of performance towards urea oxidation, induced by this process. Finally, we demonstrate that both phenomena can be employed synergistically to design highly-efficient Si-based photoanodes. These findings open doors for the manufacturing of artificial leaves that can generate H₂ under solar illumination using contaminated water.

Designing synthetic systems to convert light into fuel is crucial in renewable energy development. Here, authors study electrodissolution in nickel thin films from metal-insulator-semiconductor junctions and find decreased homogeneity to improve junction properties and catalytic performances.

A facile conversion of a Ni/Fe coordination polymer to a robust electrocatalyst for the oxygen evolution reaction

A spinel NiFe₂O₄ dominated mixed oxide prepared from Ni hexacyanometallate (NiHCF) was found to be effective for the oxygen evolution reaction (OER) in alkaline solution.

Sequential growth at the sub-10 nm scale of cyanide bridged coordination networks on inorganic surfaces

The elaboration of coordination networks' nano-objects on surfaces can be realized by sequential growth in solution (SGS). This bottom-up strategy gives the possibility to control the size, the isolation and the organization of the objects with a precision going up to the molecular scale. Detailed descriptions of the growth of the nickel(II)-iron(II) Prussian blue analog and of the copper-molybdenum cyanide-bridged coordination network are reported to give insight about the mechanisms of the growth. Then a comparative XPS analysis has been performed to explain the different reactivity of the precursors of the growth of the nickel(II)-iron(II) and nickel(II)-chromium(III) Prussian blue analogs. This perspective article proves that SGS can be optimized for each coordination system to build molecular superstructures on surfaces, with interesting physical properties towards chemical devices.

Cyanide-bridged NiCr and alternate NiFe-NiCr magnetic ultrathin films on functionalized Si(100) surface

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.