Increasing the Rate of Magnesium Intercalation Underneath Epitaxial Graphene on 6H‐SiC(0001)

Abstract

in condensed matter physics experiments due to its ease of production (typically via micromechanical cleavage) [1,2] and access to novel physics owing to its linear "Dirac" band structure at low energy. [3,4] But for graphene to be useful in device applications, we must be able to engineer [5] its electrical properties. To achieve this, various techniques such as surface chemical doping [6] or atom substitution (see refs. [5,7] for a brief review of these methods), gating, [8][9][10][11][12][13] proximity effects, [8,14] stacking, [15,16] and intercalation [17][18][19][20][21][22][23][24][25] (see ref. [26] for a brief review of intercalation) have been applied. Of these techniques, intercalation (i.e., the insertion of atoms or molecules beneath or in-between graphene sheets) has been demonstrated as a relatively simple and versatile method for achieving control over graphene's key electrical properties-carrier type, [17][18][19]21] conductivity, [20,[27][28][29] and bandgap. [25,30] For instance, engineering the carrier type and bandgap via intercalation could enable graphene p-n junctions [31][32] and transistors. [33] Whereas increasing graphene's conductivity via intercalation could enable highly conductive and transparent electrodes for solar cells, [34] interconnects, [35] or new superconductors. [20,36] Many of the intercalation experiments to date have utilized epitaxially synthesized graphene on SiC (either the 4H-or 6H-polytype on the (0001) orientation, i.e., silicon Magnesium intercalated "quasi-freestanding" bilayer graphene on 6H-SiC(0001) (Mg-QFSBLG) has many favorable properties (e.g., highly n-type doped, relatively stable in ambient conditions). However, intercalation of Mg underneath monolayer graphene is challenging, requiring multiple intercalation steps. Here, these challenges are overcome and the rate of Mg intercalation is significantly increased by laser patterning (ablating) the graphene to form micron-sized discontinuities. Low energy electron diffraction is then used to verify Mg-intercalation and conversion to Mg-QFSBLG, and X-ray photoelectron spectroscopy to determine the Mg intercalation rate for patterned and non-patterned samples. By modeling Mg intercalation with the Verhulst equation, it is found that the intercalation rate increase for the patterned sample is 4.5 ± 1.7. Since the edge length of the patterned sample is ≈5.2 times that of the non-patterned sample, the model implies that the increased intercalation rate is proportional to the increase in edge length. Moreover, Mg intercalation likely begins at graphene discontinuities in pristine samples (not step edges or flat terraces), where the 2D-like crystal growth of Mg-silicide proceeds. The laser patterning technique may enable the rapid intercalation of other atomic or molecular species, thereby expanding upon the library of intercalants used to modify the characteristics of graphene, or other 2D materials and heterostructures.

Watching (De)Intercalation of 2D Metals in Epitaxial Graphene: Insight into the Role of Defects

“…The change in photoemission intensity is directly related to the concentration of intercalants, and the abrupt "steplike" function transition in Figure 3d (top two panels) was recently reported in magnesium intercalating at the Gr/SiC interface. [32] Similarly, we can gain insight into the Ga deintercalation dynamics by fitting the data to a logistic (or Verhulst) function that is a model used for self-limiting processes. We fit the sharp decline in our data to the logistic function (Equation ( 1)),…”

“…The change in photoemission intensity is directly related to the concentration of intercalants, and the abrupt “step‐like” function transition in Figure 3d (top two panels) was recently reported in magnesium intercalating at the Gr/SiC interface. [ 32 ] Similarly, we can gain insight into the Ga de‐intercalation dynamics by fitting the data to a logistic (or Verhulst) function that is a model used for self‐limiting processes. We fit the sharp decline in our data to the logistic function (Equation ()), $$$$\begin{equation}f \left( t \right) = \frac{a}{{1 + {e}^{ - c\left( {t - d} \right)}}}\ + b\end{equation}$$$$where a represents the maximum value of the curve, b the offset, c the growth rate (or steepness of the function), t the time, and d the midpoint (or onset) of the sigmoid.…”

Tuning a quantum-confined silver monolayer beneath epitaxial graphene via surface charge-transfer doping

“…above). Note that while the first step intercalates only small fractions of the surface as judged from low-energy electron diffraction, it still seems to open up intercalation pathways, presumably near SiC step edges 74 or by inducing a small number of defects in the graphene layer 29,30,75,76 . It is only by means of such pretreated samples that silver can succesfully be intercalated during the second preparation step and the resulting band structure displays optimal quality.…”

Quasi-freestanding AA-stacked bilayer graphene induced by calcium intercalation of the graphene-silicon carbide interface

“…Graphene on SiC can either be epitaxial, i.e., directly grown on the SiC, with a buffer layer in between the graphene and the SiC interface, or quasi-freestanding graphene-most commonly created via hydrogen intercalation of epitaxial graphene Daniels et al (2017); Riedl et al (2009), in which graphene retains the properties expected for the isolated layer Sforzini et al (2015). Hydrogen is not the only element that can be used to create quasi-freestanding graphene on SiC by means of intercalation Briggs et al (2019); various other elements can be used, such as gold Sohn et al (2021); Marchenko et al (2016), iron Sung et al (2014); Shen et al (2018), oxygen Oliveira et al (2013), lithium Bao et al (2014); Caffrey et al (2016); Endo et al (2018); Virojanadara et al (2010), magnesium Kotsakidis et al (2020); Grubišić-Čabo et al (2021); Kotsakidis et al (2021), calcium Kotsakidis et al (2020);Valla et al (2009); Yang et al (2014); Endo et al (2020); Toyama et al (2022); Ichinokura et al (2016), antimony Wolff et al (2019) and ytterbium Watcharinyanon et al (2013). The majority of the intercalation studies have been done on epitaxial monolayer and bilayer graphene on SiC, with very few intercalation studies on already quasi-freestanding, hydrogen intercalated, graphene Watcharinyanon et al (2012); Kim et al (2019); Kotsakidis et al (2020).…”