Journal of Nano Research Vol. 70

Abstract: Titanium dioxide thin films were deposited by radio frequency sputtering on glass substrates at different substrate temperatures. Hence, we first optimized the preparation conditions and parameters which offer better control and reproducibility of film fabrication. Then, we investigate the structural, morphological and optical properties of the prepared titanium dioxide thin films. To do so, we used several characterization techniques: X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy and ultraviolet-visible spectroscopy. Interesting results were obtained, e.g. X-ray diffraction analysis shows that the films crystallize only in the anatase tetragonal structure with a preferential orientation along the (101) plane. The intensity of the (101) diffraction peak and the crystallite size are found to increase with increasing substrate temperature, indicating a crystallinity improvement of the films. Raman peaks observed around 144, 197, 399, 515 and 639 cm⁻¹ confirm that all samples possess anatase phase and the crystallinity is enhanced with increasing substrate temperatures. The analysis of scanning electron microscopy and atomic force microscopy images demonstrates that increasing the substrate temperature significantly affects the morphology, grain size and surface roughness of TiO₂ films. The ultraviolet-visible spectroscopy analysis put into evidence that the film deposited at RT is highly transparent in the visible region with average transmittance greater than 84%. Higher substrate temperatures result in a slight decrease of transmittance. Moreover, the direct optical band gap decreases while the refractive index increases with increasing the substrate temperature. Thus, the obtained results reveal that ultraviolet-visible can be considered as a potential material for optical and photovoltaic applications.

Abstract: The purpose of this study was to create TiN films on 430 stainless steel by electrophoretic deposition. The microstructure of the coatings was investigated by SEM. The results of the X-ray diffraction showed that after the sintering, apart from the titanium nitride, no secondary phase was observed. Sintering at 1200 °C for 1 h reduced porosity and increased adhesion between particles. Corrosion current density and corrosion potential were obtained for the best coated sample of 6.3 μA.cm^-2 and-332 mV (vs. SCE) versus 37 μA.cm^-2 (decreased to one sixth) and-453 mV (vs. SCE) for bare 430 steel, respectively. Rockwell indentation test according to VDI 3198 standard and the type and volume of the fracture area was used to evaluate the interfacial adhesion of the coatings. The results showed that all coatings resist shear stress and prevent a wide range of delamination, however the 1200 °C sintered sample has more adhesion strength.

Abstract: The deposition of Zinc Sulfide (ZnS) thin films is optimized using a radio-frequency (RF) magnetron sputtering technique with variable RF power to minimize deposition steps and lower the fabrication costs. Room temperature as-deposited film growth optimization is conducted by studying their structural, morphological, optical, and electrical properties. The target power and deposition rate were related by a slope of 0.1648 and a linear correlation coefficient (R) of 0.9893. Only one significant peak for the films in the XRD pattern indicated that the films are of a single crystalline structure. All the deposited thin films exhibited a ZB structure. It is observed that the micro-strain ranged from 36.00x10^-3 to 4.14x10^-3, and that of dislocation density ranged from 6.68 to 0.08 Line/cm². The optical energy band gaps of as-deposited ZnS films at different deposition power were found from 3.31 to 3.37 eV. The average transmittance percentage was increasing from 71.63% to 84.29%, above 400 nm wavelength. The films exhibited n-type conductivity with bulk carrier density in the order of 10¹² cm^-3. The carrier concentration and mobility ranged from 2.84x10¹¹ to 3.98x10¹² cm^-3 and 1.06 to 27.68 cm²/Vs, respectively. The minimum and maximum resistivity of 1.01x10⁴ and 2.52´10⁵ Ω-cm were noted for the film deposited at 90 and 60W power, respectively.

