Nanoscale evaluation of lubricity on well-defined polymer brush surfaces using QCM-D and AFM

For preparing a “highly lubricated biointerface”, which has both excellent lubricity and biocompatibility, we investigated the factors responsible for resistance to friction during polymer grafting. We prepared poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(methyl methacrylate) (PMMA) brush layers with high graft density and well-controlled thickness using atom transfer radical polymerization (ATRP). We measured the water absorptivity in the polymer brush layers and the viscoelasticity of the polymer-hydrated layers using a quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The PMPC brush layer had the highest water absorptivity, while the PMPC-hydrated layer had the highest fluidity. The friction properties of the polymer brush layers were determined in air, water, and toluene by atomic force microscopy (AFM). The friction on each polymer brush decreased only when a good solvent was chosen for each polymer. In conclusion, the brush layer possessing high water absorptivity and fluidity in water contributes to reduce friction. PMPC grafting is an effective and promising method for obtaining highly lubricated biointerfaces.     

Photovoltaic Properties of Titanium Dioxide Nanowires with Different Crystal Structures

Titanium dioxide(TiO₂) nanowires with different crystal structures were successfully synthesized, and their charge transfer properties were further investigated by surface photovoltage(SPV), transient photovoltage(TPV) and surface photocurrent(SPC) techniques. The results reveal that both the surface states and the charge transfer rate of different TiO₂ nanowires are highly dependent on their crystal structures.     

Structural and electrical properties of VO2/ZnO nanostructures

We examined the structural and electrical properties of uniformly-oriented VO₂/ZnO nanostructures. VO₂ was deposited on ZnO templates by using a direct current-sputtering deposition. Scanning electron microscope and transmission electron microscope measurements indicated that b-oriented VO₂ were uniformly crystallized on ZnO templates with different lengths. VO₂/ZnO formed nanorods on ZnO nanorods with length longer than 250 nm. X-ray absorption fine structure at the V K edge of VO₂/ZnO showed M₁ and R phases of VO₂ at 30 and 100 °C, respectively, suggesting structural-phase transition occurring between the two temperatures. Temperature-dependent resistance measurements of VO₂/ZnO nanostructures revealed metal-to-insulator transition at 65 °C and 55 °C during a heating and a cooling, respectively, regardless of ZnO length. Asymmetry behavior of resistance curves from VO₂/ZnO nanostructure during a heating and a cooling was attributed from a strong bond of VO₂ and ZnO.     

Profile calculation of gold nanostructures by dispersed-nanosphere lithography through oblique etching for LSPR applications

Nanosphere lithography is an inexpensive method used to fabricate gold nanostructures on a substrate. Using dispersed-nanosphere lithography, in which the nanospheres are dispersed on a substrate, 2D or 3D nanostructures can be fabricated by obliquely depositing a gold film on the nanospheres and etching the gold film afterward. These nanostructures are tunable and acute, and are thus good emitting elements for the localized surface plasmon resonance applications. So far, for the fabrication of nanostructures on a substrate with dispersed nanospheres, only 2D nanostructures have been reported through perpendicular etching. We report in this paper that the 3D nanostructures fabricated by dispersed-nanosphere lithography are rigid non-conformal structures, and perpendicular gold etching can be expanded to oblique etching, which provides more possibilities for fabricating the gold nanostructures in various shapes. The profiles of gold nanostructures after several varying angle depositions, and their final profiles after perpendicular or oblique etching, are calculated in this paper. Our profile simulations are applicable for nanospheres (or microspheres) within the range of tens of nanometers to tens of micrometers, and are consistent with our fabricated nanostructures observed using scanning electron and atomic force microscopy. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hydroxyapatite synthesis from biogenic calcite single crystals into phosphate solutions at ambient conditions

Hydroxyapatite is one of the most important bone substitute biomaterials. Here, it has been successfully overgrown on biogenic seed crystals at ambient conditions. Single crystals of calcite from Atrina rigida, Paracentrotus lividus and Heterocentrotus mammillatus have been soaked in phosphate solution with different concentrations and pHs for 2 months. X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy have been used to characterize soaking precipitates. The results show that the conversion of calcite to hydroxyapatite occurs to an extent which depends on composition and morphology of seed crystals, and starting concentration and pH of phosphate solutions. In the same experimental conditions, synthetic calcite single crystals did not convert to hydroxyapatite. The morphological observations suggest for hydroxyapatite formation, a mechanism that involves a superficial dissolution of calcite and a subsequently overgrowth of hydroxyapatite. Moreover, the final architectural assembly of the hydroxyapatite crystals resembles the shape of the starting biogenic seed crystals.     

