Electronic supplementary material

Fabrication of Tin Monosulfide Nanosheet Arrays Using Laser Ablation

Jin-Gu Kang,1Young-Dae Ko,1 Kyung Jin Choi,1 Jae-Gwan Park,1 and Dong-Wan Kim2,3

1Nanomaterials Center, KoreaInstitute of Science and Technology, Seoul 136-791, Korea

2Department of Materials Science and Engineering, AjouUniversity, Suwon 443-749, Korea

3Author to whom any correspondence should be addressed. Tel.: +82 312192468; fax: +82 312191956.

E-mail : (D. W. Kim)

Fig. S1 Schematic diagram of PLD synthetic system for SnS nanosheet growth. A pulsed KrF excimer laser (1) was focused (2) onto the SnS cylindrical target (3) placed in the center of the quartz tube (4), maintained at 590oC by electric furnace (5) and 0.01 ~ 0.03 Torr by evacuation (6). Three SS substrates (7) were laid at different positions, located 14.5, 16 and 18 cm distant from the center of the furnace. The magnified illustration includes the synthetic temperatures of the three substrates that were measured with an R-type thermocouple. As the synthetic temperature decreased,the thin film underwent morphological evolution to nanosheets.

Fig. S2 FESEM image of the SnS raw powders with lamellar microstructures used for preparing the target of the PLDprocess.

Fig. S3 FESEM images of the SnS nanosheets deposited on Si substrate for 2 min.

Fig. S4 EPMA measurement for quantitative analysis of the SnS nanosheets. This analysis revealed the almost 1:1 stoichiometric composition between the Sn and S atoms, which is the same as that of the pristine SnS target.

In-plane growth

In general, the preferential growth direction of the nanostructures is determined to have the minimum free energy consisting of the surface energy and the strain energy.R1 Hence, the sheet evolutions towards [101] andhave the minimum free energies, even though the reason for their energetic favorability has not yet been clarified. Strictly, the free energy created by [101] growth may differ slightly from that bygrowth due to the highly distorted, rock-salt crystal structure of the orthorhombic SnS.R2,R3 Despite this difference, the morphological formation of a widespread sheet rather than a narrow nanobelt suggests that the growth rates of both directions should be comparably facile.

In orthorhombic crystal systems, the three lattice constants differ from one another. Therefore, strictly speaking, a particular direction [hkl] is not perfectly normal to a particular plane (hkl) in real lattice space, so that the two actual growth directions in SnS nanosheets deviate slightly from [101] and . Furthermore, the (101) and lattice planes, which seem to be perpendicular to each other, do not actually satisfy orthogonality but deviate slightly from it due to variation amongthe lattice constants. This indicates that in real systems, one smooth edge is not exactly perpendicular to the other, as discussed above. Although general orthorhombic systems possess such anomalies resulting from the crystallographic characteristics, we could exclude these anomalies from our analysis of the in-plane growth of the nanosheets because the lattice constants of the a- and c-directions showed fewdifferences in the orthorhombic SnS crystal.

References

[R1]X. L. Gou, J. Chen, P.W. Shen, Mater. Chem. Phys. 2005, 93, 557-566.

[R2]Y.Li, J. P. Tu, X. H. Huang, H. M. Wu, Y. F. Yuan, Electrochim. Acta. 2006, 52, 1383-1389.

[R3]S. J. Kwon, J. Phys. Chem. B 2006, 110, 3876-3882.

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