A novel thin-film multijunction solar cell based on nanocrystalline silicon (nc-Si:H) is presented in this paper. Existing thin-film double junction solar cells are based on amorphous silicon carbide (aSiC:H) and amorphous silicon layers. Such solar cells have limited efficiency due to lower absorption and poor charge transport properties of the a-SiC:H layer. These solar cells have maximum achieved efficiency of about 8.8%. In this work, a-SiC:H has been replaced with nc-Si:H layer and the double junction solar cell has been redesigned. The proposed structure has been simulated with Silvaco TCAD (ATLAS). The simulated results indicated a step increase in the performance of the solar cell with open circuit voltage Voc=2 .096 V and efficiency 77 = 102%. It was proven that the nc-Si:H is a suitable material for the development of an efficient thin film multijunction solar cell.
We have calculated the vibrational frequencies of clusters of atoms from the first principles by using the density-functional theory in the local density approximation (LDA). We are also able to calculate the electronic binding energy for all of the clusters of atoms from the optimized structure. We have made clusters of BanOm (n, m=1-6) and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO2 occurs with the O-O vibrational frequency of 836.3 cm(-1). We also find that a glass network occurs in the material which explains the vibrational frequency of 67 cm(-1). The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass. We have calculated the vibrational frequencies of BaO4, GeO4 and SiO4 each in tetrahedral configuration and find that the vibrational frequencies in these systems depend on the inverse square root of the atomic mass.
Copper (Cu) ion in wastewater is considered as one of the crucial hazardous elements to be quantified. This research is established to predict copper ions adsorption (Ad) by Attapulgite clay from aqueous solutions using computer-aided models. Three artificial intelligent (AI) models are developed for this purpose including Grid optimization-based random forest (Grid-RF), artificial neural network (ANN) and support vector machine (SVM). Principal component analysis (PCA) is used to select model inputs from different variables including the initial concentration of Cu (IC), the dosage of Attapulgite clay (Dose), contact time (CT), pH, and addition of NaNO3 (SN). The ANN model is found to predict Ad with minimum root mean square error (RMSE = 0.9283) and maximum coefficient of determination (R2 = 0.9974) when all the variables (i.e., IC, Dose, CT, pH, SN) were considered as input. The prediction accuracy of Grid-RF model is found similar to ANN model when a few numbers of predictors are used. According to prediction accuracy, the models can be arranged as ANN-M5> Grid-RF-M5> Grid-RF-M4> ANN-M4> SVM-M4> SVM-M5. Overall, the applied statistical analysis of the results indicates that ANN and Grid-RF models can be employed as a computer-aided model for monitoring and simulating the adsorption from aqueous solutions by Attapulgite clay.
In this work, independent radial diffusion at arrayed nanointerfaces between two immiscible electrolyte solutions (nanoITIES) was achieved. The arrays were formed at nanopores fabricated by focused ion beam milling of silicon nitride (SiN) membranes, enabling the reproducible and systematic design of five arrays with different ratios of pore center-to-center distance (rc) to pore radius (ra). Voltammetry across water-1,6-dichlorohexane nanoITIES formed at these arrays was examined by the interfacial transfer of tetrapropylammonium ions. The diffusion-limited ion-transfer current increased with the ratio rc/ra, reaching a plateau for rc/ra ≥ 56, which was equivalent to the theoretical current for radial diffusion to an array of independent nanoITIES. As a result, mass transport to the nanoITIES arrays was greatly enhanced due to the decreased overlap of diffusion zones at adjacent nanoITIES, allowing each interface in the array to behave independently. When the rc/ra ratio increased from 13 to 56, the analytical performance parameters of sensitivity and limit of detection were improved from 0.50 (±0.02) A M(-1) to 0.76 (±0.02) A M(-1) and from 0.101 (±0.003) μM to 0.072 (±0.002) μM, respectively. These results provide an experimental basis for the design of arrayed nanointerfaces for electrochemical sensing.
