Characterization of Small-Diameter Carbon Nanotubes and Carbon Nanocaps on SiC(0001) Using Raman Spectroscopy

Abstract

The Raman spectra of carbon nanotubes (CNTs) formed on a 6H–SiC(0001) C-face substrate by surface decomposition were acquired using a 1064 nm Nd:YAG laser as the excitation source. Intense radial-breathing-mode Raman bands were successfully detected under resonant excitation from CNTs formed by the surface decomposition of SiC. Fine CNTs having diameters between 0.7 and 1.3 nm were observed on SiC after heating at 1700 °C in a vacuum electric furnace. These diameters are considerably smaller than those previously observed for CNTs grown by this technique.

In Situ High-Temperature NEXAFS Study on Carbon Nanotube and Graphene Formation by Thermal Decomposition of SiC

“…It has been reported that the initial growth process is much different between the graphene formation on the SiC Si-face and that of CNTs on the SiC C-face; low-energy electron microscopy studies have shown that on the SiC Si-face, the formation of graphene layers starts at the step edges of the SiC surface by desorption of Si atoms and proceeds in a layer-by-layer growth mode. , In contrast, on the SiC C-face, caplike structures composed of hemispherical graphene layers, that is, “carbon nanocaps”, were formed at the beginning; then, as Si atoms were desorbed, cylindrical parts of CNTs grew into the SiC, followed by the formation of vertically aligned MWCNTs films. ,, However, the formation mechanism of the carbon nanocaps on the SiC C-face remains poorly understood. Several studies have been reported regarding the formation of carbon nanocaps on the SiC C-face using transmission electron microscopy (TEM), , scanning tunneling microscopy, − and X-ray photoelectron spectroscopy (XPS) .…”

“…22,25 In contrast, on the SiC C-face, caplike structures composed of hemispherical graphene layers, that is, "carbon nanocaps", were formed at the beginning; then, as Si atoms were desorbed, cylindrical parts of CNTs grew into the SiC, followed by the formation of vertically aligned MWCNTs films. 15,23,26 However, the formation mechanism of the carbon nanocaps on the SiC C-face remains poorly understood. Several studies have been reported regarding the formation of carbon nanocaps on the SiC C-face using transmission electron microscopy (TEM), 15,27 scanning tunneling microscopy, 27−30 and X-ray photoelectron spectroscopy (XPS).…”

Near-Edge X-Ray Absorption Fine Structure Study of Vertically Aligned Carbon Nanotubes Grown by the Surface Decomposition of SiC

“…In this work, we use angular-dependent C K-edge NEXAFS measurements to study the degree of alignment of CNTs grown by the surface decomposition of SiC. [17][18][19][20][21][22][23][24][25] Previous TEM observations showed that high-density, vertically aligned CNTs were grown by heating a SiC(000 1) carbon-face in a vacuum but a comparison to vertically aligned CNTs grown by other methods for the degree of alignment has never been attempted. Here, we carried out angulardependent NEXAFS measurements for CNTs grown by the surface decomposition of SiC to show their higher vertical alignment order.…”

A Spectroscopic and ab Initio Study of the Formation of Graphite and Carbon Nanotubes from Thermal Decomposition of Silicon Carbide

“…The thermal decomposition of silicon carbide (SiC) has recently attracted considerable attention, not limited to the study of the intrinsic characteristics of a material widely used in a vast array of applications due to its exceptional properties, but also for its role as precursor of extremely pure graphite − and catalyst-free carbon nanotubes (CNTs). − Silicon carbide is a sequence of Si:C double layers stacked along the (001) direction. A slab of SiC is characterized by two polar surfaces with specific chemical reactivity, one terminated with silicon atoms, SiC(0001), and the opposite terminated with a layer of carbon atoms, SiC(000−1).…”

“…Our calculations are performed on the 2H-SiC polytype only. On the basis of previous experimental evidence, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] it is reasonable to assume that the thermal behavior of the SiC surface does not depend on the specific polytype chosen for the initial structure. Indeed, different polytypes correspond to different stacking sequences of SiC puckered bilayers, the differences only affecting the relative stacking geometry of second-neighbor bilayers and beyond.…”