Aggregation and Conductivity in Hot-Grown Petroporphyrin Films

As a follow-up to our study on aggregation of metal-etioporphyrin complexes (Colloids Surf. A. Physicochem. Eng. Asp. 2022, 648, 129284), we considered thin films of three isomers of copper(II) etioporphyrin deposited on hot substrates. Despite the almost identical absorption spectra of isomers, their solid-state superstructures differ remarkably both in form and size. The lateral conductivity of films is much less sensitive to an isomer-type, regardless of the substrate temperature. However, the dark conductivity of cold-grown films is about two orders of magnitude higher than that of hot-grown films, whereas the photoconductivity of the latter is 100–1700 times greater, depending on the isomer

Hybrid Nanofluid in a Direct Absorption Solar Collector: Magnetite vs. Carbon Nanotubes Compete for Thermal Performance

The paper presents the experimental measurements of thermal efficiency of a tubular direct absorption solar collector (DASC) with a hybrid nanofluid based on magnetite (Fe3O4) and multi-walled carbon nanotubes (MWCNT). The volumetric concentration of Fe3O4 and MWCNT was 0.0053% and 0.0045%, respectively. The experiments were carried out for the flow rates of 2–10 L/min and a temperature difference up to 20 ∘C between the environment and the DASC. The performance of the DASC with a hybrid nanofluid was in the range of 52.3–69.4%, which was just beyond the performance of the collector with surface absorption. It was also found that using a MWCNT-based nanofluid with an equivalent total volumetric concentration of particles (0.0091%), the efficiency was 8.3–31.5% higher than for the cases with the hybrid nanofluid

Hybrid Nanofluid in a Direct Absorption Solar Collector: Magnetite vs. Carbon Nanotubes Compete for Thermal Performance

The paper presents the experimental measurements of thermal efficiency of a tubular direct absorption solar collector (DASC) with a hybrid nanofluid based on magnetite (Fe3O4) and multi-walled carbon nanotubes (MWCNT). The volumetric concentration of Fe3O4 and MWCNT was 0.0053% and 0.0045%, respectively. The experiments were carried out for the flow rates of 2–10 L/min and a temperature difference up to 20 ∘C between the environment and the DASC. The performance of the DASC with a hybrid nanofluid was in the range of 52.3–69.4%, which was just beyond the performance of the collector with surface absorption. It was also found that using a MWCNT-based nanofluid with an equivalent total volumetric concentration of particles (0.0091%), the efficiency was 8.3–31.5% higher than for the cases with the hybrid nanofluid

GaAs/Ge/Si epitaxial substrates: Development and characteristics

We developed high quality 2-inch GaAs/Ge/Si (100) epitaxial substrates, which may be used instead of GaAs monolithic substrates for fabrication of solar cells, photodetectors, LEDs, lasers, etc. A 200–300 nm Ge buffer layer was grown on Si substrates using the HW-CVD technique at 300°C, a tantalum strip heated to 1400°C was used as the “hotwire”. The MOCVD method was used to grow a 1 μ GaAs layer on a Ge buffer. The TDD in the GaAs layers did not exceed (1–2)∙105 cm-2 and the surface RMS roughness value was under 1 nm

Solar-driven desalination using nanoparticles

Due to the high light absorption and the possibility of localizing boiling to the interior of the receiver, nanoparticles are promising for solar-driven desalination. The paper presents an experimental study of the nanoparticle-based photothermal boiling of water with sea salt. The experiments were carried out using a laboratory-scale system with a transparent photothermal receiver of light and a closed condensate cycle. In this study, we tested three types of nanoparticles: multiwall carbon nanotubes with two main sizes of 49 nm and 72 nm, 110 nm iron oxide particles Fe3O4, and a commercial paste based on carbon nanotubes. The concentration of nanoparticles was varied up to 10% wt. We found that the nanoparticles enhance the steam generation by 23%, relative to a conventional desalinator with a black-body receiver. The best result was obtained for the 5% wt. concentration of carbon nanotubes

