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Tuning the optical properties and ultrasensitive molecular detection capabilities of Au nanoparticle-decorated MoS2.

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.

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