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In order to study the instantaneous mechanical properties of rock mass discontinuities with different 3D morphologies during the shear process, the Brazilian splitting method is used to prepare natural rock mass discontinuities, and the high-precision 3D scanning test of discontinuities is carried out. The Z 2 is selected as the evaluation parameter of the discontinuities. Based on the graded cyclic shear test results of discontinuities, the influence of the morphology characteristics on the strength and deformation characteristics is analyzed. With the increase of shear times, the 3D morphology characteristic parameters of the structural plane decrease steadily after the graded cyclic shear. Based on the test curve, the graded cyclic shear characteristics of rock mass discontinuities are analyzed from the shear deformation, and the shear process of the discontinuities is finely divided by combining with the variation characteristics of shear stiffness. Combined with the 3D morphology parameters, an empirical formula for the shear strength of discontinuities is proposed. Through verification, the effect of the new model is better than that of the classical JRC-JCS model.

The sliding of rock blocks along rock discontinuities is caused by accumulated deformation and can result in disasters such as rock bursts and earthquakes. Creep along rock discontinuities leads to the accumulation of sliding deformation and random instability over time. The initial stress and deformation are important factors that strongly influence creep behavior. To investigate the influence of the initial state on the creep behavior of rock discontinuities, shear creep tests with loading–unloading shear pre-stress paths and shear creep tests with different initial stress and deformation states were conducted on artificial rock discontinuity samples prepared according to Barton’s standard roughness profiles. The creep behavior characteristics were investigated in detail according to the initial stress and deformation conditions. The results show that the initial stress and deformation states, which are related to crack development and plastic deformation accumulation, strongly influence creep behavior. Larger initial stress and deformation produce lower creep deformation, creep rates, and accelerated velocities. Samples with higher joint roughness coefficients produce more noticeable creep because more asperities provide additional space for creep to occur. A limit curve is also proven to exist, which allows the stress–deformation coordinate system to be divided into stable and unstable regions. When the current stress state of a sample is insufficient to drive the formation of further cracks or deformation in the rock discontinuity, the deformation and stress remain stable and no further creep is observed.

Magnetic anisotropy energy (MAE) is one of the most important properties in two-dimensional magnetism since the magnetization in two dimension is vulnerable to the spin rotational fluctuations. Using density functional theory calculation, we show that perpendicular electric field dramatically enhances the in-plane and out-of-plane magnetic anisotropies in Fe3GeTe2 and Fe4GeTe2 monolayers, respectively, allowing the change of easy axis in both systems. The changes of the MAE under the electric field are understood as the result of charge redistribution inside the layer, which is available due to the three-dimensional (3D) network of Fe atoms in the monolayers. As a result, we suggest that due to the unique structure of FenGeTe2 compounds composed by peculiar 3D networks of metal atoms, the MAE can be dramatically changed by the external perpendicular electric field.

Water ice becomes a superionic phase under the high pressure and temperature conditions of deep planetary interiors of ice planets such as Neptune and Uranus, which affects interior structures and generates magnetic fields. The solid Earth, however, contains only hydrous minerals with a negligible amount of ice. Here we combine high pressure and temperature electrical conductivity experiments, Raman spectroscopy and first-principles simulations to investigate the state of hydrogen in the pyrite-type FeO2Hx (x ≤ 1), which is a potential H-bearing phase near the core–mantle boundary. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H+ (or proton) becomes diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond the individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state, which is characterized by freely moving protons and a solid FeO2 lattice. The highly diffusive hydrogen provides fresh transport mechanisms for charge and mass, which dictate the geophysical behaviours of electrical conductivity and magnetism, as well as geochemical processes of redox, hydrogen circulation and hydrogen isotopic mixing in Earth’s deep mantle. Under conditions of Earth’s deep lower mantle, hydrogen ions diffuse freely through the FeOOH lattice framework and electrical conductivity increases rapidly, according to electrical conductivity experiments and first-principles simulations.

Force calculation, stress, and fatigue analysis are major issues in machine design to ensure the life expectancy of sprocket-gear power transmission systems. Therefore, this study aims to conduct a theoretical analysis of bending stresses to select the size and component materials for the power transmission part of a Chinese cabbage collector that is under development. The three-dimensional models of a 14T sprocket gear for two steel materials, SCr420H and SM45C, were generated, employing commercial software. The bending stresses, deformations, and fatigue damages of the designed sprocket were determined by varying the face width and pressure angle of the sprocket teeth. The Lewis and American Gear Manufacturer Association (AGMA) equations were used to calculate the bending stresses. The calculated bending-stress values were compared with the stress values obtained from finite-element analysis (FEA). The maximum stress values on the gear teeth were 650.07, 826.23, and 840.77 MPa for a 20° pressure angle by using the Lewis, AGMA, and FEA methods, respectively. The simulated maximum stress value was higher than the yield strength of the SM45C steel and lower than the yield strength of the SCr420H steel. In addition, the maximum face width showed the minimum bending stress and fatigue damage for the selected material. Hence, considering the safety factor, the steel material SCr420H was selected with a 4.5-mm face width for designing the power transmission part of the Chinese cabbage collector. The analysis of bending stresses presented in this research can guide the design of a sprocket for the efficient transfer of Chinese cabbages using the proposed Chinese cabbage collector.

