ZnO Nanorod Arrays Research Articles

Highly Semiconducting One-Dimensional Porous ZnO Nanorod Array Nanogenerators for Mechanical Energy Harvesting Functions

The development of energy harvesters based on inexpensive inorganic materials has attracted considerable attention to envisage next-generation self-powered electronic devices. In this work, we presented surface modification of ZnO nanorods (NRs) by thermochemical reaction using photoresist (PR) as an etching source. The morphological and microstructural properties of surface-etched ZnO NRs (M: ZnO) were systematically studied in detail through SEM and HRTEM. The morphological results show that the surface-etched NRs possess nanofiber-like porous structures and are penetrated throughout the NRs with high surface area. We fabricated triboelectric nanogenerators (TENG) using M: ZnO NRs with poly (dimethylsiloxane) (PDMS) as negative triboelectric material and mica as positive triboelectric material. The prepared M: ZnO NR TENG successfully delivered an output voltage of up to 20 V and a current density of 3.2 μA cm−2, which is ∼1.5 times higher than those observed for smooth ZnO NRs, respectively. The prepared M: ZnO NR TENG device can be able to lit 24 red light-emitting diodes (LEDs) as the power source. Finally, to demonstrate the practical applications of M: ZnO NR TENG, it was attached to the human body (elbow, knee, wrist, and heel) and efficiently harvested the energy from daily human activities.

Microwave-synthesized aluminum, gallium and indium-substituted stannite nanocrystal absorbers for solar cell applications

A novel family of Cu2FeXS4-x (X = Sn, Al, Ga & In) semiconductors with tetragonal stannite crystal structurehave been designed by a simple microwave assisted method. The impact of microwave power on the morphological, structural,spectroscopic and electrochemical properties were investigated. X-ray Diffraction (XRD) clearly revealed that the complete substitution of Sn (0.69 Å) with Al (0.54 Å), Ga (0.62 Å) and In (0.80 Å) did not affect the tetragonal arrangement of the stannite crystal structure except for a slight peak shift. High resonance scanning and transmission electron microscopy (HRSEM and HRTEM) revealed nano bullets, hexagonal prism, triangular nanoplates and spherical morphology with nanocrystal sizes ranging from 8 to 13 nm for CFXS nanocrystals. The UV–visible spectroscopy shows strong light absorption in the whole visible range with band gaps of between 1.2 and 1.6 eV suggesting its potential application as an absorber in thin film solar cells. Doctor blading method was used to coat CFXS nanocrystal inks on CdS coated ZnO nanorod arrays to fabricate a superstrate solar cell devices with the architecture ITO/ZnONRs/CdS/CFXS/Ag. The solar cell devices fabricated with copper iron tin sulfide (CFTS), copper iron aluminium sulfide (CFAS), copper iron gallium sulfide (CFGS) and copper iron indium sulfide (CFIS) absorbers displayed a power conversion efficiency (PCE) of 0.21%, 0.15%, 0.58% and 0.41% respectively. The photovoltaic response exhibited by the novel materials is quite positive and this shows that they can in fact be utilized to design solar cells with strong photovoltaic properties.

NiMnCo-LDH in-situ derived from ZIF-67@ZnO as self-supporting electrode for asymmetric supercapacitor device

Metal-organic frameworks have attracted much attention due to their abundant redox sites and tunable characteristics, which are advantageous for energy storage applications. However, the low electrical conductivity, poor physical strength and undesirable capacity seriously hinder their applications. Therefore, designing effective and convenient strategies to build composites with unique structures will be of practical significance. Herein, we successfully generate NMC-LDH/ZnO@CC nanocomposites by growing ortho-hexagonal nickel–cobalt layered double hydroxide (NMC-LDH) nanosheets in-situ on ZIF-67 precursor covering vertical arrays of ZnO nanorods. As a result of the unqiue ortho-hexagonal structure, highly ordered arrangement of active substances and multi-dimensional spaces of the prepared NMC-LDH/ZnO@CC binder-free electrode, its capacitance is as high as 9258 mF cm−2 at a current density of 2 mA cm−2 and the capacitance retention is maintained at 87.5 % after 5000 cycles. Furthermore, in order to explore the practical value of the prepared binder-free electrode, the NMC-LDH/ZnO@CC//AC solid-state asymmetric supercapacitor device is assembled. The energy density of the assembled supercapacitor is 24.6 W h kg−1 at a power density of 170 W kg−1 and 1020 W kg−1 at an energy density of 11.8 W h kg−1. In addition, a versatile instrument for monitoring air humidity, time and ambient temperature in portable environments can be powered by a single ultracapacitor unit for more than 30 min. Overall, this study provides a unique strategy for synthesizing ZIF derivatives with novel morphologies for electrochemical energy storage applications.

