Fabrication and Electromagnetic Properties of Conjugated NH<Subscript>2</Subscript>-CuPc@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>

Conjugated amino-phthalocyanine copper containing carboxyl groups/magnetite (NH₂-CuPc@Fe₃O₄) has been fabricated from FeCl₃·6H₂O and NH₂-CuPc via a simple solvothermal method and its electromagnetic properties investigated. Scanning electron microscopy and transmission electron microscopy revealed that the NH₂-CuPc@Fe₃O₄ was a waxberry-like nanomaterial with NH₂-CuPc molecules effectively embedded in the interior of Fe₃O₄ particles in the form of beads. Introduction of NH₂-CuPc effectively improved the complementarity between the dielectric and magnetic losses of the system, resulting in excellent electromagnetic performance. The minimum reflection loss of the as-prepared composite reached ?33.4 dB at 7.0 GHz for coating layer thickness of 4.0 mm and bandwidth below ?10.0 dB (90% absorption) of up to 3.8 GHz. These results indicate that introduction of NH₂-CuPc results in a composite with potential for use as an electromagnetic microwave absorption material.     

Solid-State Reaction Mechanism and Deliquescence Phenomenon of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.7</Subscript>Al<Subscript>0.3</Subscript>O<Subscript>3</Subscript> Ceramic

Development of (K,Na)NbO₃-based ceramics has attracted much attention in recent decades. In this work, K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K₂CO₃, Na₂CO₃, and Nb₂O₅ as well as K₂CO₃, Na₂CO₃, and Al₂O₃, which can influence the sintering behavior of the mixture. (K,Na)NbO₃ and (K,Na)AlO₂ were present in the sintered K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic, with the latter leading to deliquescence. During the sintering process, Al₂O₃ reacts with alkali oxides (Na₂O and K₂O), which are the decomposition products of carbonates, to form (K,Na)AlO₂. In addition, Al₂O₃ is more likely to react with K₂O compared with Na₂O.     

Pulsed CH<Subscript>3</Subscript>OH Terahertz Laser Emission Pumped by a TEA CO<Subscript>2</Subscript> Laser

A simple terahertz (THz) cavity and a TEA CO₂ laser for the optically pumped THz emission is studied experimentally. To obtain high peak power of pump laser, pressure ratios of gas mixture in the cavity of the TEA CO₂ laser are discussed. When CH₃OH are pumped by the 9P(16) and 9P(36) CO₂ laser lines, the generation of terahertz radiation with energy as high as 353 μJ and 307 μJ are obtained, respectively. The corresponding photon conversion efficiencies are 0.705% and 0.29%. Meanwhile, higher peak power of pump laser effectively improves the photon conversion efficiency. And the optimum THz laser pressure increases with narrower pulse width of pump laser.     

Gas-phase etching of SiO<Subscript>2</Subscript> layers in an HF/C<Subscript>2</Subscript>H<Subscript>5</Subscript>OH mixture

This paper describes a technique for dry etching SiO₂ layers in MEMS technologies without the moving elements sticking. Etching the sacrificial SiO₂ in anhydrous HF (hydrofluoric acid in the gas phase) allows avoiding the subsequent complex operations of cleaning and drying, which are mandatory in the case of liquid etching. Using the HF/C₂H₅OH anhydrous mixture under low pressures makes it possible to prevent water condensation, which is due to etching in HF vapor, and allows one to employ gas-phase etching in surface MEMS technologies. The mechanisms and physicochemical processes taking place when etching thermal SiO₂ are discussed. The rate of etching thermal SiO₂ films is investigated at temperatures ranging from 30 to 50°С and under chamber pressures ranging from 10 to 20 kPa.     

