Layered materials that do not form a covalent bond in a vertical direction can be prepared in a few atoms to one atom thickness without dangling bonds. This distinctive characteristic of limiting thickness around the sub-nanometer level allowed scientists to explore various physical phenomena in the quantum realm. In addition to the contribution to fundamental science, various applications were proposed. Representatively, they were suggested as a promising material for future electronics. This is because (i) the dangling-bond-free nature inhibits surface scattering, thus carrier mobility can be maintained at sub-nanometer range; (ii) the ultrathin nature allows the short-channel effect to be overcome. In order to establish fundamental discoveries and utilize them in practical applications, appropriate preparation methods are required. On the other hand, adjusting properties to fit the desired application properly is another critical issue. Hence, in this review, we first describe the preparation method of layered materials. Proper growth techniques for target applications and the growth of emerging materials at the beginning stage will be extensively discussed. In addition, we suggest interlayer engineering via intercalation as a method for the development of artificial crystal. Since infinite combinations of the host–intercalant combination are possible, it is expected to expand the material system from the current compound system. Finally, inevitable factors that layered materials must face to be used as electronic applications will be introduced with possible solutions. Emerging electronic devices realized by layered materials are also discussed.

Van der Waals (vdW) heterostructures have drawn much interest over the last decade owing to their absence of dangling bonds and their intriguing low‐dimensional properties. The emergence of 2D materials has enabled the achievement of significant progress in both the discovery of physical phenomena and the realization of superior devices. In this work, the group IV metal chalcogenide 2D‐layered Ge4Se9 is introduced as a new selection of insulating vdW material. 2D‐layered Ge4Se9 is synthesized with a rectangular shape using the metalcorganic chemical vapor deposition system using a liquid germanium precursor at 240 °C. By stacking the Ge4Se9 and MoS2, vdW heterostructure devices are fabricated with a giant memory window of 129 V by sweeping back gate range of ±80 V. The gate‐independent decay time reveals that the large hysteresis is induced by the interfacial charge transfer, which originates from the low band offset. Moreover, repeatable conductance changes are observed over the 2250 pulses with low non‐linearity values of 0.26 and 0.95 for potentiation and depression curves, respectively. The energy consumption of the MoS2/Ge4Se9 device is about 15 fJ for operating energy and the learning accuracy of image classification reaches 88.3%, which further proves the great potential of artificial synapses.

The helmholtz resonator with the perforated neck has demerits that the absorption performance is not so outstanding in an anti-resonance frequency and high frequency bandwidth. In order to overcome these problems, in the paper, a resonator combined with porous material is proposed.

When aiming to reduce the low frequency noise of a subway guest room through sound absorbing treatment methods inside the wall of a tunnel the resonator is often more effective than a porous sound absorbing material. Therefore, the perforated panel type resonator embedded with a perforated panel is proposed. The perforated panel is installed in the neck, which is then extended into the resonator cavity so that it can ensure useful volume. The absorption performance of the perforated panel type of resonator is obtained by acoustic analysis and experiment. The analytical results are in good agreement with the experimental results. In the case of multiple perforated panel type resonators, as the number of perforated panels increase, the 1st resonance frequency is moved to a low frequency band and sound absorption bandwidth is extended on the whole. In order to obtain excellent absorption performance, the impedance matching between multi-panels should be considered. When the perforated panel in the resonator is combined with a porous material, the absorption performance is highly enhanced in the anti-resonance and high frequency range. In case of the resonator inserted with perforated panels of 2, the 2nd resonance frequency is shifted to a low frequency band in proportion to the distance between perforated panels.Key words Resonator(공명기), Absorption coefficient(흡음계수), Perforated panel(다공 패널), Impedance(임피던스) †Corresponding author, E-mail: ldh@seoultech.ac.kr

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