The inherent properties of 2D materials—light mass, high out-of-plane flexibility, and large surface area—promise great potential for precise and accurate nanomechanical mass sensing, but their application is often hampered by surface contamination. Here we demonstrate a tri-layer graphene nanomechanical resonant mass sensor with sub-attogram resolution at room temperature, fabricated by a bottom-up process. We found that Joule-heating is effective in cleaning the graphene membrane surface, which results in a large improvement in the stability of the resonance frequency. We characterized the sensor by depositing Cr metal using a stencil mask and found a mass-resolution that is sufficient to weigh very small particles, like large proteins and protein complexes, with potential applications in the fields of nanobiology and medicine.

The electrical properties of a single facet of an individual ZnO microwire were investigated. Electrode patterns with a Hall bar structure were deposited on the surface of the top facet of the ZnO microwire. Using a suspended and cross-linked poly(methyl methacrylate) ribbon structure, it was possible to define the electrical connections only at the top surface, while avoiding those on the other five sides of the ZnO microwire. Current-voltage characteristics were examined, and Hall measurements were conducted with various magnetic fields. Through our device structure, the electrical properties could be directly probed at specific points on the ZnO surface in a reliable manner. The estimated electrical characteristics demonstrate that the carrier concentration and mobility of the ZnO surface varied along the axial direction of the wire. These results indicate that the charge carrier concentration on the surface of the micro-/nanowire can be sensitively changed according to the synthesis environment. In addition, it is worth noting that the nanoscale local Hall probes, fabricated by our technique, could probe the very slight variation of carrier concentration, which is difficult to detect by a standard transport measurement along the wire.