The stress relaxation behaviors of discontinuities under cyclic loading have been rarely investigated. In this study, cyclic loading is applied to discontinuities for shear relaxation tests, in whi...

From a sustainability point of view, the disposal of non-recyclable glasses like Pyrex, tempered glass, and borosilicate glass gradually become an environmental issue because non-recyclable glass is a non-biodegradable material. To obtain high glass recycling ratios without remelting, many researchers have used not only crushed glass as an alternative to both fine and coarse aggregate in concrete, but also used ground glass powder as a pozzolanic material to enhance the formation of calcium silicate hydroxide (C S H). In general, concrete is known as a good fast neutron moderator due to its high hydrogen content but does not contain boron compound used for absorption of a thermal neutron. In this work, borosilicate glass was, therefore, used as a form of mineral additive and fine aggregate to produce neutron shielding mortar in this work. Furthermore, it was investigated whether the use of borosilicate glass powder can mitigate the expansion caused by alkali-silica reaction (ASR) between alkali in cement and the reactive silica in borosilicate glass aggregate or not. Test results indicate that 20% borosilicate glass powder replacing cement was able to control the ASR expansion. When borosilicate glass powder and aggregates were used simultaneously, the compressive strength of the mortar mixture increased. Moreover, the combined use of borosilicate glass powder and aggregates could shield 86% additional thermal neutron, leading to the possibility of using borosilicate glass for neutron shielding purposes.

Two-dimensional van der Waals (vdW) magnetic materials have emerged as possible candidates for future ultrathin spintronic devices, and finding a way to tune their physical properties is desirable for wider applications. Owing to the sensitivity and tunability of the physical properties to the variation of interatomic separations, this class of materials is attractive to explore under pressure. Here, we present the observation of direct to indirect band gap crossover and an insulator–metal transition in the vdW antiferromagnetic insulator CrPS4 under pressure through in-situ photoluminescence, optical absorption, and resistivity measurements. Raman spectroscopy experiments revealed no changes in the spectral feature during the band gap crossover whereas the insulator–metal transition is possibly driven by the formation of the high-pressure crystal structure. Theoretical calculations suggest that the band gap crossover is driven by the shrinkage and rearrangement of the CrS6 octahedra under pressure. Such high tunability under pressure demonstrates an interesting interplay between structural, optical and magnetic degrees of freedom in CrPS4, and provides further opportunity for the development of devices based on tunable properties of 2D vdW magnetic materials.

A theoretically designed van der Waals ferromagnet Fe4GeTe2 is synthesized and shows the nearly room temperature ferromagnetism., In spintronics, two-dimensional van der Waals crystals constitute a most promising material class for long-distance spin transport or effective spin manipulation at room temperature. To realize all-vdW-material–based spintronic devices, however, vdW materials with itinerant ferromagnetism at room temperature are needed for spin current generation and thereby serve as an effective spin source. We report theoretical design and experimental realization of a iron-based vdW material, Fe4GeTe2, showing a nearly room temperature ferromagnetic order, together with a large magnetization and high conductivity. These properties are well retained even in cleaved crystals down to seven layers, with notable improvement in perpendicular magnetic anisotropy. Our findings highlight Fe4GeTe2 and its nanometer-thick crystals as a promising candidate for spin source operation at nearly room temperature and hold promise to further increase Tc in vdW ferromagnets by theory-guided material discovery.

Crystalline Si core–amorphous SiOx shell nanoparticles were synthesized from SiCl4 using an atmospheric microwave plasma process and their microstructures were investigated. It was found that the amorphous SiOx shell thickness was determined by varying the applied microwave power. The increase of applied power directly increased the length of the flame at the end of the plasma. Through observation of the microstructures with varying lengths of the flame, it was found that a highly crystalline Si phase was formed in the plasma and amorphous SiOx phase was formed in the flame. The longer flame resulted in the thicker SiOx shell around the Si core. The electrochemical properties of the varying SiOx shell thicknesses were also investigated in that the synthesized Si-SiOx nanoparticles were used as anode materials in a lithium-ion battery (LIB). Thin shells such as native oxide did not influence the electrochemical behaviour of the Si core, whilst some shells were too thick to allow Li-ions to react with the Si core. Using Si-SiOx nanoparticles with the optimum SiOx:Si ratio of 18:82, the following electrochemical properties were obtained: a first reversible capacity of 932 mAh/g, an initial columbic efficiency (ICE) of 52.5%, and a capacity retention of 83.7% at the 100th cycle.

