Bulk Stacking Research Articles

Structural optimization and growth of intrinsic hydrogenated amorphous silicon films by HWCVD

Although the silicon heterojunction (SHJ) solar cell is the crystalline silicon solar cell with highest conversion efficiency at present, its higher cost of production line has been a factor restricting its industrial development. The use of hot wire chemical vapor deposition (HWCVD) technology instead of the mainstream plasma enhanced chemical vapor deposition (PECVD) technology for the deposition of amorphous silicon films can effectively reduce the cost of equipment and processing, and has a bright future. In recent years, i-a-Si:H films grown by PECVD have obtained great improvement in passivation quality, whereas HWCVD technology has been neglected in this field. This has significantly limited the development and application of HWCVD technology in SHJ cell production. In this work, we exploited the differences in the films properties and microstructures deposited by various hot-wire temperatures and successfully developed a structure for the high-passivation-quality i-a-Si:H film grown by HWCVD, consisting of a buffer layer and a double-layer bulk stack. By introducing the buffer layer grown with the 1650 °C hot-wire temperature and pure silane, the effective minority carrier lifetime was improved from 2.3 ms to 7.5 ms, and a cell efficiency enhancement of 0.4%abs was obtained. By depositing the bulk layer sequentially with hot-wire temperatures of 1800 °C and 1900 °C, the passivation quality and the conductance were both improved. An effective minority carrier lifetime of 8 ms and a further cell efficiency enhancement of 0.15%abs were obtained. Finally, SHJ solar cell efficiency of 24.35% was obtained with a home-made HWCVD-based pilot SHJ cell line.

Bulk Solids Stacking Strategy of a Rectangular Ship Cabin

Stacking of bulk solids in terminals, ships, trains, and other bulk solids storage yards is always challenging, considering the requirements of optimal utilization of storage areas. In this study, stacking shapes of a variety of bulk solids with different particle sizes were tested, and the curved shapes of the stockpiles were extracted to establish the actual three-dimensional models of the bulk solids accordingly. The three-dimensional curved stockpiles were used to design the bulk solids stacking strategy where the bulk stacking locations, the stacking volume, and the stacking flatness were optimized. A modified golden section method with a self-influenced factor was developed to improve the calculation efficiency of the stacking algorithm for bulk solids stacking flatness. Furthermore, the bulk solids stacking strategy and algorithm were verified by experiments. The results showed that the curved three-dimensional models were very close to the actual shapes of the bulk solids stockpiles, while the improved golden section method was more accurate and efficient than the traditional golden section method in determining the optimal values of the stacking volumes in terms of flatness. For the different bulk solids tested, the experiment results showed that good flat stacking can be achieved by using the developed stacking strategy.

Two-dimensional BMD, BSF, ring-OISF and COP distributions in a dislocation-free ingot grown by the NOC method

The noncontact crucible (NOC) method has a large and deep low-temperature region in Si melt to grow a uniform large Si single ingot. The theoretical simulation pointed out that the lowest vacancy or interstitial Si atom area appears in the region with the smaller ratio between temperature gradients at melt surface and growing interface. The growth condition to obtain this region is suitable for the NOC method. The quality of a NOC ingot was first evaluated by determining the distribution of bulk micro defect (BMD), bulk stacking fault (BSF), oxidation induced stacking fault (OISF) and crystal originated particle (COP) in the cross section of the dislocation-free ingot. A ring-OISF or BSF can be clearly observed on the cross section cut from the middle and tail parts of the ingot. BMD can be observed inside and outside the ring-OISF. By estimated comparison to the none-doping case, CV (=CI) at cross point clearly has a trend to increase for the high B-doing case (5 × 1019 cm−3), where CV and CI are concentration of vacancy and interstitial Si atom, respectively. Nevertheless, in comparison with the distribution of COP in Cz and NOC ingots, COP cannot be detected inside the ring-OISF in the NOC wafer under the same etching process as many COP can be observed in the Cz wafer. This may be a unique feature for NOC growth.

