Optical Properties Of ZnO Nanorods Research Articles

Effect of aspect ratio on the nonlinear optical properties of ZnO nanorods

In this work, we synthesized ZnO nanorods with two different aspect ratios using the solution method. Morphological and crystalline structures were investigated using TEM and XRD analysis. Also investigated the effect of aspect ratio on the optical properties of ZnO nanorods. With an increasing aspect ratio of the nanorods, the absorption peak is red-shifted and near-band edge emission is suppressed. The nonlinear absorption is enhanced with the increasing aspect ratio of ZnO nanorods.

Crucial roles of structural, morphological, and optical properties in enhancing the photocatalytic performance of ZnO nanorods

ZnO nanorods with different structural, morphological, and optical properties were fabricated using hydrothermal process by controlling hydrothermal reaction temperature. It has been presented that the structural, morphological and optical properties of the nanorods are strongly influenced by the hydrothermal reaction temperature. XRD results show that ZnO nanorods have a polycrystalline structure with hexagonal wurtzite. Increasing hydrothermal reaction temperature up to 100 °C stimulates the vertically standing growth along the c-axis orientation on the substrate as shown in FESEM images. The growth is followed by the decrease of the transmittance and energy band-gap of the ZnO nanorods. The photocatalytic activity of ZnO nanorod was evaluated using the percentage degradation of Coomassie® Brilliant blue and Indigo carmine dyes as a function of irradiation time. The photodegradation efficiency of ZnO nanorods synthesized with hydrothermal reaction temperatures at 80, 90 and 100 °C for decolorization of Coomassie® Brilliant blue was 71%, 75% and 81%, respectively, while for Indigo carmine was 50%, 53% and 66%, respectively. The variations of efficiency values indicate that the structural, morphological, and optical properties of ZnO nanorods play an important role in photocatalytic activity.

Niobium doping effect on electrical and optical properties of ZnO nanorods produced by ultrasonic spray pyrolysis

Niobium metal doped ZnO nanorods were fabricated on a glass substrate using an ultrasonic spray pyrolysis system in two steps. The structural, morphological, and optical properties of the produced samples were investigated via an x-ray diffractometer (XRD), a field emission scanning electron microscopy (FE-SEM) combined with energy dispersive x-ray spectroscopy (EDX), and a spectrophotometer, respectively. The XRD patterns were indexed in the hexagonal (wurtzite) unit cell type for all the ZnO samples. In addition, according to the XRD peaks, the crystals grew in the c-axis (002) direction. The morphological features of the obtained thin films were examined. From the SEM micrographs, it was observed that ZnO thin films doped with Nb had a nanorod structure in the c-axis direction. The presence of Nb ions in the samples was proved via EDX analysis. The electrical conductivity values of the pristine and 10 % mol Nb-doped ZnO samples were 3.16 x 10−9 and 3.98 x 10−7 (ohm−1.cm−1) at 25 °C; and 7.08 x 10−7 and 5.01 x 10−5 (ohm−1.cm−1) at 300 °C, respectively. The optical transmittances of the samples were measured at wavelengths of 350–1000 nm. It was observed that the produced films had high optical transparency. The average optical transmittance value of the samples was 90 %.

Optical properties of ZnO nanorods for reduced graphene oxide

The preparation and characterization of innovative nanocomposites based on zinc oxide nanorods (ZNR) encapsulated by graphene (Gr) nanosheets and decorated with silver (Ag), and copper (Cu) nanoparticles (NP) were studied. The prepared nanocomposites (ZNR@Gr/Cu Ag) were examined by different techniques including Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), UV-Vis spectrophotometry and fluorescence spectroscopy. The results showed that the ZNR had a good cover of five layers of graphene and decorated with Ag and Cu NPs with particles size of about (10-15) nm. In comparison with ZNR, the ZNR@Gr/Cu Ag nanocomposites revealed superior absorption in the entire region of 300–1000 nm. Moreover, the band gap decreased from 3.2 eV of ZNR to 1.2 eV for ZNR@Gr/Cu Ag nanocomposites. Taking into account the superiority of ZNR@Gr/Cu Ag nanocomposites in terms of easy fabrication, low-cost method, and environmental friendliness, which made it favorable for huge-scale preparation in many applications such as water splitting, sensor, solar cell, antibacterial and optoelectronic devices.

