共查询到20条相似文献,搜索用时 375 毫秒
1.
《Journal of magnetism and magnetic materials》2005,295(2):132-138
Iron oxide nanoparticles of 8–20 nm in size were investigated as an assembly with biomolecules synthesized in an aqueous solution. The magnetic behavior of the biomolecule–nanoparticles assembly depends sensitively on the morphology and hence the distribution of the nanoparticles, where the dipole coupling between the nanoparticles governs the overall magnetic behavior. In assemblies of iron oxide nanoparticles with trypsin, we observe a formation of unusual self-alignment of nanoparticles within trypsin molecules. In such an assembly structure, the magnetic particles tend to exhibit a lower spin-glass transition temperature than as-synthesized bare iron oxide nanoparticles probably due to reduced interparticle couplings within the molecular matrix. The observed self-alignment of nanoparticles in biomolecules may be a useful approach for directed nanoparticles assembly. 相似文献
2.
K. Rumpf P. Granitzer P. Plt A. Reichmann M. Hofmayer H. Krenn 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):270
Ferromagnetic (Ni) filaments are embedded into a porous silicon template by an electrochemical deposition process. During cathodic deposition using NiCl2 as electrolyte the channels of the meso-/macroporous silicon structure are filled with metallic Ni. The resulting nanocomposite system consists of silicon as base material as well as of implemented Ni-structures, especially of highly oriented Ni-wires perpendicular to the surface showing an exceptionally high aspect ratio (>300) and is of interest for applications in microtechnology. The length of the Ni-wires is in the range of a few tens of micrometers. Concomitant with the growth of wires, spheres or ellipsoidally shaped particles are formed during the Ni-filling procedure, whose spatial frequency and distribution become tunable. Structural investigations of this system, using SEM and EDX as well as investigations of the magnetic behaviour using SQUID-magnetometry, demonstrate the dependency of the magnetic properties on the filling status of the samples. The hysteresis loops in the low-field regime up to 500 Oe as well as magnetization curves in the high-field range of a few tesla display a strong magnetic anisotropy due to magnetic rearrangements. At fields around 5 T, a decline of the magnetization followed by a steep increase is observed. This magnetic field-induced anisotropy depends on the detailed growth of the Ni within the pores which can be controlled by the deposition process. It is governed by yet unknown antiferromagnetic exchange between the wires, and inherently connected with the shape of the magnetic nano-objects. 相似文献
3.
F. C. Fonseca R. F. Jardim M. T. Escote P. S. Gouveia E. R. Leite E. Longo 《Journal of nanoparticle research》2011,13(2):703-710
In this work, we report on the magnetic properties of nickel nanoparticles (NP) in a SiO2–C thin film matrix, prepared by a polymeric precursor method, with Ni content x in the 0–10 wt% range. Microstructural analyses of the films showed that the Ni NP are homogenously distributed in the SiO2–C matrix and have spherical shape with average diameter of ~10 nm. The magnetic properties reveal features of superparamagnetism
with blocking temperatures T
B ~ 10 K. The average diameter of the Ni NP, estimated from magnetization measurements, was found to be ~4 nm for the x = 3 wt% Ni sample, in excellent agreement with X-ray diffraction data. M versus H hysteresis loops indicated that the Ni
NP are free from a surrounding oxide layer. We have also observed that coercivity (H
C) develops appreciably below T
B, and follows the H
C ∝ [1 – (T/T
B)0.5] relationship, a feature expected for randomly oriented and non-interacting nanoparticles. The extrapolation of H
C to 0 K indicates that coercivity decreases with increasing x, suggesting that dipolar interactions may be relevant in films with x > 3 wt% Ni. 相似文献
4.
E. Kelm S. Korovin V. Pustovoy A. Surkov A. Vladimirov 《Applied physics. B, Lasers and optics》2011,105(3):599-606
Silicon nanoparticles (nSi) with unusual properties were studied. After suggested treatment they became luminescent and also
acquired a magnetic moment. Nanoparticles were prepared by laser pyrolysis of silane in a gas flow reactor followed by chemical
treatment in methanol (MeOH) + HF + FeCl3 solution. After the treatment. nanoparticles gained stable luminescence with the peak position dependence on the excitation
wavelength. With increasing of the excitation wavelength from 365 to 456 nm, the photoluminescent peak shifted from 632 to
665 nm. Luminescence of such nanoparticles had blue shift in comparison with the nanoparticles etched in widely-used solution
for the silicon—MeOH + HF + HNO3. Moreover, after such treatment the magnetic moment of nanoparticles appeared, which is not inherent for the as-prepared
nSi. Multifunctional silicon nanoparticles with both stable luminescence and magnetic moment at the same time are perspective
for biology and medicine use as the optical and magnetic markers. 相似文献
5.
