Structural, electrical and electrochemical properties of ZnO nanoparticles synthesized using dry and wet chemical methods

Structural, Morphological, Electronic Structural, Optical, and Magnetic Properties of ZnO Nanostructures

ZnO nanostructures were grown on a Si(111) substrate using a vapor-liquid-solid (VLS) growth procedure (pristine ZnO) and annealed via a rapid thermal-annealing process in an argon atmosphere at 1100 °C (Ar-ZnO). The synthesized ZnO nanostructures were investigated through structural, electronic structural, morphological, optical, and magnetic characterizations. X-ray diffraction and selective area electron diffraction (SAED) measurements revealed that both samples exhibited the hexagonal wurtzite phase of nanocrystalline ZnO. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy carried out at the O K-edge inferred the presence of the intrinsic-defect states. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy images displayed the formation of ZnO nanostructures. The photoluminescence (PL) spectra demonstrated an emission band in the UV region along with an additional defect band in the visible region. PL spectral analysis confirmed the presence of intrinsic defects in Ar-ZnO nanowires, contributing to the enhanced emission in the visible region. The Raman spectra showed the characteristic band (434 cm^-1) corresponding to the vibrational modes of hexagonal wurtzite ZnO, with an additional band attributable to intrinsic defects. DC magnetization measurements showed a ferromagnetic response in both samples with enhanced coercivity in Ar-ZnO (~280 Oe). In brief, both samples exhibited the presence of intrinsic defects, which are found to be further enhanced in the case of Ar-ZnO. Therefore, it is suggested that intrinsic defects have played an important role in modifying the optical and magnetic properties of ZnO with enhanced results for Ar-ZnO.

Effect of Mn-substitution on impedance spectroscopy and magnetic properties of Al-doped ZnO nanoparticles

In this study, the role of Mn-substitution on the structural, morphological, dielectric, and magnetic properties of Al-doped ZnO nanoparticles has been examined, using XRD, FE-SEM, μAutolab/FRA2 impedance spectroscopy, and vibrating sample magnetometer (VSM) techniques. Structural investigations revealed diffraction peaks consistent with JCPDS card No. 036-1451. Morphological evaluations of the synthesized nanoparticles indicated that the shape of the nanoparticles is a slightly hexagonal and generally spherical structure with a size range of approximately 10-70 nm. Dielectric measurements were performed in frequency ranges between 10^-3 Hz and 1 MHz. The results show that the sample's dielectric behavior is affected both by crystallite size and doping material type. In addition, it can be observed that the dielectric parameters exhibit extreme frequency dependence. Mn-substituted Al-doped ZnO is a suitable candidate for high-frequency applications due to its low dielectric loss at high frequencies. The AC conductivity of the Mn-substituted Al-doped ZnO sample increases with each frequency increment, and its value is higher than for the Al-doped ZnO sample, makings it a desirable material for use in device applications. Magnetic calculations, extracted from dielectric impedance spectroscopy measurements, are also investigated. Complex magnetic permeability, together with magnetic loss curves, are also plotted. Finallly, a study of the magnetic properties of the sample, using VSM, showed room-temperature ferromagnetic behavior.