Band Gap Of ZnO Nanorods Research Articles

Effect of Morphology and Plasmonic on Au/ZnO Films for Efficient Photoelectrochemical Water Splitting.

To improve photoelectrochemical (PEC) water splitting, various ZnO nanostructures (nanorods (NRs), nanodiscs (NDs), NRs/NDs, and ZnO NRs decorated with gold nanoparticles) have been manufactured. The pure ZnO nanostructures have been synthesized using the successive ionic-layer adsorption and reaction (SILAR) combined with the chemical bath deposition (CBD) process at various deposition times. The structural, chemical composition, nanomorphological, and optical characteristics have been examined by various techniques. The SEM analysis shows that by varying the deposition time of CBD from 2 to 12 h, the morphology of ZnO nanostructures changed from NRs to NDs. All samples exhibit hexagonal phase wurtzite ZnO with polycrystalline nature and preferred orientation alongside (002). The crystallite size along (002) decreased from approximately 79 to 77 nm as deposition time increased from 2 to 12 h. The bandgap of ZnO NRs was tuned from 3.19 to 2.07 eV after optimizing the DC sputtering time of gold to 4 min. Via regulated time-dependent ZnO growth and Au sputtering time, the PEC performance of the nanostructures was optimized. Among the studied ZnO nanostructures, the highest photocurrent density (Jph) was obtained for the 2 h ZnO NRs. As compared with ZnO NRs, the Jph (7.7 mA/cm2) of 4 min Au/ZnO NRs is around 50 times greater. The maximum values of both IPCE and ABPE are 14.2% and 2.05% at 490 nm, which is closed to surface plasmon absorption for Au NPs. There are several essential approaches to improve PEC efficiency by including Au NPs into ZnO NRs, including increasing visible light absorption and minority carrier absorption, boosting photochemical stability, and accelerating electron transport from ZnO NRs to electrolyte carriers.

Structural, optical, antimicrobial and ferromagnetic properties of Zn1−xLaxO nanorods synthesized by chemical route

Nanoparticles of Zn1−xLaxO (x = 0, 0.01, 0.03 and 0.05) were successfully synthesized by a cost-effective chemical method. The influences of La on the microstructural, optical, antimicrobial and magnetic properties of these ZnO nanoparticles were investigated. XRD studies revealed the presence of hexagonal wurtzite phase of ZnO without any impurity. The samples possess nanorod morphology as confirmed by FESEM and TEM analysis. The band gap of ZnO nanorods increased from 3.25 to 3.27 eV with increasing La concentration from 0% to 5%. The presence of various defects in our samples were identified by PL spectroscopy. Magnetic studies exposed the signature of ferromagnetism in all the samples at 300 K. The magnetization of ZnO nanorods is significantly enhanced by La doping. A maximum values of magnetization was observed for 1% La doped ZnO sample which is ~6 times more than for a pure ZnO nanorods. The contributions of oxygen vacancies towards the observed ferromagnetism were confirmed. The origin of ferromagnetism was enlightened on the basis of results of a BMP model. In vitro bioassays showed that synthesized nanorods exhibited narrow-spectrum antibacterial activity against Staphylococcus aureus that compared well with commercial ZnO, nanoparticles (Sigma). Furthermore, the synthesized nanorods when tested for toxicity against Caenorhabditis elegans, but show only low toxicity at 100 µg/mL. Toxicity in zebrafish was also limited. Based on their multifunctional properties, we believe that the synthesized ZnO nanorods could be beneficial for optical device applications in the UV range, spintronic devices, as well as for biomedical purposes.

Investigation on the properties of La-doped and Dy-doped ZnO nanorods and their enhanced photovoltaic performance of Dye-Sensitized Solar Cells

Pure ZnO nanorods with various times, La-doped ZnO NRs and Dy-doped ZnO NRs were synthesized through two steps: seed layer by spin coating method and growing of nanorods by hydrothermal method. X-ray diffraction, field emission scanning electron microscopy, dispersive X-ray spectroscopy, photoluminescence spectroscopy and ultraviolet–visible spectrometer were used to investigate the structure composition and the optical properties of the products. The optical measurements indicated an enhancement in absorption and emission intensity, when the length of nanorods and impurities concentration were increased and furthermore, the band gap of ZnO nanorods was decreased. Dye-Sensitized Solar Cells were fabricated using ZnO nanorods grown on the porous TiO 2 nanoparticles film (TiO 2 NPs/ZnO NRs) as the photoanodes. The effect of different growth time and various dopants were investigated on the performance of DSSCs. The optimum performance of DSSC was achieved by ZnO NRs grown for 300 min. The performance of DSSC based TiO 2 NPs/ZnO NRs decorated with TiO 2 NPs was obtained 5.99% and cell efficiency was improved more than twice compared with the undecorated photoanode. The power conversion efficiency of DSSCs doped with Lanthanum and Dysprosium was also increased by 63.6% and 71.5%, respectively, in comparison with the conventional TiO 2 NPs photoanode. • Pure, La-doped and Dy-doped ZnO nanorods were grown by a simple hydrothermal method and characterized. • DSSCs were fabricated using pure, La-doped and Dy-doped ZnO nanorods. • The efficiency of DSSCs doped with La and Dy was increased by 63.6 % and 71.5 %, respectively, in comparison with the conventional TiO 2 NPs photoanode.

