Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating; then, ZnO nanorods (NR) and Al-doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy-dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al-doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties.

Solar-Driven Photoelectrochemical Performance of Novel ZnO/Ag2WO4/AgBr Nanorods-Based Photoelectrodes

Highly efficient photoelectrochemical (PEC) water oxidation under solar visible light is crucial for water splitting to produce hydrogen as a source of sustainable energy. Particularly, silver-based nanomaterials are important for PEC performance due to their surface plasmon resonance which can enhance the photoelectrochemical efficiency. However, the PEC of ZnO/Ag2WO4/AgBr with enhanced visible-light water oxidation has not been studied so far. Herein, we present a novel photoelectrodes based on ZnO/Ag2WO4/AgBr nanorods (NRs) for PEC application, which is prepared by the low-temperature chemical growth method and then by successive ionic layer adsorption and reaction (SILAR) method. The synthesized photoelectrodes were investigated by several characterization techniques, emphasizing a successful synthesis of the ZnO/Ag2WO4/AgBr heterostructure NRs with excellent photocatalysis performance compared to pure ZnO NRs photoelectrode. The significantly enhanced PEC was due to improved photogeneration and transportation of electrons in the heterojunction due to the synergistic effect of the heterostructure. This study is significant for basic understanding of the photocatalytic mechanism of the heterojunction which can prompt further development of novel efficient photoelectrochemical-catalytic materials.

Integration of ZnO nanorods with MOS capacitor for self-powered force sensors and nanogenerators

In this work, we present a novel force-sensing device with zinc oxide nanorods (ZnO NRs) integrated with a metal-oxide-semiconductor (MOS) capacitor and encapsulated with Kapton tape. The details of the fabrication process and working principle of the integrated ZnO NRs-MOS capacitor as a force sensor and nanogenerator have been discussed. The fabricated ZnO-MOS device is tested for both the open-circuit and resistor-connected mode. For an input force in the range of 1-32 N, the open-circuit output voltage of the device is measured to be in the range of 60-100 mV for different device configurations. In the resistor-connected mode, the maximum output power of 0.6 pW is obtained with a 1 MΩ external resistor and input force of 8 N. In addition, the influence of different seed layers (Ag and ZnO) and the patterning geometry of the ZnO nanorods on the output voltage of ZnO-MOS device have been investigated by experiments. An equivalent circuit model of the device has been developed to study the influence of the geometry of ZnO NRs and Kapton tape on the ZnO-MOS device voltage output. This study could be an example of integrating piezoelectric nanomaterials on traditional electronic devices and could inspire novel designs and fabrication methods for nanoscale self-powered force sensors and nanogenerators.

Formamidinium Lead Iodide Perovskite Films with Polyvinylpyrrolidone Additive for Active Layer in Perovskite Solar Cells, Enhanced Stability and Electrical Conductivity

In this paper, we studied the influence of polyvinylpyrrolidone (PVP) as a stabilization additive on optical and electrical properties of perovskite formamidinium lead iodide (FAPI) polycrystalline thin films on ZnO nanorods (ZNR). FAPI (as an active layer) was deposited from a single solution on ZNR (low temperature processed electron transport layer) using a one-step method with the inclusion of an anti-solvent. The role of PVP in the formation of the active layer was investigated by scanning electron microscopy and contact angle measurements to observe the effect on morphology, while X-ray diffraction was used as a method to study the stability of the film in an ambient environment. The effect of the PVP additive on the optical and electrical properties of the perovskite thin films was studied via photoluminescence, UV-Vis measurements, and electrical impedance spectroscopy. We have demonstrated that PVP inclusion in solution-processed perovskite FAPI thin films prevents the degradation of the film in an ambient atmosphere after aging for 2 months. The inclusion of the PVP also improves the infiltration of FAPI perovskite into ZnO nanostructures, increases electrical conductivity and radiative recombination of the photo-generated charge carriers. These results show promising information for promoting PVP stabilized FAPI perovskites for the new generation of photovoltaic devices.

