**2. Atomic and electronic structure of few-layer graphene synthesized on β-SiC/Si(001)**

Few-layer graphene synthesis on the β-SiC/Si(001) wafers was demonstrated for the first time in the near-edge X-ray absorption fine structure (NEXAFS), core-level photoelectron spectroscopy (PES), ARPES, and local scanning tunneling microscopy (STM) experiments [50]. Later, the few-layer graphene formation on the β-SiC/Si(001) substrates during high-temperature annealing in UHV was proved by independent Raman spectroscopy experiments [82]. These works showed quasi-free-standing character of the synthesized graphene overlayers. Raman spectroscopy data also revealed the presence of a large number of defects in the few-layer graphene grown on the β-SiC/Si(001) wafers with the average distance between them on the order of 10 nm [82]. However, the origin of these defects could be uncovered only in comprehensive studies using a set of complementary

**135**

**Figure 1.**

*the same size (100 × 100 nm2*

*and (h). Reproduced from Ref. [87] with permission of IOP.*

*Controllable Synthesis of Few-Layer Graphene on β-SiC(001)*

PES, ARPES, and atomic-resolution STM [85, 87].

calculated from the STM images of the same size (100 × 100 nm2

high-resolution micro-spectroscopic techniques, namely, low energy electron microscopy (LEEM), micro low energy electron diffraction (μ-LEED), core-level

**Figure 1** shows typical large-area STM images taken from a β-SiC(001) surface before and after trilayer graphene synthesis in UHV [85, 87]. The image of the β-SiC(001)-c(2 × 2) structure (**Figure 1(a)**) reveals extra carbon atoms (bright protrusions) on the surface and monatomic steps. The root mean square (RMS) roughness analysis of the STM images demonstrates substantial enhancement of the surface roughness after the trilayer graphene synthesis. For comparison, the histograms

trilayer graphene synthesis are shown on **Figure 1(d**), **(i)**, and **(j)**. Note that RMS of

*Large-area STM images of SiC(001)-c(2 × 2) (a) and trilayer graphene/SiC(001) ((b), (c), (g), and (h)). Panels (b) and (c) illustrate the continuity of the graphene overlayer near the multiatomic step (b) and APD boundary (c). The images in panels (g) and (h) emphasize the nanodomains elongated along the [1¯10] (g) and [110] directions (h) observed on the left (area G) and right side (area H) of the APD boundary in panel (c), respectively. The STM images were measured at U = −3.0 V and I = 60 pA (a), U = −1.0 V and I = 60 pA (b), U = −0.8 V and I = 50 pA (c), U = −0.8 V and I = 60 pA (g), and U = −0.7 V and I = 70 pA (h). The white arrows in panels (c) and (h) indicate a monatomic step on the SiC substrate. (d), (i), and (j) Roughness analysis of the STM images in panels (a), (g), and (h). The histograms were calculated from surface areas of* 

*synthesis. (e), (f), (k), and (l) Cross-sections (1–2), (3–4), (5–6), and (7–8) of the images in panels (b), (c),* 

*) for direct comparison of the surface roughness before and after trilayer graphene* 

) before and after

*DOI: http://dx.doi.org/10.5772/intechopen.86162*

*Controllable Synthesis of Few-Layer Graphene on β-SiC(001) DOI: http://dx.doi.org/10.5772/intechopen.86162*

*Silicon Materials*

substrate to another, various methods have been developed for direct growing graphene on the technologically relevant non-conducting substrates [23–30].

