Carbon Nanotube-Based Thin Films: Synthesis and Properties

Thin films composed of carbon nanotubes (CNTs) are an emerging class of material with exceptional electrical, mechanical, and optical properties that can be readily integrated into many novel devices.[1–4] These features suggest that CNT films have potential applications as conducting or semiconducting layers in different types of electronic, optoelectronic, and sensor systems. To understand better how to obtain these films and how to fabricate devices using them, film-forming techniques and experimental work that reveals their collective properties are of importance from fundamental and applied viewpoints. CNTs are a well-known class of material, whose molecular structure can be considered as a series of graphene sheets rolled up in certain directions designated by pairs of integers.[5] In fact, the exceptional electrical, mechanical, optical, chemical, and thermal properties have terms with their unique quasi-one-dimensional structure, atomically monolayered surface, and extended curved -bonding configuration.[6–10] For example, with a different chirality and diameter, an individual single-walled nanotube (SWNT) can be either semiconducting, metallic, or semimetallic, and they can be used as active channels in transistor devices because of their high mobilities (up to about 10000 cm2Vs–1 at room temperature),[11] or as electrical interconnectors, because of their low resistivities,[12,13] high current-carrying capacities (up to about 109 A cm–2),[14] and high thermal conductivities (up to 3500 W m–1 K–1).[15] With their unique structure, CNTs are stiff and strong, with Young’s moduli in the range of 1–2 TPa. Their fracture stresses can be as high as 50 GPa, exhibiting a densitynormalized strength 50 times larger than that of steel wires.[16] In addition, the weightnormalized surface area of CNTs can be as high as 1600 m2 g–1,[17] thereby rendering them suitable for various sensor applications. CNTs can be used in many areas, ranging from nanoscale circuits,[18,19] to field-emission displays,[20] to hydrogen-storage devices,[21,22] to drug-delivery agents,[23,24] to light-emitting devices,[25,26] thermal heat sinks,[27,28] electrical interconnectors,[29] and chemical/biological sensors.[30] It should be noted that the electronic features of CNTs are among their most important properties. Because of their high mobilities and ballistic transport characteristics, CNT films