Lucia ROMANO

Researcher of Physics of matter [FIS/03]
Office: DFA 262a
Email: lucia.romano@ct.infn.it
Phone: 5440


On leave of absence. Professor Romano is presently performing research at Paul Scherrer Institute (PSI) and ETH Zurich, Switzerland.


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The research activity of Lucia Romano is fully focused on gratings and optics microfabrication techniques for X-ray imaging and it is ongoing at Paul Scherrer Institute in Switzerland and ETH Zurich.

https://www.psi.ch/en/x-ray-tomography-group/research

Typical grating interferometer consists of a phase shifting grating (G1), analyzing grating (G2) and an optional absorbing source grating (G0). Usually, required grating period is in a range of few microns. The height of the lines of G1 grating should provide a certain phase shift, while the height of the grating lines of G2 should be sufficient to suppress radiation of defined energy. In both cases, structures with heights of tens (or even hundreds) of micrometers are required. However, the realization of structures with so high aspect ratios yet having sufficient quality over the large area is demanding. We develop fabrication procedures which enable such gratings. We produce G1 gratings in Si by reactive ion etching using Bosch technique 1 or by metal assisted chemical etching 2. The absorbing G0 and G2 gratings are produced by filling Si templates with metal utilizing electroplating, metal casting 3 or atomic layer deposition 4. Larger structures can alternatively be produced by laser cutting in W foils.

Grating fabrication is the main bottleneck so far preventing grating-based X-ray phase-contrast interferometry (GI) from being applied at high energies and large field of view. Metal Assisted Chemical Etching (MacEtch) is an electroless chemical etching technique that has been largely used to create high aspect ratio nanostructures in silicon substrates 5. With respect to the other wet etching techniques, MacEtch showed better performance in terms of anisotropy and feature size. However, MacEtch still suffers from some limitations such as the control of the catalyst stability for etching high aspect ratio structures in the micro-scale and off-mask undesired porosity. This research project wants to answer the fundamental open questions about MacEtch in order to fully explore the range of application and the limits of this technique for grating fabrication and to point out the real performances in terms of etching selectivity, rate, aspect ratio, feature size and X-ray optical performances in combination with other proper technique for the realization of the absorber gratings. The main goal is to use MacEtch for grating fabrication with characteristics that fulfil high energy and large field of view applications. Understanding how MacEtch works with the proper knowledge about semiconductor physics and metal nanostructures is the key to optimize this process and to make it reliable as a grating fabrication technology.

 

1              Kagias, M. et al. Fabrication of Au gratings by seedless electroplating for X-ray grating interferometry. Materials Science in Semiconductor Processing 92, 73-79, doi:https://doi.org/10.1016/j.mssp.2018.04.015 (2019).

2              Romano, L. et al. Metal assisted chemical etching of silicon in gas phase: a nanofabrication platform for X-ray optics. Nanoscale Horizons, doi:10.1039/C9NH00709A (2020).

3              Romano, L., Vila-Comamala, J., Schift, H., Stampanoni, M. & Jefimovs, K. Hot embossing of Au- and Pb-based alloys for x-ray grating fabrication. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena 35, 06G302, doi:10.1116/1.4991807 (2017).

4              Vila-Comamala, J. et al. Towards sub-micrometer high aspect ratio X-ray gratings by atomic layer deposition of iridium. Microelectronic Engineering 192, 19-24, doi:https://doi.org/10.1016/j.mee.2018.01.027 (2018).

5              Romano, L., Kagias, M., Jefimovs, K. & Stampanoni, M. Self-assembly nanostructured gold for high aspect ratio silicon microstructures by metal assisted chemical etching. Rsc Advances 6, 16025-16029 (2016).