The hexagonal silicon carbide (α-SiC) wafers are considered the most promising semiconducting substrates for technological synthesis of high-quality graphene films [31–37]. Ultrathin graphene films are usually fabricated on α-SiC using silicon atom sublimation and graphitization of the carbon-enriched surface layers at temperatures above 1000°C [31]. Epitaxial graphene layers synthesized on α-SiC in ultra-high vacuum (UHV) and argon atmosphere demonstrate 2D electronic properties [38–41], which are nearly equivalent to the properties of ultrathin graphene films mechanically exfoliated from bulk graphite crystals. The angle resolved photoelectron spectroscopy (ARPES) studies of the 11-layer graphene on 6H-SiC(000-1) revealed sharp linear dispersions at the K-points typical of monolayer graphene [42]. However, the high price and small size of the single-crystalline α-SiC wafers are not compatible with commercial applications. In order to reduce the price of SiC wafers, epitaxial growth of cubic silicon carbide (β-SiC) thin films on silicon wafers was proposed in the 1980s [43]. Using this method, β-SiC thin films with thickness of several microns could be grown on standard silicon wafers with diameters above 30 cm [44–47] that is highly appealing for direct integration into existing electronic technologies. Fabrication of ultrathin graphene films on β-SiC surfaces, using high-temperature annealing in UHV, was reported for the first time in 2009, when Miyamoto et al. succeeded in synthesizing few-layer graphene on the β-SiC/Si(011) wafers [48]. Then, a number of works demonstrating the feasibility of graphene synthesis on β-SiC/Si wafers of different orientations have been published [48–103]. Mostly, these studies have been conducted on β-SiC(111) thin films [51–61, 65–81] and single-crystalline SiC(111) wafers [62–64]. However, some studies have been carried out on

β-SiC(001) [50, 61, 82–93, 101, 102] and even on polycrystalline β-SiC substrates [94]. Since Si(001) is widely used in electronic devices, few-layer graphene films synthesized on the β-SiC/Si(001) wafers can be fully compatible with the exist-

This chapter is focused on the controllable UHV synthesis of few-layer graphene on the β-SiC thin films grown on the technologically relevant Si(001) wafers. Along with detailed atomic and electronic structure studies we present the recent results which uncover the mechanism of layer-by-layer graphene growth on β-SiC/Si(001) and pave the way to synthesize uniform few-layer graphene nanoribbons with desirable number of layers and self-aligned nanodomain boundaries on the low-cost

**2. Atomic and electronic structure of few-layer graphene synthesized** 

Few-layer graphene synthesis on the β-SiC/Si(001) wafers was demonstrated for the first time in the near-edge X-ray absorption fine structure (NEXAFS), core-level photoelectron spectroscopy (PES), ARPES, and local scanning tunneling microscopy (STM) experiments [50]. Later, the few-layer graphene formation on the β-SiC/Si(001) substrates during high-temperature annealing in UHV was proved by independent Raman spectroscopy experiments [82]. These works showed quasi-free-standing character of the synthesized graphene overlayers. Raman spectroscopy data also revealed the presence of a large number of defects in the few-layer graphene grown on the β-SiC/Si(001) wafers with the average distance between them on the order of 10 nm [82]. However, the origin of these defects could be uncovered only in comprehensive studies using a set of complementary

ing lithographic processing technologies.

**134**

silicon wafers.

**on β-SiC/Si(001)**

high-resolution micro-spectroscopic techniques, namely, low energy electron microscopy (LEEM), micro low energy electron diffraction (μ-LEED), core-level PES, ARPES, and atomic-resolution STM [85, 87].

**Figure 1** shows typical large-area STM images taken from a β-SiC(001) surface before and after trilayer graphene synthesis in UHV [85, 87]. The image of the β-SiC(001)-c(2 × 2) structure (**Figure 1(a)**) reveals extra carbon atoms (bright protrusions) on the surface and monatomic steps. The root mean square (RMS) roughness analysis of the STM images demonstrates substantial enhancement of the surface roughness after the trilayer graphene synthesis. For comparison, the histograms calculated from the STM images of the same size (100 × 100 nm2 ) before and after trilayer graphene synthesis are shown on **Figure 1(d**), **(i)**, and **(j)**. Note that RMS of

