Particular artifacts of topographic images of dielectrics in atomic-force microscopy

Particular artifacts of atomic-force microscopy (AFM) images of dielectrics, which are related to the presence of a static charge on the surface, are described. Artificial climate control with the use of a TRACKPORE ROOM-02 climatic box during measurements makes it possible to remove the static charge, owing to which the quality of AFM images and reliability of measured metric surface characteristics increase. Comparative analysis of the surface roughness measured under conventional conditions of microscope operation (static charge is present on a dielectric surface) and under the conditions of controlled artificial climate (static charge is completely removed) is performed. It is established that, in the presence of a static charge on the surface, roughness measurements may yield both overestimated and underestimated values; the largest increase in error is observed in measurements of micro-and nanosized surface areas.     

Structure of the polar (010) cleavage of a ferroelectric TGS crystal from the atomic-force microscopy data

The atomically smooth polar (010) cleavage of a ferroelectric triglycine sulfate (TGS) crystal has been studied by the method of atomic-force microscopy. It is shown that the rounded 0.6-nm-high (deep) protrusions and pits with nanometer lateral dimensions revealed on the surfaces of TGS crystals are characteristic of their microrelief. These microrelief details can be formed either as a result of crystal cleavage in the ferroelectric phase or the mechanical action of a cantilever onto the crystal surface. These two-dimensional formations are relatively stable and genetically related to the layer structure of the ferroelectric phase of TGS crystals.     

Size control and characterization of Au nanoparticle agglomeration during encapsulation in sol-gel matrices

Gold nanoparticles were encapsulated in sol-gel matrices with different amine cross-linker molecules in order to determine the cross-linker influence on nanoparticle agglomeration behaviour during encapsulation. The role of a stabilizing surfactant (SDS) was also investigated. The NP aggregate sizes were tracked using the UV surface plasmon resonance band (SPR), which red-shifts with increased particle size. It was found that use of long carbon chain cross-linkers such as 1,4-diaminobutane resulted in large Au NP aggregates, compared to short-chain analogs such as 1,2-diaminoethane, with which almost no agglomeration was observed. The SPR splitting pattern observed in samples with nanoparticle agglomeration is consistent with formation of nanodimensional objects with major and minor axes similar to nanowires during encapsulation within the cross-linked sol-gel material. The cross-linkers diethylenetriamine and triethylenetetraamine containing both terminal and internal amines demonstrated nanoparticle stabilization beyond that observed for similar sized diamine cross-linkers. This is ascribed to the multiple cross-linking sites available on these polyamines and the resulting reduction in matrix void volume.     

SANS study of clusters in aqueous magnetic fluids

Small-angle neutron scattering studies of the structure of clusters formed in aqueous magnetic fluids are reviewed. The possibilities of contrast variation using hydrogen-deuterium isotopic substitution in these complex systems are shown. Examples of the use of the method in study of the kinetics of cluster organization of aqueous magnetic fluids upon different external conditions (temperature and magnetic field) are presented. Urgent problems related to aqueous magnetic fluids, in which the method seems to be most promising, are outlined.     

Effects of magnetic interparticle coupling on the blocking temperature of ferromagnetic nanoparticle arrays

In this work we report on the study of the magnetic properties of 2D arrays and 3D dispersions of colloidal iron oxide nanoparticles prepared by Langmuir–Blodgett technique and by dilution in paraffin wax solid solution, respectively. The influence of magnetic interparticle coupling on the superparamagnetic relaxation behavior was investigated by means of DC magnetization measurements. A quantitative analysis of the field dependence of the blocking temperature and the role of the interparticle coupling is presented. We explain our results using a phenomenological model based on the random anisotropy and micromagnetic theories that account for particle coupling effects in the superparamagnetic properties.     

Electron microscopy of biomaterials based on hydroxyapatite

Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300–500 μm in diameter. Sintering of hydroxyapatite crystals at a temperature of 870°C for 2 h or at 1000°C (for 3 h) + 1200°C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870°C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200°C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 μm. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200°C.     