ZnO as photocatalyst: An approach to waste water treatment

ZnO nanorods having uniform size have been synthesized using hydrothermal method. Different standard analytical techniques were employed to investigate the microscopic structure and optical properties of the prepared sample. The formation of the hexagonal wurtzite structure of ZnO was established by XRD and SEM analyses. UV-visible spectra of the as-synthesized ZnO show absorption band edge in UV region at 373 nm, corresponding to which the calculated band gap of ZnO nanorods is found to be 3.4 eV. Photodegradation of methylene blue (MB) using ZnO as photocatalyst have also been studied. Experiments revealed that ZnO nanorods with high aspect ratio can degrade 65% of initial concentration of MB in only 50 min.

Structural, Optical, and Magnetic Properties of Hydrothermally Grown Fe-Doped ZnO Nanorod Arrays on Glass Substrate

In this paper, undoped and Fe-doped ZnO nanorod arrays were grown on glass substrate by a facile hydrothermal method. Structural, optical, and magnetic properties of the prepared nanorods were investigated. Structural investigation clearly showed that the prepared nanorods had single phase wurtzite structure without any secondary phases and the prepared undoped and Fe-doped nanorods were grown vertically. The optical characterization revealed that the optical band gap of ZnO nanorods was decreased by increasing the value of Fe concentration. Furthermore, the formation of diluted magnetic semiconductor nanorod arrays was verified. The origin of room temperature ferromagnetism is explained by the bound magnetic polaron concept.

Fast and convenient growth of vertically aligned ZnO nanorods via microwave plasma-assisted thermal evaporation

A new approach to grow vertically aligned ZnO nanorods on glass substrates under ambient pressure was developed using microwave plasma-assisted thermal evaporation (MPATE). The results revealed that ZnO nanorods grew preferentially along their (002) plane on glass substrates without using catalysts/seed layers. Interestingly, the ZnO nanorods were completely formed within 7 min, which was much faster than other methods. The optical band gap of ZnO nanorods was 3.22 eV, indicating the photoresponse at UV region (<400 nm). Moreover, room-temperature photoluminescence of the ZnO nanorods, excited by 325 nm light, showed a dominance of green-light emission and a small UV emission.

Analysis of structural and UV photodetecting properties of ZnO nanorod arrays grown on rotating substrate

ZnO nanorods (NRs) were successfully synthesized on seed layered substrate by a novel rotational hydrothermal method. The effect of substrate rotational speed on the growth of ZnO NRs were systematically characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). With an increase of the rotational speed, the mean diameter of the ZnO NRs decreased from ~ 43 nm in ZnO NRs grown on a steady substrate to ~27 nm in a sample with 60 rpm while the number density was increased about one order. The optical studies indicated that band gap of ZnO NRs was shifted towards higher values with increasing speed up to 60 rpm and then decreases gradually. The electrical resistance variation of samples was described according to structural properties of NRs and their coalescence, where the increasing of NRs lateral junction through substrate rotation, improves the electrons transition in samples. Finally, photosensing properties of ZnO based ultraviolet (UV) detectors were investigated. It was observed that the photdetector based on ZnO NRs grown at 120 rpm shows an optimum performance with sensitivity 570 and responsivity 1.9 A/W.

Effect of Precursor Concentration Ratio on The Crystal Structure, Morphology, and Band Gap of ZnO Nanorods

In this present study, the ZnO nanorods were synthesized by using the hydrothermal method with various precursor concentrations. The ZnO nanorods were characterized by X-Ray Diffractometer (XRD) to identify the crystal structure, Scanning Electron Microscopy (SEM) to determine the morphology, and UV-Vis Spectrophotometer to determine the band gap. It was shown that the ZnO nanorods have hexagonal wurtzite crystal structure with the c-axis orientation at (002) Bragg’s plane. The morphology of the ZnO particles was in a rod structure growing over the surface of the substrate. The diameter of the ZnO nanorods resulted ifrom the concentrations of 30, 35 mM, and 45 mM were 94.2, 156.3, and 76.7 nm, respectively. The data analysis of the UV-Vis data showed that the band gap of ZnO nanorods (~3.18 eV) was smaller than that of ZnO nanoparticles (~3.46 eV).

