Well-defined Colloidal 2-D Layered Transition Metal Chalcogenide Nanocrystals via Generalized Synthetic Protocols

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1 Intensity (a.u.) Supporting Information Well-defined Colloidal 2-D Layered Transition Metal Chalcogenide Nanocrystals via Generalized Synthetic Protocols Sohee Jeong, Dongwon Yoo, Jung-tak Jang, Minkyoung Kim, Jinwoo Cheon * Department of Chemistry, Yonsei University, Seoul , Korea * To whom correspondence should be addressed. jcheon@yonsei.ac.kr These authors contributed equally on this manuscript. Instruments TEM and HRTEM analyses are performed on a JEM 2100 at 200 kv and a JEOL-ARM1300S at 1250 kv, respectively. X-ray diffraction (XRD) studies are conducted using a Rigaku-G equipped with a Cu kα radiation source (30 kv, 15 ma). Elemental analysis is studied using energy dispersive X-ray spectroscopy (EDS, INCA, Oxford Instrument). A. TEM image and X-ray diffraction patterns of TiS 2 nanocrystals synthesized with elemental S. TiCl 4 (2.0 mmol), oleylamine (11.2 mmol), and elemental S (4.0 mmol) are added to a threeneck flask under Ar and the reaction mixture is heated to 300 o C. The resulting TiS 2 nanocrystals have irregular shape, size, and low crystallinity. a b θ Figure S1. (a) TEM image and (b) XRD patterns of TiS 2 nanocrystals synthesized with elemental S. Red lines indicate reference peaks of TiS 2 (JCPDS ). S1

2 B. Size controlled synthesis of TiS 2 nanocrystals. When TiCl 4 (1.5 mmol) and CS 2 (5.0 mmol) are reacted, 150 nm lateral size of TiS 2 nanocrystals are obtained (Figure 1e(i)), whereas the increase of reagent concentration of both TiCl 4 and CS 2 by 1.3 times results in 100 nm of TiS 2 nanocrystals (Figure 1e(ii)). Further increase of concentrations by 1.6 times and 2.4 times results in smaller TiS 2 nanocrystals of 60 nm and 40 nm, respectively (Figure 1e(iii), (iv)). Thus, the results show that reactant concentration is an important factor in governing the lateral size of the formed nanocrystals, where fast nucleation at high reactant concentration affords a large number of seeds, which yields small sized particles. In addition, the layered TMC nanocrystals tend to show preferential lateral growth in ab plane (Figure 1f). C. Synthesis of 2-D TiS 2, VS 2, NbS 2, TaS 2, ZrS 2, and HfS 2 nanocrystals. Representative procedure: Titanium (IV) chloride (0.22 ml, 2.0 mmol) and oleylamine (3.0 g, 11.2 mmol) are added to a 25 ml three-neck round-bottom flask under Ar atmosphere. To remove air and impurities with low boiling point, the mixtures are evacuated for 10 minutes. After purging with Ar, the reaction mixture is first heated to 300 o C at the heating rate 5 o C/min. When reaction temperature reaches at 300 o C, CS 2 (0.39 ml, 6.6 mmol) is injected into the reaction mixture. After 15 min, the reaction is stopped and cooled down to room temperature by removing heating source. By addition of excess butanol, the resulting TiS 2 nanocrystals are precipitated with the centrifugation. The nanoparticles are washed with hexane (2.0 ml) and methanol (3.0 ml). The resulting nanoparticles are redispersed in toluene. Other metal sulfide nanocrystals are synthesized under same reaction conditions with slight modification as follows. VS 2 : Vanadium (IV) chloride (0.14 g, 0.73 mmol) is mixed with oleylamine (5.0 g, 18.7 mmol). CS 2 (0.15 ml, 2.5 mmol) is injected into the flask at the 330 o C. After 6 h, the resulting VS 2 nanocrystals are obtained. NbS 2 : Niobium (V) chloride (0.12 g, 0.73 mmol) is mixed with oleylamine (3.0 g, 11.2 mmol). CS 2 (0.30 ml, 5.0 mmol) is injected into the flask at the 300 o C. After 3 h, the resulting NbS 2 nanocrystals are obtained. S2