Role of the poly-dispersity and the dipolar interaction in magnetic nanoparticle systems: Monte Carlo study

In this paper, roles of the poly-dispersity and the dipolar interaction in frozen ferrofluid are studied by Monte Carlo method. A sample containing the uniaxial anisotropy and the random orientation is used to investigate. The temperature dependence of the coercivity is calculated to consider the magnetic phase transition under the influence of the dipolar interaction. We show that in the poly-dispersity and interacting sample, the temperature dependence of coercive field does not follow the classical expression, H_C/H_A = 0.48[1 − (T/T_B)^½]. We find that the transition temperature, which separates the anti-ferromagnetic and ferromagnetic states of strongly interacting sample, is not unique and it strongly depends on the variation of concentration. We also discuss about the concentration dependence of the coercivity at the different size distributions. At the finite temperature, the curve expresses a cusp which is due to the competition between the blocking and super-paramagnetic state at the low concentration. Therefore, we can see that the poly-dispersity also contributes to the complexity of magnetic phase of frozen ferrofluids.     

Magnetic field dependence of the magnetocaloric effect in magnetic nanoparticle systems: A Monte Carlo simulation

We study the entropy change dependence on the applied magnetic field for a dipolar interacting superparamagnetic system of fine particles. Using a Monte Carlo technique, we have obtained an enhancement of the entropy for increasing applied magnetic fields; the maximum of the entropy curves occurs at higher temperatures for larger magnetic fields. It was also observed that the blocking temperature always decreases as the magnetic field increases.     

Electron microscopy of phase and structural transformations in soft magnetic nanocrystalline Fe-Zr-N films

The effect of deposition conditions (film thickness) on the structure of soft magnetic Fe_80–78Zr₁₀N_10–12 films formed by reactive magnetron deposition on a heat-resistant glass substrate has been investigated by analytical transmission electron microscopy, high-resolution electron microscopy, and diffraction analysis. The processes of evolution of the phase and structural state of films and the film-substrate interface upon annealing in the temperature range of 200–650°C have been analyzed taking into account the thermodynamic, kinetic, and structural factors and the specific features of the nanocrystalline state.     

Three-dimensional reconstruction of a surface based on scanning electron microscopy images

Modern methods of three-dimensional reconstruction of sample surfaces based on scanning electron microscopy images allow one to quantitatively estimate morphological surface characteristics (specifically, parameters of irregularities, volumes of convexities and concavities, etc.). The accuracy of the method is analyzed by an example of commercial and specially prepared test samples. Examples of application to various objects are given.     

Quantification of the In‐distribution in embedded InGaAs quantum dots by transmission electron microscopy

The In‐concentration in InGaAs quantum dots located within a GaAs matrix was determined with the composition evaluation by lattice fringe analysis (CELFA) technique. However, the results obtained with this method cannot account for the three‐dimensional shape of quantum dots and their embedding in GaAs. A correction procedure was developed that takes into consideration the shape of the quantum dots and the TEM sample thickness and quantum‐dot size. After correction, In‐concentration profiles show an increasing In‐content towards the top of the quantum dots which is consistent with the effect of In‐segregation and earlier studies using other experimental techniques. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical studies of an aqueous electrolyte in the supercooled liquid and glassy states

Some interesting aspects of the dynamical behavior of aqueous electrolyte solutions have been summarized. They are based on the ability of these systems to form glasses providing ‘ideal’ conditions to study the glass transition phenomena and to characterize the different thermodynamical states in connection with the non-linear behavior of the static properties. Structural relaxation analysis and collective vibrational dynamics are discussed pointing out their connection with the state of the system. The existence of two different scaling behaviors of the relaxation time connected to the change in the multiplicity of microscopic states is given in addition, with some information on the intramolecular stretching vibrations at the glass transition.     

