Zeitschriftenartikel: „Nanoparticule anisotrope“

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Capek, Ignác. „Noble Metal Nanoparticles and Their (Bio) Conjugates. II. Preparation“. International Journal of Chemistry 8, Nr. 1 (06.01.2016): 86. http://dx.doi.org/10.5539/ijc.v8n1p86.

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Hybrid nanoparticles of gold and silver can not only retain the beneficial features of both nanomaterials, but also possess unique advantages (synergism) over the other two types. Novel pseudospherical and anisotropic nanoparticles, bimetallic triangular nanoparticles, and core@shell nanoparticles were prepared by the different procedures for various applications and understanding both the particle evolution (nucleation) and nanoparticle anisotropy. Hybrid nanoparticles of gold and silver are considered to be low in toxicity, and exhibit facile surface functionalization chemistry. Furthermore, their absorption peaks are located in visible and near-infrared region. These nanoparticles provide significant plasmon tunability, chemical and surface modification properties, and significant advances in the growth into anisotropic nanostructures. The photoinduced synthesis can be used to prepare various (sub) nanoparticles and OD and 1D nanoparticles. Ostwald and digestive ripening provided narrower particle size distribution.

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Kijima-Aoki, Hanae, Yasushi Endo, Takamichi Miyazaki, Tsutomu Nojima, Kenji Ikeda, Nobukiyo Kobayashi, Shigehiro Ohnuma und Hiroshi Masumoto. „Shape effect of Co nanoparticles on the electric and magnetic properties of Co–SiO₂ nanogranular films“. AIP Advances 12, Nr. 3 (01.03.2022): 035229. http://dx.doi.org/10.1063/9.0000310.

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Controlling the magnetic anisotropy of nanoparticles is a crucial but challenging step for developing new magnetic functions. Here, we demonstrate a simple approach to controlling the shape of Co nanoparticles in a Co-SiO2 nanogranular film from oblate to prolate spheroid by varying the substrate rotation speed during the tandem fabrication process without changing the film composition (Co:SiO2 = 3:7). Changing the nanoparticles from oblate to prolate, increasing perpendicular length of ellipsoidal nanoparticles, changes the magnetic anisotropy axis of Co–SiO2 nanogranular films from in-plane to out-of-plane, which indicates that the shape anisotropy profoundly affects the magnetic properties. Despite the small tunneling current of a few tens of nanoamperes, a maximum tunneling magnetoresistance effect of up to 2.8 % was realized under an applied magnetic field of 12 kOe in the film plane. Achieving both in-plane and perpendicular spin-dependent tunneling, the anisotropic nanogranular films imply direction controllable tunneling materials as future topological nanoarchitecture. Such high-resistivity nanogranular films with a controllable magnetic nanoparticle shape facilitate the design of new magneto-optical devices with high withstand voltages.

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Quevedo, Daniel F., Cody J. Lentz, Adriana Coll de Peña, Yazmin Hernandez, Nahal Habibi, Rikako Miki, Joerg Lahann und Blanca H. Lapizco-Encinas. „Electrokinetic characterization of synthetic protein nanoparticles“. Beilstein Journal of Nanotechnology 11 (13.10.2020): 1556–67. http://dx.doi.org/10.3762/bjnano.11.138.

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The application of nanoparticle in medicine is promising for the treatment of a wide variety of diseases. However, the slow progress in the field has resulted in relatively few therapies being translated into the clinic. Anisotropic synthetic protein nanoparticles (ASPNPs) show potential as a next-generation drug-delivery technology, due to their biocompatibility, biodegradability, and functionality. Even though ASPNPs have the potential to be used in a variety of applications, such as in the treatment of glioblastoma, there is currently no high-throughput technology for the processing of these particles. Insulator-based electrokinetics employ microfluidics devices that rely on electrokinetic principles to manipulate micro- and nanoparticles. These miniaturized devices can selectively trap and enrich nanoparticles based on their material characteristics, and subsequently release them, which allows for particle sorting and processing. In this study, we use insulator-based electrokinetic (EK) microdevices to characterize ASPNPs. We found that anisotropy strongly influences electrokinetic particle behavior by comparing compositionally identical anisotropic and non-anisotropic SPNPs. Additionally, we were able to estimate the empirical electrokinetic equilibrium parameter (eE EEC) for all SPNPs. This particle-dependent parameter can allow for the design of various separation and purification processes. These results show how promising the insulator-based EK microdevices are for the analysis and purification of clinically relevant SPNPs.

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Belim, Sergey V. „Study of ordering in 2D ferromagnetic nanoparticles arrays: Computer simulation“. AIMS Materials Science 10, Nr. 6 (2023): 948–64. http://dx.doi.org/10.3934/matersci.2023051.

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<abstract> <p>This article describes ordering in a 2D ferromagnetic nanoparticles array by computer simulation. The Heisenberg model simulates the behavior of spins in nanoparticles. Nanoparticles interact using dipole-dipole forces. Computer simulations use the Monte Carlo method and Metropolis algorithm. Two possible types of ordering for the nanoparticles' magnetic moments are detected in the system. The magnetic anisotropy direction for the nanoparticles determines the type of ordering. If the anisotropy direction is oriented perpendicular to the substrate plane, then a superantiferromagnetic phase with staggered magnetization is realized. If the magnetic anisotropy is oriented in the nanoparticle plane, the superantiferromagnetic phase has a different structure. The nanoparticle array is broken into chains parallel to the anisotropy orientations. In one chain of nanoparticles, magnetic moments are oriented in the same way. The magnetic moments of the nanoparticles are oriented oppositely in neighbor chains. The temperature of phase transitions is calculated based on finite dimensional scaling theory. Temperature depends linearly on the intensity of the dipole-dipole interaction for both types of superantiferromagnetic transition.</p> </abstract>

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Bayram, Serene S., Klas Lindfors und Amy Szuchmacher Blum. „Tunable longitudinal modes in extended silver nanoparticle assemblies“. Beilstein Journal of Nanotechnology 7 (26.08.2016): 1219–28. http://dx.doi.org/10.3762/bjnano.7.113.

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Nanostructured materials with tunable properties are of great interest for a wide range of applications. The self-assembly of simple nanoparticle building blocks could provide an inexpensive means to achieve this goal. Here, we generate extended anisotropic silver nanoparticle assemblies in solution using controlled amounts of one of three inexpensive, widely available, and environmentally benign short ditopic ligands: cysteamine, dithiothreitol and cysteine in aqueous solution. The self-assembly of our extended structures is enforced by hydrogen bonding. Varying the ligand concentration modulates the extent and density of these unprecedented anisotropic structures. Our results show a correlation between the chain nature of the assembly and the generation of spectral anisotropy. Deuterating the ligand further enhances the anisotropic signal by triggering more compact aggregates and reveals the importance of solvent interactions in assembly size and morphology. Spectral and morphological evolutions of the AgNPs assemblies are followed via UV–visible spectroscopy and transmission electron microscopy (TEM). Spectroscopic measurements are compared to calculations of the absorption spectra of randomly assembled silver chains and aggregates based on the discrete dipole approximation. The models support the experimental findings and reveal the importance of aggregate size and shape as well as particle polarizability in the plasmon coupling between nanoparticles.

