Ferromagnetic Order at Room Temperature in Monolayer WSe₂ Semiconductor via Vanadium Dopant

Abstract

RT), precluding the use of these materials to practical implementations. [2][3][4][5]14] The ferromagnetic state in magnetic metaldoped oxides and nitrides is available at RT but is localized to aggregated metal oxide/nitride nanoparticles without a longrange magnetic order. [4] The ferromagnetic state in van der Waals 2D materials has been observed recently in the monolayer limit. [15][16][17][18][19][20][21] Intrinsic CrI 3 and CrGeTe 3 semiconductors reveal ferromagnetism but the T c is still low below 60 K. [20,21] In contrast, monolayer VSe 2 and MnSe 2 are ferromagnetic metals with T c above RT but incapable of controlling its carrier density. [22,23] Moreover, the long-range ferromagnetic order in doped diluted chalcogenide semiconductors has not been demonstrated at RT. [24][25][26][27][28] The key research target is to realize the long-range order ferromagnetism, T c over RT, and semiconductor with gate tunability. Here, we unambiguously observe tunable magnetic domains by a gate bias above RT in diluted V-doped WSe 2 , while maintaining the semiconducting characteristic of WSe 2 with a high on/off current ratio of five orders of magnitude. Figure 1a illustrates the schematic for the synthesis of V-doped monolayer WSe 2 via chemical vapor deposition (CVD). A metal precursor solution prepared by mixing V and W liquid sources at a given atomic ratio was spin-coated on SiO 2 substrate and the substrate was introduced into the CVD chamber with selenium. The metal precursors get decomposed into metal oxides at growth temperature, resulting in monolayer V x W 1−x Se 2 , followed by selenization. The atomic ratio of V to W sources in precursor solution can be precisely controlled from 0.1% to 40%, while the hexagonal flakes are retained in a monolayer form (the optical image in Figure 1a; Figure S1, Supporting Information). Meanwhile, the dendritic and multilayer flakes are partially generated at higher V-concentration. The V atoms are incorporated into monolayer WSe 2 with V/W contents similar to nominal values, as confirmed by X-ray photoelectron spectroscopy ( Figure S2, Supporting Information). With low V-doping concentration, the hexagonal V-doped WSe 2 flake is a single crystal confirmed by previous TEM study. [29] To study the doping effect of vanadium to the electronic properties of WSe 2 , field effect transistors (FETs) of V-doped mono layer WSe 2 were fabricated (Figure 1b). The CVD-grown pristine WSe 2 manifests a p-type semiconductor with a threshold voltage at −50 V. The threshold voltage is shifted to −10 V for Diluted magnetic semiconductors including Mn-doped GaAs are attractive for gate-controlled spintronics but Curie transition at room temperature with longrange ferromagnetic order is still debatable to date. Here, the room-temperature ferromagnetic domains with long-range order in semiconducting V-doped WSe 2 monolayer synthesized by chemical vapor deposition are reported. Ferromagnetic order is manifested using magnetic force microscopy up to 360 K, while retaining high on/off current rati...

Monolayer Vanadium‐Doped Tungsten Disulfide: A Room‐Temperature Dilute Magnetic Semiconductor

“…≈ 470 K fitted from the data sets is in line with the previous observation of ferromagnetic signals above 420 K from magnetic force microscopy (MFM) measurements carried out on V-doped WSe 2 monolayers. [11] Our direct observation of tunable roomtemperature ferromagnetism in the V-doped WS 2 monolayers from the magnetometry measurements is an important evidence towards establishing the existence of the ferromagnetic order in V-doped TMDs.…”

“…Dilute magnetic semiconductors (DMS) have been realized in bulk III-V systems such as Mn-doped GaAs, with long efforts toward achieving room-temperature ferromagnetism in the face of dopant clustering and phase segregation. [6][7][8] Pioneering efforts toward achieving DMS behavior in semiconducting transition metal dichalcogenides (TMD) [9,10] have recently burgeoned on atomically thin samples toward the introduction of magnetic transition metal ions such as V, [11] Ni, [12] Co, [13] and Mn [14] into the host lattice. While firstprinciples calculations predict tunable ferromagnetism in V-doped MoS 2 , [15] WS 2 , [16] and WSe 2 [17] monolayers, the reliable experimental realization of ferromagnetism in thin-film samples [18] has been challenging.…”

Probing magnetism in atomically thin semiconducting PtSe2

“…Long-range magnetic ordering in semiconductors can be achieved through the incorporation of extrinsic magnetic impurities (e.g., Mn-doped GaAs 38 and V-doped WSe 2 39 ). We rule out this possibility in our work by performing quantitative and qualitative assessment of our samples, which do not show the presence of any chemical elements except for Pt and Se and other crystal phases beside 1 T (see Supplementary Notes 7 and 8).…”

Growth Mechanism of Alternating Defect Domains in Hexagonal WS2 via Inhomogeneous W‐Precursor Accumulation

“…Confocal PL and Raman mapping were performed using 40× objectives (MPlanFL N × 40, Olympus). The laser power was modulated for PL (5,10,50, 100, 500 µW and 1 mW) and Raman (200, 400, 600, 800 µW and 1 mW) spectroscopy. In order to confirm the AFM topography and surface condition, characterizations of the as-grown WS 2 flakes on the SiO 2 /Si substrate were performed in tapping mode using a scanning probe microscope (Dimension ICON, Bruker) at room temperature.…”

“…2D transition-metal dichalcogenides (TMDs) have been intensively investigated for numerous unexplored physics and device applications. [1][2][3][4][5] Among the various methods for synthesizing TMD monolayers, chemical vapor deposition (CVD) has been widely used for high-quality TMD monolayers over a large area. [6][7][8][9] The optical and electrical properties of CVD-grown While a hexagonal WS 2 monolayer, grown by chemical vapor deposition, exhibits distinctive patterns in photoluminescence mapping, segmented with alternating S-vacancy (SV) and W-vacancy (WV) domains in a single crystal, the formation mechanism for native alternating defect domains remains unresolved to date.…”