Observation of magnetic vortex configuration in non-stoichiometric Fe3O4 nanospheres.

Theoretical and micromagnetic simulation studies of magnetic nanospheres with vortex configurations suggest that such nanostructured materials have technological advantages over conventional nanosystems for applications based on high-power-rate absorption and subsequent emission. However, full experimental evidence of magnetic vortex configurations in spheres of submicrometer size is still lacking. Here, we report the microwave irradiation fabrication of Fe3O4 nanospheres and establish their magnetic vortex configuration based on experimental results, theoretical analysis, and micromagnetic simulations. Detailed magnetic and electrical measurements, together with Mössbauer spectroscopy data, provide evidence of a loss of stoichiometry in vortex nanospheres owing to the presence of a surface oxide layer, defects, and a higher concentration of cation vacancies. The results indicate that the magnetic vortex spin configuration can be established in bulk spherical magnetite materials. This study provides crucial information that can aid the synthesis of magnetic nanospheres with magnetically tailored properties; consequently, they may be promising candidates for future technological applications based on three-dimensional magnetic vortex structures.

Adsorption of NO x (x = 1, 2) Molecules on the CoFeMnSi(001) Surface: First-Principles Insights.

In this article, the adsorption of NO x (x = 1, 2) gas molecules on the (001) surface of CoFeMnSi quaternary Heusler alloys has been investigated theoretically with density functional theory (DFT) calculations. The adsorption strength was estimated with adsorption energy (E a), magnitude of charge transfer (ΔQ), charge density difference (CDD), minimum distance between molecule and surface (d), and adsorption mechanism was analyzed with density of states. The results showed that unlike half-metallic nature of the bulk phase, the pristine CoFeMnSi(001) surface exhibited metallic character caused by the emergence of electronic states of the atoms in the top-most layer of the surface. It was found that both NO and NO2 molecules undergo chemical adsorption and strongly interact with the surface evidenced by the large value of E a and ΔQ. In particular, the NO x molecule dissociates into N and O atoms for some adsorption configurations. Bader charge analysis reveals that NO x molecules act as charge acceptors by drawing charge from the surface atoms through p-d hybridization. Such findings might be useful in the development of Heusler alloys based gas sensors.

Photoelectrochemical properties of copper pyrovanadate (Cu2V2O7) thin films synthesized by pulsed laser deposition.

Polymorphic phases of copper pyrovanadate (α- and ß-Cu2V2O7) were synthesized by solid state reaction and the mechanisms governing the phase transitions have been highlighted by the ThermoGravimetric Analysis (TGA) and the Differential Scanning Calorimetry (DSC). The thermal evolution of the lattice parameters was determined by high temperature X-ray Diffraction revealing negative thermal expansion coefficients. The thermogravimetric analysis coupled with differential scanning calorimetry was also used to determine the optimal conditions to obtain a dense target in order to produce thin films by the Pulsed Laser Deposition (PLD) technique. Thin films elaborated under different oxygen pressures and temperatures exhibit a ß-Cu2V2O7 polycrystalline phase and their band gap indicates absorption in the visible range. These oxides can be used as photoanodes and their photoelectrochemical properties were studied for both bulk (α-Cu2V2O7) and thin films (ß-Cu2V2O7), as a function of the wavelength and/or intensity of the luminous flux. The best photocurrent efficiency was obtained under 450 nm illumination. Moreover, in the case of thin films, we have observed a linear evolution of the current density with the luminous flux. Finally, the photostability of thin films was measured and shows a reduction in the photocurrent of 8% after 1 h of measurement. This photocorrosion phenomenon was also highlighted by the elemental mapping performed on thin films by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectrometry (EDS).

Adsorption of ammonia on ZrOx-modified graphene nanoribbon: a first-principle investigation.