We investigated the stoichiometry of silicon nitride film deposited by plasma-enhanced chemical vapor deposition (PECVD). Lowering the NH3/SiH4 gas flow ratio resulted in slightly Si-rich film due to the lack of reactive nitrogen in the plasma. It may reduce the film stress, but the refractive index of Si-rich nitride film can be increased by 50% at its maximum. The aforementioned stress adjustment methods are made practically useful by performing multiple experiments to achieve immediate stress release. It suffers from figures of merit of the PECVD-deposited silicon nitride film. Thin film stress was measured both before and after deposition, and the stoichiometry of deposited film on wafer was measured by Fourier transform-infrared (FT-IR) spectroscopy, while plasma chemistry and its conditions were monitored in real time during the deposition process. The purpose of this study was to correlate the optically measured film stress with the stoichiometry of the deposited film and plasma chemistry. Nitrogen-rich plasma processes tend to have higher tensile stress, and FT-IR measurements are in accordance with the measured mechanical stresses of the wafers.

Microbially induced carbonate precipitation (MICP) is a new environmentally friendly technique for grouting rock fractures and aggregates. However, this method can achieve only a limited degree of strength increase and low treatment efficiency. To address these limitations, an improved treatment method was designed and tested using bio-slurry (i.e., bacterial suspension with fine calcite particles), and the treatment effectiveness and strength of cemented rock fractures and aggregates were enhanced. The experimental results show that the rock specimens with fractures grouted using bio-slurry exhibited significantly higher shear strength values than those treated using the conventional MICP method, owing to a nearly six times higher filling ratio. The uniaxial compressive strength of the rock aggregates cemented using bio-slurry was two times higher than that treated using the conventional method, owing to the formation of more calcite crystals near the contact points between adjacent particles. The proposed bio-slurry method was demonstrated as an effective technique for cementation of rock fractures and aggregates with a higher efficiency than the traditional method.

Samples of Hwangdeung granite from Korea and Berea sandstone from USA, both containing sliding planes, were prepared by saw-cutting or polishing using either #100 or #600 grinding powders. Their basic friction angles were measured by direct shear testing, triaxial compression testing, and tilt testing. The direct shear tests and triaxial compression tests on the saw-cut, #100, and #600 surfaces indicated that the most reliable results were obtained from the #100 surface: basic friction angle of 29.4° for granite and 34.1° for sandstone. To examine the effect of surface conditions on the friction angle in tilt tests, the sliding angles were measured 50 times with two surface conditions (surfaces cleaned and not cleaned after each measurement). The initial sliding angles were high regardless of rock type and surface conditions and decreased exponentially as measurements continued. The characteristics of the sliding angles, differences between tilt tests, and dispersion between measurements in each test indicated that #100 surface produced the most reliable basic friction angle measurement. Without cleaning the surfaces, the average angles for granite (32 measurements) and sandstone (23 measurements) were similar to the basic friction angle. When 20–50 measurements without cleaning were averaged, the basic friction angle was within ± 2° for granite and ± 3° for sandstone. Sliding angles using five different tilting speeds were measured but the average was similar, indicating that tilting speed (between 0.2° and 1.6°/s) has little effect on the sliding angle. Sliding angles using four different sample sizes were measured with the best results obtained for samples larger than 8 × 8 cm.

Concrete has been used as a traditional biological shielding material. High hydrogen content in concrete also effectively attenuates high-energy fast neutrons. However, concrete does not have strong protection against thermal neutrons because of the lack of boron compound. In this research, boron was added in the form of borosilicate glass powder to increase the neutron shielding property of cement mortar. Borosilicate glass powder was chosen in order to have beneficial pozzolanic activity and to avoid deleterious expansion caused by an alkali–silica reaction. According to the experimental results, borosilicate glass powder with an average particle size of 13 µm showed pozzolanic activity. The replacement of borosilicate glass powder with cement caused a slight increase in the 28-day compressive strength. However, the incorporation of borosilicate glass powder resulted in higher thermal neutron shielding capability. Thus, borosilicate glass powder can be used as a good mineral additive for various radiation shielding purposes.

The interactions between an eco-spiral bolt and crushed rocks in a borehole were evaluated by pull-out testing in a laboratory and numerical analysis. The porosity of the crushed rock surrounding the bolt depended on the size of the eco-spiral bolt and affected the eco-spiral bolt’s axial resistance force. The axial resistance force and the porosity of the crushed rocks in the borehole showed an inverse relationship. The porosity was also related to the size of the eco-spiral bolt. The maximum principal stress between the bolt and the rock was related to the porosity of the crushed rock and the size difference between the eco-spiral bolt and the borehole. At low porosity the experimental and numerical analyses show similar relationships between the axial resistance force and the displacement. However, at high porosity, the numerical results deviated greatly from the experimental observation. The initial agreement is attributed to the state of residual resistance after the maximum axial resistance force, and the latter divergence was due to the decreasing axial resistance force owing to slippage.

The shear behavior of sand-steel interface plays an important role in the performance of steel pipe piles that support marine structures. In this study, the effects of surface roughness (from rough surface to smooth surface) and mean particle size on mobilized sand-steel interface friction were investigated by direct shear tests. Three types of calcareous sand with different particle sizes and three steel plates with different surface roughness were employed in the experimental program. Results indicate that the surface roughness of steel plate has a significant effect on the shear behavior between calcareous sand and steel. The peak shear strength increases with the surface roughness, and the interface friction angle reaches 90% of the internal friction angle of calcareous sand with various particle size. Moreover, the interface friction angle of calcareous sand is higher than that of siliceous sand, which is due to the effect of soil densification and particle breakage during the specimen preparation of calcareous sand.

