Benjamin Schumm

Precursor strategies for metallic nano- and micropatterns using soft lithography†

Soft lithographic methods describe a set of printing methods which are widely used for the preparation of structured surfaces. Structured surfaces are essential components in the field of (opto-)electronic devices such as organic light emitting diodes, photovoltaics or organic field effect transistors. In recent years, crucial progress has been achieved in the development of patterned metal coatings for these applications. This review focusses on new strategies for soft lithographical printing of metal structures emphasizing the subtle interplay of printing techniques, metal precursor chemistry, and surface functionalization strategies.

Nanoimprint patterning of thin cadmium stannate films using a polymeric precursor route

The synthesis of cadmium stannate (Cd2SnO4 CTO) nanoparticle powders and the deposition and patterning of thin Cd2SnO4 films were achieved via a polymeric precursor approach. Conditions for the phase formation of the cubic spinel phase were evaluated, and for the first time the system was obtained in single phase powder form from a precursor system. Thin Cd2SnO4 films were prepared by spin coating the polymeric precursor solution followed by thermal treatment. Highly transparent and 20 nm thick films with a minimum sheet resistance of 110 Ohm were prepared. A thermal imprint process with PDMS molds was used for patterning of the films in the sub-micrometre range. Nanostructured CTO films are essential to improve structured electrodes in opto-electronic devices such as CdTe-based thin film solar cells.

Semi-transparent silver electrodes for flexible electronic devices prepared by nanoimprint lithography

The preparation of mechanically flexible and optically transparent electronic circuits plays a key role in the development of next-generation display technologies. Silver nano-gratings are of particular interest due to their excellent conductivity and adjustable transmittance. Printed on polymeric substrates they are suitable for an application in flexible opto-electronic devices. Here, we present the preparation of a smart silver precursor system combining both the ability of cheap and scalable nanoimprint patterning and simple thermal silver reduction. Homogeneous silver line and grid patterns with line widths down to 400 nm are prepared using poly(dimethylsiloxane) stamps in a thermal nanoimprint lithography process. Relatively low process temperatures allow the film formation on polymeric substrates. Semi-transparent silver electrodes with a resistance of 2.8 ohm are patterned on polyimide foils to prepare flexible electro-luminescence devices. A detailed investigation of the precursors thermal decomposition behaviour as well as the resulting electrical and optical properties of the films is offered.

Preparation and microcontact printing of platinum and palladium thin films

Thin palladium and platinum films were prepared using a polymeric precursor method. For the first time, down to 30 nm thick films were achieved by this method. A precursor solution consisting of ethylene glycol, citric acid, a metal salt and the corresponding acid was deposited by spin coating onto various substrates. The thermal decomposition behavior of these precursors was characterized by thermal analysis methods. Dried and calcined films were characterized by XRD, UV-Vis and IR spectroscopy as well as resistance measurements to get more information about the film formation. The specific resistance of the phase pure platinum films was as low as 1.1 × 10−7 Ω m and that of the palladium films was as low as 6.0 × 10−7 Ω m. In addition, a platinum precursor was used for microcontact printing. Regular line patterns with widths between 800 nm and 15 μm were achieved, as could be shown by AFM and SEM.

Quality Control of Slot-Die Coated Aluminum Oxide Layers for Battery Applications Using Hyperspectral Imaging

Hyperspectral inspection using imaging systems is becoming more and more important for quality control tasks in several industries, replacing well trained operators or established machine vision systems based on RGB-systems. Hyperspectral imaging (HSI) on thin coated substrates is challenging due to the high reflectivity of the substrates. Nevertheless, the thin films contribute to the spectral data and can be evaluated. Therefore, the performance of inspection systems can be increased significantly. However, the large amount of data generated by HSI has to be processed and evaluated for quality information about the product. In this paper, thin aluminum oxide (Al2O3) layers on stainless steel foil are investigated by HSI. These substrates can be used for the growth of vertically aligned carbon nanotubes (VA-SWCNT) for battery electrodes. HSI and spectral ellipsometry in combination with Partial Least Squares regression (PLS) was used to estimate the thickness of the Al2O3 layers and to calculate quality parameters for a possible monitoring process. The PLS model shows a R2CV of 0.979 and a RMSECV of 3.6.