Title: Electric field breakdown at single molecule junctions
Abstract:
Scanning-tunneling microscope-based break-junction (STM-BJ) technique1 is a
method with which we can study electron transport behaviors through a single
molecule connected to two metal electrodes. In this technique an STM tip is moved
in and out of contact with a substrate in order to repeatedly form and break a metal
point-contact in a solution of molecules. These molecules can bridge the gap
between the broken metal contacts to form a metal-molecule-metal junction. The
conductance of this junction is determined by measuring the current through the
junction while applying a voltage. In this way, STM-BJ technique provides an easy
route to creating a single molecule device thousands of times and generating
statistically significant conductance data. Additionally, as we record conductance
while withdrawing the tip from the substrate, we map out the dynamics of
conductance change caused by elongating the molecular junction. This ability of subangstrom control allows us to study changes in the electronic properties of
molecular junctions corresponding to junction conformations. Therefore the STM-BJ
technique serves as an ideal experimental approach to study electronic properties of
molecular silicon.
I show measurements that illustrate voltage-induced breakdown characteristics of
chemical bonds commonly found in semiconductor materials3 in the context of
single molecule junction with STM-BJ.4 One challenge in the semiconductor industry
is to lower the dielectric constant (κ) of the dielectric material without diminishing
its ability to withstand breakdown in strong electric fields. Low-κ materials can
improve device speed as well as power efficiency, but are less robust than
traditional dielectric materials and degrade through a mechanism referred to as
time dependent dielectric breakdown.5 We study the breakdown phenomenon at
the single molecule/single bond level by simplifying networks of three-dimensional
silicon-based materials into one-dimensional nanowires containing Si—Si, Si—O,
Si—C, Ge—Ge or C—C bonds. We see completely different bond rupture behaviors
in different molecules, and use results from a statistically large number of
measurements to determine which bond is breaking. We find Si—Si and Ge—Ge
bonds rupture at above 1V applied voltage; we also observe Si—C bond is more
robust at above 1V than Si—O or Si—Si bond.
References:
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(4) Li, H.; Su, T. A.; Zhang, V.; Steigerwald, M. L.; Nuckolls, C.; Venkataraman, L.
Journal of the American Chemical Society 2015.
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