Thermal Annealing of Graphene Implanted with Mn at Ultralow Energies: From Disordered and Contaminated to Nearly Pristine Graphene

Abstract

Ultralow-energy (ULE) ion implantation is increasingly being explored as a method to substitutionally dope graphene. However, complex implantation-related effects such as defect creation and surface contamination, and how they can be minimized by thermal annealing, remain poorly understood. Here, we address these open questions taking as the model case epitaxial graphene grown on Cu(111), which was subsequently ULE implanted with Mn at 40 eV and then studied as a function of annealing temperature under ultrahigh vacuum. While significant surface cleaning occurs at annealing temperatures as low as 200 °C, recovery from the implantation-induced disorder requires at least 525 °C. Upon high-temperature annealing, in the 600−700 °C range, the Mn atoms that were incorporated upon implantation as intercalated species (between graphene and the Cu surface) experience diffusion into the Cu layer, creating a subsurface alloy. Annealing at 700 °C restored implanted graphene to a nearly pristine state, with a well-ordered graphene lattice with substitutional Mn atoms and a well-defined Dirac cone. In addition to the insight into the complex physicochemical effects induced by thermal annealing, our results provide useful guidelines for future experimental studies on graphene that is modified (e.g., substitutionally doped) by using ULE ion implantation.

Bond defects in graphene created by ultralow energy ion implantation

“…Ultralow energy (ULE) ion implantation, in which the ions have kinetic energies in the range of tens of eV, is increasingly being explored as a method to functionalize graphene. It has been successfully used to substitutionally dope graphene with N and B [1,2,3,4,5], P [6], Ge [7], Mn [8,9] and Au [10]. Recently, ULE ion implantation has also been used to create nanobubbles in graphene down to dimensions of 1 nm radius, in which the highly strained graphene layer holds the implanted (intercalated) noble-gas atoms at extremely high pressures [11].…”

Achieving High Substitutional Incorporation in Mn-Doped Graphene

“…This article focuses on the 700 °C annealed state, identified in the previous work as optimal in terms of ability to quantify the concentration of substitutional Mn, as well of minimal disorder and surface contamination. 8,9 Substitution Efficiency and Uniformity. As described in refs 8 and 9, scanning tunneling microscopy (STM) allows to identify and quantify the amount of substitutional Mn atoms incorporated in the graphene lattice (a single Mn atom substituting for a single C atom, i.e., located at a single C vacancy).…”

Lateral Controlled Doping and Defect Engineering of Graphene by Ultra-Low-Energy Ion Implantation

“…This has the advantage that, in contrast to deceleration by a capping layer [ 13 ], no recoil atoms from the capping layer enter the sample and thus only the desired atomic species is implanted and no contamination occur. For graphene and TMDs it has already been shown that properties and damage of the sample can be successfully tuned by means of laterally uniform ULE ion implantation [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. To further expand the capabilities of ULE ion implantation, we demonstrate how the surface of a graphene sample can be selectively modified by ion beams using laterally controlled implantation [ 21 ], paving the way for more complex implantation structures and thus the possibility of fabricating electrical 2D devices and the exploration of new scientific questions.…”