Chemical mechanical planarization (CMP) is an essential technique for processing semiconductor wafers that require ultra-smooth surfaces. The material removal mechanisms in this process, which are complicated because of the intertwined mechanical and chemical effects of abrasive grains and chemical solution, remain to be revealed. In this study, we conducted molecular dynamics simulation using ReaxFF focusing on the polishing of a silica substrate by a silica abrasive grain in an aqueous environment. To mimic different material removal modes, namely scratch and adhesion between the substrate and abrasive, we performed two methods of controlling the abrasive motion; i.e., displacement control and force control. Material removal was observed in both the two control methods. The formation of atomic bonds between the substrate and abrasive grain was not directly related to the amount of material removal. Our results also indicate that heat due to plastic deformation of the abrasive grain may affect material removal.

Since the recent discovery of superelastic behavior in ferroelectric BaTiO₃, understanding the mechanical and electromechanical properties of ferroelectric ceramics under high loading conditions has become crucial for engineering applications such as advanced functional nanodevices. Here, we shed light on paraelectric SrTiO₃ in contrast ot ferroelectric BaTiO₃, and investigate the mechanical strength, deformation behavior, and electromechanical response of the paraelectric ceramics SrTiO₃ under high stress conditions with ferroelectric phase transition. Under low-strain conditions, that is, in the paraelectric phase, SrTiO₃ shows mechanical properties that maintain the characteristic high stiffness of ceramics. On the other hand, after the strain-induced ferroelectric phase transition, we find that SrTiO₃ demonstrates superelastic-like nonlinear deformation behavior. Therefore, SrTiO₃ exhibits both high stiffness and deformability simultaneously due to the strain-induced ferroelectric phase transition. Additionally, we clarify the emergence of hysteresis loops in both mechanical deformation and electromechanical responses without accompanying structural phase transitions. We also reveal that giant piezoelectric coefficients manifest at discontinuous points of polarization curves. We conclude that these unique properties in SrTiO₃ originate from the displacement of oxygen atoms and the chemical bonding network due to the ferroelectric phase transition, based on analysis of the electronic structure and interatomic distances of each atom with respect to strain. Our results advance fundamental understanding of SrTiO₃ behavior under extreme loading conditions and establish a foundation for advanced engineering applications.

Machine-learning-based molecular dynamics (ML-MD) has emerged as a promising approach to resolving the trade-off between accuracy and computational cost in atomic simulations. The most conventional method in ML-MD, total energy learning (TEL), trains models by matching the sum of predicted atomic energies to the total energy of the system. However, because calculating total energy requires information from all atoms in the system, TEL poses limitations for flexible data refinement. To address this issue, we have developed atomic energy learning (AEL), which enables atomic-level data selection by directly using each atom’s energy as training data. As a fundamental study, we compare AEL and TEL using datasets based on the Embedded Atom Method (EAM). The results demonstrate the effectiveness of selective data sampling in controlling model accuracy and reveal the advantage of AEL in evaluating atomic energies near defects through targeted data selection.

Understanding how local structures govern relaxation dynamics of liquid metals is a central challenge in the physics of liquids. While the connection between viscosity and collective dynamics has been widely studied, the role of local stress states in controlling local relaxation remains poorly understood, particularly across different materials. Here, we employ molecular dynamics simulations to decompose the shear-stress autocorrelation function into atomic contributions for three model liquid metals: Zr₅₀Cu₅₀，Pd₈₂Si₁₈，Fe. We find that local shear relaxation times are strongly correlated with local pressure and von Mises stress for all systems studied. The results show that atomic sites under compression are more unstable against shear than those under tension, leading to faster relaxation of local shear stress. We also find that atomic sites with large von Mises stress relax the stress more rapidly. When expressed in terms of local volume or shear strain, the local relaxation times scaled by average relaxation time collapse onto temperature- and materialindependent linear relations, revealing a universal structure–dynamics relationship. A combined analysis of pressure and von Mises stress shows that atomic sites under high compression and large von Mises stress relax nearly twice as fast as those under tension with small von Mises stress, indicating pronounced spatial heterogeneities in local dynamics. These results establish local stress analysis as a powerful framework for linking local structure to local dynamics in liquids.