Nanoparticles having four different ratios of crystalline silicon (Si) cores and amorphous SiOx shells were synthesized by using a microwave-generated plasma. Their microstructures were analyzed to find quantitative relationships with electrochemical properties. By measuring XRD, SEM, HR-TEM, and Raman spectra of four samples with different core-shell microstructures, the quantitative fractions of crystalline Si core and amorphous SiOx shell in the nanoparticles were calculated. Also, electrochemical properties of the nanoparticles were measured and compared with the calculated fractions. The electrochemical properties such as the initial reversible capacity, the initial coulombic efficiency, and the capacity retention exhibited tendencies remarkably similar to those implied by the calculated fractions. Analysis of each sample's dQ/dV profile also gave us good evidence of understandable relationships between the fractions and electrochemical properties. Details of calculating the fractions from microstructural data are given, with suitable consideration having been given to the fact that several assumptions could lead to errors during the analysis. The approach introduced in this research offers a good means of analysis with which to further the optimal design of nanoparticle microstructure for Li-ion battery anodes.

The performance of n-type dye-sensitized solar cells (n-DSSCs) based on a Co complex redox electrolyte were investigated with a photoanode composed with mixer consists of both TiO2 and AlCl3. The surface of TiO2 films coated on FTO glass substrates was amended by soaking them in a TiCl4:AlCl3 blended aqueous solution at different molar ratios, and calcining them to yield the surface-modified photoelectrodes (Ti:Al/TiO2). An enhancement in the power conversion efficiency 2.02% of the resulting n-DSSCs with Ti:Al (9:1)/TiO2 compared to the reference cell by the plain TiO2. The dark current measurements, incident photon-to-current conversion, and efficiency electrochemical impedance spectroscopy (EIS) revealed that the combination of a mixer onto the TiO2 film led to the delay of the charge recombination among the photo-injected electrons and Co complex redox electrolyte, resulting in an enhanced short-circuit current and open-circuit current, compared to device without surface modification.

We synthesized silicon (Si) nanoparticles using an atmospheric microwave plasma process, and investigated the effects of hydrogen (H2) injection on their microstructure during the synthesis. Two nozzles were applied to inject H2 (swirling and rectilinear H2). Our microstructural analysis indicated that the amount and method of H2 injection were critical for completion of the reaction from silicon tetrachloride (SiCl4) to Si, as well as to obtain highly crystalline Si nanoparticles. The swirling H2 was especially critical due to its formation of vortex flow, which allowed relatively long residence time of the H-ions in plasma. The Si nanoparticles synthesized by the atmospheric plasma process had core-shell structures that consisted of crystalline Si cores with amorphous SiOx shells of 5–15 nm thickness. We also investigated the feasibility of the synthesized Si nanoparticles as anode materials in a lithium-ion battery (LIB). For the core-shell structured Si nanoparticles, we obtained the first reversible capacity of 1204 mAhg−1, and a capacity retention of 82.2% at the 50th cycle.

Dye sensitized solar cells (DSSCs) were fabricated using Nb2O5 energy barrier layer is coated on the TiO2 photoanode. This energy barrier (Nb2O5 layer) reduces the recombination rate of the photoin...

Effects of SiOx or C shells on electrochemical properties of Si nanoparticles were investigated. SiOx shells with thickness of 10~15 nm were formed on homogeneously crystalline Si nanoparticles. Incase of Si-C nanoparticles, there were 30~40 layers of C with a number of defects. Li-ion batteries were fabricated with the above-mentioned nanoparticles, and their electrochemical properties were measured. Pristine Si shows a high IRC (initial reversible capacity) of 2,517 mAh/g and ICE (initial columbic efficiency) of 87%, but low capacity retention of 22%, respectively. SiOx shells decreased IRC (1,534 mAh/g) and ICE (54%), while the retention increased up to 65%, which can be explained by irreversible phases such as LiO2 and Li2SiO3. C shells exhibited no differences in IRC and ICE compared to the pristine Si but an enhanced retention of 54%, which might be from proper defect structures.

P-type single crystalline silicon (Si) wafers with a thickness of 100 μm were obtained in a free abrasive (slurry on) multi-wire sawing process. When wafer thickness decreased to 100 μm, Cu-contamination on sliced wafer surface occurred. We investigated the contamination mechanism and its solution, and finally eliminated this contamination by applying the solution found herein. The thinner the wafer thickness became, the more Cu debris were detached from brass-coated wire, those ultrafine debris (0.08–0.2 μm) became aggregated on SiC abrasive particles. The aggregated Cu debris was strongly attached on wafer surface by mechanical load from wire and thermal energy during the sawing process when wafer was as thin as 100 μm. By adding a coolant to prevent aggregation during the process, Cu-contamination was successively removed. The influences of contamination on physical properties of sliced wafers such as thickness variation, roughness were also investigated. The contaminated wafers exhibited relatively higher reflectivity after texturing process, which resulted in degradation of photoelectric conversion efficiency from 17.6% to 17.0%.

