[Paper Review] Modification of the valence band electronic structure under Ag intercalation underneath graphite monolayer on Ni(111)

Yu. S. Dedkov, M. Poygin+4 more|arXiv (Cornell University)|Apr 25, 2003

Graphene research and applications3 citations

TL;DR

This study investigates silver intercalation beneath a graphite monolayer on Ni(111) using angle-resolved photoemission and Auger spectroscopy. Annealing at 350–450 °C induces 1–2 monolayers of Ag to intercalate, weakening the graphite-Ni interaction and shifting graphite-derived valence band states to lower binding energies by 1.5–2 eV for π states and 0.5–1 eV for σ states, indicating reduced hybridization due to screening by Ag.

ABSTRACT

Angle-resolved photoemission spectroscopy and Auger electron spectroscopy have been applied to study the intercalation process of silver underneath a monolayer of graphite (MG) on Ni(111). The room-temperature deposition of silver on top of MG/Ni(111) system leads to the islands-like growth of Ag on top of the MG. Annealing of the "as-deposited" system at temperature of 350-450 C results in the intercalation of about 1-2 ML of Ag underneath MG on Ni(111) independently of the thickness of pre-deposited Ag film (3-100 A). The intercalation of Ag is followed by a shift of the graphite-derived valence band states towards energies which are slightly larger than ones characteristic for pristine graphite. This observation is understood in terms of a weakening of chemical bonding between the MG and the substrate in the MG/Ag/Ni(111) system with a small MG/Ni(111) covalent contribution to this interaction.

Motivation & Objective

• To determine the optimal temperature for Ag intercalation beneath a graphite monolayer on Ni(111).
• To quantify the amount of Ag intercalated beneath the graphite monolayer using Auger electron spectroscopy.
• To investigate changes in the valence band electronic structure of graphite after Ag intercalation using angle-resolved photoemission spectroscopy.
• To understand the electronic interaction between the graphite monolayer and the Ni(111) substrate before and after Ag intercalation.

Proposed method

• Angle-resolved photoemission spectroscopy (ARPES) was used to probe the valence band electronic structure of the MG/Ag/Ni(111) system with 50 eV photon energy, 100 meV energy resolution, and 1° angular resolution.
• Auger electron spectroscopy (AES) with high kinetic energy electrons (1000 eV) and 0.25% relative energy resolution was employed to estimate the intercalated Ag amount, accounting for electron inelastic mean free path.
• UHV chambers with LEED, ion guns, and gas inlets enabled in situ sample preparation and characterization.
• Propylene (C₃H₆) was used to grow the graphite monolayer on Ni(111) via thermal cracking.
• Annealing at 350–450 °C was applied to the Ag-deposited MG/Ni(111) system to induce intercalation.
• Analysis of C, Ag, and Ni AES peak intensities was used to estimate the intercalated Ag thickness, independent of initial Ag deposition.

Experimental results

Research questions

• RQ1 What is the optimal annealing temperature range for Ag intercalation beneath a graphite monolayer on Ni(111) without system degradation?
• RQ2 How much Ag (in monolayers) intercalates beneath the graphite monolayer, and does this depend on the initial Ag thickness deposited on top?
• RQ3 How does Ag intercalation alter the valence band electronic structure of the graphite monolayer compared to the pristine MG/Ni(111) system?
• RQ4 What is the nature of the graphite-Ni(111) interaction after Ag intercalation, and how does it affect the electronic dispersion and hybridization?

Key findings

• The optimal intercalation temperature for Ag beneath the graphite monolayer on Ni(111) is 350–450 °C; above 500 °C, system degradation begins.
• The graphite-derived π states shift to lower binding energies by approximately 1.5–2 eV, and σ states by 0.5–1 eV, indicating reduced interaction with the Ni(111) substrate.
• Approximately 1–2 monolayers of Ag intercalate beneath the graphite monolayer, regardless of the initial Ag thickness (3–100 Å) deposited on top.
• The observed shift in valence band states is attributed to weakening of the π–d hybridization between graphite and Ni(111), with residual orbital mixing preserved after intercalation.
• Splitting of π states in ARPES spectra for polar angles >25° (k|| > 1.4 Å⁻¹) suggests possible domain misorientation or anisotropic electronic response in the graphite monolayer after Ag intercalation.
• LEED patterns show a (1×1) hexagonal structure with weak 15°-rotated strips, indicating ordered graphite-like domains with slight orientation mismatch relative to the Ni(111) substrate.