Na-doped ZnO Research Articles

Na-doped ZnO thin film by USP method for amperometric detection of Alura Red (E129) azo dye

Na-doped ZnO thin film by USP method for amperometric detection of Alura Red (E129) azo dye

Influence of Wrinkle Structure on Properties of Na-doped ZnO Films

Un-doped ZnO and Na-doped ZnO (NZO) thin films with various Na doping concentrations were successfully fabricated on glass substrates by a sol-gel process. The effect of Na ions at concentrations of 0, 1, 2, 3, 4, and 5% on the crystalline structure, surface morphology, and optoelectronic properties of ZnO films was studied using appropriate measurement techniques. XRD analysis revealed a polycrystalline hexagonal wurtzite structure in the NZO films. The NZO films' average crystal size ranged from 17.7 nm to 19.6 nm. SEM micrographs showed that wrinkle network appeared in the pure and doped ZnO films due to solvent evaporation during the thermal annealing process. UV-Vis spectroscopy pointed out that the average transmittance of NZO films is as large as ca. 78%. The optical bandgap of the films varied slightly between 3.235 eV for the pure ZnO and 3.246 eV for the Na 5% doped NZO film. When Na ions were doped into the NZO films, the electrical conductivity improved. Moreover, the absorption figure of merit exhibited the largest value of 0.981 Ω-1cm-1 for the fabricated NZO films, which enables the use of these films for solar cells and for other optoelectronic applications.

Introducing Fuel Cell Application Using Sodium Vacancies in Hexagonal Wurtzite Structured ZnO Nanorods for Developing Proton–Ion Conductivity

Zinc oxide, a direct band gap semiconductor of ≥3.30 eV, is prevalent in potential requests for energy devices. The early-stage demonstration of ZnO provides a new method of developing high ionic conductivity in multifunctional semiconductors for electrolyte applications in ceramic fuel cells (CFCs). In the present work, we successfully synthesized Na-doped ZnO nanorods by a hydrothermal method and employed them as an electrolyte in CFCs. The synthesized Na-doped-ZnO nanorods showed an effective ionic conductivity of 8.75 × 10−2 S cm−1 along with an excellent power density of 609 mWcm−2 ± 5% when the fuel cell was operating at 550 °C. The enhanced ionic conductivity could be due to Na+ doping into Zn2+ and the high ionic radius of Na ions producing bulk oxygen vacancies in the ZnO structure to conduct oxygen ions or protons. Furthermore, we used experimental analysis, such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), ultraviolet–visible (UV–visible), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), to evaluate the change in structural properties and mechanism of ionic transport in ZnO nanorods with sodium doping. The presented work provides insight into a novel approach of developing the high ionic conductivity of electrolytes in a low-cost ZnO semiconductor material.

Effects of Group-I Elements on Output Voltage Generation of ZnO Nanowires Based Nanogenerator; Degradation of Screening Effects by Oxidation of Nanowires.

Here, we report the successful incorporation of group I elements (K, Na, Li) to ZnO nanowires. Three distinct (2, 4, and 6 wt.%) doping concentrations of group I elements have been used to generate high piezoelectric voltage by employing a vertically integrated nanowire generator (VING) structure. X-ray photoelectron spectra (XPS) indicated the seepage of dopants in ZnO nanowires by substitution of Zn. Shallow acceptor levels (LiZn, NaZn, KZn) worked as electron trapping centers for intrinsically n-type ZnO nanowires. Free moving electrons caused a leakage current through the nanowires and depleted their piezoelectric potential. Reverse leakage current is a negative factor for piezoelectric nanogenerators. A reduction in reverse leakage current signifies the rise in output voltage. A gradual rise in output voltage has been witnessed which was in accordance with various doping concentrations. K-doped ZnO nanowires have generated voltages of 0.85 V, 1.48 V, and 1.95 V. For Na-doped ZnO nanowires, the voltages were 1.23 V, 1.73 V, and 2.34 V and the voltages yeilded for Li-doped ZnO nanowires were 1.87 V, 2.63 V, and 3.54 V, respectively. Maximum voltage range has been further enhanced by the surface enrichment (oxidized with O2 molecules) of ZnO nanowires. Technique has been opted to mitigate the screening effect during an external stress. After 5 h of oxidation in a sealed chamber at 100 ppm, maximum voltage peaks were pronounced to 2.48 V, 3.19 V, and 4.57 V for K, Na, and Li, respectively. A low-cost, high performance mechanical transducer is proposed for self-powered devices.

