Valence Band Structure Engineering in Graphene Derivatives

Abstract

Engineering of the 2D materials’ electronic structure is at the forefront of nanomaterials research nowadays, giving an advance in the development of next‐generation photonic devices, e‐sensing technologies, and smart materials. Herein, employing core‐level spectroscopy methods combined with density functional theory (DFT) modeling, the modification of the graphenes’ valence band (VB) upon its derivatization by carboxyls and ketones is revealed. The appearance of a set of localized states in the VB of graphene related to molecular orbitals of the introduced functionalities is signified both experimentally and theoretically. Applying the DFT calculations of the density of states projected on the functional groups, their contributions to the VB structure are decomposed. An empirical approach, allowing one to analyze and predict the impact of a certain functional group on the graphenes’ electronic structure in terms of examination of the model molecules, mimicking the introduced functionality, is proposed and validated. The interpretation of the arising states origin is made and their designation, pointing out their symmetry type, is proposed. Taken together, these results guide the band structure engineering of graphene derivatives and give a hint on the mechanisms underlying the alteration of the VB structure of 2D materials upon their derivatization.

Manifesting Epoxide and Hydroxyl Groups in XPS Spectra and Valence Band of Graphene Derivatives

“…This assertion was further verified by the 13 C NMR solid-state spectra of the E-xy and H-xy graphenes displayed in Figure 2 b. The acquired spectra are consistent with the literature data on GO, with the set of peaks at the chemical shifts of δ = 58 ppm, δ = 68 ppm, δ = 95 ppm, δ = 133 ppm, δ = 167 ppm, and δ = 191 ppm corresponding to hydroxyls, epoxides, ethers (O-C-O), sp 2 -hybridized carbon atoms of the unfunctionalized graphene network, carboxyl groups, and ketone groups, respectively [ 34 , 50 ]. Apparently, despite being presented in both materials, the epoxides and hydroxyls differed in their concentration in the E-xy graphene and H-xy graphene, with the dominance of epoxide in the former one and hydroxyls in the latter one.…”

“…Recently, we have revealed the appearance of a set of localized molecular-related states in graphene’s VB upon its derivatization by carboxyl groups and ketones [ 34 ], as the most stable oxygen groups in GO. In turn, no substantial effect of basal-plane thiol groups on the DOS of the graphene layer has been identified for the thiolated graphene [ 35 ].…”

“…Herein, taking advantage of our recent advances in XPS and theoretical studies of other graphene derivatives [ 34 , 35 ], the fingerprints of epoxide and hydroxyl groups in the C 1 s XPS and C K XAS spectra, as well as the molecular-related states in the valence band (VB), are revealed via the systematic study of diversely oxidized graphene layers by a set of spectroscopic methods complemented by density functional theory (DFT) modeling. Based on the comparative study of the XPS spectra with the NMR and infrared (IR) spectroscopy data, the distinctive spectral components related to the epoxide and hydroxyl groups were discerned and characterized in the C 1 s spectra.…”

A Blueprint for the Synthesis and Characterization of Thiolated Graphene

“…Compared to the WF value, no considerable effect of graphene functionalization by thiols to the VB structure was found. This is in contrast to the recently revealed introduction of new localized states related to the molecular orbitals of ketones and carboxyl groups upon the modification of graphene layer edges by the corresponding functional groups [ 84 ]. In the case of rGO–Th, the VB structure almost completely represents the one of pristine rGO ( Figure 5 b).…”

“…Finally, the observed Z peak at BE of 24.8 eV and C peak at BE of 10.1 eV rise in the acquired spectra. The former one is related to the C 1 s line excited by photons with energy of 390 eV due to incompletely damped diffraction third order, while the latter one originates from the electronic states of the σ(C=O) bonds in ketones and carboxyl groups [ 84 ]. It is worth noting that C ′ peak centered at 11.1 eV in the GO VB spectrum is due to the mix of the aforementioned states of the σ(C=O) bonds in ketones and carboxyl groups with the states of the π(O-C-O) and σ(O-H) in carboxyls, which are abundant in highly oxidized GO.…”