The thermal behavior of silicon nanoparticles (Si NPs) was investigated for the preparation of silicon thin film using a solution process. TEM analysis of Si NPs, synthesized by inductively coupled plasma, revealed that the micro-structure of the Si NPs was amorphous and that the Si NPs had melted and merged at a comparatively low temperature (~750 °C) considering bulk melting temperature of silicon (1414 °C). A silicon ink solution was prepared by dispersing amorphous Si NPs in propylene glycol (PG). It was then coated onto a silicon wafer and a quartz plate to form a thin film. These films were annealed in a vacuum or in an N₂ environment to increase their film density. N2 annealing at 800 °C and 1000 °C induced the crystallization of the amorphous thin film. An elemental analysis by the SIMS depth profile showed that N₂annealing at 1000 °C for 180 min drastically reduced the concentrations of carbon and oxygen inside the silicon thin film. These results indicate that silicon ink prepared using amorphous Si NPs in PG can serve as a proper means of preparing silicon thin film via solution process.

In this study, 1.0 mol% CuO-added (NaxK1−x)NbO3 (CNxK1−xN) ceramics with 0.0 ≤ x ≤ 0.5 were sintered at a relatively low temperature of 960°C. A large Qm value (≥1750) was obtained for the specimens with x ≤ 0.2 owing to the hardening effect of Cu2+ ions, indicating that a large number of Cu2+ ions had replaced Nb5+ ions in these ceramics. The double polarization versus electric field (P–E) hysteresis loop was observed for the specimens with x ≤ 0.2, and was explained by the defect polarization (Pd) formed between Cu2+ ions and O2− vacancies. These specimens also exhibited a sprout-shaped strain versus electric field (S–E) curves with a large strain of 0.14%–0.15% at 8.0 kV/mm because of the internal bias field produced by Pd. For the CN0.2K0.8N ceramic, a double P–E hysteresis loop was maintained at 125°C without remnant polarization. Moreover, this ceramic showed a large strain of 0.175% after 104 cycles when a high electric field of 8.0 kV/mm was continuously applied to the specimens during each cycles. Therefore, CN0.2K0.8N is a useful lead-free piezoelectric ceramic for multilayer actuators.

Thin silicon (Si) wafers with thickness of 100–140 μm were obtained by using a multi-wire slicing process with a SiC slurry. We investigated the process yields of wafer slicing as well as physical/electrical properties of the sliced wafers with various thicknesses. As the wafer thickness decreases, the process yield abruptly decreased due to wafer breakage during the slicing process, and conventional polishing the brick surface was not enough to gain a considerable process yield. However, elimination of defects on the brick surface by mirror polishing resulted in an 83.1% enhancement of yield even for wafers with a thickness of 100 μm. The number of wafers obtained was even higher than that of conventional 180 μm-thick wafers (479 vs. 415 wafers in this research). Investigation of the microstructure of brick surfaces revealed that surface defects on bricks were main parameter to determine the yield of slicing process. Surface defects containing the micro-cracks introduced residual stress, which decreased the slicing process yield especially for thinner wafers. From measurements of physical and electrical properties, it was revealed that the relative total thickness variations (TTVs) and bowings increased and the characteristic fracture strength of sliced wafer and conversion efficiencies decreased as the wafer thickness decreased. For the wafer with thickness of 100 μm, the relative TTV and bowing were 14.1% and 22.5 mm, respectively. The conversion efficiency of a solar cell using this wafer was 17.6%, while that of a conventional Si solar cell using a 180 μm-thick wafer was 18.4%.

The removal of boron is one of the main challenges in the purification of metallurgical grade silicon destined for low-cost photovoltaic applications. However, boron is very difficult to remove in its elemental form due to its large segregation coefficient in silicon and its low vapor pressure. The removal of boron by slag treatment is today regarded as a highly promising method, but its refining efficiency is relatively low. Also, the reduction of boron by plasma treatment exhibits a high refining efficiency, but the processing cost is high due to the large amount of electricity consumed by the process. In this regard, the use of an oxidizing reactive gas in the refinement process offers some advantages both in terms of low energy consumption and promising refinement rates. Boron can be extracted in various gaseous forms as B(x)O(y) and/or B(x)H(z)O(y) phases, but the vapor pressure of B(x)H(z)O(y) is much greater than that of the other specie at a temperature of 1700 K. The present study reports a modified oxidative refining method designed to enhance the vaporization of boron as B(x)H(z)O(y) by blowing gaseous water onto the silicon melt in a segmented crucible to enhance the electromagnetic force, whereby the processing cost can be dramatically reduced due to the use of a reusable quartz crucible in a graphite crucible. An initial boron content of 13 ppm in the metallurgical grade silicon was significantly decreased to 0.3 ppm by the employment of 1.7SLM Ar + 100 ml/h H2O. Also, a mechanism capable of reducing boron based on thermodynamic considerations is proposed.

