Investigation on the Stability of MoS2(1-x)Te2x
Fabricated By Tellurization Using Organic Precursor (i-C3H7)2te
Authors: Hibino Yusuke , Ishihara Seiya , Yamazaki Kota , Oyanagi Yuya , Hashimoto Yusuke , Sawamoto Naomi , Machida Hideaki , Ishikawa Masato , Sudoh Hiroshi , Wakabayashi Hitoshi , Ogura Atsushi 
Published: February 2020

Recent work on the research of layered materials has revealed the material’s unique physical properties, its applications in various fields, and fabrication processes to produce high quality samples. We have been focusing on transition metal dichalcogenides (TMD) and its alloys. Fabrication of TMD alloys enables bandgap/band offset tuning which expands the application of TMD materials in various fields to a further extent. Although it has been predicted the fabrication of TMD alloys is difficult since the alloys are expected to be thermodynamically unstable [1,2], we have so far fabricated metal alloy, Mo1-x
W
x
S2 [3], and chalcogen alloy, MoS2(1-x)Te2x
[4]. In these studies, we have confirmed the control of composition by adjusting sputtering condition as well as bandgap and band offset shift according to the composition. However, the stability of the material, especially the change of physical properties over certain period of time, has not been discussed in depth despite the fact that such alloy material are thermodynamically unstable, as mentioned above. In addition, although there are numerous results on the fabrication differences, there are not many reports discussing on the stability of the fabricated films for TMDs [5]. In this study, we focused on the stability of the materials and optimization of fabrication condition in order to prevent degradation. MoS2(1-x)Te2x
alloys are fabricated by co-sputtering MoS2 and MoTe2 followed by tellurization by inorganic Te precursor, (i-C3H7)2Te, in H2 or N2 ambient. The samples were stored in a vacuum dessicator for a period of time (which we will refer as “storage time”) and then evaluated with X-ray photoelectron spectroscopy (XPS). It was revealed that depending on the carrier gas, or the ambient, during tellurization, the amount by which Mo is oxidized after the storage time is different despite the fact that the samples showed almost identical chemical state right after the tellurization. This may be attributed to the difference in grain size where H2 ambient may have produced films with smaller grain size, i.e. longer or more grain boundaries, resulting in more area to be oxidized compared to N2 ambient.
This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 18F22879 and 16J11377.

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Figure caption:
The Mo 3d spectra of MoS2(1-x)Te2x
samples fabricated with different gas ambient, obtained by XPS. The bottom spectra show there is no or only subtle oxidation, whereas after the storage time, samples undergo oxidation with sample fabricated in H2 ambient further oxidized than that fabricated in N2 ambient.

Figure 1