• To exploit the abilities of high-quality research groups towards the development of new advanced functional applications based on the optimal modification of materials surfaces.
• To merge current bilateral research collaborations in order to create synergies for an optimised use of multidisciplinary expertise and complementary experimental facilities.
• To bring together researchers working on basic science with researchers working in applied fields. This interaction promotes the innovative optimisation of surface properties for improving advanced systems such as: gas sensors, electronic systems, solar cells, and electrochemical electrodes.
• To enhance cooperation activities between EU and Latin-American (LA) institutions, improving accessibility to different research facilities of network members and generating multidisciplinary research groups.
• To improve career perspectives of early-stage researchers (ESR) by providing them with a multinational, interdisciplinary and high-level research training in MSE.
• To establish long-term collaborations in order to confront current technological, energetic and environmental issues that can be solved with the help of surface science and engineering.
• To work towards a better ERA targeting different aspects such as increasing attractiveness of third country researchers and effective use of resources by networking.

The research activities in SUMA2 will be based on modern techniques for the deposition of layers and coatings, like e.g. magnetron sputtering; plasma assisted surface treatment such as ion nitriding; and laser structuring using direct writing or laser interference.
On one side, fundamental research will take place in order to understand the deposition and structuring itself and to explore the possibilities of new structures, materials microstructures and properties. On the other side, research towards implementing the combination of these techniques with new materials for very specific applications will be carried out. Within the broad field of functional surfaces, within SUMA2 we will concentrate on five topics, which are however interrelated through similar processing techniques as well as characterisation methods.

• Polymer Gas Sensors Modified by Carbon Nanotube Arrays

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The aim of this project is to develop polymer gas sensors with enhanced sensing properties through surface modification and incorporation of carbon nanotubes (CNT) using the Laser-Induced Forward Transfer (LIFT) technique. The LIFT technique can be used to fabricate 1D, 2D and 3D periodical structures at the micro- and nano scales. It also provides the possibility to transfer organic material in its original solid or liquid state. Thus, the increase of the surface-to-volume ratio and the incorporation of conductive arrays are expected to enhance the response of current polymeric sensors. The foreseen work comprises the development of gold and other metal nanoparticle synthesis via laser reduction, and nanocasting in mesoporous structures, the selection and synthesis of the proper polymer substrate, the dispersion of CNTs and coating of CNTs with Au nanoparticles, and the optimisation of the LIFT technique. Finally, the sensing properties will be characterised by measuring the electrical response while dosing gases under high vacuum conditions.

• Oxide films for transparent p-n junctions

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The deposition of p- and n-type layers on transparent substrates opens the way towards transparent microelectronics. The building block of most electronic conductor devices is the p-n junction. For the objective of synthesising transparent p-n junctions, it is necessary to develop a process for the deposition of p-type transparent conductors. The oxides that crystallise in a delafossite-like structure are the most promising p-type conductors. This structure is observed for materials with the following formula: ABO2 where A = Cu, Ag, Pd, Pt and B = Fe, Cr, Al, Y, Sc, La, In, Nd. We propose to build up and characterise transparent p-n junctions based on ZnO:Al and delafossite-like materials. This work includes the synthesis and characterisation of individual layers, the structural characterisation of bilayers deposited on a transparent substrate and the electrical characterisation of the junctions (I-V curves, capacitance-voltage curves). Moreover, the I-V curves and capacitance-voltage curves of junctions will be modelled in order to obtain key electrical (parasite resistances) and electronic parameters (built-in voltage, saturation currents, ideality factors) using analytical techniques.

• Improvement of solar cells efficiency by tailoring optical properties through patterning

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Photovoltaics materials selection should aim to reduce optical and electrical losses to optimize the device performance. However both approaches require normally a tradeoff and thus the organic material spectrum for photovoltaic applications becomes narrowed. To disentangle such compromise, optical design is critical, and light trapping strategies play a key role to maximize the solar light absorption. Surface structures, such as periodic gratings, surface patterns, or rough surfaces can enhance the power conversion efficiency of the solar cell by elongating the optical path of incident light inside the absorber material, or causing Bragg scattering at periodic photonic crystal geometries. Surface textures can be produced by many different technologies, traditionally using lithography with photoresist coating, exposure and transfer processes or printing, moulding and embossing methods. As an alternative, direct laser interference patterning (DLIP) technology offers a scalable process to structure polymer substrates by direct ablation of the substrate material. In addition, consistent theoretical models supported by finite element method simulations can provide useful guidelines towards optimal device design, concerning the geometric and materials parameters. Activities to be performed within SUMA2 are: surface structuring of transparent substrates such as indium-tin oxide (ITO) coated glass and flexible substrates such as polyethylene terephthalate (PET), optical characterisation of treated and untreated substrates (total and diffuse transmission), electromagnetic simulation of optical properties of patterned substrates, deposition of organic semiconductor layers based on small molecular materials such as copper phthalocyanine (CuPc), fullerene (C60), rubrene and platinum tetraphenylbenzoporphyrin (PtTPBP) on structured substrates and their electro-optical characterisation, preparation of organic solar cells and their electro-optical characterisation, and finally, finite element method simulation of solar cell performance.

