Adhesion Energy of Phosphorene on Different Pristine and Oxidized Metallic Substrates

TL;DR

The study addresses how substrate chemistry influences the lubricating performance of black phosphorus by quantifying the adhesion of phosphorene to metal substrates. Using spin-polarized density functional theory with dispersion corrections and DFT+$U$, the authors compute adhesion energies $E_{ ext{adh}}$ for pristine and oxidized phosphorene on Al, Cu, Fe, Cr and on their oxides Al$_2$O$_3$, Cu$_2$O, Fe$_2$O$_3$, Cr$_2$O$_3$. Key findings show oxidized phosphorene binds more strongly across all substrates, with Cr and Fe providing the strongest interactions due to partially filled 3d states, accompanied by notable charge redistribution $Q_{ ext{red}}$ and, in some cases, metallic character in phosphorene. These results correlate with experimental tribological trends, reinforcing layer–substrate adhesion as a primary determinant of friction reduction and guiding substrate design for BP-based solid lubricants.

Abstract

Black phosphorus and its single-layer constituent, phosphorene, have emerged as promising two-dimensional materials with remarkable tribological properties. However, recent experimental investigations revealed that the their lubricating capabilities can change with the substrate. The present computational study employs density functional theory calculations to quantify the adhesion energy of both pristine and oxidized phosphorene monolayers on various metallic substrates (aluminum, copper, iron, and chromium) and their corresponding oxides ($\mathrm{Al_2O_3}$, $\mathrm{Cu_2O}$, $\mathrm{Fe_2O_3}$, and $\mathrm{Cr_2O_3}$), correlating these interfacial property with experimentally observed tribological performance. Results demonstrate that oxidized phosphorene presents higher adhesion to all substrates with respect to pristine phosphorene, attributed to favorable interactions between oxygen non-bonding states and substrate empty states. Adhesion is systematically more favorable on pristine metals than on their corresponding oxides, with chromium and iron showing particularly strong interactions due to partially filled 3d orbitals. This result is consistent with the coefficient of friction decrease observed in tribological experiments after scratching the iron substrate, thus removing the outermost oxide layer. Charge redistribution correlates with the adhesion and electronic structure analyses reveal system-dependent interfacial bonding characteristics, with some configurations inducing metallic character in phosphorene. These findings provide fundamental insights into substrate-dependent lubricating properties of black phosphorus, highlighting the key role of layer-substrate adhesion.

Figures (5)

• Figure 1: Comparison between pristine and oxidized phosphorene structures. (a) Bottom view and (c) side view of pristine phosphorene. (b) Bottom view and (d) side view of oxidized phosphorene with 25% of oxygen coverage, determined as the most stable configuration for oxidized phosphorene benini2023interaction.
• Figure 2: Relaxed geometries of the supercells: (a, b) pristine and oxidized phosphorene on aluminum, (c, d) pristine and oxidized phosphorene on copper, (e, f) pristine and oxidized phosphorene on iron, (g, h) pristine and oxidized phosphorene on chromium, (i, j) pristine and oxidized phosphorene on $\mathrm{Al_2O_3}$ Al-terminated, (k, l) pristine and oxidized phosphorene on $\mathrm{Al_2O_3}$ O-terminated, (m, n) pristine and oxidized phosphorene on $\mathrm{Fe_2O_3}$ Fe-terminated, (o, p) pristine and oxidized phosphorene on $\mathrm{Fe_2O_3}$ O-terminated, (q, r) pristine and oxidized phosphorene on $\mathrm{Cu_2O}$ O-terminated, (s, t) pristine and oxidized phosphorene on $\mathrm{Cr_2O_3}$ Cr-terminated. Color code: P atoms are shown in yellow, Al in grey, Fe in purple, Cu in orange, Cr in cyan, and O in red.
• Figure 3: Adhesion energies for every phosphorene-substrate system.
• Figure 4: RMSD analysis for every phosphorene-substrate system.
• Figure 5: (a) Total electron charge redistribution per surface unit ($Q_{red}$) for every phosphorene-substrate system; (b) $\Delta\rho(z)$ and PDOS analysis for phosphorene deposited on pristine metals and (c) the corresponding oxides.