Clustered vacancies in ZnO: chemical aspects and consequences on physical properties

Abstract

Chemical nature of point defects, their segregation, cluster or complex formation in ZnO is an important area of investigation. In this report, 1.2 MeV Ar ion beam is used to incorporate defects in granular ZnO. Evolution of defective state with irradiation fluence 1 × 10 14 and 1 × 10 16 ions/cm 2 has been monitored using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman spectroscopic study. Choice of such fluence regime ensures spatial overlapping of successive ion-target collision cascades so that reorganization of point defects can take place in the form of more stable clusters or in the direction of possible recovery. XPS study shows presence of oxygen vacancies (VO) in the Ar ion irradiated ZnO. Zn(LMM) Auger spectra clearly identifies transition involving metallic zinc in the irradiated samples. Intense PL emission from interstitial Zn (IZn) related shallow donor bound excitons (DBX) is visible in the 10 K spectra for all samples. Although overall PL is largely reduced with irradiation disorder, DBX intensity is increased for the highest fluence irradiated sample. Raman study indicates damage in both zinc and oxygen sub-lattice by energetic ion beam. Representative Raman modes from defect complexes involving VO, IZn and IO are visible after irradiation with intermediate fluence. Further increase of fluence shows, to some extent, a homogenization of disorder. Huge reduction of resistance is also noted for this sample. Certainly, high irradiation fluence induces a qualitative modification of the conventional (and highly resistive) grain boundary (GB) structure of granular ZnO. Low resistive path, involving IZn related shallow donors, across the GB can be presumed to explain resistance reduction. Open volumes (VZn and VO) agglomerate more and more with increasing irradiation fluence and finally get transformed to voids. Results as a whole have been elucidated with a model which emphasizes possible evolution of new defect microstructure that is distinctively different from the GB related disorder. Based on the model, qualitative explanations of commonly observed radiation hardness, colouration and 3 ferromagnetism in disordered ZnO have been put forward. A coherent scenario on disorderaccumulation in ZnO has been presented, which we believe, will guide further discussion on this topic.

Green Synthesis of ZnO-GO Composites for the Photocatalytic Degradation of Methylene Blue

“…It is facilitated by the chemisorbed oxygen atom and lattice oxygen in nanocomposites [34]. As shown in Figure 2(d), the bounding energy locations of 1045.5 eV and 1021.7 eV conform to the present of two atomic states, Zn2p 1/2 and Zn2p 3/2 corresponding to the electronic configuration of Zn 2+ [35].…”

Raman investigation of N‐implanted ZnO: Defects, disorder and recovery

“…It is to be mentioned that the variation in PL with fluence is not so systematic like Raman results. In the current context, one reason could be that the probing depth of PL and Raman is different . Additional effects like sputtering (during implantation), presence of gaseous O 2 and N 2 (during annealing) can alter the near‐surface region in a different way compared with the bulk.…”

“…The first two emissions are FX and DBX emissions of ZnO. This DBX emission is generally originated from I Zn type of native defects . The most intense PL peak at 3.313 eV is the famous FA (free electron to shallow but localized acceptors) transition in ZnO .…”

Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin‐Film Transistor and Sensor Behavior of ZnO Films and Rods

“…[11] In contrast, severalr ecent studies and calculations hint at the relevance of multiple defects, in which clustering and/or pairing occurs andl eads to increased stability. [16] It has been shown that V Zn and V O appear simultaneously and remain as nearest neighbors, either as divacancies V Zn -V O or as vacancy clusters V Zn -(V O ) n . [17] Recently,d ensity functional calculations also predicted strong interactions between V O and Zn i sites.…”