Investigation of the electrode material influence on the titanium oxide nanosize structures memristor effect

The paper presents the researching results of the memristor effect on titanium oxide nanostructures obtained by local anodic oxidation. Studies have been carried out on the effect of air humidity in the process chamber during local anodic oxidation on the memristor structures main parameters. Based on oxygen vacancies distribution numerical simulation in the oxide volume formed by this method, the obtained dependences were explained. A ReRAM layout consisting of 10 memristors was developed and manufactured, and the temperature influence on its characteristics was investigated. The results can be used in the technological processes development for the formation of memristor structures based on titanium oxide nanostructures.

Local anodic oxidation (LAO) has been performed on highly oriented pyrolytic graphite (HOPG) and few layer graphene (FLG) using contact-mode (CM) atomic force microscopy (AFM) in a controlled humidity chamber. Different types of LAO patterns, namely, protrusion and trench features were observed for different tip speeds under similar conditions of LAO patterning, in both CM and noncontact-mode (NCM) AFM images. Observed LAO patterns show a variation in their dimensions over time. This paper carries out a study performed on the observed changes in dimensions of LAO patterns made on HOPG and FLG over several days, pointing to the dynamics of these LAO patterns. The stability of the LAO patterns on HOPG is compared with that for FLG. LAO patterns on HOPG show a widening and reduction in depth over a day. LAO patterns on FLG show, in contrast, a random variation in the lateral dimension “width” and stabilization in the vertical dimension “depth” over several days.

A study of LAO nanopatterns on Si substrates of different crystallographic orientations

In this work, we demonstrate the possibility of using local anodic oxidation (LAO) for fabricating optical devices based on thin transition metal dichalcogenides (TMDC) layers. By LAO we fabricated an optical cavity from 6-layered MoSe2 flake transferred on Si/Au substrate. Optical properties were investigated by measuring microphotoluminescence. The cavity exhibits three order of magnitude enhancement of the flake's photoluminescence, which is only one order of magnitude lower than the monolayer on a SiO2 substrate. Here we show that LAO is a high-precision lithography method suitable for fabricating optoelectronic devices made of thin TMDC layers.

Synthesis of alumina nanowires and nanorods by anodic oxidation method

The functionality of nanostructures fabricated via local anodic oxidation is limited byundesired leakage currents. We use low-temperature scanning gate microscopy to pin downthe spatial position where leakage currents are most likely to occur. We show that leakagecurrents do not flow homogeneously along the complete barrier but at distinct weak pointssuch as crossings of two oxide lines. These findings can be used to improve the design ofsuch nanostructures.

The nanoscale profiling modes of an (100) n-type silicon substrate surface through the local anodic oxidation (LAO) are studied. The influence of relative humidity and pulse voltage at LAO on the geometric parameters of silicon oxide nanostructures (SONs) and shaped profile nanostructures (SPNs) formed within the liquid etching of SONs is elucidated. It is shown that an increase in LAO voltage pulse amplitude from 10 to 20 V causes a gain in the SON height from 0.6 ± 0.2 to 2.0 ± 0.3 nm at a relative humidity of 70 ± 1%. The results can be applied for the design of technological processes in the element-base fabrication of silicon nanoelectronics using scanning probe nanotechnology.

We studied the properties of GaAs oxides which were grown by local anodic oxidation (LAO) nanolithography using an atomic force microscope. We find that the LAO structures desorb under irradiation with soft x-rays (130eV). We analyzed the desorption process in detail by time-resolved photoelectron spectroscopy. We observe that even in the first stages of light exposure the LAO oxide is mainly composed of Ga2O, with a small fraction of Ga2O3 and As oxides. The As oxides are located only in the surface layers of the LAO oxide where they account for 10% of the oxide. Within 160minutes of exposure they completely desorb. Moreover, we find evidence for the presence of unoxidized GaAs embedded in the LAO oxide.

Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage during local anodic oxidation (LAO) using atomic force microscope (AFM). Corona effect and segregation of cobalt in the vicinity of the rings is studied using magnetic force microscopy and energy dispersive spectroscopy. Double ring formation is attributed to the interaction of ablated material with the induced magnetic field during LAO. Steepness of forward bias transport characteristics from the unperturbed region of the CMS film suggest a non equilibrium spin contribution. Such mesoscopic textures in magnetic films by AFM tip can be potentially used for memory storage applications.

Planar-type ferromagnetic tunnel junctions fabricated by SPM local oxidation

As a unique form of TiO2, TiO2 nanotube arrays (TiO2NTAs) have been widely used. TiO2NTAs are usually prepared by Ti foil, with little research reporting its preparation by Ti mesh. In this paper, TiO2NTAs are prepared on a Ti mesh surface via an anodic oxidation method in the F-containing electrolyte. The optimal parameters for the synthesis of TiO2NTAs are as follows: the solvent is ethylene glycol and water; the electrolyte is NH4F (0.175 mol/L); the voltage is 20 V; and the anodic oxidation time is 40 min without chemical polishing. However, there is a strange phenomenon where the nanotube arrays grow only at the intersection of Ti wires, which may be caused by chemical polishing, and the other areas, where TiO2NTAs cannot be observed on the surface of Ti mesh, are covered by a dense TiO2 film. New impurities (the hydrate of TiO2 or other products) introduced by chemical polishing and attaching to the surface of the Ti mesh reduce the current of anodic oxidation and further inhibit the growth of TiO2 nanotubes. Hence, under laboratory conditions, for commercially well-preserved Ti mesh, there is no necessity for chemical polishing. The formation of TiO2NTAs includes growth and crystallization processes. For the growth process, F- ions corrode the dense TiO2 film on the surface of Ti mesh to form soluble complexes ([TiF6]2-), and the tiny pores remain on the surface of Ti mesh. Given the basic photoelectrochemical measurements, TiO2NTAs without chemical polishing have better properties.

Nanotribological properties of precision-controlled regular nanotexture on H-passivated Si surface by current-induced local anodic oxidation

Atomic force microscope (AFM) based local anodic oxidation of metallic andsemiconducting layers has emerged as a powerful tool for nanoscale fabrication. A uniquenanoscale patterning technique has been created that couples computer aided design(CAD) with the lithographic capabilities of the AFM. Target nanostructures to bedeposited on a silicon substrate are rendered as a three-dimensional model. Using AFMbased local anodic oxidation on a silicon substrate, the features are duplicated at thenanoscale using voltage bias, probe speed, and humidity modulation, as prescribed by themodel. The work presented herein highlights the advantages when three-dimensionalmodeling is linked with nanolithography; nanoscale features can be precisely replicatedfrom a design plan.

Local anodic oxidation has become a convenient technique for fabricating graphene oxide nanostructures in fundamental research (e.g., nanoelectronics). The process is typically controlled by tip-sample voltage, scanning speed, relative humidity, and tip characteristics (e.g., tip radius). The role of other parameters, such as the number of layers, load force, and graphene-substrate adhesion, is discussed in this paper. It is shown by atomic force microscopy, Kelvin probe force microscopy, and Raman spectroscopy that the oxidation of graphene is achievable only under specific conditions: low pulling force and sufficiently strong adhesion of graphene to its substrate. Such conditions ensure the stability of graphene on the surface and the proper formation of the water meniscus, which serves as a source of oxidizing ions, resulting in a reproducible oxidation process. Failure to comply with these conditions may lead to the formation of structures other than oxides (e.g., removal of graphene or the formation of air/water cavities under graphene), which is also demonstrated.

We have studied transport of a two-dimensional electron gas through a potential barrier prepared on shallow GaAs/AlxGa1-xAs/InGaP heterostructure by local anodic oxidation (LAO) with an AFM tip. The potential barrier height after LAO was 55 meV, and it increased to 270 meV after oxide line removal at 300 mV, at room temperature. Barriers with this height can be used for room temperature nanometre-sized structures and devices fabrication.