Growth and optical properties of ZnO nanorods on the full surface of porous silicon by sol–gel method and oil bath method

A method for the preparation of composites that allow the growth of ZnO nanorod structures on the full surface of porous silicon (polished surface, pore walls, and pore bottoms) is presented. The porous silicon is obtained by electrochemical etching of P-type silicon (100). The nanorods were grown in two steps: a sol–gel method and an oil bath method. The morphology of ZnO nanorods at different concentrations of the growth solution was investigated using scanning electron microscopy. X-ray diffraction confirmed the formation of ZnO hexagonal fibrous zincite structures. UV–Vis absorption spectroscopy confirmed that the composites possess good light absorption in the broad spectral region. In the wavelength range of 300 to 400 nm, the light absorption value of the porous silicon/zinc oxide (porous Si/ZnO) nanorods was increased by ~25% compared to that of the porous Si/ZnO films. The photoluminescence spectra confirmed the luminescence performance of the composites. Finally, the optical properties of the composites were further verified by simulation calculations.

Tuning the diameter and optical properties of ZnO nanorods grown onto flexible substrates at different temperatures

In this study, ZnO nanorods (NRs) have been successfully grown onto polytetrafluoroethylene (PTFE) substrates at low temperatures (85, 90, 95, 100 °C) by chemical bath deposition. Growth temperature for the prepared ZnO NRs was controlled by using electrical oven equipped with digital heat control. It is found that at 95 °C, well vertically aligned ZnO NRs are obtained with enhanced structural and optical properties. The crystallite size, lattice strain, and near-band edge emission of ZnO NRs band gap energy have been significantly improved as confirmed by X-ray diffraction and photoluminescence measurements. The crystallite size increases significantly from 52 to 94 nm as the growth temperature is raised by 10 °C only, i.e., from 85 to 95 °C. Besides, the near band edge emission to deep level emission ratio has been also enhanced, from 1.328 to 4.474 for 85 to 95 °C, respectively. The obtained results highlight that the properties of ZnO NRs can be tuned and controlled through the growth temperature. Besides, this study introduced a facile cost-effective method to produce ZnO NRs for flexible based-electronic applications.

Improved n-ZnO nanorods/p-Si heterojunction solar cells with graphene incorporation

The present research explored the effect of graphene layer and zinc oxide nanorods (NRs) on the photovoltaic performance of ZnO thin film-based heterojunction solar cells. For this purpose, ZnO thin film was deposited on p-type silicon using radio frequency sputtering to serve as an anti-reflective layer and n-type semiconductor to form a heterojunction thin film solar cell. Then, a cost-effective and facile chemical bath deposition technique was employed to synthesize ZnO NRs. To study the effect of reduced graphene oxide (rGO) on the optical properties of ZnO NRs, the colloidal suspension of rGO and ZnO NRs (rGO:ZnO NRs) was prepared. The optimized nanostructures were then transferred to the surface of the ZnO/Si sample using a drop-cast method. The morphological examination of the nanostructures showed the formation of ZnO NRs with various orientations which can significantly increase the entrapment of incident photons. The XRD results indicated an improvement in the structural properties of ZnO NRs upon adding rGO flakes. The reduction of GO was confirmed using Raman spectroscopy. The higher ID/IG ratio for the rGO:ZnO NRs sample (compared to GO layers) suggested the chemical reduction of GO. The optical investigations revealed an increment in the light absorption and PL intensity in the rGO-containing samples which can be due to the role of graphene as a reinforcement phase to inhibit the electron-hole recombination. The optoelectrical properties of fabricated solar cells were investigated via the metallization of top and rear contacts to fabricate three different solar cells based on ZnO thin film, ZnO NRs, and rGO:ZnO NRs. The results showed an enhancement in the efficiency (14.12%) and the fill factor (0.552) of the solar cell based on rGO:ZnO NRs compared to the other solar cells. Therefore, the incorporation of rGO can improve the photovoltaic properties of solar cells based on ZnO nanorods.

