Memory switching of germanium tellurium amorphous semiconductor

The dc conductivity and switching properties of amorphous GeTe thin film of thickness 262 nm are investigated in the temperature range 303-373 K. The activation energy ΔE_σ, the room temperature electrical conductivity σ_RT and the pre-exponential factor σ₀ were measured and validated for the tested sample. The conduction activation energy ΔE_σ is calculated. The I-V characteristic curves of the thin film samples showing a memory switching at the turnover point (TOP) from high resistance state (OFF state) to the negative differential resistance state (NDRS) (ON state). It is found that the mean values of the threshold electrical field E_th decreased exponentially with increasing temperatures in the investigated range. The switching activation energy ΔE_th is calculated. Measurements of the dissipated threshold power P_th and the threshold resistance R_th were carried out at TOP point at different temperatures of the samples. The activation energies ΔE_R and ΔE_P caused by resistance and power respectively are deduced. The results obtained support thermal model for initiating switching process in this system.     

One-step fabricated Fe3O4@C core–shell composites for dye removal: Kinetics,equilibrium and thermodynamics

B-Fe₃O₄@C core–shell composites were synthesized via one-pot hydrothermal carbonization (HTC) process and used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. By using sodium borate as the catalyst, the hydrothermal carbonization process of B-Fe₃O₄@C core–shell composites was optimized and a higher surface area was obtained. The adsorbent was characterized by XRD, Raman spectra, SEM, TEM and N₂ adsorption/desorption isotherms. We studied the dye adsorption process at different conditions and analyzed the data by employing the Langmuir and Freundlich models, and the equilibrium data fitted well with both models. Kinetic analyses were conducted by using the Lagergren pseudo-first-order and pseudo-second-order model and the results showed that the adsorption process was more consistent with the pseudo-second-order kinetics. To better understand the dye adsorption process from the thermodynamics perspective, we also calculated ΔH^ο, ΔS^ο, ΔG^ο and E_a, the results suggesting that the MB adsorption process was physisorption endothermic process, and spontaneous at room temperature. The as-synthesized B-Fe₃O₄@C showing high magnetic sensitivity provides a facile and efficient way to recycle from aqueous solution.     

Developing ultrasound-assisted hot-air and infrared drying technology for sweet potatoes

The influence of ultrasound (US) pretreatments combined with infrared (IRD) and hot-air (HAD) drying on drying kinetics, mathematical modeling, bioactive compounds (antioxidant activities, Vitamin C, phenolics, and flavonoid contents), qualitative properties (β-carotene, total carotenoids, color indexes, textural profile), enzyme inactivation, and exergetic analysis of sweet potatoes. The US pretreatment at 40 kHz combined with IRD and HAD (70 °C) significantly lessened the drying time and water contents. Besides, it did not affect the sweet potato's bioactive components and other quality-related attributes. The samples’ activation energy (E_a) ranged from 17.60 to 29.86 kJ/mol for both dryers, with R² (0.999–0.9809). Control samples had the highest specific energy consumption (SEC) due to the extended drying period, whereas ultrasound (40 kHz) treated samples had the lowest SEC during HAD and IRD at 80 °C. The thermodynamic parameters indicated that increasing the drying temperature lowers the enthalpy and Gibbs free energy, while entropy resulted in negative values. HAD had better textural qualities (hardness and resilience). The US pretreatments followed by HAD or IRD may lead to an energy-efficient method with acceptable quality maintenance.     

