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Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer.

Song JG, Ryu GH, Lee SJ, Sim S, Lee CW, Choi T, Jung H, Kim Y, Lee Z, Myoung JM, Dussarrat C, Lansalot-Matras C, Park J, Choi H, Kim H - Nat Commun (2015)

Bottom Line: The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap.Various spectroscopic and microscopic results indicate that the synthesized Mo1-xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number.Further, we demonstrate that a VCC Mo1-xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

View Article: PubMed Central - PubMed

Affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.

ABSTRACT
The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1-xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1-xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1-xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1-xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet-visible spectrophotometer results reveal that a VCC Mo1-xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1-xWxS2 multilayer. Further, we demonstrate that a VCC Mo1-xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

No MeSH data available.


Characterization of MoS2.(a–c) AFM images and (d) height profiles (along with white dashed line in AFM images) of transferred MoS2 on SiO2 substrate for 1l, 2l and 3l thickness, respectively. Scale bars, 0.5 μm. (e) Raman spectra and (f) PL spectra for 1l (red), 2l (blue) and 3l (black) MoS2 on SiO2 substrate. (g) HRTEM image of 1l MoS2 at a selected region and (inset) FFT pattern. Scale bars, 2 nm.
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f2: Characterization of MoS2.(a–c) AFM images and (d) height profiles (along with white dashed line in AFM images) of transferred MoS2 on SiO2 substrate for 1l, 2l and 3l thickness, respectively. Scale bars, 0.5 μm. (e) Raman spectra and (f) PL spectra for 1l (red), 2l (blue) and 3l (black) MoS2 on SiO2 substrate. (g) HRTEM image of 1l MoS2 at a selected region and (inset) FFT pattern. Scale bars, 2 nm.

Mentions: Next, layer-number-controlled MoS2 was synthesized utilizing the two-step sulfurization process described above. Figure 2a–d shows the AFM images and height profiles of the transferred MoS2, which were synthesized by sulfurizing MoOx thin films deposited by 6, 9 and 12 ALD cycles. The measured thicknesses of the synthesized MoS2 were ∼1, 1.6 and 2.3 nm for 6, 9 and 12 MoOx ALD cycles, respectively. These thicknesses correspond to mono-, bi- and tri-layer (1, 2 and 3l) MoS2, considering that the height of 1l MoS2 on SiO2 is ∼1 nm and the spacing between the first and second MoS2 layers is ∼0.6 nm (refs 3, 4). As reported previously, the larger AFM-measured spacing between the first MoS2 layer and the substrate, compared with that between the MoS2 layers, is caused by the effect of distinct tip–sample and tip–substrate interactions33032. Also, the apparent colour gains of the transferred 1, 2 and 3l MoS2 are observed in optical microscopy (OM) images (Supplementary Fig. 2). It should be noted that the MoS2 is not formed in the case of an ALD MoOx thin film with an ALD cycle number of <3 (Supplementary Fig. 3). This is attributed to a nucleation delay during the initial growth of the MoOx, and similar behaviour was observed during the synthesis of WS2 by sulfurization of ALD WO3 (ref. 30). After the nucleation delay, 1l of MoS2 is formed by the sulfurization of each three-cycle ALD MoOx thin film sample (∼0.8−0.9 nm in thickness). This observation agrees with a previous report, where ∼1 nm of MoOx film transformed into a 1l MoS2 via sulfurization33. The stoichiometry calculated from X-ray photoemission spectroscopy (XPS) result is 2 (S/Mo) as shown in Supplementary Fig. 4. As a result, we can systematically control the layer number of MoS2 by controlling the ALD MoOx cycle number.


Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer.

Song JG, Ryu GH, Lee SJ, Sim S, Lee CW, Choi T, Jung H, Kim Y, Lee Z, Myoung JM, Dussarrat C, Lansalot-Matras C, Park J, Choi H, Kim H - Nat Commun (2015)

Characterization of MoS2.(a–c) AFM images and (d) height profiles (along with white dashed line in AFM images) of transferred MoS2 on SiO2 substrate for 1l, 2l and 3l thickness, respectively. Scale bars, 0.5 μm. (e) Raman spectra and (f) PL spectra for 1l (red), 2l (blue) and 3l (black) MoS2 on SiO2 substrate. (g) HRTEM image of 1l MoS2 at a selected region and (inset) FFT pattern. Scale bars, 2 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4525162&req=5

f2: Characterization of MoS2.(a–c) AFM images and (d) height profiles (along with white dashed line in AFM images) of transferred MoS2 on SiO2 substrate for 1l, 2l and 3l thickness, respectively. Scale bars, 0.5 μm. (e) Raman spectra and (f) PL spectra for 1l (red), 2l (blue) and 3l (black) MoS2 on SiO2 substrate. (g) HRTEM image of 1l MoS2 at a selected region and (inset) FFT pattern. Scale bars, 2 nm.
Mentions: Next, layer-number-controlled MoS2 was synthesized utilizing the two-step sulfurization process described above. Figure 2a–d shows the AFM images and height profiles of the transferred MoS2, which were synthesized by sulfurizing MoOx thin films deposited by 6, 9 and 12 ALD cycles. The measured thicknesses of the synthesized MoS2 were ∼1, 1.6 and 2.3 nm for 6, 9 and 12 MoOx ALD cycles, respectively. These thicknesses correspond to mono-, bi- and tri-layer (1, 2 and 3l) MoS2, considering that the height of 1l MoS2 on SiO2 is ∼1 nm and the spacing between the first and second MoS2 layers is ∼0.6 nm (refs 3, 4). As reported previously, the larger AFM-measured spacing between the first MoS2 layer and the substrate, compared with that between the MoS2 layers, is caused by the effect of distinct tip–sample and tip–substrate interactions33032. Also, the apparent colour gains of the transferred 1, 2 and 3l MoS2 are observed in optical microscopy (OM) images (Supplementary Fig. 2). It should be noted that the MoS2 is not formed in the case of an ALD MoOx thin film with an ALD cycle number of <3 (Supplementary Fig. 3). This is attributed to a nucleation delay during the initial growth of the MoOx, and similar behaviour was observed during the synthesis of WS2 by sulfurization of ALD WO3 (ref. 30). After the nucleation delay, 1l of MoS2 is formed by the sulfurization of each three-cycle ALD MoOx thin film sample (∼0.8−0.9 nm in thickness). This observation agrees with a previous report, where ∼1 nm of MoOx film transformed into a 1l MoS2 via sulfurization33. The stoichiometry calculated from X-ray photoemission spectroscopy (XPS) result is 2 (S/Mo) as shown in Supplementary Fig. 4. As a result, we can systematically control the layer number of MoS2 by controlling the ALD MoOx cycle number.

Bottom Line: The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap.Various spectroscopic and microscopic results indicate that the synthesized Mo1-xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number.Further, we demonstrate that a VCC Mo1-xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

View Article: PubMed Central - PubMed

Affiliation: School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea.

ABSTRACT
The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1-xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1-xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1-xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1-xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet-visible spectrophotometer results reveal that a VCC Mo1-xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1-xWxS2 multilayer. Further, we demonstrate that a VCC Mo1-xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

No MeSH data available.