3 TaS 2 : Tantalum (V) chloride (0.26 g, 0.73 mmol) is mixed with oleylamine (3.0 g, 11.2 mmol). CS 2 (0.30 ml, 5.0 mmol) is injected into the flask at the 300 o C. After 1.5 h, the resulting TaS 2 nanocrystals are obtained. ZrS 2 : Zirconium (IV) chloride (0.17 g, 0.73 mmol) is mixed with oleylamine (5.0 g, 18.7 mmol). CS 2 (0.30 ml, 5.0 mmol) is injected into the flask at the 300 o C. After 3 h, the resulting ZrS 2 nanocrystals are obtained. HfS 2 : Hafnium (IV) chloride (0.23 g, 0.73 mmol) is mixed with oleylamine (3.0 g, 11.2 mmol). CS 2 (0.30 ml, 5.0 mmol) is injected into the flask at the 300 o C. After 12 h, the resulting HfS 2 nanocrystals are obtained. The top and side views of 2-D metal sulfide nanocrystals are analyzed by TEM studies. TEM images show group V TMCs VS 2 (Figure 2a ), NbS 2 (Figure 2b ) and TaS 2 (Figure 2c ) nanocrystals with 18 nm (σ 8%), 100 nm (σ 30%), and 120 nm (σ 19%) in lateral size, respectively. In addition, the group IV TMCs ZrS 2 (Figure 2d ) and HfS 2 (Figure 2e ) nanocrystals are obtained in lateral sizes of 20 nm (σ 10 %) and 20 nm (σ 14%), respectively. A top-view HRTEM image of a VS 2 nanocrystal shows lattice fringes with interplanar spacings of 2.8 Å and 1.6 Å corresponding to the (100) and (110) planes of the hexagonal 1T VS 2, respectively (Figure 2a ). In the side view, a VS 2 nanocrystal is composed of (001) layers with an interplanar spacing of 5.7 Å. (Figure 2a ). The FFT image of a VS 2 nanocrystal shows hexagonal patterns corresponding to the (100) and (110) reflections from the top view and (001) reflections from the side view, respectively (Figure 2a,a insets). Likewise, the HRTEM and FFT images of NbS 2 (2H type), TaS 2 (2H type), ZrS 2 (1T type), and HfS 2 (1T type) also show 2-D layered structures and interplanar spacings of, 6.0 Å, 6.0 Å, 5.8 Å, and 5.9 Å for each nanocrystal (Figure 2b -e ), respectively. The XRD patterns (Figure S2) show that all the diffraction peaks of 2-D metal sulfide nanocrystals are well matched to the reference peaks. Each of VS 2, NbS 2, ZrS 2, and HfS 2 layered nanocrystals has about three to four layers, whereas TaS 2 layered nanocrystal has about six layers (Figure 2a -e ). S3

4 D. XRD characterization of group IV and V transition metal sulfide nanocrystals All the diffraction peaks of metal sulfide nanocrystals are good agreement with the reference peaks of group IV and V transition metal sulfide nanocrystals with hexagonal symmetry (red lines indicate reference peaks: VS 2 (ICDS ID 45214), NbS 2 (JCPDS ), TaS 2 (ICSD ID 65400), ZrS 2 (JCPDS ), and HfS 2 (JCPDS )). Figure S2. XRD patterns of (a) VS 2, (b) NbS 2, (c) TaS 2, (d) ZrS 2, and (e) HfS 2 nanocrystals. E. Synthesis of 2-D TiSe 2, ZrSe 3, HfSe 3, VSe 2, NbSe 2, and TaSe 2 nanocrystals. Representative procedure: Titanium (IV) chloride (0.53 ml, 0.5 mmol) and elemental Se (0.78 mg, 1.0 mmol) are added to oleylamine (1.6 g, 6.0 mmol). To remove air and impurities, the mixtures are evacuated for 10 min. After purging with Ar, the reaction mixture is first heated to 300 o C at the heating rate 5 o C/min. After 0.5 h, the reaction is stopped and cooled down to room temperature by removing heating source. Butanol is added to the reaction mixture and the precipitate formed is retrieved by centrifugation. The nanoparticles are washed with hexane (2.0 ml) and methanol (3.0 ml). Other metal selenide nanocrystals are synthesized under same reaction conditions with slight modification as follows. ZrSe 3 : Zirconium (IV) chloride (0.17 g, 0.73 mmol) and elemental Se (1.13 mg, 1.46 mmol) are added to oleylamine (4.0 g, 14.9 mmol). After 1 h, the resulting ZrSe 3 nanocrystals are S4

