Analyzing the surface passivity effect of germanium oxynitride:a comprehensive approach through first principles simulation and interface state density

High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold.In this study,first-principles simulations,passivation film preparation,and metal oxide semiconductor(MOS)capacitor characterization were combined to study surface passivation.Theoretical calculations of the energy band structure of the -H,-OH,and -NH_(2) passivation groups on the surface of Ge were performed,and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state.Based on the theoretical calculation results,the surface passivation layers of the Ge_(2)ON_(2) film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure.The microstructure,C-V,and I-V electrical properties of the layers,and the passivation effect of the Al/Ge_(2)ON_(2)/Ge MOS were characterized to test the interface state density.The mean interface state density obtained by the Terman method was 8.4×10^(11) cm^(-2) eV^(-1).The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.

Evolution of helium bubbles in nickel-based alloy by post-implantation annealing

Nickel-based alloys have been considered as candidate structural materials used in generation IV nuclear reactors serving at high temperatures.In the present study,alloy 617 was irradiated with 180-keV helium ions to a fluence of 3.6×10^(17) ions/cm^(2) at room temperature.Throughout the cross-section transmission electron microscopy(TEM)image,numerous over-pressurized helium bubbles in spherical shape are observed with the actual concentration profile a little deeper than the SRIM predicted result.Post-implantation annealing was conducted at 700℃for 2 h to investigate the bubble evolution.The long-range migration of helium bubbles occurred during the annealing process,which makes the bubbles of the peak region transform into a faceted shape as well.Then the coarsening mechanism of helium bubbles at different depths is discussed and related to the migration and coalescence(MC)mechanism.With the diffusion of nickel atoms slowed down by the alloy elements,the migration and coalescence of bubbles are suppressed in alloy 617,leading to a better helium irradiation resistance.

Static and dynamic evolution of CO adsorption onγ-U(100)surface with different levels of Mo doping using DFT and AIMD calculations

Alloys of uranium and molybdenum are considered as the future of nuclear fuel and defense materials.However,surface corrosion is a fundamental problem in practical applications and storage.In this study,the static and dynamic evolution of carbon monoxide(CO)adsorption and dissociation onγ-U(100)surface with different Mo doping levels was investigated based on density functional theory and ab initio molecular dynamics.During the static calculation phase,parameters,such as adsorption energy,configuration,and Bader charge,were evaluated at all adsorption sites.Furthermore,the time-dependent behavior of CO molecule adsorption were investigated at the most favorable sites.The minimum energy paths for CO molecu-lar dissociation and atom migration were investigated using the transition state search method.The results demonstrated that the CO on the uranium surface mainly manifests as chemical adsorption before dissociation of the CO molecule.The CO molecule exhibited a tendency to rotate and tilt upright adsorption.However,it is difficult for CO adsorption on the surface in one of the configurations with CO molecule in vertical direction but oxygen(O)is closer to the surface.Bader charge illustrates that the charge transfers from slab atoms to the 2π*antibonding orbital of CO molecule and particularly occurs in carbon(C)atoms.The time is less than 100 fs for the adsorptions that forms embryos with tilt upright in dynamics evolution.The density of states elucidates that the overlapping hybridization of C and O 2p orbitals is mainly formed via the d orbitals of uranium and molybdenum(Mo)atoms in the dissociation and re-adsorption of CO molecule.In conclusion,Mo doping of the surface can decelerate the adsorption and dissociation of CO molecules.A Mo-doped surface,created through ion injection,enhanced the resistance to uranium-induced surface corrosion.

Experimental study on the oxidation behavior and microstructural evolution of NG-CT-10 and NG-CT-20 nuclear graphite

NG-CT-10 and NG-CT-20 are newly developed grades of nuclear-grade graphite from China.In this study,their oxidation behaviors were experimentally investigated using thermal gravimetric analysis.Microstructural evolution before and after oxidation was investigated using scanning electron microscope,mercury intrusion,and Raman spectroscopy.The apparent activation energy of NG-CT-10 nuclear graphite is 161.4 kJ/mol in a reaction temperature range of 550–700℃and that of NG-CT-20 is 153.5 kJ/mol in a temperature range of 550–650℃.The activation energy in the inner diffusion control regime is approximately half that in the kinetics control regime.At high temperatures,the binder phase is preferentially oxidized over the filler particles and small pores are generated in the binder.No new large or deep pores are generated on the graphite surfaces.Oxygen can diffuse along the boundaries of filler particles and through the binder phase,but cannot diffuse into the spaces between the nanocrystallites in the filler particles.Filler particles are oxidized starting at their outer surfaces,and the sizes of nanocrystallites do not decrease following oxidation.

OKMC simulation of vacancy-enhanced Cu solute segregation affected by temperature/irradiation in the Fe–Cu system

The effects of annealing and irradiation on the evolution of Cu clusters in a-Fe are investigated using object kinetic Monte Carlo simulations.In our model,vacancies act as carriers for chemical species via thermally activated diffusion jumps,thus playing an important role in solute diffusion.At the end of the Cu cluster evolution,the simulations of the average radius and number density of the clusters are consistent with the experimental data,which indicates that the proposed simulation model is applicable and effective.For the simulation of the annealing process,it is found that the evolution of the cluster size roughly follows the 1/2 time power law with the increase in radius during the growth phase and the 1/3 time power law during the coarsening phase.In addition,the main difference between neutron and ion irradiation is the growth and evolution process of the copper-vacancy clusters.The aggregation of vacancy clusters under ion irradiation suppresses the migration and coarsening of the clusters,which ultimately leads to a smaller average radius of the copper clusters.Our proposed simulation model can supplement experimental analyses and provide a detailed evolution mechanism of vacancy-enhanced precipitation,thereby providing a foundation for other elemental precipitation research.

Corrosion of New Zirconium Claddings in 500 ℃/10.3 MPa Steam: Effects of Alloying and Metallography

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions,six new zirconium alloys(named N1-N6)have been designed.The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water,and Fe,Cr,V,Cu or Mo elements were added to the alloys to adjust the corrosion behavioi\The current work focused on the rapid corrosion behavior in 500℃/10.3 MPa steam for up to 1960 h,aiming to test the corrosion resistance at high temperature.The structure of matrix and properties of second-phase particles(SPPs)were characterized to find the main differences among these alloys.All the six alloys exhibited better corrosion resistance than N36,and NI was shown to have the best performance.A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition.Elements Fe,Cr,V,Cu or Mo aggregated into SPPs with diiferent concentrations and structures.This was demonstrated to be the main reason for different corrosion resistance.Due to good processing control,all alloys had a uniform structure and a uniform distribution of SPPs.As for N4,N6 and N36,the existing of large-size SPPs(450 nm)might be a contributing factor of the relatively poor corrosion resistance.

Mechanical and magnetic properties of copper dispersed ferrum films under heat treatment

The Cu-containing steels are widely used for nuclear pressure vessel materials because of their good performance under high pressure and high temperature. In this article, magnetron sputtering was used to prepare iron films with various Cu contents. The samples were annealed at temperature range of 300–500 °C, and the structural,mechanical, and magnetic properties were studied. The results show that both hardness and modulus change along with copper content and annealing temperature. The change in coercivity after annealing is similar to that of hardness. The crystal grain growth in matrix ferrum and Cu precipitation during annealing influences both the mechanical and magnetic properties.