Ab initio morphology prediction of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates

Ishii Akio, Nakamura Nobutomo. Journal of Applied Physics. 135(9), 601 (2024) https://doi.org/10.1063/5.0187868.We energetically predict the morphology of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates, using density functional theory (DFT) simulations and the well-known Young–Dupre equation. In all cases, the contact angles exceed 90゜⁠, indicating that the nanoparticles are spherical. Notably, Au nanoparticles exhibit a higher contact angle than those of their counterparts. The validity of the proposed abinitio nanoparticle morphology prediction approach based on DFT simulations was assessed in comparison with our previous experimental findings pertaining to the time variation of the full width at half maximum (FWHM) of the resonant peak. Furthermore, the diffusivities of single Pd, Ag, Au, and Pt atoms on the substrate were evaluated by calculating the activation energy, offering insights into the underlying physics governing the timing of FWHM peaks. The analysis confirms a higher diffusivity of Au and Ag compared with Pd and Pt. According to the comparison between DFT and experiment results, although no clear relation is observed between the contact angles and timing of FWHM peaks, the diffusivity of sputtered atoms may influence the timing of FWHM peaks. Thus, timing can help to clarify the nanoparticle size, rather than shape

Mechanical oscillation accelerating nucleation and nuclei growth in hard-sphere colloidal glass

Nakamura N., Nakashima S., Ogi H.. Mechanical oscillation accelerating nucleation and nuclei growth in hard-sphere colloidal glass. Scientific Reports 9, 12836 (2019); https://doi.org/10.1038/s41598-019-49120-1.Crystallization from amorphous solids is generally caused by activating phonons in a wide frequency range during heat treatment. In contrast, the activation of phonons in a narrow frequency range using ultrasonic treatment also causes crystallization below the glass transition temperature. These behaviors indicate that crystallization is related to the atomic motion in the glass state, and it is suggested that the activation of specific atomic motion can cause crystallization without increasing temperature. In this study, we observe nucleation and nuclei growth caused by mechanical oscillation in a hard-sphere colloidal glass and evaluate the effect of mechanical oscillation on the structural evolution in the early stage of the crystallization. Oscillation between 5 and 100 Hz is applied to the colloidal glass, and it is observed that the nucleation rate increases under the 70 Hz oscillation, resulting in formation of stable nuclei in a short amount of time. The nuclei growth is also accelerated by the 70 Hz oscillation, whereas increases in the nucleation rate and nuclei growth were not observed at other frequencies. Finally, activation of the diffusion-based rattling of particles by caging is considered as a possible mechanism of the observations

Enhancement of hydrogen response by forming an Au submonolayer on nanogap Pd nanoparticles

Nakamura Nobutomo, Yoshikawa Kazushi, Ishii Akio. Applied Physics Letters 125, 021902 (2024) https://doi.org/10.1063/5.0204024.When Pd nanoparticles dispersed on a glass substrate with nanometer order gaps are exposed to H2 gas, H atoms are adsorbed on the nanoparticle surface, and the electrical resistance between the nanoparticles increases because of the tunneling current suppression. In contrast, when Au nanoparticles are exposed to H2 gas, the resistance remains unchanged because H atoms are not adsorbed on the Au surface. Considering these behaviors, the change ratio of the electrical resistance is expected to be smaller when the surface of Pd nanoparticles is partially covered with Au. However, the experimental results show the opposite resistance change. Density functional theory simulation indicates that H atoms are adsorbed and absorbed on the pure Pd surface, but H atoms are adsorbed and tend to remain on the partially covered Pd surface. These results indicate that the decrease in the resistance due to the gap narrowing by hydrogen absorption occurs in Pd nanoparticles, but it does not occur in Au/Pd nanoparticles, resulting in a larger resistivity increase compared with the Pd nanoparticles. This result implies that in certain cases, the low reactivity of Au to H2 contributes to the enhancement of the electrical resistance response

Enhancement of sensitivity of Pd-based hydrogen-gas sensor by plasma exposure studied by wireless quartz resonator

This is the Accepted Manuscript version of an article accepted for publication in Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1347-4065/ab78e2

COMPARISON AND IDENTIFICATION OF FACTORS INFLUENCING THE FLAVORS OF ENTERAL NUTRITION AGENTS

Objective:The flavor of an enteral nutrition formula affects medication adherence as well as patient's nutritional status and therapeutic efficiency on the major pathology. Therefore, it is important for medical professionals to understand the flavors of enteral nutrition formulas. This study aimed to evaluate the flavors of enteral nutrition formulas and examine the factors influencing these flavors. Methods:A total of 304 students in a pharmaceutical department were subjected to a semantic differential sensory evaluation in which they compared the flavors of digestion and semi-digestion enteral nutrition formulas using a five-point scale. In addition, factors related to good flavor were extracted via factor analyses, and subjected to a covariance structure analysis.Results:In the flavor comparison between digestion and semi-digestion nutrition formulas, semi-digestion nutrition agents scored significantly higher than digestion nutrition formulas did (Welch's t test, P < 0.001, 95% confidence interval [CI] = 0.69–0.99). The factor analyses extracted three subscales of factors related to good flavor: impression of taking, feeling of presence and sense of richness. In a path analysis model to determine the influence of these factor subscales on flavor, impression of taking feeling of presence were found to have significant influences (index of goodness of fit: χ2 = 474.883, df = 62, P < 0.001, GFI = 0.938, AGFI = 0.909, RMSEA = 0.079).Conclusion:Flavor affects medication adherence to enteral nutrition. Therefore, it is important for medical professionals to understand the factors that influence flavor and thus provide patients with better nutrition formulas