For electrospray ion beam deposition a large amount of molecules is needed to get a reasonable coverage onto the surface. For instance: 1000 ions would make a nice peak in a mass spectrum. The same 1000 molecular ions would barely be found as adsorbates on a surface by scanning probe microscopy.
The biggest losses in an ES-IBD system occur at the vacuum interface. At this place ions are generated from charged droplets. They move, influences by external electric fields, space charge fields, diffusion and hydrodynamic drag. We constructed our own interface with the idea in mind to leverage the hydrodynamic drag: indeed this is the only force that points towards the axis of the capillary.
We were quite surprised to find that with our specially shaped capillary interfaces we achieve magnificent performance of up to 100% transmission for up to 40 nA. With this magnitude of ion current we reach up to 6nA in high vacuum deposition and hence can make a monolayer coverage of a 5 mm diameter sample in approximately 10 minutes. This makes IBD comparable with thermal evaporation and opens the way for commercial applications, if the full intensity of electrosprays, which can be up to mikroamps, can be used.
In our paper in ‘Analyst’ we show the measured transmission characteristics, deposition performance and purity and simulations, which rationalize how our capillary is working.
A hydrodynamically optimized nano-electrospray ionization source and vacuum interface
M Pauly, M Sroka, J Reiss, G Rinke, A Albarghash, R Vogelgesang, H Hahne, B Kuster, J Sesterhenn, K Kern, S Rauschenbach