One-dimensional ZnO nanostructures (nanowires/nanorods) are attractive materials for applications such as gas sensors, biosensors, solar cells, and photocatalysts. This is due to the relatively easy production process of these kinds of nanostructures with excellent charge carrier transport properties and high crystalline quality. In this work, we review the photoluminescence (PL) properties of single and collective ZnO nanowires and nanorods. As different growth techniques were obtained for the presented samples, a brief review of two popular growth methods, vapor-liquid-solid (VLS) and hydrothermal, is shown. Then, a discussion of the emission process and characteristics of the near-band edge excitonic emission (NBE) and deep-level emission (DLE) bands is presented. Their respective contribution to the total emission of the nanostructure is discussed using the spatial information distribution obtained by scanning transmission electron microscopy−cathodoluminescence (STEM-CL) measurements. Also, the influence of surface effects on the photoluminescence of ZnO nanowires, as well as the temperature dependence, is briefly discussed for both ultraviolet and visible emissions. Finally, we present a discussion of the size reduction effects of the two main photoluminescent bands of ZnO. For a wide emission (near ultra-violet and visible), which has sometimes been attributed to different origins, we present a summary of the different native point defects or trap centers in ZnO as a cause for the different deep-level emission bands.

Photoluminescence of ZnO Nanowires: A Review.

Smart nanoparticles for medical applications have gathered considerable attention due to an improved biocompatibility and multifunctional properties useful in several applications, including advanced drug delivery systems, nanotheranostics and in vivo imaging. Among nanomaterials, zinc oxide nanoparticles (ZnO NPs) were deeply investigated due to their peculiar physical and chemical properties. The large surface to volume ratio, coupled with a reduced size, antimicrobial activity, photocatalytic and semiconducting properties, allowed the use of ZnO NPs as anticancer drugs in new generation physical therapies, nanoantibiotics and osteoinductive agents for bone tissue regeneration. However, ZnO NPs also show a limited stability in biological environments and unpredictable cytotoxic effects thereof. To overcome the abovementioned limitations and further extend the use of ZnO NPs in nanomedicine, doping seems to represent a promising solution. This review covers the main achievements in the use of doped ZnO NPs for nanomedicine applications. Sol-gel, as well as hydrothermal and combustion methods are largely employed to prepare ZnO NPs doped with rare earth and transition metal elements. For both dopant typologies, biomedical applications were demonstrated, such as enhanced antimicrobial activities and contrast imaging properties, along with an improved biocompatibility and stability of the colloidal ZnO NPs in biological media. The obtained results confirm that the doping of ZnO NPs represents a valuable tool to improve the corresponding biomedical properties with respect to the undoped counterpart, and also suggest that a new application of ZnO NPs in nanomedicine can be envisioned.

Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine.

Among the various approaches to grow semiconducting oxide nanowires, the thermal oxidation procedure is considered a simple, efficient, and fast method that allows the synthesis of micro and nanost...

Growth of Long ZnO Nanowires with High Density on the ZnO Surface for Gas Sensors

Ultraviolet (UV) sensors offer significant advantages in human health protection and environmental pollution monitoring. Amongst various materials for UV sensors, the zinc oxide (ZnO) nanostructure is considered as one of the most promising candidates due to its incredible electrical, optical, biomedical, energetic and preparing properties. Compared to other fabricating techniques, hydrothermal synthesis has been proven to show special advantages such as economic cost, low-temperature process and excellent and high-yield production. Here, we summarize the latest progress in research about the hydrothermal synthesis of ZnO nanostructures for UV sensing. We particularly focus on the selective hydrothermal processes and reveal the effect of key factors/parameters on ZnO architectures, such as the laser power source, temperature, growth time, precursor, seeding solution and bases. Furthermore, ZnO hydrothermal nanostructures for UV applications as well as their mechanisms are also summarized. This review will therefore enlighten future ideas of low-temperature and low-cost ZnO-based UV sensors.

Economic Friendly ZnO-Based UV Sensors Using Hydrothermal Growth: A Review.

The propagation of matter waves in curved geometry is relevant for ion transport, atomtronics and electrons in nanowires. Curvature effects are usually addressed within the adiabatic limit and treated via an effective potential acting on the manifold to which the particles are strongly confined. However, the strength of the confinements that can be achieved experimentally are limited in practice, and the adiabatic approximation often appears too restrictive for realistic guides. Here, we work out a design method for 2D sharply bent waveguides beyond this approximation using an exact inverse-engineering technique. The efficiency of the method is confirmed by the resolution of the 2D nonlinear Schr\"odinger equation in curved geometry. In this way, we realize reflectionless and ultrarobust curved guides, even in the presence of interactions. Here, the transverse stability is improved by several orders of magnitude when compared to circular guides of similar size.