Ammonia (NH3) is a main environmental pollutant related to global warming, and reduction of its emission is the subject of multiple international agreements and regulations. Accordingly, the development of highly precise detectors to monitor its content in the environment is essential to track and limit its emission. This work examines the influence of modifying of armchair-graphene nanoribbon (AGNR) by zirconium (Zr) and its oxides on its adsorption for NH3 gas. Density functional theory (DFT) computations are utilized to investigate the band structure, adsorption energy ([Formula: see text]), adsorption length ([Formula: see text]), charge transferred ([Formula: see text]), and density of states (DOS) of pristine and modified structures with ZrOx ([Formula: see text]). ZrOx is presented to AGNR nanostructure by two pathways: substitution of carbon atoms (doping) and introduction on top of the AGNR surface (decoration). The findings of the investigation illustrate great improvement of NH3 adsorption on AGNR due to its modification. Although the adsorption energy is enhanced in general upon modification, AGNR structures where ZrOx substitute carbon atoms exhibit greater adsorption energy as compared with the decoration scheme. The maximum energy of adsorption is for the AGNR structure doped with ZrO2, followed by that doped with Zr. The adsorption energy of NH3 on the ZrO2-doped AGNR is - 10.05 eV with an adsorption length of 2.4 Å and - 0.214e charge transferred. As compared to the pristine structure, the adsorption energy for NH3 on AGNR doped with ZrO2 increases 22.2 times. Therefore, AGNR nanostructure doped with ZrOx can be considered for practical sensors for the applications of detection and control of ammonia emission.

COVID-19 Detection via Silicon Nanowire Field-Effect Transistor: Setup and Modeling of Its Function.

Biomolecular detection methods have evolved from simple chemical processes to laboratory sensors capable of acquiring accurate measurements of various biological components. Recently, silicon nanowire field-effect transistors (SiNW-FETs) have been drawing enormous interest due to their potential in the biomolecular sensing field. SiNW-FETs exhibit capabilities such as providing real-time, label-free, highly selective, and sensitive detection. It is highly critical to diagnose infectious diseases accurately to reduce the illness and death spread rate. In this work, a novel SiNW-FET sensor is designed using a semiempirical approach, and the electronic transport properties are studied to detect the COVID-19 spike protein. Various electronic transport properties such as transmission spectrum, conductance, and electronic current are investigated by a semiempirical modeling that is combined with a nonequilibrium Green's function. Moreover, the developed sensor selectivity is tested by studying the electronic transport properties for other viruses including influenza, rotavirus, and HIV. The results indicate that SiNW-FET can be utilized for accurate COVID-19 identification with high sensitivity and selectivity.

Detection of DNA Bases via Field Effect Transistor of Graphene Nanoribbon With a Nanopore: Semi-Empirical Modeling.

DNA sequencing techniques are critical in order to investigate genes' functions. Obtaining fast, accurate, and affordable DNA bases detection makes it possible to acquire personalized medicine. In this article, a semi-empirical technique is used to calculate the electron transport characteristics of the developed z-shaped graphene device to detect the DNA bases. The z-shaped transistor consists of a pair of zigzag graphene nanoribbon (ZGNR) connected through an armchair graphene nanoribbon (AGNR) channel with a nanopore where the DNA nucleobases are positioned. Non-equilibrium Green's function (NEGF) integrated with semi-empirical methodologies are employed to analyze the different electronic transport characteristics. The semi-empirical approach applied is an extension of the extended Hückel (EH) method integrated with self-consistent (SC) Hartree potential. By employing the NEGF+SC-EH, it is proved that each one of the four DNA nucleobases positioned within the nanopore, with the hydrogen passivated edge carbon atoms, results in a unique electrical signature. Both electrical current signal and transmission spectrum measurements of DNA nucleobases inside the device's pore are studied for the different bases with modification of their orientation and lateral translation. Moreover, the electronic noise effect of various factors is studied. The sensor sensitivity is improved by using nitrogen instead of hydrogen to passivate the nanopore and by adding a dual gate to surround the central semiconducting channel of the z-shaped graphene nanoribbon.

