The thermal conductivities of two groups of silicon nanoribbons of ∼20 and ∼30 nm thickness and various widths have been measured and analyzed through combining the Callaway model and the Fuchs–Sondheimer (FS) reduction function. The results show that while the data for the ∼30 nm thick ribbons can be well-explained by the classical size effect, the measured thermal conductivities for the ∼20 nm thick ribbons deviate from the prediction remarkably, and size effects beyond phonon-boundary scattering must be considered. The measurements of the Young's modulus of the thin nanoribbons yield significantly lower values than the corresponding bulk value, which could lead to a reduced phonon group velocity and subsequently thermal conductivity. This study helps to build a regime map for thermal conductivity versus nanostructures’ surface-area-to-volume ratio that clearly delineates two regions where size effects beyond the Casimir limit are important or not important.

Bismuth selenide (Bi₂Se₃) nanoribbons have attracted tremendous research interest recently to study the properties of topologically protected surface states that enable new opportunities to enhance the thermoelectric performance. However, the thermoelectric characterization of individual Bi₂Se₃ nanoribbons is rare due to the technological challenges in the measurements. One challenge is to ensure good contacts between the nanoribbon and electrodes in order to determine the thermal and electrical properties accurately. In this work, we report the thermoelectric characterization of individual Bi₂Se₃ nanoribbons via a suspended microdevice method. Through careful measurements, we have demonstrated that contact thermal resistance is negligible after the electron-beam-induced deposition (EBID) of platinum/carbon (Pt/C) composites at the contacts between the nanoribbon and electrodes. It is shown that the thermal conductivity of the Bi₂Se₃ nanoribbons is less than 50% of the bulk value over the whole measurement temperature range, which can be attributed to enhanced phonon boundary scattering. Our results indicate that intrinsic Bi₂Se₃ nanoribbons prepared in this work are highly doped n-type semiconductors, and therefore the Fermi level should be in the conduction band and no topological transport behavior can be observed in the intrinsic system.

A challenge that remains to be solved in the high-throughput and low-cost nanopore DNA sequencing is that DNA translocates through the nanopore too quickly to be sequenced with enough accuracy.

Ion transport through nanopores is an important process in nature and has important engineering applications. To date, most studies of nanopore ion transport have been carried out with electrolytes of relatively low concentrations. In this paper, we report on ionic current modulation from the translocation of dsDNA through a nanopore under high ionic strength and with an electrolyte concentration gradient across the nanopore. Results show that in this case, DNA translocation can induce either negative or positive ionic current modulation, even though usually only downward peaks are expected under this high ion concentration. Through a series of experiments and numerical simulations with nanopores of different diameters and concentration gradients, it is found that the positive pulse is due to extra ions outside the electric double layer of the DNA that are brought into the nanopore by the enhanced electroosmotic flow (EOF) with the negatively charged DNA inside the nanopore.