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Register a new userMulti-wavelength Raman scattering of nanostructured Al-doped zinc oxide
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Added by
Carlo Spartaco Casari
Publication date
2013
fields
Physics
and research's language is
English
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In this work we present a detailed Raman scattering investigation of zinc oxide and aluminum-doped zinc oxide (AZO) films characterized by a variety of nanoscale structure and morphology and synthesized by pulsed laser deposition (PLD) under different oxygen pressure conditions. The comparison of Raman data for pure ZnO and AZO films with similar morphology at the nano/mesoscale allows to investigate the relation between Raman features (peak or band positions, width, relative intensity) and material properties such as local structural order, stoichiometry and doping. Moreover Raman measurements with three different excitation lines (532, 457 and 325 nm) point out a strong correlation between vibrational and electronic properties. This observation confirms the relevance of a multi-wavelength Raman investigation to obtain a complete structural characterization of advanced doped oxide materials.
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The structure-property relation of nanostructured Al-doped ZnO thin films has been investigated in detail through a systematic variation of structure and morphology, with particular emphasis on how they affect optical and electrical properties. A variety of structures, ranging from compact polycristalline films to mesoporous, hierarchically organized cluster assemblies, are grown by Pulsed Laser Deposition at room temperature at different oxygen pressures. We investigate the dependence of functional properties on structure and morphology and show how the correlation between electrical and optical properties can be studied to evaluate energy gap, conduction band effective mass and transport mechanisms. Understanding these properties opens the way for specific applications in photovoltaic devices, where optimized combinations of conductivity, transparency and light scattering are required.
Based on first-principles calculation, it has been predicted that the magnetic anisotropy energy (MAE) in Co-doped ZnO (Co:ZnO) depends on electron-filling. Results show that the charge neutral Co:ZnO presents a easy plane magnetic state. While modifying the total number of electrons, the easy axis rotates from in-plane to out-of-plane. The alternation of the MAE is considered to be the change of the ground state of Co ion, resulting from the relocating of electrons on Co d-orbitals with electron-filling.
This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on characterize resistance switching (RS), polarization rotation (PO) and surface potential changes in copper doped ZnO (ZnO:Cu) thin films. The bipolar RS behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PO with almost 180{deg} phase angle is confirmed by using the vertical and lateral Piezoresponse Force Microscopy (PFM). In addition, it elucidates that obvious polarization rotation behavior can be observed in the sample with increasing Cu concentration. Furthermore, correlation of the RS behavior with PO behavior has been studied by performing various mode SPM measurements on the same location. The electric field resulted from the opposite polarization orientation are corresponded to the different resistance states. It is found that the region with the polarization in downward direction has low resistance state (LRS), whereas the region with upward polarization has high resistance state (HRS). In addition, the Piezoresponse Force Spectroscopy (PFS) and Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the existence of the built-in field due to the uncomplemented polarization may affect the depletion region and hence contribute to the RS behavior. In addition, Kelvin Probe Force Microscopy (KPFM) results show that, when ZnO-based thin films is subjected to negative and then followed by positive sample bias, injection charge limit current is dominated.
We generalize and systematize basic experimental data on optical and luminescence properties of ZnO single crystals, thin films, powders, ceramics, and nanocrystals. We consider and study mechanisms by which two main emission bands occur, a short-wavelength band near the fundamental absorption edge and a broad long-wavelength band, the maximum of which usually lies in the green spectral range. We determine a relationship between the two luminescence bands and study in detail the possibility of controlling the characteristics of ZnO by varying the maximum position of the short-wavelength band. We show that the optical and luminescence characteristics of ZnO largely depend on the choice of the corresponding impurity and the parameters of the synthesis and subsequent treatment of the sample. Prospects for using zinc oxide as a scintillator material are discussed. Additionally, we consider experimental results that are of principal interest for practice.
Ceramics ZnO:Zn of 20mm diameter and 1.6mm thickness with an optical transparency up to 0.33 in the visible region have been prepared by hot pressing technique. Scintillating and luminescent characteristics such as emission spectra, decay time, yield, and TSL glow curve have been measured under X-ray excitation. Two emission bands peaking at 500 and 380 nm were detected, the light output was about 80% of that for standard BGO scintillator, main decay constant was 10.4 +/- 0.1 ns. The obtained data allow us to consider the ZnO:Zn ceramics as a perspective scintillator. Finally, the investigation shows that other ZnO-based fast scintillators can be fabricated in the form of optical ceramics.
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