Effects of Seed-Layer N2O Plasma Treatment on ZnO Nanorod Based Ultraviolet Photodetectors: Experimental Investigation with Two Different Device Structures

The crystalline quality of ZnO NR (nanorod) as a sensing material for visible blind ultraviolet PDs (photodetectors) critically depends on the SL (seed layer) material of properties, which is a key to high-quality nanocrystallite growth, more so than the synthesis method. In this study, we fabricated two different device structures of a gateless AlGaN/GaN HEMT (high electron mobility transistor) and a photoconductive PD structure with an IDE (interdigitated electrode) pattern implemented on a PET (polyethylene terephthalate) flexible substrate, and investigated the impact on device performance through the SL N₂O plasma treatment. In case of HEMT-based PD, the highest current on-off ratio (~7) and spectral responsivity R (~1.5 × 10⁵ A/W) were obtained from the treatment for 6 min, whereas the IDE pattern-based PD showed the best performance (on-off ratio = ~44, R = ~69 A/W) from the treatment for 3 min and above, during which a significant etch damage on PET substrates was produced. This improvement in device performance was due to the enhancement in NR crystalline quality as revealed by our X-ray diffraction, photoluminescence, and microanalysis.

Rapid synthesis of microwave-assisted zinc oxide nanorods on a paper-based analytical device for fluorometric detection of l-dopa

l-dopa is a catecholamine neurotransmitter used to treat Parkinson's disease. This paper presents a low-cost paper-based biosensor aimed at enhancing the convenience of monitoring l-dopa concentrations. ZnO nanorods (ZnO-NRs) were synthesized on papers in less than 90 min using a microwave-assisted hydrothermal method. The ZnO-NRs amplify green fluorescence signals to enhance the detection sensitivity of l-dopa, best measured at excitation/emission wavelengths of 475/537 nm. We systematically characterized the effect of reaction conditions on the corresponding fluorescence enhancements. The proposed ZnO NRs-paper biosensor presented a ∼3-fold increase in green fluorescence compared to unmodified papers. The linear range of detection for l-dopa was 25-2000 nM, with a limit of detection of 24 nM, which meets the clinical requirements for the monitoring of l-dopa in Parkinson's patients.

Ultraviolet Radiation Sensor Based on ZnO Nanorods/La3Ga5SiO14 Microbalance

The possibility of creating resonant ultraviolet (UV) sensors based on the structure of ZnO nanorods/La₃Ga₅SiO₁₄ microbalance (LCM) has been investigated. The principle of sensor operation is based on the desorption of oxygen from the surface of ZnO nanorods upon irradiation with UV light and an increase in the concentration of charge carriers that leads to an increase in the capacitance of the structure of ZnO nanorods/LCM. It has been shown that UV radiation intensity affects the resonance oscillation frequency of the LCM sensor. After the end of irradiation, the reverse process of oxygen adsorption on the surface of ZnO nanorods occurs, and the resonance frequency of the sensor oscillations returns to the initial value.

Simultaneous and sensitive detection of multiple small biological molecules by microfluidic paper-based analytical device integrated with zinc oxide nanorods

In this work, ZnO nanorods (ZnO NRs) with different sizes were hydrothermally grown on the surface of Whatman filter paper for the fabrication of a microfluidic paper-based device (μPAD) for the simultaneous detection of glucose and uric acid. As dual enzymatic reaction was employed for the colorimetric detection in this μPAD, the presence of ZnO NRs promoted the enzyme immobilization thus significantly enhancing the colorimetric signal. The coffee ring effect was effectively conquered by the uniform distribution of ZnO NR as well as a specialized double-layered μPAD design. Meanwhile, two color indicators with distinct colors were used to provide complementary results to better quantify the concentration of the analytes by naked eye. As a result, two linear calibration curves were obtained for the detection of glucose (0.01-10 mmol L^-1) and uric acid (0.01-5 mmol L^-1), along with a LOD of 3 μmol L^-1 for glucose and 4 μmol L^-1 for uric acid, respectively. The practical usefulness of the proposed μPAD was further validated by the simultaneous analysis of glucose and uric acid in serum samples and urine samples.

