Layer Number Dependence of MoS2 Photoconductivity Using Photocurrent Spectral Atomic Force Microscopic Imaging
| Autor: | Ananth Govind Rajan, Bassam Alfeeli, Richard D. Braatz, Joel A. Paulson, Chih-Jen Shih, Michael S. Strano, Sojin Kim, Young-Woo Son, Kevin Tvrdy, Qing Hua Wang |
|---|---|
| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | ACS Nano. 9:2843-2855 |
| ISSN: | 1936-086X 1936-0851 |
| DOI: | 10.1021/nn506924j |
| Popis: | Atomically thin MoS2 is of great interest for electronic and optoelectronic applications because of its unique two-dimensional (2D) quantum confinement; however, the scaling of optoelectronic properties of MoS2 and its junctions with metals as a function of layer number as well the spatial variation of these properties remain unaddressed. In this work, we use photocurrent spectral atomic force microscopy (PCS-AFM) to image the current (in the dark) and photocurrent (under illumination) generated between a biased PtIr tip and MoS2 nanosheets with thickness ranging between n = 1 to 20 layers. Dark current measurements in both forward and reverse bias reveal characteristic diode behavior well-described by Fowler-Nordheim tunneling with a monolayer barrier energy of 0.61 eV and an effective barrier scaling linearly with layer number. Under illumination at 600 nm, the photocurrent response shows a marked decrease for layers up to n = 4 but increasing thereafter, which we describe using a model that accounts for the linear barrier increase at low n, but increased light absorption at larger n creating a minimum at n = 4. Comparative 2D Fourier analysis of physical height and photocurrent images shows high spatial frequency spatial variations in substrate/MoS2 contact that exceed the frequencies imposed by the underlying substrates. These results should aid in the design and understanding of optoelectronic devices based on quantum confined atomically thin MoS2. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|