Magnetic Defects in Transitional Metal Di-Chalcogenide Semiconducting Layers
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.110
Magnetic Defects in Transitional Metal DiChalcogenide Semiconducting Layers L. M. Martinez1, M. D. Teran1, R. R. Chianelli1, S. R. J. Hennadige2, S. R. Singamaneni1* 1
Department of Physics, The University of Texas at El Paso, El Paso, Texas 79968, USA.
2
Department of Chemistry, The University of Texas at El Paso, El Paso, Texas 79968, USA.
ABSTRACT
In this work, we report on the electron spin resonance (ESR) studies performed on fewlayered nanocrystalline (NCs) MoS2, WS2, and TiS2 prepared using hydrothermal and vapor transport methods. From the temperature dependent ESR spectra collected from MoS 2 NCs, we have identified adsorbed oxygen species, sulphur vacancies, thio- and oxo-Mo5+ related paramagnetic defect centers. WS2 NCs have exhibited W+3 and oxo-W+5 paramagnetic defect spin species. TiS2 NCs showed defects such as Fe3+ (unwanted), oxygen and sulfur vacancies. This work demonstrates the usage of spin-sensitive spectroscopy such as ESR in unravelling the defects which contain unpaired electron spin centers in layered NCs two-dimensional materials. *[email protected]
INTRODUCTION Transition metal dichalcogenides (TMDs) are semiconducting materials of the form MX2 (M = Mo, W, Ti and X = S or Se) that have been attracting increasing research attention for quite some time [1-3]. This is due to fact that the band gap of these materials can be tuned from direct to indirect as the layer thickness is reduced from bulk to mono/few layered level. In addition, these materials have been widely researched for their outstanding optical and catalytic properties [4-8]. However, most of these properties strongly depend on the identification and understanding of intrinsic and extrinsic defects which can be formed during the sample growth process or can be introduced from the precursor material as foreign impurities [9-11]. Some of these defects such as sulfur vacancies and Mo antisites can be used to induce and improve the catalytic and magnetic properties. However, some of the defects (such as unwanted impurities) could be detrimental for their optoelectronic properties. Many techniques such as transmission electron microscopy (TEM) and scanning tunneling microscopy (STM) were used to probe the defects [9-11]. These techniques are of great value in probing the structure and morphology of these defects.
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But, these techniques are severely limited by sample volume, their destructive nature, and they introduce artifacts. Hence, these techniques cannot provide information on the entire sample volume, particularly if the defects contain unpaired electron spins. On the other hand, electron spin resonance (ESR) spectroscopy probes the entire sample volume and non-destructive. It is an exclusive technique of choice in atom
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