Nickel silicide is widely used to realize contact terminals of integrated circuits and is usually formed by ex-situ heating treatments. In-situ reactions during sputter depo- sition of a Ni layer onto a HF p-type [001] Si substrate have been investigated in this work, by means of trans- mission electron microscopy, X-ray diffraction and X-ray reflectivity analyses. A thin layer of polycrystalline sili- cide, with extremely flat interfaces and in fiber texture with the Si substrate, has been obtained by introducing a sputter etching step just before Ni deposition and prop- erly modulating its duration. The work has also been aimed to decouple the thermal impact of sputter etching from its effect on surface cleaning, disclosing its key role in the whole reaction process. Cross-sectional TEM analysis of a nickel silicide layer, formed by in-situ solid-state reaction, showing an ex- tremely flat interface with the Si substrate.

[object Object]

We explore a strategy to counteract aging issues in TiO2/aluminium-doped ZnO bi-layers used in hybrid solar cells photo-anodes, mainly related to Zn diffusion in the TiO2 matrix. Different Ti4+ and Zn2+ local structures within the anatase grains and along the film thickness were found as a function of post-deposition annealing treatments in the range between 200 degrees C and 500 degrees C by synchrotron radiation extended x-ray absorption fine structure analyses. In particular, in the 500 degrees C-treated sample, diffusion of zinc species along the TiO2 grain-boundaries has been observed with aging (3 years). In contrast, a mild thermal budget at 200 degrees C favours a proper atomic arrangement of the zinc-containing anatase lattice which reduces Zn diffusion, thus guaranteeing a good stability with aging. (C) 2014 AIP Publishing LLC.

We explored new strategies for efficiency enhancement in dye-sensitized solar cells (DSSCs) by combining dehydration condensation reactions with sputtering deposition methods. The photoanodes were realized by means of low-temperature preparation of mesoporous TiO2 films on thin undoped TiO2 compact (blocking) layers on ZnO:Al (AZO) substrates and sensitization with ruthenium dye, N719. For photoanodes fabrication, an 8 mu m thick mesoporous film of TiO2 and an under critical thermal budget, applied before dye loading (<= 200 degrees C: i.e., 150 degrees C for the TiO2 mesoscopic layer and 200 degrees C for the TiO2 blocking/AZO bilayer), were employed, which renders the overall process competitive for the applications. The structural properties of the sputtered TiO2/AZO bilayer were optimized, and a cell efficiency as high as the 4.6%, above the current literature limit for AZO-based DSSC (3.8% for 10 mu m thick mesoporous layers sintered at 450 degrees C and sensitized with N719), was achieved at T <= 200 degrees C. With the proposed scheme for the photoanode structure and using, instead, a conventional thermal treatment at 500 degrees C (30 s), the cell efficiencies were further raised up to 4.9%. It was thus evidenced that the use of optimized materials for the cell architecture makes the AZO-based DSSC nowadays rising devices.

TiO2/ZnO:Al (AZO) bilayers were grown by DC reactive sputtering at temperature below 200 degrees C. The AZO structure was tuned in such a way that (0002) and (11-20) preferentially oriented and fiber textured domains were formed. The TiO2 layers grown at 150 degrees C on those two kinds of substrates are partially crystalline (and not amorphous as expected) in a composition which is substrate-dependent. Anatase was selectively formed on (0002) oriented AZO substrates after deposition, and maintained for annealing temperatures up to 650 degrees C. A mixture of anatase and rutile has instead nucleated and grown on the (11-20) oriented AZO substrate, with their relative amount changing by increasing the annealing temperature. Anatase selectivity and also its nucleation at low temperature are promising issues to realise flexible dye sensitised solar cells. (C) 2013 Elsevier B.V. All rights reserved.

The role of chloride in the MAPbI(3_x)Cl(x) perovskite is still limitedly understood, albeit subjected of much debate. Here, we present a combined angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and first-principles DFT modeling to investigate the MAPbI(3-x)Cl(x)/TiO2 interface. AR-XPS analyses carried out on ad hoc designed bilayers of MAPbI(3-x)Cl(x) perovskite deposited onto a flat TiO2 substrate reveal that the chloride is preferentially located in close proximity to the perovskite/TiO2 interface. DFT calculations indicate the preferential location of chloride at the TiO2 interface compared to the bulk perovskite due to an increased chloride TiO2 surface affinity. Furthermore, our calculations clearly demonstrate an interfacial chloride-induced band bending, creating a directional 'electron funnel' that may improve the charge collection efficiency of the device and possibly affecting also recombination pathways. Our findings represent a step forward to the rationalization of the peculiar properties of mixed halide perovskite, allowing one to further address material and device design issues.

