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Abstract: The multilayer HfSe2 on sapphire is first fabricated by the ion beam‐assisted process combining ion implantation with the post annealing. The A1g mode of HfSe2 is shown in the Raman spectrum, the X‐ray photoelectron spectroscopy results indicate the existence of Hf–Se bonding, and the transmission electron microscopy analysis exactly identifies the crystal structure of HfSe2. The six‐layered (6L) octahedral HfSe2 (1T‐HfSe2), whose band structure is well realized by utilizing photoluminescence spectroscopy compared with the results of the density functional theory calculation, is formed via the Hf selenization during annealing. [ABSTRACT FROM AUTHOR]

Following the rapid and extensive development of graphene, other elemental two-dimensional (2D) materials have been regularly announced and it has been predicted that they possess significant potential for a variety of (opto)electronic devices. So far, the research reports on these 2D materials focus primarily on the growth or synthesis, but there are a few of reports concerning their use in device fabrication. In addition, most of the developed growth or synthesis methods still need to be improved for real applications. This review will include a comprehensive discussion and comparison of these methods, as well as the potential applications of these 2D materials. [ABSTRACT FROM AUTHOR]

Multilayer antimonene nanoribbons with room temperature orange light emission uniformly distributed on InSb were synthesized by the plasma-assisted process. The bandgap opening was caused by the quantum confinement effect of the nanoribbon structure and the turbostratic stacking of antimonene layers. This attractive two-dimensional material, whose band structure is proper for applications of transistors and light-emitting diodes, was first synthesized. [ABSTRACT FROM AUTHOR]

Germanene layers with lonsdaleite structure has been synthesized from a SiGe thin film for the first time using a N2 plasma-assisted process in this investigation. Multi-layered germanene can be directly observed, and the derived lattice parameters are nearly consistent with the theoretical results. Furthermore, large-scale multi-layered germanene has also been demonstrated for applications. [ABSTRACT FROM AUTHOR]

In this study, BSi cluster ions of 77 keV and B monomer ions of 22 keV were respectively implanted into silicon wafers at room temperature and geometrically tilted. Rapid thermal annealing of the as-implanted specimens at 1050 °C for 25 s was also employed. The results revealed that all the as-implanted and as-annealed range parameters (Rp, ΔRp, γ, β and ΔRt) of the BSi cluster ion implantation are smaller than those of the B monomer ion implantation. The as-annealed range parameters are larger than the as-implanted ones for both the BSi cluster ion and the B monomer ion implantations mainly due to radiation enhanced diffusion (RED) effects. RED effects also tend to drive boron atoms out-diffusion towards the specimen surface. However, the SiO2 layer at the surface acts as a diffusion barrier by which it traps boron atoms nearby. The existence of larger amounts of defects explains the presence of a more pronounced accumulation of out-diffused boron atoms in the as-annealed boron depth profile of the BSi cluster ion implantation compared to that of the B monomer ion implantation. [Copyright &y& Elsevier]

The UK nuclear innovation programme supported by the government includes preparation for future ABWR construction. The UK has significant expertise in building and operating gas-cooled nuclear reactors and some experience with PWRs, while there is limited knowledge in BWR technologies. Hence, an important aim of this work is to understand the discrepancies between codes to assess uncertainties in BWR lattice and depletion calculations, while identifying specific development demands to progress existing tools into extended applications. The objective of the study is to quantify the discrepancy between SCALE-6.2, CASMO5 and the UK WIMS-10A deterministic lattice code for BWR lattice and burnup modelling. Two models of BWR systems were considered for this new systematic comparison. They are a single BWR pin-cell with UO2 fuel only, and a 3 by 3 array of BWR UO2 fuel rods with gadolinia rod in the centre. Criticality over burnup was estimated for both models using these codes. Spectral indexes, number densities and neutron spectrum were compared for several burnup stages using SCALE-6.2 and WIMS-10A. The study showed that kinf obtained with CASMO5 was in a good agreement with the SCALE-6.2. A clear discrepancy in behaviour was observed between WIMS-10A and SCALE-6.2 as well as CASMO5. [ABSTRACT FROM AUTHOR]

