Near-room Temperatures Research Articles

A strategy of fabricating efficient Mg2Ni nano-catalysts in Mg-Ni-Ag fibers and their excellent hydrogen storage properties at near-room temperatures

In this study, a new strategy was utilized to fabricate Mg-based hydrogen storage fibers with uniform elemental distribution and diameters of 30–50 μm. The in-situ formation of nano-precipitates in Mg85Ni14.8Ag0.2 metallic glass fibers was visually observed at varied annealing temperatures. It indicates the metastable Mg6Ni phase is formed from an amorphous microstructure initially. Then, the needle-like Mg2Ni nanoparticles precipitate at 140–160 °C and subsequently grow into spherical shapes. This results in the formation of the fiber structure with well-distributed nano-Mg2Ni particles. The alloy fibers can absorb H2 at only 40 °C, and the activation energy for hydrogenation is lowed to be 46.9 kJ/mol. The onset desorption temperature of hydride is reduced to 220 °C due to the improved the catalytic efficiency by uniformly distributed Mg2Ni nanoparticles. The abundant interfaces, as well as the shortened distance by micropores, serve as paths for the fast diffusion of H atoms.

Synthesis and enhanced room-temperature thermoelectric properties of CuO-MWCNT hybrid nanostructured composites.

This work presents the synthesis of novel copper oxide-multiwalled carbon nanotube (CuO-MWCNT) hybrid nanostructured composites and a systematic study of their thermoelectric performance at near-room temperatures as a function of MWCNT wt% in the composite. The CuO-MWCNT hybrid nanostructured composites were synthesized by thermal oxidation of a thin metallic Cu layer pre-deposited on the MWCNT network. This resulted in the complete incorporation of MWCNTs in the nanostructured CuO matrix. The thermoelectric properties of the fabricated CuO-MWCNT composites were compared with the properties of CuO-MWCNT networks prepared by mechanical mixing and with the properties of previously reported thermoelectric [CuO]99.9[SWCNT]0.1 composites. CuO-MWCNT hybrid composites containing MWCNTs below 5 wt% showed an increase in the room-temperature thermoelectric power factor (PF) by ∼2 times compared with a bare CuO nanostructured reference thin film, by 5-50 times compared to mixed CuO-MWCNT networks, and by ∼10 times the PF of [CuO]99.9[SWCNT]0.1. The improvement of the PF was attributed to the changes in charge carrier concentration and mobility due to the processes occurring at the large-area CuO-MWCNT interfaces. The Seebeck coefficient and PF reached by the CuO-MWCNT hybrid nanostructured composites were 688 μV K-1 and ∼4 μW m-1 K-2, which exceeded the recently reported values for similar composites based on MWCNTs and the best near-room temperature inorganic thermoelectric materials such as bismuth and antimony chalcogenides and highlighted the potential of CuO-MWCNT hybrid nanostructured composites for applications related to low-grade waste heat harvesting and conversion to useable electricity.

The Impact of Topological States on the Thermoelectric Performance of p- and n-Type Sb2Te3/Bi2Se3-Multiwalled Carbon Nanotubes Heterostructured Networks

The resistance and magnetoresistance of flexible thermoelectric p-type Sb2Te3-MWCNT, p-type Bi2Se3-MWCNT, and n-type Bi2Se3-MWCNT heterostructures were studied in the temperature range from 2 K to 300 K to reveal the conductance mechanisms governing the thermoelectric properties of these heterostructured networks. It was found that the conductance in heterostructured networks at different temperatures is governed by different processes and components of the networks. This effect was found to be related to the growth mechanisms of the Sb2Te3 and Bi2Se3 nanostructures on the MWCNT networks. At near-room temperatures, the Sb2Te3 and Bi2Se3 nanostructures were found to have the dominant contribution to the total conductance of the p-type Sb2Te3-MWCNT and n-type Bi2Se3-MWCNT networks. In turn, the conduction of p-type Bi2Se3-MWCNT heterostructured networks in a full temperature range and p-type Sb2Te3-MWCNT and n-type Bi2Se3-MWCNT heterostructured networks at temperatures below 30 K was governed by the MWCNTs; however, with the contribution from 2D topological states of Sb2Te3 and Bi2Se3 nanostructures, these were manifested by the weak antilocalization effect (WAL) cusps observed at temperatures below 5–10 K for all heterostructured networks considered in this work.

