There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

Photoinduced reactivity of titanium dioxide

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Nano‐photocatalytic Materials: Possibilities and Challenges

Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

The stibiotantalite (ABO4) family includes a number of ferroelectrics and antiferroelectrics with excellent potential for applications. We report the deposition of phase-pure, polycrystalline thin films of BiNbO4 on Si(100) substrates using pulsed laser ablation. The deposition conditions were optimized with respect to substrate temperature, laser parameters, and the ambient oxygen pressure. The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, and Raman spectroscopy, while their microstructure was studied by atomic force microscopy and scanning electron microscopy. Dielectric hysteresis studies indicated that films with a thickness below ≈250 nm are ferroelectric, while thicker ones are antiferroelectric.

Synthesis of thin films of polycrystalline ferroelectric binbo4 on si by pulsed laser ablation

Origin of luminescence in porous silicon

The temperature dependence of the energy loss of 624-keV electrons in ferroelectric barium titanate (${\mathrm{BaTiO}}_{3}$) and triglycine sulfate [(${\mathrm{CH}}_{2}$${\mathrm{NH}}_{2}$COOH${)}_{3}$ ${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$] has been studied with the use of a single-gap magnetic spectrometer. The present measurements confirm the anomalous increase in energy loss of electrons near the Curie temperature ${T}_{C}$ and indicate its dependence on (a) the magnitude of the dielectric anomaly at ${T}_{C}$, (b) the effect of a dc electric field larger than the coercive field, and (c) the application of an alternating electric field. Probable mechanisms for the origin of the observed phenomenon are discussed.

Enhancement of energy loss of fast electrons in a ferroelectric medium near the Curie temperature.

Nanocomposite CdS-ZnO thin films deposited directly on quartz substrates by high-pressure magnetron sputtering show a completely reversible photodarkening at a very low threshold intensity (∼1kWcm−2), and a moderately fast recovery time (<1ms). This makes them ideal in optical limiting applications for both continuous wave as well as high rep-rate pulsed lasers. The same system also shows an intensity-dependent quenching of the photoluminescence. Using a pump-probe experiment, we show that photodarkening in such a quantum-dot thin film originates from excited state absorption.

Fast and reversible excited state absorption in II-VI-based nanocomposite thin films

The formation of amorphous phases in immiscible alloys with a large positive enthalpy of mixing is thermodynamically unfavorable. Co-sputter deposited Cu–Nb films exhibit a nanoscale phase separation into Cu-rich and Nb-rich amorphous regions. They show relatively high room temperature resistivity, a negative temperature coefficient of resistance (TCR), and an incomplete superconducting transition with onset at 3.7 K. Annealing the nanophase-separated amorphous films at 200 °C results in the nucleation of fcc Cu-rich nanocrystals within an Nb-rich amorphous matrix. This film exhibits multiple resistance steps, eventually showing a sharp drop with (TC)onset = 3.7 K. Annealing at 350 °C leads to complete devitrification via the formation of large bcc Nb-rich grains encapsulating the existing fcc Cu nanocrystals. These films show low room temperature resistivity, positive TCR, and a sharp superconducting transition with onset at 5.2 K. The electrical transport and superconducting behavior appear to be consistent with a two-stage crystallization process.

Pushan Ayyub

Papers

Synthesis of thin films of polycrystalline ferroelectric binbo4 on si by pulsed laser ablation

Origin of luminescence in porous silicon

Enhancement of energy loss of fast electrons in a ferroelectric medium near the Curie temperature.

Fast and reversible excited state absorption in II-VI-based nanocomposite thin films

The influence of nanoscale phase separation and devitrification on the electrical transport properties of amorphous Cu-Nb alloy thin films.