Phonons investigation of ZnO@ZnS core‐shell nanostructures with active layer

ZnO is identified as a potentially attractive n‐type oxide thermoelectric material due to its abundance, nontoxicity, and a high degree of stability. However, working with ZnO is challenging due to its high thermal conductivity from its strong ionic bonds and low electrical conductivity due to its low charge concentrations. Here, it is demonstrated that the electrical and thermal transport properties of ZnO can be simultaneously improved via the successful doping of Al and ZnS coating. The ZnS coating in Al‐doped ZnO is observed and analyzed through microstructure and spectroscopic studies. The power factor for 1% ZnS‐coated Zn0.98Al0.02O is increased to ≈0.75 mW m−1 K−2 at 1073 K, 161% higher than pure ZnO. This enhancement in the power factor can be explained by the aliovalent Al3+ doping and modifications in intrinsic defects, leading to an increased carrier concentration. Interestingly, ZnS coating significantly reduces lattice thermal conductivity to ≈2.31 W m−1 K−1 at 1073 K for 2% ZnS‐coated Zn0.98Al0.02O, a 62% decrease over pure ZnO. This large reduction in lattice thermal conductivity can be elucidated based on coherent phonon scattering via Callaway's model. Overall, the figure of merit, zT, increases to 0.2 in 2% ZnS‐coated Zn0.98Al0.02O, which is 272% higher than pure ZnO at 1073 K.

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“…The low frequency modes ≈150, 200, and 220 cm −1 indicate the formation of a ZnO/ZnS heterostructure. [ 48 ]…”

Section: Resultsmentioning

confidence: 99%

“…ZnS has been used as a coating element due to its wide bandgap (3.72 eV), and the successful use of ZnS‐coated ZnO has already been demonstrated for various applications. [ 47,48 ] Interestingly, a change in carrier concentrations combined with intrinsic defects has been observed in ZnO by adding small amounts of ZnS. [ 49 ]…”

Section: Introductionmentioning

confidence: 99%

High Thermoelectric Performance of ZnO by Coherent Phonon Scattering and Optimized Charge Transport

Acharya

Hwang

et al. 2021

Adv Funct Materials

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“…At non-resonant excitation with λ exc = 514.7 nm (figure 6), the common Raman pattern is observed for samples #2 and #3 consisting of E 2 -symmetry modes at 98 and 437 cm −1 [38,65,66], as well as their difference mode around 340 cm −1 [65,67], while no Raman features are detected for sample #1 (figure 6). As we did not observe metallic Ag in XPS, we can exclude the formation of Ag NCs in #2 and #3 and a related enhancement of the ZnO Raman signal [68].…”

Section: Raman Spectramentioning

confidence: 99%

The effect of Ag doping on the structure, optical, and electronic properties of ZnO nanostructures deposited by atmospheric pressure MOCVD on Ag/Si substrates

Євтушенко

Dzhagan

Khyzhun

et al. 2023

Semicond. Sci. Technol.

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Atmospheric pressure metal-organic chemical vapor deposition was used to synthesize Ag-containing ZnO nanostructures of different morphology on Si substrates coated by Ag. Ag from Ag/Si substrates and Ag from silver acetylacetonate after its decomposition were used as a catalyst for ZnO nanocrystal growth for deposition of ZnO nanostructures with different morphologies. We investigated the relation of the structural parameters and chemical composition probed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy with the photoluminescence (PL) properties and electron-phonon coupling (EPC) reflected in the multi-phonon Raman spectra. The Raman and PL spectra were studied at different powers of the exciting laser radiation (Pexc). The spectral position and width of the phonon Raman peaks and the near bandgap PL (NBPL) band at low Pexc are supposed to be determined by the structural quality of the surfaces/boundaries of the crystallites. The intensity of the near-bandgap and defect-related PL and the magnitude of the EPC are additionally affected by the dopant concentration. Because of the large crystallite size (>30 nm, determined from XRD), the effects of phonon or electron confinement are negligible in these nanostructures. The behaviour of the position and width of phonon and PL bands with increasing Pexc indicates that the heat dissipation in the film, which is dependent on the nanostructure morphology and Ag content, plays an important role. In addition, the cytotoxicity of ZnO:Ag nanostructures was investigated by using monolayer cell cultures of epithelioid origin MDBK (Madin-Darby bovine kidney) and MDCK (Madin-Darby canine kidney) cells at a MTT assay revealing that the level of silver doping of ZnO nanostructures, their morphology, and geometric dimensions determine their toxic effects.

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“…[30][31][32] The shoulder (at about 535 cm −1 ) of the LO mode is characteristic of a nanostructure surface optical (SO) phonon mode. 33,34 In microcrystalline ZnO the LO and its overtone peaks are very strong both in resonant (near-or above-bandgap) and off-resonant (e.g. green laser line) excitation.…”

Section: Characterization Of Zno Npsmentioning

confidence: 99%

ZnO and Ag NP-decorated ZnO nanoflowers: green synthesis using Ganoderma lucidum aqueous extract and characterization

et al. 2023

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Phonons investigation of ZnO@ZnS core‐shell nanostructures with active layer

Cited by 4 publications

References 42 publications

High Thermoelectric Performance of ZnO by Coherent Phonon Scattering and Optimized Charge Transport

High Thermoelectric Performance of ZnO by Coherent Phonon Scattering and Optimized Charge Transport

The effect of Ag doping on the structure, optical, and electronic properties of ZnO nanostructures deposited by atmospheric pressure MOCVD on Ag/Si substrates

ZnO and Ag NP-decorated ZnO nanoflowers: green synthesis using Ganoderma lucidum aqueous extract and characterization

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