Vertical ZnO Nanorods Research Articles

Key factors affecting facile growth of two precursor-based seedless vertical ZnO nanorods for haptic sensing and energy harvesting applications

Key factors affecting facile growth of two precursor-based seedless vertical ZnO nanorods for haptic sensing and energy harvesting applications

Growth of Vertical ZnO Nanorods from Patterned Films via Decomposition of Zinc Acetate by Focused Ion Beam: Implication for UV Detection

Growth of Vertical ZnO Nanorods from Patterned Films via Decomposition of Zinc Acetate by Focused Ion Beam: Implication for UV Detection

Nanopatterned rGO/ZnO:Al seed layer for vertical growth of single ZnO nanorods

In this work, we demonstrate a novel low-cost template-assisted route to synthesize vertical ZnO nanorod arrays on Si (100). The nanorods were grown on a patterned double seed layer comprised of reduced graphene oxide (rGO) and Al-doped ZnO nanoparticles. The seed layer was fabricated by spray-coating the substrate with graphene and then dip-coating it into a Al-doped ZnO sol–gel solution. The growth template was fabricated from a double-layer resist, spin-coated on top of the rGO/ZnO:Al seed layer, and patterned by colloidal lithography. The results show a successful chemical bath deposition of vertically aligned ZnO nanorods with controllable diameter and density in the nanoholes in the patterned resist mask. Our novel method can presumably be used to fabricate electronic devices on virtually any smooth substrate with a thermal budget of 1 min at 300 °C with the seed layer acting as a conductive strain-relieving back contact. The top contact can simply be made by depositing a suitable transparent conductive oxide or metal, depending on the specific application.

Initial Growth Behavior in Catalyst-Free-Grown Vertical ZnO Nanorods on c-Al2O3, as Observed Using Synchrotron Radiation X-ray Scattering

In this study, synchrotron radiation X-ray diffraction analysis is used to investigate the initial growth dynamics of metal–organic vapor-phase epitaxy-grown ZnO nanorods on c-Al2O3 substrates. A two-dimensional area detector with a grazing-incidence geometry enables projected reciprocal space mapping (RSM) using coordinate transformation of diffraction images. The projected RSM reveals multiple heteroepitaxial relationships between ZnO and Al2O3, including the dominant relationship of ZnO(101̅0)∥Al2O3(21̅1̅0). Evolution of internal strain is revealed by an additional study on diffraction images and θ–2θ scans. Surface topology from atomic force microscopy estimates the growth rate, supported by the Scherrer equation analysis of the θ–2θ diffraction.

Effects of Reaction Parameters on the Geometry and Crystallinity of Hydrothermally Synthesized ZnO Nanorods for Bio-Fouling Applications

In this present work, we have successfully synthesized vertical aligned ZnO nanorod arrays (ZnO NRs) on conductive stainless-steel substrate. These ZnO NRs were obtained by using a low temperature, low cost, and eco-friendly hydrothermal approach. The effect of the sol-gel deposited ZnO seed layer on the vertical alignment ZnO NRs has been thoroughly studied. Characterizations of the seed layer and the as-obtained nanorods were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), and water contact angles (WCA) measurement. SEM analysis shows that these nanorods were grown with a high uniformity and density over the entire substrate. TEM and XRD studies confirmed the hexagonal wurtzite structure of ZnO nanorods. Finally, field immersion tests using the optimized samples were conducted in a coastal sea environment to study biofouling settlement. To the best of our knowledge, there are few articles that investigate the influence of the seed layer deposited on stainless steel on the formation of vertically aligned nanorods for antifouling applications. The novelty of this work is manifested by optimizing the ZnO seed layer to obtain either thick or fine ZnO nanorods (NRs). Moreover, another novelty of this study is the use of the hydrothermal deposition of ZnO NRs on stainless steel for biofouling to replace paints in marine applications.

Synergistic effect of Fe and Ag co-doping on the persistent photoconductivity of vertical ZnO nanorods

Undoped, doped and co-doped vertically aligned ZnO nanorods (NRs) are synthesized using sonicated sol-gel immersion method. A significant variation in structural, morphological, optical and photoconductivity properties of ZnO NRs after incorporation of transition metal ions (Fe or/and Ag) is obtained. XRD analysis revealed that incorporation of Fe ameliorates while that of Ag deteriorates the c-axis growth of NRs. The diameter of the NRs is tuned from 236 nm to 103 nm. The Fe-doped ZnO NRs exhibit significantly thinner diameter, longer length, and highest aspect ratio. The doping and co-doping reduces the optical band gap of ZnO by 20 meV and 10 meV respectively. A reduction in near band edge emission whereas enhancement in defect-related-green-emission is obtained. Noticeable enhancement in the light harvesting efficiency and significant quenching of the persistent photoconductivity is obtained by co-doping.

