研究目的
To identify the layer number of CVD-grown MoS2 nanosheets efficiently and accurately using an optical method based on contrast differences in the R channel of optical images.
研究成果
The optical method using R channel contrast differences efficiently and accurately identifies the layer number of CVD-grown MoS2 nanosheets, providing a simple and feasible alternative to techniques like AFM and Raman spectroscopy. This supports future applications in optoelectronics by enabling rapid thickness assessment without expensive instruments.
研究不足
The method is primarily effective for identifying layer numbers up to 4 layers; for more layers, contrast differences may decrease, reducing accuracy. The study is limited to CVD-grown MoS2 on SiO2/Si substrates, and external factors like doping or impurities could affect results.
1：Experimental Design and Method Selection:
The study involved synthesizing MoS2 nanosheets via CVD and characterizing them using optical microscopy, Raman spectroscopy, and photoluminescence (PL) spectroscopy to explore the relationship between optical contrast and layer number. The method focused on extracting contrast differences from optical images using ImageJ software.
2：Sample Selection and Data Sources:
MoS2 nanosheets were grown on SiO2/Si substrates using CVD. Samples included individual triangular nanosheets and stacked or merged nanosheets with varying thicknesses.
3：List of Experimental Equipment and Materials:
Equipment included a CVD system with a quartz tube, furnace, heating ring, mass flow controller for N2, Olympus microscope (BX41RF-LED) with CCD detector, and Raman spectrometer (Renishaw inVia). Materials included S powder (Alfa Aesar, 99.999%), MoO3 powder (Alfa Aesar, 99.95%), and Si wafers with 300nm SiO
4：999%), MoO3 powder (Alfa Aesar, 95%), and Si wafers with 300nm SiOExperimental Procedures and Operational Workflow:
2. 4. Experimental Procedures and Operational Workflow: MoS2 synthesis involved heating the furnace to specific temperatures with controlled N2 flow, placing substrates, and cooling. Characterization involved capturing optical images, splitting into R, G, B channels with ImageJ, measuring contrast, and performing Raman and PL spectroscopy with a 514nm laser.
5：Data Analysis Methods:
Contrast differences (CDR) were calculated from optical images. Raman peak positions and differences (E1 2g and A1g) were analyzed to determine layer number, and PL spectra were examined for band gap changes.
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Microscope
BX41RF-LED
Olympus
Used for capturing optical images of MoS2 nanosheets.
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Raman Spectrometer
inVia
Renishaw
Used for performing Raman spectra and photoluminescence (PL) spectra measurements.
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Mass Flow Controller
Used for controlling the flow of high purity N2 gas in the CVD system.
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Quartz Tube
Part of the CVD system for housing the reaction.
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Furnace
Used for heating in the CVD process.
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S Powder
Alfa Aesar
Source material for sulfur in the CVD synthesis of MoS2.
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MoO3 Powder
Alfa Aesar
Source material for molybdenum in the CVD synthesis of MoS2.
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Si Wafer
Substrate for growing MoS2 nanosheets, with a SiO2 layer.
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ImageJ Software
Used for processing optical images to extract contrast differences in R, G, B channels.
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