Article
Electric Gap Characterization at Mesoscopic Scale with Scanning Probe Microscopy
https://doi.org/10.21203/rs.3.rs-1461674/v1
This work is licensed under a CC BY 4.0 License
posted 24 Mar, 2022
You are reading this latest preprint version
We develop a scanning probe microscopic technique to characterize the electric gap with a spatial resolution of nanometre scale. The technique probes the electric gap by monitoring the change of the local quantum capacitance via the Coulomb force at the mesoscopic scale. We showcase this technique on several 2D semiconductors and van der Waals heterostructures at ambient conditions.
scanning probe microscopy
electric force microscopy
quantum capacitance
bandgap characterization
band alignment
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Supplementary Information is available for this paper.
Acknowledgments: This work was supported by MOST 2020YFA0309603 of the Ministry of Science and Technology of the People’s Republic of China; Croucher Foundation; GRF #17304518, CRF C7036-17W and AoE/P-701/20 of the Research Grant Council of Hong Kong. DL and XW thank Dr. Yipu Xia and Prof. Maohai Xie for providing the conductive silicon carbide substrate.
Author contributions: XC conceived and supervised the project. DL conducted the experiments and analyzed the data. DL and XW fabricated the sample. XM and ET provide support on AFM. DL and XC wrote the paper.
Competing interests: Authors declare no competing interests.
Sample preparation
The few-layer TMDC samples were cleaved from the single crystal via mechanical exfoliation method by using the Scotch tape and then directly transfer to a conductive substrate like ITO glasses. For van der Waal heterostructures, monolayer samples were exfoliated severally onto a silicon substrate and the thickness was confirmed by the AFM topography mapping. Then the heterostructure was fabricated via the hot pick-up technique43 and eventually transfer to a flat conductive silicon carbide substrate.
LEFM scanning
After the topography mapping of the sample, we move the AFM tip to the area we are interested in, retrace the tip with 50 nm, and then disable the z-feedback controller to maintain a constant tip-sample distance and start the regular EFM scanning. The scanning bias voltage is in the range of -2 V to 2 V. Then adjust the tip-sample distance to get an evident vibration amplitude-external bias curve. For the 2D TMDCs sample, this distance is around 44 nm. After getting an evident vibration amplitude-external bias curve from the regular EFM scanning, we decrease the height of the cantilever every 2 nm and monitor the change of the vibration amplitude-external bias curve. The platform-like curve is shown out when the tip-sample distance is in the range of 32-42 nm. The scanning bias voltage is the same as the regular EFM scanning.
Photoluminescence measurement
Photoluminescence measurement was conducted with a homemade PL measurement system with a 532nm continuous excitation laser. The laser was focused on the sample with a micron-size spot (ϕ ~ 3μm) and the intensity was around 2 W/cm2.
References
43 Pizzocchero, F. et al. The hot pick-up technique for batch assembly of van der Waals heterostructures. Nature Communications 7, 11894, doi:10.1038/ncomms11894 (2016).
There is NO Competing Interest.
Supplementary Information
posted 24 Mar, 2022
You are reading this latest preprint version