Nanometer Range Research Articles

Cu/MgO-based resistive random access memory for neuromorphic applications

Resistive Random Access Memory (ReRAM) is considered to be a suitable candidate for future memories due to its low operating voltage, fast access speed, and the potential to be scaled down to nanometer range for ultra-high-density storage. In addition, its ability to retain multi-level resistance states makes it suitable for neuromorphic computing applications. In this paper, we report the resistive switching performance of Cu/MgO/Pt ReRAM. Repetitive resistive switching transitions with low switching voltages (around 1 V), 102 storage windows, and multi-level memory capabilities have been obtained. Biological synaptic plasticity behavior, such as long-duration potentiation/depression and paired-pulse facilitation, has been realized by the Cu/MgO/Pt ReRAM. The simulation of convolutional neural network for handwritten digit recognition is carried out to evaluate its potential application in neuromorphic systems. Finally, the conduction mechanism of the device is studied, and a resistive switching model based on Cu conducting filaments is proposed according to the dependence of I–V results on temperature and electrode size as well as the element distribution in the device. These findings indicate the potential of Cu/MgO/Pt device as high-performance nonvolatile memories and its utilization in future computer systems and neuromorphic computing.

Microwave magnonic micro-oscillator based on a nm-thick YIG film

A numerical model describing a magnonic active ring oscillator (MARO) based on a microscopic spin-wave delay line is proposed. The model considers excitation, propagation, and reception of the magnetostatic surface waves in a yttrium iron garnet (YIG) magnetic film with a thickness in the nanometer range. The waves are excited and received with a microscopic coplanar antenna. We employed the model to analyze the influence of the YIG-film thickness and the distance between the antennas on the MARO performance characteristics. We showed that an increase in the delay time inserted by the delay line reduces the phase noise of the MARO and increases the auto-oscillation threshold. In addition, we found a relation between the auto-oscillation threshold, the thickness of the YIG film, and the distance between the antennas. The relation helps design miniature MAROs and suggests a way to reduce the phase noise of the device. The model predicts a phase noise level of −115 dBc/Hz at a 10 kHz offset from an oscillation frequency in the vicinity of 5 GHz for the MARO based on a 100 nm-thick YIG film and 56 μm of distance between the coplanar nano-antennas of the YIG-film based delay line. We believe that this is a clear way forward to microminiaturize the time-delay feedback microwave auto-oscillators. A further reduction in the phase noise down to −125 dBc/Hz at a 10 kHz offset is found in a model of cascaded connection of several microscopic spin-wave delay lines.

Transferrable Alumina Membranes as High‐Performance Dielectric for Flexible 2D Materials Devices

Abstract2D materials have shown great promise for novel electronic functionality. A common challenge for 2D materials‐based transistors is forming a high‐performance gate terminal due to the challenges of depositing a dielectric of sufficient quality and controllable thickness. Herein the van‐der‐Waals integration of a free‐standing Al2O3 dielectric membrane is demonstrated as a facile, scalable, and powerful gate dielectric. A process is developed that permits the wet transfer of an amorphous alumina layer with a finely adjustable equivalent oxide thickness (EOT) in the single nanometer range. Electrical characterization demonstrates the high breakdown field and low leakage of the dielectric and integration into 2D materials transistors reveals a high performance. The wafer‐scale uniformity of the dielectric membrane permits the formation of large‐scale flexible devices that exhibit good robustness and long‐term stability.

Nafion: A Flexible Template for Selective Structuring.

The peculiarities of crystal growth on a Nafion polymeric substrate from supersaturated aqueous solutions of initial substances were studied. The solutions were prepared based on deionized natural water and deuterium-depleted water. As was found earlier, in natural water (deuterium content 157 ± 1 ppm) polymer fibers are capable of unwinding towards the bulk of the liquid, while in deuterium-depleted water (deuterium content ≤ 3 ppm) there is no such effect. Since the distance between the unwound fibers falls in a nanometer range (which is close to the size of the unit cell of the crystal lattice), and these fibers are directed normally to the polymeric substrate, the unwinding can affect crystal growth on the polymer substrate. As was obtained in experiments with X-ray diffractometry, the unwound polymer fibers predetermine syngony of crystals, for which the unit cell is either a rectangular parallelepiped (monoclinic system) or an oblique parallelepiped (triclinic system). A quantitative theoretical model that describes the local interaction of the polymer substrate with the crystalline complexes is presented. Within this model, the polymer substrate can be considered as a flexible matrix for growing crystals.

