The elastic properties of thin oxide coatings on glass have been assessed by a combination of careful nanoindentation testing and modelling. The contact modulus depends on the structure of the coatings which in turn depend on the underlying layer structure in a multilayer coating. The properties of the substrate need to be understood if the properties of the coating are to be determined accurately; in this study the air side of float glass shows a surface layer which is stiffer than the bulk and influences nanoindentation measurements. When thin oxide coatings on glass are tested the ISO14577 extrapolation method will underestimate the contact modulus of glass and a coating thickness of 400 nm or greater is needed to get reliable data using this method. A simple model for contact modulus as a function of contact depth has been extended to analyse multilayer coatings and an optimisation approach used to establish reasonable elastic property values for the coatings in a multilayer stack.
AcknowledgementsThe author would like to thank Eva Gutierrez-Berasetegui and Jinju Chen for the provision of experimental data and useful discussions. John Ridealgh and Paul Warren of Pilkington plc are also thanked for provision of samples and funding part of the work.
Co-sputtering; TiO2–W; TiO2–Nb; Sputter-yield enhancement; Resistivity
The serial co-sputtering technique, which was originally introduced by Belkind and Carlsson  ;  is a promising extension to conventional magnetron sputtering. It combines the possibility to prepare coatings with adjustable doping concentration; furthermore it neuron specific enolase
allows increasing the effective deposition rate via the so-called sputtering yield amplification effect (SYA) . The technology has the following advantages over conventional sputtering:•The secondary cathode can be equipped with virtually any kind of material, thereby increasing the freedom in material combination to an extent so far unavailable to sputter processes.•By adjusting the power ratio between primary and secondary source, the doping concentration can be freely varied without the need to acquire a large variety of target materials.•The secondary material component is applied onto the primary target by a well-defined sputtering process in metallic mode, which is separated from the inert and reactive gas pressure in the main chamber.
However the initial implementations of serial co-sputtering lacked an effective gas separation between primary and auxiliary process volumes. Thus, the reactive gas from a reactive primary sputter process always limits the performance and long-term stability of the auxiliary cathode.
To overcome this problem, an improved concept based on serial co-sputtering; the so-called » Megatron « source has been recently introduced . To ensure a good reactive gas separation and stable operation of the magnetron discharge, the cylindrical primary cathodes are surrounded by cylindrical gas shields. To prevent reactive gas from passing through the gas shield, inert gas is directly put into the gas shield thereby providing a strong reverse flow for the reactive gas. Such gas curtain concepts are already known for other types of in-line coaters , however it is not straightforward that this concept also works properly in the low pressure regime, which is typical for sputtering processes. Therefore DSMC- and PIC-MC simulations of the source design have been carried out prior to prototype manufacturing to ensure a proper gas separation in a quantitative way . This optimized source allows maintaining a pure Ar atmosphere
at the auxiliary target independent from the reactive process conditions at the primary target.
2. Experimental section
A sketch of the setup of this new process technique can be seen in Fig. 1. For the different applications, TiO2:W and TiO2:Nb, different configurations were used. In case of the SYA of TiO2:W we used a single secondary tungsten target and two rotatable targets with substoi