Electronic Structure of Colloidal 2H‐MoS₂ Mono and Bilayers Determined by Spectroelectrochemistry

Abstract

The electronic structure of mono and bilayers of colloidal 2H‐MoS2 nanosheets synthesized by wet‐chemistry using potential‐modulated absorption spectroscopy (EMAS), differential pulse voltammetry, and electrochemical gating measurements is investigated. The energetic positions of the conduction and valence band edges of the direct and indirect bandgap are reported and observe strong bandgap renormalization effects, charge screening of the exciton, as well as intrinsic n‐doping of the as‐synthesized material. Two distinct transitions in the spectral regime associated with the C exciton are found, which overlap into a broad signal upon filling the conduction band. In contrast to oxidation, the reduction of the nanosheets is largely reversible, enabling potential applications for reductive electrocatalysis. This work demonstrates that EMAS is a highly sensitive tool for determining the electronic structure of thin films with a few nanometer thicknesses and that colloidal chemistry affords high‐quality transition metal dichalcogenide nanosheets with an electronic structure comparable to that of exfoliated samples.

From Light to Dark: Dancing with Electrons in Colloidal 2D MoS2 Nanosheets

“…These changes are reversible as evident from the restoration of the spectral features after turning off the light. Similar changes in the exciton spectral features in MoS 2 films have also been observed under the application of electrochemical bias. , …”

Quantifying interfacial energetics of 2D semiconductor electrodes using in situ spectroelectrochemistry and many-body theory

“…Importantly, quantifying the extent to which applied potential, BGR, and other effects, such as illumination, tune the semiconductor band energies in these low dimensional materials remains a largely open question inspiring active research. 13,26 In addition, the large band edge movement is significant because it violates a key assumption in the field of semiconductor electrochemistry: k ET is essentially independent of E because the band edges are ''fixed''. 7 This assumption means E CB and E VB are independent of applied potential (E) and, therefore, DG1 0 is independent of E, too.…”

Quantifying interfacial energetics of 2D semiconductor electrodes using in situ spectroelectrochemistry and many-body theory

“…Importantly, quantifying the extent to which applied potential, BGR, and other effects, such as illumination, tune the semiconductor band energies in these low dimensional materials remains a largely open question inspiring active research. 13,26 In addition, the large band edge movement is significant because it violates a key assumption in the field of semiconductor electrochemistry: kET is essentially independent of 𝐸 because the band edges are "fixed". 7 This assumption means ECB and EVB are independent of applied potential (𝐸) and, therefore, Δ𝐺 ∘′ is independent of 𝐸, too.…”

“…2A agree with literature spectroelectrochemistry data for thin films of few-layer MoS2 nanosheets and colloidal film electrodes. 13,26 However, little attention has been paid to the potentialdependent A-exciton lineshape for ML-MoS2 in liquid electrolyte. Fig.…”