Developing a Versatile Platform for Nanoscale Materials Characterization Julia Bobak, Daniel Collins, Fatemeh Soltani, David W. Steuerman Department of Chemistry, University of Victoria, 2010 Device Fabrication Lithography Electrical Characterization PMMA Glass spin coating 100nm Cr Glass exposure Glass developing PMMA Glass etching PMMA Glass washing PMMA Glass E-Beam AZ5214 Si spin coatingexposure developing etchingdeposition Mask 300nm SiO 2 Si UV Si AZ5214 Si AZ5214 Si 50nm Au 20nm Ti AZ5214 Optical E-Beam and Optical Lithography Optical Feature size limited by the wavelength of UV light – used for microscale structures High throughput – all features are defined in parallel Requires an optical mask to generate the pattern Relatively inexpensive and rapid E-Beam Feature size primarily dependent on the size of the beam of electrons – nanoscale structures (~50 nm) Low throughput – each spot on a feature is exposed to the beam one-at-a-time in series Pattern written directly using the beam of electrons Can be extremely expensive References: 1.Geim, A.K. and Novoselov, K.S. Nat. Mater. 2007, 6, Geim, A.K. and Kim, P. Sci. Am. 2008, 298, Novoselov, K.S. Science, 2004, 306, Ferrari, A.C. et al. PRL, 2006, 97, Transport measurements are conducted by applying a voltage (V) through the “Source” electrode and measuring the resultant current (I) through the “Drain” electrode. If a plot of current versus voltage (termed an I-V curve) is linear then the material obeys Ohm’s Law: where R is the resistance of the material. A field effect transistor (FET) relies on an applied field to alter the conductivity of (to dope) a semi- conductor, in this case graphene. This is achieved by applying a second voltage (the gate voltage) to the backside of the substrate. Source Drain A V (100) Si-Boron doped P ohm-cm 300 nm thermal SiO 2 Gate V Graphene V = IR Acknowledgments: Jon Rudge, Uvic Nanofabrication Adam Schuetze, Uvic Advanced Microscopy Facility NSERC Canadian Foundation for Innovation BC Knowledge Development Fund graphene FWHM: 40.8 cm -1 Peak: cm -1 FWHM: 72.1 cm -1 Peak: cm -1 FWHM: 50.4 cm -1 Peak: cm -1 Graphene is a single layer of sp 2 -hybridized carbon atoms packed into a honeycomb crystal lattice. It exhibits high crystal and electronic quality making it an exciting new material for future electronics. In its pure form, it conducts electrons faster at room temperature than any other known substance. As a result, research is currently being conducted towards the use of graphene in a variety of applications such as super- tough composites, smart displays, ultra-fast transistors and quantum-dot computers. In order to further characterize the electronic properties of this novel material, a reliable platform for the fabrication of graphene devices is crucial. Conclusions An optical mask was designed using Raith software, written by electron beam lithography and etched out of a chromium-coated glass substrate. The mask was then used for optical lithography in order to generate the desired pattern in gold on a thermally oxidized silicon substrate. Graphene was deposited on the pre-patterned substrate by micro-mechanical cleavage. Raman spectroscopy was used to identify the most promising single layer graphene candidates. Single layer graphene is identifiable by (a) a small full width at half maximum (FWHM), (b) a single Lorentzian curve fit and (c) the peak centre being shifted to lower frequency (~2650 cm -1 using a 633nm excitation source). Electron beam lithography was used a second time to write small wires connecting the graphene samples to the contact pads. Characterization was then carried out using scanning electron microscopy (SEM) and transport measurements. Introduction 10 μm 7.5 mm Bilayer Graphene Graphite I-V Curve of Graphene Device Monolayer Graphene We have concluded that our alignment and wiring protocol is capable of patterning 500nm-sized features with 500nm alignment accuracy. Furthermore, this methodology has been successfully employed in the fabrication of high-quality graphene devices. Future work will focus on graphene FET measurements and the interactions of graphene and molecules. Long term goals include tuning the electronic properties of graphene with molecules to optimize more complex devices such as photovoltaics or light-emitting diodes. Resistance = 107.9kΩ