#### **Figure 1.**

*Large-area STM images of SiC(001)-c(2 × 2) (a) and trilayer graphene/SiC(001) ((b), (c), (g), and (h)). Panels (b) and (c) illustrate the continuity of the graphene overlayer near the multiatomic step (b) and APD boundary (c). The images in panels (g) and (h) emphasize the nanodomains elongated along the [1¯10] (g) and [110] directions (h) observed on the left (area G) and right side (area H) of the APD boundary in panel (c), respectively. The STM images were measured at U = −3.0 V and I = 60 pA (a), U = −1.0 V and I = 60 pA (b), U = −0.8 V and I = 50 pA (c), U = −0.8 V and I = 60 pA (g), and U = −0.7 V and I = 70 pA (h). The white arrows in panels (c) and (h) indicate a monatomic step on the SiC substrate. (d), (i), and (j) Roughness analysis of the STM images in panels (a), (g), and (h). The histograms were calculated from surface areas of the same size (100 × 100 nm2 ) for direct comparison of the surface roughness before and after trilayer graphene synthesis. (e), (f), (k), and (l) Cross-sections (1–2), (3–4), (5–6), and (7–8) of the images in panels (b), (c), and (h). Reproduced from Ref. [87] with permission of IOP.*

micrometer-scale β-SiC(001)-c(2 × 2) STM images typically varied between 1.0 and 1.5 Å, while the RMS values calculated from the images of trilayer graphene were in the range of 3.0–5.0 Å. The increase of the surface roughness after graphene synthesis is related to the atomic-scale rippling typical for free-standing graphene [104, 105]. STM investigations conducted in different surface areas of several samples [87] confirmed the continuity of the few-layer graphene films covering the β-SiC/Si(001) wafers. As an example, **Figure 1(b)** and **(c)** shows STM images measured at bias voltages corresponding to the bandgap of β-SiC. STM imaging was stable even in the vicinity of multiatomic steps (**Figure 1(b)**) and anti-phase domain (APD) boundaries (**Figure 1(c)**), separating the areas where the β-SiC crystal lattice is rotated by 90°.

STM studies [85, 87] showed that the top graphene layer consists of nanodomains connected to one another through domain boundaries (**Figure 1(g)** and **(h)**). The nanodomain boundaries (NBs) are preferentially aligned with the two orthogonal <110> directions of the SiC crystal lattice, as indicated in **Figure 1(g)** and **(h)**. The domains are elongated in the [110] and [1¯ 10] directions on the right and left side of the APD boundary, respectively (**Figure 1(c)**). The length and width of the nanodomains on the SiC(001) substrate were in the range of 20–200 nm and 5–30 nm, respectively. These values correlate well with the average distance between defects derived from the Raman spectroscopy studies [82].

The continuity and uniform thickness of the graphene overlayer synthesized on the β-SiC/Si(001) wafers were confirmed in the LEEM experiments (**Figure 2**). The bright-field (BF) LEEM image measured at small electron energy shows uniform contrast throughout the all probed micrometer-sized surface area, including the regions containing defects (steps and APD boundaries). The number of graphene layers can be determined from the number of oscillations in the reflectivity *I-V* curves measured in a small energy window [106, 107]. In the reflectivity spectra shown on **Figure 2(h)**, one can see three reproducible minima, which correspond to the uniform trilayer graphene coverage. The graphene film thickness is homogeneous

#### **Figure 2.**

*(a) 20 μm BF LEEM micrograph, recorded with an electron energy of 3.4 eV, proving the uniform thickness of trilayer graphene on β-SiC/Si(001) wafers. (b) and (c) DF LEEM images from different diffraction spots (shown in panels (e) and (f)) demonstrating the contrast reversal on micrometer-scale areas with two rotated graphene domain families. (d)–(f) μ-LEED patterns from the surface areas shown by black circles in panels (a)–(c). The diameters of the sampling areas are 5 μm (a) and 1.5 μm ((b) and (c)), E = 52 eV. (g) μ-PES C 1s spectra taken at two photon energies. The diameter of the probed area is 10 μm. (h) Electron reflectivity spectra recorded for surface regions 1, 2, and 3 as labeled in panel (b). Reproduced from [85] with permission of Tsinghua and Springer.*