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Usov, Nikolai A., Mikhail S. Nesmeyanov, Elizaveta M. Gubanova und Natalia B. Epshtein. „Heating ability of magnetic nanoparticles with cubic and combined anisotropy“. Beilstein Journal of Nanotechnology 10 (29.01.2019): 305–14. http://dx.doi.org/10.3762/bjnano.10.29.

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The low frequency hysteresis loops and specific absorption rate (SAR) of assemblies of magnetite nanoparticles with cubic anisotropy are calculated in the diameter range of D = 20–60 nm taking into account both thermal fluctuations of the particle magnetic moments and strong magneto–dipole interaction in assemblies of fractal-like clusters of nanoparticles. Similar calculations are also performed for assemblies of slightly elongated magnetite nanoparticles having combined magnetic anisotropy. A substantial dependence of the SAR on the nanoparticle diameter is obtained for all cases investigated. Due to the influence of the magneto–dipole interaction, the SAR of fractal clusters of nanoparticles decreases considerably in comparison with that for weakly interacting nanoparticles. However, the ability of magnetic nanoparticle assemblies to generate heat can be improved if the nanoparticles are covered by nonmagnetic shells of appreciable thickness.

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Wang, Xujie, Zhenlong Dou, Chi Zhang, FangFang Deng, XiaoLin Lu, ShuangShuang Wang, Li Zhou und Tao Ding. „Polarization-controlled anisotropy in hybrid plasmonic nanoparticles“. Nanophotonics 11, Nr. 5 (27.01.2022): 1003–9. http://dx.doi.org/10.1515/nanoph-2021-0691.

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Abstract Anisotropy has played a critical role in many material systems, but its controllable creation and modulation have been a long-lasting challenge for the scientific communities. Polarization-addressed anisotropy appears more attractive among all approaches due to its excellent controllability, simplicity, and accuracy, but only a limited number of material systems are applicable for such a concept, which are largely focused on oriented growth. Here, we establish a polarization-dependent anisotropic etching system made of Au@oligomer core–shell nanoparticles (NPs). As the oligomer coatings can be photochemically degraded via two-photon photolithography, the plasmonic near-field enhancement supported by the Au NP cores renders much faster degradation of the oligomer shells along the polarization, resulting in anisotropic Au@oligomer hybrid NPs. Such shape anisotropy leads to polarization-dependent photoluminescence with embedded dyes of methylene blue, which can be used as single-particle-based polarization detector. The oligomer lobes capped at the sides of the Au NP can also function as a protection agent for anisotropic photochemical growth of Au NPs, which evolve into Au nanorods and mushrooms with controlled irradiation time. Such polarization-directed etching of oligomer shells has unique advantages of high local-selectivity, controllability, and versatility for on-chip nanofabrication, which opens many new opportunities for integrated nanophotonic devices.

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Khan, I., C. Howell, T. L. McGinnity, L. Li, R. K. Roeder und A. J. Hoffman. „Effects of anisotropy, morphology, and interparticle coupling on the far-infrared optical modes of randomly oriented ZnO nanoparticles“. Applied Physics Letters 122, Nr. 4 (23.01.2023): 041104. http://dx.doi.org/10.1063/5.0128493.

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Polar dielectric nanoparticles (NPs) with uniaxial anisotropy support two-surface phonon polariton modes inside a reststrahlen band. The effective permittivity of a randomly orientated ensemble of NPs is usually assumed to be isotropic due to averaging of the optical response over all orientations. In this work, we demonstrate that this assumption is not valid for ZnO nanoparticles, and the resultant absorption of a nanoparticle film can be tailored by the nanoparticle morphology. We measure distinct features in the absorption spectrum for films or ensembles of interacting polar dielectric NPs, which we attribute to the excitation of SPhP modes due to anisotropy in the dielectric permittivity of the NPs. We identify and characterize these modes in elliptical and rod-like ZnO NPs prepared by solvothermal synthesis and dispersed within an optically transparent matrix. Localized optical modes are identified using Fourier transform infrared absorption spectroscopy and confirmed by finite element simulations. The broadening and maxima of the modes are shown to be governed by the effects of anisotropy, nanoparticle morphology, and interparticle coupling within nanoparticle ensembles.

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Osipov, Mikhail A., Alexey S. Merekalov und Alexander A. Ezhov. „Statistical Theory of Helical Twisting in Nematic Liquid Crystals Doped with Chiral Nanoparticles“. Crystals 11, Nr. 11 (22.11.2021): 1432. http://dx.doi.org/10.3390/cryst11111432.

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A molecular field theory of the cholesteric ordering in nematic nanocomposites doped with chiral nanoparticles was developed taking into consideration chiral dispersion interaction between rod-like nanoparticles. It was shown that the inverse pitch of the cholesteric helical structure is proportional to the anisotropy of the effective polarizability and the anisotropy of the effective gyration tensor of a nanoparticle in the nematic host. The theory enables one to predict the helical sense inversion induced by a change of the low-frequency dielectric susceptibility of the nematic host phase. The components of the high-frequency effective polarizability and the effective optical activity of a gold rod-like nanoparticle in a particular nematic solvent were calculated numerically.

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Afremov, Leonid L., Tatyana N. Gnitetskaya und Elena B. Ivanova. „On the Calculation of Effective Anisotropy Constant of Nanoparticle“. Advanced Materials Research 734-737 (August 2013): 2310–13. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.2310.

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A correct composition of two kind of magnetic anisotropy of ellipsoidal nanoparticles: crystalline anisotropy and shape anisotropy - has been carried out. It was shown that according to the shape anisotropy the effective anisotropy constant can change non-monotonically. The temperature dependence of effective anisotropy constant on the angle defining the position of effective axis was calculated. It was found out if the angle between the crystalline anisotropy axis and the long axis of nanoparticle exceedsπ/4, then the effective constant as well as the position of effective axis has to change non-monotonically according to changing of temperature.

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Безверхний, А. И., А. Д. Таланцев, Ю. Е. Калинин, А. В. Ситников, В. A. Никитенко, О. В. Коплак, О. С. Дмитриев und Р. Б. Моргунов. „Магнитная анизотропия многослойных гетероструктур [(Co-=SUB=-41-=/SUB=-Fe-=SUB=-39-=/SUB=-B-=SUB=-20-=/SUB=-)-=SUB=-x-=/SUB=-(SiO-=SUB=-2-=/SUB=-)-=SUB=-100-x-=/SUB=-/Bi-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=-]-=SUB=-47-=/SUB=-“. Физика твердого тела 61, Nr. 2 (2019): 266. http://dx.doi.org/10.21883/ftt.2019.02.47124.235.

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AbstractMagnetic anisotropy values are obtained for [(Co_41Fe_39B_20)_ x (SiO_2)_100 – _ x /Bi_2Te_3]_47 heterostructures consisting of SiO_2 alternating layers, CoFeB nanoparticles distributed in them, and Bi_2Te_3 layers with ferromagnetic resonance and magnetometry. The heterostructures have anisotropy of ~10^6 erg/cm^3, which orients the magnetic moment in films plane. The films are not solid, but they disintegrate into CoFeB nanoparticles with an average diameter of 5 nm during deposition, which corresponds to the blocking magnetization temperature of ~30 K during their saturation magnetization of M _ S = 720 emu/cm^3. The relationship between anisotropy constant and thickness of the layers of the heterostructures is nonmonotonic due to competition between surface and bulk anisotropies of the ferromagnetic granules, which the films are made of.

