Mariusz Drygas

Structural and magnetic properties of GaN/Mn nanopowders prepared by an anaerobic synthesis route†

A new oxygen-free molecular precursor system based on (i) ammonolysis in refluxing/liquid NH3 of selected mixtures of gallium tris(dimethyl)amide Ga(NMe2)3 and manganese bis(trimethylsilyl)amide Mn[N(SiMe3)2]2 (Me = CH3, initial Mn-contents = 0.1, 5, 20, 50 at.%) followed by (ii) pyrolysis under flowing ammonia gas at 500, 700, and 900 °C afforded a range of nanocrystalline powders in the GaN/Mn system. The nanopowders were characterized mainly by powder XRD diffraction, FT-IR spectroscopy, Raman spectroscopy, SEM/EDX morphology examination, and XRF elemental analysis. Magnetization measurements as a function of magnetic field and temperature were carried out with a SQUID magnetometer. Structurally, the materials were shown to be single-phases based on the gallium nitride lattice. The presence of small quantities of residual amorphous Mn/N/Si/C species due to an incomplete transamination/removal of the trimethylsilylamide groups during ammonolysis was deduced from the XRF, FT-IR, Raman, and magnetization data. Magnetic properties for all nanopowders consistently pointed to a paramagnetic GaMnN phase with antiferromagnetic interactions among Mn-centers that under favorable circumstances reached the level of 3.8 at.% Mn. The paramagnetic phase was accompanied by a residual antiferromagnetic phase due to a facile oxidation in air of excessive Mn-containing by-products.

Ammonolysis of gallium phosphide GaP to the nanocrystalline wide bandgap semiconductor gallium nitride GaN

The pnictogen-metathesis reaction of microcrystalline gallium phosphide GaP with ammonia NH3 at temperatures of 900–1150 °C for 6–60 hours afforded in one step nanocrystalline powders of the wide bandgap semiconductor gallium nitride GaN. A suitable choice of conditions including variations of reaction temperature/time and manual grinding or high energy ball milling of the substrate enabled control over distinct GaN particle morphologies, regularly shaped particles or nanowires, and average crystallite sizes up to a few tens of nanometers. Under the applied conditions, all by-products were conveniently removed as volatiles affording pure GaN nanopowders. In contrast to ammonolysis of the related cubic GaAs and cubic GaSb, which yielded mixtures of the hexagonal and cubic GaN polytypes, here, the nitride was made exclusively as the stable hexagonal variety. All this supported specific reaction pathways with thermodynamics solely controlling the ammonolytical conversion of the cubic GaP substrate to the hexagonal GaN product.

Adsorption Properties of Nanocrystalline/Nanoporous Gallium Nitride Powders

A diverse pool of six semiconductor GaN nanopowders was synthesized by the thermally-driven pyrolysis of gallium imide at various temperatures. The XRD-derived average crystallite sizes for the nanopowders were in the range 1-17 nm. Standard nitrogen ad- sorption measurements at 77 K yielded the basic characteristics of the powder pore structures including the BET surface areas that spanned 23-287 m 2 /g. Rare studies of adsorption of water vapor, carbon dioxide, and hydrogen on the nitride nanopowders were carried out. The data on water vapor adsorption at 295 K supported chemisorption of water molecules on the primary adsorption centers and phy- sisorption on the secondary centers. The data on carbon dioxide adsorption at 273 K and hydrogen adsorption at 77 K were used to de- termine the selectivity of adsorption for these gases defined as the ratio of the respective Henrys constants calculated from the Langmuir equation. The GaN nanopowders showed remarkably diverse pore structure characteristics and adsorption properties that could be linked to the nitrides average crystallite size and crystallite agglomeration, the latter supported by helium density data.

Correction: Structural and magnetic properties of GaN/Mn nanopowders prepared by an anaerobic synthesis route

Correction for ‘Structural and magnetic properties of GaN/Mn nanopowders prepared by an anaerobic synthesis route’ by Mariusz Drygas et al., RSC Adv., 2015, 5, 37298–37313.