Vertical hybrid inorganic-organic nanoelectronic devices

This thesis comprises different concepts for (vertical)hybrid inorganicorganic nanoelectronics devices. The work was financially supported from the NWO-nano (“Stichting voor de Technische Wetenschappen, STW‿) program, grant no. 11470 “Organic Semiconductor Vertical Quantum Dots‿. Hybrid inorganic-organic nanoelectronics devices can be seen as structures that are at least in one dimension in the sub-micrometer regime and which are built up of inorganic materials and organic materials. In most cases the stiff inorganic matter is forming the electrode material while the organic matter is used as the active component. What is the reason for the implementation of organic materials into electronic devices? In 1974 Aviram and Ratner predicted that a single molecule can function as a molecular switch[1]. The utilization of molecules as components in electronics would allow for an enormous downscaling of electronic circuits which might extent Moore’s Law, which predicts that the number of elements on one integrated circuit is doubled every two years [2, 3]. The possibilities for organic materials in nanoelectronics devices are expected to be huge due the feasibility of chemical modification. Research on “organic electronics‿ comprises singlemolecules [4], self-assembled monolayers [5], organic single-crystals [6, 7], organic semiconductors [8] and pure carbon-based materials [9]. However, contacting molecules for investigating their properties is not straightforward. In this thesis, several device structures for contacting and electrical characterization of organic materials are discussed. Chapter 2 gives a brief introduction about organic electronics especially of organic field-effect transistors and the charge transport mechanisms in organic materials. In Chapter 3, the experimental methods utilized for the fabrication of our vertical hybrid nanodevices discussed in Chapters 4 – 6 are explained. The fabrication and electrical characterization of large-area, symmetric metal- molecular monolayer are covered in Chapter 4. The soft-landing technique wedging transfer was also used for top-contacting thin films of organic semiconductors. These top-contacts were subsequently used as an etch mask to fabricated vertical metal- organic semiconductor- metal pillar structures. We fabricated these pillar structures as two-terminal devices with source and drain electrodes (Chapter 5) as well as three-terminal devices with the addition of a gate electrode (Chapter 6). The trapping of DNA over vertical nanogaps towards a chip to electrically detect hypermethylated DNA for early cancer diagnostics is discussed in Chapter 7. So far, three-dimensional (3D) devices with relatively thick organic semiconductor films of 10 to 100 nm (Chapter 5 and 6) and two-dimensional (2D)devices with organic thin films (5 nm) (Chapter 5) and self-assembled monolayers(Chapter 4) have been realized and electrically investigated. In Chapter 8, we introduce the fabrication of nanochannels with openings below 10 nm. These nanochannels will in the future be filled with molecules to enable one-dimensional (1D) molecular transport.This introduction chapter finishes with an outlook for the realization of zero-dimensional (0D) hybrid nanoelectronics devices namely few-electron/ fewhole organic semiconductor vertical quantum dots. For this goal the vertical organic field-effect transistor architectures described in Chapter 6 is proposed to be confined in the vertical dimension by very thin organic films and also in the lateral dimension by first reducing the pillar diameter and secondly by applying a sidegate.In summary, this thesis focuses on investigating the electrical properties of organic materials in 3D and 2D configurations, providing efficient ways for electrical contacting and device fabrication. It further suggests methods to proceed to building to 1D and 0D devices, which promises interesting physics to investigate in the quantum mechanical regime.