Metal-graphene heterojunction modulation via H2 interaction

Abstract

Combining experiment and theory, we investigate how a naturally created heterojunction (pn junction) at a graphene and metallic contact interface is modulated via interaction with molecular hydrogen (H2). Due to an electrostatic interaction, metallic electrodes induce pn junctions in graphene, leading to an asymmetrical resistance for electronic transport via electrons and holes. We report that an asymmetry in the resistance can be tuned in a reversible manner by exposing graphene devices to H2. The interaction between the H2 and graphene occurs solely at the graphene-contact pn junction and might be due to a modification on the electrostatic interaction between graphene and metallic contacts. We confront the experimental data with theory providing information concerning the length of the heterojunction, and how it changes as a function of H2 adsorption. Our results are valuable for understanding the nature of the metal-graphene interfaces and point out to a novel route towards selective hydrogen sensor application.Graphene is a zero-gap semiconductor which charge carrier density and conductance can be controlled electrostatically by preparing graphene devices as field effect transistors.1,2 In such architecture, the contact resistance considerably impairs device performance and is responsible for a conduction asymmetry for p-doped and n-doped graphene.3-8 This asymmetry stems from heterojunctions (pn junctions) formed at metal-graphene interfaces due to different work functions between graphene and metal -i.e. Fermi level pinning. 9-13 Effectively, the advent of the pn junction results in an additional charge scattering at the metal-graphene interface increasing device resistance. On the other hand, interesting effects can be observed as well. For instance: heterojunctions at metal-graphene interface have been used to design FabryPerot cavities 11 and to observe resonances in Josephson junctions in graphene devices. 14 In both systems, the metal-graphene interfaces have been considered a static problem, where the doping at the graphene underneath the contact is solely defined by the type of metal used. However, so far, a controllable method to probe and modulate the pn junction induced by contacts has not been reported. In addition, there are still open questions about how far a pn junction can extend from the contact into the graphene channel and if there are technological applications based on specialties of graphene contact resistance. 3,4,6,7,[14][15][16]

Enhancing the response of NH3 graphene-sensors by using devices with different graphene-substrate distances

“…1 (a). Thermal annealing of the devices is performed in situ by heating to 473 K and keeping during overnight in pure N2 atmosphere to drive out all undesirable gases [38]. Once the annealing procedure This is the authors' version pre-peer reviewed of the following article: Alisson R. Cadore et.…”

Graphene devices with bottom-up contacts by area-selective atomic layer deposition

“…[1][2][3][4][5] Despite its promising properties, the formation of good electrical contacts to graphene remains a key bottleneck for many applications even though a substantial amount of research has been devoted to this subject. [6][7][8][9][10][11][12][13][14][15] Due to its atomically thin nature, the graphene underneath metal electrodes can be heavily modified. For example, the density of states (DOS) of the graphene under the contacts can deviate from the typical Dirac cone found in pristine graphene, especially when the metal-graphene coupling strength is large.…”

Probing the Electronic Properties of Monolayer MoS2 via Interaction with Molecular Hydrogen

“…[1,16,[29][30][31] 2) If the detection of H 2 depends on the underlying substrate. [1,16,[29][30][31] 2) If the detection of H 2 depends on the underlying substrate.…”

“…[31] Therefore, if H 2 sensing is dominated by the contact resistance, i.e., H 2 molecules change the Schottky barrier height via modulation of the metal work function, we would not expect to measure a significant hydrogen response in a four-probe configuration. It is reasonable to assume that the total change in conductance (ΔG) of MoS 2 FET due to H 2 adsorption is represented by ΔG = ΔG Channel + ΔG Contacts , where ΔG Channel is directly proportional to the carrier concentration injected in the channel and ΔG Contacts is inversely proportional to the contact resistance change.…”