Effects of annealing on optical and structural properties of zinc oxide nanocrystals

Abstract

The optical and vibrational properties of zinc oxide nanocrystals (ZnO NCs), grown by chemical precipitation method, were investigated following thermal annealing treatments in oxygen, argon, and zinc vapors at temperatures up to 900∘C. Raman scattering and photoluminescence techniques were utilized to show the effect of temperature annealing in various environments on optical and structural properties of ZnO NCs, referring them to the reduction and increase of certain intrinsic defect concentrations. The experimental results are complemented by density functional theory calculations for understanding the correlation between Raman modes induced with different annealing procedures and certain intrinsic point defects.

First‐principle investigation of defect‐associated LVM and structural parameter dependency in response to the ground state on‐site Hubbard correction of w‐ZnO

“…Based on surveys, the peak's origin could belong to the E 2 family with a 15 cm −1 shift towards higher energy. However, a detailed annealing effects study was observed by Khachadorian et al [ 31 ] and assigned the origin related to interstitial Zn. Therefore, it can be concluded that additional stress due to interstitial zinc in the crystal could result in a pronounced peak.…”

Raman and photoluminescence properties of ZnO nanowires grown by a catalyst‐free vapor‐transport process using ZnO nanoparticle seeds

“…For the ZnO NWs (toluene), the maximum is located at 530 nm (i.e., green luminescent band), while for those (DCM) the maximum is located near 560 nm (i.e., yellow luminescent band). The defects responsible for the green band at about 530 nm could be attributed to surface defects such as oxygen vacancies (V O ) , whereas those responsible for the yellow band at about 560 nm are thought to be deep‐level defects as oxygen interstitials (O i ) . Based on these informations, it can be stated that the use of toluene solvent leads to the formation of V O in the ZnO NWs, whereas the DCM solvent promotes the formation of O i .…”

“…The PL properties of ZnO thin films [24] and ZnO nanocrystals [25] demonstrated a direct correlation between the intensity of the visible emission of ZnO and the degree of oxygen deficiency in the crystalline structure of the material. According to this, the concentration of crystalline defects in the crystalline structure of the ZnO NWs can be estimated based on PL measurements.…”

In situ backside Raman spectroscopy of zinc oxide nanorods in an atmospheric‐pressure dielectric barrier discharge plasma

“…For instance, Khachadorian et al showed the high diversity of different defect modes by calculating the phonon density of states for isolated Zn and O vacancies and interstitial Zn using density-functional theory (DFT) studies, where a large number of related phonon branches around 300 cm À1 and between 450 and 520 cm À1 were found. [37] Interestingly, the surface optical (SO) phonon mode (located at 555 cm À1 ) related to defects such as disorderly arranged areas and grain boundaries was observed in the spectra. [34,41,42] Additionally, the positions of the E 2 low and E 2 high are redshifted and broadened (Table S1), indicating a defect-rich structure of the deposited ZnO-NRs.…”

“…Besides, an increase in the E 2 low peak (at 97 cm À1 ), the E 2 low asymmetric tail (132 cm À1 to 300 cm À1 ), and at 555 cm À1 (SO phonon vibration mode) was seen: the E 2 low vibration is dominated by the Zn atoms (in comparison with the E 2 high (437 cm À1 ), which is dominated by the oxygen atoms of the ZnO lattice), whereas the E 2 low asymmetric tail is associated to lattice stress or displacement. [25,26] In the case of the SO phonon mode, Zeng et al assigned its appearance to the loss of the long-range periodicity (and thus the symmetry) at the T A B L E 1 Peak position and their respective assignment found in the Raman spectra before and after the respective plasma treatments Wavenumber Assignment [25,26,[34][35][36] Appear in 2LA, phonon branches, [37] and Zn i [37] All 557 cm À1 SO phonon mode [34] All 580 cm À1 A 1 (LO) and E 1 (LO) [38][39][40] Ar/O surface which they confirmed by high-resolution transmission electron microscopy (HRTEM) measurements. [34,42] Thus, additional TEM measurements were conducted before and after the Ar/H 2 O plasma treatment.…”