Basalt fibre is a promising mineral fibre that has high potential to replace synthetic based glass fibre in today's stringent environmental concern. In this study, friction and wear characteristics of glass and basalt fibres reinforced epoxy composites were studied and comparatively evaluated at two test stages. The first stage was conducted at fixed load, speed and distance under three different conditions; adhesive, abrasive and erosive wear, wherein each composite specimens slide against steel, silicon carbide, and sand mixtures, respectively. The second stage was conducted involving different types of adhesive sliding motions against steel counterpart; unidirectional and reciprocating motion, with the former varied at pressure-velocity (PV) factor; 0.23 MPa·m/s and 0.93 MPa·m/s, while the latter varied at counterpart's configuration; ball-on-flat (B-O-F) and cylinder-on-flat (C-O-F). It was found that friction and wear properties of composites are highly dependent on test conditions. Under 10 km test run, Basalt fibre reinforced polymer (BFRP) composite has better wear resistance against erosive sand compared to Glass fibre reinforced polymer (GFRP) composite. In second stage, BFRP composite showed better wear performance than GFRP composite under high PV of unidirectional sliding test and under B-O-F configuration of reciprocating sliding test. BFRP composite also exhibited better friction properties than GFRP composite under C-O-F configuration, although its specific wear rate was lower. In scanning electron microscopy examination, different types of wear mechanisms were revealed in each of the test conducted.
Since its invention, polyimide (PI) has been widely used in micro-electro-mechanical system (MEMS) devices. For fabrication, the PI membrane, PI-2723 HD-Microsystems was used as the membrane material due to its Young's modulus of 2.7 GPa and its film thickness could easily be controlled by changing the speed of the spin coater system. The application PI as membrane structure on silicon wafers therefore gave a much better mechanical performance then conventional membranes made of silicon dioxide (SiO2) or silicon nitride (Si3N4) layers. The fabrication of PI membrane was the same as for SiO2 and Si3N4 membranes; the basic step was to etch a side of the silicon wafer using wet anisotropic etching. This paper proposes an effective process for fabrication of PI membrane with f ast and little supervision. In this process, a dual step process was wet anisotropic etching of single crystal silicon using pottasium hydroxyl (KOH) with different concentrations and temperature processes. For the first process, 45% KOH under boiling temperature was used to etch at least 90%–95% of the silicon. In the second process, the silicon was submerged in 45% KOH with temperature at 70ºC–80ºC to etch away the residual silicon until a clean and transparent PI membrane was achieved. Using this method, the fabrication of PI membrane could be generated fast.
This research was conducted to study the effect of reinforcement particles on iron-cobalt (FeCo) composites. The composition of silicon carbide (SiC) was varied from 0 to 20 wt%. The composite was fabricated via powder metallurgy (PM) method, which consists of mixing, compaction and sintering processes. The powder was mixed for 2 hours to obtain uniformity between SiC and Fe-Co matrix and compacted to a cylindrical shape at 250 MPa. Samples were sintered for 2 hours at 900 o C with 10 o C/minute heating rate in argon atmosphere. The influences of reinforcement particle on the sintered samples were characterized in terms of microstructure and hardness testing. The Fe-Co/20wt%SiC composites show highest hardness value.
Forsterite (Mg2SiO4) because of its exceptionally high fracture toughness which is close to that of cortical bones has been nominated as a possible successor to calcium phosphate bioceramics. Recent in vitro studies also suggest that forsterite possesses good bioactivity and promotes osteoblast proliferation as well as adhesion. However studies on preparation and sinterability of nanocrystalline forsterite remain scarce. In this work, we use a solid-state reaction with magnesium oxide (MgO) and talc (Mg3Si4(OH)2) as the starting precursors to synthesize forsterite. A systematic investigation was carried out to elucidate the effect of preparatory procedures including heat treatment, mixing methods and sintering temperature on development of microstructures as well as the mechanical properties of the sintered forsterite body.