Gold nanoparticles-decorated MoS2 grown on ZnO nanorod array for sensitive SERS detection and efficient photodegradation of organic dye

Gold nanoparticles-decorated MoS2 grown on ZnO nanorod array for sensitive SERS detection and efficient photodegradation of organic dye

Influence of Exposure to a Wet Atmosphere on the UV-Sensing Characteristics of ZnO Nanorod Arrays.

Zinc oxide is a promising material for the creation of various types of sensors, in particular UV detectors. In this work, arrays of ordered nanorods were grown by chemical vapor deposition. The effect of environmental humidity on the sensing properties of zinc oxide nanorod arrays was investigated, and a prototype UV sensor using indium as an ohmic contact was developed. UV photoresponses were measured for the samples stored in dry and wet atmospheres. The increase in sensitivity and response of the ZnO nanorod arrays was observed after prolonged exposure to a wet atmosphere. A model was proposed to explain this effect. This is due to the formation of hydroxyl groups on the surface of zinc oxide nanorods, which is confirmed by FTIR spectroscopy data. For the first time, it has been shown that after storage in a wet atmosphere, the sensory properties of the structure remain stable regardless of the ambient humidity.

Improved charge separation by anatase TiO2 nanorod arrays for efficient solid-state PbS quantum-dot-sensitized solar cells

To improve the charge separation and transporting between PbS/TiO2 interface in PbS quantum-dot-sensitized solar cells, a 400 nm length anatase TiO2 nanorod array was successfully prepared by the conversion from ZnO nanorod array immersed in a 75 mM ammonium hexafluorotitanate acid solution. The influence of different immersion time on the microstructure, crystal phase and light absorption of the anatase TiO2 nanorod arrays were systematically studied. The PbS quantum dots (QDs) were deposited on the anatase TiO2 nanorod array via spin-coating-assisted successive ionic layer absorption and reaction (spin-SILAR) procedure using 5 mM PbI2 precursor solution, 5 mM Na2S·9H2O solution and 1% EDT/ethanol (1/99, v/v) solution. The solid-state PbS QD-sensitized anatase TiO2 nanorod array solar cell with the structure of FTO/TiO2 compact layer/PbS QD-sensitized anatase TiO2 nanorod array/spiro-OMeTAD/Au was assembled for the first time, and the champion device exhibited a photoelectric conversion efficiency of 5.47% with an open-circuit voltage of 0.62 V, a short-circuit photocurrent density of 13.71 mA cm-2 and a fill factor of 64.28%.

ZnFe2O4 nanosheets as an electron transport bridge and a hole mediator enhance solar-driven unbiased hydrogen generation of ZnO-based nanorod arrays photoanode

In this study, a novel ternary ZnO-based nanorod arrays (NRAs) photoanode is designed and constructed for the first time for unassisted solar-light-driven water splitting to generate H2 using photoelectrochemical (PEC) cell. The ternary heterojunction photoanode is constructed by modifying ZnO NRAs with ZnFe2O4 nanosheets (NSs) and CdS nanoparticles (NPs), successively. The band alignment study demonstrates that ZnFe2O4 NSs as an interfacial modification layer not only enlarge the contact area with ZnO and CdS respectively to build a stair-step band alignment of conduction band levels for the efficient transport of electrons but also make the valence band of ZnFe2O4 to be as the hole accumulation site in the ternary heterojunction. The electrochemical and photoluminescence measurements demonstrate the efficient separation of the carriers. Consequently, the ternary ZnO-based NRAs photoanode achieves a significant H2 generation rate of 92.9 μmol/h, 6.23 and 2.97 times of ZnO NRAs and ZnO/ZnFe2O4 NRAs/NSs photoanodes, respectively.