Ultrasound (US) enhances the hydration of sorghum (Sorghum bicolor) grains

The water activity (Aw) reduction technique is widely used to preserve different food products, which are further rehydrated in order to be processed or consumed. The food hydration is time-consuming and, thus, a limiting unit operation during process. Therefore, there is an ongoing need to enhance the mass transfer phenomena during processing. The ultrasound technology (US) has been widely studied to improve different mass transfer processes of food. However, there is a lack of knowledge in relation to its application in the hydration process. This work evaluated the hydration process of sorghum seeds, comparing the effect of heating and ultrasound application in order to improve the hydration rate. The sorghum hydration kinetic was described by Peleg Model, whose parameters were evaluated for both processes. The US increased both water uptake rate (related to Peleg k₁ parameter) and equilibrium moisture content (related to Peleg k₂ parameter). The time for reach 90% of the control process equilibrium moisture content was 40% lower when the US was applied. The effect of processing at 53 °C was higher than applying US at the evaluated power, and its limitations were discussed. The effect of combining both ultrasound and heating application was negligible when it was compared to the heated process. The obtained results highlighted that the US technology can be successfully used to optimize the hydration process of grains with directly industrial application.     

A performed model for band-gap narrowing of heavily doped semiconductors

The band-gap narrowing ΔE_g of n-type heavily doped crystals at an arbitrary temperature is investigated, basing on an extended Thomas-Fermi model given by Friedel and on our previous results.In highly degenerate semiconductors, the carrier-donor interaction contribution to ΔE_g is approximately proportional to the $\text{1}\text{6}$ power of electron concentration, in agreement with other theories.An exact expression for the inverse screening length is also obtained and compared with that given by Friedel.     

Piezoreflectance measurements on GaxIn1−x Sb alloys

Piezoreflective experiments between 77 and 300°K are performed on Ga_x, In_1?x Sb alloys. E_o and E_o + Δ_o transition energies, vs composition are determined. Band gap E_o variations, are obtained in good agreement with the two band dielectric model. The Δ_o splitting is observed to be linear with composition.The fundamental edge temperature coefficient β is also determined, it is found to vary linearly with composition.E_o and E_o + Δ_o energy determination permit one to deduce effective mass and g_e value variation with composition.     

Combination of ultrasound-peracetic acid washing and ultrasound-assisted aerosolized ascorbic acid: A novel rinsing-free disinfection method that improves the antibacterial and antioxidant activities in cherry tomato

Traditional ultrasound (US)-assisted disinfection is only effective during washing. Coating is an effective method to control microbial growth after washing; however, cross-contamination can occur during immersion in the coating aqueous solution. Tap water (TW) rinsing is generally used to remove sanitizer residues after US-assisted washing; however, the Food and Drug Administration stated that rinsing is unnecessary when the peracetic acid (PAA) concentration does not exceed 80 ppm. In this study, we proposed a novel US-assisted hurdle technology of 80 ppm PAA combined with low-frequency US (25 kHz) during washing, followed by US-assisted aerosolization processing (nonimmersion coating). Ascorbic acid (AA), a safe and low-cost agent, was selected as the aerosolization solution. Cherry tomatoes were selected as the model, and the proposed method was compared with traditional US-assisted disinfection methods (US-10 ppm free chlorine washing + TW rinsing and US-5 ppm chlorine dioxide washing + TW rinsing) to analyze the disinfection efficacy and quality changes. During storage, US-PAA + 1%AA facilitated additional 0.7–0.9, 0.6–0.8, 0.7–1.0, and 0.5–1.0 log CFU/g reductions in the counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic counts, and molds and yeasts, respectively, as compared with traditional US-assisted methods. Sensory properties, color index, total soluble solids, titratable acidity, and weight loss were not negatively affected by any of the treatments. Firmness was slightly reduced after all treatments; however, the firmness of the samples was maintained during storage, in contrast with the decreased firmness observed in the control. Phenolic content and antioxidant activity significantly increased after all treatments. Further analysis of two key enzymes (phenylalanine ammonia-lyase and 4-coumarate-CoA ligase) involved in phenolic synthesis showed that their levels significantly increased following all treatments, leading to an increase in phenolic content and antioxidant activity. This result also indicated that US-assisted washing could act as an abiotic elicitor to increase nutritional content. Overall, US-PAA + 1%AA treatment served as an effective method for disinfecting produce during washing and for controlling microbial growth after washing without prolonging the processing time, which is an advantage over traditional US-assisted washing.     

