Transparent conductors as solar energy materials: A panoramic review

Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

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Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Colloidal inorganic nanocrystals stand out as an important class of advanced nanomaterials owing to the flexibility with which their physical-chemical properties can be controlled through size, shape, and compositional engineering in the synthesis stage and the versatility with which they can be implemented into technological applications in fields as diverse as optoelectronics, energy conversion/production, catalysis, and biomedicine. The use of microwave irradiation as a non-classical energy source has become increasingly popular in the preparation of nanocrystals (which generally involves complex and time-consuming processing of molecular precursors in the presence of solvents, ligands and/or surfactants at elevated temperatures). Similar to its now widespread use in organic chemistry, the efficiency of "microwave flash heating" in dramatically reducing overall processing times is one of the main advantages associated with this technique. This Review illustrates microwave-assisted methods that have been developed to synthesize colloidal inorganic nanocrystals and critically evaluates the specific roles that microwave irradiation may play in the formation of these nanomaterials.

Microwave-assisted synthesis of colloidal inorganic nanocrystals.

This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements and concentrations, oxygen partial pressure, substrate and its orientation and temperature, deposition rate, post-annealing temperature and co-doping on the local structure and subsequent ferromagnetic ordering of TM-doped ZnO. It is unambiguously demonstrated that room-temperature ferromagnetism is strongly correlated with structural defects, and the carriers involved in carrier-mediated exchange are by-products of defects created in ZnO. The third part focuses on recent progress in TM-doped ZnO-based spintronics, such as magnetic tunnel junctions and spin field-effect transistors, which provide a route for spin injection from TM-doped ZnO to ZnO. Thus, TM-doped ZnO materials are useful spin sources for spintronics.

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films

Ferromagnetism usually only occurs in materials containing elements that form covalent 3d and 4f bonds. Its occurrence in pure carbon is therefore surprising, even controversial. A systematic magnetic force microscope study indicates that ferromagnetism in graphite is the result of localized spins that arise at grain boundaries.

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Room-temperature ferromagnetism in graphite driven by two-dimensional networks of point defects

Fine powders of Ni0.6 − xCuxZn0.4Fe2O4, where 0 ≤ x ≤ 0.4 was prepared by the citrate precursor method. The powders were calcined at 600 °C for a duration of 1 h and sintered at 900 °C for 3 h. The effect of compositional variation on structural, dielectric and magnetic properties of the Cu substituted NiZn ferrite was investigated. X-ray diffraction measurements confirmed the formation of single-phase cubic spinel structure at such low temperature of calcinations and sintering. A maximum density of 4.7 g/cm3 was obtained for the Cu substituted ferrite. The grain sizes were estimated from the SEM micrographs. The addition of copper promoted grain growth, resulting in increase in grain size. Curie temperature, however, was understandably lowered with the increase in Cu content. A saturation magnetization value of 92 emu/g was obtained for the composition x = 0.2. This value is higher than that reported for ferrites prepared by the conventional ceramic method. Ferrite with Cu concentration of x = 0.4, showed the highest value of initial permeability.

Structural, dielectric and magnetic properties of NiCuZn ferrite grown by citrate precursor method

Microstructural, dielectric and magnetic behavior of spin-deposited nanocrystalline nickel zinc ferrite thin films for microwave applications

In this work dc-magnetization, electronic structural, and Raman investigations of Ti1−xMnxO2 (x = 0.00, 0.05, 0.10, and 0.15) thin films deposited on fused-quartz substrate by a simple and cost effective spray pyrolysis technique have been reported. X-ray diffraction revealed the formation of pure anatase TiO2 phase devoid of elemental Mn clusters in all the Mn incorporated TiO2 films. It is established by x-ray photoelectron spectroscopic (XPS) measurements that Ti ions substituted by Mn ions in both divalent and trivalent states in the TiO2 matrix. No peak corresponding to Mn+4 could be evidenced by XPS. The Raman study has further established the formation of TiO2 in anatase structure in both pure TiO2 and Mn-doped TiO2 films. The Ti1−xMnxO2 films with x ≥ 0.05 exhibit ferromagnetic ordering at room temperature which arises most likely due to formation of bound magnetic polarons.

Room temperature ferromagnetism in Mn doped TiO2 thin films: Electronic structure and Raman investigations

Micro Raman, Mossbauer and magnetic studies of manganese substituted zinc ferrite nanoparticles: Role of Mn

It has been possible to induce room temperature ferromagnetism, exhibiting high transition temperature, in tin oxide thin films by introducing manganese in a SnO2 lattice. The observed temperature dependence of the magnetization predicts a Curie temperature exceeding 550 K. A maximum saturation magnetic moment of 0.18±0.04 μB per Mn ion has been estimated for spray pyrolized Sn1−xMnxO2−δ thin films, with x=0.10. For Mn concentration (x) higher than 0.10, the films show linear behavior. The magnetization-versus-field studies indicate that the origin of ferromagnetism lies neither in ferromagnetic metal clusters nor in the presence of metastable phases. The structure factor calculations reveal that Mn has been incorporated in the SnO2 lattice. Also, the electron transport investigation indicates that there is a change of Mn occupancy from substitutional to interstitial sites of the SnO2 lattice when the Mn concentration exceeds 7.5 at. %. These films do not exhibit anomalous Hall effects at room temperature...

Subhash C. Kashyap

Papers

Structural, dielectric and magnetic properties of NiCuZn ferrite grown by citrate precursor method

Microstructural, dielectric and magnetic behavior of spin-deposited nanocrystalline nickel zinc ferrite thin films for microwave applications

Room temperature ferromagnetism in Mn doped TiO2 thin films: Electronic structure and Raman investigations

Micro Raman, Mossbauer and magnetic studies of manganese substituted zinc ferrite nanoparticles: Role of Mn

High temperature ferromagnetism in Mn-doped SnO2 nanocrystalline thin films