Positronics of radiation-induced effects in chalcogenide glassy semiconductors

Using As2S3 and AsS2 glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models

Influence of the composition on the thermoelectric and electro-physical properties of Ge-Sb-Te thin films for phase change memory application

Influence of the composition variation along the quasi-binary line GeTe-Sb2Te3 on the thermoelectric and electro-physical properties of thin films was investigated. GST amorphous thin films have high Seebeck coefficients, which drops nearly on the order of magnitude after the crystallization. Temperature dependences of the resistivities were studied, and it was determined that crystallization temperature increases with moving along the quasi-binary line GeTe-Sb2Te3 from GeSb4Te7 to GeSb2Te4, and then to Ge2Sb2Te5, while the phase transition temperature range decreases. Current-voltage characteristics of amorphous thin films have three voltage ranges with different dependencies due to the different mechanisms of charge carrier transport

Low power reconfigurable multilevel nanophotonic devices based on Sn-doped Ge2Sb2Te5 thin films

In the past years, Ge2Sb2Te5 has been considered a promising functional material for a variety of reconfigurable multilevel devices, including photonic integrated circuits for the post-von Neumann arithmetic processing. However, despite significant advances, it is necessary to reduce the switching energy of Ge2Sb2Te5 for creation of the on-chip low power all-photonic spiking neural networks. The present work focuses on the effect of tin ion implantation on the properties of amorphous Ge2Sb2Te5 thin films, as well as on the performance of Mach-Zehnder interferometers and balanced beam splitters based on them. As a result, Sn-doping accompanied by the formation of weaker bonds in Ge2Sb2Te5 thin films is an efficient approach to significantly reduce the threshold energy of fs-laser initiated phase transitions and change the effective absorption coefficient. The possibility of using the Sn-doped Ge2Sb2Te5 thin films for fully optical multilevel reversible recording between 9 different levels (3 bits) has been demonstrated by experimental measurements of fabricated on-chip balanced beam splitters. The obtained results show that the Sn doping of Ge2Sb2Te5 layer can be used to optimize the properties of the GST225 thin films, in particular to reduce the switching energy. So, it has the potential to improve the characteristics of reconfigurable multilevel nanophotonic devices using the GST225 thin films, including fully non-volatile memory and developed on-chip low power all-photonic circuits for post-von Neumann arithmetic processin

Positronics of radiation-induced effects in chalcogenide glassy semiconductors

Using As2S3 and AsS2 glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models

Isothermal and CW laser crystallization of amorphous Ge2Sb2Te5 thin films

Transmission electron microscopy results are presented for as-deposited amorphous Ge2Sb2Te5 thin films after theirs isothermal annealing and CW laser illumination. Obtained microphotographs suggested that the crystallization process was driven solely by heterogeneous nucleation on the film boundary. The simplified model of steady-state crystallization process was developed for the case of heterogeneous nucleation mechanism. The values of nucleation rate and growth rate for isothermal and CW laser crystallization are calculated. The calculated values are in reasonable agreement with both our experimental data and with results previously published by the other authors

Isothermal and CW laser crystallization of amorphous Ge2Sb2Te5 thin films

Transmission electron microscopy results are presented for as-deposited amorphous Ge2Sb2Te5 thin films after theirs isothermal annealing and CW laser illumination. Obtained microphotographs suggested that the crystallization process was driven solely by heterogeneous nucleation on the film boundary. The simplified model of steady-state crystallization process was developed for the case of heterogeneous nucleation mechanism. The values of nucleation rate and growth rate for isothermal and CW laser crystallization are calculated. The calculated values are in reasonable agreement with both our experimental data and with results previously published by the other authors

Black hybrid iodobismuthate containing linear anionic chains

Three hybrid 1,1′-(1,n-alkanediyl)bis(4-methylpyridinium) iodobismuthates 1–3 were prepared by a facile solution route and showed thermal stability in air up to 230 °C. The structures of solids 1 and 3 contain zero-dimensional anions, and the structure of 2 contains one-dimensional linear anionic chains [BiI5]n2n−. Photoluminescence (PL) in the spectral range between 600 and 750 nm was observed for 1 and 2. DFT calculations and optical studies confirmed that compounds 1–3 are semiconductors with band gaps of 1.73–2.10 eV, which correspond with their intense black (for 2) or red (for 1 and 3) colors. The optical absorption of 2 in the red spectral range is primarily due to charge transfer from the I5p orbitals at the top of the valence band to the Bi6p orbitals at the bottom of the conduction band

One step microwave-assisted synthesis of fluorinated titania photocatalyst

Microwave-assisted high temperature hydrolysis of titanium oxysulfate, in the presence of ammonium fluoride, allows synthesizing nanocrystalline titanium dioxide photocatalysts possessing photocatalytic activity as high as the commercial photocatalyst Evonik Aeroxide® TiO2 P 25. Dye-sensitized reactions play an important role in organic dye discoloration in the presence of fluorinated titania