Showing papers in "Current Opinion in Solid State & Materials Science in 2008"

Degradable biomaterials based on magnesium corrosion

Abstract: Biodegradable metals are breaking the current paradigm in biomaterial science to develop only corrosion resistant metals. In particular, metals which consist of trace elements existing in the human body are promising candidates for temporary implant materials. These implants would be temporarily needed to provide mechanical support during the healing process of the injured or pathological tissue. Magnesium and its alloys have been investigated recently by many authors as a suitable biodegradable biomaterial. In this investigative review we would like to summarize the latest achievements and comment on the selection and use, test methods and the approaches to develop and produce magnesium alloys that are intended to perform clinically with an appropriate host response.

Combustion synthesis and nanomaterials

Abstract: The recent developments and trends in combustion science towards the synthesis of nanomaterials are discussed. Different modifications made to conventional combustion approaches for preparation of nanomaterials are critically analyzed. Special attention is paid to various applications of combustion synthesized nanosized products.

Ionic liquids for synthesis of inorganic nanomaterials

Abstract: In this review, the recent development of synthesizing inorganic nanomaterials in ionic liquids (ILs) is outlined. There are encouraging results suggesting that the ionic liquid route can guide design, production, and application of inorganic nanomaterials across the range of size, shape, composition, and functionality. All examples clearly show that ILs add great value to inorganic nanomaterials area.

Liquid-like interface complexion: From activated sintering to grain boundary diagrams

Abstract: This article reviews recent experimental and theoretical results that elucidate the mysterious subsolidus activated sintering mechanism. A related new concept of liquid-like interface complexion and its broad applications in comprehending microstructural evolution and materials properties are discussed. A recently proposed thermodynamic model is discussed and further elaborated with new analyses that have not been published before. A long-range scientific goal is to develop quantitative and predictive grain boundary diagrams as a new tool for realizing predictable fabrication of materials by design.

Synthetic polymeric vectors in gene therapy

Abstract: The synthetic polymer vectors in gene therapy have opened a very prospective field for research in gene therapy and the area in the use of these synthetic polymers as vectors in targeting oncogenes is developing very fast. With the completion of Human Genome Project, the list of genetic targets is growing very fast. These diseases sparked the initiative to create such gene based therapeutics. The low levels of transfection and expression of the gene held non-viral methods are at a disadvantage; however, recent advances in vector technology have yielded molecules and techniques with transfection efficiencies, similar to those of viruses. Amongst these synthetic polymers, polyethylenimine (PEI) and the poly(amidoamine) (PAMAM) dendrimers and poly(β-amino ester) are used extensively as vectors in gene therapy.

Luminescent and structural properties of MgNb2O6 nanocrystals

Abstract: This study investigated the synthesis and luminescence properties of MgNb2O6 nanocrystals by citric gel process. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence (PL). The PL spectra excited at 270 nm had a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO6]7−. The optical absorption spectra of the 800 °C sample exhibited the band-gap energy of 3.6 eV. Furthermore, the microstructure and luminescence spectra of the products were investigated.

Preparation and characterization of conducting polyaniline/silica nanosheet composites

Abstract: A series of polyaniline/silica nanosheet composites (PANI/SNS) with different contents of the silica nanosheets derived from vermiculite via acid-leaching were prepared via the in situ chemical oxidation polymerization. The PANI/SNS composites were characterized with Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrical conductivity measurement. It is interesting that the electrical conductivities of the PANI/SNS composites increased with the increasing of the contents of the silica nanosheets added because of the moisture absorption. It was confirmed by the TGA analysis.

X-ray photoelectron spectra and the electronic band structure for non-centrosymmetric Bi2ZnB2O7 nonlinear single crystal

Abstract: We have synthesized and characterized the bismuth borate Bi 2 ZnB 2 O 7 single crystals. The results of the experimental measurements of the X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) along with an ab initio theoretical study of the electronic band structure, and density of states, are reported. The theoretical calculations are based on crystal structure built from our experimentally determined atomic parameters. The theoretical calculations have been done by using the full potential linearized augmented plane wave (FP-LAPW) method. We applied the Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) and the Engel–Vosko GGA formalism. The observed XPS pattern is in good agreement with the theoretical one, confirming the pure phase of Bi 2 ZnB 2 O 7 . The purity and composition of the as-prepared sample are studied by XPS analysis. XPS measurements show that the bismuth possesses +3 valence state, and Zn and B species exist only in the traditional valence states of Zn 2+ and B 3+ . The O 1s spectra are broad and asymmetric and can be deconvoluted into two peaks. The lower and higher binding energy peaks (around 530.1 and 531.5 eV) are assigned to originate from O 1s(1) and O 1s(2) terms, respectively, which are attributed to non-bridging oxygen (B–O − bonds) and bridging oxygen (B–O–B bonds), respectively. Our calculations show that Bi 2 ZnB 2 O 7 has an indirect energy gap and that Bi–O bonds are of strong covalent character.

