Facile Preparation of Core-Shell Nanocomposite Microgels

Microgels with alginate (Alg) gel cores and shells of SiO₂ nanoparticles (so-called colloidosomes) were prepared by self-assembly of SiO₂ nanoparticles at ALG aqueous solution–hexane interfaces and subsequent in situ gelation caused by Ca²⁺ ions that were released from calcium-ethylenediamine tetraacetic acid chelate by decreasing the pH value through the slow hydrolysis of D-Gluconic-δ-lactone. The packing density of SiO₂ nanoparticles in the shell was about 0.906, indicating that the SiO₂ nanoparticles were present monolayer on the surfaces of the colloidosomes. The half release times of insulin microcrystals were 4 h for Alg gel microspheres and 10 h for Alg/SiO₂ colloidosomes at pH 7.4, compared to 1.5 h for bare insulin. The half release times of insulin microcrystals were 12 min for Alg gel microspheres and 30 min for Alg/SiO₂ colloidosomes at pH 1.2, compared to 30 s for bare insulin. The release rates of insulin from the colloidosomes with core–shell structure were slower than that from bare insulin crystals due to the dual barriers of the hydrogel cores and the close-packed inorganic shells. The release curves were nicely fitted by the Weibull equation and the release followed Fickian diffusion.     

Diffusion of silicon in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained film structure (B ₊ films) have been examined as diffusion barriers, preventing the silicon diffusion in silicon devices. The silicon diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) after annealing at temperatures up to 900° C, in view of application of high-temperature processes. The diffusivity from 400 to 900° C: D (m² s^–1)=2.5×10^–18 exp[–31 kJ/mol/(RT)] in B ₀ layers and D (m² s^–1)=3×10^–19 exp[–26 kJ/mol/(RT) in B ₊ TiN layers. The diffusivities determined correspond to grain boundary diffusion, the difference being due to the different microstructure. The very low diffusivity of silicon in B ₊ TiN layer makes it an excellent high-temperature barrier preventing silicon diffusion.     

TiB2-reinforced B4C composites produced by reaction sintering at high-pressure and high temperature

ABSTRACT

Obtaining both high hardness and toughness is a challenge in B₄C-nano-adhesive composites. Solving the inhomogeneous distribution of nano-adhesives in B₄C and forming the chemical bonding at grain boundary is an effective method. Here, we reported that the uniform distribution of titanium diboride (TiB₂)-reinforced B₄C composites synthesized by high-pressure and high temperature (HPHT). It is found that HPHT sintering can effectively inhibit the grain growth and increase the relative density. Moreover, HPHT sintering can cross high reaction energy barrier and effectively promote the formation of chemical bonding at grain boundary between B₄C and TiB₂. The optimal hardness and toughness value reach 30.0?±?0.9?GPa and 7.87?MPa·m^1/2, respectively. The improvement of hardness and toughness in the final products are ascribed to the strengthening of nanoTiB₂ connection of B₄C boundary and intergranular fracture mechanism. This work suggests a new way to achieve the uniform distribution of nanoTiB₂ in B₄C and form the chemical bonding at grain boundary, which is of great significance to the further development of TiB₂-reinforced B₄C composites with excellent mechanical properties.     

Ion bombardment induced phase transformations and inert gas mobility in the semiconductors Ge,Si, and GaAs

Abstract

The present study contributes some new aspects to the general understanding of the ion implantation behaviour of 3 common semiconductor materials, and of diffusion processes in these materials. Single crystals of Si, Ge, and GaAs were bombarded with Kr- or Xe-ions at energies of 40 or 500 keV and doses between 10¹¹ and 2 × 10¹⁶ ions/cm². Gas release measurements and Rutherford scattering of 1 MeV He⁺-ions combined with channeling were used to study bombardment damage (amorphization) and inert gas diffusion. At low bombardment doses (10¹¹ ions/cm²) and energy (40 keV), no damage was observed and the gas release was compatible with volume diffusion resembling Group I and VIII behaviour. Hence, the pre-exponential terms, D ₀, were low (range 10-^5±1 cm² sec^?1) and the activation enthalpies, Δ H, were much lower than those of self-diffusion or of diffusion of Group III and V elements. The Δ H's for gas diffusion followed the relation Δ H = (1.05±0.1) × 10^?3 T_m eV with the melting point, T_m , in °K. The mechanism of gas mobility might be the Turnbull dissociative mechanism. Rutherford scattering and channeling data indicated that part of the gas occupied lattice sites.

