Fig. 1: Manganese-12-Acetate single molecule and dimer on a Au(111) surface
Fig. 2: Half monolayer coverage of Manganese-12-Acetate on Au(111)
Fig. 3: Inelastic tunneling spectrum of a Mn12 molecule.
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