Bulk Nano Research Articles

THE ORIGIN OF FERROMAGNETISM IN Ni-DOPED ZnO AND SnO2

We present a detailed study of the ferromagnetism in nano- Ni -doped SnO 2 and ZnO . It is shown that the ferromagnetic behavior is not an intrinsic property of the systems but rather associated with the presence of n Ni particles in both matrices. The ferromagnetic transition of all Ni -doped samples is at 631(2) K, the same as the TC value for bulk Ni and nano- Ni powder. The saturation moments of the nano- Ni -doped samples scale with the Ni concentration and are much lower than that of pure Ni . This is due to the large surface area of nano- Ni particles which are partially oxidized due to nano- NiO . 119 Sn Mössbauer spectroscopy studies on Sn 0.96 Ni 0.04 O 2 do not show any transferred hyperfine field on the Sn nuclei, confirming that the magnetic properties stem from a different phase.

Zirconium Aluminum Carbides: New Precursors for Synthesizing ZrO2-Al2O3Composites

ZrO2–Al2O3 nanocrystalline powders have been synthesized by oxidizing ternary Zr2Al3C4 powders. The simultaneous oxidation of Al and Zr in Zr2Al3C4 results in homogeneous mixture of ZrO2 and Al2O3 at nanoscale. Bulk nano- and submicro-composites were prepared by hot-pressing as-oxidized powders at 1100°–1500°C. The composition and microstructure evolution during sintering was investigated by XRD, Raman spectroscopy, SEM, and TEM. The crystallite size of ZrO2 in the composites increased from 7.5 nm for as-oxidized powders to about 0.5 μm at 1500°C, while the tetragonal polymorph gradually converted to monolithic one with increasing crystallite size. The Al2O3 in the composites transformed from an amorphous phase in as oxidized powders to θ phase at 1100°C and α phase at higher temperatures. The hardness of the composite increased from 2.0 GPa at 1100°C to 13.5 GPa at 1400°C due to the increase of density.

Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy

The NaNO(3) droplets with sizes of 1-5 microm generated from a nebulizer were deposited on a ZnSe substrate in a Fourier transform infrared attenuated total reflection (FTIR-ATR) chamber. After solidification of the droplets with dry N(2) gas passing through the chamber, the solid NaNO(3) particles were monitored by in situ FTIR-ATR spectra in cycles of deliquescence and efflorescence processes with varying relative humidities (RHs). With an increase in the RH, a dominant peak at approximately 3539 cm(-1), together with three relatively weak peaks at approximately 3400, approximately 3272, and approximately 3167 cm(-1), in the O-H stretching band of water was resolved by the high signal-to-noise ratio FTIR-ATR spectra. The dominant peak and the three relatively weak peaks were contributed by the water monomers and the aggregated water molecules adsorbed on the surfaces of solid NaNO(3) particles, respectively. When the RH approached approximately 72%, slightly lower than the deliquescence RH (74.5%), the band component at approximately 3400 cm(-1) became the main peak, indicating that the water monomers and the aggregated water molecules aggregated to form a thin water layer on the surfaces of solid NaNO(3) particles. A splitting of the nu(3)-NO(3)(-) band at 1363 and 1390 cm(-1) at the RH of approximately 72%, instead of the single nu(3)-NO(3)(-) band at 1357 cm(-1) for the initial solid NaNO(3), was observed. We suggested that this reflected a phase transition from the initial solid to a metastable solid phase of NaNO(3). The metastable solid phase deliquesced completely in the region from approximately 87% to approximately 96% RH according to the fact that the nu(3)-NO(3)(-) band showed two overlapping peaks at 1348 and 1405 cm(-1) similar to those of bulk NaNO(3) solutions. In the efflorescence process of the NaNO(3) droplets, the nu(1)-NO(3)(-) band presented a continuous blueshift from 1049 cm(-1) at approximately 77% RH to 1055 cm(-1) at approximately 36% RH, indicating the formation of contact ion pairs between Na(+) and NO(3)(-). Moreover, in the RH range from approximately 53% down to approximately 26%, two peaks at 836 and 829 cm(-1) were observed in the nu(2)-NO(3)(-) band region, demonstrating the coexistence of NaNO(3) solid particles and droplets.

Adhesive Force Assisted Imprinting of Soft Solid Polymer Films by Flexible Foils

We report a simple, rapid, room temperature, pressure-less and large area (approximately cm2) imprinting technique for high fidelity patterning of soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, both on planar and curved surfaces. The key element of the method is the use of patterned thin flexible foils that readily and rapidly attain a conformal contact with soft (shear modulus < 0.1 MPa) solid surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous elastic deformations of the surface on the scale of the features. For example, we used the protective aluminum foils of commercial data storage discs, both with or without data stored, for micron and sub-micron pattern transfer. The patterns are made permanent by UV-ozone treatment (for PDMS) or by controlled drying (for hydrogels). Interestingly, elastic contact imprinting of very thin (< 300 nm) films results in about 50% miniaturization of the original foil feature sizes. Complex two dimensional patterns could also be formed even by using a simple one dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