At higher doses, the bombarded layers turned amorphous. Channeling experiments showed a coincidence in temperatures for a gas release process different from the above one of volume diffusion, and recrystallization of the disordered layer to the single crystalline state. Both processes occurred in the temperature range 0.60 to 0.65 T_m . The gas release indicated a (partial) single jump character with implied Δ H's following the relation Δ H = (2.1±0.1) × 10^?3 T_m eV. Contrary to previous results on oxides, this new gas release occurred at temperatures near to those or even above those of volume diffusion of the gas.

Due to the easy formation of an amorphous layer it was difficult to observe the retarded release (trapping of gas) that has been found in many materials at high gas and damage concentrations. However, in a separate series of experiments with 500 keV Kr-ions, a release retarded with respect to volume diffusion of the gas was observed in Si and Ge.     

Aluminium diffusion in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained (B ₊ films) film structures, respectively, have been examined as diffusion barriers for preventing aluminium diffusion. The aluminium diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) at temperatures up to 550° C. The diffusivity from 300° C to 550° C is: D[m²s^–1]=3×10^–18 exp[–30/(RT)] in B ₀ layers and D[m²s^–1]=1.4×10^–16 exp[–48/(RT)] in B ₊ TiN layers. The activation-energy values determined indicate a grain boundary diffusion mechanism. The difference between the diffusion values is determined implicitly by the microstructure of the layers. Thus, the porous B ₀ layers contain a considerable amount of oxygen absorbed in the intercolumnar voids and distributed throughout the film thickness. As found by AES depth profiling, this oxygen supply allows the formation of Al₂O₃ during annealing the latter preventing the subsequent diffusion of the aluminium atoms.     

Correlation of light scattering and molecular dynamics in superionic Ba1−xLaxF2+x

Abstract

The squares of the Brillouin frequencies (Δω_B)² of the LA mode in the [100] direction related to the C₁₁ elastic constant show a linear decrease with temperature followed by significant deviations that occur above the corresponding transition temperatures (T_c), being at 850, 800, 970, 950 and 920 K for samples with x = 0.05, 0.1, 0.2, 0.3 and 0.5, respectively. The Raman linewidths show linear increases with temperature followed by rapid increases around the same temperatures at which the elastic constants start to show marked decreases. The complementary studies using Molecular Dynamics show that the diffusion coefficients start to increase markedly around the same temperatures observed experimentally.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

The Vibrational Spectra of (1-Diacetylmonoximeimino-3-diacetylmonoximatoiminopropane)-methylaquocobalt (III), Perchlorate

Metal complexes of the tetradentate ligand bis(diacetyl-monoximeimino)propane 1,3 = [(DOH)₂pn] are interesting in several respects. They are representatives of molecular systems containing very short hydrogen bonds; moreover, the organo-cobalt derivatives were reported as first examples of stable water-soluble compounds besides Vitamin B₁₂ coenzyme and alkylcobalamines ¹. From this point of view they were extensively investigated as models of Vitamin B₁₂ ². However, vibrational data concerning these complexes are rather scarce: at our knowledge only a limited assignment was proposed by UHLIG and FRIEDRICH³ for some Ni derivatives.     

Structural relaxation in the CoP-CoNiP system upon low-temperature annealing

The atomic structure of alloys in the CoP-CoNiP system in the initial state and its behavior upon low-temperature annealing is investigated. It is shown that structural relaxation starts at temperatures of 150–200°C and results in local atomic ordering at the network boundaries. Crystals 2–5 nm in size start to undergo nucleation at the boundaries of structural heterogeneities when heated further to 250–300°C. The nanocrystal structure corresponds to the metastable phase delta-Co (ICSD 42684) and the unknown phase Co_{1 ? x} P _x . The estimated diffusion coefficient for CoP alloy is 10^?14 m² s^?1, according to the experimental data.     

