1 74 | Nature | Vol 581 | 14 May 2020
Article
and Fig. 3h, respectively. The states at the Fermi level comprise the
prismatic-centred Ta dz 2 orbitals hybridized with the spin-up band of
the dxy (^22) − orbital of the intercalated Ta. However, only the intercalated
Ta atoms exhibit a net spin density, as illustrated in Fig. 3i, in which the
top view spin density isosurface matches the shape of the dxy^22 − orbital.
In addition, the non-magnetic 3a × 3a charge-density wave state of Ta 7 S 12
can be ruled out owing to its relative instability compared with the fer-
romagnetic state^41.
The existence of a magnetic moment correlates with a large degree of
charge transfer between the intercalated Ta and the TaS 2 layers. Strong
charge transfer occurs when the proportion of intercalated Ta atoms
is low, whereas charge transfer becomes relatively weak in a heavily
intercalated (Fig. 3j) compound, in accordance with the calculated
charge difference and the variation of Bader charge on the Ta atoms
(Supplementary Fig. 22, Supplementary Table 2).
To investigate whether the self-intercalation phenomenon occurred
for other TMDs, we performed a high-throughput DFT study of 48 dif-
ferent intercalated TMD bilayers, using a semi-automated workflow for
maximal consistency and veracity^42. Specifically, we considered TMDs
of the transition metals Mo, W, Nb, Ta, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni,
Pd and Pt, as well as Sn, and the chalcogens S, Se and Te (Fig. 4a) at σ
values of 33.3% or 66.7%. Out of this set of TMDs, we observed that 14
bilayer configurations—Ti 8 S 12 , Ti 8 Se 12 , Ti 8 Te 12 , Co 7 S 12 , Co 7 Se 12 , Co 7 Te 12 ,
Nb 7 S 12 , Nb 7 Se 12 , Nb 7 Te 12 , Mo 7 S 12 , Mo 7 Se 12 , Ta 7 S 12 , Ta 7 Se 12 and Ta 7 Te 12
(highlighted by specific σ values and chalcogens in Fig. 4a and Sup-
plementary Table 3 for magnetic moment)—develop ferromagnetic
66.7%;Ta 8 Se 12
b
g h
l
i j
50%;Ta 10 S 16 100%;Ta 9 Se 12
Primary spots
Superspots
cd
33.3%;Ta 7 S 12
e
a
kmn
f
90°
2 a
25%;Ta 9 S 16
3 a60°
3 a
3 a
60°
3 a
3 a
60°
3 a^3 a
3 a
a
3 a
a
Ta IntercalatedTa
Se S
3 a
3 a
60°
√ 3 a
2 a
√ 33 a
2 a
3 a
2 a
3 a
3 a
3 a
3 a
Fig. 2 | Compositional engineering of TaxSy and TaxSey with different
concentrations of intercalated Ta. a, b, Atomic-resolution STEM–ADF images
of self-intercalated Ta 7 S 12 , grown by MBE, showing the well-defined 3×aa 3
superstructure (a), and an enlarged image (b). c, The corresponding FFT
pattern of a, with 3 a superspots highlighted by orange circles. d, Atomic
model of self-intercalated Ta 7 S 12. e, f, STEM cross-section view of 100%
Ta - i n t e r c a l a t e d Ta 9 Se 12 (e) and its corresponding simulated image derived from
the DFT-optimized atomic model (f). g–j, Atomic-resolution STEM images of
25% Ta-intercalated Ta 9 S 16 (g), 50% Ta-intercalated Ta 10 S 16 (h), 66.7%
Ta - i n t e r c a l a t e d Ta 8 Se 12 (i) and 100% Ta-intercalated Ta 9 Se 12 (j) ic-2D crystals.
k–n, Left, enlarged STEM images corresponding to the regions highlighted
with white boxes in g–j, respectively; right, the corresponding FFT patterns;
bottom, the corresponding atomic models. Scale bars: a, g–j, 2 nm; b, e, k–n,
0.5 nm.