Morphological and micro-structural interface characterization in multilayer inverted polymer-fullerene bulk heterojunction solar cells

Inverted polymer solar cells based on P3HT/PCBM bulk heterojunction were prepared on flexible polyethylene naphthalate (PEN) substrate. The effect of annealing of the PEN/ITO/ZnO multilayer and ZnO/P3HT:PCBM on the structural, morphological, photophysical and photovoltaic properties was investigated and scrutinized directly on the OPV devices using atom probe tomography (APT), scanning electron microscopy (SEM) and microfocus X-ray techniques. We carried out a 3D reconstruction of the interfaces of the multilayer containing PEN/ITO, ZnO/ITO and P3HT:PCBM/ZnO to address the interface micro-structure and its influence on the morphology of the photoactive film. The analyses show that the morphology of the interfaces is affected by the structure of each layer of the BHJ devices causing orientation of P3HT crystals with PCBM aggregates and ZnO, which in turn leads to a significant change of the charge transport across each layer and therefore photovoltaic performances

The early stage of formation of self-organized nanocolumns in thin films: Monte Carlo simulations versus atomic-scale observations in Ge-Mn

International audienceFormation kinetics of self-organized nanocolumns during epitaxial growth of a thin film composed of immiscible elements (A,B) has been investigated using Kinetic Monte Carlo simulations. Simulated nanostructures show a good agreement with those observed in Ge-Mn using Atom Probe Tomography and Transmission Electron Microscopy. Self organisation is observed although the rigid lattice simulations used do not account for misfit elastic strain. Simulations reveal that the final nanostructure, in term of number density and diameter of nanocolumns, is controlled by the early stages of growth of the film. The influence of both growth temperature and solute concentration on the nanostructure features is discussed in details. V C 2014 AIP Publishing LLC

Si nanoparticles in SiO 2 An atomic scale observation for optimization of optical devices

International audiencePACS 61.46.-w-Structure of nanoscale materials PACS 68.37.-d-Microscopy of surfaces, interfaces, and thin films PACS 81.15.Cd-Deposition by sputtering Abstract-Three-dimensional imaging of silicon nanoclusters array in silicon-rich silicon oxide layers was evidenced and studied. The atom probe tomography technique allows to give the composition of the nanoclusters and the composition of the interface with the silica matrix. These results give new insights for the understanding of the properties of Si-based photonic devices. Introduction.-The development and optimization of Si-based photonic or memory devices [1-5], compatible with silicon integration technology, need to understand the precipitation of Si and the characteristic of Si nanoclusters (Si-nc) and the local chemical composition in Si/SiO 2 system. These Si-nc are deeply studied as sensitizer of erbium ions for silicon-based planar optical amplifier applications at 1.54 µm which is the wavelength used as standard in optical telecommunication [6-9]. A way to synthesize these nanoparticles consists in annealing at high temperature silicon-enriched silicon oxide (SRSO) leading to phase separation between Si and SiO 2. The understanding, modelling and prediction of the optical properties of these materials require an accurate determination of the nanostructure of the system such as the phase composition, the nanoclusters size distribution and number density as well as roughness, thickness and composition of the Si/SiO 2 interface. The Si-nc/SiO 2 interface has been suspected to governs, to a large extent, the optical properties of Si-nc. The presence of a thin ∼1 nm substoichiometric silicon oxide interface has been reported as playing a critical role in the emission properties [10,11]. In addition, it has been demonstrated that very small Si-nc, even amorphous, still have an efficient sensitiz-ing effect towards Er ions [9,12] and the relating energy transfer is highly dependent on the Si-nc-Er separating distance [13,14]. For these reasons, numerous studies focu

The early stage of formation of self-organized nanocolumns in thin films: Monte Carlo simulations versus atomic-scale observations in Ge-Mn

International audienceFormation kinetics of self-organized nanocolumns during epitaxial growth of a thin film composed of immiscible elements (A,B) has been investigated using Kinetic Monte Carlo simulations. Simulated nanostructures show a good agreement with those observed in Ge-Mn using Atom Probe Tomography and Transmission Electron Microscopy. Self organisation is observed although the rigid lattice simulations used do not account for misfit elastic strain. Simulations reveal that the final nanostructure, in term of number density and diameter of nanocolumns, is controlled by the early stages of growth of the film. The influence of both growth temperature and solute concentration on the nanostructure features is discussed in details. V C 2014 AIP Publishing LLC

Investigation at the atomic scale of the Co spatial distribution in Zn(Co)O magnetic semiconductor oxide

International audienceA sputtered Zn 0.95 Co 0.05 O layer was chemically analyzed at the atomic scale in order to provide an accurate image of the distribution of Co atoms in the ZnO matrix. The investigation of the magnetic properties shows that the as-deposited Zn 0.95 Co 0.05 O is ferromagnetic at room temperature. Atom probe tomography reveals a homogeneous distribution of all chemical species in the layer and the absence of any Co clustering. This result proves that the ferromagnetic properties of this magnetic semiconductor cannot be attributed to a secondary phase or to metallic Co precipitates within the layer

Study of the effect of gas pressure and catalyst droplets number density on silicon nanowires growth, tapering, and gold coverage

We investigated the growth of silicon nanowires from Au-rich catalyst droplets by two different methods: chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). The growth rate is found to be diameter-dependent and increases with increasing precursor partial pressures. The comparison of the experimental results with models shows that the contribution of Si atoms that diffuses from the substrate and the NW sidewalls toward the catalyst droplet can be neglected in CVD for the different pressures used in this study, whereas it is the major source of Si supply for the MBE growth. In addition, by decreasing the number density of catalyst droplet prior to the NW growth in CVD, it is also found that this parameter affects the NWs morphology, increasing the tapering effect when the silane partial pressure is small enough to allow gold atom diffusion from the catalyst drople