Visic et al. Nanoscale Research Letters 2011, 6:593 http://www.nanoscalereslett.com/content/6/1/593 Page 5 of 6 Figure 5 XRD of the exfoliated nanotubes. X-ray spectra of (a) the exfoliated MoS2 in a wet, paste-like form and (b) the material after drying. unaltered. For the exfoliated bulk material, the evidence of restacking starts to occur in a few days with the reap- pearing of A and B excitons at 700 nm [11]. On the contrary, for the exfoliated nanotubes, this effect was not observed even after 3 months. The XRD patterns of the MoS2 nanotubes, exfoliated nanotubes in a wet, paste-like form, and dry, restacked MoS2 nanolayers are presented in Figures 4 and 5. Fig- ure 4 shows the XRD spectrum of MoS2 nanotubes used for exfoliation, with the peaks indexed in accor- dance with the hexagonal lattice parameters after Joint Committee on Powder Diffraction Standards card num- ber 77-1716. The spectrum of the exfoliated material was recorded in a wet, paste-like form in order to avoid drying and restacking. The absence of the (00l) peaks suggests the majority of single layers in the sample. The (002) peak is highly asymmetric with a sawtooth shape. This effect was explained as the indication of the pre- sence of the superlattice [8]. When the sample is dried, all of the peaks characteristic for 2H-MoS2 reappear. To quantify the effective size of the particles for the nanotubes and wet, paste-like MoS2, the broadening of Table 1 The calculated effective particle size of the given reflections the XRD lines is considered by applying the Debye- Scherrer equation: L = Kλ βCosθ , where L is the effective particle size, K is the shape factor, b is the XRD line broadening at half the maxi- mum intensity given in radians, l is the wavelength of X-rays, and θ is the scattering angle. In order to use the equation, peaks must be broadened due to crystallite size, not due to instrument optics, so the peaks that are not well resolved are not taken into account. The results are summarized in Table 1. Conclusion Exfoliated MoS2 coaxial nanotubes are produced via chemical exfoliation, resulting in single-layer flakes that are stable for months, with a low degree of restacking. Both X-ray spectra and TEM images confirm that the material is indeed composed of MoS2 monolayers. In addition, UV-Vis spectra show a strong quantum con- finement effects. The relatively simple process of getting one-layer-thick MoS2 can be used to provide new types of materials with possible applications in polymer com- posites, photovoltaics, and nanoelectronics. Acknowledgements The authors thank Janez Jelenc for the AFM images and Janez Kovac for the useful discussions. Author details 1Jozef Stefan Institute, Jamova cesta 39, Ljubljana, 1000, Slovenia 2National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, 1000, Slovenia 3Centre of Excellence Namaste, Jamova 39, Ljubljana, 1000, Slovenia Authors’ contributions BV acquired and interpreted the data, carried out the analysis and Uv-Vis measurements, and drafted the manuscript. RD helped in the chemical part by carrying out the lithium intercalation. MKG and NH participated in the additional UV-Vis measurements. SDS acquired the XRD data. MR has been involved in revising the manuscript and has given the final approval of the version to be published. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Reflection (002) (100) (103) (105) (110) (200) b (rad) Effective particle size (nm) MoS2 nanotubes 0.01 - 0.04 0.05 0.01 0.03 Exfoliated MoS2 0.08 0.02 0.07 0.08 - - MoS2 nanotubes 15 ± 1 - 5 ± 1 5 ± 1 30 ± 1 15 ± 1 Exfoliated MoS2 2 ± 1 7 ± 1 3 ± 1 3 ± 1 - -