From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

The successful growth of 2-in. β-Ga2O3 crystals by the edge-defined, film fed growth (EFG) method was demonstrated. The optimization of growth conditions for larger single crystalline β-Ga2O3 is discussed in detail. The seeding conditions of temperature and neck width were found to be the most important factors to grow single crystals. X-ray rocking curve measurements of β-Ga2O3 crystals were conducted to estimate the dislocation densities of the grown crystals. Etch pit densities (EPDs) of the β-Ga2O3 crystals were also measured using KOH solution to measure the dislocation densities. The results were discussed combining with crystal growth parameters such as neck width to clarify the mechanisms of propagation and the origin of dislocations in crystals from phenomenological and crystallographic points of view.

https://iopscience.iop.org/article/10.1143/JJAP.47.8506/pdf

Growth of β-Ga2O3Single Crystals by the Edge-Defined, Film Fed Growth Method

Publisher Summary This chapter discusses the reduction potentials involving inorganic free radicals in aqueous solution. Because free radicals are usually transients, knowing their thermodynamic properties is primarily useful in mechanistic studies. Thus, the useful redox couples associated with a given free radical correspond to plausible elementary steps in reaction mechanisms. All potentials are expressed against the normal hydrogen electrode (NHE). Apart from the NHE, the standard state for all solutes is the unit molar solution at 25 °C. This violates the usual convention for species, such as O 2 that occur as gases, but because the rates of bimolecular reactions in solution are significant, the unit molar standard state is most convenient. The emphasis is on electron transfer reactions in which no bonds are formed or broken, electron transfer reactions in which concerted electron transfer and bond cleavage could occur, and certain atom transfer reactions. The chapter also presents a tabulation of ∆ f G ° values for all the radicals. A common approach in estimating the thermochemistry of aqueous free radicals is to use gas-phase data with approximations of solvation energies.

Reduction potentials involving inorganic free radicals in aqueous solution

β-Ga2O3 contains two crystallographically different Ga atoms in the asymmetric unit, one with tetrahedral and the other with octahedral coordination geometry. The Ga-O distances are in the range 1.833 (1)–1.863 (2) A within the tetrahedra, but are longer within the octahedra [1.935 (2)–2.074 (1) A]. The O atoms have a distorted cubic close packing. The crystal structure of β-gallium oxide has been determined previously by Geller [J. Chem. Phys. (1960). 33, 676–684].

A reinvestigation of β-gallium oxide

/pdf/structural-studies-on-the-rare-earth-carboxylates-4-the-2py6dui94l.pdf

Structural Studies on the Rare Earth Carboxylates. 4. The Crystal and Molecular Structure of Orthorhombic Trisodium Tris(pyridine-2,6-dicarboxylato)ytterbiumate(III)-14-hydrate.

/pdf/structural-studies-on-the-rare-earth-carboxylates-1-the-1hyfgzkfar.pdf

Structural Studies on the Rare Earth Carboxylates. 1. The Crystal and Molecular Structure of Na3[M(OCOCH2OCH2OCO)3].2NaClO4.6H2O, M = Nd, Gd, and Yb.

/pdf/structural-studies-on-the-rare-earth-carboxylates-6-a-sg1rvl1940.pdf

Structural Studies on the Rare Earth Carboxylates. 6. A Reinvestigation of Trisodium-tris(oxydiacetato)lanthanoidate(III) Di(sodium Perchlorate) Hexahydrate.

/pdf/structural-studies-on-the-rare-earth-carboxylates-11-on-the-2sklsqpcry.pdf

Structural Studies on the Rare Earth Carboxylates. 11. On the Crystal Structure of Hexagonal Trisodium Tris(pyridine-2,6-dicarboxylato)ytterbate(III) Mono(sodium perchlorate) Decahydrate.

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