# Growth of Zr/ZrO\({}_{2}\) Core-Shell Structures by Fast Thermal Oxidation
###### Abstract  
This research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO\({}_{2}\)). A wire of Zr has been oxidized to form a core-shell structure, in which the core is a metal wire, and the shell is an oxide layer that is around 10 \(\upmu\)m thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO\({}_{2}\), alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, F\({}_{\text{A}}\) and F\({}_{\text{AA}}\), give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4-2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed. transition metal oxides; defects; luminescence; fast growth +
Footnote †: journal: Applied  
is gaining ever more relevance since it opens the possibility to tune the band structure over a broader range, playing not only with the combination of materials, but designing new architectures optimized for different working conditions. The feasible combinations of materials that can be made are numerous, but the \"active\" part will always be the semiconductor. Some common configurations are core-shell structures, heterostructures and arrays of heterostructures [5,6]. For a long time, zirconium oxide has been a known TMO, present in more than 40 minerals, mainly oxides and silicates. The most abundant zirconium minerals are zircon (ZrSiO\({}_{4}\)), baddeleyite (ZrO\({}_{2}\)) and eudialyte ((Na, Ca)\({}_{5}\) (Zr, Fe, Mn)[O, OH, Cl][Si\({}_{6}\)O\({}_{17}\)]); the main source of this oxide is the baddeleyite mineral. Traditionally, the main uses of zirconium oxide have been those related to its corrosion resistance, refractory properties and toughness. However, new applications have arisen, and several review papers have been recently published [7, 8, 9]. Among the new roles found for ZrO\({}_{2}\), particularly at the micro-/nanoscale, those for environmental remediation and biomedical applications are gaining relevance [9]. Antibacterial and antifungal activities play a central role among biomedical applications, inasmuch as the same mechanisms underlie both of them. The first procedure proposed is an electrostatic interaction between the negatively charged bacteria membranes and the ZrO\({}_{2}\) particles. The high surface area would favor this interaction and lead to the inhibition of the key metabolic functions carried out by reactive oxygen species such as oxygen and hydroxyl super radicals (-O\({}_{2}^{-}\), -OH) [10,11]. A similar mechanism would operate in the case of antifungal activity, inhibiting cell division [12]. On the other hand, environmental remediation is probably the most pressing challenge faced by the present society [13]. The removal of antibiotics, textile dyes and emerging pollutants such as fluoride is becoming a serious problem. The review paper published by [PERSON] et al. [9] contains a good revision of recent works on the use of zirconium oxide to eliminate different contaminants, with the added value that ZrO\({}_{2}\) is synthesized by different green routes, such as plant tissues, or microorganisms, such as bacteria, algae or fungi.