A systematic study of oxygen vacancy mediated short range and long range magnetic ordering in BaTi1-xFexO3(x = 0.02)

A systematic study on the magnetic properties of the BaTi1-xFexO3-δ (x = 0.02) system with decrease in grain sizes is presented. The combined study of long range and short range magnetic orderings together was carried out. The samples were prepared in single tetragonal phase. The grains of the pristine sample were refined from micron to nanometer range by mechanical milling. Oxygen vacancies in different charge states gave rise to ferromagnetic and antiferromagnetic orderings among the Fe3+ ions whereas oxygen atoms acted as the medium for antiferromagnetic superexchange among the Fe3+ ions. Magnetization was found to increase significantly as a result of milling and eventually the saturation magnetization became four-fold in the sample with grain size around 18 nm. The increase in magnetization is attributed to the increase in oxygen vacancies as a consequence of increase in milling time. Clear sextet patterns in the Mössbauer spectra were observed in the sample wherein 57Fe–enriched iron was used in place of natural iron. These sextets were attributed to the presence of FM and AFM orderings among Fe3+ ions. Along with the sextet patters, we also observed a doublet pattern in Mössbauer spectra because of quadrupolar interaction of the isolated Fe3+ ions arranged in non-cubic environment and lacking any kind of magnetic interactions among them. Mössbauer Spectroscopic (MS) study revealed that FM ordering increased while AFM ordering disappeared after milling. Drastic fall of coercivity in samples with grain sizes below around 40 nm indicated that they became single magnetic domain.

Local structural and sensing properties of TiO2 thin film using the PVD method

This paper studied the structural, morphological, optical, and X-ray absorption near-edge spectroscopy (XANES) and sensing properties of titanium dioxide (TiO2) thin film. The TiO2 thin film is prepared in the thin film laboratory on a clean glass plate using a physical vapor deposition (PVD) method. The structural, morphological, Optical, and electronic properties of the fabricated samples are presented by X-ray diffraction (XRD), atomic force microscope (AFM), UV-visible, and XANES. It is found from XRD the crystallite size was ∼25.66 nm with microstrain ∼0.0064 using the Williamson-Hall (W-H) plot. The fractal terms such as grain size, roughness, kurtosis, and skewness were estimated using AFM. The grain size lies in the nanometric range and found that ∼77.21 nm. The band gap of the fabricated film is ∼3.23 eV. The XANES analysis is well supported by XRD measurement and the result found that the fabricated TiO2 thin film was anatase phase. The sensing properties of TiO2 are studied for the detection of Liquified Petroleum Gas (LPG) concentration (0-5000 ppm) at room temperature. Results found that the TiO2 film is highly sensitive and is the fast response for LPG gas sensors with a maximum sensitivity of ∼198 %.

Contacts at the Nanoscale and for Nanomaterials.

Contact scaling is a major challenge in nano complementary metal-oxide-semiconductor (CMOS) technology, as the surface roughness, contact size, film thicknesses, and undoped substrate become more problematic as the technology shrinks to the nanometer range. These factors increase the contact resistance and the nonlinearity of the current-voltage characteristics, which could limit the benefits of the further downsizing of CMOS devices. This review discusses issues related to the contact size reduction of nano CMOS technology and the validity of the Schottky junction model at the nanoscale. The difficulties, such as the limited doping level and choices of metal for band alignment, Fermi-level pinning, and van der Waals gap, in achieving transparent ohmic contacts with emerging two-dimensional materials are also examined. Finally, various methods for improving ohmic contacts' characteristics, such as two-dimensional/metal van der Waals contacts and hybrid contacts, junction doping technology, phase and bandgap modification effects, buffer layers, are highlighted.