Whether or not epitaxially grown superconducting films have the same bulk-like superconducting properties is an important concern. We report the structure and the electronic properties of epitaxially grown Ba(Fe1-xCox)2As2 films using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). This film showed a different surface structure, (2sqrtx2sqrt2)R45 reconstruction, from those of as-cleaved surfaces from bulk crystals. The electronic structure of the grown film is different from that in bulk, and it is notable that the film exhibits the same superconducting transport properties. We found that the superconducting gap at the surface is screened at the Ba layer surface in STS measurements, and the charge density wave was observed at the surface in sample in the superconducting state., Comment: 24 pages 8 figures

A series of single and double branched organic dyes (1–4) utilizing two different acceptor groups, 2-cyanoacetic acid and rhodanine-3-acetic acid as anchoring moieties, were synthesized and characterized for their potential in dye sensitized solar cells (DSSCs). The DSSC based on sensitizer 3 has the best power conversion efficiency (3.51%) among all the devices assessed, which was 2 times higher than that of 1 with only one anchoring group. Compared to the 1–2 congeners with only one anchor, the dianchoring dyes 3–4 could suppress charge recombination more effectively and increase the electron injection efficiency, leading to a higher open-circuit voltage and short-circuit current.

Si nanoparticles were synthesized by inductively coupled plasma and a specially designed double tube reactor. By injection of large amount of PH3 during the synthesis, the effects of phosphorous incorporation on their microstructures and chemical binding environments were investigated. Injection of PH3 gas during the synthesis resulted in a change from crystalline to amorphous phase, a reduction of particle size as well as a process yield. All of the above results were attributed to a lower plasma density when higher amount of PH3 was injected. From energy-dispersive X-ray spectroscopy, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy analysis, it was revealed that P was doped in Si nanoparticles. However, secondary phases such as P4 and P2O5 were formed as amorphous ones in nano-scale when a relatively large amount of PH3 was injected. In addition, those nanoparticles were applied as an active material in the lithium-ion battery's anode. Unexpectedly, amorphous Si nanoparticles with secondary phases showed improved electrochemical properties. P-doping in Si nanoparticles could not directly advance cycling performance by improvement of electrical conductivity of Si nanoparticles. It was rather assumed that a secondary phase influenced and enhanced electrochemical properties by additional capacity due to a formation of Li3P and forming an effective buffer against large volumetric change of Si nanoparticles during the charge/discharge. The initial reversible capacity of amorphous Si nanoparticles synthesized with 100 sccm of PH3 flow rate was 2113 mAh g− 1, and that at the 100th cycle was still about 1000 mAh g− 1, which was twice as high as that of Si nanoparticles synthesized without PH3 injection.

The oxidation behavior of photovoltaic ribbon was measured for 48 hours over the temperature range of 300°C to 800°C using thermogravimetric apparatus (TGA). It was found that weigh-gained of both samples was found to be increased with increasing temperature and it was dramatically increased at 800°C for 30 minutes of initial oxidation time. Pure copper with 99.55% purity was successfully recovered from the photovoltaic ribbon of spent solar module using cyclic oxidation method.

A novel efficient metal free sensitizer containing unsymmetrical double branched anchoring dye ( AB ) was synthesized for dye-sensitized solar cells (DSSCs) and compared with corresponding cosensitizer ( A + B ), single ( A , B ) and symmetric double branched ( AA , BB ) dyes. Comparing to 2.23% for the DSSC based on the dye with ( A + B ), 1.29% and 1.51% for the DSSCs based on the dyes with A , B and 2.03% and 2.02% for the DSSCs based on the dyes with AA , BB , the overall conversion efficiency reaches 2.43% for AB -sensitized solar cell as a result of its complementary absorption, more efficient interfacial charge generation and transport. The results show that the performance of DSSCs can be effectively enhanced by the cooperation of two different donor-acceptor containing branches in one molecule of the dye.

This paper presents a metallurgical route that consumes much less energy than the gasification route such as Siemens process-based photovoltaic (PV) value chain including metallurgical-grade silicon (MG-Si), solar-grade silicon (SoG-Si) purified by the metallurgical route, Czochralski (Cz) ingot growth, 6″ wafer fabrication, solar cell fabrication, and PV performance evaluation. Mono-like crystalline silicon ingot for achieving high purity was continuously cast with MG-Si for the fabrication of feedstock for Cz ingot growth through the advanced electron beam melting (EBM) system. The system was developed with the combination of vacuum refining part and directional solidification (DS) part for the purification of large amounts of MG-Si, where the two parts are connected by an overflow of Si melts to undergo continuous refining and casting processes in a chamber. To grow the mono-like crystalline Si ingot in our EBM system, a single crystalline seed was placed on the graphite dummy cylinder with DS zone. The mono-like crystalline Si ingot with high purity of >99.999% (above 5N) was blended 50–50 with undoped SoG-Si chunk for the compensation of boron dopant concentration in a crucible of Cz grower. The 156 × 156 mm 2 wafers were cut from Cz ingot grown with purity of >99.99999% (above 7N) by slurry-based multi-wire sawing and were fabricated by the conventional solar cell process. The measured photovoltaic performance recorded cell efficiency of 17.1%; hence its higher potential for application to the PV industry.