Role of polyvinyl alcohol in the conductivity behaviour of polyethylene glycol-based composite gel electrolytes

An attempt has been made in the present work to combine gel and composite polymer electrolyte routes together to form a composite polymeric gel electrolyte that is expected to possess high ionic conductivity with good mechanical integrity. Polyethylene glycol (PEG) based composite gel electrolytes using polyvinyl alcohol (PVA) as guest polymer have been synthesized with 1 molar solution of ammonium thiocyanate (NH₄SCN) in dimethyl sulphoxide (DMSO) and electrically characterized. The ionic conductivity measurements indicate that PEG:PVA:NH₄SCN-based composite gel electrolytes are superior (σ _max = 5.7 × 10⁻² S cm⁻¹) to pristine electrolytes (PEG:NH₄SCN system) and conductivity variation with filler concentration remains within an order of magnitude. The observed conductivity maxima have been correlated to PEG:PVA:NH₄SCN-and PVA:NH₄SCN-type complexes. Temperature dependence of conductivity profiles exhibits Arrhenius behaviour in low temperature regime followed by VTF character at higher temperature.      

关于等离子体中的瞬变过程

利用Spitzer的广义欧姆定律分析等离子体中由垂直于磁场的压强梯度所引起的宏观瞬变性质。在垂直于磁场方向的初始流动速度为零的条件下,得出在恒稳磁场中的瞬时扩散系数(当ω_ceτ?1)为 D= (2km_ec²)/e² T/(B²τ)+(kc)/eT/Be^-m_e/(miτ)tsinω_cit,式中τ为电子离子的平均碰撞时间间隔。     

Structural and thermal studies of [PVA–LiAc] : TiO2 polymer nanocomposite system

Nanocomposite polymer electrolyte consisting of polyvinyl alcohol (PVA) and lithium acetate with TiO₂ filler has been synthesised by combination of solution cast technique and sol–gel process. The composite electrolyte films were characterised by different experimental techniques. The average particle size of composite electrolytes lies between 25 and 30?nm. System is essentially ionic with maximum conductivity of polymer electrolyte 90[80PVA–20LiAc]:10TiO₂ (～4.5?×?10^?6?S?cm^?1) at room temperature.     

Relation Between Laser Induced Infrared Fluorescence and Laser Absorption By Pollutant Gases

Symmetry coordinates were developed for the dodecaborane-ion type X₁₂Y¹² model of symmetry I_h. Two sets of force constants for the ion are reported, where it was made use of Decius' and Keating's bendings, respectively. Calculated frequencies for B₁₂H₁₂ and B₁₂D₁₂ are compared with observed data. Better agreement was obtained for the set with Keating's bendings. This conclusion is consistent with one of a previous normal coordinate analysis.     

Stability of nanovoids in amorphous Si3B3N7

The amorphous ceramic material a-Si₃B₃N₇ possesses a rather low density (≈1.9?g/cm³) compared with, for example, the weighted average of the crystalline binary compounds Si₃N₄ and BN (≈2.8?g/cm³). Our simulations show that nanosize cavities, which are created during synthesis via the sol–gel route, can survive for a very long time even at elevated temperatures (up to 1500?K), and are thus the most likely explanation for the low density of a-Si₃B₃N₇. Furthermore, we find that, at low temperatures, the application of very high pressures exceeding 10?GPa should lead to a considerable irreversible densification of the material up to ≈2.8?g/cm³.     

