We report the effective methods to induce weak ferromagnetism in pristine MoS2 persisting up to room temperature with the improved transport property, which would lead to new spintronics devices. The hydrogenation of MoS2 by heating at 300 °C for 1 h leads to the easy axis out of plane, while the irradiation of proton with a dose of 1 × 10(13) P/cm(2) leads to the easy axis in plane. The theoretical modeling supports such magnetic easy axes.

We report that the hydrogenation of a single crystal 2H -MoS 2 induces a novel-intermediate phase between 2H and 1T phases on its surface, i.e., the large-area, uniform, robust, and surface array of atomic stripes through the intralayer atomic-plane gliding. The total energy calculations confirm that the hydrogenation-induced atomic stripes are energetically most stable on the MoS 2 surface between the semiconducting 2H and metallic 1T phase. Furthermore, the electronic states associated with the hydrogen ions, which is bonded to sulfur anions on both sides of the MoS 2 surface layer, appear in the vicinity of the Fermi level (E F ) and reduces the band gap. This is promising in developing the monolayer-based field-effect transistor or vanishing the Schottky barrier for practical applications. Thickness-dependent indirect-to-direct band-gap transition of molybdenum disulfide (MoS 2 ) [1,2] and a successful realization of the field-effect transistor (FET) using a singlelayer (1L-) MoS 2 [3] have renewed interests of transition-metal dichalcogenides. This has also boosted the development of two-dimensional (2D) materials for the high performance flexible electronic and optoelectronic devices [4,5]. For a preparation of 1L-MoS 2 , the top-down exfoliation methods such as mechanical exfoliation [1][2][3]6], liquid exfoliation by sonication in a good solvent [7], and chemical exfoliation through lithium (Li) intercalation [8,9] are conventionally used. Among several exfoliation methods, the Li intercalation makes MoS 2 nanosheets only in the nanometer-sized metallic 1T phase [10,11], while other methods usually in the semiconducting 2H phase [1][2][3]. Moreover, without intercalating Li, the 1T phase can be intentionally introduced in the 2H matrix by using a high dose of incident electron beam during heating 1L-MoS 2 , which accompanies intermediate phases as precursors [12]. This 2H/1T phase transition can be realized by gliding sulfur (S) and/or molybdenum (Mo) atomic planes with a change of the d-electron counts [13]. A miniaturization of 2D devices [14] plus a local induction of the metallic 1T phase [11][12][13] controlled (i.e., stripe-patterned) hydrogenation on the MoS 2 monolayer has been theoretically shown to be metallic [19].In this Rapid Communication, we find a novel-intermediate phase between 2H and 1T phases, which consists of a highlyregular surface array of atomic stripes on the MoS 2 surface, and determine its materialization condition in the hydrogenation of a single crystal MoS 2 . This finding motivates one to investigate the interaction between hydrogen and the MoS 2 surface based on a combination of the transmission electron microscopy (TEM), scanning photoelectron microscopy (SPEM), angleresolved photoelectron spectroscopy (ARPES), and firstprinciples calculation. Further, we indicate that the electronic states associated with the emerging phase appear near the Fermi level (E F ) and reduce the band gap, promising in vanishing the Schottky barrier.For the hydrogenation, natural single cryst...

1 T phase incorporation into 2H-MoS2 via an optimal electron irradiation leads to induce a weak ferromagnetic state at room temperature, together with the improved transport property. In addition to the 1T-like defects, the electron irradiation on the cleaved MoS2 surface forms the concentric circle-type defects that are caused by the 2 H/1 T phase transition and the vacancies of the nearby S atoms of the Mo atoms. The electron irradiation-reduced bandgap is promising in vanishing the Schottky barrier to attaining spintronics device. The simple method to control and improve the magnetic and electrical properties on the MoS2 surface provides suitable ways for the low-dimensional device applications.

In particular, extensive efforts regarding chemical vapor deposition (CVD) methods resulted in a large-scale MoS 2 monolayer of high quality for practical applications. [7][8][9][10][11][12] However, despite the large on-off ratio and high mobility, [3,9] 2D field-effect transistors (FET) composed of monolayer MoS 2 have become burdened with electrical contact issues such as Fermi level pinning (FLP) and high contact resistances. [13][14][15][16][17] The simplest and most abundant mono-sulfur vacancy (V S ) defects in the monolayer MoS 2 cause strong FLP at metal electrodes, which generally induce n-type semiconductor behavior. [18][19][20][21][22] Thus, many methods, which include substitution, charge transfer, intercalation, and electrostatic doping, have been developed to improve the contact properties or modulate the polarity of transition metal dichalcogenides (TMDs). [23][24][25] Meanwhile, the alkali metal halide-assisted CVD methods enable the rapid fabrication of the continuous and waferscale uniform monolayer TMDs directly on several oxide substrates. [26][27][28][29][30][31][32][33][34] Alkali metal cations promote a rapid increase of the single domain size of monolayer TMDs due to dehydration and nucleation suppression, regardless of the halide anions. [28,31,34] However, excess amounts of alkali metals destroy the crystallinity of monolayer TMDs. [29] On the other hand, back-gated FETs based on the MoS 2 monolayers directly grown this way or transferred onto the SiO 2 /Si substrates, used in current Si processing techniques to manufacture electronic devices, [19] showed comparable electrical performances to those fabricated without using alkali metal halides. [8,9,27,34] Nevertheless, such FETs also exhibited n-type behavior. [27,34] Na impurities are notoriously prone to contaminating the SiO 2 surface. [36] Alkali Na metals readily absorb at the oxide substrates during the CVD growth process of monolayer TMDs. [28,29] Furthermore, Na's incorporation at the SiO 2 surface of siloxane or silanol releases electrons into the monolayer MoS 2 conduction band; [37] whereas, in graphene deposited on SiO 2 , Na produces holes. [38] To understand the effect of trapped Na cations, we synthesized the large-scale uniform MoS 2 monolayers on the SiO 2 / Si substrates using NaCl catalysts [27] and then performed two-probe I-V measurements by the forward and reverse bias sweeping between ±30 V in the ambient air condition at room temperature (see Figures S1-S3, Supporting Information). Notably, initial low or negligible source/drain I-V signals in the µA range enhanced to the mA range after the Alkali metal halide-assisted chemical vapor deposition (CVD) methods can produce wafer-scale uniform monolayer transition metal dichalcogenides (TMDs). Further defect engineering is necessary to obtain high-performance functional devices. While defect engineering has focused on the surface of the monolayer TMDs or the contact property, interface defect engineering is rare and non-trivial. Based on a NaCl-assisted CVD-grown l...

By using higher acceleration energies than the displacement energy of Mo atoms, the electron irradiation on the layered MoS2 single crystals is found to be an effective and simple method to induce the diamagnetic to ferromagnetic phase transition persisting up to room temperature. The easy axis can be controllable by regulating the electron dose and the acceleration energy. The ferromagnetic states are largely attributed to the strain around the vacancies.