Self-Assembled Molecular Nanowires for High-Performance Organic Transistors

Abstract

While organic semiconductors provide tantalizing possibilities for low-cost, light-weight, flexible electronic devices, their current use in transistors-the fundamental building block-is rather limited as their speed and reliability are not competitive with those of their inorganic counterparts and are simply too poor for many practical applications. Through self-assembly, highly ordered nanostructures can be prepared that have more competitive transport characteristics; however, no simple, scalable method has been discovered that can produce devices on the basis of such nanostructures. Here, we show how transistors of self-assembled molecular nanowires can be fabricated using a scalable, gradient sublimation technique, which have dramatically improved characteristics compared to those of their thin-film counterparts, both in terms of performance and stability. Nanowire devices based on copper phthalocyanine have been fabricated with threshold voltages as low as -2.1 V, high on/off ratios of 10, small subthreshold swings of 0.9 V/decade, and mobilities of 0.6 cm/V s, and lower trap energies as deduced from temperature-dependent properties, in line with leading organic semiconductors involving more complex fabrication. High-performance transistors manufactured using our scalable deposition technique, compatible with flexible substrates, could enable integrated all-organic chips implementing conventional as well as neuromorphic computation and combining sensors, logic, data storage, drivers, and displays.

Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires Built from Iron Phthalocyanine Chains

“…We then investigate FePc nanowires, which represent a particularly interesting system as the chain length can be up to five orders of magnitude larger than for the films, a configuration that significantly improves the electronic transport properties . It has already been shown that the length of the iron chains also strongly influences the magnetic properties, with an increase in coercive field observed for increasing crystal size .…”

“…Nanowires of Pcs with high aspect ratio can be obtained using specific conditions in OVPD and were first discovered for CuPc . They were also obtained for CoPc, and recent integration into field effect transistors has highlighted their exceptionally high on–off ratio, competitive mobility, and long lifetimes . FePc nanowires were also recently produced in a high vacuum system with high substrate temperature and argon partial pressure up to 0.02 mbar, but this resulted in shorter lengths, and has not been attributed to the η‐phase …”

“…We have recently shown that antiferromagnetic couplings of up to 100 K can be obtained in cobalt phthalocyanine (CoPc) films, and theory suggests that this could be further enhanced to above room temperature through further tuning of the structure . In addition, CoPc (as well as CuPc) nanowires, with no selection or postprocessing, have recently yielded high performance transistors . The next step is to search for ferromagnetic analogues which are more susceptible to small external magnetic fields and for which electron gases in transport channels (e.g., between source and drain in a transistor) could be spin polarized.…”

“…However, the magnetic anisotropy, as deduced from differences in coercivity for hysteresis curves measured along perpendicular directions, was opposite to literature values obtained from films and more conclusive data are required. Finally, we have demonstrated an FePc transistor based on conventional thin film deposition . Analogous to the other metal Pcs, FePc consists of quasi 1D FePc chains along the stacking axis ( b ‐axis), resulting in control of the molecular overlap within chains via creation of an appropriate stacking polymorph.…”

Facile Preparation of Organometallic Nanorods from Various Ethynyl‐Substituted Molecules

“…Anisotropic one dimensional (1D) and two dimensional (2D) nanomaterials, such as nanorods and nanosheets, have attracted significant attention in recent years due to their novel properties and various promising potential applications in the fields of energy storage, electronic and optoelectronic devices, photonic devices, antibacterial‐materials, and chemical and biological sensors . To prepare anisotropic nanomaterials, various methods have been developed including chemical vapor deposition, thermal decomposition of precursors, template‐assisted growth, swelling or exfoliation of layered materials and self‐assembly of anisotropic materials . Among these preparation methods, self‐assembly is one of the most facile and amenable to mass‐production for manufacturing anisotropic nanomaterials.…”