The performance of optical devices relying in vanadium dioxide (VO 2 ) technology compatible with the silicon platform depends on the polarization of light and VO 2 properties.In this work, optical switching in hybrid VO 2 /Si waveguides thermally triggered by lateral microheaters is achieved with insertion losses below 1 dB and extinction ratios above 20 dB in a broad bandwidth larger than 30 nm.The optical switching response has been optimized for TE and TM polarizations by using a homogeneous and a granular VO 2 layer, respectively, with a small impact on the electrical power consumption.The stability and reversibility between switching states showing the possibility of bistable performance is also demonstrated.

The influence of an external resistance on the performance of VO2 nanogap junctions is analyzed and experimentally characterized. The current-voltage response shows the reversible metal-insulator transition typical of VO2 based devices. When reaching the metallic state, the current through the VO2 junction is abruptly increased, which may result in electrical contact damage. Therefore, an external resistance in series with the VO2 junction is usually employed to limit the maximum current through the device. Our results indicate that the external resistance plays a key role in the switching power consumption showing an optimum value, which depends on the dimensions of the VO2 junction. In such a way, power consumption reductions up to 90% have been demonstrated by selecting the optimum external resistance value.

The change in the optical properties of VO2 across its insulator to metal to transition could give rise to novel photonic devices with beyond state-of-the art performance in terms of footprint, power consumption and speed operation. However, the final performance strongly depends on the control and efficiency of the phase transition in the VO2. For electro-optical applications, such control and efficiency is highly dependent on the electrode configuration. In this work, the influence of the electrodes is experimentally analyzed and an alternative approach is proposed to switch the VO2 to the metallic state by minimizing the electrical power consumption. The electro-optical performance of the proposed short-circuited electrode is also experimentally demonstrated. An extinction ratio of 12 dB is achieved with a 20 mu m long hybrid VO2/Si waveguide with an electrical power of only 11mW. The power consumption could be further reduced by decreasing the distance between the electrode and the silicon waveguide, which in this work has been fixed to 1.5 mu m, without affecting the optical losses.

A lateral displaced microheater is demonstrated for switching across the VO2 phase transition in ultrashort hybrid VO2/Si waveguides for both TE and TM light polarizations. Simulation and experimental results are obtained showing a very good agreement with a switching electrical power of around 10mW.

In this work, an unusual silicon chemical vapor deposition precursor is used, which allows the safe deposition of thin silica films in a controlled and reproducible manner at a lower thermal budget with a newly developed direct liquid injection − low pressure chemical vapor deposition system. The deposition is controlled by parameters such as deposition temperature, partial pressure of the gases, and flow rate of the precursor solution. X‐ray reflectivity and spectroscopic ellipsometry of the deposited samples show that the thickness of the layers is well controlled by deposition temperature, time, and oxygen flow. A growth rate of 4.5 Å min−1 is obtained without the addition of oxygen, which can be increased to 10.2 Å min−1 by the addition of oxygen. Atomic force microscopy, Rutherford backscattering spectroscopy, Fourier transform infrared spectroscopy, and drop shape analysis are used to measure roughness, composition, and hydrophobicity. Thin films of silicon dioxide are successfully grown. In addition, this newly developed system can be used for a wide range of films by varying the precursors or by co‐injecting nanoparticles suspension mixed with the chemical vapor deposition precursor in the direct liquid injection vaporizer.

Multiwall carbon nanotubes (CNTs) – carbon fibers (CFs) hybrid materials were produced by directly growing CNTs on CFs by means of chemical vapor deposition. For the latter, the oxidative dehydrogenation reaction of C2H2 and CO2 was applied, which allows growing CNTs without damaging the CF surface. Uni-directional nano-engineered carbon fiber reinforced composites (nFRCs) were fabricated by impregnating these hybrid materials with epoxy. The nFRCs subjected to single fiber push-out tests revealed a decrease of the interfacial shear strength (IFSS) of about 36% compared to the carbon fiber composites without CNTs. By means of transverse three-point bending tests performed on pre-notched composite beams inside a scanning electron microscope, the fracturing behavior parallel to the fibers was studied in-situ. The nFRCs showed significantly reduced fiber/matrix debonding while CNTs pull-out, CNTs bridging as well as matrix failure occurred. These results demonstrate that the presence of CNTs in nFRCs affects the stress distribution and consequently the damage initiation as well as the damage propagation. The presence of CNTs suppresses the stress concentration at the fiber/matrix interface and reduces the debonding of CFs from the matrix. However, our results indicate that the stress concentration shifts towards the CNTs' ends/matrix interface and causes promoted matrix failure leading to lower IFSS.