GaAs/Ge/Si epitaxial substrates: Development and characteristics

We developed high quality 2-inch GaAs/Ge/Si (100) epitaxial substrates, which may be used instead of GaAs monolithic substrates for fabrication of solar cells, photodetectors, LEDs, lasers, etc. A 200–300 nm Ge buffer layer was grown on Si substrates using the HW-CVD technique at 300°C, a tantalum strip heated to 1400°C was used as the “hotwire”. The MOCVD method was used to grow a 1 μ GaAs layer on a Ge buffer. The TDD in the GaAs layers did not exceed (1–2)∙105 cm-2 and the surface RMS roughness value was under 1 nm

MOCVD Growth of InGaAs/GaAs/AlGaAs Laser Structures with Quantum Wells on Ge/Si Substrates

The paper presents the results of the application of MOCVD growth technique for formation of the GaAs/AlAs laser structures with InGaAs quantum wells on Si substrates with a relaxed Ge buffer. The fabricated laser diodes were of micro-striped type designed for the operation under the electrical pumping. Influence of the Si substrate offcut from the [001] direction, thickness of a Ge buffer and insertion of the AlAs/GaAs superlattice between Ge and GaAs on the structural and optical properties of fabricated samples was studied. The measured threshold current densities at room temperatures were 5.5 kA/cm2 and 20 kA/cm2 for lasers operating at 0.99 μm and 1.11 μm respectively. In order to obtain the stimulated emission at wavelengths longer than 1.1 μm, the InGaAs quantum well laser structures with high In content and GaAsP strain-compensating layers were grown both on Ge/Si and GaAs substrates. Structures grown on GaAs exhibited stimulated emission under optical pumping at the wavelengths of up to 1.24 μm at 300 K while those grown on Ge/Si substrates emitted at shorter wavelengths of up to 1.1 μm and only at 77 K. The main reasons for such performance worsening and also some approaches to overcome them are discussed. The obtained results have shown that monolithic integration of direct-gap A3B5 compounds on Si using MOCVD technology is rather promising approach for obtaining the Si-compatible on-chip effective light source

Effect of UV and IR Radiation on the Electrical Characteristics of Ga₂O₃/ZnGeP₂ Hetero-Structures

The data on electrical and photoelectric characteristics of Ga2O3/ZnGeP2 hetero-structures formed by RF magnetron sputtering Ga2O3 target with a purity of (99.99%) were obtained. The samples are sensitive to UV radiation with a wavelength of λ = 254 nm and are able to work offline as detectors of short-wave radiation. Structures with Ga2O3 film that was not annealed at 400 °C show weak sensitivity to long-wavelength radiation, including white light and near-IR (λ = 808 and 1064 nm). After annealing in an air environment (400 °C, 30 min), ZnGeP2 crystals in contact with Ga2O3 show n-type conductivity semiconductor properties, the sensitivity of Ga2O3/ZnGeP2 hetero-structures increases in the UV and IR ranges; the photovoltaic effect is preserved. Under λ = 254 nm illumination, the open-circuit voltage is fixed at positive potentials on the electrode to Ga2O3, the short-circuit current increases by three orders of magnitude, and the responsivity increases by an order of magnitude. The structures detect the photovoltaic effect in the near-IR range and are able to work offline (remotely) as detectors of long-wavelength radiation

Design and Characterization of a Sharp GaAs/Zn(Mn)Se Heterovalent Interface: A Sub-Nanometer Scale View

The distribution of magnetic impurities (Mn) across a GaAs/Zn(Mn)Se heterovalent interface is investigated combining three experimental techniques: Cross-Section Scanning Tunnel Microscopy (X-STM), Atom Probe Tomography (APT), and Secondary Ions Mass Spectroscopy (SIMS). This unique combination allowed us to probe the Mn distribution with excellent sensitivity and sub-nanometer resolution. Our results show that the diffusion of Mn impurities in GaAs is strongly suppressed; conversely, Mn atoms are subject to a substantial redistribution in the ZnSe layer, which is affected by the growth conditions and the presence of an annealing step. These results show that it is possible to fabricate a sharp interface between a magnetic semiconductor (Zn(Mn)Se) and high quality GaAs, with low dopant concentration and good optical properties