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EE9.34.1

The Structure of a Molybdenum Disulfide Intercalation Compound Ralf Brüning, Kristopher Bulmer, Rabin Bissessur1, Robert I. Haines1, Pravin Varma and Stephen Emeneau Physics Department, Mount Allison University, Sackville, New Brunswick, Canada E4L 1E6 1 Department of Chemistry, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada C1A 4P3 ABSTRACT The X-ray powder diffraction spectrum of MoS2 with intercalated 5,5,7,12,12,14-hexamethyl1,4,8,11-tetraazacyclotetradecane-1-acetic acid shows well-defined peaks as well as broad scattering. The X-ray scattering of this compound was simulated by generating model particles and calculating their X-ray scattering by evaluating the Debye sum. The match between the measured and simulated spectra was improved by trial-and-error. Matching the peak widths shows that the particles contain a total of about 6600 MoS2 units in about eight layers. The layers are oriented in the same direction (not turbostratic). However, they are translated randomly in the plane perpendicular to the stacking direction. In contrast to prior work on intercalation compounds, which considered various types of periodic reconstruction within the MoS2 layer, we obtain the best match with a non-periodic reconstruction in addition to a periodic superlattice. It involves dimer and trimer groupings of the molybdenum atoms with a random choice of centers. The intercalated tetraazamacrocycles form a two-dimensional glass. The effects of the key model assumptions on the calculated spectrum are demonstrated. INTRODUCTION Yang et al. found the structure of exfoliated single MoS2 layers suspended in water by comparing the X-ray scattering calculated for different models of these layers with the experimental data [1,2]. This model for the suspended layers consists 20
20 MoS2 units, and the Mo atoms are octahedrally coordinated with six S atoms [1]. Here we extend the approach of comparing calculated and measured diffraction patterns to a MoS2 intercalation compound. Particles of the compound considered here have about 8 MoS2 layers that are separated by gallery spaces. Organic molecules (tetraazamacrocycles) occupy these gallery spaces, as shown in figure 1(c). These particles flocculate from the aqueous suspension of single MoS2 layers upon adding the guest molecules [3,4]. As shown below, the present intercalation compound exhibits aspects of crystalline order, primarily the structure of the MoS2 layers, and substantial disorder: The intercalated molecules form a two-dimensional glass, and the stacking the MoS2 layers, while preserving orientation, involves random shifts of the layers. In an alternate approach, the structures of the ordered MoS2 intercalation compounds containing metal atoms (AgxMoS2 and LiMoS2) have been solved using atomic pair distribution function analysis [5,6]. This alternate approach matches the Fourier transform of diffraction data with the radial distribution of the atoms in the model.

EE9.34.2

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Figure 1. Spatial details of the model par