Anderson Dussan

TiO₂ nanotubes and ZnO thin films were investigated as oxide-based memristive systems for resistive switching and state-endurance applications under variable environmental conditions. TiO₂ nanotubes were synthesized by electrochemical anodization, while ZnO thin films were deposited on Ti substrates by DC magnetron sputtering. Structural, chemical, and morphological properties were examined by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. TiO₂ exhibited a vertically aligned nanotubular morphology, whereas ZnO showed a granular thin-film surface. Electrical characterization was performed using Au top electrodes and Ti as the bottom electrode under atmospheric pressure and high-vacuum conditions, with temperature varied from 353 K down to 77 K. Both materials exhibited hysteretic current–voltage behavior associated with resistive switching, although their response was strongly influenced by morphology, defect distribution, and environmental conditions. TiO₂ nanotubes showed stable high- and low-resistance states, with an ON/OFF ratio of approximately 4.65, indicating robust state endurance. The observed behavior was attributed to oxygen-vacancy-mediated transport, filament stabilization, and interface effects. These results highlight the relevance of comparing TiO₂ and ZnO nanostructures for identifying oxide systems capable of maintaining resistive states under temperature and pressure variations, supporting their potential for low-power non-volatile memory applications.

In this work, TiO₂ and TiO₂:Co nanotubes were fabricated via electrochemical anodization, using Ti (99.99% purity) and Ti/Co foils as the anode and cathode. Cobalt was deposited onto the Ti foils using the DC magnetron sputtering technique under a working pressure of 2.5 × 10⁻² Torr. The resulting nanotubes exhibited wall nodes and an average length of 308.6 ± 13.07 nm for TiO₂ and 92.63 ± 2.846 nm for TiO₂:Co. The synthesized structures were characterized by X-ray diffraction (XRD), identifying anatase as the predominant phase, accompanied by an amorphous halo. Two types of MSM devices were fabricated to study bulk and surface conduction: a transverse configuration (TE/(TiO₂, TiO₂:Co)/Ti), with top electrodes (TE) of Al or Au, and a coplanar configuration (Al/TiO₂/Al). Surface topography and surface-potential variations were investigated using Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM), respectively. The device behavior is mainly governed by the TE/TiO₂ junction due to the absence of an energy barrier at the TiO₂/Ti interface. All samples exhibit asymmetric I–V behavior with higher conduction under positive bias. The Au/TiO₂/Ti device showed the lowest resistance among the Ti BE structures, displaying Schottky behavior with low reverse current leakage and a shift in the zero-current crossing depending on the scan direction. Barrier heights near the zero-current crossing, calculated via the thermionic emission model, were 0.91 eV and 0.70 eV for the reverse and forward directions, respectively. Ideality factors and series resistance exceeded 6.8 and 40 kΩ, respectively, suggesting additional transport mechanisms. In addition, magnetization as a function of the applied field was generated in the TiO₂:Co nanotubes, evidencing their ferromagnetic-like behavior.

TiO₂ nanotubes and ZnO thin films were investigated as oxide-based memristive systems for resistive switching and state-retention applications under variable environmental conditions. TiO₂ nanotubes were synthesized by electrochemical anodization, while ZnO thin films were deposited on Ti substrates by DC magnetron sputtering. Structural, chemical, and morphological properties were examined by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. TiO₂ exhibited a vertically aligned nanotubular morphology, whereas ZnO showed a granular thin-film surface. Electrical characterization was performed using Au top electrodes and Ti as the bottom electrode under atmospheric pressure and high-vacuum conditions, with temperature varied from 353 K down to 77 K. Both materials exhibited hysteretic current–voltage behavior associated with resistive switching, although their response was strongly influenced by morphology, defect distribution, and environmental conditions. TiO₂ nanotubes showed stable high- and low-resistance states, with an ON/OFF ratio of approximately 4.65, indicating robust state retention. The observed behavior was attributed to oxygen-vacancy-mediated transport, filament stabilization, and interface effects. These results highlight the relevance of comparing TiO₂ and ZnO nanostructures for identifying oxide systems capable of maintaining resistive states under temperature and pressure variations, supporting their potential for low-power non-volatile memory applications.

In this work, TiO₂ and TiO₂:Co nanotubes were fabricated via electrochemical anodization, using Ti (99.99% purity) and Ti/Co foils as the anode and cathode. Cobalt was deposited onto the Ti foils using the DC magnetron sputtering technique under a working pressure of 2.5×10⁻² Torr. The resulting nanotubes exhibited wall nodes and an average length of ~300 nm. The synthesized structures were characterized by X-ray diffraction (XRD), identifying anatase as the predominant phase, accompanied by an amorphous halo. Two types of MSM devices were fabricated to study bulk and surface conduction: a transverse configuration (TE/(TiO₂, TiO₂:Co)/Ti), with top electrodes (TE) Al or Au, and a coplanar configuration (Al/TiO₂/Al). Topographic study was analyzed using Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) in tapping mode. The device behavior is mainly governed by the TE/ TiO₂ junction due to the absence of an energy barrier at the TiO₂/Ti interface. All samples exhibit asymmetric I-V behavior with higher conduction under positive bias. The Au/ TiO₂/Ti device showed the lowest resistance among Ti BE structures, displaying Schottky behavior with low reverse current leakage and a shift in the zero-current crossing depending on the scan direction. Barrier heights near the zero-current crossing, calculated via the thermionic emission model, were 0.91 eV and 0.70 eV for reverse and forward directions, respectively. Ideality factors and series resistance exceeded 6.8 and 40 kΩ, suggesting additional transport mechanisms. In addition, magnetization as a function of the applied field was realized to TiO₂:Co nanotubes evidencing the ferromagnetic-like behavior.

