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Nanostructured properties

Final Report Summary - 3D-DEMO (Single step three-dimensional deposition of complex nanopatterned multifunctional oxide thin films)

The aim of the 3D-DEMO project was to propose a new vision in oxide thin film deposition, namely the development of a new thin film deposition technique, the so-called Chemical beam epitaxy (CBE), in order to achieve 3D patterning of thin film properties in a single step as well as the characterisation of the alkali niobate family compounds by combinatorial deposition which constitute lead-free materials for innovative piezoelectric and electro-optic applications.

By means of CBE thin films would grow epitaxially on substrates as well as the properties would be patterned in three dimensions. Pulsed laser deposition (PLD), which is a technique for small samples only, was used as a complimentary technique as it allows samples to be reliably grown fast. Several test devices and structures have been used such as thin film wave guides, frequency doubling, wave trapping in ring oscillators as well as bulk acoustic wave resonators. Furthermore, Near-field scanning optical microscopy (NSOM) was employed in order to probe optical uniformity as well as patterned features.

The project achieved in successfully implementing the CBE method for depositing 101-oriented lithium niobate (LiNbO3) on the 100-oriented magnesium oxide (MgO) substrate whereas the growth of 001-oriented LiNbO3 in 111-oriented MgO substrate failed due to its rough surface. Furthermore, compared with the PLD method, the CBE technique allowed films to be deposited at lower temperatures, i.e. 500 degrees Celsius. This result ought to directly associate with the thickness that thin films exhibit at certain temperatures. CBE films were anticipated to exhibit a greater value of critical thickness; however, it could not be proved in this project. On the other side, CBE films can be made smoother; therefore, they are likely to meet better the specifications of optical applications.

Moreover, alkali and earth alkali PLD thin films demonstrated leakage as well as poling inhibition problematic behaviour. Manganese (Mn) doping could possibly lead to much lower leakage of (NaKLi) (NbTaSb) thin films. Considering the rough and unstable surface of the crystal substrates at high temperatures and the subsequent effects of cracking and leakage as well as the poling inhibition issues, the CBE method proved to be superior to that of the PLD. Finally, the project achieved in developing a heterodyne interferometric SNOM (H-SNOM) which constitutes a detection method that allows obtaining information about structures and spectrally variant properties of nano/micro photonic thin films; namely, it enabled to better define the stop-band edge in LN/MgO thin film waveguides.

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