Chiral symmetry breaking in nonequilibrium chemical systems: Time scales for chiral selection

The process through which an extremely weak parity violating interaction, of energy ΔE, can become the selector of molecular chirality over a sufficiently long time is discussed. For a model system it is shown that ΔE ≈ 5 × 10^-15kT can give a 90% selectivity in about 300 h - smaller ΔE being relevant to prebiotic evolution.     

Temperature dependence of the energy separation between Γ and L minima in n-type GaSb

Energy separation ΔE_c between Λ and L minima of GaSb conduction band is deduced from temperature dependence of tunneling current in p−n junctions. ΔE_c is found to inceasing vx. temperature with a coefficient d(ΔE_c/dT) of about - 2.10^-4eV/dgK.     

Influence of internal stresses on field-dependent elastic modulus and damping in pure nickel

Measurements of the ΔE-effect and magnetomechanical damping are reported for crystalline pure nickel under several states of internal stresses. The different internal stresses are obtained by means of a wide variety of heat treatments and studied via microscopic examination and measurement. The influence of the heating temperature, the heating time and the cooling method on the magnetoelastic properties is studied. Our results make it possible to select the most suitable heat treatment for each application and to optimize the magnetoelastic response of nickel. Relative variations from 2% to 13% can be obtained in the ΔE-effect, whereas relative variations from 40.0% to 99.9% are possible in magnetomechanical damping, in terms of specific damping capacity.     

Current induced deformation of charge density waves in orthorhombic TaS3

The low electric field ohmic resistance R of orthorhombic TaS₃ measured at 90 and 120 K well below the Peierls transition temperature depends on the product of a temperature difference ΔT applied along the sample and the sign of a previously applied current pulse if this pulse is larger than threshold for non-ohmic conductivity. This resistance change is about ΔR/RΔT ∽ 1×10^-3 K^-1 for a pure sample and ΔR/RΔT ∽ 6×10^-3 K^-1 for a slightly electron irradiated one at 90 K. The relative resistance change is insensitive to the sample length. We deduce that the CDW current changes inhomogeneously the Peierls gap E_g. ΔE_g < O at the contact where the CDW current enters and ΔE_g > O at the exit. The effect is attributed to a CDW current induced inhomogeneous deformation of the CDW itself.     

Plasma enhanced CVD of SiOxCyHz thin film on different textile fabrics: Influence of exposure time on the abrasion resistance and mechanical properties

In order to improve textile fabric abrasion resistance, in this work a SiO_xC_yH_z thin film was realized by low pressure plasma chemical vapour deposition (PCVD) at room temperature, using hexamethyldisiloxane (HMDSO) as precursor compound. To test changes in the performance properties of the surface finished samples as a function of the type of the substrate, the deposition was carried out on different textile fabrics. The polymerization processes were followed by weight measurements of textile fabrics. It was found that, after PCVD, a significantly lower fabric weight loss was observed on treated samples after rubbing than on the untreated samples. The morphology, elemental composition and type of chemical bonding present in the film applied on textile fabrics were also investigated using electron scanning microscopy (SEM), energy dispersive X-ray (EDX) and infrared spectroscopy techniques (FT-IR (ATR)). The results showed a substantial enhancement of wear resistance for the surfaces modified with the presented process, while tensile and tearing strength were adversely affected.     

Removal of lead(II) by adsorption onto Viscumalbum L.: Effect of temperature and equilibrium isotherm analyses

The removal efficiency of Viscumalbum L. from lead containing aqueous solutions was investigated. The effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature was investigated using a batch adsorption technique. The optimum pH for Pb(II) adsorption was found as 3.0 for Viscumalbum L. Results were analyzed by the Langmuir, Freundlich, Temkin and Harkins-Jura, equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. The Langmuir model agrees very well with experimental data than the other models. According to Langmuir isoterm, the monolayer saturation capacity (Q_o) is 769.23 mg/g at 25 °C. Models and the isotherm constant were evaluated depending on temperature. Thermodynamic parameters such as ΔH^o, ΔS^o and ΔG^o were calculated. The adsorption process was found to be endothermic and spontaneous. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data.     

