Fabrication of ultra-sharp tips from carbon fiber for scanning tunneling microscopy investigations of epitaxial graphene on 6H-SiC(0001) surface

• Published in: Carbon (New York) Vol. 86; pp. 363 - 370
• Main Authors: Morán Meza, J.A., Lubin, C., Thoyer, F., Villegas Rosales, K.A., Gutarra Espinoza, A.A., Martin, F., Cousty, J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2015; Elsevier
• Subjects: Carbon fibers; Condensed Matter; Dynamics; Electronic devices; Epitaxy; Etching; Graphene; Materials Science; Physics; Scanning tunneling microscopy; Tips; AFM; carbon fiber; STM; Fowler-Nordheim plot; graphene
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2015.01.050

The fabrication of ultra-sharp tips from carbon fiber (CF), which are mounted on a qPlus probe for combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM) experiments, is reported. The carbon fiber tips were electrochemically etched in a KOH or NaOH solution, using different electronic devices. CF tips with an apex radius ∼10nm, as deduced from the measured slopes of the Fowler–Nordheim plots (kR<70nm for k∼6), were routinely obtained with a homemade electronic device that controls the intensity of the etching current. Then, these conductive CF tips were also characterized by imaging the 6H-SiC(0001) surface covered by an epitaxial graphene layer in ultra-high vacuum (UHV). The lattice of the (63×63) R30° reconstruction was regularly imaged by STM working either in non-oscillating mode or in dynamic mode, which also maps the variations of the force gradient. From these measurements with a constant mean-tunneling-current of 20pA, it was found that the STM tip suffered variations of the tip/surface force gradient in between 8.25 and 16.50N/m when it scanned the epitaxial graphene layer on the reconstructed 6H-SiC(0001) surface.