Twisted Nanostructures of 2H-MoS 2 Slabs
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1217-Y06-02
Twisted Nanostructures of 2H-MoS2 Slabs Manuel A. Ramos1, Domingo A. Ferrer2, Miguel José-Yacamán3, Gilles Berhault4, Brenda Torres1, Russell R. Chianelli1 1 Materials Research and Technology Institute, University of Texas at El Paso, El Paso, TX. 79968, U.S.A 2 Microelectronics Research Center, University of Texas at Austin, Austin, TX. 78751, U.S.A. 3 Department of Physics & Astronomy, University of Texas at San Antonio, San Antonio, TX. 78249, U.S.A 4 IRCELYON, CNRS – University of Lyon, Villeurbanne, 69100, France. ABSTRACT In the last decades, HRTEM approach has been quite fruitful to study structural characteristics of layered transition metal sulfide (LTMS) catalytic materials since providing direct local information about the structural organization of this quite important class of catalysts at the nanoscale level. However, up to now, HRTEM observations of some common localized structural organization like honeycomb-like structures have remained unexplained. In the present study, a structural model corresponding to stacked 2H-MoS2 slabs twisted along their basal direction is proposed to explain honeycomb like-structures observed by HRTEM. This model is based on a comparison between experimental and simulated images of 2H-MoS2 catalysts promoted with cobalt. The resulting Density of States (DOS) of the twisted structure was then calculated.
INTRODUCTION Molybdenum sulfide catalysts promoted with nickel or cobalt has been extensively studied in the last two decades [1] due to its quite important role in hydrotreating catalysts for the removal of sulfur-containing molecules contained in crude oil [2]. Many aspects in terms of atomistic structure and textural have been well defined in the literature using modern characterization tools such as X-ray diffraction, Mössbauer spectroscopy, and High Resolution Transmission Electron Microscopy. More recently, the application of quantum computational modeling to investigate the electronic structure of these solids has triggered a new interest in determining the local structure of 2H-MoS2 slabs at the atomic scale. Such calculations can be done using Ab initio and Monte Carlo techniques or Density Functional Theory methods which nowadays are available in commercial softwares i.e. Cerius2 or Material Studio [4,5,6]. One of the most fast and relevant characterization techniques is HRTEM since providing information about several physical properties like d-spacing, folding, surface contact, dislocations. However, even if 2H-MoS2 presents a very distinguishable layered structure characterized by “fringes” on HRTEM pictures, some features like honeycomb-like structure were never satisfactorily explained [7]. The objective of the present study was to address this problem by confronting experimental and theoretical HRTEM results.
EXPERIMENT HRTEM experiments were done using a JOEL 4000-EX TEM with a 0.17 nm of resolution equipped with a charge couple device camera. We present here a HRTEM simulation for two typical 2H-MoS2 slabs (“seeds”) models using simulaTEM c
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