In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications.

We report on self-propelled rotating liquid marbles fabricated using droplets of alcoholic solution encapsulated in hollow microtetrapods of GaN with hydrophilic free ends of their arms and hydrophobic lateral walls. Apart from stationary rotation, elongated-spheroid-like liquid marbles were found, for the first time, to exhibit pulsed rotation on water surfaces characterized by a threshold speed of rotation, which increased with the weight of the liquid marble while the frequency of pulses proved to decrease. To throw light upon the unusual behavior of the developed self-propelled liquid marbles, we propose a model which takes into account skimming of the liquid marbles over the water surface similar to that inherent to flying water lily beetle and the so-called helicopter effect, causing a liquid marble to rise above the level of the water surface when rotating.

A new type of photocatalyst is proposed on the basis of aero-β-Ga2O3, which is a material constructed from a network of interconnected tetrapods with arms in the form of microtubes with nanometric walls. The aero-Ga2O3 material is obtained by annealing of aero-GaN fabricated by epitaxial growth on ZnO microtetrapods. The hybrid structures composed of aero-Ga2O3 functionalized with Au or Pt nanodots were tested for the photocatalytic degradation of methylene blue dye under UV or visible light illumination. The functionalization of aero-Ga2O3 with noble metals results in the enhancement of the photocatalytic performances of bare material, reaching the performances inherent to ZnO while gaining the advantage of the increased chemical stability. The mechanisms of enhancement of the photocatalytic properties by activating aero-Ga2O3 with noble metals are discussed to elucidate their potential for environmental applications.

Straturi subțiri, de nucleație și proprii, de ZnO au fost sintetizate pe Si prin metoda hidrotermală din soluțiile compușilor zincului folosindu-se solvenții: apă, apă + etanol, apă + metanol, apă + propanol, apă + acetonă, etanol, propanol, metanol. La prepararea straturilor de nucleație s-a folosit acetatul de zinc dihidrat, Zn(CH3COO)2·2H2O. Depunerea straturilor proprii de ZnO pe structurile nucleate a avut loc prin fierberea lor în soluție apoasă de Zn(NO3)2 + KOH. În lucrare sunt date caracterizări structurale și morfologice ale straturilor buffer obținute, fiind demonstrată eficiența stratului buffer în prepararea straturilor de GaN. PHYSICAL PROPERTIES OF ZnO LAYERS PREPARED ON Si SUBSTRATES BY HYDROTHERMAL METHODThe nucleation and proper ZnO thin layers on Si substrates were synthesized by the hydrothermal method from the solutions of zinc compounds by using different solvents such as: water, water + ethanol, water + methanol, water + propanol, water + acetone, ethanol, propanol, methanol. Dehydrated zinc acetate, Zn(CH3COO)2·2H2O, was used for the preparation of ZnO nucleation layers . The deposition of the proper ZnO layers on the nucleated structures is carried out by boiling them in the Zn(NO3)2 + KOH aqueous solution. The structural and morphological characterisations of the obtained buffer layers are given in the paper. The efficiency of ZnO buffer layer used in the preparation of GaN layers is demonstrated as well.

GaN layers on Silicon with ZnO intermediate layer were synthesized by using the HVPE (Hydride Vapor Phase Epitaxy) method. ZnO layers were deposited from solutions of zinc compounds in ethanol or water in two steps. At the first step a ZnO nucleation layer was deposited from a solution of zinc acetate in ethanol, at the second step a ZnO precipitate was deposited from a solution of zinc nitrate and KOH in water by boiling. On the obtained structures the GaN nucleation layers were deposited at 500 ℃ for 15 min, then GaN layers were grown at 850–970 ℃ for 30 ± 5 min. Structures were studied by using the optical and SEM microscope and XRD method. The type of conductivity of the layers was determined by using the method of thermal electromotive force measurement (TEFM). The possibility of the electrical conductivity (EC) type changing from n- to p-type for the GaN layers deposited on silicon substrates with the use of intermediate ZnO layer deposited from solutions is demonstrated for the first time.

The ZnO thin layers were grown on glass, InP and pInP-nCdS substrates from zinc acetate dissolved in water-acetic acid-methanol solution having a molarity of 0.2 M by using the spray method in the argon flow in the temperature range of (250–450) °C. The dependence of optical properties of ZnO layers on growth temperature have been investigated. The optical transmittance has values of 80–85% in the wavelength range of (200–1000) nm. The using of ZnO of the thickness of (60–80) nm as antireflective layers in nCdS-pInP structures allowed to increase the photovoltaic cell efficiency by 3%. The photosensitivity of the fabricated nZnO-pInP structures covers the wavelength region from 450 nm up to 1100 nm and allows the more efficient utilization of the incident light.