Fractional melting is a good method of refining metallurgical-grade silicon. It can be used to replace the traditional Siemens process for that purpose. It is important to observe the changes in the microstructure of silicon during heating to increase the efficiency of fractional melting. The microstructures and the chemical compositions of impurity phases in heated samples were observed by using scanning electron microscopy and wavelength dispersive spectroscopy. The affinities among the various impurities were investigated using the Miedema model. Ti and Al had strong affinities with V and Ca, respectively. It is possible to use elements that have strong affinities with B and P to effectively remove B and P from the silicon matrix, which are otherwise difficult to remove because of their high segregation coefficients.

Phosphorous (P) incorporated silicon nanoparticles (Si NPs) were synthesized by using inductive coupled plasma (ICP) and a specially designed double tube reactor.Their microstructures were investigated by injecting various amounts of PH3 gas during the synthesis. Injection of PH3 gas during the synthesis resulted in a change from crystalline to amorphous phase, a reduction of particle size as well as process yield. These results were attributed to a lower plasma density when higher amount of PH3 was injected.From EDS, SIMS and XPS analysis, it was revealed that P was successively incorporated in Si NPs.However, secondary phases such as P4 (red P) and P2O5were formed as amorphous ones in nanoscale when a relatively large amount of PH3 was injected.

A silicon substrate with the dimensions of 100 × 140 × 0.3 mm was grown directly from liquid silicon with gas pressure. The silicon melt in the sealed melting part was injected into the growth part at applied pressure of 780–850 Torr. The solidified silicon substrate was then transferred by the pull of the cooled dummy bar. A desirable structure with a liquid-solid interface perpendicular to the pulling direction was formed when the mold temperature in the solidification zone of the growth part was much higher than that of the dummy bar, as this technique should be able to overcome thermal loss through the molds and the limited heat flux derived from the very narrow contact area between the silicon melt and the dummy bar. In addition, because the metallic impurities and expansion of volume during solidification are preferably moved to a liquid phase, a high-quality silicon substrate, without defects such as cracks and impurities in the substrate, could be manufactured in the interface structure. The present study reports the experimental findings on a new and direct growth system for obtaining silicon substrates characterized by high quality and productivity, as a candidate for alternate routes for the fabrication of silicon substrates.

Replicas were produced of 20 natural rock joints with different roughness. Factors affecting shear strength were examined and direct shear tests were performed using the replica joints to determine their quantitative shear strength characteristics. Results from the shear tests were best fitted by the power law equation, τ = Aσ n , where τ is the shear strength and σ n is the normal stress, and regression coefficients A and B were determined. The coefficient A (equal to τ when σ n is 1 MPa) is defined as the friction angle, and B, which determines the curvature of the plot of shear versus normal strength, is a factor that reduces the shear strength. The physical and mechanical properties of the coefficients A and B were defined, and the relationship between these coefficients and the factors affecting shear strength, such as roughness and joint wall strength, were analyzed quantitatively. A new equation, τ = σ n tan[ϕ b + ϕ J + s n], was suggested to measure and predict shear strength accurately based on results from these analyses, where ϕ b is the basic friction angle, ϕ J is the joint roughness angle, and s n is the shear component. Although the new shear strength equation is nonlinear, it is as simple to use as a linear equation and the shear strength can be estimated using only three easily measurable parameters (ϕ b , ϕ J , and σ j , the joint wall compressive strength). The failure envelope estimated using the new shear strength equation not only closely matches the measured shear strength, but also reflects the nonlinear relationship between the normal stress and shear strength.

The oxidation rate of pure copper was measured for 48 hours over the temperature range of 500°C to 700°C using thermogravimetric apparatus by means of continuous and discontinuous oxidation methods. It was found that weigh-gained of both samples was found to be increased with increasing temperature and rate laws were determined to be parabolic and linear rate law each other. The comparison of oxidation rate of copper was shown to be higher in discontinuous that in continuous process due to direct oxidation through the oxide scale and copper substrate.

With direct growth technologies for obtaining ribbon-type silicon (Si) wafers from molten Si, the horizontal growth process is much faster than the vertical one in terms of the growth rate of the wafer. However, such a fast growth rate is likely to create grains of a relatively small size in the Si wafer, resulting in limited efficiency caused by grain boundary recombination. In this regard, controlling the grain growth behavior of the Si wafer with processing parameters such as the temperature of the substrate and its moving speed is very important in the horizontal growth process. The present investigation produced the experimental findings concerning the processing parameters for controlling the grain size. The size of the grains on the surface of the Si wafer increased to around 180 μm at a lower substrate temperature and a slower the moving speed of the substrate due to the increasing thickness of the Si wafer. However, the growth rate of the grains was observed to have little relation to the variations in the wafer thickness resulting from the processing parameters unless the nucleation behavior had been controlled.

