Search results

The purpose of this paper is to describe a very low‐cost way to prepare Ge nano/microstructures by means of filling the material inside porous silicon (PS) using a conventional and cost effective technique in which thermal evaporator with PS acts as patterned substrate. Also, the potential metal‐semiconductor‐metal (MSM) photodetector IV characteristics of the structure are demonstrated.

PS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid. The Ge layer was then deposited onto the PS by thermal evaporation. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10 min. Structural analysis of the samples was performed using energy dispersive X‐ray analysis (EDX), scanning electron microscope (SEM), X‐ray diffraction (XRD) and Raman spectroscopy.

A uniform circular network distribution of pores is observed with sizes estimation of 100 nm to 2.5 μm by SEM. Also observed are clusters with near spherical shape clinging around the pores believed to be Ge or GeO₂. The EDX spectrum suggests the presence of Ge or GeO₂ on and inside the pore structure. Raman spectrum showed that good crystalline structure of the Ge can be produced inside the silicon pores. XRD showed the presence of a Ge phase with the diamond structure by (111), (220), and (400) reflections. Finally, current‐voltage (I‐V) measurement of the Si/Ge/PS MSM photodetector was carried out. It showed lower dark currents compared to control device of Si. The device showed enhanced current gain compared to conventional Si device which can be associated with the presence of Ge nanostructures in the PS.

This paper shows that it is possible to grow Ge nano/microstructure on PS by using a simple and low‐cost method of thermal evaporation and thermal annealing and demonstrates potential MSM photodetector IV characteristics from the device.

The purpose of this paper is to propose a simple physical evaporation route in which catalyst‐free zinc oxide (ZnO) nanoscrewdrivers were deposited on silicon (Si) (111) substrates.

Prior to the deposition, the Si (111) wafer was cut into pieces of 2×2 cm². Then, the wafers were dipped for 1 min into mixture buffered oxide etchant to remove native oxide. Then, the samples were rinsed in an ultrasonic bath cleaned with boiling acetone, ethanol, and de‐ionized (DI) water for 10 min. Lastly, the wafers were rinsed in 25 ml DI water in stirred and then were blown dry with nitrogen. In this technique, the starting material is high‐purity metallic zinc (Zn) powder (99.99 per cent pure). Following, the Zn films were then annealed under air environment in the furnace at 500°C for 1 h deprived of any catalysts.

These ZnO samples were studied by scanning electron microscopy, high‐resolution X‐ray diffraction (HR‐XRD), and photoluminescence (PL) spectroscopy. Atomic force microscope (AFM) images were applied to ascertain surface morphology of produced ZnO nanoscrewdrivers. XRD pattern confirmed that the ZnO nanoscrewdrivers were of polycrystalline structure in universe with a hexagonal close packed type and c‐axis is perpendicular to the substrate. The peak at 34° correspond to the reflection planes of ZnO(002) crystallographic plane is perceived. The AFM surface images disclosed that the surfaces of produced ZnO thin films are not smooth. The PL spectrum of as‐synthesized nanoscrewdrivers shows a UV emission peak at 380 nm and a broad green emission peak at 500 nm.

The paper reports on a simple physical evaporation route, ZnO nanoscrewdrivers were synthesized via the thermal evaporation of the high‐purity Zn powders and annealed at 500°C under air atmosphere without introducing any hetero‐metal catalysts or other carrier gases approach.

This paper aims to study the oxidation kinetics of the nanocrystalline Al ultrathin films. The influence of structure and composition evolution during thermal oxidation will be observed. The reason for the change in the oxidation activation energy on increasing the oxidation temperature will be discussed.

Al thin films are deposited on the silicon wafers as substrates by vacuumed thermal evaporation under the base pressure of 2 × 10⁻⁴ Pa, where the substrates are not heated. A crystalline quartz sensor is used to monitor the film thickness. The film thickness varies in the range from 30 to 100 nm. To keep the silicon substrate from oxidation during thermal oxidation of the Al film, a 50-nm gold film was deposited on the back side of silicon substrate. Isothermal oxidation studies of the Al film were carried out in air to assess the oxidation kinetics at 400-600°C.

