Tom and Carolyn Marquez Assistant Professor of Biophysics
M.Sc., Maria Curie-Sklodowska University, Lublin, Poland, 2001
Ph.D., Leopold-Franzens-University, Innsbruck, Austria, 2004
Habilitation, Leopold-Franzens-University, Innsbruck, Austria, 2011
Address: NSH 311
Phone: (574) 631-1846
Personal webpage: http://www.nd.edu/~sptasins/
Interaction of water and organic molecules with surfaces at interfaces
Near ambient and ultra-high vacuum x-ray photoelectron spectroscopy of molecular interactions at metal and semiconductor surfaces.
Recently, we focused on morphology-dependent oxidation on semiconductor surfaces. Interest in passivation of semiconductor nanostructures to improve fast optoelectronics and enhance solar cell efficiency is rapidly growing. We have focused recently on developing a fundamental understanding of the surface interaction between III-V semiconductors and common gaseous molecules such as oxygen, water vapor, and other small compounds. Interfacial chemistry is monitored in real time and under conditions close to ambient using near-ambient pressure X-ray photoelectron spectroscopy. Oxygen interaction with the GaAs surface was shown to be a dynamic oxidation processes, which involved the formation of gallium oxides (i.e., Ga2O and Ga2O3) with increased O2 pressure and/or temperature, as well as arsenic oxides. The latter mainly followed an increase of temperature. The level of total oxidation was demonstrated to strongly depend on the morphology of the GaAs sample, being distinctly higher in an ensemble of GaAs nanowires compared to a simple planar crystalline surface.
Atmospheric pressure plasma jet induced physics and chemistry
Development of plasma sources as a radiation tool for biological systems.
We have been working on 3D mapping of plasma reactive areas in biological systems such as network of cancer cells or bacteria. A nitrogen atmospheric pressure plasma jet (APPJ) is low-energy radiation, but it contains a plethora of reactive species. Many plasma species that are generated within plasma discharge diffuse across the open boundary of the visible jet into the surrounding air. As these species diffuse, their density decreases and extends the reactive area, which is difficult to quantify by the conventional plasma diagnostic techniques. We have found that oral cancer cells are very susceptible to plasma treatment; they can therefore be used as a marker of APPJ effective areas. Damaged cells were identified, visualized, and quantified using immunofluorescence assay. As a result, the effective area of damage and damage level were determined and plotted as 3D images. The obtained 3D maps showed a decrease in the number of damaged cells with a distance from direct contact of the APPJ with the cells and demonstrate a linear correlation between the increase of plasma effective area and treatment time.
Dissociative electron attachment processes
Mass spectrometry of ion and neutral formation induced by electron attachment to molecules in the gas and condensed phases.
Our recent study confirmed that we can tailor bond dissociation in gas-phase biomolecules by low-energy electrons. Gas-phase dissociative electron attachment (DEA) to N-methylformamide (NMF, HC(=O)NHCH3), measured with a locally designed and constructed, and recently optimized, high vacuum chamber, revealed site-selectivity in the DEA process leading to the formation of dehydrogenated, closed-shell anions. Based on results from theoretical modeling and experimental isotopic studies, we were able to determine the precise reaction pathways. The dominant fragmentations involved the formation of CN¯ and OCN¯, which are produced from electron capture by the π antibonding C=O orbital coupled with dissociation of the N-CH3 bond and formation of a C=N bond. Our studies contribute to the ongoing search for understanding and evaluation of biological effects involving low-energy electrons.
Zhang, X, and S. Ptasinska. “Evolution of surface-assisted oxidation of GaAs (100) by gas-phase N2O, NO, and O2 under near-ambient pressure conditions.” Journal of Physical Chemistry C 119 (2015): 262.
Zhang, X., and S. Ptasinska. "Dissociative Adsorption of Water on an H2O/GaAs(100) Interface: In Situ Near-Ambient Pressure XPS Studies." Journal of Physical Chemistry C 118 (2014): 4259.
Dawley, M.M., and S. Ptasinska. "Dissociative electron attachment to gas-phase N-methylformamide." International Journal of Mass Spectrometry 132 (2014): 365-366.
Zhang, X., and S. Ptasinska. "Growth of Silicon Oxynitride Films by Atmospheric Pressure Plasma Jet." Journal of Physics D 47 (2014): 145202.
Han, X., W.A. Cantrell, E.E. Escobar, and S. Ptasinska. "Plasmid DNA Damage Induced by Helium Atmospheric Pressure Plasma Jet." European Physical Journal D 68 (2014): 46.
Zhang, X., E. Lamere, X. Liu, J.K. Furdyna, and S. Ptasinska. "Morphology dependence of interfacial oxidation states of gallium arsenide under near ambient conditions." Applied Physics Letters 104 (2014): 181602.