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

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

https://iopscience.iop.org/article/10.1088/0034-4885/72/3/036502/pdf

X-ray diffraction of III-nitrides

We address the role of excitonic coupling on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks provides a powerfully simple means to extract the magnitude of the intermolecular coupling energy, of approximately 5 and 30 meV for films spun from isodurene and chloroform solutions, respectively.

https://arxiv.org/pdf/cond-mat/0702663.pdf

Role of Intermolecular Coupling in the Photophysics of Disordered Organic Semiconductors: Aggregate Emission in Regioregular Polythiophene

High resolution 1s core hole X-ray spectroscopy in 3d transition metal complexes—electronic and structural information

Review on grazing incidence X-ray spectrometry and reflectometry ☆

Both anatase and rutile are well-known as stable phases of TiO2. In real-life samples, TiO2 is most likely to be a mixture of those phases rather than pure anatase and rutile, and therefore quantitative analysis is extremely important. It is basically possible to determine the average ratio by X-ray diffraction (XRD) using differences in the crystal structure, but it is not easy to do so when attempting mapping by point-by-point scanning. The present paper describes the successful application of newly developed projection-type XRD imaging, which is an extremely rapid and highly efficient method.

X-ray Diffraction Imaging of Anatase and Rutile

The local structural environment of lead (Pb) atoms in lead silicate glasses has been studied by two complementary spectroscopic techniques: Pb-LIII edge X-ray absorption fine structure (XAFS) and 207Pb solid state nuclear magnetic resonance (NMR) XAFS results have been obtained with two kinds of experimental devices: a synchrotron radiation source and a laboratory spectrometer The weak photon flux is then compensated by a higher stability of the source and a longer acquisition time The experiments were carried out on selected compositions of lead silicate glasses in which we observed PbO3 and PbO4 pyramidal units with short Pb–O bond lengths typical of a covalent bonding state

Pb2+ environment in lead silicate glasses probed by Pb-LIII edge XAFS and 207Pb NMR

The clearly resolved ${}^{1}{B}_{u}$ $(\ensuremath{\nu}=1)$ exciton and its vibronic structures show up in ordinary absorption and photoluminescence spectra of films of highly ordered poly(3-octylthiophene). The electroabsorption and the two-photon absorption spectra have unraveled the charge-transfer type ${}^{1}{A}_{g}$ $(\ensuremath{\nu}=2)$ exciton state lying 0.5 eV above the ${}^{1}{B}_{u}$ $(\ensuremath{\nu}=1)$ exciton state, while the electroluminescence spectrum shows the emission from the triplet exciton ${(}^{3}{B}_{u})$ lying 0.45 eV below the corresponding ${}^{1}{B}_{u}$ exciton. On the basis of the excitonic level diagram as well as the FeCl${}_{4}^{\ensuremath{-}}$-doping induced spectral change, the distinct photoinduced band observed at 1.0 eV is assigned to the internal transition between the triplet-exciton levels, ${}^{3}{B}_{u}$ $(\ensuremath{\nu}=1)$ $\ensuremath{\rightarrow}$ ${}^{3}{A}_{g}$ $(\ensuremath{\nu}=2)$.

Experimental determination of excitonic structure in polythiophene

La limite de detection minimum obtenue avec une excitation monochromatique est inferieure a 1 ppb ou 1 pg

Kenji Sakurai

Papers

Review on grazing incidence X-ray spectrometry and reflectometry ☆

X-ray Diffraction Imaging of Anatase and Rutile

Pb2+ environment in lead silicate glasses probed by Pb-LIII edge XAFS and 207Pb NMR

Experimental determination of excitonic structure in polythiophene

Synchrotron radiation excited x-ray fluorescence analysis using total reflection of x-rays