The activation energy is positive and low for the low temperature oxidation, but it becomes apparently negative at higher temperatures. The oxide grains are nano-sized, and γ-Al₂O₃ crystals are formed at above 500°C. In light of the model by Davies, the grain boundary diffusion is believed to be the reason for the logarithmic oxidation rate rule. The negative activation energy at higher temperatures is apparent, which comes from the decline of diffusion paths due to the formation of the γ-Al₂O₃ crystals.

It is found that the oxidation kinetics of nanocrystalline Al thin films in air at 400-600°C follows the logarithmic law, and this logarithmic oxidation rate law is related to the grain boundary diffusion. The negative activation energies in the higher temperature range can be attributed to the formation of γ-Al₂O₃ crystal.

The purpose of this paper is to examine the coupled heat and mass transport of different shaped porous moist objects in a rectangular channel under the effects of convective drying. Numerical simulations were performed under turbulent conditions for cylindrical, triangular and rectangular shaped different food products in a two-dimensional channel.

Finite element method was used for the unsteady problem and, effects of drying air velocity (AV) and temperature on transport mechanism were evaluated. Three different food materials were used for the circular shaped object and drying performance of the products under different conditions was compared.

Results showed that, changing the air temperature has an important effect on drying for all shaped objects and all materials. The same effect was seen for the AV as, increasing the velocity had positive effects on drying. Two identical objects were placed in the channel one behind the other, and this configuration showed that location of the object in the channel is also important for drying. The moisture content in the object at the front is lower than in the object behind at the end of drying.

This paper can provide technical support to optimize drying performance in the industry with comprehensive data for the process.

A new recently proposed mechanism of the lenticular grain face bubble migration which controls the bubble mobility and determines the drag force exerted on the grain boundary, is further developed in application to the peripheral (edge and corner) intergranular bubbles. It is shown that contribution of the peripheral bubbles to the retarding effect can be significant, especially under irradiation conditions with high fission rates in UO2 fuel. In addition, simultaneous consideration of intergranular bubbles and pores evolution allows further improvement of the model predictions for grain growth under irradiation conditions. The improved model was implemented in the integral code MFPR, which is designed for modelling of fission product release from irradiated UO2 fuel, and validated against various tests under irradiation and annealing conditions with various types (dense and porous) fuel pellets.

Indium tin oxide (ITO) is a material belonging to the group of transparent conductive oxides, which are widely used in many fields of technology including optoelectronics and photovoltaics. However, the properties of ITO thin films depend on many factors. Therefore, the aim of the study was thorough investigation of the properties of sputtered ITO thin films of various thicknesses.

ITO coatings were deposited by magnetron sputtering in pure argon atmosphere using ceramic ITO target. Various deposition times resulted in obtaining thin films with different thickness, which had significant influence on the optoelectronic properties of deposited coatings. In this work the results of investigation of structural, surface, optical and electrical properties were presented.

Increase of the coating thickness caused change of the microstructure from amorphous to nanocrystalline and occurrence of grains with a size of 40 to 60 nm on their surface. Moreover, the fundamental absorption edge was red-shifted, whereas the average transmission in the visible wavelength range remained similar. Increase of the thickness caused considerable decrease of the sheet resistance and resistivity. It was found that even thin films with a thickness of 10 nm had antistatic properties.

The novelty and originality of presented work consists in, among other, determination of antistatic properties of ITO thin films with various sheet resistances that are in the range typical for dielectric and semiconducting material. To date, there are no reports on such investigations in the literature. Reported findings might be very helpful in the case of, for example, construction of transparent antireflective and antistatic multilayers.

The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue amount left after subjecting the samples to simulated wave soldering conditions.

Changes in the chemical structure of the activators were studied using Fourier transform infrared spectroscopy technique and were correlated to the exposure temperatures within the range of wave soldering process. The amount of residue left on the surface was estimated using standardized acid-base titration method as a function of temperature, time of exposure and the substrate material used.

The study shows that there is a possibility of anhydride-like species formation during the thermal treatment of fluxes containing weak organic acids (WOAs) as activators (succinic and DL-malic). The decomposition patterns of solder flux activators depend on their chemical nature, time of heat exposure and substrate materials. Evaporation of the residue from the surface of different materials (laminate with solder mask, copper surface or glass surface) was found to be more pronounced for succinic-based solutions at highest test temperatures than for adipic acid. Less left residue was found on the laminate surface with solder mask (∼5-20 per cent of initial amount at 350°C) and poorest acid evaporation was noted for glass substrates (∼15-90 per cent).