Patterned ZnO nanorods/indium sulfide based self-powered photoelectrochemical photodetectors

The present work reports the excellent alignment of zinc oxide nanorod arrays (ZnO NRAs) patterned via the maskless lithography technique which was used as a photoanode material for photoelectrochemical (PEC) photodetection applications. The effects of circular patterns having different diameters, different gaps between circles, and the utilization of indium sulfide (In2S3) as a light-absorbing material in the visible region have been investigated in the PEC photodetector (PD) system in two different electrolytes. PEC PD performance evaluation confirmed the positive effect of patterned ZnO NRAs-based photoanode in the presence of In2S3, enhancing 982.9 μAcm−2 of current density (Jphoto), 54.6 mA/W of responsivity (Rs), 1.98 × 1011 Jones of detectivity (D*) and 8.18 × 104 of selectivity (S%) values. Besides, the best-performing patterned ZnO NRAs/In2S3 has been used to construct a quasi-solid state assembly using the prepared ionic-gel electrolyte and consequently, 2.19 × 1011 Jones of D* value has been observed. After all, the proposed PEC PD devices exhibited fast rise/decay times(τr/τd) in millisecond extent at 400 nm of wavelength.

Growth of Chlorine-Doped ZnO Nanorod Arrays on Different Substrates

In this study, zinc nitrate (Zn(NO3)2), hexamethylenetetramine (C6H12N4), and sodium chloride (NaCl) were employed as precursor materials to synthesize ZnO nanorod arrays on two distinct types of substrates using the hydrothermal method. We investigated how different substrates and varying chlorine concentrations influence the synthesis properties of chlorine-doped ZnO nanorod arrays. Specifically, this study aimed to explore the structural, morphological, and optical properties of the synthesized ZnO nanorod arrays. The substrates investigated were an indium tin oxide (ITO) substrate with a ZnO seed layer and an ITO substrate with a self-assembled monolayer (SAM) of molecules. The formation of the SAM involved placing a clean ITO conductive glass substrate into a high-pressure reactor, along with a vial containing 0.2 mm of octadecyltrichlorosilane. Using this process, a uniform SAM was created on the ITO substrate. The molar ratio of Zn(NO3)2, C6H12N4, and NaCl was maintained at 1:1:x, where x varied as 0, 0.1, 0.2, 0.3, and 0.4. This corresponded to NaCl volumes of 0, 2.5, 5.0, 7.5, and 10.0 mM, respectively. The crystallinity and orientation of the nanorods were assessed with their surface morphology using scanning electron microscopy (SEM). By systematically varying the chlorine concentration and substrate type, the role of these parameters was understood in tailoring the characteristics of ZnO nanorod arrays for potential applications in optoelectronic devices, sensors, and photocatalysts.

Hydrothermally grown ZnO nanorods in different aspect ratios and their gas sensing properties

On a glass substrate, zinc oxide nanorods (ZnO NRs) arrays of varying aspect ratios have been grown by hydrothermal method at 90 ᴼC with variable ZnO seed layer thicknesses applied by RF sputtering. The structural properties and gas sensitivity of zinc oxide nanorods were studied by using X-ray diffraction (XRD) for analyzing the structural characteristics was discovered that ZnO NRs and seed layer films are both polycrystalline, with the same plane preferred reflection for (002). The seed layer's crystallite size ranges from 19.51 nm to 30.45 nm for thicknesses t1 and t4, respectively. The measurements of the FESEM showed aspect ratios for ZnO NRs ranging from 3.03 for t1 to 4.9 for t4, with growth in different shapes: ZnO NRs for t1, flowers and rod-like shapes for thicknesses t2 and t3, and hexagonal-rod-like shapes for t4. ZnO NRs based on gas sensors and tests of the response of prepared samples on NH3 and CO2 gases showed good sensitivity to both gases at different concentrations (1000, 2000, and 3000 ppm), reaching 65–70 at operating 50 ᴼC.