5 obtained. HfSe 3 : Hafnium (IV) chloride (0.23 g, 0.73 mmol) and elemental Se (1.13 mg, 1.46 mmol) are added to oleylamine (3.0 g, 11.2 mmol). After 1 h, the resulting HfSe 3 nanocrystals are obtained. VSe 2 : Vanadium (IV) chloride (0.14 g, 0.73 mmol) and elemental Se (1.13 mg, 1.46 mmol) were added to oleylamine (3.0 g, 11.2 mmol). After 1 h, the resulting VSe 2 nanocrystals are obtained. NbSe 2 : Niobium (V) chloride (0.20 g, 0.73 mmol) and elemental Se (1.13 mg, 1.46 mmol) are added to oleylamine (3.0 g, 11.2 mmol). After 2 h, the resulting NbSe 2 nanocrystals are obtained. TaSe 2 : Tantalum (V) chloride (0.26 g, 0.73 mmol) and elemental Se (1.13 g, 1.46 mmol) are added to oleylamine (3.0 g, 11.2 mmol). After 1 h, the resulting TaSe 2 nanocrystals are obtained. TEM images show ZrSe 3 (Figure S3a ) and HfSe 3 (Figure S3b ) nanocrystals with 20 nm (σ 18%) and 90 nm (σ 18%) in transverse diameters, respectively. In case of VSe 2 (Figure S3c ), NbSe 2 (Figure S3d ), and TaSe 2 (Figure S3e ) nanocrystals, the respective lateral sizes are 150 nm (σ 28%), 45 nm (σ 21%), and 150 nm (σ 30%). A top view HRTEM image of a ZrSe 3 nanocrystal shows lattice fringes with interplanar spacing of 5.3 Å and 3.0 Å corresponding to the (100) and (110) planes of the monoclinic ZrSe 3 nanocrystal, respectively (Figure S3a ). The side view indicates that the ZrSe 3 nanocrystal is composed of (001) layers with an interplanar spacing of 9.3 Å (Figure S3a ). Moreover, the FFT images of a monoclinic ZrSe 3 nanocrystal show patterns corresponding to the (100) and (110) reflections from the top view and the (001) reflections from the side view (Figure S3a,a inset). Similarly, HfSe 3 nanocrystals are shown to have lattice fringes with interplanar distances of 5.3 Å, 3.0 Å, and 9.3 Å corresponding to the (100), (110), and (001) planes, respectively (Figure S3b,b ). The inset FFT image contains monoclinic patterns corresponding to the characteristic spots of the monoclinic structure (Figure S3b,b inset). Also, VSe 2 (1T type), S5