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Gouget, Guillaume, Patricia Beaunier, David Portehault und Clément Sanchez. „New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies“. Faraday Discussions 191 (2016): 511–25. http://dx.doi.org/10.1039/c6fd00053c.

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Herein we highlight for the first time the ability to tune the stoichiometry of metal boride nanocrystals through nanoparticle synthesis in thermally stable inorganic molten salts. Two metal–boron systems are chosen as case studies: boron-poor nickel borides and boron-rich yttrium borides. We show that NiB, Ni₄B₃, Ni₂B, Ni₃B, and YB₆ particles can be obtained as crystalline phases with good selectivity. Anisotropic crystallization is observed in two cases: the first boron-rich YB₄ nanorods are reported, while boron-poor NiB nanoparticles show a peculiar crystal habit, as they are obtained as spheres with uniaxial defects related to the crystal structure. Crystallization mechanisms are proposed to account for the appearance of these two kinds of anisotropy at the nanoscale.

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Wang, Chungang, Ying Chen, Zhanfang Ma, Tingting Wang und Zhongmin Su. „Generalized Fabrication of Surfactant-Stabilized Anisotropic Metal Nanoparticles to Amino-Functionalized Surfaces: Application to Surface-Enhanced Raman Spectroscopy“. Journal of Nanoscience and Nanotechnology 8, Nr. 11 (01.11.2008): 5887–95. http://dx.doi.org/10.1166/jnn.2008.222.

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A universal and facile approach for the self-assembly of surfactant-coated anisotropic metal nanoparticles on the amino-functionalized planar and spherical surfaces based on electrostatic attraction has been explored. Large-scale and different surface coverage of monolayer film and metallodielectric core–shell nanostructures of anisotropic metal nanoparticles, including Au nanorods, AucoreAgshell nanorods and Ag nanoprisms, have been fabricated. The optical response in the visible and the near infrared (NIR) of resulting nanostructures can be easily controlled by varying the concentration of the anisotropic nanoparticle, the amount of silica particles, and the immersion time of the substrates. Large-scale anisotropic metal nanoparticle monolayer films with subtle control over the surface coverage and tunable plasmon resonance as surface-enhanced Raman spectroscopy (SERS) substrates for probing 4-aminothiophenol were investigated, which exhibited high SERS activity, stability and reproducibility.

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Wrigglesworth, E. G., und J. H. Johnston. „The use of dual reductants in gold nanoparticle syntheses“. RSC Adv. 7, Nr. 72 (2017): 45757–62. http://dx.doi.org/10.1039/c7ra07724f.

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Nguyen, Luu, Pham Phong, Pham Nam, Do Manh, Nguyen Thanh, Le Tung und Nguyen Phuc. „The Role of Anisotropy in Distinguishing Domination of Néel or Brownian Relaxation Contribution to Magnetic Inductive Heating: Orientations for Biomedical Applications“. Materials 14, Nr. 8 (09.04.2021): 1875. http://dx.doi.org/10.3390/ma14081875.

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Magnetic inductive heating (MIH) has been a topic of great interest because of its potential applications, especially in biomedicine. In this paper, the parameters characteristic for magnetic inductive heating power including maximum specific loss power (SLPmax), optimal nanoparticle diameter (Dc) and its width (ΔDc) are considered as being dependent on magnetic nanoparticle anisotropy (K). The calculated results suggest 3 different Néel-domination (N), overlapped Néel/Brownian (NB), and Brownian-domination (B) regions. The transition from NB- to B-region changes abruptly around critical anisotropy Kc. For magnetic nanoparticles with low K (K < Kc), the feature of SLP peaks is determined by a high value of Dc and small ΔDc while those of the high K (K > Kc) are opposite. The decreases of the SLPmax when increasing polydispersity and viscosity are characterized by different rates of d(SLPmax)/dσ and d(SLPmax)/dη depending on each domination region. The critical anisotropy Kc varies with the frequency of an alternating magnetic field. A possibility to improve heating power via increasing anisotropy is analyzed and deduced for Fe3O4 magnetic nanoparticles. For MIH application, the monodispersity requirement for magnetic nanoparticles in the B-region is less stringent, while materials in the N- and/or NB-regions are much more favorable in high viscous media. Experimental results on viscosity dependence of SLP for CoFe2O4 and MnFe2O4 ferrofluids are in good agreement with the calculations. These results indicated that magnetic nanoparticles in the N- and/or NB-regions are in general better for application in elevated viscosity media.

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Shaikh, Mubeena. „Effect of the Strength of Attraction Between Nanoparticles on Wormlike Micelle- Nanoparticle System“. Condensed Matter 3, Nr. 4 (13.10.2018): 31. http://dx.doi.org/10.3390/condmat3040031.

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The nanoparticle-Equilibrium polymer (or Wormlike micellar) system shows morphological changes from percolating network-like structures to non-percolating clusters with a change in the minimum approaching distance (EVP-excluded volume parameter) between nanoparticles and the matrix of equilibrium polymers. The shape anisotropy of nanoparticle clusters can be controlled by changing the polymer density. In this paper, the synergistic self-assembly of nanoparticles inside equilibrium polymeric matrix (or Wormlike micellar matrix) is investigated with respect to the change in the strength of attractive interaction between nanoparticles. A shift in the point of morphological transformation of the system to lower values of EVP as a result of a decrease in the strength of the attractive nanoparticle interaction is reported. We show that the absence of the attractive interaction between nanoparticles leads to the low packing of nanoparticle structures, but does not change the morphological behavior of the system. We also report the formation of the system spanning sheet-like arrangement of nanoparticles which are arranged in alternate layers of matrix polymers and nanoparticles.

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Osipov, Mikhail A., Alexey S. Merekalov und Alexander A. Ezhov. „Molecular-Theory of High Frequency Dielectric Susceptibility of Nematic Nanocomposites“. Crystals 10, Nr. 11 (26.10.2020): 970. http://dx.doi.org/10.3390/cryst10110970.

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A molecular-statistical theory of the high frequency dielectric susceptibility of the nematic nanocomposites has been developed and approximate analytical expressions for the susceptibility have been obtained in terms of the effective polarizability of a nanoparticle in the nematic host, volume fraction of the nanoparticles and the susceptibility of the pure nematic phase. A simple expression for the split of the plasmon resonance of the nanoparticles in the nematic host has been obtained and it has been shown that in the resonance frequency range the high frequency dielectric anisotropy of the nanocomposite may be significantly larger than that of the pure nematic host. As a result, all dielectric and optical properties of the nanocomposite related to the anisotropy are significantly enhanced which may be important for emerging applications. The components of the dielectric susceptibility have been calculated numerically for particular nematic nanocomposites with gold and silver nanoparicles as functions of the nanoparticle volume fraction and frequency. The splitting of the plasmon resonance has been observed together with the significant dependence on the nanoparticle volume fraction and the parameters of the nematic host phase.

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Saigusa, Masanari, Kazuma Tsuboi, Yuichi Konosu, Minoru Ashizawa, Akihiko Tanioka und Hidetoshi Matsumoto. „Highly Sensitive Local Surface Plasmon Resonance in Anisotropic Au Nanoparticles Deposited on Nanofibers“. Journal of Nanomaterials 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/829273.