**137**

**Figure 3.**

*(a and b) 19.5 × 13 nm2*

*Controllable Synthesis of Few-Layer Graphene on β-SiC(001)*

interaction of the few-layer graphene with β-SiC(001).

over the surface and *I-V* curves are almost identical in the surface areas appearing dark and white in the dark-field (DF) LEEM images, as **Figure 2(h)** illustrates.

typically revealed 12 sharp double-split spots and 12 substantially less intense singular spots, corresponding to the nanostructured graphene, and singular spots from the SiC(001) substrate. The μ-LEED patterns measured from different APDs (**Figure 2(e)** and **(f )**) demonstrate 12 non-equidistant spots and six less intense singular graphene spots. The diffraction patterns measured from the APDs are rotated relative to one another by 90°. These LEEM and μ-LEED data demonstrate that each micrometer-sized APD contains graphene nanodomain families with three preferential lattice orientations, giving six preferential lattice orientations on larger (millimeter-scale) surface areas. For the trilayer graphene, four of these six lattice orientations are prevailing in the top layer. The core-level C 1*s* spectra measured from this sample (**Figure 2(g)**) demonstrate only two components with binding energies (BE) corresponding to silicon carbide (lower BE) and graphene (higher BE) in accordance with other core-level PES studies [50], proving the weak

The μ-LEED patterns taken from micrometer-sized surface areas (**Figure 2(d)**)

Atomically resolved STM studies presented in **Figure 3** disclose the origin of 12 double-split spots in the LEED patterns (**Figure 2(d)**). STM images in **Figure 3(a)** and **(b)** demonstrate nanodomains elongated in the [110] and [1¯

directions, respectively. The 2D fast Fourier transform (FFT) of the STM images consists of two systems of spots, which are related to two graphene lattices rotated by 27°. Inset in **Figure 3(b)** shows one of the FFT patterns. According to the μ-LEED data (**Figure 2(e)** and **(f )**), the graphene domain lattices are

 *atomically resolved STM images of trilayer graphene nanodomains on SiC(001)* 

*elongated along the [110] (a) and [1¯10] directions (b). The images were taken from different surface areas at U = −10 mV and I = 60 pA. The inset in panel (b) shows an FFT pattern with two 27°-rotated systems of spots. (c–e) Models explaining the origin of the 12 double-split diffraction spots in the LEED pattern shown in Figure 2(d). The insets in panels (c) and (d) are STM images of the <110>-directed domain boundaries. The four differently colored hexagons—red, blue, green, and brown—represent the four preferential domain lattice orientations. The inset in panel (e) shows a LEED pattern taken at Ep = 65 eV, demonstrating 1 × 1 substrate spots (highlighted by yellow arrows) along with 12 double-split graphene spots, indicated by one dotted arrow* 

*for each orientation. Reproduced from Ref. [87] with permission of IOP.*

10]

*DOI: http://dx.doi.org/10.5772/intechopen.86162*

## *Controllable Synthesis of Few-Layer Graphene on β-SiC(001) DOI: http://dx.doi.org/10.5772/intechopen.86162*

*Silicon Materials*

studies [82].

micrometer-scale β-SiC(001)-c(2 × 2) STM images typically varied between 1.0 and 1.5 Å, while the RMS values calculated from the images of trilayer graphene were in the range of 3.0–5.0 Å. The increase of the surface roughness after graphene synthesis is related to the atomic-scale rippling typical for free-standing graphene [104, 105]. STM investigations conducted in different surface areas of several samples [87] confirmed the continuity of the few-layer graphene films covering the β-SiC/Si(001) wafers. As an example, **Figure 1(b)** and **(c)** shows STM images measured at bias voltages corresponding to the bandgap of β-SiC. STM imaging was stable even in the vicinity of multiatomic steps (**Figure 1(b)**) and anti-phase domain (APD) boundaries (**Figure 1(c)**), separating the areas where the β-SiC crystal lattice is rotated by 90°. STM studies [85, 87] showed that the top graphene layer consists of nanodomains connected to one another through domain boundaries (**Figure 1(g)** and **(h)**). The nanodomain boundaries (NBs) are preferentially aligned with the two orthogonal <110> directions of the SiC crystal lattice, as indicated in **Figure** 

