Formation of hexagonal boron nitride on graphene-covered copper surfaces

Abstract

Graphene-covered copper surfaces have been exposed to borazine, (BH) 3 (NH) 3 , with the resulting surfaces characterized by low-energy electron microscopy. Although the intent of the experiment was to form hexagonal boron nitride (h-BN) on top of the graphene, such layers were not obtained. Rather, in isolated surface areas, h-BN is found to form m-size islands that substitute for the graphene. Additionally, over nearly the entire surface, the properties of the layer that was originally graphene is observed to change in a manner that is consistent with the formation of a mixed h-BN/graphene alloy, i.e. h-BNC alloy. Furthermore, following the deposition of the borazine, a small fraction of the surface is found to consist of bare copper, indicating etching of the overlying graphene. The inability to form h-BN layers on top of graphene is discussed in terms of the catalytic behavior of the underlying copper surface and the decomposition of the borazine on top of the graphene. FIG 7. (a) LEEM image of graphene sample exposed to borazine at 900C, acquired with sample voltage of 9.0 V. (b) Reflectivity spectra, extracted from the points indicated in the image.

Thickness characterization of atomically thin WSe2 on epitaxial graphene by low-energy electron reflectivity oscillations

“…No discrete thickness oscillations are observed in connection with these minima; the oscillations found in the absence of inelastic effects are eliminated when the inelastic effects are included. Experimentally, a broad reflectivity minimum centered at about 8.2 eV above the vacuum level has indeed been observed in h-BN LEER spectra, 7,8 and two minima (or a minimum and a shoulder) are seen within that broad minimum. As mentioned in Section II, for the computation of Fig.…”

“…Using a quantitative method for determining the local vacuum level outlined in Ref. 8, the experimental reflectivity curves are shifted by ∆W in order to plot the spectra versus E − E vac = eV S − ∆W + σ c , including a small energy shift σ c ≈ 0.1 eV to account for the peak energy of thermionic emission from the gun cathode. With this method in place, it is possible to plot the experimental reflectivity curves together with the computed ones in Fig.…”

Layered Two-Dimensional Heterostructures and Their Tunneling Characteristics

“…No discrete thickness oscillations are observed in connection with these minima; the oscillations found in the absence of inelastic e ects are eliminated when the inelastic e ects are included. Experimentally, a broad re ectivity minimum centered at about 8.2 eV above the vacuum level has indeed been observed in h-BN LEER spectra, [4,49] and two minima (or a minimum and a shoulder) are seen within that broad minimum. As mentioned in Section 3.2, for the computation of Fig.…”

“…The tunneling transition probabilities, 4) are proportional to the square of a matrix element which includes the wavefunction overlap evaluated over the 2D surface in the middle of the barrier region,…”

“…For these reasons, LEEM is highly suited to studies of 2D materials and 2D heterostructures. There have been numerous LEEM studies of semimetallic graphene [43 48] and insulating hexagonal boron nitride, [4,49] but the expanding class of 2D semiconductors remains to be investigated in detail. [5,50,51] Here, we study atomically thin lms of WSe 2 , a semiconducting transition metal Since WSe 2 is a another layered material, it is a natural question to ask whether or not similar states exist between the quasi-2D layers of few-layer WSe 2 and can be counted by analyzing electron re ectivity.…”