A biosensor formed by a combination of silicon (Si) micropore and graphene nanohole technology is expected to act as a promising device structure to interrogate single molecule biopolymers, such as deoxyribonucleic acid (DNA). This paper reports a novel technique of using a focused ion beam (FIB) as a tool for direct fabrication of both conical-shaped micropore in Si3N4/Si and a nanohole in graphene to act as a fluidic channel and sensing membrane, respectively. The thinning of thick Si substrate down to 50 µm has been performed prior to a multi-step milling of the conical-shaped micropore with final pore size of 3 µm. A transfer of graphene onto the fabricated conical-shaped micropore with little or no defect was successfully achieved using a newly developed all-dry transfer method. A circular shape graphene nanohole with diameter of about 30 nm was successfully obtained at beam exposure time of 0.1 s. This study opens a breakthrough in fabricating an integrated graphene nanohole and conical-shaped Si micropore structure for biosensor applications.
Desensitization of teeth after cavity preparation has been recommended in an attempt to avoid post-operative sensitivity. However, there is concern regarding application effect of desensitizing agent on shear bond strength of the adhesive system used. The purpose of our study was to compare the shear bond strength of adhesive system in two different dentin surface treatments, with and without desensitizing agent. Sixteen extracted human premolars were sectioned off at the coronal portion to expose the flat dentin surfaces. The surfaces were finished using 600 Grit Wet Silicon Carbide abrasive papers. The premolars were randomly assigned to two groups: control and treated with MS Coat desensitizing agent. The desensitizer was applied according to manufacturer’s instruction. Resin composite was bonded to each dentin surface using Prime & Bond ® adhesive system. The composite resin was debonded by shear stress. Mann-Whitney Test was used in statistical analysis. Our result showed that application of MS Coat desensitizing agent on dentin surface had significantly reduced the shear bond strength of the adhesive system used (z = - 0.14, p < 0.05). Thus, we conclude that shear bond strength of Prime & Bond ® NT (Dentsply, USA) adhesive system will be reduced if dentin surface is treated with MS Coat (Sun Medical, Japan) desensitizing agent.
Indialite or α-cordierite was synthesized by glass crystallization method using mainly talc and kaolin and with small amount of MgO, Al2O3, SiO2 to compensate the chemical formulation of non-stoihiometric compositions of cordierite. (3MgO.1.5Al2O3.5SiO2). B2O3, P2O5 and CaO was also added to decrease the melting and sintering temperature of cordierite. The glasses were pelletized and sintered from 850 o C up to 1050 o C. Phase compositions of both heat treated glass was quantified by X-ray powder diffraction data by the Rietveld method using TOPAS Ver 3 software. Result shows that about 60wt% of α cordierite has successfully crystallized at 850 o C. Beside secondary phases (forsterite) which come from initial raw materials, phases from grinding media were also presents in the sample. The contamination was considered high since it has reacted with existence phases to form a new phase at higher temperature. Without any contamination from grinding it was expected to obtain more than 90wt% α cordierite using the same composition.
This study describes the synthesis of Al(2)O(3)/SiC/ZrO(2) functionally graded material (FGM) in bio-implants (artificial joints) by electrophoretic deposition (EPD). A suitable suspension that was based on 2-butanone was applied for the EPD of Al(2)O(3)/SiC/ZrO(2), and a pressureless sintering process was applied as a presintering. Hot isostatic pressing (HIP) was used to densify the deposit, with beneficial mechanical properties after 2 h at 1800 °C in Ar atmosphere. The maximum hardness in the outer layer (90 vol.% Al(2)O(3)+10 vol.% SiC) and maximum fracture toughness in the core layer (75 vol.% Al(2)O(3)+10 vol.% SiC + 15 vol.% ZrO(2)) composite were 20.8±0.3 GPa and 8±0.1 MPa m(1/2), respectively. The results, when compared with results from Al(2)O(3)/ZrO(2) FGM, showed that SiC increased the compressive stresses in the outer layers, while the inner layers were under a residual tensile stress.
Adhesive bond strength studies for the tray adhesive of an addition vinyl polysiloxane (President) impression material were conducted with an acrylic resin, chromium-plated brass, and plastic trays. Tensile and shear stress studies were performed on the Instron Universal testing machine. Acrylic resin specimens roughened with 80-grit silicon carbide paper exhibited appreciably higher bond strengths compared with different types of tray material and methods of surface preparation.
This study was to compare the effect of three different one-step polishing systems on the color stability of three different types of nanocomposites after immersion in coffee for one day and seven days and determine which nanocomposite material has the best color stability following polishing with each of the one-step polishing system.