Nitrogen-doped carbon quantum dots decorated ZnO nanorods array film for efficient UV photodetector applications

Nitrogen-doped carbon quantum dots decorated ZnO nanorods array film for efficient UV photodetector applications

Construction of a ZnO Heterogeneous Structure Using Co3O4 as a Co-Catalyst to Enhance Photoelectrochemical Performance.

Recently, heterostructured photocatalysts have gained significant attention in the field of photocatalysis due to their superior properties compared to single photocatalysts. One of the key advantages of heterostructured photocatalysts is their ability to enhance charge separation and broaden the absorption spectrum, thereby improving photocatalytic efficiency. Zinc oxide is a widely used n-type semiconductor with a proper photoelectrochemical activity. In this study, zinc oxide nanorod arrays were synthesized, and then the surfaces of ZnO nanorods were modified with the p-type semiconductor Co3O4 to create a p-n junction heterostructure. A significant increase in the photocurrent for the ZnO/Co3O4 composite, of 4.3 times, was found compared to pure ZnO. The dependence of the photocurrent on the morphology of the ZnO/Co3O4 composite allows for optimization of the morphology of the ZnO nanorod array to achieve improved photoelectrochemical performance. The results showed that the ZnO/Co3O4 heterostructure exhibited a photocurrent density of 3.46 mA/cm2, while bare ZnO demonstrated a photocurrent density of 0.8 mA/cm2 at 1.23 V. The results of this study provide a better understanding of the mechanism of charge separation and transfer in the heterostructural ZnO/Co3O4 photocatalytic system. Furthermore, the results will be useful for the design and optimization of photocatalytic systems for water splitting and other applications.

Enhanced performance of self-powered ZnO-based PEC type UV photodetectors by loading GQDs to construct heterojunctions

The construction of semiconductor heterojunctions is an effective approach to enhance the performance of optoelectronic devices. In this study, graphene-quantum-dots (GQDs) were grown on ZnO nanorods arrays in-situ to form intimate heterojunctions. The fabricated photoelectrochemical (PEC) photodetector based on ZnO/GQDs heterojunctions displayed good self-powering characteristics, with an on/off current ratio of approximately 21 at zero bias, which was almost seven-fold higher than that of the bare ZnO device. The responsivity and detectivity of the ZnO/GQDs-based photodetector were also enhanced compared with those of bare ZnO devices. A unique type-II band alignment was established at the ZnO/GQDs heterojunction interface, which facilitated the carrier transfer. Moreover, the ZnO/GQDs heterojunction reduced the passivation of the surface states, resulting in large energy-band bending and an internal electric field at the semiconductor/electrolyte interface, which provided a powerful driving force for the separation and transport of photogenerated carriers. These combined effects enhance the performance of the photodetector, indicating that this approach can be used to fabricate high-performance PEC optoelectronic devices.

Improving the optical properties of CuCoMnOx spinel absorber using ZnO nanorod arrays for thermal collector and photocatalytic applications

Solar-selective and high entropy materials are one of the key factors for thermal applications. CuCoMnOx (CCMO) spinel compound is also a suitable material for this purpose due to its spin-allowed transitions in partially filled d orbitals. In this study, the CCMO absorber compound was coated on ZnO nanorod-coated aluminum (Al) substrates for the first time by the sol-gel dip-coating method, and its optical, structural, and morphological properties were examined. According to the results obtained, ZnO nanorods increased the active surface area of the Al substrate and accordingly increased the absorptance value of the CCMO material from 87 % to 94 %. Analyzes performed with FT-IR spectrometry showed that the thermal emittance values were 90 % and 67 % for Al/CCMO and Al/ZnO/CCMO samples, respectively. The thermal emittance reduced by around 25 % with the use of ZnO nanorods on the Al substrates in the wavelength range of 2.5 μm–25 μm. The photocatalytic effect of this spinel compound was also investigated. The degradation spectra of organic methylene blue (MB) solution within 120 min were examined with UV–Vis spectroscopy, and the degradation efficiency increased by 23 % in the presence of ZnO nanorods. The obtained results showed that ZnO nanorod structures significantly changed both the solar and photocatalytic properties of the CCMO compound.

