Physicochemical mechanisms of the growth of oxide crystals on the surface of tungsten conductors heated by electric current

Physical and mathematical modeling of stationary thermal modes of heating and oxidation of tungsten conductors heated by electric current in air has been carried out. The dependences of the stationary temperature of the conductor on the strength of the heating current are obtained. The critical values of the current strength are found, which determine the transitions to the unsteady oxidation regime. The results of calculating the temperature regimes describe well the experimental data obtained by us using the electrothermographic method. As a result of experimental studies, the features of the appearance and growth of crystalline oxide structures on the surface of an oxidizing tungsten conductor have been studied. The temperatures at which filamentous crystals appear on the tungsten surface are determined, and the regularities of their growth are investigated. A physicochemical mechanism of the formation and growth of crystalline oxide structures on the surface of a tungsten conductor is proposed. It was found that carbon particles, which are part of the impurity, are the reason for the formation of nitrate crystals of tungsten trioxide on the basic oxide. With an increase in the temperature of the sample, the filaments grow, branch out and transform into dendritic structures of a complex bush-like shape. It has been proven that the rapid growth of crystal structures occurs due to the deposition of clusters and microgranules of WO3 oxide from the gas phase on the crystallization centers on the surface of the conductor. At the initial stage, these are impurity particles or mechanical inhomogeneities of the basic oxide, then a growing crystal. Clusters arise due to large temperature gradients at the surface of the conductor. It has been established that carbon atoms can migrate along the branches of oxide crystal structures. It was found that at the initial stage the crystals grow more intensively in the longitudinal direction. However, upon reaching a certain height, they begin to expand intensively in the transverse direction. The growth rates of crystal structures in the longitudinal and transverse directions are found.

Heterogeneous integration of single-crystalline rutile nanomembranes with steep phase transition on silicon substrates

Unrestricted integration of single-crystal oxide films on arbitrary substrates has been of great interest to exploit emerging phenomena from transition metal oxides for practical applications. Here, we demonstrate the release and transfer of a freestanding single-crystalline rutile oxide nanomembranes to serve as an epitaxial template for heterogeneous integration of correlated oxides on dissimilar substrates. By selective oxidation and dissolution of sacrificial VO2 buffer layers from TiO2/VO2/TiO2 by H2O2, millimeter-size TiO2 single-crystalline layers are integrated on silicon without any deterioration. After subsequent VO2 epitaxial growth on the transferred TiO2 nanomembranes, we create artificial single-crystalline oxide/Si heterostructures with excellent sharpness of metal-insulator transition ($$\triangle \rho /\rho$$ △ ρ / ρ > 103) even in ultrathin (<10 nm) VO2 films that are not achievable via direct growth on Si. This discovery offers a synthetic strategy to release the new single-crystalline oxide nanomembranes and an integration scheme to exploit emergent functionality from epitaxial oxide heterostructures in mature silicon devices.

Electrochemical Synthesis of Crystalline Niobium Oxide

Features of creation of porous nanostructured oxides of transition materials on an example of niobium are considered. It has been experimentally shown that variation in anodizing modes makes it possible to obtain non-porous and porous amorphous anodic oxide films (AOF) and films of the crystalline type. It is determined that the process of AOF formation on niobium, as well as its structure and properties depend on such parameters as the type of electrolyte, anodizing voltage, activator concentration, the duration of the process. It is confirmed that the presence of an activator in the electrolyte is a necessary and decisive factor in the process of forming a nanostructured anode oxide layer. To obtain a nanostructured surface of niobium oxide, a necessary condition is the introduction of fluoride into the electrolyte, but also an important task is to determine the type of compound with which F– ions are introduced into the electrolyte. It has been experimentally determined that the optimal solution for the rapid growth of porous crystalline oxide is a solution consisting of a background electrolyte in the form of 1M H2SO4 with the addition of a fluoride ion activator in the form of 0.5M NaF. The increase in the activator accelerates the formation of the crystal structure on the surface of niobium. It is shown that higher voltage and longer anodizing time leads to an increase in the size of microcones and their number on the surface of niobium. Optimal for the formation of porous crystalline oxide is a voltage of 60 V in the electrolyte 1M H2SO4 + 0.5M NaF for 2 hours.

Epitaxial lift-off of freestanding (011) and (111) SrRuO3 thin films using a water sacrificial layer

Two-dimensional freestanding thin films of single crystalline oxide perovskites are expected to have great potential in integration of new features to the current Si-based technology. Here, we showed the ability to create freestanding single crystalline (011)- and (111)-oriented SrRuO3 thin films using Sr3Al2O6 water-sacrificial layer. The epitaxial Sr3Al2O6(011) and Sr3Al2O6(111) layers were realized on SrTiO3(011) and SrTiO3(111), respectively. Subsequently, SrRuO3 films were epitaxially grown on these sacrificial layers. The freestanding single crystalline SrRuO3(011)pc and SrRuO3(111)pc films were successfully transferred on Si substrates, demonstrating possibilities to transfer desirable oriented oxide perovskite films on Si and arbitrary substrates.

Ultrafast Crystallization of Ordered Mesoporous Metal Oxides and Carbon in Seconds

This Communication describes a facile strategy coupling block copolymer-directed self-assembly with high-power Joule heating to form highly crystalline and long-range ordered mesoporous oxide and carbon nanostructures in just a few seconds. The combined approach is compatible with various self-assembled hybrid systems, generating mesoporous composites of γ-Al2O3-carbon, γ-Al2O3/MgO-carbon and anatase-TiO2-carbon with p6mm symmetry, as well as mesoporous non-close-packed carbon structures. Removing the polymer/carbon gives well-defined mesoporous all-γ-Al2O3 and all-anatase-TiO2 structures. Impregnation of chloroplatinic acid followed by Joule heating yields platinum nanoparticles decorated on the channel walls of mesoporous γ-Al2O3-carbon structures. The rapid formation of thermally stable and periodically ordered crystalline oxide, carbon and oxide-carbon structures. <br>

Ultrafast Crystallization of Ordered Mesoporous Metal Oxides and Carbon in Seconds

This Communication describes a facile strategy coupling block copolymer-directed self-assembly with high-power Joule heating to form highly crystalline and long-range ordered mesoporous oxide and carbon nanostructures in just a few seconds. The combined approach is compatible with various self-assembled hybrid systems, generating mesoporous composites of γ-Al2O3-carbon, γ-Al2O3/MgO-carbon and anatase-TiO2-carbon with p6mm symmetry, as well as mesoporous non-close-packed carbon structures. Removing the polymer/carbon gives well-defined mesoporous all-γ-Al2O3 and all-anatase-TiO2 structures. Impregnation of chloroplatinic acid followed by Joule heating yields platinum nanoparticles decorated on the channel walls of mesoporous γ-Al2O3-carbon structures. The rapid formation of thermally stable and periodically ordered crystalline oxide, carbon and oxide-carbon structures. <br>