Effects of substrate temperature and sodium source temperature on Na doping of ZnO by MOCVD

In this paper, Na-doped ZnO thin films were grown by MOCVD using cyclopentadienylsodium (CpNa) as the sodium source. The effects of substrate temperature and sodium source temperature on the properties of Na-doped ZnO thin films were studied. SIMS measurement verified that higher substrate temperature would result in higher Na doping content in ZnO:Na thin films. SEM and Hall measurements revealed that both surface morphology and electrical properties of ZnO:Na thin films showed nonlinear variation with substrate temperature and sodium source temperature. When the substrate temperature or the sodium source temperature was increased, the surface morphology of ZnO:Na thin films turned to sheet structures tilted in all directions first and then back to perpendicular hexagonal structure dominant morphology, and the hole concentration increased first and then decreased. This nonlinear variation trend was ascribed to be related to the variation of doping content and impurity position in ZnO:Na thin films, especially the Na impurity position.

Effect of Na doping on microstructures, optical and electrical properties of ZnO thin films grown by sol-gel method

Undoped ZnO film and Na doped ZnO films with different Na/Zn molar ratios were deposited on glass substrates by the sol-gel spin coating method. The X-ray diffraction (XRD) pattern showed that all the films exhibited a high c-axis orientation with a hexagonal wurtzite structure. The diffraction angle shifted significantly to the lower angle with sodium doping. X-ray photoelectron spectroscopy (XPS) analysis confirmed that Na was incorporated into the ZnO matrix by occupying Zn sites. Field emission scanning electron microscope (FESEM) and Atomic force microscope (AFM) analysis showed that the surfaces of the films consisted of homogeneously distributed dense grains. FESEM images also exhibited hexagonal-like shape nanoparticles. The UV–Vis–NIR spectroscopy exhibited very sharp near UV absorption edge. Hall effect measurement results indicated that the undoped ZnO film exhibited n-type conductivity, whereas the Na-doped ZnO films generally exhibited p-type conductivity and all of the films had low carrier concentration. Room temperature photoluminescence (PL) spectra showed an ultraviolet emission (380–384 nm) and a broad visible emission (450–700 nm).

Direct sunlight-active Na-doped ZnO photocatalyst for the mineralization of organic pollutants at different pH mediums

This work reports the preparation of Na-doped ZnO (Na-ZnO) as a promising photocatalyst under sunlight through a very simple precipitation method. The crystal and electronic structures of the prepared Na-ZnO were characterized by experimental techniques and Density Functional Theory (DFT) calculations. Where the DFT calculations revealed that the effect of Na-doping on the ZnO electronic structure is consistent with the experimental observations and the bandgap value found to be decreasing. Under direct sunlight, the as-prepared Na-ZnO decolorized more than 99.5% of the methylene blue dye (MB) after 1.5 h and led to mineralization of 98.3% of it after 3 h. While pure ZnO decolorized only 35% of MB dye at the same conditions. The prepared Na-ZnO has a promising photocatalytic activity at different pH's and high photostability reaching to 7 recycle with the same efficiency. Finally, the primary active species produced during the photocatalytic reaction were determined and the photocatalytic mechanism was elucidated.

Synthesis and Characterization of Na Doped ZnO Rods Grown by Simple Chemical Method

In this study, the effects of Na doped on the structure, morphology, and optical properties of the ZnO films deposited on glass substrate were investigated. The films were synthesized on glass substrates via a simple chemical method. Undoped and Na-doped ZnO films were obtained from an aqueous solution of the Zinc nitrate hexahydrate (Zn(NO3)2·6H2O), Sodium Nitrate (NaNO3) and hexamethylenetetramine-HMT (C6H12N4). Characterization of the films was examined using a Scanning electron microscope (SEM) and X-ray diffractometer (XRD), Ultraviolet-Visible spectrophotometer (UV-Vis) and X-Ray Photoelectron (XPS). The structure, morphology, and optical properties of the films were presented. The wurtzite ZnO films showed rod arrays morphology. The optical band gap increased with the doping of Na metal. The result shows that Na addition affected the properties of the ZnO films.