Simultaneous Electrochemical Determination of Erythromycin and Hemoglobin by Flexible Carbon Cloth Modified with ZnO Nanorod Arrays and Au Nanoparticles by Differential Pulse Voltammetry (DPV)

Simultaneous determination of erythromycin (Ery) and hemoglobin (Hb) is of great significance for clinical diagnosis of many diseases. ZnO nanorods modified with Au nanoparticles were fabricated as an interface on the flexible carbon cloth (CC) and utilized to simultaneously determine Ery and Hb by a simple electrochemical method. The results demonstrated that Au/ZnO/CC displayed excellent analytical performance for Ery with a low detection limit of 3.38 × 10−7 mg/L and a linear range from 1 × 10−6 to 1 × 10−1 mg/L. At the same time, the sensor also showed a sensitive response to Hb with a low detection limit of 2.07 × 10−7 mg/L and a linear range from 1 × 10−6 to 1 × 10−1 mg/L. This work provides a viable approach for designing a flexible electrode and sensitive simultaneous determination of Ery and Hb.

High performance surface plasmon enhanced ZnO-Pt @ AlN core shell UV photodetector synthesized by magnetron sputtering

ZnO, a potential optoelectronic material, is attracting significant attention in ultraviolet (UV) photodetectors. However, low photoelectric conversion efficiency is a shortcoming because of its surface defect. In this paper, a plasmonic enhanced high speed UV photodetector was fabricated by ZnO-Pt@AlN core shell nanowires arrays using chemical vapor deposition (CVD) and magnetron sputtering methods. As shown in experiment results, the core shell nanowire arrays exhibit 3.7 times enhancement of UV emission and inhibition of visible emission by surface defect. In addition, compared to the pure ZnO nanorod array detector, the introduction of Pt nanoparticles and AlN shell layer resulted in a device with faster rising and falling edges (from 5.67 s to 3.09 s; from 41.18 to 0.32 s) as well as higher bright-to-dark current ratio (from 6.6 to 310.5). As shown in simulation results, the optical field would be localized in the shell of ZnO nanorods, and the ZnO-Pt@AlN core–shell structure can effectively improve the absorption of 365 nm UV light. In one word, this paper employs two general methods to improve the optoelectronic performance of ZnO, and obtains plasmonic enhanced high speed UV photodetector fabricated by ZnO-Pt@AlN core shell nanowires array as well as the mechanism of enhancement is explained.

A stable and efficient quasi-solid-state photo/betavoltaic-powered electrochemical cell based on 3-dimensional CdS/ZnO heterostructure

Electrochemical betavoltaic (EBV) cells are promising power sources for low-power electronics in remote and harsh environments. However, their practical applications are limited by the organic liquid electrolytes with the inferior temperature stability and narrow electrochemical window. In this work, a quasi-solid-state EBV cell was fabricated using a high-conductive gel-based quasi-solid-electrolyte (QSE), a CdS-modificated ZnO nanorod arrays (ZNRAs) structure as the anode material, a radioactive 63Ni sheet as the cathode as well as the irradiation source. Monte Carlo (MC) simulations are utilized to determine the optimized length (2.97 μm) of the ZNRAs filled by electrolyte, Electrochemical photovoltaic (EPV) cells were used to assess and optimize the content of CdS loaded on the ZNRAs. The optimum EBV cell demonstrated an excellent long-term stability and a high energy-conversion efficiency of 10.09 % with a short-circuit current density of 0.755 μA cm−2 and an open-circuit voltage of 0.288 V. The porous CdS@ZNRAs core–shell structure filled by soft ionic liquids (IL)/gel-based QSE enables a large specific area of electrochemical interface network. The synergistic effects of 3-D CdS/ZnO heterostructure with type-II band alignment and IL/gel-based QSE are responsible for the enhanced ECE and improved long-term stability of EBV/EPV cells.

