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Graphene aligned with hexagonal boron nitride (hBN) undergoes significant structural reconstruction due to the formation of a moiré superlattice. Here, we look at the effect of such structural reconstruction on the Raman spectroscopy of bilayer graphene for both singly aligned and doubly aligned heterostructures. The G peak is found to be particularly sensitive to the hBN alignment as it broadens in doubly aligned bilayer graphene compared to that of singly aligned bilayer graphene. This broadening is attributed to the variation in the phonon frequency as a result of the lattice reconstruction of the bilayer graphene responding to the periodic potential exerted by hBNs on either side of the bilayer graphene. In addition, the position of the G-peak and 2D peak follows a slope of 2.2, which implies the formation of strain in the bilayer graphene, validating the argument of lattice reconstruction. [ABSTRACT FROM AUTHOR]

As a two-dimensional material, graphene has outstanding properties, with high electron mobility and mechanical resistance. Therefore, it has good prospects to be used in nanoelectromechanical resonators for sensitive mass detection. Previously, a graphene resonator with graphene/metal contact able to zeptogram level sensing and a with quality factor of 42 at RT was presented. However, over-etching under the metal contacts degrades the quality factor, and resonators with metal/graphene/metal contacts were fabricated to overcome this issue. A quality factor of 350 at RT was obtained for a device with width = 0.8 μ m and length = 1 μ m. Tunning of the resonance frequency from 9.6 to 13.5 MHz with dc gate bias is demonstrated. Temperature reduction from 300 K to 30 K increased the resonance frequency by about 4–6 MHz. The temperature influence on nonlinearity is also discussed, with a resonator demonstrating softening and hardening nonlinearities at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Controlling the heat transport and thermal conductivity through a material is of prime importance for thermoelectric applications. Phononic crystals, which are a nanostructured array of specially designed pores, can suppress heat transportation owing to the phonon wave interference, resulting in bandgap formation in their band structure. To control heat phonon propagation in thermoelectric devices, phononic crystals with a bandgap in the THz regime are desirable. In this study, we carried out simulation on snowflake shaped phononic crystal and obtained several phononic bandgaps in the THz regime, with the highest being at ≈2 THz. The phononic bandgap position and the width of the bandgap were found to be tunable by varying the neck-length of the snowflake structure. A unique bandgap map computed by varying the neck-length continuously provides enormous amounts of information as to the size and position of the phononic bandgap for various pore dimensions. We have also carried out transmission spectrum analysis and found good agreement with the band structure calculations. The pressure map visualized at various frequencies validates the effectiveness of snowflake shaped nano-pores in suppressing the phonons partially or completely, depending on the transmission probabilities. [ABSTRACT FROM AUTHOR]

In this study, we investigate the scope of molybdenum disulfide (MoS 2 ) as an electric field sensor. We show that MoS 2 sensors can be used to identify the polarity as well as to detect the magnitude of the electric field. The response of the sensor is recorded as the change in the drain current when the electric field is applied. The sensitivity, defined as the percentage change in the drain current, reveals that it has a linear relation with the magnitude of the electric field. Furthermore, the sensitivity is highly dependent on the layer thickness, with the single-layer device being highly sensitive and the sensitivity decreasing with the thickness. We have also compared the electric field sensitivity of MoS 2 devices to that of previously studied graphene devices and found the former to be exceptionally sensitive than the latter for a given electric field magnitude., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)