In the case of molecular beam epitaxy (MBE), the Mg acceptors are electrically active in the as‐grown material and a priori no additional annealing procedure is necessary. However, there are still some peculiarities in the electrical properties of ammonia‐process grown GaN:Mg and some annealing effect can be observed. Additionally, the character of weak temperature dependence in the vicinity of room temperature suggests that to describe the conduction process an additional conduction channel not related to the free carriers in the valence band must be taken into account. For these reasons, this article presents the results of low‐temperature resistivity and Hall Effect studies of Mg‐doped, ammonia‐process‐grown GaN. The studied samples are grown on low‐temperature buffers of GaN deposited on a sapphire substrate. High‐temperature annealing process (≈800 K) is carried out for all of them. The temperature dependences of the electrical transport properties before and after the annealing procedure are especially investigated at temperatures ranging from 10 up to 300 K. It is found that the low temperatures transport properties are sensitive to the annealing procedure and to describe the observed effects the hopping phenomena must be taken into account.

The π-conjugated polymer polydiphenylbutadiyne was prepared at the nanoscale confined inside the 1.2 nm 1-D pores of the aluminophosphate AlPO4-54. Molten 1,4-diphenyl-1,3-dibutadiyne (DPB) was inserted in the pores of AlPO4-54 at pressures below 0.3 GPa as confirmed by X-ray diffraction. Heating to 190 °C under a pressure of 0.4 GPa induced polymerization of DPB in the pores. Infrared microscopy indicates full polymerization in the pores and the presence of characteristic saturated C–H defects common to other nanostructured PDPB materials exhibiting important photocatalytic properties. This nanostructured PDPB confined in the hygroscopic AlPO4-54 host could be of interest for applications in gas sensing, photocatalysis and hydrogen generation.

Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B–N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)x chains per pore in BN/TON and BN/MTW, respectively. These 1-D BN chains potentially have interesting photoluminescence properties in the far ultraviolet region of the electromagnetic spectrum.

This paper presents low-temperature measurements of magnetoresistivity in heavily doped n-type GaN grown by basic GaN growth technologies: molecular beam epitaxy, metal-organic vapor phase epitaxy, halide vapor phase epitaxy and ammonothermal. Additionally, GaN crys-tallized by High Nitrogen Pressure Solution method was also examined. It was found that all the samples under study exhibit negative magnetoresistivity at low temperature (10 K < T < 50 K) and for some samples this effect is observed up to 100 K. This negative magnetoresistivity effect is analyzed in the frame of the weak localization phenomena in the case of three-dimensional electron gas in a highly doped semiconductor. This analysis allows to determine the phasing coherence time τφ for heavily doped n-type GaN. The obtained τφ value is proportional to T-1.34, indicating that the electron–electron interaction is the main dephasing mechanism for the free carriers.

This paper presents a comparative study of electron transport phenomena in n-type gallium nitride strongly doped, above the Mott transition, with silicon and germanium. The samples under study were grown by molecular beam epitaxy, metal-organic vapor phase epitaxy and halide vapor phase epitaxy. The temperature dependence of resistivity and Hall Effect was investigated at temperatures ranging from 10 K up to 650 K. The measurements at sub-room temperatures allow the study of scattering mechanisms related to extrinsic material properties. The observed temperature dependences of the electrical transport properties were analyzed in the frame of the model taking into account a typical scattering mechanism and degree of degeneracy of free carrier electron gas. The limitations of the applied models will be presented.

We determine the structural origin of an “atomic-spring-like effect”in a glassy silica-helium composite, which exhibits this mechanical property thatreversibly accumulates and restores energy at the subnanoscale based on a high-pressure experimental pair distribution function study combined with atom-scalemolecular simulations. These unexpected experimental results were obtained byusing a 3 μm spot size 61 keV X-ray beam and large area detector and bysubtracting the scattered intensity due to helium outside the sample from the silicasignal at the same focal point for each pressure point. The compression behavior ofthe glassy silica-helium composite is characterized on a structural level by the change from a uni- to bimodal distribution in the inter- tetrahedral distances in the amorphous isotropic structure of silica. We propose a simple characterization of this atomic-spring-like glass property using impedance spectroscopy measurements.

Phenylacetylene was inserted and polymerized in 5 nm diameter silica nanotubes under high pressure – high temperature conditions of 0.5 GPa and 437 K in an inert gas. The resulting nanocomposite was characterized by infrared and Raman spectroscopy and scanning and transmission electron microscopy. The vibrational spectroscopic data confirmed the formation of π-conjugated polyphenylacetylene and the absence of crystallization of the amorphous nanotubes. Scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, STEM-EDX, measurements confirmed the insertion of the polymer in the channels of the nanotubes and electron diffraction confirmed the amorphous nature of both the polymer and the host SiO 2 nanotubes. The obtained nanocomposite is a candidate material for gas sensing applications.