articles by Azizollah Shafiekhani
Elsevier Ltd, 2018
Ultrasonic waves and temperature effects on graphene structure fabricated by electrochemical exfo... more Ultrasonic waves and temperature effects on graphene structure fabricated by electrochemical exfoliation method. Materials Chemistry and Physics, 212, 95-102. Abstract It is a challenge to fabricate high-quality graphene sheets due to the different effects of external factors on the fabrication process. Ultrasonic waves and temperature can be used as two important external factors to fabricate graphene. We conducted a research to study the effects of ultrasonic waves and temperature on the graphene fabrication process. To show the effects of the external factors on graphene sheets, we fabricated three samples. The first sample has been fabricated using electrochemical exfoliation method without applying any external factors. To fabricate two other samples, we used the same fabrication method but applying ultrasonic waves and temperature to homogenize the electrolyte. Second sample has been fabricated using 420 W ultrasonic waves. To fabricate third sample, 100 °C temperature has been applied to the electrolyte using heater stirrer. We studied the three fabricated samples using Fourier transform infrared spectroscopy, ultraviolet-visible, X-Ray diffraction, Energy-dispersive X-ray spectroscopy and Scanning electron microscope and Transmission electron microscopy. As a result of this research, we found that applying ultrasonic waves to homogenize the electrolyte during the fabrication process plays an important role to decrease oxygen groups and increase IG to ID rate in graphene structure.
Elsevier B.V., 2018
(2018). Synthesis of galaxite, Mn0.9Co0.1Al2O4, and its applications a novel nanocatalyst for ele... more (2018). Synthesis of galaxite, Mn0.9Co0.1Al2O4, and its applications a novel nanocatalyst for electrochemical hydrogen evolution reaction. Physica B: Condensed Matter, 538, 172-178. https://doi. Abstract A new compound Mn 0.9 Co 0.1 Al 2 O 4 nanowires were synthesized by thermal method. The resulting powder samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). We found that a set of phase transformation occurred during the process. Eventually, five phases including three spinal phases, the corundum (á-Al 2 O 3) and MnO were formed at 1100 °C.As dominant morphology, the cubic galaxite nanowires were identified by X-ray analysis. Moreover, X-ray analysis showed that Mn 3 O 4 and Co 3 O 4 nanoparticles were formed in tetragonal and cubic symmetry respectively. The SEM image revealed that a dominate morphology of product has cubic nanowires shape with an average diameter in range 38-43 nm. Furthermore, we observed that influence of temperature was very important in the nanowire formation process. Electrochemical hydrogen evolution reaction (HER) of synthetic composite was evaluated and the over potential of HER was calculated about 110 mV with low Tafel slope equal to 42 mV dec−1, which was comparable with amounts reported transition metal dichalcogenides with satisfying durability.
Nature Publishing Group, 2019
Pure and co-doped Titania thin films were prepared on aluminum substrates through the sol-gel met... more Pure and co-doped Titania thin films were prepared on aluminum substrates through the sol-gel method. The co-doped sample showed higher photocatalytic activity on benzene degradation compared to pure tio 2 under visible light illumination. XRD results showed the anatase phase for both tio 2 and co-doped tio 2 lattices with an average crystalline size of 12.9 and 10.4 nm, respectively. According to the UV-visible absorption spectra results, co-doped Titania showed higher visible light absorption compared to pure Titania. The synergistic effect of dopants caused a redshift to visible light absorption and also the lifetime of the photogenerated electron-hole were increased by induced electron levels in Titania lattice. The novelty of this study is the reactor's specific design. We employed Al mesh as thin film substrate for 3 main reasons, first, the large surface area of the Al mesh causes to increase specific surface area of the photocatalysts, also it is a formable substrate which can be engineered geometrically to decrease the shadow spots so the thin films will receive the highest light irradiation. Also, the Al mesh flexibility facilitates the procedure of reactor design to reach a minimum pressure drop of airflow while it is installed in the air conditioners or HVAC systems.