Quantum Control beyond the Adiabatic Regime in 2D Curved Matter-Wave Guides.

The quest of different materials with nano scale properties which can fulfill the 21st century requirement has paves the way for the progress of one dimensional nanostructure mainly nanowires. Nanowires have a profound impact in nano electronics, nano devices and systems, nano composite materials, and renewable energy resources. The utilization of nanowires for biological sciences is expected to improve a lot to provide efficient treatments otherwise it would not have been possible. Metal oxide nanowires such as zinc oxide (ZnO), tin oxide (SnO2), silicon oxide (SiO2), indium oxide (In2O3), and titanium oxide (TiO2) etc. are widely used for various applications. However ZnO nanowires are first choice for researcher because of its fascinating properties like biocompatibility, biodegradability and bio safety not only for medical purpose but other applications also like gas sensor, biosensor, and nanogenerator or as a photocatalyst etc. Individual zinc oxide nanowire or groups of nanowires are generally used as active element for the different applications. The main aim of this article is to elaborate the various routes for synthesis of nanowires with challenges in the field of device fabrication and to review all possible applications of ZnO nanowires. Firstly possible mechanisms for the growth of ZnO nanowire from various methods, such as vapor liquid solid (VLS), chemical vapor deposition (CVD), r.f. sputtering, template based and chemical approach are discussed in detail. Secondly a wide range of ZnO nanowire applications like as gas sensor, biosensor, optoelectronic devices, nano generator and photo catalyst are explained in detail.

Synthesis and applications of ZnO nanowire: A review

The design and fabrication of nichrome based coplanar microheater for LPG sensing applications is presented in this work. Nichrome based coplanar microheater is fabricated using photolithography process. The surface morphology of DC sputtered nichrome is characterized using scanning electron microscope. Electrothermal behaviour of the fabricated microheater is characterized by varying the applied current while the thermal distribution pattern over the active heating area is recorded using thermal imaging camera. The silicon thickness under microheater active area is varied by silicon etching with different time duration in TMAH solution. Silicon thickness effect on maximum temperature of microheater is also investigated experimentally. The tin oxide (SnO2) thin film as LPG sensor is deposited on fabricated coplanar heating platform and it is tested with different amount of LPG concentration.

Fabrication of coplanar microheater platform for LPG sensing applications

Nanostructured tin oxide (SnO2) thin films are deposited using reactive r.f. sputtering by varying deposition time and substrate temperature during deposition. A wide range of tin oxide film thicknesses between 100 nm to 550 nm are deposited by varying the deposition time while substrate temperature during deposition is also varied from room temperature to 400 °C. The homogeneity of the deposited film during deposition is ensured using secondary electron microscopy system (SIMS). The crystal structure and microstructure of the deposited films are investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively while the sheet resistance of deposited film is determined by four point probe method. The x-ray diffraction study showed that deposited films are orientated along (110) plane at elevated temperature, manifested with increase of grain size with thickness and substrate temperature except at 300 °C where it decreases. Microstructural studies using cross sectional SEM reveals that 470 nm tin oxide film deposited at room temperature shows highest porosity. The porosity of the films is quantified by using spectroscopic ellipsometry results and it varies from 23.2% to 8.99% for the film deposited at room temperature and 400 °C respectively. LPG response for all deposited films is also measured. The LPG sensitivity for the sensor film of various thicknesses shows linear response with porosity. SnO2 thin films deposited from room temperature to 300 °C shows no significant variation in sensitivity for LPG. The sensor response for LPG decreases sharply for the film deposited above 300 °C. Minimum resistivity 0.3536 Ω.cm is obtained for the tin oxide film deposited at 400 °C. The mechanism of LPG sensing property of nanostructured tin oxide thin film is also explained.

https://iopscience.iop.org/article/10.1088/2053-1591/aadd40/pdf

Shobi Bagga

Papers

Synthesis and applications of ZnO nanowire: A review

Fabrication of coplanar microheater platform for LPG sensing applications

Influence of porosity on the properties of nanostructured tin oxide thin film

Ammonia gas sensing with tin oxide thin film sensor and coplanar microheater