Kinetically Controlled Epitaxial Growth of Fe₃GeTe₂ van der Waals Ferromagnetic Films

Abstract

We demonstrate that kinetics play an important role in the epitaxial growth of Fe3GeTe2 (FGT) van der Waals (vdW) ferromagnetic films by molecular beam epitaxy. By varying the deposition rate, we control the formation or suppression of an initial tellurium-deficient non-van-der-Waals phase (Fe3Ge2) prior to realizing epitaxial growth of the vdW FGT phase. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111) substrate. The magnetic properties of our high quality material are confirmed through magneto-optic, magnetotransport, and spin-polarized STM studies. Importantly, this demonstrates how the interplay of energetics and kinetics can help tune the re-evaporation rate of chalcogen atoms and interdiffusion from the underlayer, which paves the way for future studies of van der Waals epitaxy.

Scanning tunneling microscopy study of epitaxial Fe3GeTe2 monolayers on Bi2Te3

“…This was accomplished by co-depositing Fe (99.99%, Alfa Aesar), Ge (99.9999%, Alfa Aesar), and Te with a calibrated atomic flux ratio of 3:1:20, as measured by BFM. These growth conditions match our earlier work of FGT growth on Ge(111) substrates [21]. The deposition rate was calibrated by fringes in the Xray reflectivity of a ∼24 nm thick FGT film.…”

Progress and Prospects in Metallic FexGeTe2 (3≤x≤7) Ferromagnet

“…Although many methods including SSR [106], CVT [14,15,17,19,59,118,121,135], flux [39,[43][44][45] and MBE [7,[53][54][55][56][57][58]64,136], have been used to prepare 2D FGT, there was still a lack of an economical method to prepare large-scale of few or single layer FGT nanoflakes. As a typical example, Ma et al [50] developed three-stage sonication-assisted liquid-phase exfoliation (TS-LPE) (Figure 6A) to achieve large-size semiconductive FGT nanoflakes.…”

“…Recently, FexGeTe2 (3≤x≤7) has received intense attentions as a metallic and high curie temperature (TC) ferromagnet. Importantly, six synthesis methods including solid-state reaction (SSR) [35,36], chemical vapor transport (CVT) [8,13,37], the flux method [11,21,[38][39][40][41][42][43][44][45], exfoliation [14,15,34,[46][47][48][49][50], chemical vapor deposition (CVD) [51,52] and molecular beam epitaxy (MBE) [7,[53][54][55][56][57][58], have been used to attempt to obtain wafer-scale FexGeTe2 (3≤x≤7) materials with room-temperature ferromagnetism (RTFM). More interestingly, RTFM has been mediated with ten strategies, such as Fe stoichiometry [9,39,51,[59][60][61][62][63][64], strain engineering [46,48,[65][66]…”

Progress and Prospects in Metallic FexGeTe2 (3 ≤ x ≤ 7) Ferromagnets

“…Although many methods including SSR [107], CVT [14,15,17,19,61,119,121,134], flux [39,[43][44][45], and MBE [7,[53][54][55][56][57][58][59][60] have been used to prepare 2D FGT, an economical method for the large-scale preparation of few-or single-layer FGT nanoflakes is still lacking. As a typical example, Ma et al [50] developed three-stage sonication-assisted liquid-phase exfoliation (TS-LPE) (Figure 6A) to produce large semiconductive FGT nanoflakes.…”

“…Recently, Fe x GeTe 2 (3 ≤ x ≤ 7) has received intense attention as a metallic and high Curie temperature (T C ) ferromagnet. Six synthesis methods, including solid-state reaction (SSR) [35,36], chemical vapor transport (CVT) [8,13,37], the flux method [11,21,[38][39][40][41][42][43][44][45], exfoliation [14,15,34,[46][47][48][49][50], chemical vapor deposition (CVD) [51,52], and molecular beam epitaxy (MBE) [7,[53][54][55][56][57][58], have been used to attempt to obtain wafer-scale Fe x GeTe 2 (3 ≤ x ≤ 7) materials with room-temperature ferromagnetism (RTFM). However, the T C of the MBEprepared Fe x GeTe 2 (3 ≤ x ≤ 7) samples (see Figure 1) ranges from 390 to 530 K, with FGT (T C ≈ 400 K) [56], Fe 4 GeTe 2 (F4GT; T C ≈ 530 K) [59], and Fe 5 GeTe 2 (F5GT; T C ≈ 390 K) [60].…”