Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2015. Supporting Information for Adv. Mater., DOI: 10.1002/adma.201502134 Stable Metallic 1T-WS 2 Nanoribbons Intercalated with Ammonia Ions: The Correlation between Structure and Electrical/Optical Properties Qin Liu, Xiuling Li, Zhangru Xiao, Yu Zhou, Haipin Chen, Adnan Khalil, Ting Xiang, Junqing Xu, Wangsheng Chu, Xiaojun Wu,* Jinlong Yang, Chengming Wang, Yujie Xiong, Chuanhong Jin, Pulickel M. Ajayan, and Li Song*
DOI: 10.1002/adma.201502134 Supporting on-line material for: Stable Metallic 1T-WS 2 Nanoribbons Intercalated with Ammonia Ions: The correlation between Structure and Electrical/Optical Properties Qin Liu, Xiuling Li, Zhangru Xiao, Yu Zhou, Haipin Chen, Adnan Khalil, Ting Xiang, Junqing Xu, Wangsheng Chu, Xiaojun Wu*, Jinlong Yang, Chengming Wang, Yujie Xiong, Chuanhong Jin, Pulickel M. Ajayan, and Li Song* (1) AFM characterization Figure S1: a) SEM image and b) TEM image of our as-prepared N-WS2. c) AFM image and d) line-scan profile, showing an N-WS 2 nanoribbon with average thickness of 3.9 nm.
(2) STEM elemental mapping Figure S2: The high angle annular dark-field scanning TEM (HAADF-STEM) image and corresponding elemental mapping images of the synthesized samples, indicating the distribution of W, S and N. The signal of Cu arises from TEM grid substrate. (3) Zeta potential test Figure S3: Zeta-potential measurement of as-prepared samples dispersed in water. The magnitude of the zeta potential (-43 mv) shows great colloidal stability in aqueous media, indicating the presence of ammonium ions.
(4) XRD analysis of aging-sample Figure S4: XRD patterns of half-year aging N-WS 2 samples, strongly indicating high stability of ammonium ions intercalation. (5) XPS analysis Figure S5: XPS spectra of W 5p and 4f, S 2p and N 1s core levels of the ammonium ion-intercalated WS 2, in contrast with bulk WS 2. The spectrum curves are deconvoluted (black dashed curves) by Gaussian fitting (red curves). Table S1: Elemental analyses of the N-WS 2 ultrathin nanoribbons. atom% of nitrogen atomic ratio of W/S by XPS by EDS N-WS 2 3.48-10 1:2.00
(6) STEM analysis on 2H-WS 2 Figure S6: (a) High-resolution HADDF-STEM images of 2H-WS 2. Scale bar is 1 nm. (b) The intensity profile along the red lines indicated in (a) compare with that of N-WS 2. The bottom schematic diagram illustrates the structure of 2H-WS 2 with trigonal prism coordination and metallic N-WS 2 with octahedral coordination. (c) The corresponding simulated structural model of WS 2 with trigonal prismatic coordination (2H semiconducting phase). We have used the high-angle annular dark field (HAADF) imaging mode in an aberration-corrected scanning transmission electron microscope (STEM) to observe microstructure of 2H-WS 2 as reference. In Figure S6a, we observed W-W distance of 3.15 Å for pristine 2H-WS 2, while the value decreases to 2.7 Å forming zigzag chain superlattices in N-WS 2 (shown in Figure 3 of our main text). Meanwhile, we have further utilized the Z-contrast in STEM HAADF images to build a patent distinction of microstructures between 2H-WS 2 and N-WS 2. The variations of intensity profiles in Figure S6b demonstrate an obvious difference between the two samples. Pristine WS 2 exhibits a lower contrast in the honeycomb lattice intensity variation between two adjacent sites, while N-WS 2 shows a larger contrast variation. The octahedral coordination model of N-WS 2 can be obtained from the trigonal prism structure of 2H-WS 2 by rotating one of the sulfur basal planes by 60 o around the c-axis, as shown in the bottom schematic diagram of Figure S6b. This can be easily used to explain the various variations in the signal intensities. A similar structure was previously reported in the lithium-assisted exfoliated metallic MoS 2 and WS 2 (Ref 5, 15 and 16 in the MS).
