The lab that sucks the most…..

Ultra high vacuum science. Sticking samples in chambers which hold one trillionth of the number of atoms per unit volume than the lab you’re standing in. You already know it’s gonna have to do something cool. But what, exactly?


Since commencing Honours year in 2010, I’ve had the privilege of working in the MIES lab here at Flinders. The rig – which holds a vacuum of 10-11mbar in the main chamber – is capable of in situ deposition techniques as well as analysis techniques. The rig uses X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), neutral impact collision ion scattering spectroscopy (NICISS) and metastable induced electron spectroscopy (MIES) to investigate samples, and is capable of investigating both solid and liquid films. Details of the techniques themselves can be found elsewhere [1,2, 3] so won’t be included in this blog, but an example of some results will be. Some of the current work in the lab includes monolayer formation of organic molecules on metal oxides, ionic liquids, the diffusion of salts through organic layers, functionalization of graphene and nanotubes, gold cluster formation, and the impact of doping on semiconducting materials. Several of the projects using the MIES lab are working towards ‘green’ energy solutions such as solar cells.

A study published in Physical Chemistry Chemical Physics [2] investigates the active layer of an organic photovoltaic device and shows some of the unique capabilities of the MIES apparatus. The rig is able to obtain information pertaining to the elemental depth profile (NICISS) as well as valence band structure of the outermost layer (MIES) and near surface area (UPS). In some instances the valence band structure can be used to determine the composition of the outermost layer and near surface area. For applications such as solar cells, this vertical distribution of components and the outermost layer composition plays a critical role in charge transfer.

A typical active layer for an organic photovoltaic cell is a 50:50 blend film of Poly(3-hexylthiophene-2,5-diyl) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM) which is spin coated onto the high workfunction electrode of the cell. For this investigation films were replicated on silicon wafers.  It was found via MIES that the outermost layer was comprised predominantly of P3HT, and the film had a non- uniform distribution showing a near surface area rich in PCBM and a gradient throughout the measured depth (NICISS and UPS). This PCBM rich phase would assist in charge transfer at the low workfunction electrode interface but the gradient (as opposed to a uniform blend) would most likely hinder it.

[1] Andersson G., Morgner H., Surface Science 405 (1998) 138-151

[2] Schmerl N., Andersson G., Phys. Chem. Chem. Phys  13 (2011) 14993-15002

[3] Seo H.,, Surf. Interface Anal. 46 (2014) 544-549


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