The modern development of nanotechnology requires the discovery of simple approaches that ensure the controlled formation of functional nanostructures with a predetermined morphology. One of the ...simplest approaches is the self-assembly of nanostructures. The widespread implementation of self-assembly is limited by the complexity of controlled processes in a large volume where, due to the temperature, ion concentration, and other thermodynamics factors, local changes in diffusion-limited processes may occur, leading to unexpected nanostructure growth. The easiest ways to control the diffusion-limited processes are spatial limitation and localized growth of nanostructures in a porous matrix. In this paper, we propose to apply the method of controlled self-assembly of gold nanostructures in a limited pore volume of a silicon oxide matrix with submicron pore sizes. A detailed study of achieved gold nanostructures’ morphology, microstructure, and surface composition at different formation stages is carried out to understand the peculiarities of realized nanostructures. Based on the obtained results, a mechanism for the growth of gold nanostructures in a limited volume, which can be used for the controlled formation of nanostructures with a predetermined geometry and composition, has been proposed. The results observed in the present study can be useful for the design of plasmonic-active surfaces for surface-enhanced Raman spectroscopy-based detection of ultra-low concentration of different chemical or biological analytes, where the size of the localized gold nanostructures is comparable with the spot area of the focused laser beam.
A series of Co
2+
substituted Li
0.5
Co
x
Fe
2.5−x
O
4
(x = 0.1, 0.3, 0.5) has been prepared by a citrate precursor method. The distribution of cations on A-site and B-site was studied by X-ray ...Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Mössbauer Spectroscopy. XRD confirmed the formation of ordered α-phase with prominent peaks at (220), (311), (400), (422), (511), (440). SEM and TEM confirmed the homogeneous formation of cubic phase with an average crystallite size of 50 nm. From FTIR studies, the bands at 603.78, 606.14 and 610.08 cm
−1
confirmed the formation of Fe
3+
–O
2−
bond at tetrahedral (A-site), whereas bands at 477.25, 474.84 and 471.69 cm
−1
confirmed the formation of Fe
3+
–O
2−
bond at octahedral site (B-site); shifting in frequency was observed with an increased amount of cobalt doping. Further, Raman spectra revealed the distribution of cations at tetrahedral and octahedral site by means of modes A
1g
, T
2g
, E
g
. Mössbauer spectra with two magnetic sextets confirmed two different environments of Fe
3+
ions. With an increase in cobalt doping, the crystallite size was observed to increase and hence an increase in relative area B/A ratio confirming the occupancy of Co
2+
at B-site. The temperature dependence of DC resistivity was found to decrease with an increase in temperature. With an increase in cobalt substitution, DC resistivity was observed to increase from 2.32 × 10
6
to 3.46 × 10
7
Ω cm. A decrease in activation energy is noticed in the present investigation and this observed semiconducting behavior makes these nanomaterials suitable in NTC (negative temperature coefficient) devices. These observations were explained on various models and theories.
We analyzed and organized the reasons why the amorphous wire CMOS IC magneto-impedance sensor (MI sensor) has rapidly been mass-produced as the electronic compass chips for the smart phones, mobile ...phones, and the wrist watches. Comprehensive advantageous features regarding six terms of (1) microsizing and ultralow power consumption, (2) high linearity without any hysteresis for the magnetic field detection, (3) high sensitivity for magnetic field detection with a Pico-Tesla resolution, (4) quick response for detection of magnetic field, (5) high temperature stability, and (6) high reversibility against large disturbance magnetic field shock are based on the magneto-impedance effect in the amorphous wires. We have detected the biomagnetic field using the Pico-Tesla resolution MI sensor at the room temperature such as the magneto-cardiogram (MCG), the magneto-encephalogram (MEG), and the self-oscillatory magnetic field of guinea-pig stomach smooth muscles (in vitro) that suggest the origin of the biomagnetic field is probably pulsive flow of Ca2+ through the muscle cell membrane.
