We report here a method for synthesizing ZnO:Ga and ZnFe2O4 films and ZnFe2O4/ZnO:Ga heterostructure and studying them as peroxidase enzyme mimetics for hydrogen peroxide determination and simulation-based detection has been proposed. A method for forming ZnO:Ga films by the DC magnetron sputtering method and ZnFe2O4 films and ZnFe2O4/ZnO:Ga heterostructures by the RF-sputtering method using a target consisting of ZnFe2O4 nanoparticles has been described. Thus, the procedure for synthesizing a heterostructure, which is based on the principle of self-assembly in a glow discharge plasma generated by a magnetron sputtering source, the cathode of which is a target consisting of zinc ferrite nanoparticles, has been optimized. Using the SEM and AFM methods, it has been revealed that with an increase in the argon pressure to 8.1 Pa, intergranular voids are formed in the resulting films due to the occurrence of the shading effect. These conditions provide the formation of a structure with a developed surface. This in turn typically leads to an increase in the valence electron concentration due to a large number of broken interatomic bonds and the formation of a large number of free oxygen sites on the film surface, which are donor centers involved in the redox process. Experimental results showed that the ZnFe2O4/ZnO:Ga film heterostructure exhibits peroxidase-like activity in a linear range of 0.017–0.240 μM. In addition, the color change dependent on hydrogen peroxide concentration can offer a convenient approach to detecting H2O2 both with the naked eye and spectrophotometrically. Therefore, the ZnFe2O4/ZnO:Ga film heterostructure is a promising candidate for the colorimetric detection of H2O2, ascorbic acid, and similar oxidizers.

The interrelationships between the topological features, such as surface roughness deduced from atomic force microscopy (AFM), and wettability properties expressed by the contact angle of a water droplet on the surface of nanostructured wide bandgap oxide films prepared by spray pyrolysis are investigated for a wide range of compositions. A direct relationship between the surface roughness and the value of the contact angle was found for nanocomposite (In2O3)1−x(MgO)x, (In1−xGax)2O3, and Zn1−xMgxO films, for which both the surface roughness and the contact angle increase with the increasing x-value. On the other hand, in ITO films doped with Ga, it was found that the surface roughness increases by increasing the Ga doping, while the contact angle decreases. Both the surface roughness and the contact angle proved to increase in Ga2O3 films when they were alloyed with Al2O3, similar to other nanocomposite films. An inverse relationship was revealed for a nanocomposite formed from Ga2O3 and SnO2. The contact angle for a (Ga2O3)0.75(SnO2)0.25 film was larger as compared to that of the Ga2O3 film, while the surface roughness was lower, similar to ITO films. The highest value of the contact angle equal to 128° was found for a (In2O3)1−x(MgO)x film with an x-value of 0.8, and the largest RMS roughness of 20 nm was showed by a Ga1.75Al0.25O3 film. The optical properties of the prepared films were also analyzed from optical absorption spectroscopy, demonstrating their bandgap variation in the range of (4 to 4.85) eV, corresponding to the middle ultraviolet spectral range.

Porous semiconductor compounds represent a class of materials which is under an intense research focus over the last years. Herein, morphologies and topologies produced by anodization in binary semiconductor compounds having various bandgaps and crystallographic orientations are demonstrated with a focus on technological procedures applied for generating arrays of pores with a controlled design. The mechanism of pores growth under the photoresist masks is discussed and the connection between the design of the mask and the architecture of the produced porous structure is disclosed. The evolution of physical characteristics of the materials such as luminescence, optical, photonic, vibrational, hydrophilic, and hydrophobic properties as a result of anodization is investigated. Investigations are performed by means of scanning electron microscopy, photoluminescence and cathodoluminescence spectroscopy, and contact angle measurements. Some possible practical applications of the proposed technological approaches and the produced porous structures are briefly discussed.

Porous templates are widely used for the preparation of various metallic nanostructures. Semiconductor templates have the advantage of controlled electrical conductivity. Site-selective deposition of noble metal formations, such as Pt and Au nanodots and nanotubes, was demonstrated in this paper for porous InP templates prepared by the anodization of InP wafers. Metal deposition was performed by pulsed electroplating. The produced hybrid nanomaterials were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). It was shown that uniform deposition of the metal along the pore length could be obtained with optimized pulse parameters. The obtained results are discussed in terms of the optimum conditions for effective electrolyte refreshing and avoiding its depletion in pores during the electroplating process. It was demonstrated that the proposed technology could also be applied for the preparation of metal nanostructures on porous oxide templates, when it is combined with thermal treatment for the oxidation of the porous semiconductor skeleton.

A room-temperature two-step cost-effective electrochemical technology is proposed for the preparation of free-standing Au nanomembranes. A thin Au film with the thickness less than 100 nm was deposited by pulsed electroplating on a GaAs substrate in the first step, while electrochemical etching was applied in the second technological step to introduce porosity into the GaAs substrate underneath the Au film. It has been shown that detachment of the film from the substrate occurs at optimized parameters of anodic etching. Scanning electron microscopy imaging of the deposited Au film revealed its nanoparticulate structure generated via the mechanism of hopping electrodeposition, i.e. the film proved to consist of a monolayer of Au nanoparticles with the mean diameter around 20–30 nm. It was found that nanoholes with the diameter controlled by the duration of negative voltage pulses can be introduced into the Au film during electroplating. The purity of the detached Au nanomembranes was demonstrated by the energy dispersive X-ray analysis. The flexibility, nanoparticulate structure along with possibilities to transfer the prepared nanomembranes to various substrates make them promising for new optical, plasmonic and electronic applications.

. In this paper, the design and elaboration of a cost-effective technological process for the fabrication of the platform for the study of flexoelectric properties of GaN microtubes with the diameter of 2 - 5 μm and the thickness of the microtube walls of 50 nm is proposed. The impact of the design as well as the electrochemical etching parameters (applied voltage, duration of anodization) on the obtained channel dimensions is investigated. The proposed technological route implies electrochemical etching of n-InP semiconductor crystal in an environmentally friendly electrolyte at high etch rate. The technological process was optimized experimentally. It was proposed to introduce a perpendicular channel in which the microtube will be placed to reach a higher stability on the platform during the measurements.

A comparative study of the anodization processes occurring at the GaAs(111)A and GaAs(111)B surfaces exposed to electrochemical etching in neutral NaCl and acidic HNO3 aqueous electrolytes is performed in galvanostatic and potentiostatic anodization modes. Anodization in NaCl electrolytes was found to result in the formation of porous structures with porosity controlled either by current under the galvanostatic anodization, or by the potential under the potentiostatic anodization. Possibilities to produce multilayer porous structures are demonstrated. At the same time, one-step anodization in a HNO3 electrolyte is shown to lead to the formation of GaAs triangular shape nanowires with high aspect ratio (400 nm in diameter and 100 µm in length). The new data are compared to those previously obtained through anodizing GaAs(100) wafers in alkaline KOH electrolyte. An IR photodetector based on the GaAs nanowires is demonstrated.

We report on fabrication of metal nanotubes in semiconductor nanotemplates possessing ordered two-dimensional hexagonal arrays of pores grown in n-InP crystalline substrates using anodic etching in neutral electrolyte. Electrochemical pulsed deposition of arrays of Pt nanotubes with diameters of 70 and 140nm is demonstrated. The produced metallo-semiconductor tubular structure behaves like a layered nanomaterial allowing one to easily cleave thin films consisting of rows of Pt nanotubes in semiconductor envelope.