Thermoluminescence of Chromium Doped Cd2Nb2O7 Crystals

The exposure of the Cd₂Nb₂O₇:Cr crystal to monochromatic light with wavelength shorter than 600 nm at 12 K decreases the Cr^3? photoluminescence emission and allows us to observe thermoluminescence within 60–200 K during subsequent heating of the crystal at a rate of 0.077 K/s. The glow curve of thermoluminescence revealed a rather complex structure with two pronounced intensive glow peaks at 91 and 180 K and four rather weak peaks at 99, 117, 132, and 155K. An analysis of the glow peaks by “an initial rise” gave evidence of many various charge carrier traps with activation energies from 150 to 470 meV. Since a comparison of the thermoluminescence and photoluminescence emission spectra showed that these spectra are identical, it was concluded that the thermoluminescence glow peaks are associated with thermal release of charge carriers from shallow traps followed by Cr^4?→Cr^3?(²E) and/or Cr^2?→Cr^3?(²E) charge capture and ²E→⁴A₂ radiative decay of Cr^3?(²E) ions.     

强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.     

Effect of Calcium Ion Concentration on Small Molecule Desorption from Alginate Beads

Spherical alginate beads were prepared by ionotropic gelation of sodium alginate through the use of calcium ions. Pyranine (Py) was added to the alginate solution as a small molecule probe for fluorescence studies. Desorption of Py in water from the alginate beads cross-linked with calcium ions was studied by using the steady state fluorescence technique. The fluorescence emission intensity (I) from Py was monitored during the desorption process at 512 nm using the time drive mode of the spectrofluorometer. The increase in I was attributed to Py release from the beads. The Fickian diffusion model was used to calculate the desorption coefficients, D_, which were found to be increased up to 3% (w/v) CaCl₂ concentration in the beads, and then decreased with a further increase of CaCl₂ content. On the other hand, the encapsulation efficiency of Py in the calcium alginate beads presented the reverse behavior compared to D. It was observed that, when the content of CaCl₂ was increased, the incubation time, t_0, for the start of desorption increased.     

Stimulated Emission Pumping Spectroscopy of SiH2: First Observation of the Spin-Orbit Interaction between the X?A1 and the ãB1 States

Stimulated emission pumping spectra of the ùB₁-X?¹A₁ transition of the SiH₂ radical were observed in order to obtain information about the ã³B₁ state through the spin-orbit interaction. The vibrational level structure of the X? state, which is the basis for the present observation of the triplet state, was well described with a polyad structure, in which both the 1ν₁ : 2ν₂ Fermi and the 2ν₁ : 2ν₃ Darling-Dennison anharmonic resonances were considered. In the P=10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm⁻¹ from the (000) level of the X? state was tentatively assigned as the ã³B₁ (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm⁻¹. This value is rather smaller than that expected based on the comparison with CH₂. This is considered to be due to poor overlap between the vibrational wave functions in the ã and the X? state.     

Cation self-diffusion and the isotope effect in Mn1−δO

Diffusion of ⁵⁴Mn in Mn_1?δO single crystals has been measured by a serial sectioning technique as a function of temperature (1000–1500°C) and deviation from stoichiometry (0.00003 < δ < 0.12). The value of m in the expression varies from about 6 at low Po₂ at all temperatures to a value approacing 2 at high Po₂ and high temperatures, thus suggesting that diffusion occurs by doubly charged vacancies at low Po₂ with increasing contributions from singly charged and neutral vacancies as Po₂ (and vacancy concentration) increases. For δ near 0.1, the values of D fall below the values extrapolated from smaller defect concentrations. The isotope effect for cation self-diffusion was measured by simultaneous diffusion of ⁵²Mn and ⁵⁴Mn in Mn_1?δO (0.0004 < δ < 0.116) at 1300 and 1500°C. The measured values of fΔK are independent of temperature within experimental error, and decrease from a value of 0.70 at low defect concentrations to 0.37 for large values of δ. The isotope-effect results suggest that diffusion occurs by single non-interacting vacancies at low defect concentrations; defect-defect interactions become important for δ ? 0.01. The defect-defect interactions may involve essentially individual defects or may result in defect clusters; the similarity between the present isotope-effect results and those for Fe_1?δ0 suggests that defect clustering plays a significant role in mass transport in Mn_1?δO at large values of δ.