Classification of superconducting transition temperature over 150K of metal polyhydrides using support vector machine

The search for room-temperature superconductors have shed light on metal polyhydrides as their superconducting transition temperature (TC) vary from a few kelvins to near-room temperatures. One major drawback in the quest for hydrogen-based superconductors is that the calculation of TC through the electron-phonon spectral function consumes large amount of time and computational resources. Here we propose a method of using the support vector machine (SVM) to classify the ranges of TC of the metal polyhydrides without actual calculation of the electron-phonon spectral function. The input variables are chosen based on the effect of hydrogen atoms and the electron localization function (ELF). These set of features can be obtained quickly from the electronics simulations, compare with the actual spectral function calculations. We found that the SVM can classify the superconductors with accuracy over 80 percent with respect to all the metal polyhydrides in the dataset. Our goal of this work is to help screen for the high value of TC of the hydrogen-based compounds, and reduce the time required for the direct calculations of TC.

Preparation of near room temperature gas sensor based on regular octahedral porous ZnO/SnO2 composite

ZnO/SnO 2 often is used as the gas sensitive materials, but the gas sensors based on ZnO/SnO 2 shows the gas sensing property at the higher temperature because of its much higher initial resistance. In this study, porous ZnO/SnO 2 material with regular octahedral structure was successfully prepared, and the ZnO was wrapped into SnO 2 to form the heterostructure which improved the separation efficiency of electron-hole to decrease the initial resistance in the prepared materials. The prepared material showed much better gas sensing property at the room and near-room temperatures (35 °C, NRT). The response of the octahedral ZnO/SnO 2 to 100 ppm ethanol gas was 17.8, and the response time was only 1 s at NRT. Moreover, the prepared gas sensor had the much better gas selectivity to ethanol gas detection. The excellent gas sensing performance could be attributed to which the porous structure, the large specific surface area and the n-n heterojunctions could provide the more gas adsorption active sites and the electronic transmission channels to make the gas sensor with the better gas sensitive response to the target gas. • Regular octahedral ZnO/SnO 2 composite is prepared. • This sensor exhibits the higher gas-sensitive property at the lower operating temperature (35 °C). • The composite has high response speed and fast response/recovery process. • The composite has the larger specific surface area and the n-n heterojunction.

Estimation of the nonlinear dependence of the indications of a fiber Bragg grating on temperature and strain from experimental data

The readings of the Bragg grating are determined based on the optical radiation reflected from it. A quantitative characteristic of this radiation is the wavelength at which the maximum power of the optical signal is achieved. This characteristic is called the central wavelength of the grating. The central wavelength shift depends on temperature and strain. As a rule, a linear approximation of this dependence is used. However, from the available literature it is known that, the grating wavelength shift demonstrates a strong nonlinear dependence on temperature at 5<T<200K and a weak quadratic dependence close to room temperature. Thus far, the authors have not found studies that consider all terms in the quadratic expansion of the central wavelength of the Bragg grating as a function of temperature and strain at near-room temperatures. Our work is intended to fill this gap. The article describes an experiment in which an optical fiber with Bragg grating was subjected to loading using three different weights. A step-wise temperature change from 5 to 100 0С was realized for each weight. Based on these data, all terms of the quadratic expansion of the desired function are determined. The contribution of each term is estimated.

Membrane-free osmotic desalination at near-room temperatures enabled by thermally responsive polyionic liquid hydrogels

A chloride-anion-rich TPIL hydrogel, acting as a separation and a drawing agent, is used for membrane-free osmotic desalination. Salt-depleted water can be retrieved easily by mild heating originating from human body or solar energy assisted by photothermal fillers.

Sustainable process for enhanced CO2 mineralization of calcium silicates using a recyclable chelating agent under alkaline conditions