In this paper, fabrication of a new material is reported, the so-called Aero-Ga2O3 or Aerogallox, which represents an ultra-porous and ultra-lightweight three-dimensional architecture made from interconnected microtubes of gallium oxide with nanometer thin walls. The material is fabricated using epitaxial growth of an ultrathin layer of gallium nitride on zinc oxide microtetrapods followed by decomposition of sacrificial ZnO and oxidation of GaN which according to the results of X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) characterizations, is transformed gradually in β-Ga2O3 with almost stoichiometric composition. The investigations show that the developed ultra-porous Aerogallox exhibits extremely low reflectivity and high transmissivity in an ultrabroadband electromagnetic spectrum ranging from X-band (8–12 GHz) to several terahertz which opens possibilities for quite new applications of gallium oxide, previously not anticipated.

•The synthesis of GaN/Fe nanoparticles using HVPE method.•Mesenchymal stem cells interact with GaN-based nanoparticles.•GaN/Fe nanoparticles rearrange cells under the influence of magnetic field.

Nature utilizes hydrophilic-hydrophobic biomolecular entities to perform self-organized structural and functional tasks, including the formation of cellular compartments and motion, separation of chemicals or self-healing properties in a highly energy efficient manner. So far, no inorganic artificial micro/nanostructure units are known that self-organize and mimic such functions just by adding liquid. Here we develop the first nanomaterial exhibiting hydrophobic wetting and hydrophilic dewetting. Consisting of gallium nitride nanoscopically thin membranes shaped as hollow microtetrapods, which we term aerogalnite (AGaN), the nanomaterial is extremely porous, mechanically flexible, stretchable, and exhibits hydrophilicity under tension and hydrophobicity when compressed against water. Self-assembling the AGaN tetrapods on water enabled us to develop self-healing waterproof rafts carrying liquid droplets 500-times as heavy as rafts, and to demonstrate self-propelled liquid marbles exhibiting velocity of rotation as high as 750 rot/min. The specific force of the detachment of AGaN from the water surface was experimentally determined equal to 35 mN/cm2. The new developed material aerogalnite and its peculiar characteristics are promising for applications in sensorics, microfluidic devices and microrobotics.

The electrodynamic properties of the first aero-material based on compound semiconductor, namely of Aero-GaN, in the terahertz frequency region are experimentally investigated. Spectra of complex dielectric permittivity, refractive index, surface impedance are measured at frequencies 4–100 cm−1 and in the temperature interval 4–300 K. The shielding properties are found based on experimental data. The aero-material shows excellent shielding effectiveness in the frequency range from 0.1 to 1.3 THz, exceeding 40 dB in a huge frequency bandwidth, which is of high interest for industrial applications. These results place the aero-GaN among the best THz shielding materials known today.

In this paper, we report on the viability and proliferation of mesenchymal stem cells after exposure to different types of semiconductor nanoparticles. The nanoparticles used for the tests are based on GaN thin layers grown on commercial ZnO and ZnFe2O4 nanoparticles. Different quantities of nanoparticles incubated with mesenchymal stem cells influence the metabolic activity of cells, which was assessed by the MTT assay. The cytotoxic effect of ZnO nanoparticles on MSC was demonstrated and no harmful effect of the other materials.

We investigate the electromagnetic shielding properties of an ultra-porous lightweight nanomaterial named aerogalnite (aero-GaN). Aero-GaN is made up of randomly arranged hollow GaN microtetrapods, which are obtained by direct growth using hydride vapor phase epitaxy of GaN on the sacrificial network of ZnO microtetrapods. A 2 mm thick aero-GaN sample exhibits electromagnetic shielding properties in the X-band similar to solid structures based on metal foams or carbon nanomaterials. Aero-GaN has a weight four to five orders of magnitude lower than the weight of metals.

This work reports on the fabrication and characterization of a robust pressure sensor based on aero‐GaN. The ultraporous aeromaterial consists of GaN interconnected hollow micro‐tetrapods with the wall thickness of about 70 nm. The inner surface of hollow micro‐tetrapods contains an ultrathin film of ZnO genetically related to the sacrificial template used for epitaxial deposition of GaN. The pressure sensing measurements disclose a nearly linear dependence of the electrical conductance versus applied pressure up to 40 atm, a stable state signal being attained after an interval of about 10 s.

