Functional molecular transport junctions based on nanogap structures

The use of individual molecules as functional components in electronic circuits offers the great opportunity to improve and revolutionize electronic systems. With the rapid achievement of nanofabrication, molecular electronic devices have been realized based on the investigation of electron properties of molecules. However, the study to build molecular architectures with electronic functions still leaves us a lot of room for improvement and optimization. Hence, this dissertation focuses on the exploration of hybridized electronic systems with judiciously designed molecules and metal nanostructures, to undertake advanced and complex functions. Herein, the newly-developed on-wire lithography (OWL) is employed to fabricate nanogaps as nanoelectrode pairs for the formation of molecular transport junctions (MTJs), the most essential structures in molecular electronics. In order to obtain more complex nanodevices with advanced functions, rationally designed or selected molecules are utilized to functionalize the nanogap structure, while several external stimulations are also introduced to modulate the device performance. Firstly, photo-modulable MTJs are developed via OWL-generated nanogaps functionalized by rationally designed and synthesized complexes with the photochromic dithienylethene unit(s) bearing the electro-active ruthenium fragments. A reversible and repeatable bi-state conductive switching upon alternate irradiation of UV and visible light is distinctly observed. Then, more external stimulations are introduced and orthogonally modulated MTJs are further achieved. The addressable and stepwise control of molecular isomerization is repeatedly and reversibly completed with a judicious use of the orthogonal optical and electrochemical. Through the rational design, these photo-/electro-cooperative nanodevices can be applied as resettable electronic logic gates for Boolean computing. Besides chemically synthesized organometallic complexes, natural biomolecules are also used to functionalize nanogap structures. A programmable controllable and reproducible memristive behavior is achieved by natural ferritin-based MTJs, which can be applied for nonvolatile memory. Additionally, the rapid development of biotechnology provides us another option to improve the device function or performance. By tuning the amount of iron inside an engineered ferritin, the ON/OFF ratio of conductance switching of such protein-based nanodevices is modulated accordingly, suggesting that protein molecules can be tailored using biotechnology to suit the specific requirements of molecular devices. These works provide direct proof that natural biomolecules as a parallel choice of chemically synthesized complex can be used to fabricate functional nanodevices. In conclusion, we develop advanced molecular nanodevices based on the feasible platform of precise nanogap structures fabricated by OWL, under various external controls. Both the synthetic chemistry and natural biosystem have been demonstrated to present enormous resources that fulfill the requirement of molecular devices. With chemical or biological modification of molecular architectures, the function and performance can be obviously improved. Therefore, after optimizing fabrication and operative conditions, such functional MTJs show promising applications in multifunctional nanocircuits.DOCTOR OF PHILOSOPHY (MSE