Sabine Lay

Undoped TiO2 and nitrogen-doped TiO2 thin films deposited by atomic layer deposition on planar and architectured surfaces for photovoltaic applications

Undoped and nitrogen doped TiO2 thin films were deposited by atomic layer deposition on planar substrates. Deposition on 3D-architecture substrates made of metallic foams was also investigated to propose architectured photovoltaic stack fabrication. All the films were deposited at 265 degrees C and nitrogen incorporation was achieved by using titanium isopropoxide, NH3 and/or N2O as precursors. The maximum nitrogen incorporation level obtained in this study was 2.9 at. %, resulting in films exhibiting a resistivity of 115 Omega cm (+/-10 Omega cm) combined with an average total transmittance of 60% in the 400-1000 nm wavelength range. Eventually, TiO2 thin films were deposited on the 3D metallic foam template.

Reactive chemical vapor deposition of heteroepitaxial Ti1−xAlxN films

Processing of Ti1−xAlxN thin films by the reactive chemical vapor deposition (R-CVD) technique has been performed from the reaction between a titanium tetrachloride (TiCl4–H2) gas mixture and (0001) c-plane monocrystalline aluminium nitride (AlN) films at high temperatures, in the 800–1200 °C range. As a typical result, the growth of epitaxial 70 nm thick layers of (111)-fcc Ti1−xAlxN (0.05 = x = 0.65) has been processed. Multicomponent mass transport and diffusion modelling is proposed to assess the experimental results. A good agreement is found between the experimental thickness of the transformed zones and the calculated titanium diffusion length in AlN. Fcc-Ti1−xAlxN phase formation can be regarded as a diffusion-controlled mechanism. The novel experimental methodology developed in this work could help in understanding the complex formation and stability of this technologically important material.

Evaluation of Alternative Atomistic Models for the Incipient Growth of ZnO by Atomic Layer Deposition

ZnO thin films are interesting for applications in several technological fields, including optoelectronics and renewable energies. Nanodevice applications require controlled synthesis of ZnO structures at nanometer scale, which can be achieved via atomic layer deposition (ALD). However, the mechanisms governing the initial stages of ALD had not been addressed until very recently. Investigations into the initial nucleation and growth as well as the atomic structure of the heterointerface are crucial to optimize the ALD process and understand the structure–property relationships for ZnO. We have used a complementary suite of inxa0situ synchrotron x-ray techniques to investigate both the structural and chemical evolution during ZnO growth by ALD on two different substrates, i.e., SiO2 and Al2O3, which led us to formulate an atomistic model of the incipient growth of ZnO. The model relies on the formation of nanoscale islands of different size and aspect ratio and consequent disorder induced in the Zn neighbors’ distribution. However, endorsement of our model requires testing and discussion of possible alternative models which could account for the experimental results. In this work, we review, test, and rule out several alternative models; the results confirm our view of the atomistic mechanisms at play, which influence the overall microstructure and resulting properties of the final thin film.