In this work, TiO ₂ :Co nanotubes were fabricated via electrochemical anodization, using Ti foils (99.99% purity) as the cathode, onto which Co layers were deposited via DC magnetron sputtering. To design a nanotube-based memristor structure, PET tape composed of polyester with 0.05 mm thick, was used. With this PET tape, the active area was reduced to two square regions of 0.7 cm per side, separated by 0.3 cm. I-V measurements revealed a hysteresis-like behavior, with SET and RESET processes characteristic of resistive switching. Additionally, robustness tests at room temperature over 1200 cycles showed a slight increase in both, high and low resistance states (HRS and LRS, respectively) as the number of cycles was increased. This effect could be related to the stability of the conductive filament formation, influenced by the presence of Co in the material matrix, which may introduce defects that enhance the operating voltage and resistive switching behavior. The analysis of the current signal under the defined operating conditions of the memory unit confirmed that the resistive switching behavior of the device enables binary logic functionality, allowing it to operate as the core element of a logic system. The proposed device integrates four digital systems that interpret a discrete signal. Using demultiplexers and analog switches, it executes a write/read process by applying two electrical potentials (6 V and 2 V) to induce resistive changes in the material within a range of 2 MΩ to 100 Ω. These variations were subsequently interpreted as a binary structure through a comparator amplifier, which defines two digital states readable as a discrete signal.

The system consists of Co diluted in TiO2 nanotubes obtained by electrochemical anodization process over Co/Ti foils, with NH4F, distilled water, and ethylene glycol. Cobalt was deposited on the Ti foils (99.99% purity) via DC magnetron sputtering at room temperature. The anodization process establishes the percentage of Co dilution into the TiO2 matrix around 0.67 wt. % through EDXS measurements. The nanostructure of the nanotubes was evidenced by the SEM micrographs. These measurements permitted the observation of nanotubes with a hollow hexagonal morphology. Nevertheless, we model this nanotube as a cylindrical-hollow nanotube with inner and outer radii ∼15 and 30 nm, respectively, and the height is 96.6 nm according to the SEM micrographs. The I–V curves show a bipolar resistive behavior with the resistance ratio high resistance state/low resistance state remaining essentially stable, around 1.22. The results obtained through Ubermag environment simulations were compared with experimental magnetization measurements as a function of the magnetic field at room temperature for Co-doped TiO2 nanotubes. This comparison enabled their analysis as a diluted magnetic material for potential applications in information storage memories.

Resistive Random Access Memories (RRAMs) traditionally utilize a metal/insulator/metal architecture. This study introduces an innovative configuration employing metal/oxide-diluted magnetic semiconductors (O-DMS)/metal on flexible substrate, leveraging the enhanced performance of magnetic control in resistive switching. We investigated the structural, morphological, magnetic, and electrical properties of cobalt-doped ZnO and TiO₂ thin films, synthesized via DC magnetron sputtering. XRD measurements stablish the presence of Co₃O₄ phases in the samples of Co-doped ZnO thin films with substrate temperature (Ts) of 423 K, while Raman spectra of Co-doped TiO₂ thin film not evidencing the formation of the Co–O binary phases associated to the low substrate temperature (Ts = 293 K). High-resolution SEM and AFM analyses revealed the formation of small grains on the film surfaces, indicative of the growth mechanisms. When Co target power was increased between 20 and 40 W, the grain size increased from 158.89 ± 4.76 nm to 460.97 ± 13.82 nm. Electrical and magnetic characterizations demonstrated contributions from lattice free electrons, generated by oxygen vacancies, and randomly distributed Co ions within the oxide semiconductor matrix, influencing the SET and RESET states. Comparative analysis of ZnO and TiO₂ matrices indicated reduced energy consumption and increased storage capacity, attributed to the modulation of high and low resistive states by magnetic ions within the semiconductor matrix, associated to change between low resistive state (LRS) and HRS occurs (~ 1–3 V).

Breast cancer is the second cause of cancer death in women worldwide. The search for therapeutic and preventive alternatives has increased in recent years. One synthetic drug for patients with hormone receptor-positive tumours is tamoxifen citrate (TMX). Curcumin (Cur) is a natural compound that is being tested. Both were coupled with nanoscale-controlled and sustained release systems to increase the effectiveness of the treatment and reduce adverse effects. We produced a controlled release system based on uniaxial and coaxial polymeric nanofibers of polycaprolactone (PCL), alginate (Alg) and gelatine (Gel) for the transport and release of TMX and Cur, as a new alternative to breast cancer treatment. Nanofibers combining PCL–Alg and PCL–Gel were fabricated by the electrospinning technique and physicochemically characterised by thermal analysis, absorption spectroscopy in the infrared region and X-ray diffraction. Morphology and size were studied by scanning electron microscopy. Additionally, the release profile of TMX and Cur was obtained by UV-Vis spectroscopy. Additionally, the cytotoxic effect on breast cancer cell line MCF7 and peripheral-blood mononuclear cells (PBMCs) from a healthy donor were evaluated by a Resazurin reduction assay. These assays showed that PCL–TMX nanofiber was highly toxic to both cell types, while PCL–Cur was less toxic.

GaSb:Ni ternary alloys thin films were deposited via sputtering method (DC magnetron Co-Sputtering) varying the substrate temperature (Ts). From spectra transmittance measurements and X-ray diffraction (XRD) were obtained the optical constants and structural properties of material, respectively. Predominant phases of GaSb and NiSb were observed for all Ts variations. From absorption measurements, the value of energy band forbidden or "band gap" was obtained varying between 0,63 eV and 0,72 eV. The extinction coefficient k as a function of wavelength of the GaSb:Ni thin films, was reported.