Graphene and monolayer transition-metal dichalcogenides: properties and devices
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Graphene and monolayer transition-metal dichalcogenides: properties and devices Olaf M.J. van ’t Erve,a) Aubrey T. Hanbicki, Adam L. Friedman, Kathleen M. McCreary, Enrique Cobas, Connie H. Li, Jeremy T. Robinson,b) and Berend T. Jonker Naval Research Laboratory, Washington, D.C. 20375, USA (Received 25 September 2015; accepted 16 December 2015)
2D materials play a special role in the race to make smaller and smaller devices. Their unique and strong in-plane bonding makes them impervious to diffusion into other layers and provides excellent thickness control. Their van der Waal’s bonding with other monolayers or substrates allows for heterostructures unattainable by any other technique. This is reflected by the abundant popularity of research into graphene and other 2D materials. In this review article, we will describe the out-of-plane properties of graphene and functionalized graphene. We will use three specific examples to illustrate how these out-of-plane properties can be used in spintronic devices, in section “Graphene as a Tunnel Barrier” we will describe a magnetic tunnel junction (MTJ) based on graphene. Section “Graphene Based MTJs” will describe the spin injecting properties of a graphene tunnel barrier on silicon. Section “Graphene in Semiconductor Spintronic Devices” describes how you can use functionalized graphene to make a homoepitaxial graphene device. The second part of this article reviews monolayer transition-metal dichalcogenides (TMDs). First, we will show how TMDs are grown and specifically how we can grow large-area TMDs by chemical vapor deposition. Secondly, we will describe the optical properties of several TMDs and compare the results from several authors. Finally, we choose a chemical sensor as a specific example to show how TMDs can be used in a device.
I. GRAPHENE AS A TUNNEL BARRIER
In this section, we describe the novel use of graphene as a tunnel barrier for both charge and spin transport. Graphene is typically studied for its extraordinary in-plane conductance properties,1–3 while its out-of-plane transport properties are largely ignored.4 Graphene is metallic inplane due the large availability of conduction channels. In contrast, there are substantially fewer out-of-plane conduction channels, resulting in a low resistivity in that configuration.5 A tunnel barrier is comprised of two electrodes separated by a thin insulator where current flows between the electrodes entirely by quantum mechanical tunneling. Graphene exhibits many of the characteristics expected for an ideal tunnel barrier. The strong in-plane sp2 bonding of carbon atoms results in a strong Contributing Editor: Joshua Robinson a) Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/. A previous error in this article has been corrected, see10.1557/jmr.2016.129. DOI: 10.1557/j
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