• PDF / 16,610,758 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 6 Downloads / 224 Views

DOWNLOAD

REPORT

---

Electrochemical Functionalization in Wavefunction Engineering of Epitaxial Graphene Santanu Sarkar Center for Nanoscale Science and Engineering, Department of Chemistry, University of California, Riverside, California, CA-92521, USA. Present address: Intel Corporation, Ronler Acres Campus, Hillsboro, Oregon, OR-97124, USA. E-mail: [email protected]; [email protected]

ABSTRACT Chemical modification of graphene web has attracted strong interest in engineering a band gap in graphene and in altering its magnetic and solubility properties. Electrochemical methods to functionalize graphene have emerged as attractive protocols to covalently modify graphene. Kolbe reaction, which involves the electrochemical oxidation of arylacetates (generation of α-naphthylmethyl radicals, in our present case), allows reversible grafting of radicals to graphene surface; the electro-erasing of the functional groups leads to graphene at its nearly pristine state. The surface coverage can be controlled from densely-packed (ideal as organic dielectrics) to sparsely functionalized surface (ideal for introducing reasonable band gap in graphene) with well-ordered structural patterning of the functional groups on EG surface by fine adjustment of electrochemical conditions. Such a control of the layer structure and packing of the functional groups over the graphene surface is an essential issue in the development of graphene chemistry. INTRODUCTION The next wave micro- and nanoelectronics technology is looking towards the newest carbon allotrope discovered in the third wave of carbon revolution, called graphene with its ultrahigh mobility of the electrons moving on its one-atom thick two-dimensional crystal to allow for next generation electronics and spintronics device applications.[1-3] Despite all the superior qualities the use of graphene as future devices is limited by the fact that graphene devices can not be turned off due to its zero-band-gap electronic structure.[4] Several approaches are adopted to engineer a band gap in graphene,[4-8] and electrochemical methods to functionalize graphene have emerge as very attractive methods to covalently modify graphene. Several electrochemical approaches to graphene modification are: (method 1) aryl radical addition to graphene: from diazonium precursors,[9] (method 2) electro-oxidation of graphene wafers,[10] and (method 3) Kolbe reaction: electro-oxidation of α-naphthylacetates on graphene and electro-erasing.[6] Application of nitrophenyl radical addition (diazonium chemistry – method - 1) has rendered graphene with room-temperature ferromagnetism[11] and a band-gap of 0.36 eV (measured by ARPES).[12] On the other hand, the electro-oxidation (EO) of epitaxial graphene (method - 2), although could not open a band-gap, shows a strong photoresponse in the electro-oxidized epitaxial graphene (EOEG).[13] Kolbe reaction (method - 3), which is the present case, leads to the generation of αnaphthylmethyl radicals (which are more stable than nitrophenyl radicals), allows reversible

grafting of rad