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2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license. See: http://creativecommons.org/licenses/by/4.0/ Downloaded to IP: 54.152.109.166 On: Sat, 26 Dec 2015 12:48:54

AIP ADVANCES 4, 047107 (2014)

Substrate induced modulation of electronic, magnetic and chemical properties of MoSe2 monolayer A. H. M. Abdul Wasey, Soubhik Chakrabarty, and G. P. Dasa Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India (Received 18 November 2013; accepted 28 March 2014; published online 9 April 2014)

Monolayer of MoSe2 , having a typical direct band gap of ∼1.5 eV, is a promising material for optoelectronic and solar cell applications. When this 2D semiconductor is supported on transition metal substrates, such as Ni(111) and Cu(111), its electronic structure gets modulated. First principles density functional investigation shows the appearance of de-localized mid-gap states in the density of states. The work function of the semiconductor overlayer gets modified considerably, indicating n-type doping caused by the metal contacts. The charge transfer across the metal-semiconductor junction also significantly enhances the chemical reactivity of the MoSe2 overlayer, as observed by Hydrogen absorption. Furthermore, for Ni contact, there is a signature C 2014 Author(s). All article content, of induced magnetism in MoSe2 monolayer.  except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4871080]

I. INTRODUCTION

Since the discovery of graphene,1–4 enormous attentions have been given to exploit its unique properties to realize graphene based devices. Notwithstanding its useful electronic properties, gapless electronic structure of pristine graphene imposes a limitation over its use in nanoelectronics. An appropriate electronic band gap is essential for switching of the electron flow in an electronic device. Accordingly, a number of ways to introduce band gap in graphene have been attempted, such as cutting into nano-ribbons,5 modulation of edge states,6 introducing defects,7 doping with some suitable dopants8 etc. In order to fulfill the ever increasing demand of 2D flexible, light weight electronic devices, several graphene analogues such as hexagonal boron nitride, silicene, germenene etc. that have similar honeycomb topology, have been probed. More recently, TM dichalcogenides (TMDC), such as MoS2 , has been reported9 to be a potential candidate whose 2D layered structure with moderate band gap can be used for applications in nanoelectronics. Bulk TMDC’s are well known since the seventies for their charge density wave (CDW) behavior and their concomitant electrical and optical properties.10–15 MoSe2 is a layered material, structurally similar to MoS2 . The Mo layer is sandwiched between two Se layers along [001] direction. Such a composite MoSe2 trilayer is stacked together along the [001] direction via weak van der Waals interaction. However, intra planar bonding is strong covalent type which gives the system its mechanical strength. MoSe2 layer is free of surface states because all the chalcogenides ions are saturated in this compound which reduces its chemical reactivity. As the inter-layer binding is relatively weak, the monolayer of MoSe2 can be synthesized by techniques like liquid exfoliation or micromechanical cleavage etc.16, 17 In the post graphene era, attempts are being made to study the monolayers of the same compounds. In order to exploit the device potential of these TMDC monolayers, it is important to investigate how they behave electronically while in contact with the metal. Accordingly, people have investigated MoS2 -metal contact both experimentally16–18 and theoretically19 for different transition metal

a E-mail of corresponding author: [email protected]

2158-3226/2014/4(4)/047107/9

4, 047107-1

 C Author(s) 2014

© 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license. See: http://creativecommons.org/licenses/by/4.0/ Downloaded to IP: 54.152.109.166 On: Sat, 26 Dec 2015 12:48:54

047107-2

Wasey, Chakrabarty, and Das

AIP Advances 4, 047107 (2014)

FIG. 1. Optimized ground state geometries of MoSe2 /Ni(111) system. (a) Side view and (b) top view of the MoSe2 /Ni(111) heterostructure. Ni atoms closer to the interface are shown by bigger gray spheres.

substrates viz. Au (111) and Ti (0001). However, while bulk MoS2 has good electron mobility11, 20 single layer MoS2 is found to have low mobility when grown on some substrate.9, 17 Popov et al had argued that it is the contact material which plays the crucial role in controlling the device performance, and a detailed explanation was proposed for the low mobility of MoS2 monolayer with Au contact. Therefore, search for suitable metal contact to MoS2 is still on to design hetero-junctions with improved functionality.18, 21 Monolayer of MoSe2 is a direct band gap semiconductor with a