Enhancing the Sensing Performance of Zigzag Graphene Nanoribbon to Detect NO, NO2, and NH3 Gases.

In this article, a zigzag graphene nanoribbon (ZGNR)-based sensor was built utilizing the Atomistic ToolKit Virtual NanoLab (ATK-VNL), and used to detect nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3). The successful adsorption of these gases on the surface of the ZGNR was investigated using adsorption energy (Eads), adsorption distance (D), charge transfer (∆Q), density of states (DOS), and band structure. Among the three gases, the ZGNR showed the highest adsorption energy for NO with -0.273 eV, the smallest adsorption distance with 2.88 Å, and the highest charge transfer with -0.104 e. Moreover, the DOS results reflected a significant increase of the density at the Fermi level due to the improvement of ZGNR conductivity as a result of gas adsorption. The surface of ZGNR was then modified with an epoxy group (-O-) once, then with a hydroxyl group (-OH), and finally with both (-O-) and (-OH) groups in order to improve the adsorption capacity of ZGNR. The adsorption parameters of ZGNR were improved significantly after the modification. The highest adsorption energy was found for the case of ZGNR-O-OH-NO2 with -0.953 eV, while the highest charge transfer was found for the case of ZGNR-OH-NO with -0.146 e. Consequently, ZGNR-OH and ZGNR-O-OH can be considered as promising gas sensors for NO and NO2, respectively.

Nanostructured Metal Oxide-Based Acetone Gas Sensors: A Review.

Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors.

Fabrication and Characterization of Nanocomposite Flexible Membranes of PVA and Fe3O4.

Composite polymer membranes of poly(vinyl alcohol) (PVA) and iron oxide (Fe3O4) nanoparticles were produced in this work. X-ray diffraction measurements demonstrated the formation of Fe3O4 nanoparticles of cubic structures. The nanoparticles were synthesized by a coprecipitation technique and added to PVA solutions with different concentrations. The solutions were then used to generate flexible membranes by a solution casting method. The size and shape of the nanoparticles were investigated using scanning electron microscopy (SEM). The average size of the nanoparticles was 20±9 nm. Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) were utilized to investigate the structure of the membranes, as well as their vibration modes. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated the thermal stability of the membranes and the crystallinity degree. Electrical characteristics of the thin membranes were examined using impedance spectroscopy as a function of the nanoparticles' concentrations and temperatures. The resistivity of the fabricated flexible membranes was possible to adjust by controlled doping with suitable concentrations of nanoparticles. The activation energy decreased with the nanoparticles' concentrations due to the increase in charge carriers' concentrations. Therefore, the fabricated membranes may be applied for practical applications that involve the recycling of nanoparticles for multiple application cycles.

Graphene-based nanopore approaches for DNA sequencing: A literature review.

DNA (deoxyribonucleic acid) is the blueprint of life as it encodes all genetic information. In genetic disorder such as gene fusion, copy number variation (CNV) and single nucleotide polymorphism, DNA sequencing is used as the gold standard for successful diagnosis. Researchers have been conducting rigorous studies to achieve genome sequence at low cost while maintaining high accuracy and high throughput, as such sequencer devices have been developed which led to the evolvement of this technology. These devices are categorized into first, second, and third DNA sequencing generations. One successful endeavor for DNA sequencing is nanopore sequencing. This specific method is considered desirable due to its ability to achieve DNA sequencing while maintaining the required standards such as low cost, high accuracy, long read length, and high throughput. On the other hand, non-nanopore sequencing techniques require extensive preparation as well as complex algorithms, and are restricted by high cost, small throughput, and small read lengths. In this review, the concepts, history, advances, challenges, applications, and potentials of nanopore sequencing are discussed including techniques and materials used for nanopore production and DNA translocation speed control. Additionally, in light of the importance of the nanopore material configuration and fabrication, graphene which is a common and effective material will be discussed in the context of nanopore fabrication techniques. Finally, this review will shed light on some nanopore-related investigations in the area of molecular biology.