10] directions on

**1(g)** and **(h)**. The domains are elongated in the [110] and [1¯

the right and left side of the APD boundary, respectively (**Figure 1(c)**). The length and width of the nanodomains on the SiC(001) substrate were in the range of 20–200 nm and 5–30 nm, respectively. These values correlate well with the average distance between defects derived from the Raman spectroscopy

The continuity and uniform thickness of the graphene overlayer synthesized on the β-SiC/Si(001) wafers were confirmed in the LEEM experiments (**Figure 2**). The bright-field (BF) LEEM image measured at small electron energy shows uniform contrast throughout the all probed micrometer-sized surface area, including the regions containing defects (steps and APD boundaries). The number of graphene layers can be determined from the number of oscillations in the reflectivity *I-V* curves measured in a small energy window [106, 107]. In the reflectivity spectra shown on **Figure 2(h)**, one can see three reproducible minima, which correspond to the uniform trilayer graphene coverage. The graphene film thickness is homogeneous

*(a) 20 μm BF LEEM micrograph, recorded with an electron energy of 3.4 eV, proving the uniform thickness of trilayer graphene on β-SiC/Si(001) wafers. (b) and (c) DF LEEM images from different diffraction spots (shown in panels (e) and (f)) demonstrating the contrast reversal on micrometer-scale areas with two rotated graphene domain families. (d)–(f) μ-LEED patterns from the surface areas shown by black circles in panels (a)–(c). The diameters of the sampling areas are 5 μm (a) and 1.5 μm ((b) and (c)), E = 52 eV. (g) μ-PES C 1s spectra taken at two photon energies. The diameter of the probed area is 10 μm. (h) Electron reflectivity spectra recorded for surface regions 1, 2, and 3 as labeled in panel (b). Reproduced from [85] with permission* 

**136**

**Figure 2.**

*of Tsinghua and Springer.*

over the surface and *I-V* curves are almost identical in the surface areas appearing dark and white in the dark-field (DF) LEEM images, as **Figure 2(h)** illustrates.

The μ-LEED patterns taken from micrometer-sized surface areas (**Figure 2(d)**) typically revealed 12 sharp double-split spots and 12 substantially less intense singular spots, corresponding to the nanostructured graphene, and singular spots from the SiC(001) substrate. The μ-LEED patterns measured from different APDs (**Figure 2(e)** and **(f )**) demonstrate 12 non-equidistant spots and six less intense singular graphene spots. The diffraction patterns measured from the APDs are rotated relative to one another by 90°. These LEEM and μ-LEED data demonstrate that each micrometer-sized APD contains graphene nanodomain families with three preferential lattice orientations, giving six preferential lattice orientations on larger (millimeter-scale) surface areas. For the trilayer graphene, four of these six lattice orientations are prevailing in the top layer. The core-level C 1*s* spectra measured from this sample (**Figure 2(g)**) demonstrate only two components with binding energies (BE) corresponding to silicon carbide (lower BE) and graphene (higher BE) in accordance with other core-level PES studies [50], proving the weak interaction of the few-layer graphene with β-SiC(001).