Nanostructure formation aided by self-organised Bi nanolines on Si(0 0 1)

We provide a mini review of recent theoretical investigations of nanostructure formation aided by self-organised Bi nanolines on the Si(0 0 1) surface. It is suggested that hydrogen-passivated single-domain Si(0 0 1) produced by the formation of defect-free, hundreds of nm long, and 1.2-1.5 nm wide Bi nanolines provides an appealing template with preferential sites for adsorption of other elements. Based on ab initio pseudopotential calculations it is suggested that using the Bi nanoline template it should be possible to grow the following structures: mixed Ge-Si dimer structures on the Si(0 0 1) terrace between two neighbouring Bi nanolines; small In nanoclusters along the nanoline; and line and cluster structures of Fe atoms with novel electronic and magnetic properties.     

Sonochemical rate enhanced by a new nanomagnetic embedded core/shell nanoparticles and catalytic performance in the multicomponent synthesis of pyridoimidazoisoquinolines

A sonochemical approach for the one-pot three-component synthesis of pyridoimidazoisoquinolines via by using phthalaldehyde, trimethylsilylcyanide and aminopyridines the presence of a catalytic amount of a new nanomagnetic catalyst Fe₃O₄@SiO₂-CO-C₆H₄-NH₂ is described. The characterization of the nanocatalyst and the product was done by various methods, such as FT-IR, SEM, EDX, TGA/DTA, NMR, MS and CHN analyses. This is the first design, preparation, characterization and application of the present core/shell nanomaterial and also the first ultrasound irradiated synthesis of the biologically and pharmaceutically important fused polycyclic compounds in ethanol as a green solvent. This novel protocol offers several advantages such as high yields, short reaction times, environmentally-friendly reaction media, easily isolation of the products, simple preparation and recoverability of the nanocatalyst by an external magnet and reusing several times without significant decrease in catalytic activity.     

Preparation of Ni3B2O6 nanosheet-based flowerlike architecture by a precursor method and its electrochemical properties in lithium-ion battery

A novel flower-like nickel borate of Ni₃B₂O₆ nanostructure was prepared through a hydrothermal treatment and sequential thermal decomposition of precursor without employing any template or surfactant. All the samples were characterized by XRD, IR, XPS, TG–DTA, nitrogen adsorption, SEM and TEM. The flower-like Ni₃B₂O₆ nanostructure was self-assembled by nanosheets with the thickness of about 40 nm. The electrochemical properties in lithium-ion battery of flower-like Ni₃B₂O₆ nanostructure were studied by the cyclic voltammetry, galvanostatic cycling test, and electrochemical impedance spectroscopy, which showed it had a high initial discharge capacity and a good reversibility.     

3D-TEM characterization of nanometric objects

The increasing level of research that is nowadays performed on the nanoscale requires specific powerful tools to characterize objects on that scale. We demonstrate in this work the usefulness of three-dimensional transmission electron microscopy (3D-TEM) used in a quantitative way to image and characterize nanomaterials with complex structures and morphologies. The tomographic recording process is a powerful tool to improve the signal-to-noise ratio when imaging nano-objects that cannot strongly extinguish electrons and to clear up the ambiguity of image interpretation due to superposition effects. The resulting ability to distinguish between the “inner” and the “outer” parts of an object as well as to determine its 3D characteristics can in turn yield quantitative information and constitutes the main focus of this paper. Complex morphologies and internal structures on the nanometer scale can thus be resolved in all spatial dimensions, and numerical densities of particles or porosities can be quantified. For porous materials, it is also possible to get the connectivity of the pores, their shapes and distribution. The 3D-TEM technique associates tomographic recording to a careful repositioning of the recorded 2D images, followed by a 3D reconstruction. It allows the recovery of a spatial resolution close to (1.5 nm)³ that can be used to perform quantitative analysis relevant to almost all types of nanometric samples encountered when 3D information down to a few nanometers is required.     

Electrical characterisation of local electronic properties of self-assembled semiconductor nanostructures using AFM

Scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) have been used to characterise self-assembled Ge nanoislands embedded in silicon. High contrast in capacitance and in surface potential are found between areas with nanostructures and areas without any nanostructures. The local dC/dV spectroscopy shows flat band voltage shift attributed to the presence of electric charges in the nanostructures. The KPFM contrast has been correlated with the band structure offsets between the nanostructure and the matrix barrier. Effects of the charging have been measured from the dC/dV curve and discussed in terms of the wetting layer influence that contributes to the escape of the charges when percolation of charges is observed.