Effect of Nb incorporation in Mo[formula omitted]BC coatings on structural and mechanical properties — Ab initio modelling and experiment

This article presents theoretical and experimental findings on the stability of orthorhombic (Mo1−xNbx)2BC phase in magnetron sputtered coatings, where molybdenum is gradually replaced by niobium. Magnetron co-sputtering of Mo2BC and Nb2BC targets was used to best preserve the metal/non-metal ratio of 1/1. The theoretical calculations were based on replacing Mo atoms in orthorhombic Mo2BC cell, thus creating a (Mo1−xNbx)2BC solid solution. It is predicted to be stable up to 37.5% of Mo atoms replaced by Nb, at which point also the elastic modulus and the shear modulus are the highest. Simultaneously, the enthalpy of formation of this material suggests that it should be more stable than, e.g. the commonly used and studied TiAlN. Experiments have confirmed that orthorhombic (Mo1−xNbx)2BC does not form at high Nb contents, and fcc NbC-like structure was observed instead. All coatings were shown to be columnar with grains in the nanometre range with amorphous regions between the columns. This led to reduced stability of the orthorhombic Mo2BC-like phase compared to the theoretical calculations. At the limit of the stability of the orthorhombic cell, the hardness of the coating was enhanced by 25% and the elastic modulus by 60%. Ab initio calculations indicate that lattice strain is responsible for the mechanical properties’ enhancement.

Instrument with an ultra-wide dynamic detection range for the optical counting and sizing of individual particles in suspensions.

The characterization of dispersions, suspensions, and emulsions is important in a wide range of scientific applications and industries. Samples can consist of different materials and a wide range of particle sizes and concentrations. A single particle sizing and counting instrument with a dynamic detection range of ≥6 decades has been developed to detect single nano- and microparticles in aqueous suspensions based on light scattering measured in two directions. Hydrodynamic focusing is employed for particle separation and to provide stable conditions for light scattering detection. This gives the advantage of size resolution in the nm range, allowing, e.g., number based size distributions, classification of nanomaterials, determination of particle agglomerates, developments for dispersion stability analysis, or cutoff of filter media. In addition, concentration determination is based on sample volume measurement with <20 nl measurement uncertainty. We present results of particle detection in a size range from approximately above 40 nm for gold nanoparticles to 8μm for polystyrene particles using a prototyped instrument of the LUMiSpoc® series produced by LUM GmbH. The data obtained demonstrate the advantages of single-particle detection, particularly for characterizing polydisperse systems, such as precise particle sizing in the nanometer range through light scattering intensity based on Mie scattering theory. In addition, we present particle concentration data based on the integrated measurement of sample volume, which allows particle concentration to be determined with an uncertainty of 2.5% (95% confidence interval). To achieve such small uncertainties, dilution series measurements must be used to correct for coincidence losses and particle adhesion.

Ellipsometry of very thin Al2O3-HfO2 stacks for nano-memory applications

Nowadays, the way towards manufacturing of advanced flash memory devices with conformal layers in stacks or laminates depends on their physical characterisation, i.e. the layer and interface thicknesses, density and composition. The transition dimension between thin and very thin stacks is in the range of few nanometres. The assumption that the oxide layer properties in the very thin stacks are constant in depth or are the same as for the bulk material values is not correct. We have applied ellipsometry (Variable Angle Spectral Ellipsometry, and Multiple Angle Incident Ellipsometry) with appropriate algorithms for data interpretation to investigate very thin Al2O3/HfO2 stacks (5 bioxide blocks) grown by ALD with a total thickness below 20 nm. Depth profiling was used in simulations as a complimentary tool. A quantitative determination of HfO2 volume fraction in the stack depth was obtained. An independent determination of the thicknesses and the composition of blocks in the stacks were achieved. Lorenz-Lorentz mixing model was applied for the estimation of dielectric properties of the different layers in the stack depth.