Nature Publishing Group, 2018
It is well known that all biological systems which undergo oxidative metabolism or oxidative stre... more It is well known that all biological systems which undergo oxidative metabolism or oxidative stress generate a small amount of light. Since the origin of excited states producing this light is generally accepted to come from chemical reactions, the term endogenous biological chemiluminescence is appropriate. Apart from biomedicine, this phenomenon has potential applications also in plant biology and agriculture like monitoring the germination rate of seeds. While chemiluminescence capability to monitor germination has been measured on multiple agriculturally relevant plants, the standard model plant Arabidopsis thaliana has not been analyzed for this process so far. To fill in this gap, we demonstrate here on A. thaliana that the intensity of endogenous chemiluminescence increases during the germination stage. We showed that the chemiluminescence intensity increases since the second day of germination, but reaches a plateau on the third day, in contrast to other plants germinating from larger seeds studied so far. We also showed that intensity increases after topical application of hydrogen peroxide in a dose-dependent manner. Further, we demonstrated that the entropy of the chemiluminescence time series is similar to random Poisson signals. Our results support a notion that metabolism and oxidative reactions are underlying processes which generate endogenous biological chemiluminescence. Our findings contribute to novel methods for non-invasive and label-free sensing of oxidative processes in plant biology and agriculture. Biological systems continuously generate a light (visible band electromagnetic radiation) of ultra-weak intensity 1. The currently accepted generating mechanism of this light is as follows 2. Organisms endogenously produce a small amount of reactive oxygen species (ROS) in the course of their normal metabolism and in an enhanced manner when they undergo stress. A reaction of ROS with biomolecules leads to the formation of, apart from other products, unstable biomolecular intermediates such as dioxetanes and tetraoxides which can produce excited electron species when decomposed. The primary electron excited species considered to be generated are the triplet excited carbonyls and singlet oxygen. Excitation energy can also be transferred to energy acceptor to produce secondary electron excited species. If not deactivated or quenched, these excited states decay radiatively via emission of photons. Therefore, although through a chain of events, the intensity of photon emission reflects a rate of oxidative processes ongoing in the organism (Fig. 1). This connection suggests that detection and analysis of the endogenous biological chemiluminescence (EBC) could be used to monitor oxidative processes in a non-invasive and label-free manner 1. Majority of investigations on EBC, which appears in the literature under a variety of names such as ultra-weak photon emission 1 , biophoton emission or autoluminescence 3 , is focused on microorganisms and organisms from animal kingdom reaching to a human with potential relevance in biomedical research and applications. However, a great potential of EBC is also in plant biology and agriculture 4,5. A model organism in plant biology is A. thaliana (rockcress or thale cress). Botanists and biologists began to research A. thaliana in the early 1900s, and the first systematic description of mutants was done around 1945 6. A. thaliana is now widely used in plant sciences 7 , including genetics 8 , evolution 9 , population genetics 10 , and plant development 11. Although A. thaliana has a little direct significance for agriculture, it has several traits that make it a useful model for understanding the genetic, cellular, and molecular biology of flowering plants.
American Chemical Society, 2016
A novel insight into the effect of Pt decoration on electrochemical and photoelectrochemical beha... more A novel insight into the effect of Pt decoration on electrochemical and photoelectrochemical behavior of TiO 2 nanotube arrays (TNA) was developed in this study. TNA samples were prepared via a two-step anodization of a titanium foil and decorated with Pt by a facile photodeposition method. The formation of metallic Pt were confirmed by X-ray photoelectron spectroscopy (XPS). On the basis of our calculations, the localized states and surface states induced by Pt deposition into the bandgap of titania nanotubes, play a dominant role in trapping/detrapping charge carriers and electron transfer to electrolyte. In Pt/TNAs the appropriate electrical connection between Pt nanoparticles and TNA induces sufficiently shallow traps in the vicinity of conduction band edge of TNA which creates a fast lane for electrons toward semiconductor/electrolyte interface and decreases the density of deep trap levels compared to the pristine TNA. However, there is an optimum amount for deposited Pt. Higher amount of optimum Pt can impose the monoenergetic deep trap levels which act as recombination centers.
