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About Me
I graduated from UCL in 2018 with an MSci in Physics with Physical Chemistry. In completed my final year project, under Prof. Alex Shluger, which investigated the possibility of using tight binding methods to model organic molecules on rutile titania surfaces. The adsorption properties of different binding geometries of Coumarin 343 on rutile titania surfaces as predicted by tight binding were compared to theoretical data obtained by ab initio methods and previous experimental work. In September 2018, I started my PhD in the same group, continuing the work that was started in my final year.
Research
My research focusses on modelling molecules on oxide surfaces using theoretical methods, to study the interactions that govern the adsorption of molecules on semi-conducting and insulating surfaces. The adsorption of molecules on surfaces are important in applications such as catalysis and sensors.
Rutile TiO2 (r-TiO2) has attractive intrinsic properties such as a wide band gap of about 3 eV, high dielectric constant, and a high refractive index. These attributes have prompted extensive research into the material due to the range and variety of potential applications including solar cells, gas sensors, photocatalysis, paints and coatings. Carboxylate molecules are seen as favourable precursors molecules when designing and selecting molecules that are used to functionalize titania surfaces due their polar COOH group, which is found to strongly anchor to the (110)-1x1 surface. Imaging techniques such as Non-Contact Atomic Force Microscopy (NC-AFM) and Scanning Tunnelling Microscopy (STM) have shown small carboxylates form ordered arrays on the (110)-1x1 surface [1-2]. This work studies the adsorption of small carboxylates of the rutile TiO2 surfaces with Density Functional Theory (DFT) and Density Functional Theory Tight Binding (DFTB). The energetic contributions of different binding geometries and periodicities (Figure 1) of small carboxylates on rutile titania surfaces are studied. This work has been carried out in collaboration with the group under Prof. Geoff Thornton, UCL.
Figure 1: Schematic diagram of acetate adsorption on the TiO2 (110) surface in the 2x1 periodicity.
Gas Sensing with Silicon Nanowires
Solid state gas sensors are used in a variety of industries such as aerospace, automotive and the oil industry. These devices are used to detect gas compounds that may be explosive or harmful to lifeforms and play an important role in society. There exists constant demand to develop smaller, more robust devices which have high sensitivity and selectivity. In many practical applications, they will need to work in conditions, where the concentrations of target gases maybe as low as 10 ppm and compete with processes that include background gases, which may interfere with the response mechanism. Furthermore, fast recovery and response times are essential components towards the making of a high-quality sensor. For this project, we are in collaboration with the group of Prof. Yossi Rosenwaks at Tel Aviv University, Israel, which has fabricated a novel gas sensor that exploits the properties of electrostatically formed Si nanowires (EFN) covered by SiO2 active layer and exhibits high sensitivity to volatile gases. [3, 4] This sensor is found to work in ambient conditions and detect gas concentrations as low as 20 ppm. It has selectively towards ammonia, alcohols and small hydrocarbons. [5-7] In this study, potential sensing mechanisms of the EFN device will be investigated. This work is being conducted using DFT and molecular dynamics methods, to model the interactions of said molecules on SiO2 surfaces in the presence of water (Figure 2).
Figure 2: Screenshot of molecular dynamics trajectory of water adsorption on the alpha-quartz SiO2(001) surface.
References
[1] Grinter, D. C.; Woolcot, T.; Pang, C. L.; Thornton, G. Ordered Carboxylates on TiO<sub>2</sub>(110) Formed at Aqueous Interfaces. Journal of Physical Chemistry Letters 2014. https://doi.org/10.1021/jz502249j.
[2] Hussain, H.; Torrelles, X.; Cabailh, G.; Rajput, P.; Lindsay, R.; Bikondoa, O.; Tillotson, M.; Grau-Crespo, R.; Zegenhagen, J.; Thornton, G. Quantitative Structure of an Acetate Dye Molecule Analogue at the TiO 2 -Acetic Acid Interface. J. Phys. Chem. C 2016, 120 (14), 7586-7590. https://doi.org/10.1021/acs.jpcc.6b00186.
[3] Swaminathan, N.; Henning, A.; Vaknin, Y.; Shimanovich, K.; Godkin, A.; Shalev, G.; Rosenwaks, Y. Dynamic Range Enhancement Using the Electrostatically Formed Nanowire Sensor. ACS Sens. 2016, 1 (6), 688-695. https://doi.org/10.1021/acssensors.6b00096.
[4] Henning, A.; Molotskii, M.; Swaminathan, N.; Vaknin, Y.; Godkin, A.; Shalev, G.; Rosenwaks, Y. Electrostatic Limit of Detection of Nanowire-Based Sensors. Small 2015, 11 (37), 4931-4937. https://doi.org/10.1002/smll.201500566.
[5] Henning, A.; Swaminathan, N.; Vaknin, Y.; Jurca, T.; Shimanovich, K.; Shalev, G.; Rosenwaks, Y. Control of the Intrinsic Sensor Response to Volatile Organic Compounds with Fringing Electric Fields. ACS Sens. 2018, 3 (1), 128-134. https://doi.org/10.1021/acssensors.7b00754.
[6] Swaminathan, N.; Henning, A.; Jurca, T.; Hayon, J.; Shalev, G.; Rosenwaks, Y. Effect of Varying Chain Length of N-Alcohols and n-Alkanes Detected with Electrostatically-Formed Nanowire Sensor. Sensors and Actuators B: Chemical 2017, 248, 240-246. https://doi.org/10.1016/j.snb.2017.03.150.
[7] Henning, A.; Swaminathan, N.; Godkin, A.; Shalev, G.; Amit, I.; Rosenwaks, Y. Tunable Diameter Electrostatically Formed Nanowire for High Sensitivity Gas Sensing. Nano Res. 2015, 8 (7), 2206-2215. https://doi.org/10.1007/s12274-015-0730-1.