Multilayered dielectric/ferroelectric thin films and superlattices

Abstract: We briefly review the status and new progress on the preparation and characterization of dielectric/ferroelectric multilayered thin films and superlattices and present some of our own research work in this field. It is pointed out that constructing multilayered dielectric/ferroelectric thin films and superlattices is an effective way to improve properties of dielectric/ferroelectric thin films and to probe new physical phenomena. There is no doubt that study on dielectric/ferroelectric multilayered thin films and superlattices will have been a topic of great interest in the forthcoming years, and it is expected that more well-designed dielectric/ferroelectric superlattices will be prepared and some new physical phenomena might emerge.

Birefringence, linear and nonlinear second-order optical susceptibilities of a noncentrosymmetric chalcopyrite compound HgGa2S4

Abstract: We present the results of the ab initio theoretical study of the linear and nonlinear optical susceptibilities for the HgGa2S4 single crystals using the all electron full potential-linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. We have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band structure and optical susceptibilities calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function e(ω) and its zero-frequency limit e1(0). The optical properties are analyzed, and the origin of some of the spectral peaks is discussed in terms of the calculated electronic band structure. The edge of optical absorption for e 2 xx ( ω ) and e 2 zz ( ω ) is located at 2.8 eV. The linear optical properties shows a large negative uniaxial anisotropy and birefringence which favors large second-order susceptibility χ ijk ( 2 ) ( ω ) . The imaginary and real parts of the second-order SHG susceptibility were evaluated. Our calculation show that χ 213 ( 2 ) ( ω ) is the dominant component which shows the largest total Re χ ijk ( 2 ) ( 0 ) valve 5.4 pm/V.

Temperature anomalies of emission spectra of Nd:Yb:La2CaB10O19 single crystals

Abstract: We have performed experimental investigations of absorption and emission spectra of Nd:Yb:La2CaB10O19 single crystals at different impurity content and temperatures. It was established that intensity of the Nd emission line at 910–930 nm is changed inversely after addition of Yb to the Nd doped crystals. This fact can indicate principal role of the Yb ions in the observed temperature features. Moreover, efficiency of transfer process increases with the temperature’s rising. The maximum efficiency is gained for 350 K and afterwards it is diminished. Modification of population occurs among Stark’s energy levels. The possible explanations for observed temperature dependences are connected by change of the phononassisted relaxation process and emission spectra and the back transfer Nd +3 Yb +3 that is thermally activated.

Structural characterisation of tribologically influenced silicon carbide ceramic surfaces

Abstract: Tribologically influenced ceramic surfaces are usually only looked at in terms of the wear effects: surface topography, friction coefficient, loss rates. Current efforts go towards a deeper understanding of mechanisms and kinetics. To gain this, the effects of the wear of ceramics on the phases and microstructures have to be analysed in detail. As an example for this, we studied tribologically influenced silicon carbide ceramics worn under water lubrication. Because structural changes occur within the uppermost μm and tribochemical reaction layers are often restricted to the nm-range, appropriate analytical tools have to be used and those come only now available. We will show how the currently developed techniques of X-ray microdiffraction combined with Raman spectroscopy can resolve many issues. Another recent improvement, transmission electron microscopy (TEM) on cross-sections prepared via the focused ion beam technology (FIB), helps to verify the findings of the former techniques.

Processing dependences of microstructure of ferroelectric thin films

Abstract: Ferroelectric thin film has been widely investigated in detail in recent years. The ferroelectric properties of thin films are obviously dependent on the microstructure of the film, which is influenced by some processing parameters for preparing the films, including precursor solution chemistry, nature of substrate, film thickness, and condition of heat treatment etc. In this paper, these processing dependences of the films are reviewed.

Optical properties of some laves phases compounds

Abstract: The optical properties for laves phase compounds have been calculated within the farm work of the full-potential linearized-augmented plane wave. The generalized gradient approximation (GGA) and the Engel–Vosko-generalized gradient approximation (EV-GGA) were used. Our calculations show that these compounds are metallic with more bands cuts the Fermi energy (EF) as we moving from Nb to Ta, Hf, Ti, in a consistent with the increasing the values of the density of states at Fermi level N(EF). The optical properties were calculated with and without Drude term, we analyzed the imaginary part of the optical properties using our calculated electronic band structure. The ground state properties of these compounds such as equilibrium lattice constant, bulk modulus are calculated and compared with available literature.