Abstract: Heterostructure thin films of indium and zinc oxides (IZO) were prepared by spray pyrolysis from an aqueous solution of the precursors at different substrate temperatures (T_S). The polycrystalline structure of bixbyite appeared at a low temperature. The crystallinity was enhanced with the emergence of the zinc oxide phase. By increasing the T_S to 623 K, the crystallite size was increased. SEM images reveal that the deposited sample at 523 K is composed of irregularly shaped nanoparticles with a lack of links. Increasing the T_S to 573 K increases the average particle diameters, and the particles appeared as polyhedrons well connected with cavities between them, which candidates for gas sensing applications. Increasing T_S to 623 K resulted in the particles merging. NO₂ gas sensor results confirmed the enhancement of IZO sensitivity performance at 573 K. Keywords: Gas sensor, thin film metal oxide, spray pyrolysis, In₂O₃– ZnO

Abstract: The spontaneous progress in scientific bases to combat infections resulting from pathogenic microbial colonies has led to the development of nanomaterials capped with plant phytochemicals that possess exceptional bacterial growth resistance. In this study, the Authors report an economical biogenic synthesis of zinc oxide nanoparticles and its nanocomposites with silver, gold, and silver-gold bimetal to evaluate their antibacterial potency towards bacterial colonies. Further, these nanomaterials were functionalized with tea-phytochemicals for cost-effective synthesis, as a biogenic capping and reducing agent, for modulating the growth kinetics of nanomaterials, and because of their synergy with the nanomaterials in improving their antibacterial property. The identification of the biosynthesized nanomaterials was performed through various microscopic and spectroscopic techniques. The model microbes chosen to undergo this study were Escherichia coli, a gram-negative bacterium, and Staphylococcus aureus, a gram-positive bacterium. Based on the anti-bacterial essay, certain factors, such as the nature of the bacteria and nanomaterials, the production rates of superoxide radicals, etc. determined the extent of microbial growth inhibition.

Abstract: Gold nanoparticles (AuNPs) have received considerable attention recently because of their chemical properties and potential applications in the medical field.Monodispersed AuNPs in this paper are successfully synthesized by using some stabilized ligands including 3,5-dinitrobenzoic acid (DNBA) and sodium acetate (SA) dispersible in aqueous media, where NaBH₄ was used as a reducing agent to reduce KAuCl₄ from Au (III) to Au (0).The synthesized AuNPs are characterized by using UV–Vis spectroscopy to evaluate their surface plasmon resonance (SPR) absorption in a wavelength range of 500–650 nm. The size and morphology of AuNPs were determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS), where the results displayed that AuNPs with a strong SPR peak around 530 nm and 536 nm with an average size of 10 ± 1.2 nm and 14.0 ± 0.9 nm at the initial time for both DNBA-AuNP and SA-AuNP respectively. The synthesized AuNPs illustrate perfect chemical stability for more than 24 weeks in an aqueous solution. Therefore, the size of DNBA-AuNP was smaller and most stable than SA-AuNP, which may be due to 2 nitro groups that have resonance with the benzene ring leading to an increase in the stability of AuNPs.The stability of AuNPs in this work was monitored at a range of pH 2-12. Where high stability was showed at pH 6.6 ± 0.5, while the aggregation appears at more than pH 10 and less than pH.3.5.Herein, in this paper AuNPs have shown remarkable results against multi-drug resistance Pseudomonas aeruginosa. AuNP functionalized by SA ligand is shown to have a greater biological effect and be more effective than DNBA-AuNP. Due to the high stability of AuNP prepared in this work, it can be further tested to be an improved choice for more biomedical applications in the future.

Abstract: This paper reports the results of a numerical study on the thermal performance of forced convection laminar flow of nanofluids flowing through a heated horizontal annular duct considering various nanoparticles types has been investigated. A numerical study is carried out for an annular duct filled with ordinary water, and three nanoparticles types of titanium dioxide (TiO₂), alumina (Al₂O₃) and copper (Cu) formed three different nanofluids. The outer cylinder is heated by a uniform and constant heat flux while the inner cylinder is thermally insulated. A numerical solution of the partial differential equations of dimensionless cylindrical coordinates associate with boundary conditions are discretized by the finite volume technique with a second-order precision and solved via a FORTRAN program. Impacts of diverse parameters of the study such as nanoparticles volume fraction from 0 to 6% of titanium dioxide, alumina, copper, and Reynolds number on the thermal and hydrodynamic characteristic are examined. The axial and average Nusselt number increases with increasing nanoparticle concentration and Reynolds number. In addition, the skin friction coefficient decreases with increasing Reynolds number. Also, no significant effect on the skin friction coefficient with the increase in nanoparticle concentration. Furthermore, the improvement was seen higher when using nanofluids made of copper (Cu).