Uniformity analysis of temperature distribution in an industrial MOCVD reactor

Three‐dimensional models, coupling fluid flow and heat transfer, have been adopted to analyze influences of the process parameters on the temperature uniformity in an industrial MOCVD reactor. Important factors, such as the inlet gas flow, the susceptor rotation, the heater power, the distance between the heat shield and the susceptor (d₁), as well as the distance between the heater and the susceptor (d₂), have been investigated carefully. The system heating condition is characterized by temperature uniformity denoted as the standard deviation of temperature, and by thermal efficiency expressed as a combination parameter of the dissipated energy. The results reveal that decrease of the gas flow and the rotation rate, as well as increase of the distance d₁, could monotonically enhance the temperature uniformity. The results also show that decrease of the above three parameters could improve the thermal efficiency. Furthermore, increase of the distance d₂ enhances the temperature uniformity, and reduces the thermal efficiency slightly. The influences of the parameters on the uniformity vary at the different locations of the susceptor as divided into Zone A, Zone B and Zone C. The conclusions help the growth engineer optimize the system design and process conditions of the reactor.     

Quantum-chemical simulation and experimental study of some magnetic nanoparticles stabilized in fluid suspensions by using organic coating

Abstract

The biomedical applications of magnetic nanoparticles require the surface modification with organic, hydrophilic molecules, able to ensure the stability of the resulted colloidal suspensions. We present the quantum mechanical approach of two molecules developing stable interfaces with magnetic Co_0.5Fe_2.5O₄ nanoparticles. Sodium oleate, and citric acid, ensuring steric and respectively electrostatic stabilization are comparatively analyzed. The roles of dipole moment and frontier orbitals energies were emphasized to better understanding of some interface phenomena for the optimization of magnetic nanoparticle suspension preparation. Further, practical yielding of colloidal Co_0.5Fe_2.5O₄ nanoparticles by coating with sodium oleate and respectively with citric acid is discussed.     

On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

Memory effect in the glass transition region of silicate glass based on light scattering data

The experimental results of the changes of the visible light scattered intensity after temperature jumps in the glass transition region of silicate glass were presented. The influence of the thermal prehistory on the height and location of the scattered intensity maximum was studied. The conditions corresponding to the maximum value of the scattered intensity were determined. The non-monotone character of the dependence of the limit height of the maximum as a function of the stabilization temperature was obtained. It was shown that the relaxation times of the increasing of the intensity considerably exceeded the structural relaxation times. These features were similar to the results obtained for the phosphate glass earlier. The universal character of the non-linear coupling of the laser irradiation with the glass structure formed in the process of development of the maximum intensity was found.     

Solubility data of trisodium citrate hydrates in aqueous solution and crystal‐solution interfacial energy of the pentahydrate

In this paper, the solubility of trisodium citrate dihydrate and trisodium citrate pentahydrate in water was experimentally determined. From solubility data, it was found that the relationship between trisodium citrate dihydrate and trisodium citrate pentahydrate is enantiotropic with a transition temperature at 315.4±1.0 K. Different hydrates can be isolated safely by controlling the crystallization temperature. The induction periods of trisodium citrate pentahydrate in aqueous solution were measured at different temperatures. The crystal–solution interfacial energy was calculated by using classical nucleation (CL) theory, mononuclear (MN) and polynuclear (PL) mechanisms through the relationship between induction period and supersaturation. It was found that the interfacial energy values calculated by using the CL theory and the MN model are nearly the same while interfacial energy calculated by PN model are about 40% higher. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of unilamellar vesicles: Numerical analysis based on small-angle neutron scattering data

The structure of polydispersed populations of unilamellar vesicles is studied by small-angle neutron scattering for three types of lipid systems, namely, single-, two-and four-component vesicular systems. Results of the numerical analysis based on the separated-form-factor model are reported.     

Correlations between electric,magnetic, and galvanomagnetic quantities in stable icosahedral phases based on aluminum

On the basis of the results of the experimental investigation of the correlations between the electric, magnetic, and galvanomagnetic properties, the nature of the electronic phenomena leading to the difference of icosahedral quasicrystals from typical metals and insulators (low conductivity and negative temperature coefficient of resistance, diamagnetism of the ground state and its decrease with increasing temperature, and existence of residual and thermally induced charge carriers) is discussed.