New Paper: Highly Reactive Molecule Deposition

Electrospray ionization is know to be a soft ionization method and it even works well for highly reactive molecules like oligoyns, polymers containing several triple C-C bonds. In this recent paper we demonstrate that our ion beam deposition is just as gentle and we can build structures from these reactive molecules.

oligoyne

[20]
Soft-landing electrospray ion beam deposition of sensitive oligoynes on surfaces in vacuum.
G. Rinke, S. Rauschenbach, S. Schrettl, T. N. Hoheisel, J. Blohm, R. Gutzler, F. Rosei, H. Frauenrath and K. Kern

NEW PAPER: 100% transmission nano-electrospray ion source

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.

funnel forces

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.

 funnel figure

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

Analyst, 2014,139, 1856-1867

New Paper on Photocurrent Microscopy

I supported the work of my colleague Ulrich Stuetzel for a while now and a nice paper came out of his thesis. He really prepared very good graphene nanoribbons. Even after ambient processing in acid (and what not) we were able to image the graphite ridges with atomic resolution on top. Never published that, but below is how the photocurrent images look like in the paper. Nice work of Ulrich.

image of FIG. 3.

see in peer reviewed publications

[15]
Spatially resolved photocurrents in graphene nanoribbon devices
Eberhard Ulrich Stützel, Thomas Dufaux, Adarsh Sagar, Stephan Rauschenbach, Kannan Balasubramanian, Marko Burghard and Klaus Kern
Applied Physics Letters 102 (2013) 043106

MBE and Proteins

Two new works out this week. Both key works for our lab. In the first we show that the deposition of charged particle beams can in fact be equivalent to conventional molecular beam epitaxy.

see entry [13] on the publications page:
Crystalline Inverted Membrane Growth by Electrospray Ion Beam Deposition in Vacuum.
S. Rauschenbach, R. T. Weitz, N. Malinowski, N. Thontasen, Z. Deng, G. Rinke, G. Costantini, T. Lutz, P. Martins de Almeida Rollo, L. Harnau, K. Kern
Adv. Mater. 24 (2012), pg. 2761-2767

inverted membrane deposition

 

The second one is even nicer: We deposited proteins a while a ago and found so many things you can do with them in vacuum: deposit them folded and unfolded and refold them and in the end look at the single amino acid. Now we only need to find a way to know which amino acid you see.

see [14] on the publications page:
A Close Look at Proteins: Submolecular Resolution of Two- and Three-Dimensionally Folded Cytochrome c at Surfaces
Zhitao Deng, Nicha Thontasen, Nikola Malinowski, Gordon Rinke, Ludger Harnau, Stephan Rauschenbach, Klaus Kern
Nano Lett. 12 (2012) 2452–2458

Proteins on surfaces in UHV

single molecular magnets probed individually

Electrospray ion beam deposition is also known under term soft landing. The softness of this approach was actually crucial in our work with molecular magnets:

S. Kahle, Z. Deng, N. Malinowski, C. Tonnoir, A. Forment-Aliaga, N. Thontasen, G. Rinke, D. Le, V. Turkowski, T. S. Rahman, S. Rauschenbach, M. Ternes, and K. Kern, “The Quantum Magnetism of Individual Manganese-12-Acetate Molecular Magnets Anchored at Surfaces.” Nano Lett. 12, 518-521 (2012), http://dx.doi.org/10.1021/nl204141z

The project was really tough: the molecule is fragile, only charged negatively, so we build a new TOF. Then we needed a UHV suitcase, we had a really crazy malfunction in the beginning. It took us several attempts to get the sample to the 1K STM. And then we saw much less features then we thought we would. Today we know that it has to be like this…

… and, there are two great things about this work:

First great thing: it worked! That was not straight forward. Manganese-12-Acetate is a notoriously unstable molecule. Even gold reacts with it, reducing the acetate ligands, which eventually causes the loss of the magnetic properties. With ES-IBD we could softly bring it to a surface and identify the individual molecules. You see the individual molecule in the first STM image (Fig. 1). Also films could be prepared nicely (Fig. 2).

Second great thing: A single Manganese12 moelcule is really a magnet. The guys at the 1K STM could actually find the signature of a high spin single entity. In the next image (Fig. 3) you see a typical tunneling spectrum. The two features – four, since its symmetric – correspond to a spin flip from S=10 to S=9 and an excitation of the spin angular momentum.

One more nice thing. The project was very ambitious and needed a lot of real experts, who in this case happen to be real nice people too and it was a real pleasure to work with them. Starting with synthetic chemists who can make such a molecule, we were able to deposit it intactly, our 1K STM guys could measure the spectra at such low energy and finally we got theory support from Florida.

… in the end this one was even featured by Nature Materials.

Abstract: The high intrinsic spin and long spin relaxation time of manganese-12-acetate (Mn12) makes it an archetypical single molecular magnet. While these characteristics have been measured on bulk samples, questions remain whether the magnetic properties replicate themselves in surface supported isolated molecules, a prerequisite for any application. Here we demonstrate that electrospray ion beam deposition facilitates grafting of intact Mn12 molecules on metal as well as ultrathin insulating surfaces enabling submolecular resolution imaging by scanning tunneling microscopy. Using scanning tunneling spectroscopy we detect spin excitations from the magnetic ground state of the molecule at an ultrathin boron nitride decoupling layer. Our results are supported by density functional theory based calculations and establish that individual Mn12 molecules retain their intrinsic spin on a well chosen solid support.

Keywords: Electrospray mass spectrometry; ion beam deposition; molecular magnetism; scanning tunneling microscopy; inelastic tunneling spectroscopy