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This paper reports the facile and high-throughput fabrication method of anisotropic Au nanoparticles with a highly sensitive local surface plasmon resonance (LPR) using cylindrical nanofibers as substrates. The substrates consisting of nanofibers were prepared by the electrospinning of poly(vinylidene fluoride) (PVDF). The Au nanoparticles were deposited on the surface of electrospun nanofibers by vacuum evaporation. Scanning electron microscopy revealed the formation of a curved Au island structure on the surface of cylindrical nanofibers. Polarized UV-visible extinction spectroscopy showed anisotropy in their LPR arising from the high surface curvature of the nanofiber. The LPR of the Au nanoparticles on the thinnest nanofiber with a diameter of ~100 nm showed maximum refractive index (RI) sensitivity over 500 nm/RI unit (RIU). The close correlation between the fiber diameter dependence of the RI sensitivity and polarization dependence of the LPR suggests that anisotropic Au nanoparticles improve RI sensitivity.

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Chandra, Grish, R. C. Srivastava und V. R. Reddy. „Modification in Magnetic Properties of CoFe₂O₄ Ferrite Nanoparticles Induced by 100MeV O⁺⁷ Ion Irradiation“. IOP Conference Series: Materials Science and Engineering 1291, Nr. 1 (01.09.2023): 012011. http://dx.doi.org/10.1088/1757-899x/1291/1/012011.

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Abstract In this work CoFe2O4 ferrite nanoparticles were prepared via sol-gel method using citric acid as chelating agent. The prepared nanoparticles was sintered at 700°C and the crystallite size is found 34 nm. In this investigation the effect of irradiation of 100 MeV O+7 beam on these nanoparticles with two fluences 5×1012 and 5×1013 ions/cm2 are studied. After irradiation the crystallite size is found to be reduced which is confirmed by transmission electron micrograph. The retentivity and coercivity changes with a measurable value while the saturation magnetization reduces slightly. The value of remanent magnetization increased from 30 emu/g to 34.6 emu/g, it can be attributed to increase of magnetic hardness. The increase in squareness ratio after irradiation leads to increase in anisotropic energy barrier of CoFe2O4 ferrite nanoparticles. Anisotropy field about doubles after irradiation and corresponding anisotropy constant also doubles with the used fluences.

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Zaluzhnyy, Ivan, Ruslan Kurta, Marcus Scheele, Frank Schreiber, Boris Ostrovskii und Ivan Vartanyants. „Angular X-ray Cross-Correlation Analysis (AXCCA): Basic Concepts and Recent Applications to Soft Matter and Nanomaterials“. Materials 12, Nr. 21 (23.10.2019): 3464. http://dx.doi.org/10.3390/ma12213464.

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Angular X-ray cross-correlation analysis (AXCCA) is a technique which allows quantitative measurement of the angular anisotropy of X-ray diffraction patterns and provides insights into the orientational order in the system under investigation. This method is based on the evaluation of the angular cross-correlation function of the scattered intensity distribution on a two-dimensional (2D) detector and further averaging over many diffraction patterns for enhancement of the anisotropic signal. Over the last decade, AXCCA was successfully used to study the anisotropy in various soft matter systems, such as solutions of anisotropic particles, liquid crystals, colloidal crystals, superlattices composed by nanoparticles, etc. This review provides an introduction to the technique and gives a survey of the recent experimental work in which AXCCA in combination with micro- or nanofocused X-ray microscopy was used to study the orientational order in various soft matter systems.

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Su, K. P., Zhong Wu Liu, X. X. Shan, Z. G. Zheng, X. C. Zhong, Hong Ya Yu und De Chang Zeng. „Synthesis and Characterization of Core-Shell Structured Bimagnetic Cobalt-Coated Iron Nanoparticles“. Materials Science Forum 688 (Juni 2011): 370–75. http://dx.doi.org/10.4028/www.scientific.net/msf.688.370.

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Core-shell structured nanoparticles with ferromagnetic core (Fe) and shell (Co) were prepared by a chemical reduction method. By adjusting the deposition parameters, the core-shell particles with various Fe:Co molar ratios were obtained. The saturation magnetization decreased with the increase of Cobalt content. The properties of core-shell nanoparticles synthesized under a magnetic field were compared with those prepared without a magnetic field. For the nanoparticles prepared without magnetic filed, the coercivity (Hc) increased with increasing Co content due to the large anisotropy of Co, whereas for the nanoparticles prepared under a magnetic field, theHcwas much lower. The ZFC/FC curves suggested that these particles were ferromagnetic at room temperature. The anisotropy constant K at 340K for core-shell nanoparticle is estimated to be 0.83×105erg/cm3. The second ferromagnetic phase transition may occur at the temperature lower than 25 K, which led to a drastic change of magnetization at low temperatures.

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Sekar, S., V. Lemaire, H. Hu, G. Decher und M. Pauly. „Anisotropic optical and conductive properties of oriented 1D-nanoparticle thin films made by spray-assisted self-assembly“. Faraday Discussions 191 (2016): 373–89. http://dx.doi.org/10.1039/c6fd00017g.

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We report on the fabrication of oriented anisotropic metal nanoparticle thin films made by Grazing Incidence Spraying (GIS) and on the anisotropic plasmonic properties of the resulting thin films. Gold nanorods of two different aspect ratios and silver nanowires were self-assembled as a uniaxially aligned monolayer with the GIS approach. In particular, we examine the influence of the nanowire/nanorod length and diameter on the degree of ordering determined by electron microscopy pictures. Furthermore, we show that the anisotropy of the optical properties (probed by polarized UV-visible-near infrared spectroscopy) strongly depend on the quality of alignment. The prepared monolayer thin films have an orientation order parameter of up to 0.83 for silver nanowires, which is reflected in an optical anisotropy of 0.57 in the UV-visible and 0.76 in the near infrared through the selective excitation of transverse and longitudinal surface plasmon resonance modes. The electronic transport in oriented silver nanowire monolayers is also shown to be highly directional, with the sheet resistance varying over almost an order of magnitude depending on the transport direction. Such anisotropic conductive plasmonic thin films may find applications in various fields like biochemical sensing, energy transport and harvesting or optoelectronic devices.

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Selvakumaran, Lakshmi, und Gilles Lubineau. „Validation of Micro-Meso Electrical Relations for Laminates with Varying Anisotropy“. Applied Mechanics and Materials 784 (August 2015): 435–42. http://dx.doi.org/10.4028/www.scientific.net/amm.784.435.

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For electrical impedance tomography (EIT) to be useful in monitoring transverse cracks in composites, it is imperative to establish the relation between conductivity and cracking density. Micro to meso scale homogenization has been developed for classical carbon fiber reinforced polymer (CFRP) laminate which provides such a relationship. However, we have shown in previous studies that the detectability of transverse cracks in such CFRP, which are characterized by very anisotropic electrical properties, is poor. Then, it is better to lower the electrical anisotropy, which can be achieved by various technologies including doping the polymeric resin by conductive nanoparticles. However, the validity of mesoscale homogenization for laminates with such low anisotropy has not been tested before. Here, we show that the mesoscale damage indicator is intrinsic for composites with varying anisotropy.