Plasmonic Sensing from Vertical Au-Coated ZnO Nanorod Arrays Templated by Block Copolymers

Plasmonic Sensing from Vertical Au-Coated ZnO Nanorod Arrays Templated by Block Copolymers

Electrical transport properties and impedance analysis of Au/ZnO nanorods/ITO heterojunction device

Our work involves the growth of well aligned vertical nanorods of ZnO on transparent indium doped tin oxide (ITO) conductive substrate and fabrication of Au/ZnO Nanorods/ITO Heterojunction device. The observation of non-ideal diode current density-voltage (J-V) characteristics of the device has been evaluated with various conduction mechanisms [Ohmic, space-charge limited conduction (SCLC)]. The charge carrier mobility is estimated to be ∼0.05 cm2/Vs. The presence of deep level defects in the ZnO nanorods is accountable for these two different transport mechanisms and it is backed by photoluminescence, distinctly. The estimated density of deep trap states is ntrap ∼ 5.76 × 1013 cm−3. The charge carrier density and built-in potential of this device are obtained from electrochemical impedance spectroscopy (EIS). The average work function of vertical ZnO nanorods is found out to be ∼4.93 eV. Henceforth, our results explain the charge transport mechanism which plays a key role in optoelectronic based devices for various applications.

Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods.

Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical nanorod arrays. The ability to define the morphology and structure of the nanorods is essential to maximizing the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show that the O-polar nanorods (∼0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (∼0.37 eV). Oxygen plasma treatment is shown by cathodoluminescence spectroscopy to affect midgap defects associated with radiative emissions, which improves the Schottky contacts from weakly rectifying to strongly rectifying. Interestingly, the plasma treatment is shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc-vacancy-related hydrogen defect complexes (VZn-nH) in Zn-polar nanorods that evolve to lower-coordinated complexes. The effect on HO in the O-polar nanorods coincides with a large reduction in the visible-range defects, producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled, enhancing devices such as dynamic photodetectors, strain sensors, and light-emitting diodes while showing that the O-polar nanorods can outperform Zn-polar nanorods in such applications.

Incremental photocatalytic reduction of graphene oxide on vertical ZnO nanorods for ultraviolet sensing

Graphene oxide nanosheets were coated on thin films of vertical ZnO nanorods and incrementally reduced into rGO by the photocatalytic effect of ZnO for different times. The photocatalytic reduction (1) slightly decreased bandgap, considerably increased the ultraviolet absorption, and significantly enhanced the charge carrier separation in rGO–ZnO, while (2) increased the defects in rGO sheets. We tested the rGO/ZnO thin films for ultraviolet sensing and found that 60-min reduction is the optimal case. We discussed the result based on competition between the above (1) and (2) findings.

Realization of Superhydrophobic Surface for the Detection of Residual Detergent Concentration

A superhydrophobic surface was realized on a glass substrate and on the inner wall of a capillary tube, employing a combination of ZnO nanorod arrays and stearic acid. The vertical ZnO nanorod arra...

Stable Electrochemical Measurements of Platinum Screen-Printed Electrodes Modified with Vertical ZnO Nanorods for Bacterial Detection

The study is aimed at investigating the stability of electrochemical and biosensing properties of ZnO nanorod-based platinum screen-printed electrodes (SPEs) applied for detection of bacterial pathogens. The platinum SPEs were designed and patterned according to standard photolithography and lift-off process on a silicon wafer. ZnO nanorods (NRs) were grown on the platinum working electrode by the hydrothermal method, whereas Salmonella polyclonal antibodies were selected and immobilized onto ZnO NR surface via a crosslinking process. Morphological and structural characteristics of ZnO NRs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the ZnO NRs were grown vertically on platinum electrodes with a diameter around 20-200 nm and a length of 5-7 μm. These modified electrodes were applied for detection of Salmonella enteritidis at a concentration of 103 cfu/mL by electrochemical measurements including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The ZnO NR-modified platinum electrodes could detect Salmonella bacteria well with stable measurements, and the signal to noise ratio was much higher than that of 3 : 1. This study indicated that ZnO NR-modified platinum SPEs could be potential for the development of biochips for electrochemical detection of bacterial pathogens.

Diffusion-Driven Al-Doping of ZnO Nanorods and Stretchable Gas Sensors Made of Doped ZnO Nanorods/Ag Nanowires Bilayers.

