Effects of helium irradiation dose and temperature on the damage evolution of Ti3SiC2 ceramic

The effects of 400 keV helium ion irradiation dose and temperature on the microstructure of the Ti3SiC2 ceramic were systematically investigated by grazing incidence x-ray diffraction, scanning electron microscopy, and transmission electron microscopy.The helium irradiation experiments were performed at both room temperature(RT) and 500℃ with a fluence up to 2.0 × 1017 He+/cm2 that resulted in a maximum damage of 9.6 displacements per atom.Our results demonstrate that He irradiations produce a large number of nanometer defects in Ti3SiC2 lattice and then cause the dissociation of Ti3SiC2 to TiC nano-grains with the increasing He fluence.Irradiation induced cell volume swelling of Ti3SiC2 at RT is slightly higher than that at 500℃, suggesting that Ti3SiC2 is more suitable for use in a high temperature environment.The temperature dependence of cell parameter evolution and the aggregation of He bubbles in Ti3SiC2 are different from those in Ti3AlC2.The formation of defects and He bubbles at the projected depth would induce the degradation of mechanical performance.

Surface defects,stress evolution,and laser damage enhancement mechanism of fused silica under oxygen-enriched condition

Oxygen ions(O;)were implanted into fused silica at a fixed fluence of 1×10^(17) ions/cm^(2) with different ion energies ranging from 10 ke V to 60 ke V.The surface roughness,optical properties,mechanical properties and laser damage performance of fused silica were investigated to understand the effect of oxygen ion implantation on laser damage resistance of fused silica.The ion implantation accompanied with sputtering effect can passivate the sub-/surface defects to reduce the surface roughness and improve the surface quality slightly.The implanted oxygen ions can combine with the structural defects(ODCs and E′centers)to reduce the defect densities and compensate the loss of oxygen in fused silica surface under laser irradiation.Furthermore,oxygen ion implantation can reduce the Si-O-Si bond angle and densify the surface structure,thus introducing compressive stress in the surface to strengthen the surface of fused silica.Therefore,the laser induced damage threshold of fused silica increases and the damage growth coefficient decreases when ion energy up to30 ke V.However,at higher ion energy,the sputtering effect is weakened and implantation becomes dominant,which leads to the surface roughness increase slightly.In addition,excessive energy aggravates the breaking of Si-O bonds.At the same time,the density of structural defects increases and the compressive stress decreases.These will degrade the laser laser-damage resistance of fused silica.The results indicate that oxygen ion implantation with appropriate ion energy is helpful to improve the damage resistance capability of fused silica components.

First-principles study of stability of point defects and their effects on electronic properties of GaAs/AlGaAs superlattice

When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_(0.5)Ga_(0.5)As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_(0.5)Ga_(0.5)As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states,we propose an effective strategy that AlAs, GaAs, and AlGaantisite defects are introduced to improve the hole or electron mobility of GaAs/Al_(0.5)Ga_(0.5)As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.

Non-parabolic effect for femtosecond laser-induced ultrafast electro-absorption in solids

A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented.Our numerical results show that,in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime,the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same.While,in the case of high intensity where the interaction is in the tunneling regime,spectrums from the parabolic band and real band are quite different.The physical mechanism for the difference in the tunneling regime is found.We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries,which are neglected in previous studies,strongly influence the electro-absorption spectrum in the tunneling regime.These two physical processes cause the difference of spectrums.Our theoretical results are in accordance with the experiment result.

Joule-Thomson expansion of the regular(Bardeen)-AdS black hole

We study the Joule-Thomson expansion of the regular black hole in an anti-de Sitter background,and obtain the inversion temperature for the Bardeen-AdS black hole in the extended phase space.We investigate the isenthalpic and inversion curves for the Bardeen-AdS black hole in the T-P plane and find that the intersection points between them are exactly the inversion points discriminating the heating from the cooling process.The inversion curve for the regular(Bardeen)-AdS black hole is not closed and there is only a lower inversion curve,in contrast to the Van der Waals fluid.Most importantly,we find that the ratio between the minimum inversion temperature and the critical temperature for the regular(Bardeen)-AdS black hole is 0.536622,which is larger than any known ratio for the singular black hole.The large ratio for the Bardeen-AdS black hole may be due to the repulsive de Sitter core near the origin of the regular black hole.

Deformed dispersion relation constraint with hydrogen atom 1S-2S transition

We use the latest results of the ultra-high accuracy 1S-2S transition experiments in the hydrogen atom to constrain the forms of the deformed dispersion relation in the non-relativistic limit.For the leading correction of the non-relativistic limit,the experiment sets a limit at an order of magnitude for the desired Planck-scale level,thereby providing another example of the Planck-scale sensitivity in the study of the dispersion relation in controlled laboratory experiments.For the next-to-leading term,the bound is two orders of magnitude away from the Planck scale,however it still amounts to the best limit,in contrast to the previously obtained bound in the non-relativistic limit from the cold-atom-recoil experiments.

Generalized uncertainty principle and black hole thermodynamics

Banerjee-Ghosh's work shows that the singularity problem can be naturally avoided by the fact that black hole evaporation stops when the remnant mass is greater than the critical mass when including the generalized uncertainty principle(GUP)effects with first-and second-order corrections.In this paper,we first follow their steps to reexamine Banerjee-Ghosh's work,but we find an interesting result:the remnant mass is always equal to the critical mass at the final stage of black hole evaporation with the inclusion of the GUP effects.Then,we use Hossenfelder's GUP,i.e.,another GUP model with higher-order corrections,to restudy the final evolution behavior of the black hole evaporation,and we confirm the intrinsic self-consistency between the black hole remnant and critical masses once more.In both cases,we also find that the thermodynamic quantities are not singular at the final stage of black hole evaporation.

Preliminary assessment of high-entropy alloys for tritium storage

Tritium is the key fuel in nuclear fusion reactors.With the development of the international thermonuclear experimental reactor(ITER)project,the annual requirement of tritium has increased up to several kilograms.The candidate materials for tritium storage have many shortcomings such as insufficient kinetic performance,disproportionation effect,poor oxidation resistance,and poor helium(He)retaining ability.Therefore,it is urgent to develop a novel material system which satisfies all the requirements of tritium storage materials.High-entropy alloys(HEAs)have a unique structure of severe lattice distortion and have attracted much attention as hydrogen storage materials due to their high storing capacity and great hydrogenation performance.The distorted lattice helps to provide more interstitial sites for accommodating H atoms and enhance the He retaining ability by slowing down the He diffusion in the HEA lattice.In this work,the current research status of tritium storage materials,including the background and the basic criterion of tritium storage materials,as well as the disadvantages of the current materials,has been reviewed.Moreover,the theoretical and experimental studies of HEAs,focusing on the hydrogenation properties and the defect evolution in the distorted lattice,have been summarized.The HEAs may have great potential as tritium storage materials due to their potential hydrogenation performance and He retaining ability.Finally,the existing challenges and future development directions are also proposed.