Giacomo Benvenuti

Combinatorial Discovery and Optimization of Amorphous HfO2-Nb2O5 Mixture with Improved Transparency

Combinatorial high vacuum chemical vapor deposition (HV-CVD) of mixed HfO2-Nb2O5 thin films has been demonstrated to yield amorphous layers at substrate temperatures where individually deposited pure HfO2 and Nb2O5 films are polycrystalline. Spectroscopic ellipsometry of the films shows that adding HfO2 to Nb2O5 improves the transparency of the films while still maintaining a high refractive index. Atomic force microscopy measurements show that the root-mean-square surface roughness of the films is about 1.2 nm

Combinatorial Chemical Beam Epitaxy of Lithium Niobate Thin Films on Sapphire

A combinatorial chemical beam epitaxy technique was used to optimize deposition of (001) lithium niobate thin films on {001} sapphire substrates. Lithium tert-butoxide [Li(OBut)] and niobium tetra-ethoxy di-methyl-amino-ethoxide [Nb(OEt)(4)(dmac)] were used as precursors. The highest quality films obtained exhibited rocking curve full-width at half-maximum values of about 0.03 degrees and lithium contents {[Li]/[(Li)) + (Nb)]} larger than 48 (mol %) estimated by Raman spectroscopy. High-resolution transmission electron microscopy observations revealed that the lithium niobate film consists of a buffer layer (thickness <8 nm) with a high density of defects above which the epitaxial lithium niobate film was obtained

Chemical Vapor Deposition Kinetics and Localized Growth Regimes in Combinatorial Experiments

Laser-assisted deposition: The discovery of chemical vapor deposition (CVD) conditions under which the growth rate is a decreasing function of the precursor flux has the potential to boost the resolution of laser-assisted CVD processes whereas flux- and desorption-limited conditions appear to be the ideal environment for spatially addressable combinatorial experiments (see picture). Copyright

Determination of local refractive index variations in thin films by heterodyne interferometric scanning near-field optical microscopy

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 (lambda/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.

Geometry of Chemical Beam Vapor Deposition System for Efficient Combinatorial Investigations of Thin Oxide Films: Deposited Film Properties versus Precursor Flow Simulations

An innovative deposition system has been developed to construct complex material thin films from single-element precursors by chemical beam vapor deposition (CBVD). It relies on well distributed punctual sources that emit individually controlled precursor beams toward the substrate under high vacuum conditions combined with well designed cryo-panel surfaces that avoid secondary precursor sources. In this configuration the impinging flows of all precursors can be calculated at any substrate point considering the controlled angular distribution of the emitted beams and the ballistic trajectory of the molecules. The flow simulation is described in details. The major advantage of the deposition system is its ability to switch between several possible controlled combinatorial configurations, in which the substrate is exposed to a wide range of flow compositions from the different precursors, and a uniform configuration, in which the substrate is exposed to a homogeneous flow, even on large substrates, with high precursor use efficiency. Agreement between calculations and depositions carried out in various system configurations and for single, binary, or ternary oxides in mass transfer limited regime confirms that the distribution of incoming precursors on the substrate follows the theoretical models. Additionally, for some selected precursors and in some selected conditions, almost 100% of the precursor impinging on the substrate is incorporated to the deposit. The results of this work confirm the potentialities of CBVD both as a research tool to investigate efficiently deposition processes and as a fabrication tool to deposit on large surfaces.

TiO2 laser and electron beam assisted chemical deposition

Chemical Beam Deposition is a gas phase deposition technique with chemical precursors, operated under high vacuum conditions (10−6 mbar). One of the advantages over conventional Chemical Vapour Deposition (CVD) technique is that the highly reduced pressure allows the use of highly energetic beam particles (photons with energy over 3–3.5 eV, electrons, or ions) to assist the deposition without any gas phase interactions with the chemical precursor molecules. Densification of TiO2 thin films with anatase crystalline phase by a laser-assisted growth process is discussed.

Combinatorial Chemical Vapor Deposition of Lithium Niobate Thin Films

Combinatorial lithium niobate deposition on 150 mm naturally oxidized silicon (100) wafers in a high-vacuum chemical vapor deposition reactor using Li(OBut) and Nb(OEt)4(dmae) is presented. The novel precursor supply system allows individual spatial control of precursors impinging rates on the substrate. This results in variations of the film properties in a single experiment at a certain substrate temperature due to the influence of different precursors flow rates and ratios. It efficiently leads to deposition conditions to achieve highly oriented polycrystalline lithium niobate films.

Efficient optimization of high vacuum chemical vapor deposition of niobium oxide on full wafer scale

A systematic study of niobium oxide deposition using niobium tetraethoxy-dimethyl- amino-ethoxide (Nb(OEt)4(dmae)) precursor is presented. The deposition process was conducted in a high-vacuum chemical vapor deposition machine with precursor flux gradient capability. An efficient optimization of the deposition process was achieved and both mass-transport- and chemical-reaction-limited regimes were identified.