Growth Mechanism for Single- and Multi-Layer MoS2 Nanocrystals

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• 作者：Lars P. Hansen ; Erik Johnson ; Michael Brorson ; Stig Helveg
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：October 2, 2014
• 年：2014
• 卷：118
• 期：39
• 页码：22768-22773
• 全文大小：349K
• ISSN：1932-7455

文摘

Transmission electron microscopy (TEM) is used to study growth of MoS₂ nanocrystals in situ. The nanocrystals are formed from a submonolayer molybdenum oxide dispersed on an oxide support by sulfidation in an H₂S/H₂ atmosphere. From series of time-resolved TEM images, it is revealed that single-layer MoS₂ nanocrystals form preferentially and that multi-layer nanocrystals form late in the sulfidation process. The TEM images pinpoint that step sites in the support can act as nucleation centers for single-layer nanocrystals and that single-layer nanocrystals grow along the support surface. Moreover, the TEM images reveal that multi-layer MoS₂ nanocrystals form in a layer-by-layer mode by the homogeneous nucleation of additional MoS₂ layers onto already formed single-layer MoS₂ nanocrystals. Hereby, the atomic-scale observations suggest that the formation of multi-layer MoS₂ nanocrystals is an energetically more activated process than growth of single-layers. These findings explain why process parameters, such as temperature, can tune the relative fraction of single- to multi-layer MoS₂ nanocrystals, which is important for their use in, e.g., hydrotreating catalysis.