Many of our results are presented this year on the ICN+T 2012 conference in Paris (http://www.icnt2012.org/). I find the meeting very good, since it really focuses the surface science community in one place and can recommend it thus highly.

It is even more enjoyable, since Paris is such a lively city and the Sorbonne turns out to be an extraordinary meeting place.

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

electrospray ion beam deposition (ES-IBD) source (short version)

Our experiment consists of two parts: (1) the deposition source and (2) the tunneling microscope with the sample preparation.

Here I briefly introduce the deposition source, that we use to deposit nonvolatile molecules onto surfaces in ultrahigh vacuum (UHV). It is a differentially pumped apparatus consisting of six differential pumping stages starting at 0.1 mbar and reaching to 1e-11 mbar in the UHV deposition chamber.

Scheme of the ES-IBD setup

Fig. 1: Scheme of the ES-IBD setup

everything starts with the spray source (1) at ambient pressure. Sometimes we use curtain gas (2) to dry the droplets and help the electrospray desolvation. The ions enter the vacuum trough a capillay (3). In the first and second vacuum chamber they are bundeled by RF ion optics, one ion funnel (4) and one quadrupole (5). The next quadrupole (6) in in high vacuum, so no more collimation is possible, but we use it for mass selection. Further throughout the machine we use electrostatic lenses (7) to focus the beam through the apertures (8). We have a time-of-flight (TOF) mass spectrometer (9) to measure the chemical composition and then we can deposit: in high vacuum (10) for ex situ analysis, in a vacuum suitcase (11) to transfer the sample to another UHV instrument, and finally in UHV (12) to move the sample in our own STM.

More details in the future.



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