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UBC Theses and Dissertations

Coupling spatially and spectrally resolved optical measurements with a scanning probe system Roussy, Tanya


Developing a bottom-up understanding of the physics behind charge transfer processes on the nanometer scale will enable the focused design and synthesis of new materials which will revolutionize everything from solar cells to wearable electronics. Pushing our understanding of these processes to the nanometer scale is critical for next generation device development for two primary reasons. Firstly, modern electronic devices are fabricated ever smaller; to date IBM Research has already produced working chips using with gate widths only 14 atoms (7 nm) wide [1]. Secondly, for many devices which rely on charge transfer the important action is at the interface between materials; it is here that the energy level offset and other parameters can make or break a device. For modern organic devices, the interfacial region is in essence a nanometer-wide region: energy levels can differ by hundreds of meV only a few molecules away from an interface [2]. This thesis presents the design and execution of experiments which couple optical measurements with a scanning probe system. The marriage of optical and scanning probe systems enables simultaneous exploration of two complementary dimensions (optical and electronic) of the physics of the system under study, enabling the probing of parameters affecting charge transfer between single molecules. The custom-built system was used to explore optical and electronic properties of two prototypical organic molecules forming an acceptor-donor pair: 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and copper (II) pthalocyanine. This proof-of-concept will allow future users to explore a wide variety of systems which may offer clues to how charge transfer processes occur at the nanometer scale. In the first part of this work I describe the motivation for our experiment as well as the experimental design and set-up. In the second part I detail how we used the enhanced optical-electrical scanning probe to observe real-space energy levels, luminescence (or lack thereof), and attempted optical excitations between two single organic molecules. Analysis of scanning tunnelling spectroscopy data coupled with laser excitation as well as the results from experiments which in principle can measure sub-molecularly resolved luminescence show that the new optical system works as expected.

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