Hydrogen Selective NH2‐MIL‐53(Al) MOF Membranes with High Permeability

Hydrogen‐based energy is a promising renewable and clean resource. Thus, hydrogen selective microporous membranes with high performance and high stability are demanded. Novel NH₂‐MIL‐53(Al) membranes are evaluated for hydrogen separation for this goal. Continuous NH₂‐MIL‐53(Al) membranes have been prepared successfully on macroporous glass frit discs assisted with colloidal seeds. The gas sorption ability of NH₂‐MIL‐53(Al) materials is studied by gas adsorption measurement. The isosteric heats of adsorption in a sequence of CO₂ > N₂ > CH₄ ≈ H₂ indicates different interactions between NH₂‐MIL‐53(Al) framework and these gases. As‐prepared membranes are measured by single and binary gas permeation at different temperatures. The results of singe gas permeation show a decreasing permeance in an order of H₂ > CH₄ > N₂ > CO₂, suggesting that the diffusion and adsorption properties make significant contributions in the gas permeation through the membrane. In binary gas permeation, the NH₂‐MIL‐53(Al) membrane shows high selectivity for H₂ with separation factors of 20.7, 23.9 and 30.9 at room temperature (288 K) for H₂ over CH₄, N₂ and CO₂, respectively. In comparison to single gas permeation, a slightly higher separation factor is obtained due to the competitive adsorption effect between the gases in the porous MOF membrane. Additionally, the NH₂‐MIL‐53(Al) membrane exhibits very high permeance for H₂ in the mixtures separation (above 1.5 × 10^?6 mol m^?2 s^?1 Pa^?1) due to its large cavity, resulting in a very high separation power. The details of the temperature effect on the permeances of H₂ over other gases are investigated from 288 to 353 K. The supported NH₂‐MIL‐53(Al) membranes with high hydrogen separation power possess high stability, resistance to cracking, temperature cycling and show high reproducibility, necessary for the potential application to hydrogen recycling.     

Simple Short-Pulse CO<Subscript>2</Subscript> Laser Excited by Longitudinal Discharge without High-Voltage Switch

We have developed a longitudinally excited CO₂ laser without a high-voltage switch. The laser produces a short laser pulse similar to those from TEA and Q-switched CO₂ lasers. This system, which is the simplest short-pulse CO₂ laser yet constructed, includes a pulsed power supply, a high-speed step-up transformer, a storage capacitor, and a laser tube. At high pressure (4.2 kPa and above), a rapid discharge produces a short laser pulse with a sharp spike pulse. In mixed gas (CO₂: N₂: He = 1: 1: 2) at a pressure of 9.0 kPa, the laser pulse contains a spike pulse of 218 ns and has a pulse tail length of 16.7 μs.     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser,using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions. These FIR emissions correspond to thirty one different wavelengths in the 50–400 μm range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

Synergistic CO2‐Sieving from Polymer with Intrinsic Microporosity Masking Nanoporous Single‐Layer Graphene

High‐flux nanoporous single‐layer graphene membranes are highly promising for energy‐efficient gas separation. Herein, in the context of carbon capture, a remarkable enhancement in the CO₂ selectivity is demonstrated by uniquely masking nanoporous single‐layer graphene with polymer with intrinsic microporosity (PIM‐1). In the process, a major bottleneck of the state‐of‐the‐art pore‐incorporation techniques in graphene has been overcome, where in addition to the molecular sieving nanopores, larger nonselective nanopores are also incorporated, which so far, has restricted the realization of CO₂‐sieving from graphene membranes. Overall, much higher CO₂/N₂ selectivity (33) is achieved from the composite film than that from the standalone nanoporous graphene (NG) (10) and the PIM‐1 membranes (15), crossing the selectivity target (20) for postcombustion carbon capture. The selectivity enhancement is explained by an analytical gas transport model for NG, which shows that the transport of the stronger‐adsorbing CO₂ is dominated by the adsorbed phase transport pathway whereas the transport of N₂ benefits significantly from the direct gas‐phase transport pathway. Further, slow positron annihilation Doppler broadening spectroscopy reveals that the interactions with graphene reduce the free volume of interfacial PIM‐1 chains which is expected to contribute to the selectivity. Overall, this approach brings graphene membrane a step closer to industrial deployment.     

Combined effect of V<Subscript>2</Subscript>O<Subscript>5</Subscript> and NH<Subscript>3</Subscript> on thermal oxidation of InP

The combined effect of V₂O₅ and NH₃ on thermal oxidation of InP in a wet oxygen atmosphere is investigated experimentally.Translated from Mikroelektronika, Vol. 34, No. 1, 2005, pp. 51–55.Original Russian Text Copyright © 2005 by Mittova, Lavrushina, Sycheva.     

Segmented Generator Modules Using Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Based Materials

Previously, the Institute of Thermoelectricity has created Bi₂Te₃-based modules with an efficiency of ~7% in the temperature range of 30°C to 300°C, with legs that employed homogeneous thermoelectric materials. Herein, we present the results of development of such modules with legs made of inhomogeneous materials. Based on the theory of optimal control and object-oriented computer technology, programs to determine the requirements for material properties in the inhomogeneous legs were created. It was established that introduction of inhomogeneity in the form of continuous and step changes in three-segment n- and p-type legs yields almost identical efficiency increases of about 15%. Use of two segments reduces this value of 10% to 12%. Modules with two-segment legs encapsulated in thin-walled metal cases filled with inert gas have been built, yielding improved efficiency of 7.8% to 8%.