Abstract As compared to the conventional smart-cut technology based on single H ion implantation, sequential implantation of H and He ions has been demonstrated to be effective in reducing the implantation fluence and the thermal budget needed for Si layer splitting process. However, the sequential implantation method involves complicated process parameters such as ion energy and implantation sequence. The purpose of this study is to clarify the dependence of He ion energy on Si blistering characteristics by sequential implantation of H and He ions into Si in various sequences. The accelerated energy of H ions was fixed at 40 keV, while that of He ions was changed to 30, 50, and 70 keV. Both the implantation fluences of H and He ions were 1 × 1016 cm−2. The non-isothermal and isothermal annealing methods in combination with an in-situ optical microscopy (OM) detection system were adopted to determine the threshold temperatures and the onset times for blister and crater formation as well as to examine the thermal evolution of blisters and craters. The results revealed that the threshold temperatures for blister and crater formation are highly correlative to the He ion energy and implantation sequence. Higher He ion energy is preferable to blistering for the specimens first implanted with He ions, but the opposite is true for the reverse implantation sequence. This statement can be also supported by the activation energy levels required for blister and crater formation obtained from kinetics analysis. In addition, the variation of hydrogenated complexes induced by sequential implantation and annealing can be evidently identified from the Raman spectra, showing a noticeable transformation of H-related defect complexes from VH 3 to Si(100):H bonding configuration due to the emergence of blisters and craters. Highlights • H/He sequential implantation is proved to be effective for smart-cut technology. • Two-step ion implantation process varied in sequence and He ion energy was done. • Blistering characteristics were assessed using quantitative and kinetics analysis. • Blistering effectiveness depends on implantation sequence and He ion energy. [ABSTRACT FROM AUTHOR]

This study aims to propose a model for dynamically simulating the online-refueling process in pebble-bed reactor (PBR) using MCNPX. PBR has a special feature of online-refueling which can greatly reduce the outage time and enable a higher burnup in spent fuel. However, this feature also results in the dynamical fuel movements which may significantly increase the difficulty and the computational time in computer simulation. Therefore, an appropriate model is necessary to be proposed to simulate the burnup characteristics of online-refueling and to reduce the computational time simultaneously. All the calculations in this study were performed using MCNPX 2.7.0 with the ENDF/B-VII continuous energy nuclear data library. The PBR model was built according to the core design of HTR-10 but adopted some reasonable assumptions. The refueling process was emulated by utilizing the fuel loading scenario of the once through then out (OTTO) in combination with the layer-mixed-shell fuel movement. Additionally, the layer-mixed-shell fuel movement considered the concept of fuel channels, where the fuel pebbles only move in the same fuel channel, such that the burnup characteristics of fuel pebbles in both radial and axial direction can be identified separately. The core was divided into 9 fuel zones with a fixed volume and 3 fuel channels with a variety of fuel zones. Furthermore, the number of fuel zones in each fuel channel was determined based on the relative residence time of fuel pebbles in the core. The results revealed that the core can achieve an equilibrium fuel cycle after refueling several times, and after that all the core characteristics can nearly maintain unchanged between different cycles. Although the refueling process was modeled based on the OTTO fuel loading scenario instead of the multi-pass one, the discharged burnup can still reach the target burnup of the spent fuel for HTR-10, i.e. 72 GWd/tHM. In addition, the average discharged burnup under the equilibrium fuel cycle is approximate to 80 GWd/tHM, which also coincides the design value of the spent fuel for HTR-10. Therefore, the layer-mixed-shell movement model can consider the fuel movements in either radial or axial directions simultaneously and enable a more accurate prediction to the real refueling process of HTR-10 than our previous studies. • A proposed model for the dynamical simulation of PBR. • Both the axial and burnup characteristics were performed. • The core can achieve an equilibrium fuel cycle. • The average discharged burnup can reach the design value of HTR-10. [ABSTRACT FROM AUTHOR]

Abstract: Crystallization and thermal stability of Ge2Sb2Te5 (GST), the benchmark working material in phase-change non-volatile memory, were modified via Si-ion implantation. Through 5×1015 Si-ions/cm2 ion-implantation, crystallization temperature increases from 165°C to 177°C. Furthermore, the activation energy of crystallization increases from 2.9eV in the pristine film to 3.3eV and 4.0eV in films implanted with the doses of 5×1015 and 5×1016 Si-ions/cm2, respectively. Temperatures corresponding to a 10-year failure-time increase from 83°C in the pristine film to 96°C and 107°C in films implanted with 5×1015 and 5×1016 Si-ions/cm2, respectively. Thermal stability of Si-ion implanted GST thus improves significantly. It was also found that grain growth is inhibited with higher implantation doses. In the case of the 5×1016 ion/cm2 dose, the second-phase transition from face-centered cubic to hexagonal closed-packed structure of the GST is completely inhibited. However, crystallization time increases slightly due to Si-ion implantation. [Copyright &y& Elsevier]