Ultrasonic and mechanical soil washing processes for the removal of heavy metals from soils

In order to determine the optimal operating conditions of full-scale soil washing processes for the removal of heavy metals, the effect of high-power ultrasound on the conventional mechanical soil washing process was investigated in a large lab-scale 28 kHz sonoreactor. The soil samples were obtained from an abandoned railway station site in Seoul, Korea, which was contaminated with Cu (242.7 ± 40.0 mg/kg), Pb (441.3 ± 49.8 mg/kg), and Zn (358.0 ± 35.7 mg/kg). The treated concentrations of three heavy metal species in each process were compared with the regulation levels. It was found that higher performance, satisfying the regulation levels, was obtained in the ultrasonic/mechanical process due to the combined effects of macroscale mixing and microscale sonophysical effects. Moreover ultrasound played a more important role in less favorable conditions for the mechanical washing process (less acidic or less washing liquid conditions). Considering the application of the ultrasonic/mechanical soil washing process in real contaminated sites, the optimal conditions for the reactor with the bottom area of 15 × 15 cm² and the input ultrasound power of 250 W were determined as follows: (1) the amount of soil per an operation was a 300 g; (2) the ratio of soil and liquid was 1:3; (3) the concentration of acidic washing liquid was 0.5 M HCl.     

Ultrasonic assisted dyeing: Dyeing of acrylic fabrics C.I. Astrazon Basic Red 5BL 200%

The dyeing of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% has been studied with both conventional and ultrasonic techniques. The effect of dye concentration, dye bath pH, ultrasonic power, dyeing time and temperature were studied and the resulting shades obtained by dyeing with both techniques were compared. Colour strength values obtained were found to be higher with ultrasonic than with conventional heating. The results of fastness properties of the dyed fabrics were studied. X-ray and Scanning Electron Microscope SEM were carried out on dyed samples using both methods of dyeing to find out an explanation for the better dyeability of acrylic fabrics with (US) method. Dyeing kinetics of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% using conventional and ultrasonic conditions were compared. The time/dye-uptake isotherms are revealing the enhanced dye-uptake in the second phase of dyeing. The values of dyeing rate constant, half-time of dyeing and standard affinity and ultrasonic efficiency have been calculated and discussed.     

Large-scale ultrasonic cleaning system: Design of a multi-transducer device for boat cleaning (20kHz)

The present study is part of a global project which consists in the development of an automatic cleaning station for immersed boats (cockle, ninepin, etc.) in a self-service mode, associating an innovative ultrasonic device for cleaning with a specific water treatment. The originality of the process is that cleaning is performed by three transducers operating simultaneously at low frequency and moving along the surface, thanks to programmable logic controllers, and that it includes a suction to collect the dirt removed. Therefore, the time required for boat maintenance is shortened, ensuring high quality cleaning without the need for dry docks and avoiding additional pollution in the harbor areas. One of the key points was the evaluation of washing efficiency, as it is really hard to give a quantitative estimation of the dirt removed. To obtain the first design laws, feasibility tests have been carried out on dirty cockle samples and on real boat hulls with a laboratory ultrasonic device. The influence of a large number of parameters was tested such as transducer-probe distance, displacement speed and transmitted power. The obtained data allowed us to design an optimized cleaning device combining high efficiency and speed.     