Plasma‐Activated Coated Glass: A Novel Platform for Optimal Optical Performance and Cell Culture Substrate Customization

Borosilicate glass surpasses polystyrene in optical quality; however, it is less frequently used for cell culture due to poor protein and cell adhesion. To overcome this impasse, the surface of glass coverslips requires functionalization to enable facile covalent attachment of proteins to promote cell attachment and differentiation. Herein, a novel approach is presented to covalently attach proteins to glass by depositing a thin layer of radical‐rich carbon film using a plasma polymerization process. The surface chemistry of these plasma‐activated coatings can be controlled by varying the gas composition used during the deposition. Mass spectrometry reveals different protein profiles attached to functionalized glass coverslips when they are exposed to cell culture media. Mouse embryonic stem cell adhesion and subsequent differentiation into neural lineage on plasma‐treated coverslips are significantly enhanced compared to bare coverslips. Importantly, the coatings are in the nanometer range, preserve the optical properties of the glass coverslips for imaging, and remain stable for at least 4 weeks in simulated body fluid. These results demonstrate the utility of covalently attaching proteins to glass for enhanced cell attachment and stem cell differentiation and provide a promising technique to achieve better outcomes in cell culture in a range of biomedical applications.

Multicolor Tunable Upconversion Luminescence via Near‐Infrared Manipulation of Population Pathways of Er3+ Ions Excited‐State Levels for Volumetric Color Displays

AbstractPrecise control over multicolor luminescence of upconversion nanoparticles (UCNPs) is of significant importance for their applications in widespread fields of research. However, realizing the tunable emissions in single UCNPs with a single lanthanide element remains a great challenge. Herein, without multiple lanthanide elements, a new strategy for the regulation of the excited‐state level population pathways of the same lanthanide activator Er3+ ion to obtain multicolor‐tunable upconversion luminescence is proposed through utilizing 980 nm coupled 1973 nm synergistic excitation. Unlike typical single wavelength excitation, the synergistic excitation may affect population pathways of the excited‐state level of Er3+ ion by adjusting excitation wavelength and power density, resulting in a dynamically adjustable change in luminescence color output. Notably, multicolor luminescence involving green, chartreuse, yellow, orange, and red can be tuned dynamically in the NaYF4:Er3+ single UCNPs by using the tunable 980/1973 nm synergistic excitation. This dynamic luminescence color variation from these UCNPs has demonstrated promising potential applications in volumetric color display. The results provide a new approach to achieve multicolor‐tunable upconversion luminescence at single nanoparticles level and open up the possibility of developing true three‐dimensional volumetric color display technologies with resolution at the nanometer range.

Excited state absorption induced optical limiting behavior of pure, single, and co-doped copper oxide nanoparticles

Underneath nano pulsed green laser (Nd: YAG), nonlinear absorption and optical limiting behavior were analyzed using Z-scan technique for pure CuO, Ag, and Mn-doped CuO (single dopant), and Ag/Mn-doped CuO (co-dopant) nanoparticles intermediated from M. Oleifera leaf extract. X-ray diffraction pattern confirmed that the synthesized nanoparticles were in good crystalline nature with a monoclinic phase and the average crystallite size was estimated in the range of nanometer. FE-SEM analysis displayed that the pure CuO, Ag-doped CuO, and Ag/Mn-doped CuO appear as nanospheres whereas Mn-doped CuO forms themselves as nanorods. The existence of Cu, O, Ag, and Mn elements in synthesized nanoparticles was affirmed by an EDAX spectrum. FT-IR analysis confirms the presence of functional groups. In zeta potential analysis the negative (-ve) potential values −34.23 mV to −34.80 mV indicate the stability of the nanoparticles. The optical study revealed that the nanoparticles possess absorbance maxima in the UV region between 260 nm to 294 nm. The occurrence of a single ionized oxygen vacancy defect was affirmed by the photoluminescence studies. Z-scan studies with nano pulsed Nd: YAG lasers show all the samples exhibit two-photon absorption (2 PA) and optical limiting behavior. In contrast with pure and co-dopant materials (Ag/Mn-doped CuO), the dominant nonlinear absorption coefficients (0.90 × 10−10 m/W, & 0.98 × 10−10 m/W) and submissive values of optical limiting threshold (1.69 × 1012 W/m2 & 1.31 × 1012 W/m2) were found for single dopant materials (Ag & Mn-doped CuO). Thus single metal doped CuO finds potential application in the creation of laser safety devices against massive power nano pulsed green laser beams.

