Metal Contacts on Physical Vapor Deposited Monolayer MoS₂

Abstract

The understanding of the metal and transition metal dichalcogenide (TMD) interface is critical for future electronic device technologies based on this new class of two-dimensional semiconductors. Here, we investigate the initial growth of nanometer-thick Pd, Au, and Ag films on monolayer MoS2. Distinct growth morphologies are identified by atomic force microscopy: Pd forms a uniform contact, Au clusters into nanostructures, and Ag forms randomly distributed islands on MoS2. The formation of these different interfaces is elucidated by large-scale spin-polarized density functional theory calculations. Using Raman spectroscopy, we find that the interface homogeneity shows characteristic Raman shifts in E2g(1) and A1g modes. Interestingly, we show that insertion of graphene between metal and MoS2 can effectively decouple MoS2 from the perturbations imparted by metal contacts (e.g., strain), while maintaining an effective electronic coupling between metal contact and MoS2, suggesting that graphene can act as a conductive buffer layer in TMD electronics.

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

“…Such approaches may, for example, be relevant for achieving 2D metal film growth on 2D crystals, including graphene and Mo 2 S, and thereby synthesize low-resistivity electrical contacts on nanoelectronic devices [4,5,[7][8][9][10][11][12][13][14] or fabricate catalytic devices that exhibit enhanced turnover frequencies [6].…”

“…A notable example is the deposition of metal films on twodimensional (2D) crystals (e.g., graphene and MoS 2 ) [4][5][6] for which the tendency toward the formation of 3D agglomerates imposes technological obstacles for the use of 2D materials in a wide range of switching and, in some cases, catalytic devices [4][5][6][7][8][9][10][11][12][13][14]. Thus, understanding atomistic mechanisms that govern 3D island formation and shape evolution is a key step toward controlling film morphology and, by extension, the functionality of devices based on weakly interacting film/substrate materials systems.…”

“…Following the early categorization and description of 3D (Volmer-Weber) film growth by Bauer [31], recent studies of metal-film and nanostructure growth on graphite [32], graphene [4], and other 2D materials [5,6] have explained experimentally observed growth morphologies as a function of the ratio between the adsorption energy (E ads ) of metal atoms on the substrate and the bulk-metal cohesive energy (E coh ); the lower the E ads /E coh ratio, the stronger the tendency toward 3D growth. Intuitively, this can be understood as the metal atoms being more weakly bound to the substrate, which facilitates their ascent onto the first layer of an island by either direct hopping or an exchange mechanism [33].…”

Seeded growth of highly crystalline molybdenum disulphide monolayers at controlled locations

“…Raman mapping (Fig. 3e,f) was used to confirm that the Raman spectrum was uniform over the monolayer region as well as distinct from the spectra associated with multilayer regions and the substrate [25][26][27] (Maps of Raman peak positions are also shown in Supplementary Fig 8.). We performed PL and reflection measurements to confirm that the existence of a direct bandgap, which is known to be characteristic of monolayer MoS 2 (refs 28-31).…”

Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family

“…The drain–source current is controlled by the gate voltage on the dielectric layer. High carrier mobility, high switching ratio and low subthreshold swing means high performance FET, which depends on the metal contacts,247 channel materials (thickness,248, 249 doping,192, 250, 251, 252, 253, 254 heterostructures200, 208), dielectric materials (back‐gate,86, 255 top‐gate,256 liquid gate257), and so forth. 2D GIVMCs based FETs have demonstrated exciting performance.…”