Liliya Nikolova

Liliya Nikolova

Tel.: +1 (514) 228-6978
Fax: +1 (450) 929-8102
nikolova@emt.inrs.ca

The recent surge of interest in nanostructured materials stems from the remarkable effects arising due to the size reduction. Interesting novel properties (optical, electronic, catalytic, magnetic, etc.) occur as the dimensions from a practically infinite solid crystal are reduced to a system composed of a small number of atoms. To optimize the properties of such novel systems however, more knowledge needs to be acquired on their structure and how it affects their properties.
The equilibrium states of the materials are well known and probed by large variety of techniques for characterisation, while the information on the intermediate states is not complete. To reveal the process of structural transformation and to understand the dynamics, a description of the states during the transition is need. At present, there is no well-developed general method for the atomic-level structural determination of short-lived transient states.
The transmission electron microscope (TEM) is a powerful and versatile tool for materials characterisation offering very high spatial resolution. However, it is not suitable for direct imaging of structural transitions because of the poor temporal resolution. In fact, the images capture could require few seconds. The goal of this research project is the modification of a TEM to Dynamic TEM (DTEM) to improve the temporal resolution and to reveal the dynamics of irreversible processes of structural transformation (as nucleation, interphase boundary motion, shock propagation, radiation damage, solid state chemical reactions, etc). Therefore, one of the key modifications of the TEM is the replacement of the conventional thermionic or field emission gun with a source of type photocathode. By this manner generation of packets of electrons with high density through pulsed laser excitement is obtained. Hence, high temporal resolution (nanosecond or better) is achievable while maintaining the high spatial resolution (few nanometers). The structural transition in the sample is initiated by a ‘pump’ laser pulse. The specimen images are taken at a variable time-delay after the excitation using the short burst of electrons that takes a ‘snapshot’ of the sample. The method permits to make a movie of the evolution of the sample’s structure.

NFL publications


L. Nikolova, M. J. Stern, J. M. MacLeod, B. W. Reed, H. Ibrahim, G. H. Campbell, F. Rosei, T. Lagrange, and B. J. Siwick. In situ investigation of explosive crystallization in a-Ge: Experimental determination of the interface response function using dynamic transmission electron microscopy. Journal of Applied Physics, 116, 093512 (2014). (PDF).
S. Li, R. Nechache, I. A. V. Davalos, G. Goupil, L. Nikolova, M. Nicklaus, J. Laverdière, A. Ruediger, and F. Rosei. Ultrafast Microwave Hydrothermal Synthesis of BiFeO3 Nanoplates. Journal of the American Ceramic Society, 96, 3155–3162 (2013). (PDF).
K. T. Dembele, R. Nechache, L. Nikolova, A. Vomiero, C. Santato, S. Licoccia, and F. Rosei. Effect of multi-walled carbon nanotubes on the stability of dye sensitized solar cells. Journal Of Power Sources, 233, 93–97 (2013). (PDF).
L. Nikolova, T. LaGrange, M. J. Stern, J. M. MacLeod, B. W. Reed, H. Ibrahim, G. H. Campbell, F. Rosei, and B. J. Siwick. Complex crystallization dynamics in amorphous germanium observed with dynamic transmission electron microscopy. Physical Review B, 87, 064105 (2013). (PDF).
T. LaGrange, B. W. Reed, M. K. Santala, J. T. McKeown, A. Kulovits, J. M. K. Wiezorek, L. Nikolova, F. Rosei, B. J. Siwick, and G. H. Campbell. Approaches for ultrafast imaging of transient materials processes in the transmission electron microscope. Micron, 43, 1108–1120 (2012). (PDF).
S. Li, R. Nechache, C. Harnagea, L. Nikolova, and F. Rosei. Single-crystalline BiFeO3 nanowires and their ferroelectric behavior. Applied Physics Letters, 101, 192903 (2012). (PDF).
L. Nikolova, T. LaGrange, B. W. Reed, M. J. Stern, N. D. Browning, G. H. Campbell, J. C. Kieffer, B. J. Siwick, and F. Rosei. Nanocrystallization of amorphous germanium films observed with nanosecond temporal resolution. Applied Physics Letters, 97, 203102 (2010). (PDF).
M. L. Taheri, S. McGowan, L. Nikolova, J. E. Evans, N. Teslich, J. P. Lu, T. LaGrange, F. Rosei, B. J. Siwick, and N. D. Browning. In situ laser crystallization of amorphous silicon: Controlled nanosecond studies in the dynamic transmission electron microscope. Applied Physics Letters, 97, 032102 (2010). (PDF).
C. Yan, L. Nikolova, A. Dadvand, C. Harnagea, A. Sarkissian, D. F. Perepichka, D. Xue, and F. Rosei. Multiple NaNbO3/Nb2O5 Heterostructure Nanotubes: A New Class of Ferroelectric/Semiconductor Nanomaterials. Advanced Materials, 22, 1741–1745 (2010). (PDF).