Atomistic mechanisms of codoping-induced p- to n-type conversion in nitrogen-doped graphene

Abstract

It was recently shown that nitrogen-doped graphene (NG) can exhibit both p- and n-type characters depending on the C-N bonding nature, which represents a significant bottleneck for the development of graphene-based electronics. Based on first-principles calculations, we herein scrutinize the correlations between the atomic and electronic structures of NG and particularly explore the feasibility of converting p-type NG with pyridinic, pyrrolic, and nitrilic N atoms into n- or bipolar type by introducing an additional dopant atom. Of the nine candidates B, C, O, F, Al, Si, P, S, and Cl, we find that B-, Al-, and P-codoping can anneal even relatively large vacancy defects in p-type NG. It will be also shown that, while the NG with pyridinic N can be converted into the n-type via codoping, only a bipolar type conversion can be achieved for the NG with nitrilic or pyrrolic N. The amount of work function reduction was up to 0.64 eV for the pyridinic N next to a monovacancy. The atomistic origin of such diverse type changes is analyzed based on Mulliken and crystal orbital Hamiltonian populations, which provide us with a framework to connect the local bonding chemistry with the macroscopic electronic structure in doped and/or defective graphene. Moreover, we demonstrate that the proposed codoping scheme can recover the excellent charge transport properties of pristine graphene. Both the electronic type conversion and conductance recovery in codoped NG should have significant implications for the electronic and energy device applications.

Nitrogen Dopants in Carbon Nanomaterials: Defects or a New Opportunity?

“…While two carbon atoms around the Pyr‐N 1 can form a pentagon‐like structure (from D 3h to C s ), Pyr‐N 3 preserves the graphitic‐plane structural symmetry (D 3h ) . As Pyr‐N 3 has fewer electrons compared to pristine graphene (considering MV defects), it exhibits a p‐type band structure due to the electron deficiency . For N arrangement around a DV defect, where two C atoms are removed, theoretical and experimental studies have shown that four N atoms energetically prefer to substitute the C atom with unpaired electrons and form Pyr‐N 3 (Figure d) .…”

“…As Pyr‐N 3 has fewer electrons compared to pristine graphene (considering MV defects), it exhibits a p‐type band structure due to the electron deficiency . For N arrangement around a DV defect, where two C atoms are removed, theoretical and experimental studies have shown that four N atoms energetically prefer to substitute the C atom with unpaired electrons and form Pyr‐N 3 (Figure d) . In this case, porphyrinic N (labelled Por‐N 4 ) refers to a configuration with four pyridinic N atoms in a porphyrinic planar architecture, which has a similar formation energy (2.55 eV) to that of Pyr‐N 3 (2.51 eV) .…”

Covalent functionalization of N-doped graphene by N-alkylation

“…Therefore, N-doping provides the possibility of tuning the band gap of graphene which makes these doped materials great candidates for applications in electronic devices. 10,11,12 It should also be considered that doping could play an adverse effect by deteriorating the thermal and mechanical properties of G. Compared to doping of graphene with elements such as nitrogen, chemical functionalization of G using techniques such as alkylation are based on standard organic reactions through which a wide spectrum of functional groups can be anchored onto G. In principle, doped G could also be modified by specific reactions at the dopant heteroatom through different routes depending on the nucleophilic or electrophilic nature of the dopant element. 2 Specifically, in the present case, pyridinic N atoms in (N)G should act as anchoring sites for N-alkylation reactions often used in organic chemistry.…”

Nitrogen Doping of Carbon Nanoelectrodes for Enhanced Control of DNA Translocation Dynamics

“…Recent experimental studies have shown that the nature of Ndoped graphene can be rather complicated due to the diverse atomic bonding possibilities, 70 and we recently demonstrated that the Mulliken charge visualization is a powerful tool to develop the atomistic understanding of the bonding nature of N atoms embedded in an sp 2 carbon network. 71 A key finding from these studies was that there arise significant local charge fluctuations near the substitutional N atoms before a rather uniform net electron doping is achieved in the long-range region (beyond ~ 7 Å radius). For the N-doped graphene, we found the Mulliken population of −0.402 e per nitrogen atom, 71 which is in good agreement with the experimentally estimated value of −0.42 e. 70 We will now show that overall similar N-induced charge transfer characters are developed even within the curved geometry of CNT caps.…”