Carbon nanotube (CNT) and graphene films form on silicon carbon (SiC) using a metal-catalyst-free thermal decomposition approach. In this work, the growth conditions used in the decomposition process are varied to investigate their impact on the type and quality of carbon allotrope formed on the SiC substrate. The nanostructure growth is performed using two approaches, both of which involve intense heating (1250-1700oC) under moderate vacuum conditions (10-2 – 10-5 Torr) without the aid of carbon rich feed gases or metal catalysts commonly used in Chemical Vapor Deposition (CVD) growth approaches. The first growth method uses a graphite resistance furnace capable of annealing wafer-sized samples. The second approach uses a high-intensity laser to heat a micro-meter scale spot size. The high-intensity laser heats the illuminated area of the SiC substrate while under vacuum conditions, resulting in a small-scale growth process similar to the conventional resistance furnace technique. Unique to this micro-scale approach is that in situ Raman spectroscopy is performed yielding instantaneous characterization of the resultant carbon nanostructure as it is formed. The laser-induced growth mechanism enables the impact of varied background vacuum pressures and temperatures to be evaluated in situ. This work reports the findings for various parameter sets implemented during growth, and provides insight into the physical mechanism influencing the growth process.