Study on the Optimization of Proportion of Fly Ash-Based Solid Waste Filling Material with Low Cost and High Reliability

In order to solve the problem of the high cost of coal-based solid waste bulk stacking and paste filling in the large-scale coal electrification base in East NingXia, in this study, fly ash is skillfully used to replace the broken coal gangue as the mixed filling material. As using a jaw crusher for crushing large coal gangue is expensive, and its energy consumption is relatively high, paste filler using fly ash as aggregate is studied through micro and macro test analyses. Using response surface methodology design software, 29 groups of mix proportion schemes are designed to obtain the best mix proportion. In addition, the radar results of slump, slump flow, and comprehensive strength are obtained by the normalization method. According to the radar chart results of the three normalized indexes, the optimal ratio parameters are as follows: the fly ash in solid phase is 79%, the mass of fly ash to the mass of cement (FA/C) is 6:1, the solid mass concentration is 78%, the fly ash to gasification slag is 1:1, and the results show that σ3d = 2.20 MPa, slump = 205 mm, and flow = 199 mm. Taking the solid mass concentration, FA/C, the fly ash content in solid phase, and the coal gangue-to-gasification slag ratio as independent variables, the influence of single-factor and multi-factor interactions of the independent variables are analyzed based on the response surface model. It is found that the solid mass concentration and FA/C have a very significant effect on the early strength. Replacing coal gangue base with fly ash base can effectively reduce the crushing cost and energy consumption and provide low-cost and highly reliable technical reserves for large-scale filling.

Cellular automaton-based simulation of bulk stacking and recovery

Stockpiling is a key issue in bulk material handling. A small-scale, quasi-two-dimensional physical model was used to investigate size segregation during stacking and gravitational reclaim of stockpiles and to compare experimental results to those ones generated by a simplified mathematical model. This mathematical model is based on cellular automata and was used to simulate size segregation in conical stockpiles of non-cohesive granular material and gravity flow during its reclaim, through a ground level discharge opening. The present model has taken into account only three particle size class. Banded layers of fine, medium-sized, and coarse particles appear during the pile growth. These stratification patterns have been observed during stockpile formation both in the physical model and in the cellular automaton-based model. Also, experiments in both physical and cellular automaton-based model were carried out to quantify the particle size time evolution of granular material leaving the discharge opening during reclaim. Furthermore, the cellular automaton-based model has successfully simulated segregation phenomena during gravitational discharging, as well as the topological features of segregation during stockpiling and reclaim.

Impact of the stacking sequence on the bandgap and luminescence properties of bulk, bilayer, and monolayer hexagonal boron nitride

We examine the effects of stacking sequence and number of layers on the electronic and luminescence properties of hexagonal boron nitride (h-BN) structures with first-principles calculations based on density functional and many-body perturbation theory. We explored the variations of the magnitude and character (direct or indirect) of the quasiparticle bandgap and interband optical matrix elements for bulk, bilayer, and monolayer stacking polytypes. Although the fundamental gap for most structures is indirect, phonon-assisted transitions are strong (typically 600 times stronger than bulk Si) and enable efficient deep-ultraviolet (UV) luminescence. The polarization of the emitted light is transverse electric, which facilitates light extraction perpendicularly to the h-BN basal plane. Random stacking in turbostratic BN breaks the crystal symmetry and enables optical transitions across the quasi-direct bandgap, albeit with a weak matrix element. Our results demonstrate that h-BN is a promising material for efficient deep-UV light emitters.

Quasiparticle electronic structure of honeycomb C3N: from monolayer to bulk

Layer-dependent quasiparticle band structures of the newly emerged honeycomb C3N are systematically studied using both density functional theory and GW methods. The calculated GW band gap for monolayer C3N is about 1.5 eV. This moderate band gap may be ideal for future electronics applications. Our result is in marked contrast with a recent experimental report of 0.39 eV and calls for future experimental verifications. Interlayer chemical coupling effects on the electronic structure of C3N are investigated using several bilayer models. The electronic structure of bilayer C3N depends sensitively on the layer stacking pattern with the calculated quasiparticle band gap ranging from 0.87 to 1.35 eV. Finally, we illustrate the effects of interlayer chemical interaction and bulk dielectric screening on the electronic properties of C3N. Depending on the specific bulk stacking, C3N may be metallic or semiconducting with a narrow gap of about 0.6 eV, even though different bulk phases are essentially degenerate energetically. As a result, it may be challenging to prepare single-phase semiconducting bulk C3N unless synthetic kinetics can somehow prefer or prohibit certain stacking patterns. This issue deserves further investigations.