Structure Dependent Product Selectivity for CO2 Electroreduction on ZnO Derived Catalysts

Electrochemical conversion of CO2 is an attractive alternative to releasing it to the atmosphere. Catalysts derived from electroreduction of metal oxides are often more active than when starting with metallic phase catalyst. The origin of this effect is not yet clear. Using ZnO nanorods, we show that the initial structure of the oxide as well as the electrolyte medium have a profound impact on the structure of the catalytic active Zn phase, and thereby the selectivity of the catalysts. ZnO nanorods with various aspect ratios were electrochemically reduced in different electrolytes leading to metallic Zn with different structures; a sponge-like structure, nanorods and nanoplates. The sponge-like Zn produced syngas with H2 : CO=2, and some formate, the nanorods produced only syngas with H2 : CO=1, while Zn nanoplates exhibited 85 % selectivity towards CO. These results open a pathway to design new electrocatalysts with optimized properties by modifying the structure of the starting material and the electroreduction medium.

Fabrication and Characterization of High-Quality UV Photodetectors Based ZnO Nanorods Using Traditional and Modified Chemical Bath Deposition Methods

Ultraviolet (UV) photodetectors (PDs) based on high-quality well-aligned ZnO nanorods (NRs) were fabricated using both modified and conventional chemical bath deposition (CBD) methods. The modified chemical bath deposition (M-CBD) method was made by adding air bubbles to the growth solution during the CBD process. The viability and effectiveness of M-CBD were examined by developing UV PDs based on ZnO NRs. The ZnO nano-seed layer was coated on a glass substrate utilizing radiofrequency (RF) sputtering. The impact of the different growth-times on morphology, growth rate, crystal structure, and optical and chemical properties were investigated systematically using different characterization techniques, such as field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) analysis, UV–VIS double beam spectrometer, and energy dispersive X-ray analysis (EDX), respectively. The Al/ZnO UV PDs based on ZnO nanorods were fabricated with optimum growth conditions through the two methods of preparation. This study showed that the synthesized ZnO NRs using the M-CBD method for different growth times possess better properties than the conventional method under similar deposition conditions. Despite having the highest aspect ratio and growth rate of ZnO NRs, which were found at 4 h growth duration for both methods, the aspect ratio of ZnO NRs using the M-CBD technique was comparatively higher than the conventional CBD method. Besides, the UV PDs fabricated by the M-CBD method at 5 V bias voltage showed high sensitivity, short response time, quick recovery time, high gain, low dark current, and high photocurrent compared with the UV PD device fabricated by the conventional CBD method.

Green synthesis of stable antioxidant, anticancer and photocatalytic activity of zinc oxide nanorods from Leea asiatica leaf

The present work reveals zinc oxide nanorods (ZnO NRs) obtained via green synthesis approach utilizing phytochemicals present in the Leea asiatica plant. The synthesized ZnO NRs was confirmed by various characterization methods like X-ray diffraction, FTIR, SEM-EDX, UV-vis, TEM and Raman spectra analysis. The obtained nanorods show less particle size with a distinctive high surface area. The photodegradation activity of obtained ZnO NRs shows 81.3 % of dye degradation at high concentration whereas 42.9 % in low concentration and also antioxidant test shows a better result for free radical scavenging. To understand the safety of the ZnO NRs zebrafish embryos was utilized as a model and found to be less toxic after assessment. Furthermore, to understand the anticancer activity of ZnO NRs it was assessed against breast cancer cell line through MTT, XTT, NRU, and LDH assay. The ZnO NRs exposed against breast cancer cell line (MCF-7) had resulted in necrosis and apoptosis which was further confirmed by genotoxicity assay. Also, the molecular mechanisms behind the necrosis and apoptosis are also discussed to show the involvement of ZnO NRs towards breast cancer cells (MCF-7). The present study on ZnO NRs gives a wide spectrum understanding of using ZnO NRs as a potential drug for human breast cancer by showing its physiological pathways as well as a novel way to synthesize ZnO NRs using Leea asiatica plant extract.