This study aims to investigate the neutronic characteristics of spallation targets for Accelerator-Driven subcritical System (ADS) and find the optimal target design for reducing the strength of the required beam current. All the calculations were conducted using the MCNP6.1 with cross-section library ENDF/B-VII. In this study, the influence of several parameters on spallation targets is investigated, such as neutron production with various spallation target layouts, spallation neutron distribution with different proton beam energy levels, and spallation neutron spectrum. • Neutron production analysis with different spallation target geometries. • Spatial and energy neutron flux distribution for spallation target. • Fixed-source problem simulation with high proton beam fixed-source. [ABSTRACT FROM AUTHOR]

• A modified simulation model in MCNP 6.1 was developed for the dynamic HTR-10 core. • Applying the composition library can simplify processes with accurate results. • Due to longer residual time, the discharge burnup in the outer channel is higher. • Core power distribution using multi-pass refueling is more uniform compared to OTTO. This study aims to precisely investigate the core characteristics of HTR-10 using an online-refueling fuel loading scenario through an innovative approach that incorporates a pre-generated fuel composition library. HTR-10 is an experimental high-temperaturegas- cooled pebble-bed reactor constructed in China. Applying multi-pass fuel loading scenario, the pebbles in HTR-10 pass through the core several times via onlinerefueling. In this study, we proposed a model that simulates the dynamic operation of HTR-10 by using continuously static calculations. The model was constructed by dividing the core into 3 flow channels with different amounts of horizontal zones according to the residence time of fuel pebbles. However, random distribution of the pebbles with various burnup values complicates the refueling process. In order to simulate online-refueling more conveniently, a comprehensive method based on multipass fuel loading scenarios was thus developed. Firstly, a pre-generated fuel composition library containing the content of both actinides and fission products of fuel pebbles as a function of burnup, was built by implementing full core depletion calculations. During the refueling processes, a specific ratio of discharged fuel pebbles to fresh fuel pebbles was reloaded into the top zones. Thus, the average burnup values in the top zones can be resulted by considering the supplement of fresh fuel pebbles. Eventually, the fuel composition in the top zones were obtained by interpolating the average burnup value from the pre-generated library. In this study, all the calculations were performed using the MCNP6 computer code together with the ENDF/B-VII continuous energy neutron data library. The results revealed that the core reached a state of equilibrium after seven refueling processes with an increased rate of volume fraction. Our findings correspond to those of other studies. Another model constructed by locating the actual distribution of fresh pebbles also confirms the verification of the refueling method. Eventually, the burnup characteristics as well as the power and flux distributions in the HTR-10 core were analyzed using the simulation method. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional material with honeycomb arrays of carbon atoms, has shown outstanding physical properties that make it a promising candidate material for a variety of electronic applications. To date, several issues related to the material synthesis and device fabrication need to be overcome. Despite the fact that large-area graphene films synthesised by chemical vapour deposition (CVD) can be grown with relatively few defects, the required transfer process creates wrinkles and polymer residues that greatly reduce its performance in device applications. Graphene synthesised on silicon carbide (SiC) has shown outstanding mobility and has been successfully used to develop ultra-high frequency transistors; however, this fabrication method is limited due to the use of costly ultra-high vacuum (UHV) equipment that can reach temperatures over 1500 °C. Here, we show a simple and novel approach to synthesise graphene on SiC substrates that greatly reduces the temperature and vacuum requirements and allows the use of equipment commonly used in the semiconductor processing industry. In this work, we used plasma treatment followed by annealing in order to obtain large-scale graphene films from bulk SiC. After exposure to N2 plasma, the annealing process promotes the reaction of nitrogen ions with Si and the simultaneous condensation of C on the surface of SiC. Eventually, a uniform, large-scale, n-type graphene film with remarkable transport behaviour on the SiC wafer is achieved. Furthermore, graphene field effect transistors (FETs) with high carrier mobilities on SiC were also demonstrated in this study.