This study explored a key challenge of aqueous indirect CO2 mineralization: the consumption of chemicals for a large pH swing between acidic and alkaline conditions and the production of waste fluid. Herein, we proposed and experimentally examined the technical feasibility of a sustainable process for enhanced CO2 mineralization using a new potentially recyclable alkaline solution of chelating agent [N,N-dicarboxymethyl glutamic acid (GLDA)] at near-room temperatures. This process comprising the following: enhanced Ca extraction from silicates with suppressed formation of silica-rich passivation layer via the combined actions of proton and chelating agent attacks at weakly alkaline conditions; Ca carbonation using sodium carbonate at high pH and temperature; and regeneration of the extraction solution (i.e., a decrease in pH and silicon removal) via CO2 gas dissolution. Ca extraction experiments using representative calcium silicate (CaSiO3) at various GLDA concentrations and initial pHs under 50 °C demonstrated the possibility of enhanced Ca extraction with almost all GLDA molecules combining with Ca (Ca/GLDA≈1) at an optimum condition (0.1 M GLDA and pH 8 in this study). This type of extraction is desirable as it contributes to an efficient Ca carbonation in addition to a decreased stability of the Ca-GLDA complex; indeed, most of the extracted Ca were carbonated to aragonite at 80 °C. Moreover, such extraction with the relatively low pH of 8 was found to be desirable for solution regeneration that involves pH adjustment (reduction) because of low silica solubility at lower pH. It was demonstrated that room-temperature CO2 bubbling removed almost all Si as amorphous SiO2, during which CO2 captured as NaHCO3 was also occurring. The recyclability of extraction solution was also demonstrated in this paper. This study encourages further extensive studies to optimize reaction conditions, particularly for using alkaline solid wastes, to make the process both technically and economically feasible.

Minority carrier lifetime in HgCdTe(100) epilayers and their potential application to background radiation limited MWIR photodiodes

Measurements of minority carrier lifetime have been carried out on nonintentionally doped HgCdTe(100) layers grown by metal organic chemical vapor deposition on GaAs substrates. The studies have been carried out in order to investigate the possibility of applications of HgCdTe(100) epilayers to fully depleted P–i–N photodiodes operated at near-room temperatures and the background-radiation limit. Post-growth annealed layers show n-type conductivity with a residual donor concentration of about 1015 cm−3. The cadmium molar composition (0.262 < x < 0.336) was chosen for mid-wave infrared devices operating at 230 K to 300 K. Results show that at high temperatures, the samples show clearly Auger-limited lifetimes determined by the background doping. The measured lifetimes at 300 K range from 5 to 11 µs, and from 0.2 to 1 µs, for the cut-offs of 4 µm and 5.4 µm, respectively.

Impact ionization in HgCdTe avalanche photodiode optimized to 8 µm cut–off wavelength at 230 K

If the impact ionization occurs in a region of high electrical field then it can result in avalanche multiplication of carriers. This process is used in avalanche photodiodes enabling individual photons to be detected when the incident flux of light is very low. HgCdTe is an almost ideal material for avalanche photodiodes, however to achieve the highest performance in near-room temperatures, a careful design of device structure is needed, to reach the highest performance in near-room temperatures. N+-ν-p-P+ photodiode meets the requirements of the separated absorption and multiplication regions. This paper describes the results of research aimed at investigation of the impact ionization mechanism in HgCdTe N+-ν-p-P+ photodiode optimized for 8 μm cut-off wavelength at 230 K. The results show that the parameters of the ν-region greatly influenced on the distribution of the electric field and the generation rate due to the impact ionization. In addition, ν-region has the effect on reduction of undesirable tunneling in the space charge region. For this purpose, it is necessary to keep the doping in this region as low as possible and to extend the energy gap in relation to the absorbing region.

Flexible thermoelectric module based on zinc oxide thin film grown via SILAR

In this work, we used the low temperature solution growth Successive Ionic Layer Adsorption and Reaction (SILAR) for a deposition of the nanostructured undoped and indium doped (ZnO and ZnO:In) thin films on flexible polyimide (PI) substrates for their use as cheap non-toxic thermoelectric materials in the flexible thermoelectric modules of planar type to power up portable and wearable electronics and miniature devices. The use of a zincate solution in the SILAR method allows to obtain ZnO:In film, which after post-growth annealing at 300 °C has low resistivity ρ ≈ 0.02 Ω m, and high Seebeck coefficient −147 μV/K and thermoelectric power factor ~1 μW K−2 m−1 at near-room temperatures. As evidence of the operability of the manufactured films as the basis of the TE device, we have designed and tested experimental lightweight thin-film thermoelectric module. This TE module is able to produce specific output power 0.8 μW/m2 at ΔT = 50 K.

