Field Emission Induced UV Electroluminescence of Carbon Nanotubes Coated with Atomic Layer Deposited ZnO...

A brief introduction to nanotechnology will be followed by a description of two recent projects. In the first, atomic layer deposition (ALD) was used to coat carbon nanotubes (CNTs) with a thin film of ZnO. ALD is a highly conformal deposition technique in which films are deposited on a surface one monolayer at a time. CNTs are well known to have excellent field emission properties. ZnO is a versatile wide bandgap transparent semiconductor material with unique piezoelectric, UV photo luminescent (PL), gas sensing, and field emission properties that hold much promise for nanotech applications. Annealing of the ZnO coated CNTs led to the formation of ZnO nanoparticles on the surface of the CNTs. These unique structures were investigated with a combination of field emission, electroluminescence (EL), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. It was found that ZnO nanoparticle coated CNTs exhibited improved field emission characteristics and a UV EL peak at 382 nm that was not detectable in uncoated CNTs. This work demonstrates the utility of ALD for surface modification of nanostructures The second part of the seminar will discuss the directed assembly and integration of ZnO nanobridges into working devices on silicon-on-insulator substrates. The work is unique in that the most widely used methods of nanowire (NW) growth (vapor-liquid-solid using metal catalysts such as Au) and NW integration (the "pick and place" method in which NWs are grown on one substrate, harvested into solution, and then deposited randomly onto a device substrate) were avoided. Instead, ZnO NWs were grown selectively via a vapor-solid method using a patterned ZnO thin-film seed layer that was deposited on Si trench sidewalls via ALD. ZnO NWs grew to span the trench and self-terminated on the opposing surface, effectively forming electrically accessible ZnO horizontal nanobridge devices. Vertical bridge devices were also constructed using undercut islands. Directly grown horizontal ZnO nanobridge devices were operated as gas and UV sensors, demonstrating that this method represents a potential step towards practical large-scale integration of nanodevices into Si microelectronics. Finally, future research plans will be discussed.