Solubility enhancement of meloxicam by phospholipid complexation

The best solubility enhancement approach is phospholipids complexation. It has been effectively employed by a number of writers to enhance the permeability, oral bioavailability, and solubility of several medicinal substances. The meloxicam is a member of BCS Class II, and because of its poor solubility and high permeability, its clinical application may have been constrained. Therefore, it is necessary to use a method that modifies the biopharmaceutical features. In this work, meloxicam, an NSAID with demonstrated anticancer action, was combined with phospholipid to increase its solubility. Utilizing solvent evaporation, the meloxicam phospholipid complex was produced. Particle size, zeta potential, SEM analysis, in vitro drug release, and solubility were assessed for the produced complex. The results obtained in this study showed the smaller particle size in nanometer range and physical stability with desired zeta potential. Meloxicam's prolonged release from the phospholipid complex is demonstrated by the in vitro drug release investigation. The apparent solubility analysis of meloxicam phospholipid complex. Pure meloxicam showed that the drug's solubility was several times higher than that of the pure form. Hence in conclusion we can say that the phospholipid complexation could be the ideal method for solubility enhancement of drug like meloxicam.&#x0D; Keyword: Meloxicam, phospholipid complex, solubility, drug release

Synthesis and characterization of zinc oxide nanoparticles

Zinc Oxide (ZnO) nanoparticles were synthesized by hydrothermal method and analyzed for various properties. Analysis of the XRD spectra of the synthesized nanoparticles showed 46 % crystalline zincite and the average grain size was calculated to be around 39.63 nm, studies of the FTIR spectra measured over the range between 4000–500cm−1 proved the presence of Zn Obonding of the synthesized nanoparticles at 734.26 to 1473.71 cm1 .SEMimage of the synthesized nano particles showed the formation of agglomerated nanoparticles of different shapes whose size are within the nanometer range while, cyclic voltamo gram of the immobilized ZnO nanoparticles on GCE also showed significant increase in redox peak current when compared to the bare (unimmobilized) GCE. It can be concluded from the obtained results that ZnO nanoparticles have been successfully produced which can be used to improve the performance of electrochemical sensors. Keywords :- XRD analysis, FTIR studies, SEM image analysis, Cyclic voltammogram

An Adjoint Method for High-Resolution EPMA Based on the Spherical Harmonics (PN) Model of Electron Transport

Electron Probe Microanalysis (EPMA) is a nondestructive technique to determine the chemical composition of material samples in the micro- to nanometer range. Based on intensity measurements of x-radiation, the reconstruction of the material composition and structure poses an inverse problem. The reconstruction methods currently applied are based on models that assume a homogeneous or a layered structure of the studied material. To increase the spatial resolution of reconstruction in EPMA the combination of a more sophisticated reconstruction method, which is based on a model that allows complex material structure, together with multiple measurements with varying beam configurations is required. We present a deterministic k-ratio model that is based on the PN model, an approximation of the radiative transfer equation for electron transport. Our goal is to approximate a maximum likelihood solution of the inverse problem using gradient-based optimization. We detail the application of the model in the context of algorithmic differentiation, in particular by deriving its continuous adjoint formulation. Algorithmic differentiation provides the flexibility to adapt the reconstruction method to various material parametrizations and thus to regularize and take into account prior knowledge. Through examples, we verify our implementation and demonstrate the flexibility of the reconstruction/differentiation method.

Triplet-triplet annihilation-based photon upconversion using nanoparticles and nanoclusters.

The phenomenon of photon upconversion (UC), generating high-energy photons from low-energy photons, has attracted significant attention. In particular, triplet-triplet annihilation-based UC (TTA-UC) has been achieved by combining the excitation states of two types of molecules, called the sensitizer and emitter (or annihilator). With TTA-UC, it is possible to convert weak, incoherent near-infrared (NIR) light, which constitutes half of the solar radiation intensity, into ultraviolet and visible light that are suitable for the operation of light-responsive functional materials or devices such as solar cells and photocatalysts. Research on TTA-UC is being conducted worldwide, often employing materials with high intersystem crossing rates, such as metal porphyrins, as sensitizers. This review summarizes recent research and trends in triplet energy transfer and TTA-UC for semiconductor nanoparticles or nanocrystals with diameters in the nanometer range, also known as quantum dots, and for ligand-protected metal nanoclusters, which have even smaller well-defined sub-nanostructures. Concerning nanoparticles, transmitter ligands have been applied on the surface of the nanoparticles to efficiently transfer triplet excitons formed inside the nanoparticles to emitters. Applications are expanding to solid-state UC devices that convert NIR light to visible light. Additionally, there is active research in the development of sensitizers using more cost-effective and environmentally friendly elements. Regarding metal nanoclusters, methods have been established for the evaluation of excited states, deepening the understanding of luminescent properties and excited relaxation processes.

