Letter pubs.acs.org/JPCL
Tuning Magnetism and Electronic Phase Transitions by Strain and Electric Field in Zigzag MoS2 Nanoribbons Liangzhi Kou,*,† Chun Tang,‡,§ Yi Zhang,‡ Thomas Heine,∥ Changfeng Chen,‡ and Thomas Frauenheim† †
Bremen Center for computational Materials Science, University of Bremen, Am Falturm 1, 28359, Bremen, Germany Department of Physics and Astronomy and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, United States § School of Engineering, University of California, Merced, California 95343, United States ∥ School of Engineering and Science, Jacobs University Bremen, 28759 Bremen, Germany ‡
S Supporting Information *
ABSTRACT: Effective modulation of physical properties via external control may open various potential nanoelectronic applications of single-layer MoS2 nanoribbons (MoS2NRs). We show by first-principles calculations that the magnetic and electronic properties of zigzag MoS2NRs exhibit sensitive response to applied strain and electric field. Tensile strain in the zigzag direction produces reversible modulation of magnetic moments and electronic phase transitions among metallic, half-metallic, and semiconducting states, which stem from the energy-level shifts induced by an internal electric polarization and the competing covalent/ionic interactions. A simultaneously applied electric field further enhances or suppresses the strain-induced modulations depending on the direction of the electric field relative to the internal polarization. These findings suggest a robust and efficient approach to modulating the properties of MoS2NRs by a combination of strain engineering and electric field tuning. SECTION: Physical Processes in Nanomaterials and Nanostructures
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chemical method or in carbon nanotubes.18−20 The edges of 2D MoS2 flakes and ribbons have been characterized by STM, and 1D metallic states have been reported.21,22 Along with successful experimental fabrication, an explosion of theoretical studies on MoS2 has recently occurred, leading to discoveries of interesting electronic and magnetic properties. Their different edge chiralities lead to distinct properties: zigzag MoS2NRs (ZMoS2NRs) are ferromagnetic metals, whereas armchair ones are semiconductors with a width-dependent band gap.11,12 Their properties also depend on external factors such as absorbed atoms and defects.23−25 MoS2 edge geometries are size-dependent and show strong chemical activity,26,27 a property that is exploited in catalysis: MoS2 flakes are excellent catalysts for the hydrodesulfurization of various petrol products, most importantly diesel.28 Owing to the outstanding properties (high mobility: 200 cm2 V−1 s−1 and large on/off ratios: 1 × 108) and controlled monolayer production by Scotch tape technique5 or liquid exfoliation large availability,29,30 MoS2 has been suggested for application in transistors, photovoltaic cells, photocatalysts, and lithium batteries.5,6,31 The latest studies have demonstrated special electronic properties of single-layer MoS2 that hold great promise for optoelectronic applications.32−34 These studies have suggested MoS2NRs as a
ow-dimensional nanomaterials, especially 1D nanoribbons, nanowires, and nanotubes, are promising building blocks for next-generation nanoelectronic devices because of their unique physical, mechanical, and chemical properties.1 In the past few years, the most widely investigated nanomaterials are graphene and its derived nanoribbons owing to their rich physical properties and high electron mobility.2 However, their applications have been hindered by the absence of an electronic band gap in pristine graphene. The search for alternative materials has turned attention to other inorganic layered materials, such as boron nitride, 3 tungsten disulfide, 4 molybdenum disulfide (MoS 2),5−7 and others.8 As an exemplary case of intrinsically semiconducting layered materials, single-layer MoS2 has attracted considerable interest because of its excellent properties for potential applications.9−12 Unlike the one-atom thin graphite and boron nitride sheets or ribbons, the single-layer MoS2 comprises three atomic layers with a Mo-layer sandwiched between two S-layers. The Mosandwich layer bounds tightly internally and interacts with neighboring MoS2 layers through weak van der Waals interactions;13 however, the interlayer interaction does affect the electronic structure of the material, influencing its electronic properties from an 1.2 eV indirect band gap semiconductor to a 1.9 eV direct band gap material as monolayer.14,15 This structural characteristic facilitates the fabrication of ultrathin layered MoS2 by micromechanical cleavage and exfoliation methods.16,17 Besides its monolayer structure, MoS2 nanoribbons (MoS2NRs) have been synthesized using an electro© 2012 American Chemical Society
Received: September 3, 2012 Accepted: September 26, 2012 Published: September 26, 2012 2934
dx.doi.org/10.1021/jz301339e | J. Phys. Chem. Lett. 2012, 3, 2934−2941
The Journal of Physical Chemistry Letters
Letter
plane-wave cutoff of 300 hartree is chosen for all simulations, and atomic positions are fully relaxed so that the force on each atom is