Ki-Chul Kim Eung-Kwon Kim Jae-Won Lee Sung-Lyul Maeng Young-Sung Kim 《Current Applied Physics》2008,8(6):758-760
We have synthesized the iron oxide nanoparticles using the newly developed mechanical ultrasonication method with the FeSO4 · 7H2O. We have also investigated the crystallographic structural properties, morphology, and magnetic properties of the nanopowders. According to the high resolution X-ray diffraction result, the as-synthesized iron oxide nanoparticles were magnetite (Fe3O4). The particle size of the magnetite nanoparticles was about 6 nm confirmed by transmission electron microscopy image. The particle shape was almost a sphere confirmed by scanning electron microscopy image. The coercivity and saturation magnetization of the as-synthesized iron oxide nanopowders were 114 Oe, and 3.7 emu/g, respectively. 相似文献
6.
P. Granitzer K. Rumpf A.G. Roca M.P. Morales P. Poelt M. Albu 《Journal of magnetism and magnetic materials》2010,322(9-12):1343-1346
Magnetite nanoparticles, which are coated with oleic acid in a hexane solution and exhibit an average diameter of 7.7 nm, were embedded in a porous silicon (PS) matrix by immersion under defined parameters (e.g. concentration, temperature, time). The porous silicon matrix is prepared by anodization of a highly n-doped silicon wafer in an aqueous HF-solution. Magnetic characterization of the samples has been performed by SQUID-magnetometry. The superparamagnetic behaviour of the magnetite nanoparticles is represented by temperature-dependent magnetization measurements. Zero field (ZFC)/field cooled (FC) experiments indicate magnetic interactions between the particles. For the infiltration into the PS-templates different concentrations of the magnetite nanoparticles are used and magnetization measurements are performed in respect with magnetic interactions between the particles. The achieved porous silicon/magnetite specimens are not only interesting due to their transition between superparamagnetic and ferromagnetic behaviour, and thus for magnetic applications but also because of the non-toxicity of both materials giving the opportunity to employ the system in medical applications as drug delivery or in medical diagnostics. 相似文献
7.
P. Allia P. Tiberto M. Coisson A. Chiolerio F. Celegato F. Vinai M. Sangermano L. Suber G. Marchegiani 《Journal of nanoparticle research》2011,13(11):5615-5626
Magnetite nanoparticles having mean diameter of about 8 nm have been prepared by a thermo-chemical route. Different amounts
(5 and 10% wt) of a stable dispersion of magnetite nanoparticles in n-hexane were added to polyethylene glycol diacrylate (PEGDA-600) oligomer containing 2% wt of radicalic photoinitiator. The
homogenized mixture was poured on a silica glass substrate and the resulting film was photoreticulated in N2 atmosphere using a UV lamp. As a result, a polymer-based magnetic nanocomposite was obtained, where the magnetic nanoparticles
are dispersed in the diamagnetic matrix, as checked by SEM. Morphology, composition, and size of as-prepared nanoparticles
were checked by SEM and X-ray diffraction. The magnetic properties of magnetite nanoparticles prior to and after inclusion
in the polymeric matrix have been studied by means of an alternating-gradient magnetometer (T interval: 10–300 K, HMAX: 18 kOe). FC-ZFC curves were obtained in the same temperature interval. The results show that the nanocomposites cannot be
simply described as containing superparamagnetic particles undergoing an anisotropy-driven blocking and that collective magnetic
interactions play a non-negligible role. Low-temperature hysteretic properties indicate that the polymeric matrix affects
the effective anisotropy of magnetite nanoparticles. Dispersion of magnetite NPs in PEGDA has non-trivial consequences on
their magnetic properties. 相似文献
8.