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Pundir, Sudhir Kumar, Mukesh Kumar Awasthi und Vivek Kumar. „Soret Driven Instability in an Anisotropic Porous Layer Saturated by a Darcy-Maxwell Nanofluid“. Journal of Nanofluids 11, Nr. 5 (01.08.2022): 795–802. http://dx.doi.org/10.1166/jon.2022.1874.

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A theoretical and numerical study has been made of a Soret driven Darcy-Maxwell anisotropic porous medium filled with nanofluid. The linear theory of stability analysis is employed and the well-known normal mode procedure is used to test the stability/instability. It is established that stationary mode Rayleigh number independent from relaxation time parameter and modified particle-density increment. The modified particle-density increment does not affect the oscillatory Rayleigh number. A comparison between an isotropic porous medium and an anisotropic porous medium has been made. The presence of nanoparticles helps in early convection while the solute parameter tries to stop early convection. The solute parameter does not change its destabilizing nature with the Soret parameter although the Soret parameter creates resistance in early convection. Soret effect increases the stationary Rayleigh number means to delay the convection. The mechanical anisotropy parameter is responsible for early convection while thermal anisotropy parameters delay the convection.

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Thanh Nguyen, Hoang, und Tuan Manh Nguyen. „Investigation of Magnetic Properties of Magnetic Poly (glycidyl methacrylate) Microspheres: Experimental and Theoretical“. Advances in Materials Science and Engineering 2021 (24.06.2021): 1–10. http://dx.doi.org/10.1155/2021/6676453.

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Biocompatible magnetic poly (glycidyl methacrylate) microsphere is a novel nanocomposite with a myriad of promising bioapplications. Investigation of their characteristics by experimental analysis methods has also been carried out in the past. However, a survey of the magnetic anisotropy constant has not been mentioned and the influence of the poly (glycidyl methacrylate) polymer matrix on the Fe3O4 magnetite nanoparticles embedded inside has also not been discussed. Moreover, the accurate characterization of the magnetite nanoparticle size distribution remains challenging. In this paper, we present an effective approach was used to solve these problems. First of all, we combine both experiment and theory to estimate the effective magnetic anisotropy constant. Besides that, we implement an accurate method to determine magnetite nanoparticle size distribution in the magnetic poly (glycidyl methacrylate) microspheres composite nanomaterial.

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Andrade, Priscyla L., Valdeene A. J. Silva, Kathryn L. Krycka, Juscelino B. Leão, I.-Lin Liu, Maria P. C. Silva und J. Albino Aguiar. „The effect of organic coatings in the magnetization of CoFe₂O₄ nanoparticles“. AIP Advances 12, Nr. 8 (01.08.2022): 085102. http://dx.doi.org/10.1063/5.0078167.

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Cobalt ferrite has attracted considerable attention in recent years due to its unique physical properties, such as high Curie temperature, large magnetocrystalline anisotropy, high coercivity, moderate saturation magnetization, large magnetostrictive coefficient, and excellent chemical stability and mechanical hardness. This work focuses on the neutron scattering results of the magnetic response characteristics of polysaccharide fucan coated cobalt ferrite nanoparticles for their application as a solid support for enzyme immobilization and other biotechnology applications. Here, we unambiguously show that surfactant coating of nanoparticles can significantly affect their magnetic response throughout the nanoparticle volume. While it has been recently suggested that oleic acid may preserve nanoscale magnetism in ferrites, we present evidence that the influence of oleic acid on the magnetic response of CoFe2O4 nanoparticles is more than a surface effect, instead pervading throughout the interior of the nanoparticle.

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Srinath, S., P. Poddar, Deepti S. Sidhaye, B. L. V. Prasad, J. Gass und H. Srikanth. „Static and Dynamic Magnetic Properties of Co Nanoparticles“. Journal of Nanoscience and Nanotechnology 8, Nr. 8 (01.08.2008): 4086–91. http://dx.doi.org/10.1166/jnn.2008.an06.

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Co nanoparticles have been synthesized using wet-chemical methods. As-synthesized particles show a sharp low temperature peak in zero-field cooled (ZFC) magnetization well below the blocking transition temperature and this feature is associated with surface spin disorder. We have investigated the dynamic magnetic properties of Co using ac susceptibility and resonant RF transverse susceptibility (TS). We also studied the memory and relaxation effects in these nanoparticle systems. From these measurements we show a typical blocking behavior of an assembly of superparamagnetic nanoparticles with a wide distribution of blocking temperatures. The transverse susceptibility measurements on these particles show the presence of anisotropy even above the blocking temperature. The role of surface anisotropy and the size distribution of the particles on the observed memory and magnetic relaxation effects are discussed.

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Kúdelčík, Jozef, Peter Bury, Štefan Hardoň, Peter Kopčanský und Milan Timko. „Influence Of Nanoparticles Diameter On Structural Properties Of Magnetic Fluid In Magnetic Field“. Journal of Electrical Engineering 66, Nr. 4 (01.07.2015): 231–34. http://dx.doi.org/10.2478/jee-2015-0037.

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AbstractThe properties of magnetic fluids depend on the nanoparticle diameter, their concentration and the carrier liquid. The structural changes in magnetic fluids with different nanoparticle diameter based on transformer oils TECHNOL and MOGUL under the effect of a magnetic field and temperature were studied by acoustic spectroscopy. At a linear and jump changes of the magnetic field at various temperatures a continuous change was observed of acoustic attenuation caused by aggregation of the magnetic nanoparticles to structures. From the anisotropy of acoustic attenuation and using the Taketomi theory the basic parameters of the structures are calculated and the impact of nanoparticle diameters on the size of structures is confirmed.

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FAZELZADEH, S. AHMAD, und ESMAEAL GHAVANLOO. „RADIAL VIBRATION CHARACTERISTICS OF SPHERICAL NANOPARTICLES IMMERSED IN FLUID MEDIUM“. Modern Physics Letters B 27, Nr. 26 (10.10.2013): 1350186. http://dx.doi.org/10.1142/s0217984913501868.

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The vibrational properties of nanoparticles coupled with surrounding media are of recent interest. These nanostructures can be modeled as nanoscale spherical solids. In this paper, new formulation based on the nonlocal elasticity theory is proposed to investigate radial vibrations of the nanoparticles immersed in fluid medium. The nanoparticles with size ranging from 1 nm to 10 nm are discussed. The nanoparticles are considered elastic, homogeneous and anisotropic. Along the contact surface between the nanoparticle and the fluid, the compatibility requirement is applied and the Bessel functions are used to obtain the complex frequency equation. Numerical results are evaluated, and their comparisons are performed to confirm the validity and accuracy of the proposed method. Furthermore, the model is used to elucidate the effect of small scale on the vibration of several nanoparticles. Our results show that the small scale is essential for the radial vibration of nanoparticles when the nanoparticle radius is smaller than 2 nm.

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Laramy, Christine R., Lam-Kiu Fong, Matthew R. Jones, Matthew N. O'Brien, George C. Schatz und Chad A. Mirkin. „Understanding nanoparticle-mediated nucleation pathways of anisotropic nanoparticles“. Chemical Physics Letters 683 (September 2017): 389–92. http://dx.doi.org/10.1016/j.cplett.2017.01.050.

