Designing organic semiconductors--whether polymers or small molecules--involves a myriad of synthetic choices. Every choice, from incorporating heteroatoms to substituents, effects the optoelectronic properties of the material, its morphology, and its ultimate device performance. This chapter presents the reader with current design strategies and known structure-property relationships. For context, this chapter also briefly discusses the history of the field, theories of charge transport, device applications, and concludes with a selection of reported organic semiconductors.
Binary equilibrium phase diagrams are ubiquitous tools for predicting the behavior of multiphase systems. For a binary mixture with fixed global composition and temperature, a equilibrium phase diagram predicts the number and type of phases in equilibrium, and their respective fraction and composition. Equilibrium phase diagrams are computed from empirical thermodynamic properties of the existing phases and solutions. The calculations does not take into account energy terms that may arise because of surface, interface, strain, etc. With the emergence of nanoparticles (NPs) research, several attempts were made to compute binary nano-phase diagram. These studies consider only the energy term of the outer surface, which scales with the inverse of the radius of the NP. However, three important factors are typically omitted from the calculations: first, the shape and the energy of the solid-solid or solid-liquid interface; second, a mass balance constraint that can limit the phase composition of a nanoparticle and third the relative stability of a single, supersatured phase against a two-phase NP system. In this Chapter, we compute the nano-phase diagram of a binary mixture of Au and Pt, with a solid core-liquid shell configuration by incorporating these three principles. We demonstrate that the liquidus and solidus phase boundaries of an Au-Pt nano-phase diagram for a two-phase core-shell configuration is restricted to a much smaller compositional range than the phase composition. Of note, we show that the stability of the two-phase region shrinks significantly with decreasing size, even for NPs as large as 100 nm in diameter, and disappears below ~41.5 nm, where the NP no longer sustains an interface.
In this chapter, we present an overview of different methods and techniques used for directing the self-assembly of nanoparticles. For exploiting nanoparticle selfassembly in technological applications, both a high level of direction and control as well as an extended assembly size are required to guarantee an efficient scaleup. We focus on tools used for controlling the interparticle forces responsible for triggering self-assembly, outlining both templated and non-templated assembly techniques, including the most common templates used for guiding nanoparticles, as well as externally imposed directing fields that enhance the inherent thermodynamic forces driving the self-assembly process. In addition, we discuss interfacial or surface tension effects that direct the assembly at interfaces or in thin films. Internal and external self-assembly methods are distinguished, where the former relies on modulating the intrinsic properties of the nanoparticles and the latter employs extrinsic fields and forces to guide the assembly. Finally, we also review the application of rod-shaped and sphere-like viruses in organizing molecules and nanoparticles.
Carbon nanomaterials, especially carbon nanotubes and graphene, have been among the most studied materials in the past fifteen years owing to their outstanding physcial properties. To obtain the desired properties, these nanomaterials need to be well-defined and as pure as possible, especially for electronic applications. In this chapter, we present the most promising strategies for the purification of singlewalled carbon nanotubes(SWNTs), with an emphasis on the sorting of semiconducting SWNTs using conjugated polymers, and the synthesis of graphene nanoribbons.