Structural and Electrical Characteristics of Carbon Nanotubes Formed on Silicon Carbide Substrates by Surface Decomposition

Abstract

Aligned carbon nanotubes (CNT’s) are formed on the surface of silicon carbide (SiC) wafers during high temperature anneals. The exposed 4H SiC surface transforms into CNT’s for temperatures in the range of 1400-1700°C and under moderate vacuum conditions (10-2 – 10-5 torr). The rate of formation on the C-face (0001,‾) is about three times the rate on the Si-face (0001), but both rates increase with anneal temperature. SEM, TEM and Raman scattering measurements have confirmed the presence of both single-wall and multi-wall CNT’s. The carbon source is believed to be residual carbon from the SiC left on the surface after preferential evaporation of Si. CNT formation is believed to be catalyzed by low concentrations of residual oxygen in the chamber. Subsequent I-V measurements provide insight into the electrical characteristics of the CNT’s and the SiC/CNT interface.

Evaluation of metal-free carbon nanotubes formed by SiC thermal decomposition

“…These results suggest that a maximum growth rate is achievable at 1700°C and 10 −3 Torr, although the growth rate at 10 −3 Torr is only slightly larger than at 10 −5 Torr. Our earlier study 12 showed that CNTs are partially damaged at 1800°C. As shown in Fig.…”

“…This observation is in agreement with the TEM analysis. 12 Figure 6 shows that the CNT layer for the samples grown at 10 −5 Torr at various temperatures consists of 30%-50% CNTs, 35%-60% voids, and 5%-12% of a-C in volume. With increasing temperature, the void content increases while the CNT/void ratio remains almost unchanged.…”

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.…”