A comparison of optical properties of ZnO nanorods and ZnO nanotips for improving light absorption in rGO/ZnO nanostrctures

In this study, two types of ZnO nanostructures (ZnO nanotips and ZnO nanorods) were synthesized through a chemical bath deposition (CBD) method. These two structures were then compared by optical and structural analyses. The result showed the significant effect of ammonia concentration and the preferential etchings along the c axis on the formation of ZnO nanotips (NTs). To improve the absorption, nanostructures were optimized by reflectance analysis. To enhance the optical properties of the optimized sample, reduced graphene oxide (rGO) layers were transferred on the ZnO NTs surface by the electrophoretic deposition (EPD) method. The deposition of rGO layers on ZnO NTs can increment the optical absorption over a wide range of frequencies. The reflectance results showed enhanced adsorption capacity in the case of rGO/ZnO NTs.

Optical properties of ZnO nanorods and ZnO/CdZnS thin films

"Zinc oxide nanorods (ZnO NRs.) film prepared by hydrothermal method and zinc oxide film chemically coated with a trinary semiconductor (CdZnS) thin layer was investigated in this work. Optical properties include transmission, absorption spectra and energy band gaps have been tested for prepared thin films. it was observed that the absorption edge of the films after coating shifted towards higher wavelengths. Also there is a remarkable reduction in energy gap for ZnO/CdZnS film with compare to ZnO NRs. Film. The energy gap of ZnO NRs was 3.2 eV and 2.5 eV for ZnO/CdZnS film. "

Influence of thallium doping on structural, electrical, and optical properties of ZnO nanorods for TCO applications

Influence of thallium doping on structural, electrical, and optical properties of ZnO nanorods for TCO applications

Structural and optical properties of ZnO nanorods: The effect of concentration and pH of the growth solution

We prepared ZnO nanorods using a hydrothermal method in the c-axis orientation and perpendicular on an ITO substrate. The structural and optical properties were examined for samples prepared under various concentrations and pHs. The XRD results showed that the Bragg peak (002) is more intense than other peaks. This result reveals the tendency of the uniaxial growth of nanorods. The FE-SEM images showed that increasing the concentration increases the diameter and length of the nanorods, while the orientation remains almost constant. On the other hand, with increasing the pH, the diameter and length of nanorods decrease, so that at pH = 11, there is even no trace of nanorods formation. The photoluminescence spectra show that the intensity of near band edge emission (NBE) peaks was higher than the intensity of deep-level emission (DLE) peaks, which indicates the high crystalline quality of the samples. These results show the distinct effect of concentration and pH and provide a possibility to find an optimal condition to yield a sample with selected structural and optical properties.

Effect of low energy Ag+ ION implantation ON ZnO nanorods for enhanced visible light absorption- structural and optical analysis