Nature Publishing Group, 2018
Nowadays, increasing awareness of environment and fossil fuels protection stimulates intensive re... more Nowadays, increasing awareness of environment and fossil fuels protection stimulates intensive research on clean and renewable sources of energy. Production of hydrogen from water through solar-driven splitting reactions is one of the most promising approaches in the field of photoelectrochemistry (PEC). In this work we have fabricated well-aligned, highly-ordered, smooth-mouth TiO 2 nanotube arrays (TNAs) in a two-step anodization process of titanium foil, which were then used as photoelectrodes for PEC water splitting. It demonstrates for the first time correspondence between non-linear component characteristics of multiscale rough surface and crystalline structure of annealed TNAs measured at various fabrication stages and their photoelectrochemical response. The as-anodized TNAs with isotropic surface (deduced from AFM and SEM images) and largest figure of merit (according to their PEC performance) were annealed at 450 °C in air. Scale-invariant descriptors of the surface structure of the deposits involved: fractal dimension, corner frequency, roughness, size of nanostructures and their dominant habits. Moreover, X-ray diffraction data processed using the Rietveld method confirmed coexistence of various oxides, for example: TiO 2 in the form of anatase, TiO and Ti 3 O 5 phases in the TNAs under study pointing that previous well-established mechanisms of the TNA growth were to certain degree incomplete. Photoelectrochemical (PEC) water splitting is one of the most favorable approaches for H 2 production as a clean energy vector of the future. Since the work by Fujishima and Honda in 1972 1 , increasing research has been carried out towards this issue using electrodes made of various materials, e.g. semiconductors. Unfortunately, their practical application has encountered a number of technical complications. Among the metal oxides that has been taken into consideration, titanium dioxide (TiO 2) is found to be promising in PEC water splitting 2-9 due to its appropriate band-gap structure, superior chemical and optical stability and low cost. In particular, TiO 2 nanotube arrays prepared in anodization processes have numerous advantages over TiO 2 nanoparticle films resulting from facile preparation procedure, high surface-to-volume ratio for contact with the electrolyte, large light harvesting efficiency improved by light scattering into tubular morphology, and high electron mobility induced by their unidirectional channel 10,11. Some strategies such as doping or semiconductor heterocoupling were used for modification of TiO 2 nanotube arrays to be activated under visible light 12-14 .
Wiley-VCH Verlag, 2018
Knowing the exact pressure of the process has a great impact on the validity of the results, prod... more Knowing the exact pressure of the process has a great impact on the validity of the results, product quality, energy efficiency, and in some processes, on the security of work with the system. Hence, the calibration of the barometers and the accuracy of the readings should be taken seriously. Choosing the appropriate time interval for re-calibration is done according to the extent and conditions of use, uncertainty, and the inaccuracy allowed in measurement, constructive suggestion, and some other things. Failure to pay attention to the importance of periodic calibration in vacuum gauges leads to some irreparable losses in the research project and the vacuum generator system. In this study, using McLeod's barometer, the deviation of capacitive and Pirani vacuum gauges is investigated at different time intervals in the middle vacuum range, and it is determined that the vacuum gauge faces a serious deviation from the actual calibrated amount for upper and lower ranges of middle vacuum in the same working pressure range over time.
Elsevier B.V., 2019
Phenotypic variation-such as disease susceptibility and differential drug response-has a strong g... more Phenotypic variation-such as disease susceptibility and differential drug response-has a strong genetic component. Substantial effort has therefore been made to identify causal genomic variants explaining such variation among humans. Point mutations (PMs), which are single nucleotide changes in the genome, have been identified to be the most abundant form of causal genomic variants, making them useful, reliable diagnostic markers. Methods developed to genotype PMs have moved towards solid-phase assays, which not only show greater sensitivity and specificity, but also enable scalability and faster processing time. Most current assays are, however, based on fluorescent probes, which makes them relatively expensive. To develop a more cost-effective label-free genotyping method, we used a porous silicon (PSi) base as an efficient support for DNA biosensing and coupled it with reflectometric interference Fourier transform spectroscopy (RIFTS). To assess the versatility of this approach, we tested both a single nucleotide substitution in VKORC1 (-1639G > A; rs9923231) and a single nucleotide insertion in BRCA1 (5382insC; rs80357906). We demonstrate that the PSi-RIFTS method can efficiently detect both PM types with high sensitivity where hybridization of complementary DNA can be quantifiably differentiated from mismatch and non-complementary hybridization events. In addition, we show that the PSi base with immobilized DNA not only can be re-used to type further samples, but it also remains stable for 14 days, suggesting its potential for high-throughput applications.
