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Transition metal dichalcogenide growth via close proximity precursor supply.

O'Brien M, McEvoy N, Hallam T, Kim HY, Berner NC, Hanlon D, Lee K, Coleman JN, Duesberg GS - Sci Rep (2014)

Bottom Line: TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup.A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented.Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

View Article: PubMed Central - PubMed

Affiliation: 1] School of Chemistry, Trinity College Dublin, Dublin 2, Ireland [2] Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and Advanced Materials and BioEngineering Research (AMBER) Centre, Trinity College Dublin, Dublin 2, Ireland.

ABSTRACT
Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

No MeSH data available.


(a) Phase mode AFM image of the corresponding red box in Fig. 3(c). (b) Topography mode AFM image of the same area. (c) Height profiles over dark blue lines shown in (b).
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f5: (a) Phase mode AFM image of the corresponding red box in Fig. 3(c). (b) Topography mode AFM image of the same area. (c) Height profiles over dark blue lines shown in (b).

Mentions: Having established patterned growth, it is worthwhile to discuss the effectiveness of grain boundary closure in the films, as it is possible to investigate the same features with atomic force microscopy (AFM) and Raman. In Fig. 4 below, we have shown selected area growth of 100 μm features. The AFM phase mode and topography mode imaging scans in Fig. 5(a) and (b), respectively show that the film is flat over the area of the scan, and consists of individual grains that grow together. The phase map, which would have better lateral resolution in samples of different material properties, shows a higher response in the vicinity of the grain boundaries, as seen by comparison with the optical image, while the topography map indicates all the grain boundaries are slightly elevated in comparison with the rest of the film. Various height profiles over raised grain boundaries, as indicated by the dark blue lines in Fig. 5(b), are shown in Fig. 5(c). The height in each case was observed to be ~2.2 nm. This indicates that the areas shown are not gaps in the film, but rather buckled MoS2 which forms as the grains grow together and upwards from different crystal lattice orientations. Similar features have previously been observed for CVD graphene5455. The PL map in Fig. 4(d) also interestingly shows enhanced and diminished PL at different areas of the grain boundaries of the MoS2 monolayers. Previous reports have linked an increase in PL intensity with p-doping36 which suggests that these regions are sulfur rich. A decrease in PL intensity can similarly be attributed to n-doped molybdenum rich regions36, as discussed previously, and in the Supporting Information, section S5. Future TEM investigations will be required to confirm this observation, and allow further analysis of the grain boundaries present in the as-grown materials. The grain boundary observations also confirm that the monolayer films are continuous, while possessing boundaries and defects similar to those observed in CVD grown graphene56. We further propose that Raman and PL mapping could act as a quick and viable method to identify and locate the grain boundaries of monolayer materials grown on a variety of substrates. We envisage that this methodology could be extended to other members of the TMD family, such as the transition metal diselenides, and other layered material sets by varying the precursors chosen. As a proof of principle, we have also demonstrated the growth of WS2 monolayers using an analogous method, as shown in Section S6 of the Supporting Information, with similar high quality monolayers shown.


Transition metal dichalcogenide growth via close proximity precursor supply.

O'Brien M, McEvoy N, Hallam T, Kim HY, Berner NC, Hanlon D, Lee K, Coleman JN, Duesberg GS - Sci Rep (2014)

(a) Phase mode AFM image of the corresponding red box in Fig. 3(c). (b) Topography mode AFM image of the same area. (c) Height profiles over dark blue lines shown in (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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f5: (a) Phase mode AFM image of the corresponding red box in Fig. 3(c). (b) Topography mode AFM image of the same area. (c) Height profiles over dark blue lines shown in (b).
Mentions: Having established patterned growth, it is worthwhile to discuss the effectiveness of grain boundary closure in the films, as it is possible to investigate the same features with atomic force microscopy (AFM) and Raman. In Fig. 4 below, we have shown selected area growth of 100 μm features. The AFM phase mode and topography mode imaging scans in Fig. 5(a) and (b), respectively show that the film is flat over the area of the scan, and consists of individual grains that grow together. The phase map, which would have better lateral resolution in samples of different material properties, shows a higher response in the vicinity of the grain boundaries, as seen by comparison with the optical image, while the topography map indicates all the grain boundaries are slightly elevated in comparison with the rest of the film. Various height profiles over raised grain boundaries, as indicated by the dark blue lines in Fig. 5(b), are shown in Fig. 5(c). The height in each case was observed to be ~2.2 nm. This indicates that the areas shown are not gaps in the film, but rather buckled MoS2 which forms as the grains grow together and upwards from different crystal lattice orientations. Similar features have previously been observed for CVD graphene5455. The PL map in Fig. 4(d) also interestingly shows enhanced and diminished PL at different areas of the grain boundaries of the MoS2 monolayers. Previous reports have linked an increase in PL intensity with p-doping36 which suggests that these regions are sulfur rich. A decrease in PL intensity can similarly be attributed to n-doped molybdenum rich regions36, as discussed previously, and in the Supporting Information, section S5. Future TEM investigations will be required to confirm this observation, and allow further analysis of the grain boundaries present in the as-grown materials. The grain boundary observations also confirm that the monolayer films are continuous, while possessing boundaries and defects similar to those observed in CVD grown graphene56. We further propose that Raman and PL mapping could act as a quick and viable method to identify and locate the grain boundaries of monolayer materials grown on a variety of substrates. We envisage that this methodology could be extended to other members of the TMD family, such as the transition metal diselenides, and other layered material sets by varying the precursors chosen. As a proof of principle, we have also demonstrated the growth of WS2 monolayers using an analogous method, as shown in Section S6 of the Supporting Information, with similar high quality monolayers shown.

Bottom Line: TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup.A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented.Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

View Article: PubMed Central - PubMed

Affiliation: 1] School of Chemistry, Trinity College Dublin, Dublin 2, Ireland [2] Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and Advanced Materials and BioEngineering Research (AMBER) Centre, Trinity College Dublin, Dublin 2, Ireland.

ABSTRACT
Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

No MeSH data available.