The role of reduced graphene oxide capping on defect induced ferromagnetism of ZnO nanorods

Abstract

In this study, the effect of different numbers of layers of reduced graphene oxide (RGO) on the ferromagnetic behavior of zinc oxide-reduced graphene oxide (ZnO-RGO) hybrid architectures has been investigated. Scanning and transmission electron microscopy along with x-ray diffraction of these hybrids confirm that ZnO nanorods are wrapped with different numbers of layers of RGO in a controlled way and their hexagonal phase is unaffected by these layers. Raman and photoelectron spectroscopy of these hybrids reveals that RGO does not alter the nonpolar optical phonon E(2) (high) mode and chemical state of Zn(2+) in ZnO. Electron paramagnetic resonance (EPR) spectra show that RGO passivates singly charged oxygen vacancies (VOS⁺) in ZnO. It correlates the passivation efficiency of VOS⁺ to the number of RGO layers and this has been achieved up to 90% by ∼31 layers of RGO. Due to passivation of VOS⁺ in ZnO by RGO, the ferromagnetic behavior (saturation magnetization and divergence between zero field cooled and field cooled) in ZnO-RGO hybrids is suppressed as compared to ZnO. Combining the EPR and magnetic behavior, a direct link between the passivation of the singly charged oxygen vacancies present on the surface of ZnO nanorods and the number of RGO layers is established.

A Review of EPR Studies on Magnetization of Nanoparticles of Dilute Magnetic Semiconductors Doped by Transition-Metal Ions

“…However, for them at liquid helium temperature, EPR lines are observed due to localized moments, whose shape is distorted because of a distribution of SHP and formation of exchangecoupled clusters [14]. [5][6][7][8][9][10][11][12][13][14][15]. The details of synthesis, size, structure, maximum doping level for which ferromagnetism appears, and EPR frequencies of study are summarized in Table 1.…”

Controllable fabrication and optical properties of Sn-doped ZnO hexagonal microdisk for whispering gallery mode microlaser

“…The reduction of electron charge density in the oxygen vacancy area results in less screening of the O 2− 1s electrons from their nucleus, this increases the effective nuclear charge and the binding energy of O 2− 1s electron, so the peak at 531.0 eV is attributed to oxygen deficient state. 34,35 To confirm the state of the oxygen vacancy, the EPR spectrum(g = 1.96) of the ZnO:Sn microdisks is shown in Figure 4(c), the characteristics of ferromagnetism indicates the states of paramagnetic oxygen vacancies with unpaired singly electron (V O+ ) in the ZnO:Sn microdisks. 31,34 So the green emission band from the ZnO:Sn microdisks is attributed to the singly charged oxygen vacancy defects, this result is similar to the defect emission mechanism of the undoped ZnO micro/nanostructures.…”

“…34,35 To confirm the state of the oxygen vacancy, the EPR spectrum(g = 1.96) of the ZnO:Sn microdisks is shown in Figure 4(c), the characteristics of ferromagnetism indicates the states of paramagnetic oxygen vacancies with unpaired singly electron (V O+ ) in the ZnO:Sn microdisks. 31,34 So the green emission band from the ZnO:Sn microdisks is attributed to the singly charged oxygen vacancy defects, this result is similar to the defect emission mechanism of the undoped ZnO micro/nanostructures. As the excitation power increased to 40 KW/cm 2 , there is a weak UV emission band containing two emission peaks at 379 nm and 390 nm on the PL spectrum, which indicates that a minor part of the electrons in the conductance band recombine with the holes in the 2013) valence band, so the UV emission has a very weak emission intensity.…”

Brush-like SnO2/ZnO hierarchical nanostructure: Synthesis, characterization and application in UV photoresponse

“…The low binding energy at 529.9 eV correspond to O 2− in the regular structure of wurtzite ZnO matrix, and the high binding energy peak at 531.0 eV is attributed to oxygen deficient state. [40][41][42] The optical properties of the SnO 2 nanowires and SnO 2 /ZnO hierarchical structures were investigated by photoluminescence spectrometer. Figure 5(a) shows the PL spectrum of the SnO 2 nanowires excited by 280 nm line from a Xe lamp, a broad emission band can be observed, which is deconvocated into two emission bands centered at 361 nm (3.43 eV) and 445 nm (2.78 eV).…”