CHARGE TRANSPORT BY TUNNELING
Tunneling is a prototypical quantum-mechanical phenomenon. We are interested in the mechanism(s) of tunneling in organic matter for three reasons: i) In a number of redox enzymes, and throughout pathways involving energy and charge transport in biology, tunneling has been invoked as a mechanism. The evidence for this type of mechanism (as opposed, for example, to Ohmic conductivity, or charge hopping) is not strong in many cases, and understanding the fundamental science of tunneling would clarify electronic charge transport throughout biology. ii) Processes associated with tunneling are of possible interest in the design and fabrication of new types of electronic devices. So-called “molecular electronics” is a field that has had a checkered history, but new techniques are beginning to uncover new phenomena. New devices based on molecular electronics and organic matter will not compete with CMOS, which is a highly developed and enormously powerful technology. There may, however, be new types of applications in sensing, information transduction, interfacing with biological structures, or others, where conventional silicon-based electronics is not applicable. Iii) Tunneling is intrinsically interesting in fundamental studies of energy transport, since the rules for transmission losses in tunneling are fundamentally different from those in Ohmic conductors, where resistive losses are typically due to electron scattering
We have developed a new system for studying charge transport by tunneling in ultrathin (< 2 nm). organic films (self-assembled monolayers, or SAMs). This system uses template-stripped gold or silver films as one electrode, a self-assembled monolayer (SAM) as the organic insulator, and a second electrode fabricated from a sharp tip of liquid indium gallium eutectic (EGaIn), covered with a thin film of semiconducting gallium oxide. The system has proved to be exceptionally flexible and convenient for physical-organic studies of tunneling. We are now exploiting it to develop structure-property relationships connecting the molecular structure of SAMs to tunneling current densities in so-called “large-area” junctions having the form Au/SR//Ga2O3/EGaIn.
NEW SOFT MACHINES INSPIRED BY BIOLOGY
Most machines used by humans are based either on heat engines (for example, steam or gas turbines, or internal combustion engines), or on electricity (often, but not always, generated by heat engines). Motion and force are generated in biological systems using fundamentally different mechanisms. The most common “motor” in biology is, of course, muscle, which converts the free energy of hydrolysis of ATP into force or motion based on protein filaments that slide past one another
We are developing a research program whose objective is to mimic some of the functions and motions found in biological actuators (although not using muscle-mimetics). The work initially to be pursued focuses on synthetic structures designed to have functional analogy to structures in insects (and, particularly, spiders). These structures combine the function of an exoskeleton (in the form of thin, semi-rigid polymeric tubes or box beams) with simple actuators modeled on the functional characteristics of muscles in the joints of insects. One objective of this work is to develop new types of functions for systems of actuators; the second is to explore actuators whose properties are sufficiently different from the mechanical and electrical motors commonly used throughout economically developed societies that they might offer alternatives to these conventional systems – especially in applications where “cooperativity “ (that is, the ability to work safely and synergistically with humans) is important