A crystal-damage-free nanodoping method, which utilized the vacuum drive-in diffusion of Al into ZnO nanorods, was developed. In this method, vertical ZnO nanorod arrays that were grown by chemical bath deposition beforehand were deposited with Al thin film and subsequently heat-treated under a high vacuum. At an optimum condition, the surface Al atoms were completely diffused into ZnO nanorods, resulting in Al-doped ZnO nanorods. Stretchable gas sensors were fabricated by sequentially drop-casting the Al-doped ZnO nanorods and silver nanowires on polydimethylsiloxane substrate. The resistance and response of the sensor could be optimized through the elaborate control of relative densities of Al-doped ZnO nanorods and silver nanowires. The sensor showed a high response of 32.3% to 10 ppm of NO2 gas at room temperature, even under a large strain of 30%. The NO2-sensing mechanism of Al-doped ZnO nanorod/silver nanowire bilayer sensors is discussed on the basis of a synergistic interplay of Al-doped ZnO nanorods and silver nanowires.

Effective control of the length of ZnO-TiO2 nanorod arrays as electron transport layer of perovskite solar cells with enhanced performance

Vertical ZnO nanorod arrays were synthesized by a polymer template method and modified by TiO2 shell via a sol-gel method. The core-shell structure of ZnO-TiO2 nanorod arrays was used as an electron transport layer (ETL) of perovskite solar cells (PSCs) and the length of the nanorod arrays was controlled by changing the hydrothermal growth time. The photovoltaic performance of the PSC prepared in ambient atmosphere was found to be crucially dependent on the length of ZnO-TiO2 nanorod arrays. ZnO-TiO2 nanorod arrays with a suitable length enabled complete infiltration of CH3NH3PbI3 perovskite into nanorod arrays and an increasement of carrier lifetime, eventually resulting in better cell performance. The PSC based on ZnO-TiO2 nanorod arrays with the length of 600 nm shows a power conversion efficiency of 10.24% under ambient air (RH~40%, 25 °C), which is higher than the mean level of previous report. Meanwhile, the PCE of the unencapsulated device based on ZnO-TiO2 nanorod arrays retains 80% of the initial efficiency after 7 days in ambient atmosphere. This work provides the potential application of ZnO-TiO2 nanorod arrays with a suitable length as an effective ETL of efficient and stable all-solid-state PSCs.

High performance and low temperature coal mine gas sensor activated by UV-irradiation

In this work, well-aligned vertical ZnO nanorod (ZnO NRs) on p-type Si substrate was fabricated by a microwave-assisted hydrothermal reactor to study the coal mine methane (CMM) gas sensing properties. The XRD diffraction peaks and Raman spectra of the ZnO NRs confirmed the hexagonal wurtzite structure with strong preferential orientation along the c axis and well crystal quality. SEM analysis showed NRs with 100 nm average diameter and ~600 nm length. The variations of the sensor electrical resistance in the presence of CMM were investigated at different gas concentrations and various temperatures in the dark and under UV light. The selectivity and response time of the sensor to CMM gas were improved under UV irradiation. The optimal operating temperatures were 225 °C and 100 °C in dark and exposing UV-irradiation, respectively. Also the response of ZnO NRs sensor under UV excitation in humid condition was higher. The sensor was more selective to CMM than CO2. The sensor stability was considered by repeating CMM detection for 90 days.

Characterisation of the heterojunction microstructure for electrodeposited vertical ZnO nanorods on CVD-graphene

A low-cost heterostructure of a wide-bandgap nanostructured semiconductor on top of a transparent conductor (TC) fabricated from abundant sustainable materials is of great interest for optoelectronic devices, such as heterojunction photovoltaic cells. Due to its high optical transparency and electron mobility, graphene is an attractive carbon-based material to replace the costly traditional TCs (i.e. ITO), which pose health hazards and destructive environmental impact thorough their life cycle. However, for the industrial application of graphene as TC it is necessary to interface it with other materials, like oxides, while maintaining the sp2 network that provides its excellent electronic properties. We report the optimized electrodeposition of ZnO on graphene to obtain a textured layer of vertically aligned crystalline semiconducting nanorods (ZVNRs) evenly coating the graphene surface. Lattice distortions and mosaicity in the crystals indicate that the ZVNRs grow under out-of-plane compressive strain. The stability of the sp2 network of graphene during in situ growth of ZnO is demonstrated using Raman spectroscopy from the front and backside of the heterostructure, in a novel approach to investigate junctions of 2D–3D nanomaterials. Despite the structural stability of graphene, its R□ is found to increase by ∼100% with ZVNRs electrodeposition, which is attributed to reduction of mobility due to charge carrier scattering, reduction of carrier concentration due to doping, and/or interfacial strain. The cathodic electrodeposition is demonstrated to be an effective and versatile method to grow crystalline nanostructures in the surface of single layer-graphene while protecting its sp2 hybridization, and it provides relative fast deposition rates, affordability, and low processing temperatures that would allow using polymeric flexible substrates and. These findings on interfacial properties are important to advance the functionality of graphene as TC material and develop nano-heterostructures for myriad technological applications.

