Abstract
Despite the great promise of InSe for electronic and optoelectronic applications, Fröhlich interaction plays an important role in electrical transport due to the polar nature of it, which can become more significant in reduced dimensionality. Here, we report on how the dimensionality influences the strength and nature of the Fröhlich polaronic effect in InSe with the aid of plasmonic hot electrons injection. Polar optical phonons couple to hot electrons via the Fröhlich interaction in InSe and enable us to monitor them in conventional Raman measurements. We observed that the intensity of these phonon modes initially increases gradually with decreasing layer number and then drops drastically from 7 L to 6 L (transition from quasi-direct to indirect bandgap at room temperature). Additionally, a gradual decrease of intensity of the polar modes with further decreasing layer number is observed due to the increasing indirect bandgap nature of InSe suggesting reduced Fröhlich coupling below this thickness.
Highlights
Despite the great promise of InSe for electronic and optoelectronic applications, Fröhlich interaction plays an important role in electrical transport due to the polar nature of it, which can become more significant in reduced dimensionality
We studied the Fröhlich interaction in InSe by monitoring the strength of polar longitudinal optical phonons (LO) modes induced by injected plasmonic hot electrons
The combination of the strong local field at the corners of the NTs and the hot electrons generated due to near localized surface plasmon resonance (LSPR) excitation activates and enhances these polar phonon modes enabling their observation in the Raman measurements
Summary
Despite the great promise of InSe for electronic and optoelectronic applications, Fröhlich interaction plays an important role in electrical transport due to the polar nature of it, which can become more significant in reduced dimensionality. 1234567890():,; Among all 2D semiconductors, InSe (a member of metal monochalcogenides) has emerged as an outstanding candidate for post-silicon electronic devices It possesses a high electron mobility (~103 cm2V−1 s−1) due to its small effective mass (~0.14 me) at room temperature (RT)[1]. Ma et al.[7] and Li et al.[10] laid the theoretical ground for understanding the To accomplish this goal, a systematic investigation of layerdependent Fröhlich interaction in InSe via the injection of plasmonic hot electrons was performed. The electric field carried by the free carrier plasmons (here the hot electrons collected by the CB of InSe) interact with the long-range macroscopic field of the longitudinal optical phonons (LO) breaking the Raman selection rules[14]. Raman spectroscopy can directly measure coupled modes[15] enabling the investigation of the polar LO phonons via plasmonic hot electrons doping as a function of InSe layer number
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