Na-Doped ZnO and RGO Composite-Based Flexible Acetone Gas Sensor Operated in Room Temperature

Real-time health monitoring is important in disease prediction, prevention, and early treatment. In this study, based on Na-doped ZnO/reduced graphene oxide (RGO) heterojunction, an ultrasensitive flexible room temperature gas sensor was developed for lung cancer surveillance diagnosis. The sensing material was synthesized using a simple solution route. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy were carried out to investigate the structure and chemical properties. The fabricated material has a surface-to-volume ratio, which was important to the sensing property. The gas-sensing performance was measured from 5 ppm to 200 ppm at room temperature (25 °). The proposed sensor demonstrated fast response and recovery time, as well as great repeatability and long-term stability. Furthermore, it exhibited mechanical robustness, and can be bent to different angles with almost no resistance change. Moreover, performance investigation at low acetone concentrations (0.2 ppm to 1.0 ppm) revealed its capability of distinguishing acetone gas as low as 0.2 ppm, with good linearity under different acetone concentration. As such, the developed sensor could provide a promising basis for disease monitoring through detecting the concentration of acetone gas exhaled by human.

Na-doped ZnO UV filters with reduced photocatalytic activity for sunscreen applications

Due to its physical and chemical stability in addition to its transparency in the visible region with ultraviolet protective activity, ZnO can be used in sunscreen applications. In our article, Na-doped zinc oxide nanoparticles were prepared in different concentrations by sol–gel and solvothermal techniques to reduce their photocatalytic activity. The photocatalytic activity of the doped samples was suppressed effectively at a concentration of 0.03 at% Na doping up to 90% by conducting the sol–gel process rather than the solvothermal process which resulted in about 70% photocatalytic reduction in a period of time from (0–30 min) when exposed to ultraviolet and visible light. In addition, the nanoparticles resulted by sol–gel route show a reduction in photoactivity under solar simulation about 98% rather than those resulted via solvothermal process which shows a reduction around 92% for 30 min which is the same period of time used for the photocatalytic degradation test. The particle size was around 64.6–84.6 nm for samples prepared by both methods.

Microstructure and optical properties of Na-doped ZnO system, synthesized by the sol–gel method

Pure and Na-doped ZnO (2 at.%, 5 at.%, and 10 at.%) films are synthesized by sol–gel method and annealed at 500 °C for 4 h. The as-synthesized nanoparticles are characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS). The samples exhibited hexagonal ZnO lattice structure and another Na2O2 phase was detected in the 5 at.% Na-doped ZnO sample. The calculated average crystalline size increases from 42.0 nm to 43.5 nm when Na content increased from 0 to 10 at.%. FESEM and TEM analysis identifies that the average size of the Na-doped ZnO nanoparticles lies in between 50 nm and they appear in spheroid-like or rod-like shaped particles. The transmittance of the sample was above 80% and the results of photocatalytic activity show that Na-doped ZnO nanoparticles exhibit higher photodegradation activity (about 91%) than pure ZnO nanoparticles under UV irradiation.

UV-illumination and Au-nanoparticles enhanced gas sensing of p-type Na-doped ZnO nanowires operating at room temperature

High density p-type Na-doped ZnO nanowires were uniformly grown on glass substrate via the hydrothermal method, and then examined by SEM, XRD, PL, XPS, and TEM analysis. The p-type characteristic of the nanowires was verified through Hall and humidity measurements. 2∼6 nm Au nanoparticles were sputtered on the nanowires to fabricate a room temperature sensor and strengthen its p-type property, which was enhanced by the Schottky barrier at Au NPs/ZnO interface. The p-type gas sensor has a high response, sensitivity and selectivity under UV illumination at room temperature.

