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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 burnup credit calculations for PBR spent fuel pebbles were performed using MCNP6. • The impact on the k eff as a function of water density in the storage cask was investigated. • Three single effects and four compound effects were studied. • The mechanisms of all the single and compound effects were researched in depth. This study attempts to investigate the influence due to the use of burnup credit in the criticality safety analysis for pebble-bed reactor (PBR) spent fuel pebbles. Recently, the development of PBR is very quick in China, thus the storage of spent fuel pebbles will become a significant issue in the foreseeable future. For the safe storage, the criticality safety analysis is of vital important. Furthermore, the utilization of burnup credit in the criticality safety analysis is essential due to the fact that it can result in a more compact design of storage system. In this study, all the calculations were performed using MCNP6 associated with the continuous energy neutron data library ENDF/B-VII. In addition, two geometrical models which represent the HTR-10 core and a proposed storage cask were adopted. The proposed storage cask model was established based on the real storage cask for HTR-10 spent fuel pebbles, but the capacity was increased in order to evaluate the impact of burnup credit. Moreover, the most conservative condition for this proposed cask occurs when the cask is full of water with a water density around 0.35 g/cm3. For burnup credit calculations, three operating parameters related to HTR-10 were investigated, including the usage of control rod, the fuel temperature, and the volume fraction of fuel pebbles in total pebbles. Additionally, these operating parameters were combined and classified as three single effects and four compound effects. The single and compound effects were defined as the influence on the effective multiplication factor (k eff) due to simultaneous variations of one and multiple operating parameters, respectively. It is worth noting that in most of the compound effects, the reactivity deviation (or the change of k eff , Δ k) resulting from the compound effect was not a summation of Δ k 's resulting from the associated single effects. This phenomena may affect the precise assessment to some extent. Finally, the mechanisms of both the single and compound effects were explored in depth from the analysis of the spectral distribution of fission. From this analysis, a harder spectral distribution of fission resulting from the single and compound effects corresponds a larger value of Δ k. [ABSTRACT FROM AUTHOR]

• Quasi-vertical Schottky barrier diodes were fabricated on GaN on Si substrate. • The diodes exhibited ultra-low turn on voltage of 0.23 V and ideality factor of 1.02 being close to the ideal value. • Schottky barrier height was extracted from both current–voltage and capacitance–voltage curves. • Experimental current–voltage characteristics are consistent with the simulation results obtained using Silvaco TCAD software. • Temperature dependent reverse leakage current is attributed to variable range hopping mechanisms through dislocations. Quasi-vertical Schottky Barrier Diodes (SBDs) with near to ideal turn-on voltage and ideality factor (n) of 1.02, were fabricated on a GaN on Si substrate. The average turn-on voltage and on-resistance values were found to be 0.23 ± 0.005 V (at 1 A/cm2) and 1.76 ± 0.11 mΩcm2, respectively with diode series resistance of 11 Ω. The analysis of the current–voltage curve revealed a temperature-independent barrier height, however the capacitance–voltage method showed a negative temperature coefficient. This discrepancy is discussed in the paper. Variable range hopping through dislocations is shown to be the dominant reverse current leakage mechanisms identified in the fabricated diode, with a characteristic temperature, T 0 of 2 × 1010 K. [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]

In this study, the displacement damage dose (DDD) effects of proton irradiation on bulk crystal and interfacial properties of 4H-SiC MOS capacitors (MOSCs) were investigated. The Monte Carlo calculation code named SRIM (Stopping and Range of Ions in Matter) was first used to predict the depth profiles and damage distributions of protons. The 4H-SiC MOSCs were irradiated with 60, 100, 150 keV protons to fluences ranging from 5 × 1011 to 5 × 1013 cm−2. Capacitance-voltage (C-V) curves of the MOSCs were then measured to characterize the variation of the electrically active defects in 4H-SiC MOSCs. The results revealed that the non-ionization energy loss of incident protons leads to the accumulation of the primary defects in bulk SiC crystal as well as the increase of the interface traps between SiO 2 and SiC crystal. A distinctive bump phenomenon was found in the weak inversion region of the C-V curve and it became more prominent with the increase of proton fluence, providing evidence for the existence of bulk traps. Furthermore, the incident proton energy is also a crucial factor in interface deterioration, suggesting that more interface traps would be formed when the proton damage peak is closer to the SiO 2 /SiC interface. • Displacement damage effects of proton irradiation on 4H-SiC MOSCs were investigated. • Non-ionization energy loss of protons leads to the buildup of bulk and interface traps. • A distinctive bump in weak inversion region of C V curve implies the existence of bulk traps. • Lowering proton incident energy accelerates the interface deterioration of SiC MOSCs. [ABSTRACT FROM AUTHOR]

This study employs nuclide sensitivity coefficients to investigate the spent fuel reactivity of pressurized water reactors (PWRs) in terms of differences in predicted inventories under various depletion conditions. Considering a representative PWR spent fuel, the study began by selecting the top 20 nuclides of large macroscopic neutron absorption cross sections, which are expected to have a substantial effect on reactivity. The sensitivity coefficients (Δ k ∞ /Δ N i ) of each nuclide were first evaluated at various burnups and cooling times using MCNPX. These coefficients were used to facilitate a detailed analysis of the spent fuel reactivity and to identify which nuclides cause the effect in a quantitative manner. The approach was demonstrated by analyzing the effects on spent fuel reactivity of several depletion parameters, including the initial enrichment, specific power, operating history, boron concentration, fuel temperature, moderator temperature, control rod effect, and axial burnup profile. The results were generally in good agreement with those obtained from direct MCNPX criticality calculations. Two major advantages of this approach are: (1) the changes in spent fuel reactivity with various depletion parameters can be closely related to composition changes; and (2) it provides a quantitative estimate of the contribution of each nuclide to the reactivity effect based on the predicted inventory differences. [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]

Highlights: [•] Comparisons of the HTR-10 criticality calculations with SCALE6/CSAS6 and MCNP5 were performed. [•] The DOUBLEHET unit-cell treatment provides the best k eff estimation among PBR criticality calculations using SCALE6. [•] The continuous-energy SCALE6 calculations present a non-negligible discrepancy with MCNP5 in three PBR cases. [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]