Volume 59, Nº 4 (2023)

Ammonium iodide (NH4I) has been shown to have an inhibiting effect on the growth kinetics of lead sulfide films at initial NH4I concentrations in solution from 0.05 M to 0.40 M. The addition of the inhibitor leads to a decrease in grain size, an increase in the fraction of nanoparticles in the PbS films to ~13%, and an increase in the iodine content of the films to 3.7 at %, depending on growth conditions. X-ray diffraction characterization has shown that the films have a B1 cubic structure (sp. gr. 
). Increasing the inhibitor concentration in solution leads to an increase in the lattice parameter of the lead sulfide from 0.59315(1) to 0.59442(3) nm, due to iodine substitution for sulfur in the PbS crystal lattice. The spectral sensitivity peak and the long-wavelength edge of the photoresponse of the PbS films shift to shorter wavelengths from 2.5 to 2.2 and from 3.0 to 2.8 μm, respectively, which is attributable to the formation of the wide-band-gap phase PbI2. Using low-temperature measurements, the thermal band gap of the films grown in the presence of 0.15 and 0.25 mol/L NH4I has been determined to be 0.46 and 0.51 eV. The respective activation energies for acceptor impurity levels are 0.135 and 0.153 eV. The iodine-doped PbS films offer a relatively high voltage responsivity in the IR spectral region owing to an n- to p-type conversion, in combination with an anomalously short response time.

In this paper, we report on the growth of aluminum molybdenum oxide (AlxMoyOz) films via atomic layer deposition (ALD) with the use of trimethylaluminum (TMA) (Al(CH3)3), molybdenum oxytetrachloride (MoOCl4), and water. The film growth process was studied in situ using a quartz crystal microbalance and ex situ using various X-ray techniques. AlxMoyOz ALD was performed using supercycles consisting of TMA/H2O and MoOCl4/H2O subcycles. We obtained two types of films, with the subcycles in the ratio 1 : 1 (1Al1MoO) and 1 : 7 (1Al7MoO). Film growth at 150°C was shown to be a linear process, with growth rate of 3.0 and 5.7 Å/supercycle for 1Al1MoO and 1Al7MoO, respectively. The density of the 1Al1MoO and 1Al7MoO films were 3.7 and 3.9 g/cm3, respectively, and their surface roughness did not exceed 20 Å. The oxidation state of the molybdenum in the films found to be 6+, 5+, and 4+. X-ray diffraction characterization showed that the films had an amorphous structure.

This paper reports on the preparation and properties of phosphate materials for medical applications: brushite (CaHPO4·2H2O) or monetite (CaHPO4) based cements prepared from β- and α-Ca3(PO4)2 (TCP) via isomorphous substitutions of Na+ or K+ for Ca2+ and of SiO4-4  or SO42-  for 
. The mixing liquid used to prepare phosphate cements from substituted TCP was orthophosphoric acid or H2O, and TCP was mixed with dry Ca(H2PO4)2·H2O. Isomorphous substitutions of Na+ and K+ for Ca2+ ions and PO43- and PO42-  for SiO44-, SO42  were confirmed by scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. It has been shown that, as a result of hardening of cement pastes with the use of different mixing liquids, one can obtain materials differing in microstructure, in which brushite or monetite prevails, depending on the TCP phase used in the preparation of the cement. In addition, we have studied interaction of the cements with water for a long time (16 days). The pH of the aqueous medium has been shown to vary from 5 to 7.5. This pH range is favorable for medical applications of the phosphate materials studied.

This paper presents results of femtosecond laser micromachining of a transparent glass-ceramic in the Li2O–Al2O3–SiO2 system with a near-zero linear thermal expansion coefficient in the thermal and athermal regimes. Electron microscopy and electron diffraction data confirm complete amorphization of nanocrystals of β-eucryptite-like solid solutions under the effect of laser pulses. Using quantitative phase microscopy, we have evaluated refractive index changes in individual laser-written tracks. In the athermal regime at a pulse repetition rate of 10 kHz, complete glass-ceramic amorphization leads to a decrease in the refractive index of the material (Δn = −0.0035) in the laser treatment region, which opens up the possibility of using direct laser writing of channel waveguides in a thermally stable glass-ceramic matrix.

Self-propagating high-temperature synthesis has been used to nitride zircon with aluminum additions (5–30%). We have examined the influence of the key process parameters (composition of the starting mixture, gas pressure, and sample diameter) on the combustion speed, nitrogen content, and phase composition of the synthesis products and found critical parameters at which combustion was impossible: less than 20% aluminum, nitrogen pressure under 2 MPa, and sample diameter less than 35 mm. The addition of 20–30% aluminum has been shown to change the phase composition of the synthesis products. On the addition of 20–25% Al, the phase composition was ZrN, Al2O3, Si3Al3O3N5, ZrO2, and ZrSi2; at 30% Al, it was ZrN, Al2O3, ZrSi2, Al3O3N5. The combustion products have been shown to contain aluminum oxynitride (Al3O3N5) forming from the gas phase. We have identified the mechanism underlying nitridation of a ZrSiO4 + Al mixture in combustion mode. A composite powder with the composition ZrN–Al2O3–ZrSi2–Al3O3N was tested as a material for producing coatings by nonvacuum electron-beam cladding.

Analysis of impact bending test results for a large number of specimens is used to investigate fracture of a weld metal consisting predominantly of acicular ferrite. The metal has a very broad ductile-to-brittle transition interval: from +20 to below –60°C. In the temperature range studied, we observe three stable impact toughness levels. Transitions between them with decreasing temperature determine the scatter in the work done to fracture the specimen. According to fractography results, the ductile-to-brittle transition is due to a single-step change from a ductile fracture mechanism to cleavage. Cleavage cracks nucleate at large acicular ferrite grains. Their different arrangements on a cleavage site determine the impact toughness level. Comparison of dynamic fracture curves and the macroscopic structure of fracture surfaces demonstrates that cleavage cracks nucleate at the tip of a stably growing ductile crack. Examination of fracture surfaces makes it possible to identify individual cleavage events observed in the corresponding dynamic curve.