Studies of chemical reactivity at the single-molecule level
To develop a better understanding of chemical reactivity a tthe atomic scale, we have designed and constructed a novel scanning tunneling microscope (STM) optimized for tip-enhanced optical spectroscopy. This instrument operates in a cryogenic, ultrahigh vacuum environment that facilitates atomic resolution imaging, single molecule manipulation and tunneling spectroscopy. The combination of low-temperature STM with tip-enhanced optical spectroscopy gives us a versatile and unique set of tools to study surface chemistry at the single-molecule level:
• Atomic-resolution STM images provide information on adsorption sites and molecular configurations.
• Energetic tunneling electrons can synthesize single molecules by making and breaking individual chemical
• Tunneling and tip-enhanced Raman spectroscopies complement each other to better identify molecules on surfaces
and the products of STM-induced reactions.
• Raman spectra measured in the presence of a tunneling current provides a direct measure of
electron-vibrational coupling in molecules.
• Photochemical reactions can be studied under the influence of tip-enhanced optical fields.
Our initial efforts will focus on reactions of functionalized benzene-based molecules on a Ag(lll) surface. We
will explore the variety of molecules that can be synthesized with the STM, building upon simple Ullman-type reactions that have already been demonstrated. The overlap of strong optical transitions in such conjugated molecules with plasmon resonances of the tip and sample will be optimal for structure determination via tip-enhanced Raman spectroscopy.
Arnold O. Beckman exemplifies the meaning of the word humanitarian. Combined with his unwavering enthusiasm for life, his keen sense of humor and his strong moral and ethical principles, he is a national icon.