Conductance of a Single Conjugated Polymer as a Continuous Function of Its Length Lafferentz et al, Science Florent Martin, EE235, 05/03/09

Experiment and context STM image of a conjugated polymer on a Au surface Schematic view of a polymer chain lifted by an STM tip Organic-based photovoltaics Cover MRS bulletin January 2005 Molecular switch Liljeroth et al Science Credit: IBM Zurich Research Labs

Schematic view of a Scanning Tunneling Microscope Credit: Michael Schmid, TU Wien Experimental set up: STM Surface temperature: 10 K High mechanical stability of the STM junction: lateral and vertical drift of less than 7 pm/min Ultra high vacuum (<10 -9 torr, < bar)

Preparation of weakly bonded polymer chains on Au(111) Chemical structure and STM image of a monomer Sublimation technique fail for long molecular weight In situ polymerization in the STM chamber STM images of the polymers on the Au surface

Single polymer chain lifted with the STM tip Proposed model of the polymer lift experiment Intensity distance curve during approach and retraction of the tip STM image before and after polymer lift

Experimental (A) and calculated (C) Conductance vs distance curves during retraction of the tip IV characteristics of the molecular wire at fixed wire length Non resonant tunneling (left) G = G o x e –βz (β decay factor) Kink = one monomer detached from the surface Resonant tunneling (down) starts when eV > E F_Au - E HOMO

Wire detached from the surface Bias voltage increased as the tip lifts the polymer a. and b. STM image before and after polymer lift c. Current vs distance and bias d. Schematic view of the lifting process

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