In-package inhibition of E. coli O157:H7 on bulk Romaine lettuce using cold plasma

Dielectric barrier discharge atmospheric cold plasma (DACP) treatment was evaluated for the inactivation of Escherichia coli O157:H7, surface morphology, color, carbon dioxide generation, and weight loss of bulk Romaine lettuce in a commercial plastic clamshell container. The lettuce samples were packed in a model bulk packaging configuration (three rows with either 1, 3, 5, or 7 layers) in the container and treated by DACP (42.6 kV, 10 min). DACP treatment reduced the number of E. coli O157:H7 in the leaf samples in the 1-, 3-, and 5-layer configurations by 0.4–0.8 log CFU/g lettuce, with no significant correlation to the sample location (P > 0.05). In the largest bulk stacking with 7 layers, a greater degree of reduction (1.1 log CFU/g lettuce) was observed at the top layer, but shaking the container increased the uniformity of the inhibition. DACP did not significantly change the surface morphology, color, respiration rate, or weight loss of the samples, nor did these properties differ significantly according to their location in the bulk stack. DACP treatment inhibited E. coli O157:H7 on bulk lettuce in clamshell containers in a uniform manner, without affecting the physical and biological properties and thus holds promise as a post-packaging process for fresh and fresh-cut fruits and vegetables.

Optical magnetoplasmons in rhombohedral graphite with a three-dimensional Dirac cone structure

Rhombohedral graphite has a three-dimensional Dirac cone structure, differing only perturbatively from the bulk stack of independent graphene layers, so that the three-dimensional integer quantum Hall effect can be well exhibited in this system. In this paper, optical magnetoplasmons are obtained by using the random phase approximation. Such collective excitations do not exist in monolayer graphene but are shown to originate from Landau level mixing due to interlayer Coulomb interaction in the quantum Hall effect regime. The three-dimensional character of rhombohedral graphite is thus demonstrated. The results should be realized in response to a longitudinal external electric field or an incident infrared electromagnetic wave.

Processing and characterisation of two-dimensional nanostructures

Low-dimensional nanostructured materials such as organic and inorganic nanotubes, nanowires and platelets are potentially useful in a number of areas of nanoscience and nanotechnology due to their remarkable mechanical, electrical and thermal properties. However difficulties associated with their lack of processability have seriously hampered both. In the last few years dispersion and exfoliation methods have been developed and demonstrated to apply universally to 1D and 2D nanostructures of very diverse nature, offering a practical means of processing the nanostructures for a wide range of innovative technologies. Among the first materials to have benefitted most from these advances are carbon nanotubes [6] and more recently graphene. Recently this work has been extended to boron nitride and a wide range of two-dimensional transition metal chalcogenides. These are potentially important because they occur in >40 different types with a wide range of electronic properties, varying from metallic to semiconducting. To make real applications truly feasible, however, it is crucial to fully characterize the nanostructures on the atomic scale and correlate this information with their physical and chemical properties. Advances in aberration-corrected optics in electron microscopy have revolutionised the way to characterise nano-materials, opening new frontiers for materials science. With the recent advances in nanostructure processability, electron microscopes are now revealing the structure of the individual components of nanomaterials, atom by atom. Here we will present an overview of very different low-dimensional materials issues, showing what aberration-corrected electron microscopy can do to answer materials scientists' questions. Particular emphasis will be given to the investigation of hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and tungsten disulfide (WS2) and the study of their structure, defects, stacking sequence, vacancies and low-atomic number individual adatoms. The analyses of the h-BN data showed that majority of nanosheets retain bulk stacking. However several of the images displayed stacking different from the bulk. Similar, to 2D h-BN, images of MoS2 and WS2 have shown the stacking previously unobserved in the bulk. This novel stacking consists of Mo/W stacked on the top each other in the consecutive layers.

Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.

Research on Automatic Stacking and Loading System in Major Logistics

This document introduces the current status of the stacking and loading technology in major logistics. It introduces the development of a kind of automatic stacking and loading system in major logistics from Chengdu University of Information Technology, including the function, composition, characteristics, key technology of structure design for Non bulk cargo object, automatic extract, automatic loading and stacking. Then the main technical parameters are put forward. It is pointed out that the system has a good social, economic significance.

Imaging and diffraction characterisation of 2D inorganic nanostructures

2D nanomaterials are a novel class of materials, noted for their potential in a range of high impact applications, such as sensing catalysis, and composite reinforcement. However, their structural features have not yet been fully characterised. In this work we have shown that 2D nanostructures of hBN, MoS2, and WS2, prepared by liquid exfoliation, can stack in sequences different from the bulk stacking. In 2D hBN non-sequential stacking was observed. 2D MoS2 and WS2 appear to have stacking where Mo/W atoms are located on the top of each other which differs from naturally occurring 2H and 3R polytypes. The majority of the hBN and MoS2 2D nanostructures retain the stacking of their bulk counterparts, while in 2D WS2 non-bulk stacking dominates. The conclusions are based primarily on the atomically resolved ADF STEM images with supporting evidence from electron diffraction.

First-Principles Study of Photoinduced Water-Splitting on Fe2O3

Photoinduced water-splitting on hematite (Fe(2)O(3)) is investigated by first-principles calculations. (HO)(3)-Fe-H(3)O(3)-R, (HO)(3)-Fe-O(3)-R, O(3)-Fe-O(3)-R, (HO)(3)-Fe-R and O(3)-R terminations are considered, where R represents the bulk stacking sequence. The stability under photoelectrochemical conditions and the free energy of all reaction intermediates in a simple one-electron transfer reaction mechanism is calculated and the ability of different surface terminations to function as a photoanode is analyzed. Our results show that (i) under relevant photoelectrochemical conditions only O(3)-Fe-O(3)-R and O(3)-R are stable and that (ii) the water-oxidation is only allowed on (HO)(3)-Fe-H(3)O(3)-R, (HO)(3)-Fe-O(3)-R, O(3)-Fe-O(3)-R from thermodynamic considerations. The results suggest that hematite, as long as the (HO)(3)-Fe-H(3)O(3)-R termination is present under normal conditions, is a promising candidate for the photoanode.

Charge Trapping and Detrapping Behavior of Fluorinated $\hbox{HfO}_{2}/\hbox{SiON}$ Gate Stacked nMOSFET

The charge trapping and detrapping characteristics of the fluorinated hafnium oxide/oxynitride (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiON) gate stack are investigated. Although incorporation of fluorine in the bulk stack had been proven to eliminate both bulk and interface trap densities due to Hf-F and Si-F bond formation, respectively, the effective trapping barrier of the device with fluorine incorporation (1.29 eV) is deeper than without fluorine incorporation (1.13 eV), indicating that the detrapping ability of the fluorinated devices may limit future fluorine process applications.

Electronic states of Ag thin films with a laterally periodic insertion of stacking faults

Electronic states of Ag thin films containing stacking faults periodically in a direction parallel to the surface are studied theoretically. Such Ag stacking-fault superlattice thin films were recently fabricated on the $\text{Si}(111)4\ifmmode\times\else\texttimes\fi{}1\text{-In}$ surface, and the formation mechanism of the one-dimensional electronic states observed in photoemission experiments has not been clarified. These systems are suitable for studying stacking faults on nanometer scales in well-defined conditions. Main results obtained in the present study are threefold. One is that the double stacking-fault model proposed in this paper reproduces better the observed dispersions than the originally proposed model. In addition the fact that the stacking-fault thin films have the (111) surface is the origin of the strong deformation near the bottom of the quantized subbands. Second is that the tilt of the stacking-fault plane with respect to the normal of the surface causes mixing of states in different subbands, which is an important factor to form the flat band structures observed. Third is the discussion on the mechanism of the anomalous perfect transmission through the bulk stacking faults of noble metals. In contrast to usual potential scattering, stacking faults change only the phase of orbitals. The condition for perfect transmission is that the effects of scattering are canceled out by renormalization using single phase factor, which is excellently satisfied in the case of noble metals. In addition the symmetry in atomic positions between regular and stacking-fault structures with respect to an axis is the origin of the directional dependence of transmission property.