Anna Lähde Noora Kokkonen Antti J. Karttunen Sirpa Jääskeläinen Unto Tapper Tapani A. Pakkanen Jorma Jokiniemi 《Journal of nanoparticle research》2011,13(9):3591-3598
Atmospheric pressure chemical vapor synthesis was used to produce copper nanoparticle composites in an amorphous silicon dioxide,
i.e., either copper nanoparticles coated with amorphous silicon dioxide or copper nanoparticles embedded in amorphous silicon
dioxide matrix. Synthesized metal–organic copper(I) complex was used as a precursor that provided well-defined ratio (1:2)
of copper and silicon. The thermal decomposition of the Cu(I) complex molecule leads to homogenous nucleation and formation
of copper nanoparticles which are subsequently coated with Si/SiO2 in the gas phase. The decomposition was greatly enhanced when reductive atmosphere, i.e., H2/N2 10 v% were used instead of pure nitrogen. A narrow size distribution with the geometric mean diameter of the particle agglomerates
around 30 nm was observed while the primary size of the copper core particles was around 5 nm. 相似文献
9.
Control on the size of copper oxide (CuO) in the nano range is a highly motivating approach to study its multifunctional nature. The present investigation reports a sol-gel derived Ni doped CuO nanoparticles (Cu1-xNixO). Rietveld refinement of the XRD spectra confirms the formation of single monoclinic phase of Cu1-xNixO nanoparticles having crystallite size within the range of 19–21 nm. Raman spectra show the presence of characteristics Raman active modes and vibrational bands in the Cu1-xNixO samples that corroborate the monoclinic phase of the samples as revealed by refinement of XRD data. The estimated band gap of pure CuO is found to be ∼1.43 eV, which decreases with the increase of dopant concentration into CuO matrix. This result is in line with estimated crystallite size. Magnetization curves confirm the weak ferromagnetic nature of Cu1-xNixO nanoparticles which reveal the DMS phase. This weak magnetic nature may be induced in the samples due to the exchange interaction between the localized magnetic d-spins of Ni ions and carriers (holes or electrons) from the valence band of pristine CuO lattice. Replacement of Cu+2 by Ni+2 ions into the host CuO lattice induces the magnetization. The quantified value of squareness ratio (S < 0.5) confirms the inter-grain magnetic interactions in the Cu1-xNixO nanoparticles which is also the reason of weak induced magnetization. 相似文献
10.
M. D��az L. Mart��nez M. M. Ruano D. Llamosa P E. Rom��n M. Garc��a-Hernandez C. Ballesteros R. Fermento A. Cebollada G. Armelles Y. Huttel 《Journal of nanoparticle research》2011,13(10):5321-5333
We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean diameter of 10.3 ± 1.8 nm) grown using a gas aggregation source and embedded in a silicon oxide matrix by sequential deposition of nanoparticles and silicon oxide. We show that the Co nanoparticles ??soft-land?? on the substrates and suffer a moderate oxidation in contact with the silicon oxide. Despite this moderate oxidation, it is found that, at room temperature, the magnetic volume of the resulting nanoparticles is below the superparamagnetic limit. The results presented in this article are compatible with the presence of an assembly of magnetically independent particles that also display a moderate exchange bias at low temperature. 相似文献
11.
P. Granitzer K. Rumpf P. Plt A. Reichmann H. Krenn 《Physica E: Low-dimensional Systems and Nanostructures》2007,38(1-2):205
Porous silicon (PS) channels fabricated during an electrochemical anodization process in hydrofluoric acid solution, without pre-structuring, normally arrange in an irregular morphology. In this work self-organized quasi-2D regular pore arrangements have been fabricated by accurate mutual control of various process parameters. Self-organized pore formation can be tailored and periodic pore arrangements are possible. A particular parameter to vary the inter-pore spacing is mainly the HF concentration, whereas the pore diameter primarily depends on the current density. The well-separated pores are highly oriented perpendicular to the surface and the pattern of self-organized pores is quadratic like due to the (1 0 0)-crystal orientation of the wafer. The isolated pores show little dendritic growth and their diameter can be tuned between 10 and 100 nm, thus belonging to the meso-porous up to the macro-porous regime. The pore growth occurs in an anisotropic manner which means that the channels grow significantly faster in (1 0 0) direction than in (1 1 1) direction. Into this self-assembled PS template metallic Ni is deposited using an electrochemical deposition step which results in a PS/Ni-nanocomposite with potential for applications as magnetic and magneto-optical devices. The filling process is performed under cathodic conditions and could be refined by pulsed current charging. 相似文献
12.