• Advanced fabrication of electrochemical ultramicroelectrode arrays

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Electrochemical reactions on solid electrodes of soluble substances are controlled by electron transfer at the electrode/solution interface or by diffusion of the substance from the bulk solution. One important goal in the measurements of compounds in solution by electrochemical methods is trying to make the diffusional control of the soluble substances independent of time because it simplifies the analytical measurements. The mass transport in macroscopic planar electrodes is normal to the surface and time dependent. A method of increasing the diffusion involves the use of ultramicroelectrodes consisting of a repetitive one- or two-dimensional structure. Since these electrodes have at least one dimension of size comparable to the diffusion layer (1-100 µm), not only does the diffusion to the electrode occur in the direction normal to the surface, but also spherical or cylindrical diffusion is possible. Although the diffusion is stationary, the decreasing geometric dimensions imply a reduction of the active area. Since the current depends on the area, small currents are present in the microelectrodes and are therefore difficult to be detected above the electronic noise. One way to solve this problem is to combine several microelectrodes in an array, obtaining the sum of the currents of each microelectrode. We propose to generate ultramicroelectrodes by means of Direct Laser Interference Patterning (DLIP). A plane electrode surface (e.g. a gold thin film on glass) will be covered with a non-conductive polymer (e.g. polystyrene) by spin coating. The polymer layer will then be ablated using DLIP to generate micrometric circular holes where the underlying conductive electrode is exposed to the solution. The electrodes will be tested with model redox compounds (e.g. ferrocyanide) and also with other relevant analytical substances (e.g. hydrogen peroxide or dopamine).

• Design of plasma-assisted surface treatments to achieve wear resistance, and anticorrosive and functional properties

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This collaboration topic is subdivided in three parts. The first one concerns the implementation of the duplex processes (diffusion and coating) on ferritic steels. The second one will be focused on surface functionalisation of austenitic stainless steel. Finally, patterning with laser can help tayloring friction coefficients. In the duplex processes, coatings will be combined with a previous diffusion treatment such as nitriding or carbonitriding. The objective is to reach the best performance in different industrial situations where corrosion and wear degradation mechanisms are present. The performance of this duplex process will be compared with the diffusion process and the coating acting alone and independently. The surface will be further modified by chemical (silane reaction) and electrochemical (diazonium reduction) surface reactions. The silane reaction is enhanced by the plasma treatment and allows the incorporation of different functional groupes by reduction of diazonium salt. The silane reaction is a simple method that involves the inmersion of the surface in a silane solution. In the “surface functionalisation of austenitic stainless steel” part of this project, the expanded austenite phase will be studied in order to optimise potential surface functionalisation of austenitic stainless steel. Some fundamental aspects like the position of nitrogen atoms in the ferromagnetic and paramagnetic phases will be studied by combining in situ X-ray diffraction during heat treatements, Mössbauer spectroscopy and neutron diffraction. The potential industrial application will be explored for surface texturation as a means to reduce the friction coefficient by performing PATD with removable or fixed masks and by combining PADT and DLIP. The corrosion behaviour of such functionalised surfaces will also be tested in this program. A further posibility for tayloring friction and/or decreasing wear behaviour in tribological contacts is the deposition of thin films with optional succesive patterning via laser interference (DLIP). For high-temperature applications (>800° C) such as metal-cutting tools, arc-evaporated metalnitride, carbide, oxide, and boride alloy coatings are the prime candidates. Examples include Ti-Al-N, Ti-Si-C-N, Al-O and B-N alloys. Common for these systems is that metastable states can be achieved with improved performance if grown under the correct conditions. A key point to understand is the evaporation process and generation of the highly ionized plasma in arc evaporation, which we intend to adress. This has become an outstanding question as the target materials have evolved from single-element targets to multicomponent targets with numerous phases and different workfunctions for evaporation. Intermetallic material systems such as Ni-Al, Ti-Al and Ni-Ti deposited on single-crystalline Si, amorphous Si3N4 and fused silica are of interest for laser patterning and show promising results. However, the microstructure evolution and phase formation behaviour after ns-pulse laser irradiation remains to be understood. The present proposal will study inter-reactions between the constituent layers due to laser interference irradiation with focus on studying reactions yielding crystalline or amorphous products and uncovering mechanisms which influence this transition (e.g. bilayer period, substrates and influence of oxygen and nitrogen). Besides the mentioned materials systems Ti-Al-N will also be studied.