Al-doped ZnO thin films have been prepared by spray pyrolysis, which facilitates the incorporation of a higher percentage of dopant atoms. The vacuum thermally annealed at 420 °C temperature thin films have been characterized by X-ray diffraction (XRD), optical spectroscopy. Electrical conductivity and the Hall effect are investigated in the temperature interval (77–300) K. X-ray analysis results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (002) plane. Different characters of the temperature dependence of conductibility are observed in the Al-doped ZnO films vacuum thermally annealed at 420 °C temperature. In all cases, the conductivity, mobility carriers and carriers’ concentration of ZnO thin films obtained under Ar are higher than under O2 atmosphere, unless they are not doped. of your paper no longer than 300 words.

The development of functional microstructures with designed hierarchical and complex morphologies and large free active surfaces offers new potential for improvement of the pristine microstructures properties by the synergistic combination of microscopic as well as nanoscopic effects. In this contribution, dedicated methods of transmission electron microscopy (TEM) including tomography are used to characterize the complex hierarchically structured hybrid GaN/ZnO:Au microtubes containing a dense nanowire network on their interior. The presence of an epitaxially stabilized and chemically extremely stable ultrathin layer of ZnO on the inner wall of the produced GaN microtubes is evidenced. Gold nanoparticles initially trigger the catalytic growth of solid solution phase (Ga1- x Znx )(N1- x Ox ) nanowires into the interior space of the microtube, which are found to be terminated by AuGa-alloy nanodots coated in a shell of amorphous GaOx species after the hydride vapor phase epitaxy process. The structural characterization suggests that this hierarchical design of GaN/ZnO microtubes could offer the potential to exhibit improved photocatalytic properties, which are initially demonstrated under UV light irradiation. As a proof of concept, the produced microtubes are used as photocatalytic micromotors in the presence of hydrogen peroxide solution with luminescent properties, which are appealing for future environmental applications and active matter fundamental studies.

ZnO thin layers were grown from zinc acetate dissolved in methanol-acetic acid-water solution with the molarity of 0.2M by using the pulverization method in an argon flow at the temperatures of 250-450°C. The temperature dependence of electrical and optical properties of the obtained layers were studied. The optical transmittance at the wavelengths of (300 -1000) nm has the values of 80-85%. The resistivity of ZnO thin layers grown at 450°C decreases from 33W•cm to 0,028 W•cm after annealing in hydrogen at 450°C during an hour. The radiative recombination is related to the electron transitions to the deep levels and band to band transitions at the charge carriers transitions with the LO type phonons.

Au fost obținute celule fotovoltaice (CF) cu heterojoncțiunea nCdS-pInP și strat intermediar epitaxial poInP, fiind cercetate proprietățile lor electrice și fotoelectrice. Grosimile straturilor pInP și al celui frontal nCdS au variat respectiv în intervalul 2,7...6,2 – 0,9...3,6 µm în dependență de durata de depunere. S-a constatat că parametrii fotoelectrici au valorile maximale pentru grosimile de 4,5...5 µm pentru stratul poInP și de 0,9 µm pentru stratul nCdS, eficiența maxi­mală a CF cu structura n+CdS-po-p+InP fiind de 14,6% (100 mW×cm-2).PHOTOVOLTAIC CELLS WITH n+CdS-po-p+InP HETEROJUNCTION: TEHNOLOGICAL APPLICATIONS, METHODS AND RESEARCH RESULTSPhotovoltaic cells (PVC) with nCdS-pInP heterojunction and an intermediate poInP epitaxial layer were obtained and their electrical and photoelectric properties were investigated. The thicknesses of the pInP layer and of the nCdS frontal layer varied in the range of 2.7 to 6.2 μm and 0.9 to 3.6 μm respectively, depending on the deposition time. It was found that photoelectric parameters have maximum values when the thickness of poInP layer is of 4.5 ... 5 μm and for nCdS layer is of 0.9 μm, the maximum efficiency of PCV with the structure n+CdS-po-p+InP was of 14.6% (100 mW×cm-2).

Polycrystalline undoped and Al-doped ZnO thin films were deposited by spray pyrolysis using oxygen and argon atmospheres. The influence of postdeposition vacuum annealing on the structure, morphology and optical properties was studied by X-ray diffraction, atomic force microscopy and UV-VIS spectroscopy. The thermal vacuum annealing induces structural and morphological changes, especially in Al-doped ZnO thin films synthetized in oxygen atmosphere. Further on, the electrical conductivity in dependence of the nature of gas atmosphere and Al concentration is discussed.