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We are surface scientists, interested in understanding phenomena that arise from the atomic-scale interplay between electronic structure and chemical reactivity at surfaces and interfaces,
in thin films and 2-dimensional structures. Surface science is fascinating due to its interdisciplinary nature and due to the proximity of fundamental studies and applications. Most of the
important processes in living organisms happen at interfaces. One might define nanotechnology as the study of materials whose bulk properties are dominated by their interfaces. Surfaces are
complex systems (Wolfgang Pauli: "Solids were made by god, but surfaces are the work of the devil."), yet they can be studied systematically if one chooses the right systems. Over the years
our research group has worked on a range of different 2D systems that promise interesting science along with relevant applications, including gold-covered oxidized GaAs substrates for nanowire
growth; doping of carbon nanotubes (CNTs); mechanisms of corrosion inhibition on steel and magnesium alloys using oligoanilines; nanoscale pattern formation during electropolishing;
nanostructured anodic oxide films; switchable interfacial dopants and water quality sensors. Our current focus is on chemiresistive devices to monitor water quality parameters.
Chemiresistors are solid state devices that change their electronic properties as a result of chemical interactions with their environment. They are a well-established and widely commercialized technology
for gas or vapor sensor applications. Water quality sensors are a surprisingly underserved area of sensor applications. Important chemical water quality parameters include pH, dissolved gases, common ions
and a range of toxic trace contaminants which may be ionic or uncharged, inorganic or organic. They are usually monitored using colorimetric or electrochemical sensors, and large lab-based instruments.
These methods suffer from high maintenance, need for reagents, high power needs, or inability to operate autonomously and continuously. Chemiresistors have the potential to eliminate all these disadvantages,
but there has been slow progress in adapting them to aqueous analytes. Challenges include the need to prevent electrical shorts through the aqueous medium and the need to keep the sensing voltage low enough
to avoid electrochemical reactions at the sensor. The active sensor elements in our devices consist of a percolation network of low-dimensional materials particles that form a conducting film, e. g. from
carbon nanotubes, pencil trace, and different forms of graphene or graphene oxide. These networks can be made selective by 3 principal approaches: (1) by introduction of chemical defects into the network
itself, (2) by functionalizing the network with switchable dopant molecules, or (3) by coating the network with selective membranes. After demonstrating free chlorine sensors using the second approach, we
have also introduced pH sensors and ion sensors. While there are some challenges associated with expanding the range of accessible analytes, we have recently exploited all three principal approaches to
expand the applicability of our platform, in particular to anions and cations.
(pk) 12 September 2022