In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. Unless otherwise noted, all seminars are held on Wednesdays in the Molecular Science and Engineering Building ("M" Building) in G011 (Cherry Logan Emerson Lecture Theater) at 4 p.m. Refreshments are served at 3:30 p.m. in the Emerson-Lewis Reception Salon.

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"Nanomaterial Heterostructures for Electronic and Energy Technologies"

Mark C. Hersam, Professor, Department of Materials Science and Engineering, Northwestern University

Abstract:
Improvements in nanomaterial purity have yielded corresponding enhancements in the performance of electronic, optoelectronic, sensing, and energy technologies. However, as purities approach 100%, other strategies are required to achieve further improvements in device performance.

Toward this end, our laboratory has focused on the integration of disparate nanomaterials into heterostructures with well-defined interfaces. For example, organic self-assembled monolayers on graphene act as effective seeding layers for atomic layer deposited (ALD) dielectrics, resulting in metal-oxide-graphene capacitors with wafer-scale reliability and uniformity comparable to ALD dielectrics on silicon.

Similarly, the traditional trade-off between on/off ratio and mobility in semiconducting carbon nanotube (CNT) thin-film transistors (TFTs) is overcome by replacing conventional inorganic gate dielectrics with hybrid organic-inorganic self-assembled nanodielectrics, yielding on/off ratios approaching 106 while concurrently achieving mobilities of ~150 cm2/V-s. By utilizing unconventional gate electrode materials (e.g., Ni), the threshold voltage of semiconducting CNT TFTs can be further tuned, thus enabling the realization of CNT CMOS logic gates with sub-nanowatt static power dissipation and full rail-to-rail voltage swing.

Finally, p-type semiconducting CNT thin films are integrated with n-type single-layer MoS2 to form p-n heterojunction diodes. The atomically thin nature of single-layer MoS2 implies that an applied gate bias can electrostatically modulate both sides of the p-n heterojunction concurrently, thereby providing 5 orders of magnitude gate-tunability over the diode rectification ratio in addition to unprecedented anti-ambipolar behavior when operated as a three-terminal device.

Overall, this work establishes that nanomaterial applications can be substantially enhanced and diversified into new areas through precise integration into heterostructure devices.