We report on a heterodyne interferometric scanning near-field optical microscope developed for characterizing, at the nanometric scale, refractive index variations in thin films. An optical lateral resolution of 80 nm (λ/19) and a precision smaller than 10−4 on the refractive index difference have been achieved. This setup is suitable for a wide set of thin films, ranging from periodic to heterogeneous samples, and turns out to be a very promising tool for determining the optical homogeneity of thin films developed for nanophotonics applications.

We present an innovative dielectric layer composed of a ternary oxide composite, including high-k materials Al2O3, ZrO2, and HfO2. These composite films were deposited using the Chemical Beam Vapor Deposition (CBVD) technique with a combinatorial approach. We investigated their structural, nanostructural, morphological, and electrical properties for three different Al:Zr:Hf atomic concentrations (∼27:61:12), (∼44:42:13), and (∼67:20:12), which are normalized as AZH (2.2:5:1), AZH (3.3:3.2:1), and AZH (5.5:1.6:1), respectively. X-ray diffraction (XRD) and Raman spectroscopy revealed cubic phase Al2O3 and monoclinic phases of ZrO2 as well as HfO2 in all AZH films. X-ray photoelectron spectroscopy (XPS) showed +3, +4, and +4 oxidation states for Al, Zr, and Hf, respectively. Transmission electron microscopy (TEM) images demonstrated a uniform, dense morphology with no signs of interdiffusion. Among the films, the AZH (5.5:1.6:1) sample exhibited the lowest leakage current density (∼4 × 10−11 A/mm2 at 10 V) and the highest capacitance density (∼15 fF/μm2 at 100 Hz). These results suggest that the proposed dielectric layer has significant potential for advanced applications requiring high capacitance and low leakage.

Combinatorial approach has been widely recognized as a powerful strategy to develop new-higher performance materials and shed the light on the stoichiometry-dependent properties of known systems. Herein, we take advantage of the unique features of chemical beam vapor deposition to fabricate compositionally graded Na_1+xTaO_3±δ thin films with −0.6 < x < 0.5. Such a varied composition was enabled by the ability of the employed technique to deliver and combine an extensive range of precursors flows over the same deposition area. The film growth occurred in a complex process, where precursor absolute flows, flow ratios, and substrate temperature played a role. The deviation of the measured Na/Ta ratios from those predicted by flow simulations suggests that a chemical-reaction limited regime underlies the growth mechanism and highlights the importance of the Ta precursor in assisting the decomposition of the Na one. The crystallinity was observed to be strongly dependent on its stoichiometry. High under-stoichiometries (e.g., Na_0.5TaO_3−δ) compared to NaTaO₃ were detrimental for the formation of a perovskite framework, owing to the excessive amount of sodium vacancies and oxygen vacancies. Conversely, a well-crystallized orthorhombic perovskite structure peculiar of NaTaO₃ was observed from mildly under-stoichiometric (e.g., Na_0.9TaO_3−δ) to highly over-stoichiometric (e.g., Na_1.5TaO_3+δ) compositions.