Copper oxide (CuO) nanoparticles with an average size of 25 nm were prepared by a sol-gel method. A detailed study was made of the magnetization of CuO nanoparticles using a maximum field of 60 kOe for temperatures between 8 and 300 K. Antiferromagnetic CuO nanoparticles exhibit anomalous magnetic properties, such as enhanced coercivity and magnetic moments. Significantly, the magnitude of the hysteresis component tends to weaken upon increase in temperature (>8 K). In addition, a hysteresis loop shift and coercivity enhancement are observed at 8 K in the field-cooled (FC, at 50 kOe) case. It is thought that the change in hysteresis behavior is due to the uncompensated surface spins of the CuO nanoparticles. The susceptibility (χ) plot showed that χ varied substantially at temperatures below 12 K, and this transition is due to the exchange interactions between the neighboring atoms at the nanoscale. 相似文献
13.
Enis Tuncer Adam J. Rondinone Jonathan Woodward Isidor Sauers D. Randy James Alvin R. Ellis 《Applied Physics A: Materials Science & Processing》2009,94(4):843-852
In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed
magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that
the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters
are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation
and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide
particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful
as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties
of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity
values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have
low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a
low dielectric permittivity surfactant. 相似文献
14.
Daniela Carta Maria F. Casula Salvatore Bullita Andrea Falqui Anna Corrias 《Journal of nanoparticle research》2011,13(8):3489-3501
A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared
using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic
nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal
stability. Low-angle X-ray diffraction, N2 physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction
in H2 flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy
nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix
and they seem in a large extent to be allocated inside the pores. 相似文献
15.
Mohamed A. Ballem José M. Córdoba Magnus Odén 《Journal of nanoparticle research》2011,13(7):2743-2748
Nanoparticles of zirconium oxide (ZrO2) were synthesized by infiltration of a zirconia precursor (ZrOCl2·8H2O) into a SBA-15 mesoporous silica mold using a wet-impregnation technique. X-ray diffractometry and high-resolution transmission
electron microscopy show formation of stable ZrO2 nanoparticles inside the silica pores after a thermal treatment at 550 °C. Subsequent leaching out of the silica template
by NaOH resulted in well-dispersed ZrO2 nanoparticles with an average diameter of ~4 nm. The formed single crystal nanoparticles are faceted with 110 surfaces termination
suggesting it to be the preferred growth orientation. A growth model of these nanoparticles is also suggested. 相似文献
16.
Thin films of silicon nanoparticles (diameter 5-10 nm) were deposited on highly oriented pyrolytic graphite (HOPG) by low-pressure DC magnetron sputtering. The effect of different room-temperature oxidation techniques was investigated using XPS sputter-depth profiling. Both oxygen treatment during deposition (using an argon-oxygen mixture in the sputter gas) as well as post-deposition oxidation techniques (exposure to oxygen plasma beam, ambient air conditions) were studied. In all cases oxidation was found to involve the whole film down to the film/substrate interface, indicating a network of open pores. Depending on the type of oxidation between 15 and 25 at% of oxygen, mostly associated with low oxidation states of silicon, were detected in the interior of the film and attributed to oxidized surfaces of the individual silicon nanoparticles. The highest oxygen concentrations were found at the very film surface, reaching levels of 25-30% for films exposed to air or prepared by reactive magnetron sputtering. For the oxygen plasma-treated films even oxygen surface concentrations around 45% and fully oxidized silicon (i.e., SiO2) were achieved. At the Si/HOPG interface formation of silicon carbide was observed due to intermixing induced by Ar-ion beam used for sputter-depth profiling. 相似文献
17.
Superparamagnetic iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysts,
gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy. Combustion synthesis
of nanoparticles has significant advantages, including improved nanoparticle property control and commercial production rate
capability with minimal post-processing. In the current study, superparamagnetic iron oxide nanoparticles were produced by
flame synthesis using a coflow flame. The effect of flame configuration (diffusion and inverse diffusion), flame temperature,
and additive loading on the final iron oxide nanoparticle morphology, elemental composition, and particle size were analyzed
by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy.
The synthesized nanoparticles were primarily composed of two well known forms of iron oxide, namely hematite αFe2O3 and magnetite Fe3O4. We found that the synthesized nanoparticles were smaller (6–12 nm) for an inverse diffusion flame as compared to a diffusion
flame configuration (50–60 nm) when CH4, O2, Ar, and N2 gas flow rates were kept constant. In order to investigate the effect of flame temperature, CH4, O2, Ar gas flow rates were kept constant, and N2 gas was added as a coolant to the system. TEM analysis of iron oxide nanoparticles synthesized using an inverse diffusion
flame configuration with N2 cooling demonstrated that particles no larger than 50–60 nm in diameter can be grown, indicating that nanoparticles did not
coalesce in the cooler flame. Raman spectroscopy showed that these nanoparticles were primarily magnetite, as opposed to the
primarily hematite nanoparticles produced in the hot flame configuration. In order to understand the effect of additive loading
on iron oxide nanoparticle morphology, an Ar stream carrying titanium-tetra-isopropoxide (TTIP) was flowed through the outer
annulus along with the CH4 in the inverse diffusion flame configuration. When particles were synthesized in the presence of the TTIP additive, larger
monodispersed individual particles (50–90 nm) were synthesized as observed by TEM. In this article, we show that iron oxide
nanoparticles of varied morphology, composition, and size can be synthesized and controlled by varying flame configuration,
flame temperature, and additive loading. 相似文献
18.