Antibacterial, Antiviral, and Self-Cleaning Mats with Sensing Capabilities Based on Electrospun Nanofibers Decorated with ZnO Nanorods and Ag Nanoparticles for Protective Clothing Applications

The COVID-19 pandemic has clearly shown the importance of developments in fabrication of advanced protective equipment. This study investigates the potential of using multifunctional electrospun poly(methyl methacrylate) (PMMA) nanofibers decorated with ZnO nanorods and Ag nanoparticles (PMMA/ZnO-Ag NFs) in protective mats. Herein, the PMMA/ZnO-Ag NFs with an average diameter of 450 nm were simply prepared on a nonwoven fabric by directly electrospinning from solutions containing PMMA, ZnO nanorods, and Ag nanoparticles. The novel material showed high performance with four functionalities (i) antibacterial agent for killing of Gram-negative and Gram-positive bacteria, (ii) antiviral agent for inhibition of corona and influenza viruses, (iii) photocatalyst for degradation of organic pollutants, enabling a self-cleaning protective mat, and (iv) reusable surface-enhanced Raman scattering substrate for quantitative analysis of trace pollutants on the nanofiber. This multi-functional material has high potential for use in protective clothing applications by providing passive and active protection pathways together with sensing capabilities.

Surface Modification of Basalt Fibres with ZnO Nanorods and Its Effect on Thermal and Mechanical Properties of PLA-Based Composites

The composites based on basalt fibres and poly(lactic acid) (PLA) show promising applications in biomedical and automotive fields, but their mechanical performance is still largely hindered by poor interfacial properties. Zinc oxide nanorods have been successfully used to tune the PLA/basalt fibre interface by growing them on commercially available basalt fabrics. The hierarchical fibres significantly enhanced the mechanical properties of PLA-based composites, especially their flexural strength and stiffness. These values are 26% and 22% higher than those of unmodified basalt/PLA composites, and 24% and 34% higher than those of glass/PLA composites used as a baseline. The increase in tensile and flexural properties hinges on the mechanical interlocking action promoted by ZnO nanorods and on the creation of a compact transcrystallinity structure. A degradation of PLA matrix was detected but it was positively counteracted by the better interfacial stress transfer. This study offers a novel approach for modifying the fibre–matrix interface of biocomposites intended for high-performance applications.

Decoration of Zinc Oxide Nanorods into the Surface of Activated Carbon Obtained from Agricultural Waste for Effective Removal of Methylene Blue Dye

Zinc oxide (ZnO) nanorods incorporated activated carbon (AC) composite photocatalyst was synthesized using a hydrothermal process. The AC was prepared from lapsi (Choerospondias axillaris) seed stone, an agricultural waste product, found in Nepal by the chemical activation method. An aqueous suspension of AC with ZnO precursor was subjected to the hydrothermal treatment at 140 °C for 2 h to decorate ZnO rods into the surface of AC. As-obtained ZnO nanorods decorated activated carbon (ZnO/AC) photocatalyst was characterized by various techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. Results showed that highly crystalline hexagonal ZnO nanorods were effectively grown on the surface of porous AC. The photocatalytic property of the as-prepared ZnO/AC composite was studied by degrading methylene blue (MB) dye under UV-light irradiation. The ZnO/AC composite showed better photocatalytic property than that of the pristine ZnO nanorods. The enhanced photocatalytic performance in the case of the ZnO/AC composite is attributed to the combined effects of ZnO nanorods and AC.