Atomically resolved STM studies presented in **Figure 3** disclose the origin of 12 double-split spots in the LEED patterns (**Figure 2(d)**). STM images in **Figure 3(a)** and **(b)** demonstrate nanodomains elongated in the [110] and [1¯ 10] directions, respectively. The 2D fast Fourier transform (FFT) of the STM images consists of two systems of spots, which are related to two graphene lattices rotated by 27°. Inset in **Figure 3(b)** shows one of the FFT patterns. According to the μ-LEED data (**Figure 2(e)** and **(f )**), the graphene domain lattices are

#### **Figure 3.**

*(a and b) 19.5 × 13 nm2 atomically resolved STM images of trilayer graphene nanodomains on SiC(001) elongated along the [110] (a) and [1¯10] directions (b). The images were taken from different surface areas at U = −10 mV and I = 60 pA. The inset in panel (b) shows an FFT pattern with two 27°-rotated systems of spots. (c–e) Models explaining the origin of the 12 double-split diffraction spots in the LEED pattern shown in Figure 2(d). The insets in panels (c) and (d) are STM images of the <110>-directed domain boundaries. The four differently colored hexagons—red, blue, green, and brown—represent the four preferential domain lattice orientations. The inset in panel (e) shows a LEED pattern taken at Ep = 65 eV, demonstrating 1 × 1 substrate spots (highlighted by yellow arrows) along with 12 double-split graphene spots, indicated by one dotted arrow for each orientation. Reproduced from Ref. [87] with permission of IOP.*

preferentially rotated by ±13.5° from the [110] and [1¯ 10] crystallographic directions of the substrate, which almost coincide with the preferential directions of the nanodomain boundaries. These two families of 27°-rotated domains are rotated by 90° relative to one another and produce two systems of 12 non-equidistant spots in the FFT and μ-LEED patterns (e.g. see **Figure 2(e)** and **(f )**). The sum of two 90°-rotated patterns with 12 non-equidistant spots produce the LEED pattern of graphene/β-SiC/Si(001) with 12 double-split spots, as the models shown in **Figure 3(c–e)** illustrate. These two orthogonal 27°-rotated domain families are usually resolved as horizontal and vertical nanoribbons in STM experiments (**Figure 1(g)** and **(h)**). The DF LEEM images taken from different reflexes in either of the double-split spots show a reversed contrast and confirm that the 27°-rotated domain families typically cover micrometer-sized surface regions in different APDs (**Figure 2(b)** and **(c)**).

Atomic-resolution STM images of the trilayer graphene on β-SiC(001) measured inside the nanodomains usually revealed either hexagonal (**Figure 4(a)**) or honeycomb (**Figure 4(d)**) patterns distorted by atomic-scale rippling [104]. The line profile shown in **Figure 4(c)** reveals random vertical corrugations related to the atomic-scale rippling and regular oscillations with a period of ~ 2.5 Å corresponding to the graphene honeycomb lattice. Typical dimensions of the ripples are about several nanometers laterally and 1 Å vertically (**Figure 4(b)**), coinciding with values predicted by the theory for free-standing monolayer graphene [104]. The random picometer-scale distortions of the sp2 -hybridized carbon bond lengths in graphene/β-SiC/Si(001) are illustrated using smaller area STM images presented in **Figure 4(d–f )**.

#### **Figure 4.**

*(a) 13.4 × 13.4 nm2 STM image of trilayer graphene on β-SiC(001), illustrating atomic-scale rippling. The image was measured at U = 0.1 V and I = 60 pA. (b) and (c) Cross-sections (1–2) and (3–4) from the image in panel (a). (d–f) STM images of the trilayer graphene, demonstrating random picometer-scale distortions of the honeycomb lattice. The images were measured at U = 22 mV and I = 70 pA (d) and U = 22 mV and I = 65 pA (e and f). One of the distorted hexagons is shown in (f) for clarity. Reproduced from Ref. [103] with permission of Elsevier.*

**139**

trilayer graphene formed on β-SiC(001).