Effects of Na Doping on Structural, Optical, and Electronic Properties of ZnO Thin Films Fabricated by Sol–Gel Technique

Undoped and Na-doped ZnO thin films were fabricated by sol–gel technique on quartz glass substrates and annealed at 500°C for 1 h. The structural properties of the films were characterized using x-ray diffraction analysis, which revealed hexagonal wurtzite structure with no peaks corresponding to Na2O or other Na phases being found. Surface morphology observations by scanning electron microscopy revealed that the crystallite size and topographical properties of the ZnO films were influenced by the Na doping concentration. X-ray photoelectron spectra revealed presence of Na+ in ZnO regime. The transmittance spectra indicated that the average transmittance of Na-doped ZnO film was above 80% in the visible range, superior to that of the undoped film. There was a blue-shift in the ultraviolet absorption edge with increase of the Na content. Photoluminescence spectra illustrated two peaks, corresponding to ultraviolet near-band-edge and visible emission.

Photovoltaic performance of p-Si/Cd1-xZnxO heterojunctions

Heterojunctions of p-Si/Cd1-xZnxO were synthesized by depositing of Cd1-xZnxO films on p-Si substrates by electrochemical deposition. The morphological properties of the films were studied by scanning microscopy. The electric and photoelectrical properties of heterojunctions were investigated depending on the deposition potential and films composition. Heterojunctions of p-Si/Cd1-xZnxO, which deposited at cathode potential of -1.2 V, shows good rectification (k=1640). Under AM1.5 conditions the maximal values of open-circuit voltage, short-circuit current, fill factor and efficiency of our best nano-structured cell, were Uoc = 442 mV, Jsc = 19.9 mA/cm2, FF = 0.59 and n = 5.1 %, respectively. Full Text: PDF ReferencesX. Li, et al. "Role of donor defects in enhancing ferromagnetism of Cu-doped ZnO films", J. Appl. Phys., 105, 103914 (2009). CrossRef X. Han, K. Han and M. Tao, "Electrodeposition of Group-IIIA Doped ZnO as a Transparent Conductive Oxide", ECS Trans., 25, 93 (2010). CrossRef W. Liu et al. "Na-Doped p-Type ZnO Microwires", J. Am. Chem. Soc., 132, 2498 (2010). CrossRef R.A. Ismail and O.A. Abdulrazaq, "A new route for fabricating CdO/c-Si heterojunction solar cells", Sol. Energy Mater. Sol. Cells, 91, 903 (2007). CrossRef R.S. Mane, H.M. Pathan, C.D. Lokhande and S.H.Han, "An effective use of nanocrystalline CdO thin films in dye-sensitized solar cells", Sol. Energy, 80 185 (2006). CrossRef E. Martin et al. "Properties of multilayer transparent conducting oxide films", Thin Solid Films, 461, 309 (2004). CrossRef Y. Caglar, M. Caglar, S. Ilican and A. Ates, "Morphological, optical and electrical properties of CdZnO films prepared by sol?gel method", J. Phys. D: Appl. Phys., 42, 065421 (2009). CrossRef F. Wang, Z. Ye, D. Ma, L. Zhu and F. Zhuge, "Formation of quasi-aligned ZnCdO nanorods and nanoneedles", J. Cryst. Growth, 283, 373 (2005). CrossRef A. Abdinov, H. Mamedov, S. Amirova, "Investigation of Electrodeposited Glass/SnO2/CuInSe2/Cd1-xZnxS1-ySey/ZnO Thin Solar Cells", Jpn. J. Appl. Phys., 46, 7359 (2007). CrossRef A. Abdinov, H. Mamedov, H. Hasanov, and S. Amirova, "Photosensitivity of p,n-Si/n-Cd1?xZnxS heterojunctions manufactured by a method of electrochemical deposition", Thin Solid Films, 480-481, 388 (2005). CrossRef A. Abdinov, H. Mamedov, and S. Amirova, "Investigation of electrodeposited p-Si/Cd1 ? xZnxS1 ? ySey heterojunction solar cells", Thin Solid Films, 511-512, 140 (2006) CrossRef H. Mamedov, V. Mamedov, V. Mamedova, Kh. Ahmadova, "Investigation of p-GaAs/n-Cd1-xZnxS1-yTey/Cd1-xZnxO heterojunctions deposited by electrochemical deposition", J. Optoelectrom. Adv. M., 17, 67 (2015). DirectLink H. Mamedov et al. "Preparation and Investigation of p-GaAs/n-Cd1-xZnxS1-yTey Heterojunctions Deposited by Electrochemical Deposition", J. Solar Energy Engineering, 136, 044503 (2014). CrossRef S. Sadofev, S. Blumstengel, J. Cui, J. Puls, S. Rogaschewski, P. Schafer and F. Henneberger, "Visible band-gap ZnCdO heterostructures grown by molecular beam epitaxy", Appl. Phys. Lett., 89, 201907 (2006). CrossRef G. Torres-Delgado et al. "Percolation Mechanism and Characterization of (CdO)y(ZnO)1?y Thin Films", Adv. Funct. Mater., 12, 129 (2002). CrossRef H. Tabet-Derraz, N. Benramdane, D. Nacer, A. Bouzidi and M. Medles, "Investigations on ZnxCd1?xO thin films obtained by spray pyrolysis", Sol. Energy Mater. Sol. Cells, 73, 249 (2002). CrossRef M. Tortosa, M. Mollar and B. Mar?, "Synthesis of ZnCdO thin films by electrodeposition", J. Cryst. Growth, 304, 97 (2007). CrossRef A. Singh, D. Kumar, P. K. Khanna, M. Kumar, and B. Prasad, "Phase Segregation Limit in ZnCdO Thin Films Deposited by Sol?Gel Method: A Study of Structural, Optical and Electrical Properties", ECS Journal of Solid State Science and Technology, 2 (9), Q136 (2013). CrossRef F.Z. Bedia, A. Bedia, B. Benyoucef and S.Hamzaoui, "Electrical Characterization of n-ZnO/p-Si Heterojunction Prepared by Spray Pyrolysis Technique", Physics Procedia, 55, 61 (2014). CrossRef M. Jing-Jing et al. "Rectifying and Photovoltage Properties of ZnO:A1/p-Si Heterojunction", Chin. Phys. Lett., 27 (10), 107304 (2010). CrossRef