In this work, the use of a newly developed direct liquid injection low pressure chemical vapor deposition (DLI‐LPCVD) system is described, which allows for the deposition of thin films in a controlled and reproducible manner. The capabilities of this system are described via silica thin films deposited using the precursor tetraethyl orthosilicate (TEOS). The deposition of thin films is controlled by parameters, such as deposition temperature, partial pressure of the gases, and flow rate of the precursor solution. The thickness of the deposited layer is varied simply by changing deposition temperature and time. X‐ray reflectivity and spectroscopic ellipsometry of the deposited samples show that the thickness of the layers is well controlled by deposition temperature and time. Auger electron spectroscopy, in addition, motivates our choice to use cyclohexane as a solvent. A growth rate of 12.2 Å min−1 is obtained. Atomic force microscopy, Rutherford backscattering spectroscopy, Fourier transform infrared spectroscopy, and drop shape analysis are used to measure roughness, composition, and hydrophobicity. Thin films of silicon dioxide are successfully grown by the newly developed DLI‐LPCVD system. This system can be used for a wide range of films by varying the precursors.

The integration of active materials on silicon is emerging as a promising field in silicon photonics to improve the performance metrics of key photonic components, in particular active components. Active materials allow tuning their optical properties as function of external stimuli. Amongst them, vanadium dioxide (VO 2 ) has been largely investigated for different applications due to its controllable change between an insulating and a metallic phase. For photonic applications, VO 2 shows a promising performance due to the abrupt change in the refractive index between the two phases across the semiconductor to metal transition (SMT). In this work, we will present our recent results for enabling disruptive electrical switching performance in hybrid VO 2 /Si photonic structures. Results have been obtained in the framework of the FP7-ICT-2013-11-61456 SITOGA project.

We have grown epitaxial Cr-doped V2O3 thin films with Cr concentrations between 0% and 20% on (0001)-Al2O3 by oxygen-assisted molecular beam epitaxy. For the highly doped samples (>3%), a regular and monotonous increase of the resistance with decreasing temperature is measured. Strikingly, in the low doping samples (between 1% and 3%), a collapse of the insulating state is observed with a reduction of the low temperature resistivity by up to 5 orders of magnitude. A vacuum annealing at high temperature of the films recovers the low temperature insulating state for doping levels below 3% and increases the room temperature resistivity towards the values of Cr-doped V2O3 single crystals. It is well-know that oxygen excess stabilizes a metallic state in V2O3 single crystals. Hence, we propose that Cr doping promotes oxygen excess in our films during deposition, leading to the collapse of the low temperature insulating state at low Cr concentrations. These results suggest that slightly Cr-doped V2O3 films can be interesting candidates for field effect devices.

An ultra-low power 2×2 photonic switch based on VO 2 /Si technology is proposed. The switch structure consists of an add-drop ring resonator with a footprint below 50 μm 2 . The waveguide structure is based on a fully etched silicon waveguide with a VO 2 film on top of it. Electro-optical switching is achieved by means of the metal-insulator-transition (MIT) that can be induced in VO 2 . This MIT provides an ultra-large change of the refractive index at 1550 nm optical wavelengths that yields to ultra-low power operation. Waveguide structures have been fabricated by a combination of molecular beam epitaxy (MBE) growth, ex-situ annealing, e-beam lithography and lift-off. Experimental results have also been carried out to evaluate propagation losses as well as the electro-optical performance.

VO2 thin films were produced on sapphire and silicon substrates through post-deposition ex-situ thermal treatment of V2O3 and VOx films. Thin epitaxial films of V2O3 on sapphire and amorphous VOx films on silicon substrates were grown using oxygen assisted molecular beam epitaxy. The post-deposition annealing was performed at different temperatures using an Ar flow. Structural, optical and electrical characterizations were performed to confirm the transformation of the films. The transformed films present a change in resistance across the metal to insulator transition of four orders of magnitude for annealed V2O3 on sapphire and around one order of magnitude in the case of annealed VOx on silicon.

One-dimensional single crystalline InGaO3(ZnO)n (IGZO) nanostructures have great potential for various electrical and optical applications. This paper demonstrates for the first time, to our knowledge, a non-vacuum route for the synthesis of IGZO nanowires by annealing ZnO nanowires covered with solution-based IGZO precursor. This method results in nanowires with highly periodic IGZO superlattice structure. The phase transition of IGZO precursor during thermal treatment was systematically studied. Transmission electron microscopy studies reveal that the formation of the IGZO structure is driven by anisotropic inter-diffusion of In, Ga, and Zn atoms, and also by the crystallization of the IGZO precursor. Optical measurements using cathodoluminescence and UV-vis spectroscopy confirm that the nanowires consist of the IGZO compound with wide optical band gap and suppressed luminescence.