Soft lithography meets self-organization: Some new developments in meso-patterning

This is a brief review of our recent and ongoing work on simple, rapid, room temperature, pressure-less and large area (∼ cm2) imprinting techniques for high fidelity meso-patterning of different types of polymer films. Examples include soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, thermoplastics like polystyrene (PS), polymethylmethacrylate (PMMA) etc both on planar and curved surfaces. These techniques address two key issues in imprinting: (i) attainment of large area conformal contact with the stamp, especially on curved surfaces, and (ii) ease of stamp detachment without damage to the imprinted structures. The key element of the method is the use of thin and flexible patterned foils that readily and rapidly come into complete conformal contact with soft polymer surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous deformations of the film surface on the scale of the features. Complex two-dimensional patterns could also be formed even by using a simple one-dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

Small scale mechanical properties of polycrystalline materials: in situ diffraction studies

The recent developments in the fields of processing, mechanical characterisation as well as simulation allow for a deeper study of the relationships between the microstructure and the mechanical properties of nanostructured materials (thin films and bulk nano materials). The understanding of size effect on the elastic and plastic deformation mechanisms is of both fundamental and practical interests in particular for the optimisation of industrial applications. Understanding of the relationships between their fabrication, microstructure, and mechanical properties is also fundamental. In particular, one of the key factors is related to the deformation mechanisms responsible of the elevated mechanical properties of such materials. In situ structural studies during deformation process allow quantifying the strain stress relationship of nanomaterials in the elastic and plastic regimes in relation with the microstructure since the spacing d of the material is used as a strain gage. Due to the very small dimensions of the crystallites, very intense sources are necessary such as neutron reactors for bulk nanomaterials and synchrotrons for nanostructured thin films and bulk nanomaterials. For more than a decade, our group has developed in situ tensile testing in diffractometers at the laboratory using rotating anodes as X-ray sources or at dedicated beam lines of synchrotron and Neutron facilities such as LURE (France), ESRF (France), PSI (Switzerland), ALS (USA or in a near future SOLEIL (France). A close connection has been made recently with this last facility through an ANR-Pnano project called Cmonano. In addition, local analyses are done using nanoindentation for intrinsic mechanical properties and atom probe tomography for structural characterisation. Atomistic and molecular dynamics simulations are completing the instrumental study. This paper will give an overview of the subject considering recent experiments on nanometric multilayers (WCu) and thin films (MoCr) encountered in micro electronic applications as well as bulk CuNb and CuTa nanocomposites processed by severe plastic deformation.

Preparation and mechanism study of bulk pure rare-earth metals with amorphous and nanocrystalline structures

The preparation and the mechanism study of bulk pure rare-earth metals with amorphous and nanocrystalline structures, which were produced by spark plasma sintering (SPS), were carried out in this paper. With different processing parameters, the amorphous, two phases of amorphous and nanocrystalline, and complete nanocrystalline microstructures have been obtained. The nano-grain sizes in the bulk nanocrystalline materials are found smaller than the original powder particles sizes, which may change the conventional viewpoint that the grains in the sintered bulk are generally coarser than the raw powder particles. The technique developed in the present work can be extended to the preparation of many other nano bulk metal materials, and thus enables the studies of the nano-size effects on the physical, chemical and mechanical properties of bulk nano materials.

Fabrication of amorphous bulk and multi-phase ceramics by melting method in the HfO2-Al2O3-Gd2O3-Eu2O3system

Ceramics have generally been fabricated from powders by shape forming & sintering methods except for glasses and glass ceramics. Glasses and glass ceramics can be fabricated by melting methods. The melting method has not only higher productivity but also higher shape forming ability than powder processes via forming & sintering methods. Thus we have reinvestigated melting methods in binary and ternary oxides systems to fabricate amorphous bulk ceramics and bulk nano composites. We have successfully fabricated amorphous phases by simple melt solidification methods in ternary eutectic melts in the HfO2-Al2O3-Gd2O3system. The present study demonstrates the formation of the amorphous phases in quaternary systems HfO2-Al2O3-Gd2O3-Eu2O3. Furthermore, we have also succeeded to fabricate nano-structured bulk ceramics, which consisted of constituent oxide grains with 20–100 nm in size, by post annealing of the amorphous phase.

Structure and properties of confined sodium nitrite

The temperature evolution of the structure of NaNO(2) nanocomposite ferroelectric material in a porous glass with 7 nm pores was studied by neutron diffraction in temperature region from room temperature up to the melting, i.e. in the ferro- and paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with the structure of the bulk, but above the ferroelectric phase transition (and up to approximately 513 K) a volume premelted state is formed, manifesting itself in a growth of amplitudes of ion thermal vibrations, a steep increase of elementary cell volume and "softening" of lattice. For the first time the temperature dependence of order parameter eta for confined sodium nitrite is determined. eta (T) follows a power law with T(C)=425.6+/- 2.1 K and beta= 0.31+/- 0.04, which is essentially different from that for bulk NaNO(2). Our obtained data are in a good agreement with the results of earlier dielectric and neutron diffraction measurements.