6 NbSe 2 (2H type), 11b and TaSe 2 (2H type) have hexagonal structure with 6.1 Å, 6.3 Å, and 6.3 Å interplanar spacings, which are confirmed by the HRTEM images, the FFT images, and XRD patterns (Figure S3c -e and S4). Figure S3. (a-e) Illustration of shape of 2-D metal selenide nanocrystals. TEM images of (a ) ZrSe 3 (20 nm ± 3.5 nm), (b ) HfSe 3 (90 nm ± 16.2 nm), (c ) VSe 2 (150 nm ± 42 nm), (d ) NbSe 2 (45 nm ± 9.4 nm), and (e ) TaSe 2 (150 nm ± 45 nm). (a -e ) Top and (a -e ) sideview HRTEM images of metal selenide nanocrystals. TEM images show ZrSe 3 (Figure S3a ) and HfSe 3 (Figure S3b ) nanocrystals with 20 nm (σ 18%) and 90 nm (σ 18%) in transverse diameters, respectively. In case of VSe 2 (Figure S3c ), NbSe 2 (Figure S3d ), and TaSe 2 (Figure S3e ) nanocrystals, the respective lateral sizes are 150 nm (σ 28%), 45 nm (σ 21%), and 150 nm (σ 30%). A top view HRTEM image of a ZrSe 3 nanocrystal shows lattice fringes with interplanar spacing of 5.3 Å and 3.0 Å corresponding to the (100) and (110) planes of the monoclinic ZrSe 3 nanocrystal, respectively (Figure S3a ). The side view indicates that the ZrSe 3 nanocrystal is composed of (001) layers with an interplanar spacing of 9.3 Å (Figure S3a ). Moreover, the FFT images of a monoclinic ZrSe 3 nanocrystal show patterns corresponding to the (100) and (110) reflections from the top view and the (001) S6

7 reflections from the side view (Figure S3a,a inset). Similarly, HfSe 3 nanocrystals are shown to have lattice fringes with interplanar distances of 5.3 Å, 3.0 Å, and 9.3 Å corresponding to the (100), (110), and (001) planes, respectively (Figure S3b,b ). The inset FFT image contains monoclinic patterns corresponding to the characteristic spots of the monoclinic structure (Figure S3b,b inset). Also, VSe 2 (1T type), NbSe 2 (2H type), 1 and TaSe 2 (2H type) have hexagonal structure with 6.1 Å, 6.3 Å, and 6.3 Å interplanar spacings, which are confirmed by the HRTEM images, the FFT images, and XRD patterns (Figure S3c -e and S4). F. XRD characterization of group IV and V transition metal selenide nanocrystals All the diffraction peaks of metal selenide nanocrystals are good agreement with the reference peaks of group IV and V transition metal selenide with monoclinic or hexagonal symmetry (red lines indicate reference peak: ZrSe 3 (JCPDS ), HfSe 3 (JCPDS ), VSe 2 (ICSD ID 45215), NbSe 2 (JCPDS ), and TaSe 2 (JCPDS )). Figure S4. XRD patterns of (a) ZrSe 3, (b) HfSe 3, (c) VSe 2, (d) NbSe 2, and (e) TaSe 2 nanocrystals. S7

8 G. TEM image of TiSe 2 nanocrystals treated with azobisisobutyronitrile (AIBN). As-synthesized TiSe 2 (1.0 mmol) in oleylamine (11.2 mmol) is treated with AIBN (0.5 mmol) at 300 o C for 1 h, respectively. Degradation of TiSe 2 is clearly observed (Figure S5). Figure S5. (a) TEM image of TiSe 2 nanocrystals treated with AIBN. H. TEM images of ZnS nanocrystals treated with AIBN. ZnS nanocrystals are synthesized according to the literature procedure. 2 As-synthesized ZnS (1.0 mmol) is treated with AIBN (0.5 mmol) in oleylamine (11.2 mmol) at 300 o C for 1 h, respectively. As shown in Figure S6, any change of ZnS is not observed. Figure S6. TEM images of ZnS nanocrystals treated with AIBN. References 1. Sekar, P.; Greyson, E. C.; Barton, J. E.; Odom T. W. J. Am. Soc. Chem. 2005, 127, Joo, J.; Na, H. B.; Yu, T.; Yu, J. H.; Kim. Y. W.; Wu, F.; Zhang, J. Z.; Hyeon, T. J. Am. Chem. Soc. 2003, 125, S8