The importance of magnetic micro- and nanoparticles for applications in biomedical technology is widely recognised. Many of these applications, including tissue engineering, cell sorting, biosensors, ...drug delivery, and lab-on-chip devices, require remote manipulation of magnetic objects. High-gradient magnetic fields generated by micromagnets in the range of 10
-10
T/m are sufficient for magnetic forces to overcome other forces caused by viscosity, gravity, and thermal fluctuations. In this paper, various magnetic systems capable of generating magnetic fields with required spatial gradients are analysed. Starting from simple systems of individual magnets and methods of field computation, more advanced magnetic microarrays obtained by lithography patterning of permanent magnets are introduced. More flexible field configurations can be formed with the use of soft magnetic materials magnetised by an external field, which allows control over both temporal and spatial field distributions. As an example, soft magnetic microwires are considered. A very attractive method of field generation is utilising tuneable domain configurations. In this review, we discuss the force requirements and constraints for different areas of application, emphasising the current challenges and how to overcome them.
This paper reports on the study of series of tungsten doped Ni0.5Zn0.5WxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites synthesized by a co-precipitation scheme. The crystallite size varies from ...62 to 49 nm and the scanning electron microscope (SEM) images show the spinel cubic structure of the powder sample. Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF) confirms the presence of Ni, Zn, W and Fe elements in the prepared samples. The specific surface areas of the Ni0.5Zn0.5W0.2Fe1.8O4, Ni0.5Zn0.5W0.4Fe1.6O4 and Ni0.5Zn0.5W0.6Fe1.4O4 samples calculated from Brunauer-Emmett-Teller (BET) method are 18.9 m2/g, 21.5 m2/g and 24.6 m2/g, respectively. The metal oxide pellet type resistive sensor was made for gas sensor application. These sensors are selective for hydrogen (H2) gas. The performance of these sensors for sensing hydrogen gas at a concentration of 1000 ppm in the temperature range 80–300 °C has been investigated. Platinum electrodes were deposited on all the pellets by RF sputtering technique. The subsequent decomposition of platinum oxides on the metal oxide pellet surface results in an increase in surface roughness and electrical resistivity. The sensor shows a change in resistance from 1.21 × 105 Ω to 7.83 × 104 Ω in the presence of H2 gas even at alow temperature. The composition with x = 0.2 at an optimum temperature of 180 °C showed a fast response (14 s) and recovery time (20 s). High sensitivity, low cost, long term stability, high selectivity and fast response at low temperature makes this sensor useful for industrial applications.
The study encompasses an investigation of optical, photothermal and biocompatibility properties of a composite consisting of golden cores surrounded by superparamagnetic CoFe2O4 nanoparticles. ...Accompanied with the experiment, the computational modeling reveals that each adjusted magnetic nanoparticle redshifts the plasmon resonance frequency in gold and nonlinearly increases the extinction cross‐section at ~800 nm. The concentration dependent photothermal study demonstrates a temperature increase of 8.2 K and the photothermal conversion efficiency of 51% for the 100 μg/mL aqueous solution of the composite nanoparticles, when subjected to a laser power of 0.5 W at 815 nm. During an in vitro photothermal therapy, a portion of the composite nanoparticles, initially seeded at this concentration, remained associated with the cells after washing. These retained nanoparticles effectively heated the cell culture medium, resulting in a 22% reduction in cell viability after 15 min of the treatment. The composite features a potential in multimodal magneto‐plasmonic therapies.
We present an optical modeling, photothermal and biocompatibility study of the composite nanoparticles (CNPs) consisting of Au with CoFe2O4 (CFO) nanoparticles aggregates. The optical modeling reveals nonlinear increase of the CNP absorption with increasing the number of CFO nanoparticles around Au cores with the absorption in CFO become dominant. Photothermal performance, evaluated photothermal conversion coefficient and results on photothermal therapy in vitro suggest the utilization of CNP in multimodal anticancer therapies.