Rajesh Patel 《Journal of magnetism and magnetic materials》2011,323(10):1360-1363
Mechanism of structure formation in bidispersed colloids is important for its physical and optical properties. It is microscopically observed that the mechanism of chain formation in magnetic nanofluid based magnetorheological (MR) fluid is quite different from that in the conventional MR fluid. Under the application of magnetic field the magnetic nanoparticles are filled inside the structural microcavities formed due to the association of large magnetic particles, and some of the magnetic nanoparticles are attached at the end of the chains formed by the large particles. The dipolar energy of the large particles in a magnetic nanofluid matrix becomes effective magnetic permeability (μeff) times smaller than that of the neutral medium. Inclusion of magnetic nanoparticles (∼10 nm) with large magnetic particles (∼3-5 μm) restricts the aggregation of large particles, which causes the field induced phase separation in MR fluids. Hence, nanofluid based MR fluids are more stable than conventional MR fluids, which subsequently increase their application potentiality. 相似文献
19.
Size-tuned copper oxide nanoparticles with sizes of 9, 12, and 15 nm were fabricated by laser ablation and on-line size selection
using a differential mobility analyzer at a gas pressure of 666 Pa. The dependence of the particle properties on the in situ
annealing temperatures and selection sizes was investigated. The crystalline phases of the nanoparticles fabricated at temperatures
below 973 K were assigned to monoclinic cupric oxide (CuO) which converted into cubic cuprous oxide (Cu2O) when the annealing temperature was above 1,173 K. This indicates that the crystalline phases can be easily controlled by
changing the annealing temperature. TEM images confirmed that well-crystallized and well-dispersed CuO and Cu2O nanoparticles with narrow size distributions were obtained using this method. This fabrication process is useful and promising
for the future investigation of the intrinsic size-dependent properties of CuO and Cu2O. 相似文献
20.
Jin Zhang Jiaxin Li Fereidoon S. Razavi Abdul Md. Mumin 《Journal of nanoparticle research》2011,13(5):1909-1916
A new method to produce elaborate nanostructure with magnetic and fluorescent properties in one entity is reported in this
article. Magnetite (Fe3O4) coated with fluorescent silica (SiO2) shell was produced through the one-pot reaction, in which one reactor was utilized to realize the synthesis of superparamagnetic
core of Fe3O4, the formation of SiO2 coating through the condensation and polymerization of tetraethylorthosilicate (TEOS), and the encapsulation of tetramethyl
rhodamine isothiocyanate-dextran (TRITC-dextran) within silica shell. Transmission electron microscopy (TEM), energy dispersive
X-ray (EDX) analysis, and X-ray diffraction (XRD) were carried out to investigate the core–shell structure. The magnetic core
of the core–shell nanoparticles is 60 ± 10 nm in diameter. The thickness of the fluorescent SiO2 shell is estimated at 15 ± 5 nm. In addition, the fluorescent signal of the SiO2 shell has been detected by the laser confocal scanning microscopy (LCSM) with emission wavelength (λem) at 566 nm. In addition, the magnetic properties of TRITC-dextran loaded silica-coating iron oxide nanoparticles (Fe3O4@SiO2 NPs) were studied. The hysteresis loop of the core–shell NPs measured at room temperature shows that the saturation magnetization
(M
s) is not reached even at the field of 70 kOe (7T). Meanwhile, the very low coercivity (H
c) and remanent magnetization (M
r) are 0.375 kOe and 6.6 emu/g, respectively, at room temperature. It indicates that the core–shell particles have the superparamagnetic
properties. The measured blocking temperature (T
B) of the TRITC-dextran loaded Fe3O4@SiO2 NPs is about 122.5 K. It is expected that the multifunctional core–shell nanoparticles can be used in bio-imaging. 相似文献