The findings are attributed to the chemistry of WOAs typically used as solder flux activators. The results show the importance WOA type in relation to its melting/boiling points and the impact on the residual amount of contamination left after soldering process.

The results show that the evaporation of the flux residues takes place only at significantly high temperatures and longer exposure times are needed compared to the temperature range used for the wave soldering process. The extended time of thermal treatment and careful choice of fluxing technology would ensure obtaining more climatically reliable product.

Refractance window drying (RWD) has been identified as the method that can give high-quality products at a relatively low production cost. However, knowledge about its use and adoption remains lacking both in academic curricula and industry in the developing world.

A lab-scale batch RWD of a closed-loop control system was designed, fabricated and evaluated for drying rates, evaporation rate, the energy of evaporation, energy efficiency and throughput. Testing was done using mango and tomato pulps.

Drying rates at 95°C of 1.32 gg⁻¹min⁻¹ and 0.854 gg⁻¹min⁻¹ at 2 and 3 mm, respectively, for tomato, 0.6 gg⁻¹min⁻¹ and 0.33 gg⁻¹min⁻¹ at 2 and 3 mm for mango pulp were obtained. The dryer had an evaporation rate of 4.63 × 10^–4 kg/s and 4.25 × 10^–4 kg/s, the energy of evaporation of 1.05 kW and 0.96 kW and thermal energy efficiency of 25.64% and 21.73% while drying tomato and mango pulps, respectively. Dryer throughput of 0.6 kg/h of dried mango Pulp and 0.47 kg/h of dried tomato pulp was obtained.

The designed RWD can be adequately used in laboratory experiments on different products to produce powders. This will enable the transfer of knowledge about RWD technology in developing countries.

Eight kinds of knitted fabrics, made from wool, polyester, cotton, acrylic, porous acrylic, polypropylene, viscose and polyester/cotton blend, were studied by both objective laboratory measurements and subjective wearer trials. The transport properties of the fabrics: thermal resistance, water vapor permeability, air permeability, demand wettability, water absorbency (drop wettability) and water evaporation propensity were measured. The psychological responses of subjects for the 8 kinds of fabrics were obtained in a series of psychophysiological wearer trials, in which subjective responses to 19 clothing sensations were recorded and their overall preference votes to 8 kinds of garments made from the fabrics were obtained. Significant differences were found for all the transport properties measured on the 8 kinds of fabrics.

By Spearman rank correlation analysis, it has been found that the overall preference votes after wearing in hot and Cool conditions were significantly correlated with drop and demand wettability and thermal resistance of fabrics. The thermal-wet sensations were mainly correlated with thermal resistance, water evaporation rate, water vapor and air permeability. The tactile sensations showed high correlation with thermal resistance, drop and demand wettabilities of fabrics, and also there were close correlations between body-fit sensations and demand and drop wettabilities, water evaporation rate of fabrics.

The purpose of this paper is to produce and investigate the interfacial reaction between Sn‐3.0Ag‐0.5Cu (SAC305) thin films and Cu substrates by solder reflow at various temperatures and times.

SAC305 thin films were deposited on copper substrates using a thermal evaporation technique. The as‐deposited SAC305/Cu was then reflowed on a hot plate at temperatures of 230, 240, 250 and 260°C for 30 s. In addition, solder reflow was conducted at a constant temperature of 230°C for 5, 10, 15 and 20 s. The microstructure, phase and thickness of the intermetallic compounds (IMCs) formed were determined after cross‐sectional metallographic preparation.

Cu₆Sn₅ and Cu₃Sn were observed at the as‐reflowed SAC305/Cu interfacial region. The IMC thicknesses increased with the higher reflow temperature and longer reflow times.

Up to now, studies on the thin film characteristics of SAC305 lead‐free solder have been very limited. Thus, this paper presents the deposition of SAC305 thin film by a thermal evaporation technique and its characteristics after solder reflow.