Tuning of structural, optical, and magnetic properties of ultrathin and thin ZnO nanowire arrays for nano device applications

Nanostructural Design of ZnO Using an Agro-Waste Extract for a Sustainable Process and Its Photocatalytic Activity

The use of agro-waste extracts (AWEs) as a sustainable medium for developing cost-effective and ecologically friendly nanomaterials has piqued the interest of current researchers. Herein, waste extracts from papaya barks, banana peels, thumba plants, and snail shells were used for synthesizing ZnO nanostructures via a hydrothermal method, followed by calcination at 400 °C. The crystallinity and pure wurtzite phase formation of ZnO nanostructures were confirmed via X-ray diffraction. ZnO nanostructures with various morphologies such as tight sheet-like, spherical, porous sheet-like, and bracket-shaped, comprising small interconnected particles with a highly catalytically active exposed (0001) facet, were observed via field emission scanning electron microscopy and transmission electron microscopy. The formation mechanism of the various morphologies of the ZnO nanostructures was proposed. Ultraviolet-visible spectra showed different absorption band edges of ZnO nanostructures with a bandgap in the range of 3.17-3.27 eV. Photoluminescence studies showed the presence of various defect states such as oxygen and zinc vacancies and oxygen and zinc interstitials on ZnO nanostructures, which are usually observed in traditionally prepared ZnO. The photocatalytic activity of ZnO nanostructures was evaluated under direct sunlight using rhodamine B (RhB) and Congo red (CR) dyes as probe pollutants. Furthermore, prepared ZnO nanostructures could potentially adsorb anionic dyes (e.g., CR) in the absence of light. Superoxide and hydroxide radicals played a vital role in the photocatalytic activity of ZnO. The photocatalyst could be reused for up to three cycles, indicating its stability. Therefore, this study reports the diverse use of AWEs as cost-effective media for nanomaterial synthesis.

Emission Spectroscopy Investigation of the Enhancement of Carrier Collection Efficiency in AgBiS2-Nanocrystal/ZnO-Nanowire Heterojunction Solar Cells

Eco-friendly solar cells were fabricated using interdigitated layers comprising ZnO nanowires (NWs) and infrared absorbing AgBiS₂ nanocrystals (ITO/ZnO NWs/AgBiS₂/P3HT/Au). The quality of ZnO NWs was studied using photoluminescence and Raman spectroscopy to identify the defects in ZnO NWs influencing solar cell performance. Oxygen vacancies and Zn interstitial sites, among various recombination sites, were observed to be the main sites for carrier recombination, which hinders the carrier collection in the solar cells. Accordingly, the power conversion efficiency of AgBiS₂ solar cells exhibited a good correlation with the number of oxygen vacancies. The structural order and electron-phonon interaction in ZnO NWs were also investigated via Raman scattering spectroscopy. A lower concentration of oxygen vacancies and zinc interstitials (Zn_i) resulted in a higher structural order as well as a weaker electron-phonon interaction in ZnO NWs. When ZnO NWs were treated at 500 °C in oxygen with the lowest oxygen vacancy concentration, the solar cells (500-O₂ solar cell (SC)) demonstrated an external quantum efficiency of approximately 70% in the visible region and a corresponding internal quantum efficiency of more than 80%. The 500-O₂ SC exhibited a power conversion efficiency of 5.41% (J_SC = 22.21 mA/cm², V_OC = 0.41 V, and FF = 60%) under quasi one-sun illumination. New methods that can efficiently reduce oxygen vacancies and Zn_i without affecting the structural order of ZnO NWs would further enhance the carrier collection efficiency. Moreover, since ZnO is a key electron transport material for constructing not only colloidal quantum dot solar cells but also other emerging solar cells, such as organic thin-film solar cells, the present findings provide significant information for improving their performance.

Improve the Performance of Porous Silicon for solar application by the embedding of Lithium Oxide nanoparticle

The present research concerns the manufacture of porous silicon (PSi) by means of electrochemical etching method at (10 mA.cm−2)current density and approximately 10 minute etching time. The porous silicone layer was investigated by XRD, AFM and FTIR, and then Li2O nanoparticles (NPs) were prepared by a simple chemical method. And freshly embedding three drops of (Li2O) solution using the drop casting technique on the 40°C porous silicon(n-Psi) method to produce the heterojunction Al / Li2O / PSi / Al. The results of current-voltage ( I-V) test showed that the solar cell’s maximum power conversion efficiency ( PCE) was 2.49% and thus the fill factor was 66.12%. A diffusion of Li2O NPs on PSi solar cell characteristics assures an improvement on their properties.

Low-Temperature PLD-Growth of Ultrathin ZnO Nanowires by Using Zn x Al1-x O and Zn x Ga1-x O Seed Layers

ZnO nanowires (NWs) are used as building blocks for a wide range of different devices, e.g. light emitters, resonators, and sensors. Integration of the NWs into such structures requires a high level of NWs' diameter control. Here, we present that the doping concentration of Zn _x Al_1-x O and Zn _x Ga_1-x O seed layers has a strong impact on the NW growth and allows to tune the diameter of the NWs by two orders of magnitude down to less than 7 nm. These ultrathin NWs exhibit a well-oriented vertical growth and thus are promising for the investigation of quantum effects. The doping of the ZnO seed layers has also an impact on the deposition temperature which can be reduced down to T≈400^∘C. This temperature is much smaller than those typically used for the fabrication of NWs by pulsed laser deposition. A comparison of the NWs indicates a stronger impact of the Ga doping on the NW growth than for the Al doping which we attribute to an impact of the size of the dopants. The optical properties of the NWs were investigated by cathodoluminescence spectroscopy which revealed a high crystalline quality. For the thin nanowires, the emission characteristic is mainly determined by the properties of the surface near region.

