Recent Publications

Elton J Santos

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  1. Title: Graphene/MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics

    Author(s): Yu L., Lee Y., Ling X., Santos E.J.G., Shin Y.C., Lin Yuxuan, Dubey M., Kaxiras E, Kong J., Wang H., Palacios T.

    Nano Letters, 14, No. 6, pp. 3055-3063 (8 May 2014)

    doi: 10.1021/nl404795z

    Two-dimensional (2D) materials have generated great interest in the past few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2), and insulating boron nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. In this paper, we demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition. We have fabricated high-performance devices and circuits based on this heterostructure, where MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects. We provide a systematic comparison of the graphene/MoS2 heterojunction contact to more traditional MoS2-metal junctions, as well as a theoretical investigation, using density functional theory, of the origin of the Schottky barrier height. The tunability of the graphene work function with electrostatic doping significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics.

  2. Title: Epitaxial Growth of Molecular Crystals on van der Waals Substrates for High-Performance Organic Electronics

    Author(s): Lee C.H., Schiros T., Santos E.J.G., Kim B., Yager K.G., Kang S.J., Lee S., Yu J., Watanabe K., Taniguchi T., Hone J., Kaxiras E., Nuckolls C., Kim P.

    Advanced Materials, 26, No. 18, pp. 2812-2817 (23 January 2014)

    doi: 10.1002/adma.201304973

    Epitaxial van der Waals (vdW) heterostructures of organic and layered materials are demonstrated to create high-performance organic electronic devices. High-quality rubrene films with large single-crystalline domains are grown on h-BN dielectric layers via vdW epitaxy. In addition, high carrier mobility comparable to free-standing single-crystal counterparts is achieved by forming interfacial electrical contacts with graphene electrodes.

  3. Title: Direct Observation of a Long-Lived Single-Atom Catalyst Chiseling Atomic Structures in Graphene

    Author(s): Wang W.L., Santos E.J.G., Jiang B., Dogus Cubuk E., Ophus C., Centeno A., Pesquera A., Zurutuza A., Ciston J., Westervelt R., Kaxiras E.

    Nano Letters, 14, No. 2, pp. 450-455 (21 January 2014)

    doi: 10.1021/nl403327u

    Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.