Enhanced Energy Harvesting Ability of ZnO/PAN Hybrid Piezoelectric Nanogenerators

Miniaturization of energy conversion and storage devices has attracted remarkable consideration in the application of wearable electronics. Compared with film-based flexible electronics, fiber-based wearable electronics (e.g., nanogenerators and sensors made from electrospun nanofibers) are more appealing and promising for wearables. However, there are two bottlenecks, a low power output and poor sensing capability, limiting the application of piezoelectric nanofibers. Herein, we integrated zinc oxide nanorods (ZnO NRs) to a less known piezoelectric polymer, polyacrylonitrile (PAN) nanofiber, forming a ZnO/PAN nanofabric, which significantly improved the pressure sensitivity and vibrational energy harvesting ability by about 2.7 times compared with those of the pristine PAN nanofiber, and the maximum output power density of ∼10.8 mW·m^-2 is achieved. Noteworthily, the ZnO/PAN nanofabric showed a power output about twice of the one made of ZnO and polyvinylidene fluoride. It was revealed that the integration of ZnO NRs clearly improved the planar zigzag conformation in microstructures of the PAN nanofiber. Further, successful demonstrations of a mechanically robust pressure sensor and wearable power source confirm the potential applications in human activity monitoring and personal thermal management, respectively.

Synthesis of ZnO Nanorod Film Deposited by Spraying with Application for Flexible Piezoelectric Energy Harvesting Microdevices

Industry 4.0 and the Internet of Things have significantly increased the use of sensors and electronic products based on flexible substrates, which require electrical energy for their performance. This electrical energy can be supplied by piezoelectric vibrational energy harvesting (pVEH) devices. These devices can convert energy from ambient mechanical excitations into electrical energy. In order to develop, these devices require piezoelectric films fabricated with a simple and low-cost process. In this work, we synthesize ZnO nanorod film by a solvothermal method and deposit by spraying on ITO (indium-tin-oxide)/PET (polyethylene terephthalate) flexible substrate for a pVEH microdevice. The results of the characterization of the ZnO nanorod film using X-ray diffraction (XRD) confirm the typical reflections for this type of nanomaterial (JCPDS 36-145). Based on transmission electron microscopy (TEM) images, the size of the nanorod film is close to 1380 nm, and the average diameter is 221 ± 67 nm. In addition, the morphological characteristics of the ZnO nanorod film are obtained using atomic force microscopy (AFM) tapping images. The pVEH microdevice has a resonant frequency of 37 Hz, a generated voltage and electrical power of 9.12 V and 6.67 μW, respectively, considering a load resistance of 107.7 kΩ and acceleration of 1.5 g. The ZnO nanorod film may be applied to pVEH microdevices with flexible substrates using a low-cost and easy fabrication process.

SERS Effect on Spin-Coated Seeding of Tilted Au-ZnO Nanorods for Low-Cost Diagnosis

Uniformly parallel Au-coated ZnO nanorods have previously been shown to amplify local Raman signals, providing increased sensitivity to disease markers in the detection of inflammation and cancer. However, practical and cost-effective fabrication methods of substrates for surface-enhanced Raman spectroscopy (SERS) fail to produce highly uniform surfaces. Here, the feasibility of Raman enhancement on less-uniform substrates is assessed. ZnO nanorod structures were fabricated by hydrothermal synthesis, starting from spin-coated seed substrates. Following analysis, the nanostructures were coated with Au to create stochastically variant substrates. The non-uniformity of the fabricated Au-coated ZnO nanorod structures is confirmed morphologically by FE-SEM and structurally by X-ray diffraction, and characterized by the angular distributions of the nanorods. Monte Carlo finite element method simulations matching the measured angular distributions and separations predicted only moderate increases in the overall Raman enhancement with increasing uniformity. Highly variant substrates exhibited approximately 76% of the Raman enhancement of more uniform substrates in simulations and experiments. The findings suggest that, although highly inhomogeneous Au-coated ZnO nanorod substrates may not attain the same Raman enhancement as more uniform substrates, the relaxation of fabrication tolerances may be economically viable.

Selective Detection of Nano-Sized Diagnostic Markers Using Au-ZnO Nanorod-Based Surface-Enhanced Raman Spectroscopy (SERS) in Ureteral Obstruction Models

Background

This study investigated the diagnosis of renal diseases using a biochip capable of detecting nano-sized biomarkers. Raman measurements from a kidney injury model were taken, and the feasibility of early diagnosis was assessed.

