Kruse Research Group - Research

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Below you can find descriptions of the research projects that are currently going on in our group. Surface Science is a wide field, and there are many topics that intersect in some way or another with our main interests. Smaller side projects often spring from our need to gain a better understanding of a particular item.

I. Mechanisms and Applications of Switchable Interfacial Dopants

Carbon nanotubes are a popular field of research. They have been functionalized covalently and non-covalently in order to enhance their mechanical, electrical and optical properties for use in composites, printable electrodes, solar cells, sensors, transistors, etc. But do we really know what we are doing? As it turns out, in many cases we don't. Nanotubes are truly nanoscale objects, in that they are too big to still be thought of as molecules, yet they are too small to be easily subjected to traditional solid state physics paradigms. Worst of all, they are not pure mixtures of identical species, but rather in most cases used as mixtures of tubules with different diameters, chiralities and electronic structures. Our initial fascination with carbon nanotubes was rooted in the desire to understand spatial patterns in covalent functionalization. However, it became clear to us very quickly that the role of doping of carbon nanotubes was significantly under-appreciated in the carbon nanotube chemistry literature, and as a result a number of experimental results had been misinterpreted. Having achieved a better understanding of the role of dopants, we then went on to develop the concept of switchable dopant molecules. This has enabled us to demonstrate a new class of carbon nanotube based sensors with favourable properties. The conductivity of a random carbon nanotube network (i.e. a thin film deposited by drop-casting or printing) strongly depends on its doping state. While for most conventional sensing applications, the removal of the dopants from the film present one challenge and the selectivity to a particular dopant another, even bigger, challenge, our devices keep the dopants in place. The sensing performance is achieved by switching the dopants between active and inactive states. A redox sensor for measuring chlorine concentrations in drinking water is the first member of this new class of sensors, although the concept certainly can be applied to many other systems.

Selected Publications:
- United States Patent Application 20160047773 "Sensors and Methods for Detecting an Oxidant" P. R. Selvaganapathy, P. Kruse, E. Hoque, H.-H. Hsu, published 2016/02/18 (Link) (Link)
- L. (H. H.) Hsu, E. Hoque, P. Kruse, and P. R. Selvaganapathy, A carbon nanotube based resettable sensor for measuring free chlorine in drinking water. Appl. Phys. Lett. 106 (2015) 063102. DOI: 10.1063/1.4907631
- K. R. Moonoosawmy and P. Kruse, Cause and consequence of carbon nanotube doping in water and aqueous media. J. Am. Chem. Soc. 132 (2010) 1572-1577. DOI: 10.1021/ja906820n

II. Mechanisms of Corrosion Inhibition

Polyaniline is capable of inhibiting corrosion of iron or steel by inducing the formation of a passive oxide film. It is our goal to understand the mechanisms behind the observation that coatings made of polyaniline or certain aniline oligomers can remain corrosion inhibitive even when the coating has been scratched through to the underlying metal. An interesting and unexpected outcome of our project was the finding that aniline oligomers are likely to be mobile on the iron oxide surface, a possible explanation for an ill-defined effect of them preventing corrosion in areas of the sample where they had not been applied. Recently, we have found strong evidence that in certain oxidation states aniline oligomers are indeed mobile, a finding of great importance for designing 'smart' self-healing corrosion inhibiting coatings, especially since the oligomers would not be subject to the same breakdown mechanism responsible for catastrophic failure of polyaniline coatings. The oligomers electronically interact with native iron oxide films and cause a decrease in substrate work function wherever present. We are currently working to further quantify this effect in order to analyze the underlying mechanism of migration and its dependence on environmental factors, and extend the concept to other corrosion inhibitors.

Selected Publications:
- T. Chowdhury, A. Mohtasebi, and P. Kruse, Nature of the Interaction of N,N'-Diphenyl-1,4-benzoquinonediimine with Iron Oxide Surfaces and Its Mobility on the Same Surfaces. J. Phys. Chem. C 121 (2017) 2294-2302. DOI: 10.1021/acs.jpcc.6b12568 (OPEN ACCESS after 12 Months)
- A. Mohtasebi, T. Chowdhury, L. H. H. Hsu, M. C. Biesinger, and P. Kruse, Interfacial Charge Transfer between Phenyl-Capped Aniline Tetramer Films and Iron Oxide Surfaces. J. Phys. Chem. C 120 (2016) 29248-29263. DOI: 10.1021/acs.jpcc.6b09950 (OPEN ACCESS after 12 Months)
- M. T. Greiner, M. Festin, and P. Kruse, Investigation of corrosion inhibiting aniline oligomer thin films on iron using photoelectron spectroscopy. J. Phys. Chem. C 112 (2008) 18991-19004. DOI: 10.1021/jp805533v

III. Mechanisms of Nanoscale Pattern Formation during Electropolishing

Nanoscale surface patterning is of great importance for applications ranging from catalysts to biomaterials. We have shown the formation of ordered nanoscale dimple arrays on tantalum, titanium, tungsten and zirconium during electropolishing. This is a rare example of an electrochemical pattern formation process that can be translated to other materials. The dimpled surfaces have been characterized with a variety of techniques including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, nuclear reaction analysis and x-ray photoelectron spectroscopy. The electrochemical conditions were optimized for each material. While conditions for titanium and tungsten resemble those for tantalum, zirconium requires a different type of electrolyte. Given the appropriate electropolishing chemistry, formation of these patterns should be possible on any metal surface. The process is very robust on homogeneous surfaces, but sensitive to inhomogeneities in chemical composition, such as in the case of differentially etched alloys. Of particular interest are the understanding of the underlying mechanism (selective oxide growth or dynamics of the liquid phase) and possible extensions to other materials systems.

Selected Publications:
- A. Imbault, Y. Wang, P. Kruse, E. Strelcov, E. Comini, G. Sberveglieri, and A. Kolmakov, Ultrathin gas permeable oxide membranes for chemical sensing: Nanoporous Ta2O5 test study. Materials 8 (2015) 6677-6684. DOI: 10.3390/ma8105333
- A. Awez Mohammad, Z. L. Arnott, Y. Wang, and P. Kruse, Benign and reproducible preparation of titanium tips. Rev. Sci. Instrum. 85 (2014) 026113. DOI: 10.1063/1.4865759
- A. D. Pauric, S. A. Baig, A. N. Pantaleo, Y. Wang, and P. Kruse, Sponge-like porous metal surfaces from anodization in very concentrated acids. J. Electrochem. Soc. 160 (2013) C12-C18. DOI: 10.1149/2.001302jes
- S. Singh, W. R. T. Barden, and P. Kruse, Nanopatterning of transition metal surfaces via electrochemical dimple array formation. ACS Nano 2 (2008) 2453-2464. DOI: 10.1021/nn800488h

Page background is an AFM image of reduced phenyl-capped aniline tetramers deposited on hematite.

(pk) 23 May 2017