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Osipov, Mikhail A., Alexey S. Merekalov und Alexander A. Ezhov. „Effect of Rod-like Nanoparticles on the Dielectric Susceptibility of Nematic Nano-Composites: A Molecular Theory“. Crystals 12, Nr. 12 (15.12.2022): 1827. http://dx.doi.org/10.3390/cryst12121827.

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The effect of rod-like nanoparticles on the high-frequency dielectric susceptibility of the nematic nano-composites has been investigated in the framework of a molecular theory. Analytical expressions for the components of the effective polarizability of a rod-like nanoparticle in the nematic host have been obtained and used in the calculations of the dielectric susceptibility of the composites as functions of the nanoparticle volume fraction. Numerical calculations of the susceptibility have been undertaken using the nematic liquid crystal 5CB as a host doped with either gold or silver particles for different values of the concentration of nanoparticles. It has been shown that the rod-like nanoparticles have a much stronger effect on the components of the dielectric susceptibility of the nano-composites including, in particular, the one with gold nanoparticles in the vicinity of the plasmon resonance. The main conclusion is that at sufficiently large concentration of nanoparticles, the anisotropy of the dielectric susceptibility of the nano-composites may even change the sign with an increasing concentration which may be important for various applications.

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Krylova, Karina A., Liliya R. Safina, Ramil T. Murzaev, Julia A. Baimova und Radik R. Mulyukov. „Effect of Nanoparticle Size on the Mechanical Strength of Ni–Graphene Composites“. Materials 14, Nr. 11 (04.06.2021): 3087. http://dx.doi.org/10.3390/ma14113087.

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The effect of the size of nickel nanoparticles on the fabrication of a Ni–graphene composite by hydrostatic pressure at 0 K followed by annealing at 1000 and 2000 K is studied by molecular dynamics simulation. Crumpled graphene, consisting of crumpled graphene flakes interconnected by van der Waals forces is chosen as the matrix for the composite and filled with nickel nanoparticles composed of 21 and 47 atoms. It is found that the main factors that affect composite fabrication are nanoparticle size, the orientation of the structural units, and temperature of the fabrication process. The best stress–strain behavior is achieved for the Ni/graphene composite with Ni47 nanoparticle after annealing at 2000 K. However, all of the composites obtained had strength property anisotropy due to the inhomogeneous distribution of pores in the material volume.

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Izzati Khalidah Khalid, Nor Fadzillah Mohd Mokhtar und Nurul Hafizah Zainal Abidin. „Thermogravitational Convection in a Controlled Rotating Darcy-Brinkman Nanofluids Layer Saturated in an Anisotropic Porous Medium Subjected to Internal Heat Source“. Journal of Advanced Research in Numerical Heat Transfer 14, Nr. 1 (11.10.2023): 70–90. http://dx.doi.org/10.37934/arnht.14.1.7090.

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Thermogravitational convection in a controlled rotating Darcy-Brinkman nanofluids layer saturated in an anisotropic porous medium heated from below is Thermogravitational convection in a controlled rotating Darcy-Brinkman nanofluids layer saturated in an anisotropic porous medium heated from below is investigated. The presence of a uniformly distributed internal heat source and considers the Brinkman model for different boundary conditions: rigid-rigid, free-free, and lower-rigid and upper-free are considered. The effect of a control strategy involving sensors located at the top plate and actuators positioned at the bottom plate of the nanofluids layer is analysed. Linear stability analysis based on normal mode technique is employed. The resulting eigenvalue problem is solved numerically using the Galerkin method implemented with Maple software. The model used for the nanofluids associates with the mechanisms of Brownian motion and thermophoresis. The influences of the internal heat source strength, mechanical anisotropy parameter, modified diffusivity ratio, nanoparticles concentration Darcy-Rayleigh number and nanofluids Lewis number are found to advance the onset of convection. Conversely, the Darcy number, thermal anisotropy parameter, porosity, rotation, and controller effects are observed to slow down the process of convective instability.investigated. The presence of a uniformly distributed internal heat source and considers the Brinkman model for different boundary conditions: rigid-rigid, free-free, and lower-rigid and upper-free are considered. The effect of a control strategy involving sensors located at the top plate and actuators positioned at the bottom plate of the nanofluids layer is analysed. Linear stability analysis based on normal mode technique is employed. The resulting eigenvalue problem is solved numerically using the Galerkin method implemented with Maple software. The model used for the nanofluids associates with the mechanisms of Brownian motion and thermophoresis. The influences of the internal heat source strength, mechanical anisotropy parameter, modified diffusivity ratio, nanoparticles concentration Darcy-Rayleigh number and nanofluids Lewis number are found to advance the onset of convection. Conversely, the Darcy number, thermal anisotropy parameter, porosity, rotation, and controller effects are observed to slow down the process of convective instability.

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Gilbert, Benjamin. „Finite size effects on the real-space pair distribution function of nanoparticles“. Journal of Applied Crystallography 41, Nr. 3 (07.05.2008): 554–62. http://dx.doi.org/10.1107/s0021889808007905.

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The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.

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Soleimani, Hojjatollah, Surajudden Sikiru, Hassan Soleimani, Leila Khodapanah und Maziyar Sabet. „Impact of Anisotropy and Electromagnetic Modified Effect on Fluid Mobility in Reservoir Sandstone“. Defect and Diffusion Forum 429 (12.12.2023): 179–88. http://dx.doi.org/10.4028/p-wmzwk3.

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The oil and gas sector faces challenges in optimizing oil recovery from reservoirs due to trapped oil due to interfacial tension and surface forces. Characterizing anisotropic dielectric properties is crucial. The petroleum business is quickly changing, and a massive advancement in the application of nanotechnology in this field is envisaged. Because magnetic nanoparticles (MNP) are solid, tiny, and adsorb at the oil-water interface, they might be helpful. The interaction of MNP with electromagnetic waves appears to be capable of altering interfacial tension, which will boost oil recovery. The interaction of an oscillating B-field of electromagnetic waves with magnetic domains causes energy dissipation due to a shift in magnetic anisotropy from the easy axis of magnetization. The use of anisotropy energy in mobilizing oil in a porous media has recently been investigated. BaTiO3 nanoparticles (NPs) were synthesized for this purpose, and their influence on oil mobility under electromagnetic waves (EM) was studied. The anisotropy energy was computed and determined to be 7.34kJ/mol. Under EM, the easy axis magnetization of BaTiO3 nanoparticles oscillates and changes direction continually, facilitating oil mobilization in the porous media. The EM findings for reducing interfacial tension (IFT) between oil and water ranged from 4.5mN/m to 0.89mN/m. Under EM, it was discovered that BaTiO3 nanoparticles might lower IFT by roughly 60%. The IFT must be small enough to allow oil flow during mobilization. The simulation findings demonstrate that the adsorption energy of n-hexane on the surface of hematite has a 47.9% lower energy value than water. With a 115.4% percentage difference, the stress autocorrelation function of n-hexane with hematite is greater than that of water.

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Amirabadizadeh, Ahmad, Amir Zelati und Zahra Lotfollahi. „Studying the Temperature Effect on the Magnetic Behavior of Fe₃O₄ Water Based Ferrofluid“. Key Engineering Materials 744 (Juli 2017): 468–72. http://dx.doi.org/10.4028/www.scientific.net/kem.744.468.