Electrodeposition of template free hierarchical ZnO nanorod arrays via a chloride medium

We have successfully grown template and buffer free ZnO nanorod films via chloride medium by controlling bath temperature in a simple and cost effective electrochemical deposition method. Thin films of ZnO nano-rods were obtained by applying a potential of −0.75 V by employing Ag/AgCl reference electrode for 4 h of deposition time. The CV measurements were carried out to determine potential required to deposit ZnO nanorod films whereas chronoamperometry studies were carried out to investigate current and time required to deposit ZnO nanorod films. The formation of ZnO nanorod has been confirmed by scanning electron microscopy (SEM) and Raman spectroscopy. Low angle XRD analysis confirms that ZnO nanorod films have preferred orientation along (101) direction with hexagonal wurtzite crystal structure. The SEM micrographs show nice surface morphology with uniform, dense and highly crystalline hexagonal ZnO nanorods formation. Bath temperature has a little influence on the orientation of nanorods but has a great impact on their aspect ratio. Increase in bath temperature show improvement in crystallinity, increase in diameter and uniform distribution of nanorods. Compositional analysis shows that the amount of oxygen is ~49.35 % and that of Zn is ~50.65 %. The optical band gap values were found to be 3.19 and 3.26 eV for ZnO nanorods prepared at bath temperature 70 and 80 °C respectively. These results indicate that by controlling the bath temperature band gap of ZnO nanorods can be tailored. The obtained results suggest that it is possible to synthesize ZnO nanorod films by a simple, cost effective electrodeposition process which can be useful for opto-electronic devices fabrication.

Hydrothermal growth and characterization of Al-doped ZnO nanorods

Pure and Al doped (0 - 5 at%) ZnO nanorods were prepared by two step hydrothermal method. In the first step, ZnO thin films were deposited on glass substrates by sol-gel spin coat method. In the next step, Al doped ZnO nanorods were grown on the ZnO film coated glass substrates by hydrothermal method using the aqueous solution of [Zn(NO3)2.6H2O] (0.1M), [HMT;C6 H12N4] (0.1M) and [AlCl3.6H2O] prepared using double distilled water. The growth was carried out by maintaining the temperature of the autoclave at 90 °C for 6 h. The structural, morphology and optical properties of the grown ZnO nanostructures were characterized by XRD, FESEM, EDX, UV-Vis and PL spectroscopy. XRD spectra shows both ZnO and Al doped nanorods have the hexagonal wurtzite structure with a strong (002) preferred orientation. As Al doping percentage increases, the XRD spectra show dominance of (101) orientation. The surface morphology of the films were studied using SEM, shows that the both pure and Al doped ZnO films have hexagonal shaped nanorods. The band gap of ZnO nanorods increases with Al doping concentration. The optical parameters such as refractive index, extinction coefficient and dielectric constants were determined using the absorbance and the reflectance data. The PL spectrum shows emission peaks in UV and visible region related to near band emission (NBE) and deep level emission (DLE), respectively. As Al doping increases NBE intensity decreases, this may be due to the doping related defects.

Band Gap Engineering of ZnO using Core/Shell Morphology with Environmentally Benign Ag2S Sensitizer for Efficient Light Harvesting and Enhanced Visible-Light Photocatalysis

Band gap engineering offers tunable optical and electronic properties of semiconductors in the development of efficient photovoltaic cells and photocatalysts. Our study demonstrates the band gap engineering of ZnO nanorods to develop a highly efficient visible-light photocatalyst. We engineered the band gap of ZnO nanorods by introducing the core/shell geometry with Ag2S sensitizer as the shell. Introduction of the core/shell geometry evinces great promise for expanding the light-harvesting range and substantial suppression of charge carrier recombination, which are of supreme importance in the realm of photocatalysis. To unveil the superiority of Ag2S as a sensitizer in engineering the band gap of ZnO in comparison to the Cd-based sensitizers, we also designed ZnO/CdS core/shell nanostructures having the same shell thickness. The photocatalytic performance of the resultant core/shell nanostructures toward methylene blue (MB) dye degradation has been studied. The results imply that the ZnO/Ag2S core/shell nanostructures reveal 40- and 2-fold enhancement in degradation constant in comparison to the pure ZnO and ZnO/CdS core/shell nanostructures, respectively. This high efficiency is elucidated in terms of (i) efficient light harvesting owing to the incorporation of Ag2S and (ii) smaller conduction band offset between ZnO and Ag2S, promoting more efficient charge separation at the core/shell interface. A credible photodegradation mechanism for the MB dye deploying ZnO/Ag2S core/shell nanostructures is proposed from the analysis of involved active species such as hydroxyl radicals (OH(•)), electrons (e(-)(CB)), holes (h(+)(VB)), and superoxide radical anions (O2(•-)) in the photodegradation process utilizing various active species scavengers and EPR spectroscopy. The findings show that the MB oxidation is directed mainly by the assistance of hydroxyl radicals (OH(•)). The results presented here provide new insights for developing band gap engineered semiconductor nanostructures for energy-harvesting applications and demonstrate Ag2S to be a potential sensitizer to supersede Cd-based sensitizers for eco-friendly applications.