*Controllable Synthesis of Few-Layer Graphene on β-SiC(001)*

The uniformity of the atomic and electronic structure of the trilayer graphene/β-SiC/Si(001) on a millimeter-scale was confirmed by ARPES [85]. As an example, the photoemission studies of the *π* band are shown in **Figures 5** and **6**. Since ARPES technique probes millimeter-scale sample areas, the effective surface Brillouin zone of graphene on β-SiC(001) comprises Brillouin zones of all rotated lattices (**Figure 5(a)**). The identical sharp linear dispersions typical of quasifree-standing graphene are observed for all rotated domain variants (**Figure 5(b)** and **(c)**), with the Dirac points located at the Fermi level. The ARPES dispersion measured from the trilayer graphene/β-SiC/Si(001) sample along the Γ¯ – *K*¯ direction of the surface Brillouin zone (**Figure 6(b)**) reveals the *π* band reaching the Fermi level. **Figure 6(b)** also displays a dispersion of the *π* band that backfolds at ~2.5 eV BE and originates from the *M*-point of the rotated graphene domain. In order to determine the position of the Dirac point, the dispersions were measured in a detection geometry perpendicular to the Γ¯ – *K*¯-direction (short black line in **Figure 6(a)**) where the interference effects are suppressed and both sides of the Dirac cone are observed [108]. The ARPES data shown in **Figure 6(c)** reveal sharp linear dispersions and tiny additional bands between the two split Dirac cones. According to the theoretical calculations presented in Ref. [93], the observed ARPES dispersions may correspond to a quasi-free-standing Bernal-stacked ABA-

*ARPES characterization of trilayer graphene grown on β-SiC(001). (a) Effective surface Brillouin zone due to superposition of four domain lattices (A, B, A′, and B′). (b) and (c) Dispersion of π-band in trilayer graphene measured by ARPES along directions 1 and 2 in (a). Reproduced from Ref. [85] with permission of Tsinghua* 

*ARPES characterization of trilayer graphene grown on β-SiC(001). (a) Effective surface Brillouin zone due to superposition of four rotated domain variants (A, B, A′, and B′). (b) and (c) Dispersion of π-band in graphene measured along directions 1 and 2 in (a). Reproduced from Ref. [85] with permission of Tsinghua and* 

The experimental data presented in this section were obtained during highresolution studies of the trilayer graphene grown on a low-index β-SiC/Si(001) wafer using high-temperature annealing in UHV. They demonstrate the fabrication of uniform nanostructured graphene with two preferential NB directions

*DOI: http://dx.doi.org/10.5772/intechopen.86162*

**Figure 5.**

*Springer.*

**Figure 6.**

*and Springer.*

#### **Figure 5.**

*Silicon Materials*

in **Figure 4(d–f )**.

preferentially rotated by ±13.5° from the [110] and [1¯

regions in different APDs (**Figure 2(b)** and **(c)**).

The random picometer-scale distortions of the sp2

tions of the substrate, which almost coincide with the preferential directions of the nanodomain boundaries. These two families of 27°-rotated domains are rotated by 90° relative to one another and produce two systems of 12 non-equidistant spots in the FFT and μ-LEED patterns (e.g. see **Figure 2(e)** and **(f )**). The sum of two 90°-rotated patterns with 12 non-equidistant spots produce the LEED pattern of graphene/β-SiC/Si(001) with 12 double-split spots, as the models shown in **Figure 3(c–e)** illustrate. These two orthogonal 27°-rotated domain families are usually resolved as horizontal and vertical nanoribbons in STM experiments (**Figure 1(g)** and **(h)**). The DF LEEM images taken from different reflexes in either of the double-split spots show a reversed contrast and confirm that the 27°-rotated domain families typically cover micrometer-sized surface

Atomic-resolution STM images of the trilayer graphene on β-SiC(001) measured inside the nanodomains usually revealed either hexagonal (**Figure 4(a)**) or honeycomb (**Figure 4(d)**) patterns distorted by atomic-scale rippling [104]. The line profile shown in **Figure 4(c)** reveals random vertical corrugations related to the atomic-scale rippling and regular oscillations with a period of ~ 2.5 Å corresponding to the graphene honeycomb lattice. Typical dimensions of the ripples are about several nanometers laterally and 1 Å vertically (**Figure 4(b)**), coinciding with values predicted by the theory for free-standing monolayer graphene [104].