Abstract: A novel electrocatalyst has been developed based on polypyrol-carbon nanofiber (PPy-CNF) support material to increase the stability of Pt/ PPy-CNF/GDL electrocatalyst in direct methanol fuel cell (DMFC). A novel conducting polymer (PPy)-CNF nanocomposites was prepared by a solution dispersion technique and used to support platinum nanoparticles. For preparation of catalyst ink, 20 wt.% Pt/PPy-CNF electrocatalyst with a platinum loading of 0.4 mg cm^-2 was prepared by ethylene glycol (EG) method. Physical and electrochemical properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) imaging and cyclic voltammetry (CV) experiments. FTIR results prove the existence of PPy in the support. SEM images showed that the one–dimensional CNFs were efficaciously covered by PPy. The TEM characterization revealed that the fine Pt nanoparticles prepared by polyol method were dispersed on the surface of the electrocatalyst successfully. XRD patterns also revealed that the mean size of Pt crystal nanoparticles was about 3.69, 6.51 and 2.91 nm for Pt/PPy-CNF, Pt/CNF and Pt/C electrocatalyst respectively. The size of the PPy on carbon paper has been measured in the range of 35-40nm by AFM. Based on the electrochemical properties and acceleration tests evaluated by cyclic voltammetry measurements and Chronoamperometric experiments it was found that the as prepared Pt/PPy-CNF/GDL electrode exhibited a comparable electrochemical surface are (ECSA), MOR activity and so stability (in the presence of methanol) with respect to the Pt/CNF /GDL and Pt/C/GDL commercial one. A rather significant reduction in the peak potential of methanol electro-oxidation from 0.69V for Pt/C/GDL to 0.76V for Pt/PPy-CNF/GDL electrode indicates that an increase in the activity for MOR is achieved by replacing the C by PPy-CNF. The corresponding ECSA values for the Pt/PPy-CNF/GDL, Pt/CNF/GDL and Pt/C/GDL electrodes were 108.69, 53.93 and 17.98 m²g^-1 respectively.

Abstract: In this work, the impact of uniaxial strain on the current-voltage characteristics and the key performance metrics of armchair graphene nanoribbon (AGNR) field-effect transistors (FETs) are thoroughly studied by means of an analytical quasi-ballistic transport model that incorporates the effects of hydrogen passivation and third nearest-neighbor interactions. The model leads to compact expressions for the current-voltage characteristics of the device with only two fitting parameters and is verified by atomistic quantum simulations. The values of these parameters should be changed fromdevice to device. The obtained results reveal the tunable nature of the performance metrics of AGNRFETs with the application of tensile strain. Gate capacitance, cutoff frequency, on/off drain-current ratio, intrinsic delay and power-delay product under strain applied to the three distinct families ofAGNRs, are evaluated. This study can offer useful insight and guidance for strain engineering of GNR-based FETs.

Abstract: Nanotechnology and nanomedicine have been shown to provide a novel and safe platform to combat a variety of viruses like SARS-CoV-2. Secondary metabolites implanted into a carrier of functionalized titanium dioxide (TiO₂) nanoparticles (SMNP) were tested for efficacy versus SARS-CoV-2 infectivity, and cytotoxicity on healthy cells. Viral load; from a clinical point of view, it is not as important as the number of infective viral particles, which relates to the viral particles capable of causing the disease. To measure viral infectivity SARS-CoV-2 was placed into cell cultures and evaluating the destructive effect on cultured cells. In this system, SMNP demonstrated significant reduction of viral infectivity in vitro. Lytic plaques of viral infectivity were observed at a dilution of 4x10^-8 in VERO E6 cells, while SARS-CoV-2 preincubated with the SMNP compound, tissue damage was observed only up to the 3x10^-5 dilution. SMNP reduced the number of infective viral particles by 3 orders of magnitude. Surprising minimal toxicity to healthy cells was observed when compared to other commercially available antiseptics (glutaraldehyde, chlorine, chlorhexidine, ethanol and Lysol™), cell viability decreased only by 5.5%. SMNP is a safe and effective antiviral against SARS-CoV-2, and further studies are warranted to explore this compound further.