Atomic-scale characterization of nitrogen-doped graphite: Effects of dopant nitrogen on the local electronic structure of the surrounding carbon atoms

Abstract: We report the local atomic and electronic structure of a nitrogen-doped graphite surface by scanning tunnelling microscopy, scanning tunnelling spectroscopy, X-ray photoelectron spectroscopy, and first-principles calculations. The nitrogen-doped graphite was prepared by nitrogen ion bombardment followed by thermal annealing. Two types of nitrogen species were identified at the atomic level: pyridinic-N (N bonded to two C nearest neighbours) and graphitic-N (N bonded to three C nearest neighbours). Distinct electronic states of localized {\pi} states were found to appear in the occupied and unoccupied regions near the Fermi level at the carbon atoms around pyridinic-N and graphitic-N species, respectively. The origin of these states is discussed based on the experimental results and theoretical simulations.

• The paper identifies two primary nitrogen species—pyridinic-N and graphitic-N—and details their distinct roles in altering local electronic states.
• It employs STM, STS, XPS, and DFT to analyze bonding configurations and detect localized states near the Fermi level with precise spectroscopic peaks.
• The findings suggest that tailored nitrogen doping can enhance the performance of carbon-based devices in nanoelectronics and energy applications.

Atomic Scale Characterization of Nitrogen-Doped Graphite: Insights into Local Electronic Structure Modifications

The paper provides an in-depth exploration of nitrogen-doped graphite, focusing specifically on atomic and electronic structural features using cutting-edge techniques such as scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The study explores the modifications in electronic structures induced by nitrogen dopants at the atomic level, elucidating the nature and implications of these changes through experimental and theoretical analyses.

The research identifies two primary nitrogen species within nitrogen-doped graphite: pyridinic-N and graphitic-N. These species exhibit distinctive bonding configurations with carbon atoms, resulting in diverse effects on the electronic structure near the Fermi level. The study systematically analyzes the local modification in electronic structures triggered by these nitrogen species and contextualizes these findings within the broader electronic landscape of nitrogen-doped graphite.

Methodology and Nitrogen Species Identification

Nitrogen-doped graphite samples were produced through nitrogen ion bombardment followed by thermal annealing. XPS analysis identified pyridinic-N and graphitic-N species as dominant components in the samples. Pyridinic-N species, where nitrogen is bonded to two carbon atoms, and graphitic-N species, where nitrogen bonds to three carbon atoms, were interrogated for their electronic impacts.

The STM and STS analyses revealed nuanced differences in the local electronic structures adjacent to these dopant sites. The pyridinic-N species were characterized by a rearrangement resulting in a pentagonal carbon ring structure. Conversely, graphitic-N integrates more seamlessly into the graphite lattice, minimally disturbing its structure.

Electronic Structure Implications

The electronic analysis near the Fermi level shows that pyridinic-N induces localized states in the occupied region, a finding supported by STS spectra indicating a prominent peak at approximately -370 mV. Theoretical simulations attribute this peak to localized π states. In this context, nitrogen atom’s negative charge alters the surrounding electronic environment, with potential applications as a Lewis base in molecular interactions.

Graphitic-N species, however, affect the electronic structure differently. The unoccupied region shows localized states with a key peak around +500 mV electronic structure, suggesting electron transfer from nitrogen to the carbon π system, which introduces a positive charge screened by adjacent carbons. This indicates potential functionality as a Lewis acid, opening avenues in electron transport devices.

Future Directions and Implications

The findings promise advancements in material science applications, potentially enhancing the functionality of devices that involve nitrogen-doped graphite, such as biosensors, electronics, and energy devices. Understanding the localized electronic states offers pathways for tailoring material properties through specific doping techniques.

The demonstrated ability to engineer electronic properties on an atomic scale outlines future research trajectories in material design. Subsequent investigations may explore the precise control over nitrogen concentration and its influence on electronic characteristics, thereby refining applications in nanoelectronics and energy conversion devices.

By uncovering detailed electronic structure changes associated with distinct nitrogen dopants, this paper enriches the foundational understanding required for the strategic design of advanced carbon-based materials. The integration of experimental and theoretical approaches underscores the importance of comprehensive characterization techniques in the landscape of modern material science research.