Flexible Finely and Directly Patternable Liquid Metal Electrodes via Selective Surface Wetting Technique

Eutectic gallium–indium (EGaIn) is an ideal material for preparing flexible electrodes, but its high surface tension poses a challenge during deposition and patterning. Herein, we propose a laser-induced selective surface wetting technique (SSWT) to enable the facile and straightforward fabrication of flexible finely and directly patternable EGaIn liquid metal electrodes. Our proposed technique selectively controls the wettability of EGaIn by establishing a perfluorinated self-assembled monolayer on a zinc oxide nanorod array to impart superhydrophobicity and then inducing specific sites on the hydrophilized surface by ultraviolet (UV) pulsed laser ablation, thereby enabling fine patterning (linewidth, ~50 μm). Surface analysis of the effect of laser ablation was also performed to elucidate the mechanism of SSWT. The patterned EGaIn liquid metal electrode fabricated by SSWT exhibited superior flexibility, with a resistance change (ΔR/R0) of only 18.6% compared with a Ag thin film electrode, which showed a dramatic increase in ΔR/R0 to nearly 500% after 50,000 folding cycles at a peak strain of 2.5%. The simple and easily implementable liquid metal patterning technique proposed in this study may potentially be applied in the field of wearable and stretchable electronics, which requires extreme flexibility.

ZnO/Au/GaN heterojunction-based self-powered photoelectrochemical Sensor for alpha-fetoprotein detection

In recent years, the development of miniature and portable sensors has been a major focus of research. PEC self-powered sensors have emerged as a potential solution to the power supply issue, eliminating the need for external power supplies and operating without bias voltage. This study developed a ZnO/Au/GaN sensor for highly sensitive detection of alpha-fetoprotein (AFP). The sensor uses GaN substrates with nanogold films to provide an auxiliary bias voltage, promoting high photogenerated current density. Using ZnO/Au/GaN as a photoanode resulted in significantly higher photocurrent generated by the sensor compared to Au/GaN or ZnO/ITO alone. To enable selective detection of AFP, antibody modification of the ZnO nanorod arrays was employed. The linear range of the sensor response to AFP was determined to be 0.080–5.0 ng/mL, with an impressively low detection limit of 0.027 ng/mL (S/N = 3). These results demonstrate the potential of this self-powered sensor for detecting AFP content in human serum samples. Overall, this study presents a novel approach for developing highly sensitive and selective self-powered sensors for biomarker detection, which could facilitate early detection and clinical diagnosis of various types of cancer.

Hydrothermally grown molybdenum doped ZnO nanorod arrays. The concept of novel ultrafast nanoscintillator

Molybdenum doped ZnO was hydrothermally grown as the arrays of nanorods deposited onto the fused silica glass substrate. The molybdenum doping level varied from 1 to 30 %. The influence of Mo on the electronic and crystalline structure as well as luminescence and defects in the ZnO nanorods is under study of the bundle of experimental techniques complemented with density functional theory calculations. The tendency of Mo to create energy states within the bandgap of ZnO and their influence on the energy levels of native defects as well as excitons were proven by the synergy of experiment and theory. The improvement of the timing characteristics of the exciton- and zinc vacancy-related emission bands upon Mo doping (1–10 %) was observed. This paves the way for the defect engineering strategy in the search of effective and ultrafast scintillator with the improved light yield as well as compared to other materials. The new concept is based on the combination of the exciton and the defect emission. It is expected to have the potential of application in the detection of gamma rays implemented in time-of-flight positron emission tomography (TOFPET). The 20 and 30 % Mo doping levels resulted in the zinc molybdates creation strongly outnumbering ZnO nanorods.