Desorption of n-alkanes from graphene: a van der Waals density functional study

TL;DR

This study uses van der Waals density functional calculations to analyze the desorption energy of n-alkanes from graphene, revealing a linear relationship with chain length and an offset consistent with experimental TPD data.

Contribution

It provides a theoretical explanation for the desorption energy scaling and offset observed experimentally, using advanced density functional methods.

Findings

Desorption energy scales linearly with chain length N.

An offset at N=0 explains the experimental data.

Polyethylene calculations suggest the offset's origin.

Abstract

A recent study of temperature programmed desorption (TPD) measurements of small n-alkanes (CNH2N+2) from C(0001) deposited on Pt(111) shows a linear relationship of the desorption energy with increasing n-alkane chain length. We here present a van der Waals density functional study of the desorption barrier energy of the ten smallest n-alkanes (N = 1 to 10) from graphene. We find linear scaling with N, including a nonzero intercept with the energy axis, i.e., an offset at the extrapolation to N = 0. This calculated offset is quantitatively similar to the results of the TPD measurements. From further calculations of the polyethylene polymer we offer a suggestion for the origin of the offset.