Nanostructured one-dimensional ZnO nanorods (NRs) were grown on seeded borosilicate glass substrates through chemical bath deposition. The synthesised ZnO NRs were implanted with Ag + ions at low energy of 50 keV and varying fluences of 1 × 1015, 2 × 1015, 3 × 1015, 1 × 1016, and 3 × 1016 ions/cm2. The influence of injected Ag + ions was investigated on the structural and optical properties of ZnO NRs. A variation of X-ray diffraction (XRD) extracted and calculated microstructural parameters confirmed the presence of Ag+ ions on the grown ZnO NRs. XRD and Raman analysis revealed that the hexagonal wurtzite structure of ZnO was maintained, even at elevated fluences of Ag+ ions. Peak shifting to higher angles and lattice expansion were observed and attributed to substitutional doping. A red shift was observed in the absorbance spectra of Ag+ implanted ZnO NRs, suggesting a possibility of modification of the electronic structure which was confirmed through a calculation of the optical band gap and the refractive index. The energy band gap of Ag+ ion implanted ZnO NRs decreased with increase in the Ag+ ion fluence, whereas an increase was found for the calculated refractive index. The ZnO NRs implanted with 3 × 1016 ions/cm2 depicted different behaviour for structural and optical analysis, indicating a possibility of saturation of point defects and formation of different type of defects at fluences above 1 × 1016 ions/cm2. Corroboration of the structural and optical parameters demonstrate that low energy Ag + ion implantation can provide an effective and efficient approach to modify the structural and optoelectronic properties of ZnO for visible light driven photocatalytic applications.

The influence of addition of citric acid on the physical properties of metallic oxide nanorods via Sol-Gel route preparation

Abstract ZnO nanorods of 25 – 100 nm in diameter and 0.2 – 1 lm in length were fabricated through a citric acid assisted annealing process. The nanorods were characterized by means of X-ray diffraction, field-emission scanning electron microscopy, fourier transform infrared spectroscopy spectrophotometry, ultraviolet visible spectroscopy and photoluminescence spectroscopy. The obtained ZnO nanorods have good crystal quality and excellent optical properties. The effects of addition of citric acid with Chirality Multi-acid Chemistry function on the optical properties of ZnO nanorods have been investigated.

Hydrothermally derived co, Ni co-doped ZnO nanorods; structural, optical, and morphological study

Thin films of ZnO and Co, Ni co-doped ZnO nanorods were successfully synthesized on the silicon substrate (100) by the hydrothermal method. The grown thin films were annealed at 105 °C for 4.5 h and characterized by employing different analytical techniques to investigate the effects of co-doping on structural, morphological, and optical properties of ZnO nanorods. X-ray diffraction (XRD) analysis confirmed the successful substitution of dopants (Co and Ni) without altering the hexagonal wurtzite structure of ZnO. The crystallite size and micro-strain of grown films were calculated by employing Scherer, W–H, and SSP methods. The unit cell volume and lattice parameters were increased for Co doping, moreover by increasing Ni concentration as a co-dopant these parameters were decreased. Crystallite size of ZnO, ZnCo, ZnCoNi3, ZnCoNi6 and ZnCoNi9 grown thin films were 73 nm, 42 nm, 71 nm, 60 nm, and 52 nm respectively. The Fourier transform infrared spectroscopy (FTIR) has shown the existence of characteristic vibrational bonds of Zn–O in all co-doped samples at 499.35 cm −1 , 561.25 cm −1 , 570.89 cm −1 , 565.10 cm −1 , and 553.53 cm −1 , respectively. SEM images show the surface morphology of grown thin films, which indicates that the diameter of nanorods is increased by increasing Ni contents. The UV–visible spectroscopy was employed to measure the energy bandgap ( E g ) using Tauc's plot. The optical energy band gap was decreased (3.37–3.16) eV for all co-doped samples. The redshift in energy bandgap by Co and Ni co-doping is mainly due to the strong orbital coupling and generation of new energy states between the VB and CB . The other optical parameters including optical absorption coefficient ( α ) , transmittance (T) , skin depth, optical density (OD) , extinction coefficient ( k ), refractive index ( n ), optical conductivity ( σ opt ), and dielectric constants ( ε r , ε i ) of the grown thin films were also discussed. • Hydrothermally derived Co, Ni co-doped ZnO nanorods; Structural, optical, and morphological study. • Variation in microstructural parameters calculated by Scherrer, W–H, and SSP methods. • Nanorods are successfully grown on thin film of Si (100) substrate. • The optical parameters i.e. energy band gap, optical absorption coefficient, transmittance, skin depth, etc. were studied.