Thermoelectric textile with fibers coated by copper iodide thin films

Here we obtained thermoelectric (TE) textiles on the base of the commercial cotton and polyester fabrics. For this we used deposition of copper iodide (CuI) thin films via low-temperature cheap and scalable method Successive Ionic Layer Adsorption and Reaction (SILAR). The TE textiles are comfortable to wear, breathable, nontoxic, light-weight, flexible and air-permeable. The CuI films in the TE textiles are composed of accreted flakes with nanoscale thickness (<50 nm) or of nanowalls. Their crystal grains are less than 50 nm, contain a significant number of dislocations and an increased lattice parameter, and consequently have large compression microstrains. The TE textiles with CuI coated cotton and polyester have the Seebeck coefficients in the range of 120–180 μV K−1, which are constant at the temperatures 290–365 K. The most effective single p-CuI thermoelectric leg has low internal resistance 2 kΩ. Its specific output power at temperature gradient 50 K is 31 μW/m2. Three experimental flexible wearable TEGs of simple and affordable designs having each four thermocouples with n-Alumel and p-CuI thermoelectric legs on the thick cotton, thin cotton and polyester confirm the possibility of obtaining electricity using the developed TE textiles under conditions of temperature gradients from 5 to 50 K at near-room temperatures. The best TEG obtained on the polyester fabric has at temperature difference 50 K output TE characteristics: open circuit voltage 44 mV, short circuit current 1.3 µA, output power 16 nW. These characteristics remain unchanged after repeated bends of TEGs in the different directions.

Semi-transparent copper iodide thin films on flexible substrates as p-type thermolegs for a wearable thermoelectric generator

The article presents crystal structure, composition, optical, electrical and thermoelectric properties of semi-transparent CuI films produced in different modes of the cost-effective and large scalable method Successive Ionic Layer Adsorption and Reaction (SILAR) on flexible poly(ethylene terephthalate) (PET) substrates. The obtained data together with the analysis of output thermoelectric characteristics of p-type thermolegs based on these CuI films are used to select the SILAR mode to create semi-transparent p-type thermolegs for a new flexible wearable thin film thermoelectric generator (TEG). The best obtained flexible p-CuI thin film single thermoleg demonstrates output power 17.1 μW/m2 at the temperature gradient ∆T = 35 K at near-room temperatures. Therefore, CuI films produced in such mode of the SILAR method on the flexible PET substrates can be used as a part of a new lightweight low cost flexible wearable thin film TEG for a production of electrical energy for low-power devices due to absorption of low-potential heat.

Breaking the Energy-Symmetry-Based Propagation Growth Blockade in Magneto-Optical Rotation.

The magneto-optical polarization rotation effect has myriad applications in many research areas spanning the scientific spectrum, including space and interstellar research, nanotechnology, material science, biomedical imaging, and subatomic particle research. In the nonlinear magneto-optical rotation (NMOR) effect, the angle of rotation of a linearly polarized optical field in a magnetized medium is dependent upon its intensity. However, typical NMOR signals of conventional single-beam -scheme atomic magnetometers are peculiarly small, requiring sophisticated magnetic shielding and high-frequency phase-sensitive detection. Here, we show the presence of an energy-symmetry-based propagation growth blockade that undermines the NMOR effect in conventional single-beam -scheme atomic magnetometers. We further demonstrate, both experimentally and theoretically, an inelastic wave-mixing technique that breaks this NMOR blockade, resulting in more-than-2-orders-of-magnitude enhancement of the NMOR signal power amplitude that cannot be achieved with conventional single-beam -scheme atomic magnetometers. This technique, demonstrated here with substantially reduced light intensities at near-room temperatures, may lead to many applications, especially in the field of biomagnetism and high-resolution low-field magnetic imaging.

Semitransparent p-CuI and n-ZnO thin films prepared by low temperature solution growth for thermoelectric conversion of near-infrared solar light

In this work by means studying the crystal structure, optical, electrical, and thermoelectric properties of chip, available and safe for the environment copper iodide CuI, zinc oxide ZnO and indium-doped zinc oxide ZnO:In films we have developed and improved low temperature solution growth Successive Ionic Layer Adsorption and Reaction (SILAR) technique, which allows to deposit these materials over large areas. Output thermoelectric parameters were analyzed for several single p-CuI, n-ZnO and n-ZnO:In thin film thermolegs. The possibility of combining of the obtained p-CuI and n-ZnO:In thin film thermolegs into a thermocouple is shown for the use in new semitransparent planar solar thermoelectric generator working at near-room temperatures through harvesting near-infrared solar light as an energy source to supply electric power to the wireless sensors and microscale devices.

