Research

1. Production of N@C60

How can you convince a nitrogen atom to live inside a molecular "cage"?

We use ion implantation to fill C60 and C70 fullerenes with nitrogen atoms. First, a garden-variety fullerene mixture is sublimed from an effusion cell and deposited on a copper target. At the same time, low energy nitrogen ions are produced in a plasma source and guided to conincide with the fullerenes at the target. In this process, the nitrogen ions probably take up the missing electrons from the fullerene molecules they hit. The fullerenes in turn get their now missing electron back from the copper target which is electrically grounded for this reason. After several hours of this implantation process, the fullerenes are harvested, i.e. scratched off and dissolved in toluene. As a first purification step we now remove C70 and all higher fullerenes (C72, C74, etc.) from the mixture.

 

ion implantation setup
Fig. 1. Home-built ion implantation setup.
fast filtration
Fig. 2. Removing C70 and higher fullerenes

2. ESR spectra of N@C60

The material produced thus far can be analyzed with electron spin resonance (ESR). This advanced technique is sensitive to ratios of N@C60 : C60 as low as 1 in 10 million. We use an affordable benchtop ESR machine from Magnettech GmbH, Berlin, which is quite sufficient for sample characterization and spin counting.

 

ESR (Miniscope)
Fig. 3. X-band cw-ESR machine "Miniscope MS100".
ESR spectrum of N@C60
Fig. 4. ESR spectrum of N@C60 in solution at room temperature.

2. ESR spectra of N@C60

The material produced thus far can be analyzed with electron spin resonance (ESR). This advanced technique is sensitive to ratios of N@C60 : C60 as low as 1 in 10 million. We use an affordable benchtop ESR machine from Magnettech GmbH, Berlin, which is quite sufficient for sample characterization and spin counting.

analytical HPLC
Fig. 5. Analytical HPLC setup to control sample quality.
preparative HPLC
Fig. 6. Preparative HPLC to separate empty & filled C60.

4. Scanning probe microscopy: AFM and STM

On the road towards building up a quantum computer the arrangement of spins in a desired manner is essential. The right tool to do so on a surface is a scanning probe microscope, especially either a scanning tunneling microscope (STM) or an atomic force microscope (AFM).  We deposit the endohedral fullerenes on a surface like silicon and align them with nano-lithography.

 

AFM lithography
Fig. 7. The XE-100 from PSIA, AFM/STM at ambient conditions. Inset: A C60-like pattern of Silicon oxide, written with the lithography mode (image width = 2um x 2um).

 

STM chamber
Fig. 8. The VT-STM from Omicron, STM UHV chamber with cryostat and sample heater for measurements in a broad temperature range.

5. Chemical modification of N@C60

Once we have enriched the N@C60 content of our samples, we can functionalize them chemically by attaching side groups to the C60 cage. This influences both their ESR spectroscopic properties and their self-assembly behaviour.

fullerene malonate adducts
 

Fig. 9. Chemically modified of P@C60 molecules and their ESR spectra. Note that the linewidth generally increases due to anisotropy and interaction with the protons.

shuttlecock molecule
C60 shuttlecocks on HOPG

Fig. 10. Chemically modified C60 molecules ("suttlecocks") moving around on graphite (HOPG), at room temperature.

 

6. Bulk ESR quantum computing expriments

Coming soon...

7. Single-spin read-out techniques

Coming soon...