Structural, thermal and optical characteristics of Fe 1−X Zr X alloy by using mechanical milling approach: influence of Zr4+ ion

By changing Zr concentrations, Fe1-x-Zrx(x = 0.25 & 1 at%) alloys were successfully produced in an argon atmosphere using the mechanical alloying method. The produced Fe1-x-Zrxalloys were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersion x-ray analysis (EDAX), fourier transform infrared spectroscopy (FTIR), thermogravimetry analyzer (TG-DTA), ultraviolet-visible spectroscopy (UV–vis) absorption, and photoluminescence (PL) spectroscopy. According to XRD pattern analysis, the prepared alloys had a cubic crystalline structure and complete solid solution formation. The prepared alloy samples the average crystallite size was calculated using the Scherrer formula. The average crystallite size for the 0.25 at% Zr concentration is found to be 7.79 nm and 11.8 nm for the 1 at% Zr concentration. Lattice parameter changes are a very important tool for confirming the complete dissolution of the Zr atom in the Fe matrix.The TEM-dark field image confirms that the grain size is in the nanometric range (<100 nm). TEM-SAED spotty continuous ring pattern confirmed the complete solution formation is well correlated with the XRD results. The elemental composition of materials can be determined quantitatively through energy dispersive x-ray analysis in the Fe1-x-Zrxalloy. The elemental distribution of the mechanically alloyed samples shows that Zr elements are homogeneously distributed in the Fe matrix. Bands at 3428 cm−1 in the FTIR spectrum have been linked to O–H stretching vibrations. CH2 and CH stretching vibrations were associated with peaks of about 2920 cm−1 and 2850 cm−1. The weight loss and gain changes were observed and represented in the TG-DST graph; we found that overall weight changes are + 10.7% (gain) at 1023 °C for Fe 1-x-Zr x (x = 0.25 at%) alloy. However, when compared to 0.25 at% of Zr alloy, Fe-Zr (x = 1 at%) exhibits a low weight gain (+ 6.54%). The UV–visible absorbance edge revealed a blue shift when Zr was added, indicating alloy production. The energy band gap of materials was calculated using UV–vis, and it has been observed that the band gap reduces as Zr concentration increases. Zr was added to Fe1-x-Zrxalloy nanoparticles, resulting in 514 nm and 775 nm emission wavelengths. The greatest emission wavelengths and strong flawless sharp emission peaks were discovered to be between 450 nm and 550 nm. The higher PL emission peak was 514 nm at 0.25 at% of Zr.

Nanotechnology in Agriculture: Mini Review

In order to increase agricultural yields, new technologies are frequently used in agriculture. Using nanoparticles in farming, known as nano-agriculture, can provide crops with a number of advantageous impacts. Potential new uses in biotechnology and agriculture are made possible by the advent of nanotechnology and the creation of new nanomaterials and gadgets. Materials that fit into the nanometric range and have at least one dimension less than a few hundred nanometers are referred to as nanoparticles. These substances would discharge fertilizers or insecticides at predetermined times and locations. Chemical discharge into the environment and harm to other plant tissues may be minimized by using nanoparticles labelled with agrochemicals or other compounds. The important function that nanoparticles play in plants is highlighted in this review. Furthermore, nanoscience offers fresh perspectives that help us comprehend the most effective way for nanoparticles to function in plants. Better plant growth and development result from the proper understanding of the physiological, biochemical, and molecular mechanism of nanoparticles in plants.

Room temperature nanoarchitectonics of ultrafine SnO2 and Cu-doped SnO2 crystallites for advanced H2S sensing

We report a generalized route for synthesizing pure SnO2 and Cu (1 and 3 at%) doped SnO2 at room temperature with crystallite size in a nanometer range of 1.0–3.0 nm using CuCl2, nitric acid and Sn metal.