Effect of the Diameter on the Band Gap of ZnO Nanorods

ZnO nanomaterials have different properties from the bulk. One interesting property is band gap. It is found that the band gap is dependent on the dimensions of the nanostructures. Many methods have been used by researchers [1-7] to produce ZnO nanostructures but amongst the soft chemistry methods, chelating agents are normally used [1,6,7]. In this work zinc oxide nanostructures have been synthesized using the sol-gel synthesis method. The effect of a synthesis with and without the use of gelling agent is investigated. One sample is done using a sol-gel synthesis route using tartaric acid and the other sample is synthesized without using a gelling agent at all. Results showed that the samples are pure, however the sample prepared without using the gelling agent are made up of rods with long aspect ratios while the one obtained using the gelling agent are made up of rods with lower aspect ratios. It is found that the band gap of the high aspect ratio ZnO is smaller than the one with low aspect ratio. This is attributable to the lattice expansion of the lower aspect ratio ZnO nanorods as obtained from quantitative X-Ray diffraction. Therefore, a characteristic of ZnO nanomaterials is dependent on their dimensions.

Influence of different growth environments on the luminescence properties of ZnO nanorods grown by the vapor–liquid–solid (VLS) method

ZnO nanorods (NRs) are grown in different atmospheres (argon, air, oxygen and nitrogen) by using the vapor–liquid–solid (VLS) method. The influence of different growth atmospheres on the luminescence properties has been investigated by using the photoluminescence (PL), cathodoluminescence (CL) and electroluminescence (EL) spectra measurements at room temperature. The PL spectra investigations reveal that the air, the oxygen and the nitrogen growth atmospheres have strongly affected the oxygen interstitial (Oi) and oxygen vacancy (VO) related deep level emission (DLE) bands in ZnO and this fact is also found consistent with the cathodoluminescence (CL) and electroluminescence (EL) spectra investigations. The color rendering investigations reveal that the growth atmospheres have also influenced the color quality of the emitted light. These results indicate that the defects related emissions from the band gap of ZnO NRs can be tuned by using different growth atmospheres. These results can be useful for the development of white light emitting diodes (WLEDs).

Optical and magnetic properties of copper doped ZnO nanorods prepared by hydrothermal method

Surfactant free ZnO and Cu doped ZnO nanorods were synthesized by hydrothermal method. The formation of ZnO:Cu nanorods were confirmed by scanning electron microscopy, X-ray diffraction and Raman analysis. Diffuse reflectance spectroscopy results shows that band gap of ZnO nanorods shifts to red with increase of Cu content. The orange-red photoluminescent emission from ZnO nanorods originates from the oxygen vacancy or ZnO interstitial related defects. ZnO:Cu nanorods showed strong ferromagnetic behavior, however at higher doping percentage of Cu the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced. The presence of non-polar E 2 and E 2 Raman modes in nanorods indicates that Cu doping didn’t change the wurtzite structure of ZnO.

Synthesis and Optical Properties of Vertically Aligned ZnO Nanorods

ZnO nanorods were grown on an n-type silicon (111) substrate with the assistance of Au catalyst by chemical vapor deposition (CVD). The ZnO nanorods were about 200 nm diameter with uniform lengths of about 1.2 microm. The ZnO nanorods exhibited [0001] orientation. ZnO nanorods grow in dense arrays perpendicular to the (111)-plane of silicon due to [0001]ZnO perpendicular [111]Si, [2110]ZnO perpendicular [110]Si, [1210]ZnO perpendicular [101]Si and [1120]ZnO perpendicular [011]Si epitaxy. Room-temperature photoluminescence (PL) measurements show three near band-edge emission peak at 377, 379, 389 nm. These peaks are attributed to exciton transitions. Analysis indicates that the band gap of ZnO nanorods is 3.301 eV and exciton binding energy is 0.114 eV.