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In this study, Iron Oxide (Fe3O4) nanoparticles water based ferrofluid, was synthesized by co-precipitation method. XRD was used to study the structural characterization of the sample and to measure the size of the crystallites (using Scherrer equation). TEM was utilized to examine the shape, the size distribution and the morphology of the nanoparticles. VSM was carried out to measure the magnetic properties (like Mr, Ms and Hc) of the Fe3O4 (magnetite) nanoparticle and magnetite ferrofluid at 80 and 300 K. The results indicate that the average size of the magnetite roughly spherical shape nanoparticles is 13nm. The VSM results show that the magnetite ferrofluid contains single domain magnetic nanoparticles with superparamagnetic behavior. In addition, the magnetic measurements demonstrate that with decreasing the temperature of the ferrofluid, its magnetic softness decreases while its anisotropy increases.

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Chen, Sen, Juncheng E und Sheng-Nian Luo. „SLADS: a parallel code for direct simulations of scattering of large anisotropic dense nanoparticle systems“. Journal of Applied Crystallography 50, Nr. 3 (13.04.2017): 951–58. http://dx.doi.org/10.1107/s1600576717004162.

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SLADS(http://www.pims.ac.cn/Resources.html), a parallel code for direct simulations of X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations, is presented. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. Parallelization is achieved in real space for the sake of memory limitation. The system sizes attempted are up to one billion atoms, and particle concentrations in dense systems up to 0.36. Anisotropy is explored in terms of superlattices. One- and two-dimensional small-angle scattering or diffraction patterns are obtained.SLADSis validated self-consistently or against cases with analytical solutions.

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Tan, Michael, und Mary Donnabelle Balela. „One-Pot Synthesis of High Aspect Ratio Copper Nanowires in Aqueous Solution“. Advanced Materials Research 1119 (Juli 2015): 34–37. http://dx.doi.org/10.4028/www.scientific.net/amr.1119.34.

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We report a one-pot, low temperature process for the synthesis of high-aspect ratio copper nanowires in aqueous solution for 1 hr. Ethylene diamine (EDA) was utilized to promote anisotropic reduction of Cu (II) by hydrazine. Cu nanowires with mean diameters around 90 nm and lengths exceeding 50 μm were synthesized using 180 mM EDA at 60°C, giving an effective aspect ratio of about 450. Without EDA, nanoparticle growth is observed. The synthesis temperature was also significant in limiting nanoparticle formation. Decreasing the temperature resulted to 1D growth and fewer nanoparticles.

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Tolea, Felicia, Monica Sorescu, Lucian Diamandescu, Nicusor Iacob, Mugurel Tolea und Victor Kuncser. „Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures“. Nanomaterials 12, Nr. 6 (12.03.2022): 938. http://dx.doi.org/10.3390/nano12060938.

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MoO2-Fe2O3 nanoparticle systems were successfully synthesized by mechanochemical activation of MoO2 and α-Fe2O3 equimolar mixtures throughout 0–12 h of ball-milling. The role of the long-range ferromagnetism of MoO2 on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mössbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO2, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mössbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects.

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Zhou, Wenjie, Zizhuo Liu, Ziyin Huang, Haixin Lin, Devleena Samanta, Qing-Yuan Lin, Koray Aydin und Chad A. Mirkin. „Device-quality, reconfigurable metamaterials from shape-directed nanocrystal assembly“. Proceedings of the National Academy of Sciences 117, Nr. 35 (17.08.2020): 21052–57. http://dx.doi.org/10.1073/pnas.2006797117.

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Anchoring nanoscale building blocks, regardless of their shape, into specific arrangements on surfaces presents a significant challenge for the fabrication of next-generation chip-based nanophotonic devices. Current methods to prepare nanocrystal arrays lack the precision, generalizability, and postsynthetic robustness required for the fabrication of device-quality, nanocrystal-based metamaterials [Q. Y. Lin et al. Nano Lett. 15, 4699–4703 (2015); V. Flauraud et al., Nat. Nanotechnol. 12, 73–80 (2017)]. To address this challenge, we have developed a synthetic strategy to precisely arrange any anisotropic colloidal nanoparticle onto a substrate using a shallow-template-assisted, DNA-mediated assembly approach. We show that anisotropic nanoparticles of virtually any shape can be anchored onto surfaces in any desired arrangement, with precise positional and orientational control. Importantly, the technique allows nanoparticles to be patterned over a large surface area, with interparticle distances as small as 4 nm, providing the opportunity to exploit light–matter interactions in an unprecedented manner. As a proof-of-concept, we have synthesized a nanocrystal-based, dynamically tunable metasurface (an anomalous reflector), demonstrating the potential of this nanoparticle-based metamaterial synthesis platform.

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Scarabelli, Leonardo. „Recent advances in the rational synthesis and self-assembly of anisotropic plasmonic nanoparticles“. Pure and Applied Chemistry 90, Nr. 9 (25.09.2018): 1393–407. http://dx.doi.org/10.1515/pac-2018-0510.

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Abstract The field of plasmonics has grown at an incredible pace in the last couple of decades, and the synthesis and self-assembly of anisotropic plasmonic materials remains highly dynamic. The engineering of nanoparticle optical and electronic properties has resulted in important consequences for several scientific fields, including energy, medicine, biosensing, and electronics. However, the full potential of plasmonics has not yet been realized due to crucial challenges that remain in the field. In particular, the development of nanoparticles with new plasmonic properties and surface chemistries could enable the rational design of more complex architectures capable of performing advanced functions, like cascade reactions, energy conversion, or signal transduction. The scope of this short review is to highlight the most recent developments in the synthesis and self-assembly of anisotropic metal nanoparticles, which are capable of bringing forward the next generation of plasmonic materials.

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Yannopapas, Vassilios, und Emmanuel Paspalakis. „Anisotropic Purcell Effect and Quantum Interference in Fractal Aggregates of Nanoparticles“. Photonics 10, Nr. 8 (03.08.2023): 898. http://dx.doi.org/10.3390/photonics10080898.

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We study theoretically the emergence of an anisotropic Purcell factor in random two-dimensional fractal aggregates of nanoparticles. These nanoparticles can either be metallic nanoparticles made of silver, which exhibit surface plasmon resonances, or high-index dielectric nanoparticles like silicon, which possess optical Mie resonances. To calculate the spontaneous emission rates of a quantum emitter, we utilize the electromagnetic Green’s tensor within the framework of the coupled-dipole method. Our findings reveal that the Purcell factor exhibits spatial variations, with certain regions, referred to as hot spots, displaying high values for dipoles oriented within the plane of the fractal aggregate, while dipoles oriented vertically to the aggregate have values close to unity. This anisotropy in the Purcell factor leads to significant quantum interference effects in the spontaneous emission paths of multi-level quantum emitters. As a consequence of this quantum interference, we demonstrate the occurrence of population trapping in a V-type quantum emitter embedded within a fractal aggregate of nanoparticles which cannot otherwise take place if the emitter is placed in vacuum.

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Bear, Joseph C., Bin Yu, Cristina Blanco-Andujar, Paul D. McNaughter, Paul Southern, Marc-Krystelle Mafina, Quentin A. Pankhurst und Ivan P. Parkin. „A low cost synthesis method for functionalised iron oxide nanoparticles for magnetic hyperthermia from readily available materials“. Faraday Discuss. 175 (2014): 83–95. http://dx.doi.org/10.1039/c4fd00062e.