Wiley-Liss Inc., 2019
Microstructure, micromorphology, and fractal geometry of hard dental tissues: Evaluation of atomi... more Microstructure, micromorphology, and fractal geometry of hard dental tissues: Evaluation of atomic force microscopy images. Microscopy Research and Technique, 82(11), 1884-1890. https://doi. Abstract Determining surface topography of different tissues of the molar tooth with novel analytical methods has opened new horizons in dental surface measurements which characterize tooth surface quality in dentistry. Studying surface topological measurements and comparing surface morphology of hard tissue of the molar tooth are the ultimate goals of the present study. Ten molar teeth have been chosen for investigating their surface characteristics through image processing techniques. The power spectral density (PSD) and fast Fourier transform algorithms of every molar tooth containing enamel, dentin, and cementum have determined that the characterization of surface profiles is possible. As can be seen, PSD along with fractal dimensions leads to good results for teeth surface topography. Moreover, PSD angular plot assures appropriate description of surface.
Royan Institute (ACECR), 2019
Objective: Substantial effort has been put into designing DNA-based biosensors, which are commonl... more Objective: Substantial effort has been put into designing DNA-based biosensors, which are commonly used to detect presence of known sequences including the quantification of gene expression. Porous silicon (PSi), as a nanostructured base, has been commonly used in the fabrication of optimally transducing biosensors. Given that the function of any PSi-based biosensor is highly dependent on its nanomorphology, we systematically optimized a PSi biosensor based on reflectometric interference spectroscopy (RIS) detecting the high penetrance breast cancer susceptibility gene, BRCA1. Materials and Methods: In this experimental study, PSi pore sizes on the PSi surface were controlled for optimum filling with DNA oligonucleotides and surface roughness was optimized for obtaining higher resolution RIS patterns. In addition, the influence of two different organic electrolyte mixtures on the formation and morphology of the pores, based on various current densities and etching times on doped p-type silicon, were examined. Moreover, we introduce two cleaning processes which can efficiently remove the undesirable outer parasitic layer created during PSi formation. Results of all the optimization steps were observed by field emission scanning electron microscopy (FE-SEM). Results: DNA sensing reached its optimum when PSi was formed in a two-step process in the ethanol electrolyte accompanied by removal of the parasitic layer in NaOH solution. These optimal conditions, which result in pore sizes of approximately 20 nm as well as a low surface roughness, provide a considerable RIS shift upon complementary sequence hybridization, suggesting efficient detectability. Conclusion: We demonstrate that the optimal conditions identified here makes PSi an attractive solid-phase DNA-based biosensing method and may be used to not only detect full complementary DNA sequences, but it may also be used for detecting point mutations such as single nucleotide substitutions and indels.
Electrochemical Society Inc., 2019
Among the different synthesizing method of graphene, besides having a most suitable and cost-effe... more Among the different synthesizing method of graphene, besides having a most suitable and cost-effective method, it is essential to have high-quality graphene. For this reason, the effects of the cathode electrode, the time and type of voltage variation, dispersion time, the electrolyte salt and washing solvent on process performance of electrochemical exfoliation of graphite (EE-G) were investigated. Here, we show great promise for few-layer and few-defective graphene by optimum EE-G. The most suitable condition to produce graphene is performing the process in (NH4) 2 SO 4. Moreover, the NaOH as salt is suitable in the synthesis of graphene quantum dots. Raman analysis clearly showed the G, D band, and 2D band of carbon for samples.
Pleiades Publishing, 2020
Further to traditional corrosion monitoring techniques for rated deteriorations, nowadays modern ... more Further to traditional corrosion monitoring techniques for rated deteriorations, nowadays modern electrochemical monitoring methods are promising for the control of non-rated damage mechanisms. Considering carbon steel as the most commonly used alloy in the oil and gas industry, there are special grades under NACE MR0175 standard which are immune to sour corrosion. However, according to the industry reports, their immunity can be terminated by upset conditions or on site repairs. This issue will impose either a high operational risk or exorbitant maintenance and inspection costs. Hence, in this paper, a new monitoring technology framework is discussed to lessen a catastrophic failure risk for carbon steel under wet H 2 S corrosion. In this regard, the application of a developed hybridized ZnO-graphene micro-electrode (ZnOG) with a mix band gap of 1.17 eV is studied. Under hydrogen sulfide attack and when ZnOG hybrids are excited by UV illumination, their photo-electrochemical responses are analyzed. ZnOG hybrids emanate informative impedance signals in a response to the formation of ZnO (1-x) S x nano-crystals.
