Freestanding n-Doped Graphene via Intercalation of Calcium and Magnesium into the Buffer Layer–SiC(0001) Interface

Kotsakidis, Jimmy C.; Čabo, Antonija Grubišić; Yin, Yuefeng; Tadich, Anton; Myers-Ward, Rachael L.; Dejarld, Matthew T.; Pavunny, Shojan P.; Currie, Marc; Daniels, Kevin M.; Liu, Chang; Edmonds, Mark T.; Medhekar, Nikhil V.; Gaskill, D. Kurt; Parga, Amadeo L. Vázquez de; Fuhrer, Michael S.

doi:10.1021/acs.chemmater.0c01729

Cited by 36 publications

(49 citation statements)

References 98 publications

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“…These observations imply that the buffer layer has disappeared, and a graphene bilayer has formed, respectively. [24,25] Furthermore, the SiC(√3 × √3)R30° diffraction spots which are related to the concurrent formation of the Mg-silicide, are much more distinct, in agreement with these observations. The results presented in Figure 3 are in stark contrast to the observations in Figure 2 for the EMLG-p sample, which showed evidence of intercalation and conversion to Mg-QFSBLG already at the 1 st Mg-intercalation step.…”

Section: Resultssupporting

confidence: 83%

“…[24,25] Thus, our LEED results in Figure 2a imply significant conversion of EMLG-p to Mg-QFSBLG after only the 1 st Mg intercalation. As for the coordination of the Mg atoms, recent modeling of the Mg-QFSBLG structure (based also upon previous LEED results), [24] has found that the Mg atoms on the surface of the SiC likely forms a unit cell with a ratio of Mg:Si of 1:3. [25] After the 2 nd Mg intercalation shown in Figure 2b, the intensity of the SiC(√3 × √3)R30° diffraction spots increases, implying that more Mg has intercalated underneath the buffer layer to form Mg-silicide.…”

Section: Resultsmentioning

confidence: 63%

“…The buffer layer subsequently becomes a second layer of graphene. [24,25] Since intercalation rate increases proportionally with length (increased graphene discontinuities), this implies the suppressed intercalation efficiency of standard "pristine" EMLG samples is likely due to significant reduction of Mg flux to the substrate surface, as there are minimal discontinuities in pristine graphene which provide pathways to the SiC(0001) surface (and so intercalation begins at the edges of the sample, far from the center). A reason for multi-atomic graphene discontinuities being the preferred site of intercalation rather than step edges or flat terraces, is that Mg likely lacks the "reactivity" [47,55,73] with carbon (under the conditions of intercalation used here).…”

Section: Resultsmentioning

confidence: 99%

“…(The formation of a metal silicide at the surface of the SiC after intercalation has been shown to occur with many other elements). [55,[58][59][60][61][62][63][64][65] Importantly, it was found that Mg-QFSBLG was relatively stable in ambient conditions for 6 h. [24] Additional measurements showed that Mg was unable to intercalate hydrogen-intercalated quasi-freestanding bilayer graphene on 6H-SiC(0001) [24] -opening up the attractive possibility of a hybrid Mg/H intercalation procedure to create localized n-p type junctions. To achieve intercalation, Mg was evaporated onto the graphene, and then the sample was annealed.…”

Section: Introductionmentioning

confidence: 99%

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

Kotsakidis

Currie

Čabo

et al. 2021

Adv Materials Inter

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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.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Kotsakidis

Currie

Čabo

et al. 2021

Adv Materials Inter

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“…An additional implication is that the surface of a graphene sample must be prepared to mitigate the effects of adsorbed molecules on transport properties. For example, heating the sample to temperatures~400 • C in ultra-high vacuum (UHV) results in a clean, usable surface [109].…”

Section: Effect Of Epitaxial Graphene-ambient Interactionmentioning

confidence: 99%

Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review

2020

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The electronic and transport properties of epitaxial graphene are dominated by the interactions the material makes with its surroundings. Based on the transport properties of epitaxial graphene on SiC and 3C-SiC/Si substrates reported in the literature, we emphasize that the graphene interfaces formed between the active material and its environment are of paramount importance, and how interface modifications enable the fine-tuning of the transport properties of graphene. This review provides a renewed attention on the understanding and engineering of epitaxial graphene interfaces for integrated electronics and photonics applications.

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2D Oxides Realized via Confinement Heteroepitaxy

Türker

Dong

Wetherington

et al. 2022

Adv Funct Materials

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Novel confinement techniques facilitate the formation of non-layered 2D materials. Here it is demonstrated that the formation and properties of 2D oxides (GaO x , InO x , SnO x ) at the epitaxial graphene (EG)/silicon carbide (SiC) interface is dependent on the EG buffer layer properties prior to element intercalation. Using 2D Ga, it is demonstrated that defects in the EG buffer layer lead to Ga transforming to GaO x with non-periodic oxygen in a crystalline Ga matrix via air oxidation at room temperature. However, crystalline monolayer GaO 2 and bilayer Ga 2 O 3 with ferroelectric wurtzite structure(FE-WZ') can then be formed via subsequent high-temperature O 2 annealing. Furthermore, the graphene/X/SiC (X = 2D Ga or Ga 2 O 3 ) junction is tunable from Ohmic to a Schottky or tunnel barrier depending on the interface species. Finally, using vertical transport measurements and electron energy loss spectroscopy analysis, the bandgap of 2D gallium oxide is identified as 6.6 ± 0.6 eV, significantly larger than that of bulk β-Ga 2 O 3 (≈4.8 eV), suggesting strong quantum confinement effects at the 2D limit. The study presented here is foundational for development of atomic-scale, vertical 2D/3D heterostructure for applications requiring short transit times, such as GHz and THz devices.

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Freestanding n-Doped Graphene via Intercalation of Calcium and Magnesium into the Buffer Layer–SiC(0001) Interface

Cited by 36 publications

References 98 publications

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

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

Electronic and Transport Properties of Epitaxial Graphene on SiC and 3C-SiC/Si: A Review

2D Oxides Realized via Confinement Heteroepitaxy

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