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The synthesis of iron oxide nanocrystals from reagents taken from high street sources using thermal decomposition of an iron–fatty acid precursor in a high boiling point solvent in the presence of surfactants is presented. The nanocrystals were characterised using a variety of techniques including: electron microscopy, X-ray dispersive spectroscopy, infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and magnetometry. Thermogravimetric analysis (TGA) is also used to compare the decomposition behaviour of iron oleate and iron palmitate, our nanoparticle precursors. The nanoparticles also exhibit shape anisotropy when prepared under optimum conditions. We show that these nanoparticles have potential in magnetic hyperthermia after transfer to aqueous media via an amphiphilic polymer.

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Dalakova, N. V. „Spin-dependent transport in compacted powders of chromic dioxide CrO2 with anisotropy of nanoparticle shapes“. Functional materials 22, Nr. 4 (15.12.2015): 455–60. http://dx.doi.org/10.15407/fm22.04.455.

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Londoño Navarro, Juanita, Juan Carlos Riaño-Rojas und Elisabeth Restrepo-Parra. „Competition between anisotropy and dipolar interaction in multicore nanoparticles: Monte Carlo simulation“. DYNA 82, Nr. 194 (21.12.2015): 66–71. http://dx.doi.org/10.15446/dyna.v82n194.44297.

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Monte Carlo simulations combined with the Heisenberg model and Metropolis algorithm were used to study the equilibrium magnetic properties of magnetic multi-core nanoparticles of magnetite. Three effects were considered in this simulation: the Zeeman effect, magneto crystalline anisotropy, and dipolar interaction. Moreover, the influence of the size distribution (mean diameter and standard deviation) on the magnetization was analyzed. As an important result, a reduction of the equilibrium magnetization caused by the dipolar interaction and the magneto crystalline anisotropy was observed. On the other hand, the nanoparticle size increase produces an enhancement in the equilibrium magnetization, because of the lower influence of dipolar interaction. Cooling temperature effect was also observed, presenting a decrease in the equilibrium magnetization as the temperature was increased. The influence of the easy axis direction was studied.

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Shytyi. A.M., Vasilevskaya T. M. und Sementsov D. I. „Resonant dynamics of the magnetization of uniaxial nanoparticle“. Physics of the Solid State 64, Nr. 6 (2022): 635. http://dx.doi.org/10.21883/pss.2022.06.53825.279.

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Analysis of equilibrium conditions was carried out and resonant precessional dynamics of magnetization of a single-domain magnetically uniaxial ellipsoidal particle. Considered the case when magnetic field is along the easy magnetization axis. the easy magnetization axis is directed parallel to the axis of symmetry of the ellipsoid and transverse to pumping by a weak high-frequency field. Features of the behavior of the magnetization were discovered. It has been revealed that the magnetization has features of resonant behavior: large resonant precession angles with amplitude 0.5M0, elliptical deviations of the precession trajectory from circular at a negative value of the effective anisotropy field, and the presence of a frequency region with nonlinear precession for an oblate nanoparticle. Keywords: ferromagnetic resonance, elliptical nanoparticles, transverse bias field, effective anisotropy, bistability, easy magnetization axis, nonlinear effects.

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Habibi, Nahal, Ava Mauser, Jeffery E. Raymond und Joerg Lahann. „Systematic studies into uniform synthetic protein nanoparticles“. Beilstein Journal of Nanotechnology 13 (28.02.2022): 274–83. http://dx.doi.org/10.3762/bjnano.13.22.

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Nanoparticles are frequently pursued as drug delivery carriers due to their potential to alter the pharmacological profiles of drugs, but their broader utility in nanomedicine hinges upon exquisite control of critical nanoparticle properties, such as shape, size, or monodispersity. Electrohydrodynamic (EHD) jetting is a probate method to formulate synthetic protein nanoparticles (SPNPs), but a systematic understanding of the influence of crucial processing parameters, such as protein composition, on nanoparticle morphologies is still missing. Here, we address this knowledge gap by evaluating formulation trends in SPNPs prepared by EHD jetting based on a series of carrier proteins and protein blends (hemoglobin, transferrin, mucin, or insulin). In general, blended SPNPs presented uniform populations with minimum diameters between 43 and 65 nm. Size distributions of as-jetted SPNPs approached monodispersity as indicated by polydispersity indices (PDISEM) ranging from 0.11–0.19. Geometric factor analysis revealed high circularities (0.82–0.90), low anisotropy (<1.45) and excellent roundness (0.76–0.89) for all SPNPs prepared via EHD jetting. Tentatively, blended SPNPs displayed higher circularity and lower anisotropy, as compared to single-protein SPNPs. Secondary statistical analysis indicated that blended SPNPs generally present combined features of their constituents, with some properties driven by the dominant protein constituent. Our study suggests SPNPs made from blended proteins can serve as a promising drug delivery carrier owing to the ease of production, the composition versatility, and the control over their size, shape and dispersity.

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Köseoglu, Yüksel, und Hüseyin Kavas. „Size and Surface Effects on Magnetic Properties of Fe3O4 Nanoparticles“. Journal of Nanoscience and Nanotechnology 8, Nr. 2 (01.02.2008): 584–90. http://dx.doi.org/10.1166/jnn.2008.b012.

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In this study, size and surface effects on temperature and frequency dependent magnetic properties of superparamagnetic Fe3O4 nanoparticles in a size range of 1.1–11 nm are investigated by SPR technique. We used a theoretical formalism based on a distribution of diameters or volumes of the nanoparticles following lognormal proposed by Berger et al.18 The nanoparticles are considered as single magnetic domains with random orientations of magnetic moments and thermal fluctuations of anisotropic axes. The individual line shape function is derived from the damped precession equation of Landau-Lifshitz. Magnetic properties of the samples were strongly temperature and size dependent. The increase in SPR line width, the decrease in the resonance field and also increase in anisotropy filed by decreasing the temperature core–shell type structure of the nanoparticles and disordered magnetic structure (spin-glass like phase) of the particle surface. A linear microwave frequency dependence of the resonance field and the increase in the blocking temperature of the particles by the particle size were also observed.

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Omelyanchik, Alexander, María Salvador, Franco D’Orazio, Valentina Mameli, Carla Cannas, Dino Fiorani, Anna Musinu et al. „Magnetocrystalline and Surface Anisotropy in CoFe2O4 Nanoparticles“. Nanomaterials 10, Nr. 7 (30.06.2020): 1288. http://dx.doi.org/10.3390/nano10071288.

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The effect of the annealing temperature Tann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe2O4/SiO2), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing Tann from 700 to 900 °C. The effective magnetic anisotropy constant (Keff) increases with decreasing Tann, due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, Keff is much larger (1.7 × 106 J/m3) than that of the 15% w/w sample (7.5 × 105 J/m3) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments.

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Kokorina, E. E., und M. V. Medvedev. „Anisotropic superparamagnetic states of an isolated ferromagnetic nanoparticle with uniaxial single-ion anisotropy“. physica status solidi (c) 3, Nr. 5 (Mai 2006): 1291–94. http://dx.doi.org/10.1002/pssc.200563112.

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