Single mode waveguiding effect of ZnO nanorods to enhance the luminance of conjugated polymer based light emitting diodes

In the present work, a unique strategy to improve light emission from poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) based polymer light emitting diodes (PLEDs) has been reported. It was observed that integration of vertical ZnO nanorods (NRs) in the PLED structure drastically enhances the luminance (more than 20 times) as compared to that of basic MEH-PPV device. The analysis reveals that the waveguiding effect of NR structure is responsible for this phenominal enhancement. ZnO NRs possess large acceptance angle and are able to direct the collected light perpendicular to the ITO plane through single mode propagation. This rectifies the problem of undesired total internal reflection at ITO/glass and glass/air interfaces, which is the root cause of reduced light extraction from PLEDs.

A high photocurrent gain in UV photodetector based on Cu doped ZnO nanorods on PEN substrate

Vertical well-aligned Cu-doped ZnO nanorods were successfully synthesized by chemical bath deposition (CBD) method on low cost and flexible polyethylene naphthalate (PEN) substrate. The structural and optical investigations exhibited the high quality of the Cu-doped ZnO nanorods on a flexible PEN substrate. The metal-semiconductor-metal (MSM) configuration was used to fabricate UV photodetector based on the Cu-doped ZnO nanorods grown on PEN substrate. Under a 5 V applied bias, the values of dark current and photocurrent of the Cu-doped ZnO nanorods photodetector were 14.9 µA and 3.27 mA, respectively. Meanwhile, calculated photocurrent gain of the UV photodetector was 219 at 5 V bias voltage. Upon exposure to 365 nm UV light, the UV device exhibited fast response time and recovery time of 0.317 and 0.212 s, respectively, at a bias voltage of 5 V.

Seed layer effect on different properties and UV detection capability of hydrothermally grown ZnO nanorods over SiO2/p-Si substrate

Hydrothermally grown one dimensional ZnO nanostructures are among the most widely used semiconductor materials to build high-efficiency electronic devices for various applications. Few researchers have addressed the growth mechanism and effect of ZnO seed layer on different properties of ZnO nanorods grown by hydrothermal method, instead, no one has synthesized ZnO nanorod over SiO2/p-Si substrate. The aim of this study is to study the effect of ZnO seed layer and the growth mechanism of ZnO nanorods over SiO2/p-Si substrate. To achieve the goal, we have synthesized ZnO nanorods over different thickness ZnO seed layers by using the hydrothermal method on SiO2/p-Si substrate. The effects of c-plane area ratio were identified for the growth rate of c-plane, reaction rate constant and stagnant layer thickness also calculated by using a modified rate growth equation. We have identified maximum seed layer thickness for the growth of vertical ZnO nanorod. A step dislocation in the ZnO nanorods grown on 150and200nm thick seed layers was observed, the magnitude of Burges vector was calculated for this disorder. The seed layer and ZnO nanorods were characterized by AFM, XPS, UV-visible, XRD (X-ray diffraction, and SEM(scanning electron microscope). To justify the application of the grown ZnO nanorods Ti/Au was deposited over ZnO nanorods grown over all seed layers for the fabrication of photoconductor type UV detector.

High-sensitivity UV photodetector based on oblique and vertical Co-doped ZnO nanorods

Oblique and the vertical Co-doped ZnO nanorod arrays were successfully synthesized on a flexible polyethylene naphthalate (PEN) substrate using chemical bath deposition method. The metal-semiconductor-metal (MSM) configuration was used to fabricate UV photodetector based on the Co-doped ZnO nanorods grown on a flexible PEN substrate. At 5 V bias voltage, the calculated responsivity of the UV photodetector was 8.76 A/W. Meanwhile, calculated photosensitivity of the UV photodetector was 250 at bias voltage of 5 V. Under 5 V applied bias voltage, the UV photodetector based on Co-doped ZnO nanorods showed fast response time of 0.229 s and recovery time of 0.276 s.