Tailoring the SiC Subsurface Stacking by the Chemical Potential

The stacking orientation of bilayers determines the polytype of SiC material. For the development of polytype heterojunctions a controlled switch from one stacking sequence to another is required. In the present paper it is demonstrated for 4H-SiC and 6H-SiC, that the chemical environment during preparation of the ( √ 3×√3)R30◦ reconstruction on SiC(0001) influences the bilayer stacking in the topmost surface region. A silicon rich growth environment results in three bilayers in identical orientation at the very surface, which in the case of 4H-SiC corresponds to breaking the bulk stacking sequence. Oxygen rich preparation conditions lead to a reduction to two identically oriented bilayers for both polytypes. The reconstruction geometry of the ( √ 3×√3)R30◦ phase is independent of the polytype and the terminating stacking sequence of the underlying material. In consequence, the surface stacking and as such the starting point of a polytype heterojunction can be taylored by the chemical potential.

Direct determination of epitaxial film and interface structure: Gd 2O 3 on GaAs (1 0 0)

We present a new method of sub-Angstrom resolution imaging of the 3D structure of epitaxial films and their interface with the substrate. The method utilizes the diffraction intensities along the substrate-defined Bragg rods and some crude knowledge of the system structure to determine the complex scattering factors (CSFs) along the Bragg rods. The system electron density and the structure is obtained by Fourier transforming the CSFs into real space. We have applied this method to study the structure of a Gd 2O 3 film and its interface with the GaAs substrate. The results show that the Gd 2O 3 abandons the bulk stacking order and adopts that of GaAs. Moreover, the atoms in the first few layers move to in-plane positions that overlap those of the underlying Ga and As. This behavior may be at the heart of its ability to passivate GaAs.

Effect of oxygen precipitation on voids in bulk silicon

The effect of oxygen precipitation on flow pattern defects (FPDs) relative to voids in bulk silicon was investigated. FPDs and voids were measured after different annealing time, and with various interstitial oxygen contents and bulk stacking faults (BSFs). It was found that, during annealing, interstitial oxygen in bulk silicon precipitated, however the FPDs density remained constant. The density of BSFs increased with annealing time at 1100 °C. After annealing, the morphology of voids was found to be octahedral with the oxide films inside them, the same as as-grown samples. Therefore, it is concluded that the interstitial silicon atoms released during oxygen precipitation did not enter the voids because of the resistance of the oxide films inside the voids, but condensed into stacking faults. The dissolution of the oxide films is believed to be the principal cause for the annihilation of voids.

Direct determination of epitaxial interface structure in Gd2O3 passivation of GaAs.

Obtaining accurate structural information on epitaxial films and interfaces is nowhere more critical than in semiconductor passivation layers, where details of the atomic structure and bonding determine the nature of the interface electronic states. Various non-destructive methods have been used to investigate the structure of films and interfaces, but their interpretation is model-dependent, leading occasionally to wrong conclusions. We have developed a new X-ray method for the direct determination of epitaxial structures, coherent Bragg rod analysis (COBRA). The usefulness of our technique is demonstrated by mapping, with atomic precision, the structure of the interfacial region of a Gd2O3 film grown epitaxially on a (100) GaAs substrate. Our findings reveal interesting behaviour not previously suggested by existing structural methods, in particular a lock-in of the in-plane Gd atomic positions to those of the Ga/As atoms of the substrate. Moreover, we find that the bulk stacking of the Gd2O3 atomic layers is abandoned in favour of a new structure that is directly correlated with the stacking sequence of the substrate. These results have important implications for Gd2O3 as an effective passivation layer for GaAs (ref. 7). Our work shows that the COBRA technique, taking advantage of the brilliance of insertion device synchrotron X-ray sources, is widely applicable to epitaxial films and interfaces.