1. The document discusses optimizing the growth conditions for monolayer tungsten disulfide (WS2) using chemical vapor deposition (CVD). 2. Experiments were conducted varying the weight of WO3 precursor, carrier gas flow rate of argon, and reaction time to determine the optimal conditions for high quality monolayer WS2 growth. 3. The best results were obtained with 20mg of WO3, 200mg of S2, 850°C temperature, 150 sccm argon gas flow rate, and 15 minute reaction time, yielding 40 micron WS2 with a band gap of 1.97eV.

1. Optimization of Growth Condition for
Monolayered Tungsten Disulphide
By- Aditya Narayan Singh
IPH/10034/17
Integrated MSc, Physics, 2017
Supervisor – Dr Dilip Kumar Singh
Assistant Professor
Department of Physics
Birla Institute of Technology

2. Contents
• Introduction
• Properties of WS2
• Specific Applications
• CVD process and schematics
• Growth mechanism
• Results
• Summary
• References
2

3. Introduction
2-D materials
• What ?
• Why ?
• Future ?
• WS2 shows very interesting properties when it is monolayered , as high carrier mobility makes it good for transistors and
FETs, and Photoresponsivity is very high when photodetector is fabricated from monolayer WS2
• Comes under the family of transition metal Di chalcogenides with the form MX2.
• Have a tuneable band gap ranges from 1.2 eV to 1.98 eV depending on the number of layers.
3
* Zouyuan et al.Molecules 2019, 24(1), 88

4. Properties of WS2 Monolayer
1. Photodetector responsivity – (0.1-5.7) A W-1
2. Two phases 2H and 1T, 2H is more stable than 1T phase. Fig 2
3. Raman peaks at 351 cm-1, 356 cm-1 and 417 cm-1 on Raman shift scale. Means monolayer formation is there as
the gap between two peaks is less than 54 cm-1 . Fig 1
4
Fig 1 Fig 2
*Maceij R Molas et al. Scientific Reports 7,5036
*Rasidul islam et al. 2nd International Conference on Electrical & Electronic Engineering (ICEEE), 27-29 December 2017
*A N Barbosa et al. Materials Chemistry and Physics. 2020 Mar 1

5. 5
Direct band gap
semiconductor
monolayered, strong PL
efficiency confirms the
statement, band gap
ranges from (1.82-1.98)
eV.
Fig 3 & 4
Fig 3
Fig 4
High carrier mobility (ranges from
0.01 to 0.91 cm2 V −1 s −1 ) but
reacts less with chalcogen.
• Mak et al. Physical review letters 105, no. 13 (2010)
• Weijie Zhao et al. ACS Nano 2013, 7, 1, 791–797

6. 1. Transistors(FETs and MOSFETs)
2. Photo – Detectors
3. Gas Sensors(ammonia specially)
4. Chemical Sensing
5. Electro Catalysis
6. Optical Modulators
7. Communication Devices
8. Light sources fabrication
SPECIFIC APPLICATIONS
6
* Wonbong choi et al. materials today volume 20
issue 3, April 2017.

7. CVD process and schematics
1. Nucleation (isolation of nuclei, of order angstrom). Fig 6
2. Nuclei growth (nuclei becomes larger). Fig 7
3. Island coalescence (start finding each other and forms clusters)
4. Bulk film
7
Fig 6
Fig 5
Fig 7

8. Growth Mechanism
A single zone furnace used
Weight of WO3 – (10, 15, 20) mg
Weight of S2 – 200 mg
Growth temperature – 850 centigrade
Reaction time – 15 minutes
Position of WO3 precursor – at centre of furnace
Position of S2 precursor – 17 cm from centre
Carrier gas flow – 50, 100, 150 sccm (argon)
50 100 150 200 250 300
0
100
200
300
400
500
600
700
800
900
30
150
150
850
850
250
Temperature(
0
C)
Time (minutes)
8
Temperature of CVD throughout the reaction

9. 9
Optical and FESEM Image of the WS2 Sample Prepared by Variation of WO3
10 mg 15 mg 20 mg

10. Sl no S2 (mg) WO3 (mg) Gas flow Rn time Result
1 200 10 100 15 Growth
2 200 15 100 15 Growth
3 200 20 100 15 Growth
10
Effect of WO3 Weight Variation
WS2 grown based on 20 mg of
WO3 there is four peaks, peak 1
at 295.8 cm-1 , peak 2 at 322.2
cm-1 , peak 3 at 350.6 cm-1 and
peak 4 at 417.8 cm-1 in the
spectra
Peak difference are, 27 cm-1 28
cm-1, 68 cm-1

11. 11
Photoluminescence curve of WO3 Weight variation
Bandgap
1.96 eV  632 nm
1.95 eV  634 nm

12. 12
Optical and FESEM Image of the WS2 Sample Prepared by Variation of Gas Flow.
50 sccm 100 sccm 150 sccm

13. Sl no S2 (mg) WO3 (mg) Gas flow Rn time Result
1 200 20 50 15 No Growth
2 200 20 100 15 Growth
3 200 20 150 15 Growth
13
Effect of Carrier Gas Flow Variation
WS2 grown based on 150 sccm
there is four peaks, peak 1 at 296
cm-1 , peak 2 at 323.2 cm-1 , peak
3 at 351.6 cm-1 and peak 4 at
418.3 cm-1 in the spectra
Peak difference are, 26 cm-1 28
cm-1, 66 cm-1

14. 14
Bandgap
1.97 eV  630 nm
1.92 eV  643 nm
Photoluminescence Curve of Gas Flow Variation

15. 15
SUMMARY
1. We have been able to grow 2D WS2 with side length 40 microns with the condition , WO3 weight 20 mg,
S2 weight 200mg, temperature 850 ᵒC , Ar gas flow was kept 150 sccm , reaction time was 15 minutes.
2. The band gap was found to be 1.97 eV for the above mentioned condition

16. 16
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