Phase transformation behaviors at interfaces between BCC and HCP in pure titanium were investigated using molecular dynamics simulations. This study focused on the influences of orientation relationships on the BCC-to-HCP phase transformation. For the Mao orientation relationship, planar migration of the BCC-HCP interface was observed, and the interface migration velocity decreased with increasing temperature. On the other hand, for the Burgers orientation relationship, which differs from the Mao orientation relationship by a rotation of 5.26° about the [110]_BCC axis, growth with protrusions was observed instead of planar migration of the interface. Additionally, the (̅1010)_HCP//(121̅)_BCC interface which bounded the protruding growth regions, did not sustain stable migration. These molecular dynamics simulations demonstrate that orientation relationships at the BCC-HCP interfaces strongly affect the phase transformation behavior.

The fundamental characteristics of defect structures and the effect of radiation defects on plastic deformation were investigated by atomistic and continuum models. Self-interstitial atom (SIA) loops, vacancy loops, and the effect of stacking fault tetrahedra were studied as typical irradiation defects. The fault energies of these defects were evaluated by atomistic models and dislocation theory with non-empirical measurement. The effects of size and densities of SIA and vacancy loop on the critical shear stresses were systematically estimated. A mesoscopic framework based on the crystal plasticity model was proposed, in which fundamental properties are applied to a database for mesoscopic computational models.

In this paper, creep-fatigue behavior of Hastelloy XR, candidate material for High Temperature Gas-cooled Reactor (HTGR), was clarified based on experimental data of uniaxial round bar specimen and perforated plate at 950℃. Applicability of creep-fatigue life evaluation methods for these data was also examined. In the strain-controlled uniaxial creep-fatigue tests with hold time up to 30 min, rapid relaxation due to creep was observed. The stress after relaxation during hold time was almost within 20% of the initial stress. In the creep-fatigue tests of perforated plate on the basis nominal-strain control, stress relaxation during hold time was slower than that in uniaxial tests, due to the effect of elastic-follow-up behavior. The life reduction of perforated plate was about 1/5, larger reduction when compared with that in the uniaxial tests. In the uniaxial tests, predicted lives on the basis of the linear damage rule of fatigue and creep were almost within a factor of 3 of experimental life, for both cases of time-fraction and ductility exhaustion rules for creep damage. In the perforated plate test, predicted lives, on the basis of the detailed inelastic analysis were also within a factor of 3 of experimental life. An applicability of a simplified creep-fatigue life evaluation method based on elastic analysis to the perforated plate was discussed.

Since the internal temperature of lithium-ion batteries rise to 80°C during charging or discharging, this study investigated the macroscopic creep properties at high temperature of negative electrodes in lithium-ion batteries and their estimation methods based on the microscopic structure of the electrodes. Tensile and creep tests at several temperature levels were conducted on a negative electrode consisting of carbon powder and polyvinylidene fluoride (PVDF) binder. The stress-strain curve, the time history of the tensile strain, and the creep rupture time were measured in these tests and estimated using the simple model proposed in this study. The proposed model approximates the alignment of carbon particles as body-centered cubic (bcc) or face-centered cubic (fcc). The test results showed that the stiffness and the strength of the negative electrode decreased with the increase of the test temperature. The PVDF binder gradually shrank in the creep test at high temperature. This affected the creep properties of the negative electrode. The time history of the tensile strain and the creep rupture time were located between the upper and lower limits of the proposed model taking the thermal shrinkage of the PVDF binder into account.

The objective of this research is to deposit β-Phase (Ga_1-xIn_x)₂O₃ alloyed films on c-plane sapphire substrates via chemical solution deposition and utilize them for visible-blind UV photodetectors. An aqueous hydrochloric acid solution, containing a mixture of gallium chloride and indium chloride, was employed as the precursor solution. By increasing the indium composition ratio up to x = 0.21, the optical band gap was reduced from 4.88 eV to 4.50 eV. Au/Ni comb-shaped electrodes were formed on β-Ga₂O₃ and β-(Ga_0.79In_0.21)₂O₃ films to fabricate metal-semiconductor-metal-structured photodetectors. The former only responded to UV-C irradiation, whereas the latter responded to both UV-C and UV-B irradiation. The responsivity (R), detectivity (D^*), and external quantum efficiency (EQE) of the UV-C radiation (λ = 255 nm) were compared. The latter photodetector exhibited significantly higher values of R = 2.4×10³ A/W, D^* = 2.7×10¹³ Jones, and EQE = 1.2×10⁶ %. Notably, the values of R and EQE are approximately seven orders of magnitude higher than those of the former. This result is attributed to the fact that the alloying of Ga₂O₃ and In₂O₃ reduces both electrical resistivity and bandgap energy. Our findings demonstrate that (Ga_1-xIn_x)₂O₃ alloyed films deposited by a non-vacuum process using an aqueous precursor solution are promising candidates for application in visible-blind UV photodetectors.