Figure S6c shows the corresponding schematics of pristine 2H-WS 2 to visualize the atomic structure. The bottom schematic diagram in Figure S6c illustrates the structure of 2H-WS 2 with trigonal prism coordination. (7) First principle calculations on structural stability and electrical properties Figure S7: Four types of WS 2 structure models are considered, including (a) regular phase of 1T-WS 2 (1 1 superlattice), (b) hybrid trimer phase (2 2 superlattice), (c) trimer phase ( 3 3 superlattice), and (d) zigzag-chain phase (2 1 superlattice). When NH 4 species are introduced between WS 2 layers, only two types of distorted structures are observed after a full geometric optimization, including (e) trimer phase and (f) zigzag-chain phase. There are a lot of experimental and theoretical works having reported on restacked 1T-MoS 2 and1t-ws 2 (Ref 14 in the MS). Here, we have adopted four
possible structural models, as shown in Fig. S7 (a-d).among them, 2 2, 3 3 or 2 1 supercell is considered as model for the possible reconstruction of structure, corresponding to the hybrid-trimer, trimer, and zigzag-chain phase, respectively. The optimized lattice constants and calculated average binding energy per atom were summarized in Table S2. It shows that the zigzag-chain phase has the highest value of average binding energy. When NH 4 specie was embedded, the regular 1T-WS 2 and hybrid-trimer phase WS 2 spontaneously change to trimer phase while the zigzag-chain phase is still stable (Figure S7 (e) and (f)). All hydrogen atoms in NH 4 point to the nearest S atoms in WS 2. The calculated binding energies of 3 3and 2 2N-WS 2 were 2.43 ev and 2.69 ev, respectively. It suggests that the interaction between ammonia and N-WS 2 with zigzag chain is stronger. Table S2. The lattice parameters of WS 2 with 1 1, 2 2, 3 3and 2 1 superlattices. a, b, and c are the lattices lengths. α, β, and γ are angles. E b is the binding energy of WS 2. a (Å) b (Å) c (Å) α β γ E b /atom (ev) 1 1 3.17 3.17 6.07 90.0 90.0 120.0 7.52 2 2 6.44 6.44 6.12 90.3 90.3 60.3 7.60 3 3 5.63 5.63 6.99 90.0 90.0 120.0 7.61 2 1 6.50 3.17 6.41 90.8 91.9 60.8 7.63
(8) Additional X-ray absorption fine structure analysis Figure S8 : (a) Fitting curves for EXAFS data at the W L 3 -edge for bulk WS 2 and (b) N-WS 2, respectively. To obtain structural parameters around W and S atoms in N-WS 2 the least-squares curve parameter method was used with the ARTEMIS module of both IFEFFIT and USTCXAFS software packages (Ref 24, 25 in the MS). Effective scattering amplitudes and phase-shifts of W-S and W-W bonds were calculated with the ab initio code FEFF8.0 (Ref 26 in the MS). The coordination numbers in the first two coordination shells of the bulk WS 2 were fixed to the nominal values, while the interatomic distances R, Debye-Waller factor σ 2 and the edge-energy shift E 0 were left free. The amplitude reduction factor S 0 2 was also treated as an adjustable parameter and the obtained value was 0.9 at the W L 3 -edge. This value was fixed in the subsequent fit at the W L 3 -edge data in the spectrum of the N-WS 2. Results are in excellent agreement with crystallographic values, showing the high accuracy of EXAFS in the determination of structural parameters. Fitting the W L 3 -edge data of N-WS 2, the intensities of the two peaks decreased significantly and this change is associated with the shift of the W-W peak to 2.7 Å which is comparable to the value of 3.16 Å in the bulk WS 2. Fitting was performed on the k-weighted EXAFS function χ(k) from 2 to 14 Å -1 in the R-range 1.2 3.0 Å. Within this framework we got a satisfactory fit as shown in Figure S8. The obtained parameters are listed in Table S3. Table S3. Structural parameters for W and S atoms in bulk 2H-WS 2 and N-WS 2 fitted from EXAFS data. The structure of N-WS 2 is strongly distorted compared to bulk 2H-WS 2. R is the
length of bond, N is the coordination number, σ 2 is Debye-Waller factor and E 0 is the edge-energy shift. Sample# Path R(Å) N σ 2 (10-3 Å 2 ) ΔE 0 (ev) W-S 2.405 6.0 2.9 6.6 Bulk 2H-WS 2 W-W 3.167 6.0 3.5 5.9 N-WS 2 W-S 2.420 5.3 5.2 5.0 W-W 2.774 2.7 6.0 4.0 (9) Electrical transport of 2H-WS 2, annealed WS 2 and sonicated WS 2 Figure S9: Temperature-dependent resistance curves of bulk 2H-WS 2, annealed WS 2 and sonicated WS 2 exhibit a continuous reduction in the curve with the increase in the temperature range of 30~300 K, implying a semiconducting characteristic. The inset image represents an optical microscope image of the tested devices with four electrodes.
(10) Test calculation of NH 3 molecule intercalated WS 2 and the effect of spin orbit coupling Figure S10: The calculated DOS of NH 3 -molecule intercalated WS 2 with the weak interaction. Test calculation show that less than 0.05 electrons per NH 3 molecule are transferred from NH 3 molecule to WS 2 and the shortest distance between NH 3 and WS 2 is larger than 2.7 Å. The calculated density of states shows that WS 2 -NH 3 with zigzag chain configuration is semiconductor with a small gap of about 0.04 ev, as shown in above. Figure S11: A test calculation of N-WS 2 with and without spin orbit coupling. We performed a test calculation (a) without and (b) with spin orbit coupling. As shown in above, the WS 2 - NH 4 + ionic complex still exhibits metallic properties.
(11) The UV-Vis absorption spectra of N-WS 2 and 2H-WS 2 Figure S12: The UV-Vis absorption spectra performed on both N-WS 2 and bulk WS 2 powder. (12) Raman spectrum of aging-sample without any treatments Figure S13: Raman spectrum of aging N-WS 2 kept in air for half-year indicates high stability of metallic phase.