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Device Fabrication

To gain the highest degree of control possible about the material and the device performance, we synthesize and functionalize the carbon nanotubes (CNTs) by ourselves and also do the sophisticated fabrication of nano-electronic devices within our group.

CNT synthesis and chemical functionalization

CNTs are grown by chemical vapor deposition (CVD) using methane as carbon precursor and Fe/Mo based catalyst. The growth temperature is used to tune the number of walls of the resulting CNTs. Single-walled CNTs grow at 860°C, while at 940°C most of the CNTs yielded are double-walled.

Compare: C. Spudat, C. Meyer, K. Goss, C. M. Schneider, Phys. Status Solidi B 246, 2494 (2009).

CNTs are functionalized from inside as well as from outside. In both cases, the CNTs are first oxidized in air. The defects created open the tube so that molecules that are sufficiently small can enter. Raman spectra prove the low defect density in our pristine CNTs (no D-mode visible) as well as the creation of defects due to oxidation.

Compare:C. Meyer et al., Phys. Status Solidi B 249, 2412 (2012).

We use supercritical CO₂ for filling, a method developed by A. Khlobystov that produces very clean peopods without solvent residue inside or outside the CNTs.

The alcoholic and carboxylic groups that are present on the CNTs after oxidation are also used for further covalent chemical functionalization based on ligand exchange under mild conditions. We used this method to attach magnetic {Mn₄}-complexes to the CNTs in a way that electronic transport is still possible.

Compare: R. Frielinghaus et al., RSC Adv. 5, 84119 (2015).

Device fabrication

Our devices are based on a field effect transistor structure with source, drain, and gate electrodes. Fabrication is done using electron-beam lithography and lift-off. The gate is either designed as a side gate. This is especially the case when we fabricate devices on Si₃N₄ membranes so that the devices can be investigated in TEM. If fabrication is done on Si wafers with Si0₂ as insulator, we use highly doped Si as back-gate.