Elsevier Ltd, 2020
In the present study, Ag nanoparticles were synthesized in amorphous hydrogenated carbon films on... more In the present study, Ag nanoparticles were synthesized in amorphous hydrogenated carbon films on glass substrates by RF-PECVD and RF-sputtering co-deposition method at the room temperature. Methyl orange was utilized as an analyte with different concentrations on Ag nanoparticles that were embedded in diamond-like carbon (DLC). Ultraviolet-visible (Uv-vis) spectroscopy, XRD analysis, Raman spectroscopy, Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM) were performed to characterize films. Ag-DLC with an average size of less than 14 nm was the active site for surface-enhanced Raman scattering (SERS). Sensitivity of measurements in SERS spectra was increased by these types of thin films. This method of nano-particle synthesis is cost-effective and just requires a one-step synthesis. Such substrates can be used for several times. Moreover, they are useful for biosensors because of their hardness and other properties that may be subsequently referred.
The free field realization of irreducible representations of osp (2\1) is constructed, by a unifi... more The free field realization of irreducible representations of osp (2\1) is constructed, by a unified and systematic scheme. The q-analog of this unified scheme is used to construct q-free field realization of irreducible representations of Uq(osp(2|1)). By using these realization, the two-point function of N = 1 superconformai (q-superconformal) model based on osp(2|1) (Uq(osp(2|1))) symmetry have been calculated.
The exactly and quasi-exactly solvable problems for spin one-half in one dimension on the basis o... more The exactly and quasi-exactly solvable problems for spin one-half in one dimension on the basis of a hidden dynamical symmetry algebra of Hamiltonian are discussed. We take the supergroup, OSP(2|1), as such a symmetry. A number of exactly solvable examples are considered and their spectrum are evaluated explicitly. Also, a class of quasi-exactly solvable problems on the basis of such a symmetry has been obtained.
It is shown explicitly that the correlation functions of conformal field theories (CFT) with the ... more It is shown explicitly that the correlation functions of conformal field theories (CFT) with the logarithmic operators are invariant under the differential realization of Borel subalgebra of W∞-algebra. This algebra is constructed by tensor-operator algebra of differential representation of ordinary sl(2, ℂ). This method allows us to write differential equations which can be used to find general expression for three- and four-point correlation functions possessing logarithmic operators. The operator product expansion (OPE) coefficients of general logarithmic CFT are given up to third level. © World Scientific Publishing Company.
Using a unified and systematic scheme, the free field realization of irreducible representations ... more Using a unified and systematic scheme, the free field realization of irreducible representations of osp(2|2) is constructed. By using these realizations, the correlation functions of N = 2 superconformal model based on osp(2|2) symmetry and free field representation of osp(2|2) generators are calculated. Free field representation of currents are used to determine the stress-energy tensor and the central charge of the model.
We obtain the Picard-Fuchs equations of N = 2 supersymmetric Yang-Mills theory with the exception... more We obtain the Picard-Fuchs equations of N = 2 supersymmetric Yang-Mills theory with the exceptional gauge group E6. Such equations are based on E6 spectral curve.
Liquid gas was used to produce diamond-like carbon (DLC) films on Cu, Al and steel substrates by ... more Liquid gas was used to produce diamond-like carbon (DLC) films on Cu, Al and steel substrates by a dc plasma technique. The absorption in IR reflectance indicates that the grown films are DLC. By deconvolution of room temperature UV visible spectra of the films grown at 50 mTorr and 200°C, in addition to the spectra lines reported for cathodoluminescence, photoluminescence, positron-life-time spectroscopy and electron-spin resonance, some new spectral lines were obtained. We have also seen an exciton absorption line at room temperature.
The Jahn-Teller effect is used semi-theoretically to analyse UV visible spectra of the diamond-li... more The Jahn-Teller effect is used semi-theoretically to analyse UV visible spectra of the diamond-like carbon films on Si substrates. By deconvolution of UV visible absorption spectra of the typical films, different absorption lines are found. For each sample, six lines are distinguished, which were related to V° by the Jahn-Teller effect,. Our theoretical approach, based on the distortion of the V° as the consequence of the stress in the films, is in agreement with experimental results. The shift of the Jahn-Teller lines toward the zero phonon line of V° were found to be in accordance with stress decrease in the films. The difference between room temperature and low temperature spectra is discussed. We found that the splitting of the excited state of V° in the films under stress is twice as large as that of the ground state.
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articles by Azizollah Shafiekhani