Ni-Mn-Ga alloys are generally brittle, making it difficult for shaping complex components by conventional plastic deformation. Here we demonstrated that superplastic deformation capability occurred ...in a Ni47.4Mn31.5Ga21.1 alloy prepared by extrusion. The extrusions were carried out at 1273K and 1323K with extrusion ratios of 9:1, 12:1 and 16:1, in which equiaxed grains and a 〈111〉 texture were created by the coupled dislocation slip and dynamic recrystallization process. The size of the equiaxed grains, varied from 61.8–75.7μm, showed a stronger dependence on extrusion temperature than the extrusion ratio. At a strain rate of 10−3s−1 and temperature of 1073K, the extruded alloy exhibited a tensile superplastic elongation of 225.0%, much higher than that in the as-cast alloy (57.9%). This shows that the B2 phase exhibits a good superplastic deformation capacity at temperature above the ordering temperature. The mechanism of the superplasticity in the extruded alloys was determined to be the dynamic recrystallization process driven by the accumulated dislocations formed through dislocation slip.
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•Ni47.4Mn31.5Ga21.1 alloy was extruded at temperatures 1273 and 1323K with maximum extrusion ratio of 16:1.•Equiaxed grains with diameters 61.8-75.7μm and texture were created in the extruded Ni47.4Mn31.5Ga21.1 rods.•The superplasticity of the extruded alloys with maximum elongation 225 % was demonstrated at 1073K and 10–3s–1.•The superplastic deformation mechanism of Ni-Mn-Ga alloys was determined to be dislocation slip and dynamic recrystallization.
1D cylindrical magnetic nanostructures (FeNi, FeCo, FeCoP) of complex topology such as nanowires (NWs), nanotubes (NTs), multilayered nanowires, and core–shell structures are discussed from the ...perspective of engineering a wide variety of magnetic materials from hard to semihard to soft. Most of recent data are given for the materials synthesized in the pores of polymer ion‐track membranes, which makes it possible to tune systematically the geometrical parameters, morphology, and composition. The key properties including crystal and micromagnetic structure, magnetic anisotropy, and coercivity are analyzed. Co‐based NWs with uniform morphology demonstrate coercivity of more than 10 kOe due to the combination of crystalline and shape anisotropies. In the case of NTs, the demagnetizing effect is reduced owing to a helical arrangement of the magnetization, which leads to low values of coercivity and remanence magnetization. Varying the geometrical parameters of multilayered NWs, the alternating soft and semihard magnetic layers can be made within a single nanowire, which is important for spin‐valve magnetoresistance. Au‐coated ferromagnetic nanostructures are biocompatible and can be used to enhance optical absorption. Ni@Au NTs used as substrates for Raman spectroscopy demonstrate the enhancement factor of the order of 104. Some aspects related to applications of 1D magnets are briefly overviewed.
Electrochemical synthesis in pores of track‐etched polymer membranes produces ferromagnetic 1D‐nanostructures of complex topology. They show a wide variety of magnetic properties due to engineered magnetic anisotropy and coercivity. In multilayered nanowires, a sequence of hard and soft magnetic layers is realized which is important for spin‐valve giant magnetoresistance. Au coated Ni‐nanotubes are biocompatible and suitable for optical absorption.
The use of amorphous ferromagnetic microwires has potential for applications in biomedicine and biophysics. Microwire arrays create magnetic fields that are characterized by strong spatial gradients. ...A system of ferromagnetic microwires with magnetizations across the diameter may efficiently accumulate paramagnetic particles along the wire due to forced diffusion. For typical system parameters, the particles concentration at the wire surface increases more than twice for a characteristic time of 30 s. A pair of closely spaced microwires with diametric magnetizations (referred to as a dipole pair) yields a unique potential landscape with a two-dimensional minimum. The possibility of levitation of diamagnetic particles just above the dipole pair array was numerically demonstrated.
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