Copyright © 2016 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 16, 1–4, 2016 www.aspbs.com/jnn Effects of Precursor Concentration on Morphology of MoS 2 Nanosheets by Hydrothermal Synthesis Chang Min Lee, Geun Chul Park, Seung Muk Lee, Jun Hyuk Choi, Sang Hyeon Jeong, Tae Yang Seo, Seung-Boo Jung, Jun Hyung Lim ∗ , and Jinho Joo ∗ School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, Korea MoS 2 nanosheets were fabricated with different precursor concentrations to investigate their effects on crystal structure, chemical state of elements, and morphology. MoS 2 nanosheets were prepared by conventional hydrothermal routes at 200  C for 24 h, while maintaining the Mo/S precursor mol ratio of 1:12. The XRD and XPS analyses showed that a hexagonal structure of 2H-MoS 2 nanosheets was formed without a second phase for all samples and crystallinity was enhanced along the c-axis with increasing precursor concentration. The FESEM and TEM images revealed that MoS 2 nanosheets were aggregated and formed nanoflowers, and that their irregular shape changed to nearly spherical as the concentration increased. The size of the nanoflowers was closely related to the dimension of the nanosheets and their sizes slightly increased with increasing con- centration ranging from 0.14 M to 0.7 M, then rapidly increased at 1.4 M. We believe that these results are related to not only the enhanced growth rate but also the decreased additives-absorption on the S layers with precursor concentration. Keywords: Mesoporous Tin Oxide, Hazardous Gas Sensor, Impregnated Palladium. 1. INTRODUCTION In recent years, MoS 2 has attracted much attention because of its two-dimensional (2D) structure. The MoS 2 mono- layer consists of three atomic layers; a Mo atom layer is sandwiched between two S atom layers and Mo and S atoms bond covalently within the three layers. MoS 2 nanosheets are stacked along the c-axis and held together by van der Waals interactions. The structure of MoS 2 shows promising properties such as weak van der Waals interactions, faceted edges, high electric performance, and chemical stability, which are important in applications in solid superlubricants, 1 catalysts, 2 hydrogen storage, 3 sensors, 4 Li ion batteries, 5 6 and solar cells. 7 Efforts have been concentrated on enhancing the properties of MoS 2 nanosheets, and the thickness of nanosheets is an important factor for applications because the thickness relates to the band gap energy and type, 8 work function, 9 charge trans- port properties, 10 and so on. When the thickness decreases to below 100 nm, the band gap increases and reaches about 1.9 eV for a monolayer, 8 while bulk MoS 2 has a band gap of 1.3 eV. In addition, the reduction in thickness leads ∗ Authors to whom correspondence should be addressed. to a change in the band gap from indirect to direct and increases the work function. 9 To achieve superior MoS 2 nanosheets, the hydrother- mal process has been widely used due to its ease in the control of morphology, high uniformity and crystallinity, acceptable yield, and reduced cost. In the hydrothermal process, the pH adjustment, sulfur source content, and pre- cursor concentration are important experimental conditions for the control of the thickness of the nanosheets. 11–13 The pH adjustment affects the sulfurated reaction or reduc- tion reaction during the formation of MoS 2 , and hence the thickness decreases as the amount of pH adjustment increases. 5 A reduced thickness was also obtained when the precursor ratio of S to Mo was reduced from 3 to 2. 11 However, the effect of precursor concentration has rarely been reported and, in the few reports, the results are not consistent each other. Xie et al. reported that the thickness of nanosheets was reduced as precursor concen- tration increased, 12 but Li et al. showed that the thick- ness increased with increasing precursor concentration. 13 In this current work, we synthesized MoS 2 nanosheets by hydrothermal method and evaluated the effects of precursor concentration on the thickness, morphology, J. Nanosci. Nanotechnol. 2016, Vol. 16, No. xx 1533-4880/2016/16/001/004 doi:10.1166/jnn.2016.13549 1