We implemented a low-temperature approach to fabricate efficient photoanodes for dye-sensitized solar cells, which combines three different nanoarchitectures, namely, a highly conductive and highly transparent AZO film, a thin TiO2-blocking layer, and a mesoporous TiO2 nanorod-based working electrode. All the components were processed at T 200 degrees C. Both the AZO and the TiO2 blocking layers were deposited by reactive sputtering, whereas the TiO2 nanorods were synthesized by surfactant-assisted wet-chemical routes and processed into photoelectrodes in which the native geometric features assured uniform mesoporous structure with effective nanocrystal interconnectivity suitable to maximize light harvesting and electron diffusion. Because of the optimized structure of the TiO2-blocking/AZO bilayer, and thanks to the good adhesion of the TiO2 nanorods over it, a significant enhancement of the charge recombination resistance was demonstrated, this laying on the basis of the outstanding power conversion efficiency achievable through the use of this photoanode's architecture: a value of 4.6% (N719) was achieved with a 4-mu m-thick electrode processed at T = 200 degrees C. This value noticeably overcomes the current literature limit got on AZO-based cells (N719), which instead use Nb-doped and thicker blocking layers, and thicker nanostructured photoanodes, which have been even sintered at higher temperatures (450-500 degrees C).

Rear contact terminals of integrated circuits have to satisfy electrical and mechanical requirements, such as low specific contact resistance, good adhesion to the substrate and good solderability with external elements. A new metallization scheme, made of sputtered Ni and Au layers, with the addition of a process step needed to ensure nickel silicide formation at low temperature, has been proposed for p-type silicon substrates and investigated in this work. Its electrical and structural properties have been compared with conventional Cr/Ni/Au and Ti/Ni/Au contacts, showing lower specific contact resistance values (rho(c)), an ohmic behaviour in the explored range of resistivity (i.e. 3 m Omega cm < rho < 18 m Omega cm) despite of the rectifying one of conventional materials, better adhesion with the substrate and limited consumption of nickel and silicon during the reaction process. The proposed metallization scheme provides an effective solution to meet both electrical and mechanical requirements with a single material, with a consequent reduction of logistic and economic effort to realize integrated circuits.

Thin nanoporous TiO2 layers, deposited by dc reactive sputtering, have been functionalized with a novel unsymmetrical Zn(II) phthalocyanine (ZnPc-II) bearing a push-pull system, properly designed for application in dye sensitized solar cells. The anchoring process has been studied by combining visible absorption (vis), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) in order to investigate the molecular assembly during the early stage of the sensitizing process. The vis and XPS measurements indicate that the ZnPc-II surface density (dsurf, molecules/cm2) and its binding geometry are strongly affected by the concentration of the grafting solutions. It has been observed that the ZnPc-II surface density monotonically increases by increasing the solution concentration up to a saturation of dsurf 1.0 × 1013 molecules/cm2. Angle resolved XPS analyses indicate that at low molecular surface density a strong interaction between the ZnPc-II aromatic macrocycle and the TiO2 surface occurs, suggesting a planar binding geometry. The increase of the molecular surface density is accompanied by a mitigation of the surface-molecule interaction that leads to a different ZnPc-II binding geometry. Conductive atomic force microscopy has demonstrated that the charge transport through the dye-TiO2 interface strongly depends on the binding arrangements which exhibit different threshold values in the local I-V characteristics.

TiO2 thin films were deposited at an effective surface temperature of 150 degrees C by dc-reactive magnetron sputtering on ZnO : Al oriented substrates having a fiber texture along the [0 0 0 1] axis, and studied by transmission electron microscopy and x-ray diffraction analyses. The substrate texturing was used to tailor the TiO2 structure in such a way that a porous matrix made of anatase nano-grains (10 nm in diameter) is formed instead of an amorphous layer (as observed at 150 degrees C on glass). Additionally, we demonstrate that, by adding an ex situ 200 degrees C annealing, the anatase domains also gain a fiber texture with the axes aligned to that of the substrate. The TiO2/AZO structural coupling is expected to play a crucial role for the carrier transport through the interface as required in dye-sensitized solar cells. Moreover, the low temperatures used render the process compatible with commonly used plastics substrates.

[object Object]

Self-nanostructured ZnO center dot Al conductive layers consisting of [11 (2) over bar0] oriented domains were coated by a conformal TiO(2) thin film and sensitized by 5, 10, 15, 20-tetrakis-(4-carboxyphenyl)porphyrin (TCPP) to be used as transparent conductive electrodes in dye-sensitized solar cells. In addition to the higher surface availability due to the nanopatterning, the TCPP surface density increases by 330% (UV-vis) with respect to a flat conventional substrate thanks to a more sense molecular arrangement, as evidenced by combining high-resolution X-ray photoelectron spectroscopy and atomic force microscopy. Furthermore, the presence of zinc atoms in the TiO(2) overlayer (Ti(:Zn)O(2)) crucially influences the electronic properties of the assembled TCPP. As a consequence of the orbitals rearrangement attributed to the presence of zinc, a significant quenching of luminescence is observed in the emission spectra of TCPP-sensitized Ti(:Zn)O(2,) suggesting that electrons could be more effectively injected from the molecular orbitals to the conduction band of the semiconductor.