Morphology and optical properties of ZnO nanorods coupled with metal oxides of various bandgaps by photo-oxidation

This work aims to compare the effects on the morphology and optical properties of ZnO NRs (Eg: 3.33 eV) when coupled with metal oxides of various bandgaps, i.e. CuO (Eg: 1.72eV), NiO (Eg: 3.76 eV), and Al2O3 (Eg: 7.07 eV). The amount of metal oxide deposited on the hydrothermally grown ZnO NRs was controlled by the UV irradiation duration of the photo-oxidation process. The deposition of CuO on ZnO NRs produced flake-like structures while Al2O3 deposition created tubular structures. However, when coupled with NiO, ZnO NRs were uniformly covered by a thin layer of NiO without morphological change. The optical bandgap of ZnO NRs was modified slightly from 3.20 eV to 3.17, 3.28 or 3.16 eV after coupling with CuO, NiO, or Al2O3, respectively. The strongest enhancement of IUV/Ivis ratio in the RTPL spectra of ZnO NRs was achieved from Al2O3 coupling.

Binder-Free Electrode Based on ZnO Nanorods Directly Grown on Aluminum Substrate for High Performance Supercapacitors.

Herein, for the first time, the growth of ZnO nanorods directly on aluminum (Al) substrate via a low temperature (80 °C) wet chemical method, and used as binder-free electrode for supercapacitors were reported. XRD pattern and HRTEM images showed that high crystalline nanorods grown on Al substrate with c-axis orientation. Morphological studies revealed that the nanorods possessed well defined hexagon phase with length and diameter of ~2 µm and 100–180 nm, respectively. Raman spectrum of ZnO nanorods showed that the characteristic E2H mode corresponds to the vibration associated with the oxygen atoms of ZnO. The optical properties of ZnO nanorods studied using Room-temperature PL spectra revealed a near-band-edge (NBE) peak at ~388 nm emission and deep level (DLE) at ~507 nm. Electrochemical measurements showed that ZnO nanorods on Al substrate exhibited remarkably enhanced performance as electrode for supercapacitors with a value of specific capacitance of 394 F g−1 measured with scan rate of 20 mV s−1. This unique nanorods structures also exhibited excellent stability of >98% capacitance retention for 1000 cycles that were measured at 1A g−1. The presented easy and cost-effective method might open up the possibility for the mass production of binder-free electrodes for efficient electrochemical energy storage devices.

Enhancement in green luminescence of ZnO nanorods grown by dc-unbalanced magnetron sputtering at room temperature

Abstract ZnO nanorods are one of the most studied materials for optoelectronics applications, thanks to their superior properties, such as high-surface-to-volume ratio, unique chemical, and physical properties. Sputtering method is believed as a promising technique to fabricate ZnO nanorods in a large-scale area. However, this method requires high substrate temperature which may provoke intermixing of samples at the interface. In the present study, the optical properties of ZnO nanorods grown by room-temperature DC-unbalanced magnetron sputtering at room temperature are studied. ZnO thin film is also deposited as a reference. By selected sputtering parameters, SEM images show that the nanorods are grown mainly horizontal on the silicon substrate with a diameter of ~90 nm. Spectroscopic ellipsometry is used as the main optical characterization in the present study. The excitonic states of ZnO nanorods are suppressed compared to the thin film due to the high concentration of oxygen vacancies (VO) leading to excitonic screening effects. This result is also supported by UV–Visible spectra, which shows a high optical transition of ZnO nanorods in the visible region. Photoluminescence spectra confirm that the ZnO nanorods have a high density of VO defects as indicated by a dominant green emission located at 2.42 eV. The value of IGreen/IUV in ZnO nanorods is 12.019 which is much higher than the thin film with a value of 0.158. Our results suggest that nanorods structure improved green emission in ZnO materials and can be applied as a light-emitting device.