Structure and Electric Conduction in Pulsed Laser-Deposited ZnO Thin Films Individually Doped with N, P, or Na

N-, P-, and Na-doped ZnO films with c-axis orientation were produced by pulsed laser deposition using N2O or O2 as the reaction gas. The effects of deposition temperature and deposition pressure on the lattice structure, morphology, and electric conduction have been investigated. High gas pressure leads to large-sized grains with large grain barriers, which cause a reduced mobility. P acts as an acceptor and the number of compensating defects in the P-doped film is reduced under high O2 pressure. Na also acts as an acceptor, and the effects of high temperature on Na-doped films are encouraging as the solubility of the dopant is high. However, high temperature may cause less incorporation of N and P in the film. In the present work, p-type conduction has not been obtained in N- and P-doped films despite a wide range of processing parameters employed. Na-doped films display an increasing trend towards p-type films at high temperatures and high O2 pressures. These results provide an insight on how these dopants behave in ZnO films and indicate that the careful selection of the deposition conditions is necessary in order to obtain p-type films by pulsed laser deposition.

Effect of Substrate Temperatures on the Structural and Optical Properties of Na-Doped ZnO Thin Films

Effect of Substrate Temperatures on the Structural and Optical Properties of Na-Doped ZnO Thin Films

Structural and optical properties of Na-doped ZnO films

Zn1-xNaxO (x = 0.0–0.05) solutions have been synthesized by the sol-gel technique using Zinc acetate dihydrate and Sodium acetate which were dissolved into solvent and chelating agent. Na-doped ZnO nanoparticles were obtained from solutions to find phase and crystal structure. Na-doped ZnO films have been deposited onto glass substrate by using sol-gel dip coating system. The effects of dopant concentration on the structure, morphology, and optical properties of Na-doped ZnO thin films deposited on glass substrate are investigated. Characterization of Zn1-xNaxO nanoparticles and thin films are examined using differential thermal analysis (DTA)/thermogravimetric analysis (TGA), Scanning electron microscope (SEM) and X-Ray diffractometer (XRD). Optical properties of Zn1-xNaxO thin films were obtained by using PG Instruments UV–Vis–NIR spectrophotometer in 190–1100 nm range. The structure, morphology, and optical properties of thin films are presented.