Silicon (Si) nanoparticles were synthesized using a double tube reactor and inductive coupled plasma (ICP), and their microstructures with various process conditions were investigated in terms of plasma density and residence time of reactive gas in the plasma zone. Homogeneous amorphous or single crystalline Si nanoparticles were synthesized depending on applied power to ICP coil. The SiH4 flow rate mainly determined the particle size. Average particle sizes of the synthesized Si nanoparticles were 14–34 nm, and the maximum production rate was as high as 1000 mg h−1. The purity of synthesized Si nanoparticles was higher than 99.99%. When Si nanoparticles were applied as an active material in the anode of a Li-ion battery (LIB), the high first reversible capacities of 2540 (initial coulombic efficiency (ICE) = 61.4%) and 1358 mAh g−1 (ICE = 62.5%) for crystalline and amorphous Si nanoparticles were attained, respectively. However, capacity fadings were detected in both nanoparticles, and capacity retentions at 100th cycle were only 17.1% and 34.8% for crystalline and amorphous Si nanoparticles.

A new polycrystalline silicon (Si) wafering process directly from Si melt is introduced. As Si is known to have high latent heat, maintaining the steady state solidification condition in target area could be a main issue to achieve proposing wafering process. In addition, as the proposed process is based on horizontal growth, another critical issue is to keep grains growth parallel to the wafer growth direction, which results in large grain sizes. At first, simple numerical modeling was used to evaluate the possibility of realizing this new conceptual process, and to determine the main process parameters. From the simulation results, growth velocity and heat transfer rate at the solidification zone was identified as main process parameters for the steadily grown Si wafer within target area. Based on the simulation results, a growth system was set up experimentally, and the feasibility of the process was examined. A Si wafer with dimensions of 156×156×0.3 mm3 was successively obtained and grains growth parallel to wafer growth direction as calculated in the simulation were observed.

The development of high performance p-type dye sensitized solar cells (DSSCs) is essential for producing tandem configurations that can overcome the theoretical limitations of single-junction DSSCs. This study evaluates a suitable organic dye for producing high performance p-type DSSCs. The photovoltaic properties of the carbazole monomer (MCBZ) and dimer (DCBZ) were examined to determine the effects of the molecular structure of the photosensitizer on the photovoltaic performance. MCBZ absorbs a larger amount of visible light photons with wavelengths between 400 and 600 nm, and provides better p-type DSSCs than conventional coumarin 343-sensitized solar cells. Furthermore, DCBZ exhibits better photovoltaic performance under standard global AM 1.5 solar conditions than the MCBZ-sensitized solar cells because of the synergistic effects of the enhanced electron injection efficiency and reduced charge recombination probability.

A novel strategy for introducing ion-permselective properties in a conventional polyethylene (PE) separator to inhibit the shuttle effect of polysulfides in high-performance lithium–sulfur batteries is reported. This was accomplished by taking advantage of the pH-responsive multilayers of weak polyelectrolytes such as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) assembled on the PE separator using layer-by-layer (LbL) assembly. It was found that the cationic permselectivity (permeability of cation/anion) of an ultrathin multilayer coated separator is highly tunable with respect to the number of bilayers and external pH, benefiting from fine tuning of the internal charge density of the multilayered films. The movement of polysulfide anions was significantly inhibited by five bilayers of PAH/PAA (ca. 98% with multilayers assembled at pH 3/3), while the movement of Li cations was preserved. As a result, the ion-permselective separator demonstrated a high initial reversible capacity of ca. 1418 mA h g−1 with multilayers assembled at pH 3/3 because of the good permselectivity and the enhanced wetting properties of the LbL treated separator for electrolytes, leading to a significantly improved Coulombic efficiency as compared to a conventional PE separator, i.e., almost 100% over 50 cycles. We anticipate that the permselectivity controllable coating method will be applied for various other membrane technologies.

Lithium ion transport was accelerated within graphite by controlling its d-spacing as well as its functional groups. By oxidizing bare graphite under a mild condition, expanded graphites (EG* where * = functional groups) were obtained with increasing d-spacing from 0.3359 nm to 0.3395 nm as well as with functional groups formed on the plane or at the edges of graphites. The subsequent thermal reduction of EG* led to an insignificant change of d-spacing (0.3390 nm), simultaneously eliminating a portion of the functional groups (EG). The enlargement of d-spacing reduced kinetic hindrance of lithium ion movement within the expanded graphites (EG* and EG) by reserving more space for the ionic transport route. In addition, the activation energy of lithium ion intercalation in EG* was reduced by surface charge polarization of graphites induced by hydrogen bonds between oxygen atoms of carbonates in electrolytes and hydrogen atoms of surface functional groups of the expanded graphites, even if the degree of graphitization decreased. Re-graphitization induced by the subsequent thermal reduction increased delithiation capacities (QdLi) of EG as an anode for lithium ion batteries especially at high currents: QdLi at 50 C = 243 mA h g−1 for EG versus 66 mA h g−1 for bare graphite.

The recovery of copper from spent photovoltaic ribbon was conducted using thermal treatment method at the range of temperature of to under inert atmosphere. The coating layer consisted of lead of 68.99 wt.% and tin of 31.21 wt.% was melted down at elevated temperatures and was collected on the bottom of crucible. The chemical composition of copper ribbon after thermal treatment was analyzed by ICP-MS (Inductively coupled plasma mass spectrometry) and the purity of copper was found to be obtained up to about 96 wt.% regardless of temperatures. The cross-sectional area of the specimen was also examined by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray microscopy).