in graphene/β-SiC/Si(001) are illustrated using smaller area STM images presented

 *STM image of trilayer graphene on β-SiC(001), illustrating atomic-scale rippling. The* 

*image was measured at U = 0.1 V and I = 60 pA. (b) and (c) Cross-sections (1–2) and (3–4) from the image in panel (a). (d–f) STM images of the trilayer graphene, demonstrating random picometer-scale distortions of the honeycomb lattice. The images were measured at U = 22 mV and I = 70 pA (d) and U = 22 mV and I = 65 pA (e and f). One of the distorted hexagons is shown in (f) for clarity. Reproduced from Ref. [103] with* 

10] crystallographic direc-


**138**

**Figure 4.** *(a) 13.4 × 13.4 nm<sup>2</sup>*

*permission of Elsevier.*

*ARPES characterization of trilayer graphene grown on β-SiC(001). (a) Effective surface Brillouin zone due to superposition of four rotated domain variants (A, B, A′, and B′). (b) and (c) Dispersion of π-band in graphene measured along directions 1 and 2 in (a). Reproduced from Ref. [85] with permission of Tsinghua and Springer.*

**Figure 6.**

*ARPES characterization of trilayer graphene grown on β-SiC(001). (a) Effective surface Brillouin zone due to superposition of four domain lattices (A, B, A′, and B′). (b) and (c) Dispersion of π-band in trilayer graphene measured by ARPES along directions 1 and 2 in (a). Reproduced from Ref. [85] with permission of Tsinghua and Springer.*

The uniformity of the atomic and electronic structure of the trilayer graphene/β-SiC/Si(001) on a millimeter-scale was confirmed by ARPES [85]. As an example, the photoemission studies of the *π* band are shown in **Figures 5** and **6**. Since ARPES technique probes millimeter-scale sample areas, the effective surface Brillouin zone of graphene on β-SiC(001) comprises Brillouin zones of all rotated lattices (**Figure 5(a)**). The identical sharp linear dispersions typical of quasifree-standing graphene are observed for all rotated domain variants (**Figure 5(b)** and **(c)**), with the Dirac points located at the Fermi level. The ARPES dispersion measured from the trilayer graphene/β-SiC/Si(001) sample along the Γ¯ – *K*¯ direction of the surface Brillouin zone (**Figure 6(b)**) reveals the *π* band reaching the Fermi level. **Figure 6(b)** also displays a dispersion of the *π* band that backfolds at ~2.5 eV BE and originates from the *M*-point of the rotated graphene domain. In order to determine the position of the Dirac point, the dispersions were measured in a detection geometry perpendicular to the Γ¯ – *K*¯-direction (short black line in **Figure 6(a)**) where the interference effects are suppressed and both sides of the Dirac cone are observed [108]. The ARPES data shown in **Figure 6(c)** reveal sharp linear dispersions and tiny additional bands between the two split Dirac cones. According to the theoretical calculations presented in Ref. [93], the observed ARPES dispersions may correspond to a quasi-free-standing Bernal-stacked ABAtrilayer graphene formed on β-SiC(001).

The experimental data presented in this section were obtained during highresolution studies of the trilayer graphene grown on a low-index β-SiC/Si(001) wafer using high-temperature annealing in UHV. They demonstrate the fabrication of uniform nanostructured graphene with two preferential NB directions

on millimeter-sized samples. Such nanoribbon systems supported on the Si(001) wafers are very promising because the presence of the self-aligned boundaries can provide a sizeable energy gap in graphene [10]. However, for technological applications it is highly desirable to control the thickness of the graphene overlayer and reduce the number of the preferential NB orientations from two to one. Note that thickness of the few-layer graphene synthesized on β-SiC/Si(001) wafers by different groups, utilizing very similar UHV thermal treatment procedures, varied from one to several monolayers [50, 82–93, 101].