Improvement of gas-sensing performance of ZnO nanorods by group-I elements doping

In the present work, a comparative study of gas sensor performance of group-I-doped (Na- and K-doped) ZnO nanorods to ethanol was carried out for the first time. The nanorods were grown on SiO2/Si substrates by a thermal evaporation method, using a tube furnace. X-ray photoelectron spectroscopy (XPS) results confirmed that the K and Na were doped in the ZnO nanorods. Furthermore, the XPS spectra indicated that the K-doped ZnO nanorods were grown by more oxygen vacancy compared with the Na-doped ZnO nanorods. Room temperature photoluminescence results confirmed the XPS results about oxygen vacancy level of the doped samples. The doped ZnO nanorods showed excellent gas-sensing performance against ethanol in comparison with the undoped ZnO nanorods. The K-doped ZnO nanorods revealed a high gas sensing at the operating temperature of 300 °C, while the operating temperature of the Na-doped was 280 °C. Moreover, the response and recovery time of the doped samples were shorter than those of the undoped sample. The enhanced gas-sensing performance of doped ZnO nanorods is attributed to the larger amount of oxygen vacancy in the doped ZnO nanorods. Furthermore, group-I-doped ZnO nanorods performed good selectivity compared with the undoped ZnO nanorods.

Effect of NaZn/Nai ratio on structural, optical, and electrical properties of Na-doped ZnO thin films

In this paper, Na-doped ZnO (NZO) thin films were prepared via a dip-coating sol-gel method with Na doping content in a range of 0 at. %–3 at. %. X-ray photoelectron spectroscopy analysis showed that the NaZn/Nai ratio (r) increased with Na doping contents from 1 at. %–3 at. %. The effect of the NaZn/Nai ratio on the structural, optical, and electrical properties of NZO thin films was investigated. As the NaZn/Nai ratio increased, the lattice constant exhibited a continuous increase and resulted in the presence of increasing compressive stress in the NZO films. When the NaZn/Nai ratio was less than 1 (r<1), the electron concentration of NZO films increased continuously. However, when r>1, it decreased. The Hall mobility was mainly limited by ionized impurity scattering and displayed a decrease trend with the increasing NaZn/Nai ratio. Due to the Burstein-Moss effect, the optical energy band gaps (Eg) of NZO films got slightly enlarged as compared with that of the undoped ZnO film. Considering the relationship between the Burstein-Moss shift and the carrier concentration, the enlargement of Eg was actually determined by the NaZn/Nai ratio as well as the doping content.

Ultrasensitive Room-Temperature Operable Gas Sensors Using p-Type Na:ZnO Nanoflowers for Diabetes Detection.

Ultrasensitive room-temperature operable gas sensors utilizing the photocatalytic activity of Na-doped p-type ZnO (Na:ZnO) nanoflowers (NFs) are demonstrated as a promising candidate for diabetes detection. The flowerlike Na:ZnO nanoparticles possessing ultrathin hierarchical nanosheets were synthesized by a facile solution route at a low processing temperature of 40 °C. It was found that the Na element acting as a p-type dopant was successfully incorporated in the ZnO lattice. On the basis of the synthesized p-type Na:ZnO NFs, room-temperature operable chemiresistive-type gas sensors were realized, activated by ultraviolet (UV) illumination. The Na:ZnO NF gas sensors exhibited high gas response (S of 3.35) and fast response time (∼18 s) and recovery time (∼63 s) to acetone gas (100 ppm, UV intensity of 5 mW cm-2), and furthermore, subppm level (0.2 ppm) detection was achieved at room temperature, which enables the diagnosis of various diseases including diabetes from exhaled breath.