A tunneling spectroscopy study of the temperature dependence of the forbidden band in Bi2Te3 and Sb2Te3

Tunneling measurements of dI/dV, d ² I/dV ², and d ³ I/dV ³ were formed along the C ₃ axis (normally to layers) for Bi₂Te₃ and Sb₂Te₃ layered semiconductors in the temperature range 4.2<T>29 5 K. Temperature dependences of the forbidden band energy E _g were obtained. The forbidden band energy in Bi₂Te₃ was 0.20 eV at room temperature and increased to 0.24 eV at T=4.2 K. The E _g value for Sb₂Te₃ was 0.25 eV at 295 K and 0.26 eV at 4.2 K. The distance between the top of the higher valence band of light holes and the top of the valence band of heavy holes situated lower was found to be ΔE _V≈19 meV in Bi₂Te₃; this distance was independent of temperature. The conduction bands of Bi₂Te₃ and Sb₂Te₃ each contain two extrema with distances between them of ΔE _c≈25 and 30 meV, respectively.     

High-resolution electroreflectance measurements of GaAs

High-resolution surface-barrier electroreflectance measurements are reported for GaAs, taken at 4.2 K in the Schottky barrier configuration. Interference effects between the bulk and space-charge regions are seen at the n = 1 exciton line for both E₀ and E₀ + Δ₀ transitions. We calculate the value μ_T = (0.055 ± 0.008) m_e for the transverse mass of the E₁ + Δ₁ transition from Franz-Keldysh oscillations observed at high fields. The E'₀ structure is resolved into separate critical points of Γ and Δ symmetry. Threshold and broadening energies are obtained at 4.2 K for the E₀,E₀, E₀ + Δ₀, E₁, E₁ + Δ₁, E'₀ (Γ and and E₂ (Σ and X) critical points.     

Infrared modulated reflectance spectra of n and p type gallium antimonide and n type indium antimonide

We have observed the modulated reflectance spectra of n and p type GaSb at 300, 80, and 5 K from 0.56 to 2 eV. The modulated reflectance of intrinsic n type InSb was measured at 80 K from 0.2 to 2 eV. The “dry sandwich” vapor deposition technique was used to make the electroreflectance (ER) samples. The low-temperature spectrum of the undoped p type GaSb sample shows three peaks at the band edge that could be associated with transitions from the top of the valence band, the light (0.903 eV) and heavy (1.014eV) hole state Fermi levels to the conduction band. The energies of the observed peaks are in agreement with the Fermi level determination from Hall effect and Faraday rotation measurements. This modulation mechanism is based on band population effects. The ER signal of InSb under flatband condition at 80 K has five half oscillations at the direct band gap. The contribution of piezoelectric strain to ER is present since the dc bias required to achieve flatband condition is different at the band gap than at E₁. The ER signal corresponding to the direct gap energy E₀ and to the spin-orbit energy E₀ + Δ₀ was determined in the n and p type samples of GaSb at different temperatures. We have measured the intrinsic energy gap in GaSb at room temperature. E_g = 0.74 eV. The corresponding spin-orbit splitting was found to be Δ₀ = 0.733 ± 0.002 eV.     

Temperature compensating Elinvar character in Fe-Mn-Si alloys

Young's modulus-temperature and thermal expansion curves were measured in γ-Fe-31Mn-(0.25-8.67) Si-0.77C (at%) alloys by dynamic audio resonance method and in a light dilatometer. The results show that the anomalies in Young's modulus and thermal expansion appear near the Néel temperature. The temperature coefficient of Young's modulus, (1/E_p)(dE_p/dT), is controlled by Si content below the Néel temperature. When Si content increases to 5.31 at%, (1/E_p)(dE_p/dT) is close to zero in temperature range from 260 to 335 K, i.e. the Fe-31Mn-5.31Si-0.67C (at%) alloy shows Elinvar character. The temperature range in which the Elinvar character appears is wider than that of γ-Fe-Mn Elinvar alloys. The change in exchange energy and the ΔE effect result from the effect of Si on the antiferromagnetic behavior in γ-Fe-Mn alloys since it induces or enhances localized magnetic moment. When the increase in normal Young's modulus due to lowering temperature is compensated by the ΔE effect caused by the antiferromagnetic ordering, Elinvar character appears.