HfS₂is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS₂has the potential for well-balanced mobility (1,800 cm²/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS₂flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS₂flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS₂transistor with the robust current saturation. The on/off ratio was more than 10⁴and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO₄:PEO electrolyte, the drain current of the HfS₂transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm²/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS₂. These results provides the basic information for the experimental researches of electron devices based on HfS₂.

We propose a tunable metasurface consisting of an array of graphene ribbons on a silver mirror with a SiO₂ gap layer to control reflected wavefront at terahertz frequencies. The graphene ribbons exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO₂ layer, phase shift through the system is largely accumulated, covering the 0-to-2π range for full control of the wavefront. Numerical simulations prove that wide-angle beam steering up to 53° with a high reflection efficiency of 60% is achieved at 5 THz within a switching time shorter than 0.6 ps.

The collisional equipartition rate between the parallel and perpendicular velocity components is calculated for a weakly correlated electron plasma that is immersed in a uniform magnetic field. Here, parallel and perpendicular refer to the direction of the magnetic field. The rate depends on the parameter κ̄=(b̄/r_c)/, where r_c=(T/m)^1/2/Ω_c is the cyclotron radius and b̄=2e²/T is twice the distance of closest approach. For a strongly magnetized plasma (i.e., κ̄≫1), the equipartition rate is exponentially small (ν∼exp[−5(3πκ̄)^2/5/6]). For a weakly magnetized plasma (i.e., κ̄≪1), the rate is the same as for an unmagnetized plasma except that r_c/b̄ replaces λ_D/b̄ in the Coulomb logarithm. (It is assumed here that r_c<λ_D; for r_c>λ_D, the plasma is effectively unmagnetized.) This paper contains a numerical treatment that spans the intermediate regime κ̄∼1, and connects onto asymptotic results in the two limits κ̄≪1 and κ̄≫1. Also, an improved asymptotic expression for the rate in the high‐field limit is derived. The present theoretical results are in good agreement with recent measurements of the equipartition rate over eight decades in κ̄ and four decades in the scaled rate ν/nv̄b̄², where n is the electron density and v̄=(2T/m)^1/2.

Dust particles in plasmas are often confined near the boundary between the plasma bulk and the sheath where the gravitation is balanced by electrostatic force. To keep dust particles from running away horizontally, an electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and, under appropriate conditions, we have finite two-dimensional lattices of dust particles. Modeling the interaction between dust particles as the isotropic Yukawa interaction, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by numerical simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems.

Sintering, structural correlations and mechanical behavior of nanophase silica glasses are investigated using large-scale, parallel molecular-dynamics simulations. During the sintering process, the pore sizes and distribution change without any discernible change in the pore morphology. The height and position of the first sharp diffraction peak in the neutron static structure factor shows significant differences in the nanophase glasses relative to the bulk silica glass. The effect of densification on mechanical properties is also examined.

Daytime radiative cooling potentially offers efficient passive cooling, but the performance is naturally limited by the environment, such as the ambient temperature and humidity. Here, we investigate the performance limit of daytime radiative cooling under warm and humid conditions in Okayama, Japan. A cooling device, consisting of alternating layers of SiO₂ and poly(methyl methacrylate) on an Al mirror, is fabricated and characterized to demonstrate a high reflectance for sunlight and a selective thermal radiation in the mid-infrared region. In the temperature measurement under the sunlight irradiation, the device shows 3.4 °C cooler than a bare Al mirror, but 2.8 °C warmer than the ambient of 35 °C. The corresponding numerical analyses reveal that the atmospheric window in λ = 16 ∼ 25 μm is closed due to a high humidity, thereby limiting the net emission power of the device. Our study on the humidity influence on the cooling performance provides a general guide line of how one can achieve practical passive cooling in a warm humid environment.