Materials and Methods

Rat models with mild and severe unilateral ureteral obstructions were created, with the injury to the kidney varying according to the tightness of the stricture. After generating the animal ureteral obstruction models, urine was collected from the kidney and bladder.

Results and Discussion

After confirming the presence of renal injury, urine drops were placed onto a Raman chip whose surface had been enhanced with Au-ZnO nanorods, allowing nano-sized biomarkers that diffused into the nanogaps to be selectively amplified. The Raman signals varied according to the severity of the renal damage, and these differences were statistically confirmed.

Conclusion

These results confirm that ureteral stricture causes kidney injury and that signals in the urine from the release of nano-biomarkers can be monitored using surface-enhanced Raman spectroscopy.

Graphene Quantum Dot-Sensitized ZnO-Nanorod/GaN-Nanotower Heterostructure-Based High-Performance UV Photodetectors

The fabrication of a superior-performance ultraviolet (UV) photodetector utilizing graphene quantum dots (GQDs) as a sensitization agent on a ZnO-nanorod/GaN-nanotower heterostructure has been realized. GQD sensitization displays substantial impact on the electrical as well as the optical performance of a heterojunction UV photodetector. The GQD sensitization stimulates charge carriers in both ZnO and GaN and allows energy band alignment, which is realized by a spontaneous time-correlated transient response. The fabricated device demonstrates an excellent responsivity of 3.2 × 10³ A/W at -6 V and displays an enhancement of ∼265% compared to its bare counterpart. In addition, the fabricated heterostructure UV photodetector exhibits a very high external quantum efficiency of 1.2 × 10⁶%, better switching speed, and signal detection capability as low as ∼50 fW.

New Insights towards High-Temperature Ethanol-Sensing Mechanism of ZnO-Based Chemiresistors

In this work, we investigate ethanol (EtOH)-sensing mechanisms of a ZnO nanorod (NRs)-based chemiresistor using a near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). First, the ZnO NRs-based sensor was constructed, showing good performance on interaction with 100 ppm of EtOH in the ambient air at 327 °C. Then, the same ZnO NRs film was investigated by NAP-XPS in the presence of 1 mbar oxygen, simulating the ambient air atmosphere and O₂/EtOH mixture at the same temperature. The partial pressure of EtOH was 0.1 mbar, which corresponded to the partial pressure of 100 ppm of analytes in the ambient air. To better understand the EtOH-sensing mechanism, the NAP-XPS spectra were also studied on exposure to O₂/EtOH/H₂O and O₂/MeCHO (MeCHO = acetaldehyde) mixtures. Our results revealed that the reaction of EtOH with chemisorbed oxygen on the surface of ZnO NRs follows the acetaldehyde pathway. It was also demonstrated that, during the sensing process, the surface becomes contaminated by different products of MeCHO decomposition, which decreases dc-sensor performance. However, the ac performance does not seem to be affected by this phenomenon.

Au nanoparticle-decorated ZnO nanorods as fluorescent non-enzymatic glucose probe

ZnO nanorods (NRs) synthesized by a hydrothermal method and decorated with Au nanoparticles (NPs) were used for fluorescent non-enzymatic glucose detection. The detection is based on the photoluminescence (PL) quenching of ZnO NRs/Au NPs (at 382 nm under 325 nm excitation) exposed to glucose. The sensor exhibits a high sensitivity of (22 ± 2) % mM^-1 (defined as percentage change of the PL peak intensity per mM) and a limit of detection (LOD) as low as 0.01 mM, along with an excellent selectivity and a short response time (less than 5 s). In comparison with a fluorescent non-enzymatic ZnO nanostructure-based glucose sensor, the addition of Au NPs significantly enhances the sensitivity. This is attributed to the surface plasmon resonance, which increases not only the photoluminescence intensity but also the photo-oxidation property of the ZnO NRs. Thus, ZnO NRs/Au NPs can act as an efficient photocatalyst for glucose detection. Most importantly, the probe is applicable to glucose detection in human blood serum. The outstanding performance of the material and its cost-effectiveness allow for potential application in single-use, noninvasive glucose devices.Graphical abstract A sensitive non-enzymatic fluorescent glucose probe-based ZnO nanorod decorated with Au nanoparticles.