The effect of cation doping on the morphology, optical and structural properties of highly oriented wurtzite ZnO-nanorod arrays grown by a hydrothermal method

Undoped and C-doped (C: Mg²⁺, Ni²⁺, Mn²⁺, Co²⁺, Cu²⁺, Cr³⁺) ZnO nanorods were synthesized by a hydrothermal method at temperatures as low as 60 °C. The effect of doping on the morphology of the ZnO nanorods was visualized by taking their cross section and top SEM images. The results show that the size of nanorods was increased in both height and diameter by cation doping. The crystallinity change of the ZnO nanorods due to each doping element was thoroughly investigated by an x-ray diffraction (XRD). The XRD patterns show that the wurtzite crystal structure of ZnO nanorods was maintained after cation addition. The optical Raman-active modes of undoped and cation-doped nanorods were measured with a micro-Raman setup at room temperature. The surface chemistry of samples was investigated by x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy. Finally, the effect of each cation dopant on band-gap shift of the ZnO nanorods was investigated by a photoluminescence setup at room temperature. Although the amount of dopants (Mg²⁺, Ni²⁺, and Co²⁺) was smaller than the amount of Mn²⁺, Cu²⁺, and Cr³⁺ in the nanorods, their effect on the band structure of the ZnO nanorods was profound. The highest band-gap shift was achieved for a Co-doped sample, and the best crystal orientation was for Mn-doped ZnO nanorods. Our results can be used as a comprehensive reference for engineering of the morphological, structural and optical properties of cation-doped ZnO nanorods by using a low-temperature synthesis as an economical mass-production approach.

Recent developments of zinc oxide based photocatalyst in water treatment technology: A review

Today, a major issue about water pollution is the residual dyes from different sources (e.g., textile industries, paper and pulp industries, dye and dye intermediates industries, pharmaceutical industries, tannery and craft bleaching industries, etc.), and a wide variety of persistent organic pollutants have been introduced into our natural water resources or wastewater treatment systems. In fact, it is highly toxic and hazardous to the living organism; thus, the removal of these organic contaminants prior to discharge into the environment is essential. Varieties of techniques have been employed to degrade those organic contaminants and advanced heterogeneous photocatalysis involving zinc oxide (ZnO) photocatalyst appears to be one of the most promising technology. In recent years, ZnO photocatalyst have attracted much attention due to their extraordinary characteristics. The high efficiency of ZnO photocatalyst in heterogeneous photocatalysis reaction requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable effort has to be exerted to further improve the heterogeneous photocatalysis under UV/visible/solar illumination. Lately, interesting and unique features of metal doping or binary oxide photocatalyst system have gained much attention and became favourite research matter among various groups of scientists. It was noted that the properties of this metal doping or binary oxide photocatalyst system primarily depend on the nature of the preparation method and the role of optimum dopants content incorporated into the ZnO photocatalyst. Therefore, this paper presents a critical review of recent achievements in the modification of ZnO photocatalyst for organic contaminants degradation.

Effect of atomic layer deposition temperature on the performance of top-down ZnO nanowire transistors

This paper studies the effect of atomic layer deposition (ALD) temperature on the performance of top-down ZnO nanowire transistors. Electrical characteristics are presented for 10-μm ZnO nanowire field-effect transistors (FETs) and for deposition temperatures in the range 120°C to 210°C. Well-behaved transistor output characteristics are obtained for all deposition temperatures. It is shown that the maximum field-effect mobility occurs for an ALD temperature of 190°C. This maximum field-effect mobility corresponds with a maximum Hall effect bulk mobility and with a ZnO film that is stoichiometric. The optimized transistors have a field-effect mobility of 10 cm(2)/V.s, which is approximately ten times higher than can typically be achieved in thin-film amorphous silicon transistors. Furthermore, simulations indicate that the drain current and field-effect mobility extraction are limited by the contact resistance. When the effects of contact resistance are de-embedded, a field-effect mobility of 129 cm(2)/V.s is obtained. This excellent result demonstrates the promise of top-down ZnO nanowire technology for a wide variety of applications such as high-performance thin-film electronics, flexible electronics, and biosensing.

Fabrication and sensing behavior of one-dimensional ZnO-Zn2GeO4 heterostructures

Well-crystalline one-dimensional ZnO-Zn2GeO4 (ZGO) heterostructures were successfully synthesized using a high-temperature solid-state reaction between the ZnO and Ge layers of ZnO-Ge core-shell nanostructures. The polycrystalline ZGO crystallites had a thickness in the range of 17 to 26 nm. The high-temperature solid-state reaction induced grooves and crystal defects on the surfaces of the ZGO crystallites. The sensors made from the ZnO-ZGO heterostructures exhibited a marked photocurrent response to UV light at room temperature and a gas sensing response to acetone gas at 325°C. The observed sensing properties are attributed to the rugged surface of the ZGO heterointerfaces between ZnO and ZGO, surface crystal defects of ZGO, and cross-linked contact regions of ZnO-ZGO.