Analysis of the nBn-type barrier structures for infrared photodiode detectors

Modern trends in the technology of CdxHg1–xTe-based photosensitive barrier structures for the middle and far infrared bands, which can operate at near-room temperatures, are analyzed. Main approaches to solving the problem of increasing the photodiode-detector operating temperature have been considered and analyzed.

Investigation of hillocks formation on (1 0 0) HgCdTe layers grown by MOCVD on GaAs epi-ready substrates

In this paper we present the recent progress in the growth of (100) HgCdTe epilayers using metal organic chemical vapour deposition on GaAs epi-ready substrates. Particular progress has been achieved in the reduction of macro-defects known as “hillocks”, revealed on the surface of HgCdTe epilayers with (100) crystallographic orientation. The large-scale defects can arise from such sources as poor substrate processing, dust and remnants from previous deposition, and non optimal parameters of nucleation and growth process. In our experiment, hillocks density was decreased to <102cm−2 by proper choice of the growth parameters.Obtained epilayers are suitable for device fabrication. So far, significant improvements has been obtained in photoconductors operated at near-room temperatures. Devices fabricated from (100) HgCdTe have about one order of magnitude higher voltage responsivity than their (111) B counterparts.

Excitonic effects in two-dimensional semiconductors: Path integral Monte Carlo approach

One of the most striking features of novel 2D semiconductors (e.g., transition metal dichalcogenide monolayers or phosphorene) is a strong Coulomb interaction between charge carriers resulting in large excitonic effects. In particular, this leads to the formation of multi-carrier bound states upon photoexcitation (e.g., excitons, trions and biexcitons), which could remain stable at near-room temperatures and contribute significantly to optical properties of such materials. In the present work we have used the Path Integral Monte Carlo methodology to numerically study properties of multi-carrier bound states in 2D semiconductors. Specifically, we have accurately investigated and tabulated the dependence of single exciton, trion and biexciton binding energies on the strength of dielectric screening, including the limiting cases of very strong and very weak screening. The results of this work are potentially useful in the analysis of experimental data and benchmarking of theoretical and computational models.

‘Blue phases’ of highly chiral thermotropic liquid crystals with a wide range of near-room temperature

The phase transitions of pure cholesteric liquid crystals, based on right- or left-handed chiral dopants (ChDs) (enantiomers R-811 and S-811, Merck, Darmstadt, Germany) with various concentrations dissolving in the nematic liquid crystal mixture CHCA (ZhK-805, Russia, NIOPIK) were experimentally studied. For the first time, blue phases of cholesterics were found at the concentration range of ChDs 32–36 wt.%. Experimentally it was observed that during the cooling process the blue phase of cholesterics is stable over a wide temperature range about ~15°C including human body and near-room temperatures. Thermal phase transitions, spectral characteristics and electro-optical features of blue phases were examined. Planar and homeotropic alignment layers were used to study the influence of various boundary conditions on platelet textures of blue phases.

Flower-shaped ZnO nanoparticles synthesized by a novel approach at near-room temperatures with antibacterial and antifungal properties

Due to enormous applications of metal oxide nanoparticles in research and health-related applications, metal oxide nanoparticles are increasingly being developed through cheaper and more user-friendly approaches. We have formulated a simple route to synthesize zinc oxide nanoparticles (ZNPs) by a sol–gel method at near-room temperatures 25°C, 35°C, 55°C, and 75°C. The results are analyzed by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and ultraviolet-visible absorption spectroscopy. The effect of different temperature conditions (25°C–75°C) on the particulate sizes (23.7–88.8 nm), pH levels (11.7–11.9), and morphologies (slender needle–broad arrow) of flower-shaped ZNP colonies is studied. A possible mechanism depicting the growth rates at different temperatures and of different facets, mainly towards the <0 0 0 I> and <0 I Ī 0> planes of the ZNPs has also been discussed. The values of λmax (293–298 nm) suggest that ZNPs prepared at 55°C are the most effective ultraviolet B absorbers, and that they can be used in sunscreens. Highly significant antimicrobial activity against medically important Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and fungi (Candida albicans) by these ZNPs was also revealed. As S. aureus and C. albicans are responsible for many contagious dermal infections such as abscesses, furuncles, carbuncles, cellulitis, and candidiasis, we can postulate that our fabricated ZNPs may be useful as antimicrobial agents in antiseptic creams and lotions for the treatment of skin diseases.