Modeling and Piezoelectric Analysis of Nano Energy Harvesters

The expedient way for the development of microelectromechanical systems (MEMS) based devices are based on two key steps. First, perform the simulation for the optimization of various parameters by using different simulation tools that lead to cost reduction. Second, develop the devices with accurate fabrication steps using optimized parameters. Here, authors have performed a piezoelectric analysis of an array of zinc oxide (ZnO) nanostructures that have been created on both sides of aluminum sheets. Various quantities like swerve, stress, strain, electric flux, energy distribution, and electric potential have been studied during the piezo analysis. Then actual controlled growth of ZnO nanorods (NRs) arrays was done on both sides of the etched aluminum rod at low-temperature using the chemical bath deposition (CBD) method for the development of a MEMS energy harvester. Micro creaks on the substrate acted as an alternative to the seed layer. The testing was performed by applying ambient range force on the nanostructure. It was found that the voltage range on topside was 0.59 to 0.62 mV, and the bottom side was 0.52 to 0.55 mV. These kinds of devices are useful in low power micro-devices, nanoelectromechanical systems, and smart wearable systems.

Flower-Like ZnO Nanorods Synthesized by Microwave-Assisted One-Pot Method for Detecting Reducing Gases: Structural Properties and Sensing Reversibility

In this work, flower-like ZnO nanorods (NRs) were successfully prepared using microwave-assisted techniques at a low temperature. The synthesized NRs exhibited a smooth surface and good crystal structure phase of ZnO. The sharp peak of the XRD and Raman spectrum confirmed the high crystallinity of these ZnO NRs with a pure wurtzite structure. The nanorods were ~2 μm in length and ~150 nm in diameter, respectively. The electron diffraction pattern confirmed that the single crystal ZnO nanorods aligned along the [001] plane. The NRs were applied to fabricate a gas sensor for reducing gases such as CH4, CO, and H2. The sensor showed a good performance and sensitivity toward the target gases. However, its response toward CH4 and CO was higher compared to H2 gas. Although the operating temperature was varied from room temperature (RT) up to 350°C, the sensor did not show a response toward any of the target gases in the range of RT-150°C, but dramatic enhancement of the sensor response was observed at 200°C, and up to higher temperatures. This behavior was ascribed to the activity of the smooth surface and the reactivity of surface oxygen species with the targeted gases. The sensor response was measured at various gas concentrations, where the calibration curve was shown. The gas sensing mechanism was described in terms of the reaction of the gases with the transformed oxygen species on the surface of the oxides.

Ultraviolet Photodetection Based on High-Performance Co-Plus-Ni Doped ZnO Nanorods Grown by Hydrothermal Method on Transparent Plastic Substrate

A growth scheme at a low processing temperature for high crystalline-quality of ZnO nanostructures can be a prime stepping stone for the future of various optoelectronic devices manufactured on transparent plastic substrates. In this study, ZnO nanorods (NRs) grown by the hydrothermal method at 150 °C through doping of transition metals (TMs), such as Co, Ni, or Co-plus-Ni, on polyethylene terephthalate substrates were investigated by various surface analysis methods. The TM dopants in ZnO NRs suppressed the density of various native defect-states as revealed by our photoluminescence and X-ray photoelectron spectroscopy analysis. Further investigation also showed the doping into ZnO NRs brought about a clear improvement in carrier mobility from 0.81 to 3.95 cm2/V-s as well as significant recovery in stoichiometric contents of oxygen. Ultra-violet photodetectors fabricated with Co-plus-Ni codoped NRs grown on an interdigitated electrode structure exhibited a high spectral response of ~137 A/W, on/off current ratio of ~135, and an improvement in transient response speed with rise-up and fall-down times of ~2.2 and ~3.1 s, respectively.

Seedless Hydrothermal Growth of ZnO Nanorods as a Promising Route for Flexible Tactile Sensors

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm², was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2-4 N and vibrations over frequencies in the range of 20-800 Hz.