Silver nanoparticles coupled ZnO nanorods array prepared using photo-reduction method for localized surface plasmonic effect study

Coupling of selected metal nanoparticles (NPs) on the surface of ZnO nanorods (NRs) array grown on conductive glass substrates is one of the approaches to tailor the optical properties of ZnO NRs. It is a metal oxide deposition process followed by an annealing treatment to convert the deposits to metal NPs. However, the conductive glass substrates could easily deform during this annealing process. This issue limits the application of ZnO NRs array that grown on glass substrates for the fabrication of ZnO based devices. Thus, the development of metal NPs deposition technique without the need of post-deposition annealing is highly desired. This work demonstrated a successful and controlled deposition of silver (Ag) NPs on ZnO NRs array grown on fluorine doped tin oxide (FTO) glass substrates without any post-deposition annealing and, the product has exhibited localized surface plasmonic resonance (LSPR) phenomenon. The ZnO NRs arrays were grown on FTO glass substrates that pre-seeded with ZnO layer using hydrothermal method. The controlled coupling of Ag NPs particles on ZnO NRs was performed by adjusting the duration of photo-reduction process. The optical bandgap ZnO NRs was widened because of Ag NPs coupling, i.e. from 3.16 to 3.22 eV; as estimated from the result of UV–Vis measurement. The shift of near band-edge emission (NBE) in room temperature photoluminescence (RTPL) suggests that the presence of Ag NPs on the surface of ZnO NRs could block the transitions of electrons in ZnO whereas the shift in defect-related emission indicates the generation of defects at the interfaces between Ag NPs and ZnO NRs. The 5-folds increment of IUV/Vis ratio of Ag NPs/ZnO NRs in RTPL, indicating the specimens experienced LSPR effect. The LSPR effect of Ag NPs/ZnO NRs could be used to improve the performance of ZnO-based devices such as solar cells, light-emitting diodes and photocatalysts applications.

Enhanced optical properties of ZnO nanorods decorated with gold nanoparticles for self cleaning surface enhanced Raman applications

Raman is a very useful tool to identify chemical substances. However, Raman signal is normally not very strong and hence it is important to fabricate surface enhance Raman scattering (SERS) substrates of good repeatability and high enhancement factor. In this study, ZnO nanorods were prepared by a facile hydrothermal process assisted with galvanic effect. Gold nanoparticles were decorated on the as-prepared nanorods by sputtering method. The results showed that the Au nanoparticles enhance photoluminescence, Raman scattering and photocatalyst properties of ZnO nanorods. The ZnO@Au based SERS substrate showed high enhancement factor and can detect methylene blue at low concentration of 10–9 M. In combination with self cleaning under UV irradiation, the ZnO@Au SERS substrates can be reusable and hence it is promising for quantitative analyzing based on Raman scattering.

Growth of ZnO Nanorods by Template-Free Sol-Gel Dip-Coating Technique: Effect of Pre-Annealing Temperature

In this work, we studied the effect of pre-heating temperature on the structural and optical properties of ZnO nanorods grown by free template sol-gel dip-coating technique. The prepared films were pre-heated at different temperatures: 240, 260, 280 and 300 °C, then annealed at 500 °C for one hour. The structural properties of the prepared samples were investigated by X-ray diffraction (XRD) and the surface morphologies were studied by scanning electron microscope (SEM). The optical properties were studied by means of UV-Visible spectrophotometer. The XRD diffraction spectra show that all the prepared samples have a ZnO wurtzite structure with a preferential orientation along (002) axis. SEM micrographs revealed the formation of well-aligned ZnO nanorods for the sample preheated at 280 °C. The prepared ZnO nanorod structured thin films are highly transparent in the visible region with an average transmittance above 85 % in the 400–800 nm wavelength range.