Wafer-scale Films and Devices of Spontaneously Aligned Carbon Nanotubes
Doctor of Philosophy
One of the grand challenges in nanoscience and nanotechnology is how to create macroscopic devices by assembling nano-objects while preserving their extraordinary properties. For example, individual single-wall carbon nanotubes (SWCNTs) possess unique one-dimensional properties that have stimulated much interest in diverse disciplines, and worldwide efforts are in progress to produce large-scale architectures of aligned SWCNTs. Various methods have been proposed and/or demonstrated, including both direct-growth and post-growth schemes, but the current state of this field is that there is still no method available for producing large-area single-domain films of highly aligned, densely packed and chirality-enriched SWCNTs. In this thesis, we describe a new process of controlled differential pressure filtration (CDPF) for producing a wafer-scale (i.e., inch-size) ﬁlm of aligned SWCNTs. This method works for SWCNTs synthesized by various methods and can be scaled up in three dimensions (i.e., in lateral size and thickness). We extensively characterized the produced large-area ﬁlms with different microscopy, spectroscopy and transport methods to demonstrate perfect global alignment with extraordinary photonic and optoelectronic properties. We developed ideal terahertz/infrared polarizers using this approach. The strikingly high degree of alignment with nematic order parameter (S) ~1 and the scalability with thickness ~ 100 nm distinguish CDPF from both existing two-dimensional (2D) and three-dimensional (3D) post-growth assembly techniques. We investigated the underlying mechanisms based on a proposed model of 2D confinement induced phase transition. We identified factors affecting the degree of alignment, including filtration speed, SWCNT concentration, surfactant concentration, hydrophilicity of the filter membrane, SWCNT length, and SWCNT diameter, in order to optimize filtration conditions for an optimally aligned film. Furthermore, by combining CDFP with well-developed solution-based chirality separation techniques (the gel chromatography and aqueous two phase extraction methods), we succeeded in producing chirality-enriched aligned films. The globally aligned chirality-enriched SWCNT films are promising for optoelectronic and electronic device applications. We demonstrated polarized luminescent devices, polarization-sensitive photodetectors, and anisotropic thin-ﬁlm transistors using semiconducting SWCNTs. CDPF-produced SWCNT films will produce a range of new opportunities not only in fundamental research of physics, chemistry, and materials science but also applications in electronics, optoelectronics, sensing, imaging, and medicine.
Carbon Nanotubes; Electronic Devices; Optoelectronic Devices; Macroscopic Alignment.