Narrow atomically precise graphene nanoribbons hold great promise for electronic and optoelectronic applications, but the previously demonstrated nanoribbon-based devices typically suffer from low currents and mobilities. In this study, we explored the idea of lateral extension of graphene nanoribbons for improving their electrical conductivity. We started with a conventional chevron graphene nanoribbon, and designed its laterally extended variant. We synthesized these new graphene nanoribbons in solution and found that the lateral extension results in decrease of their electronic bandgap and improvement in the electrical conductivity of nanoribbon-based thin films. These films were employed in gas sensors and an electronic nose system, which showed improved responsivities to low molecular weight alcohols compared to similar sensors based on benchmark graphitic materials, such as graphene and reduced graphene oxide, and a reliable analyte recognition. This study shows the methodology for designing new atomically precise graphene nanoribbons with improved properties, their bottom-up synthesis, characterization, processing and implementation in electronic devices.

There has been tremendous progress in designing and synthesizing graphene nanoribbons (GNRs). The ability to control the width, edge structure, and dopant level with atomic precision has created a large class of accessible electronic landscapes for use in logic applications. One of the major limitations preventing the realization of GNR devices is the difficulty of transferring GNRs onto nonmetallic substrates. In this work, we developed a new approach for clean deposition of solution-synthesized atomically precise chevron GNRs onto H:Si(100) under ultrahigh vacuum. A clean transfer allowed ultrahigh-vacuum scanning tunneling microscopy (STM) to provide high-resolution imaging and spectroscopy and reveal details of the electronic structure of chevron nanoribbons that have not been previously reported. We also demonstrate STM nanomanipulation of GNRs, characterization of multilayer GNR cross-junctions, and STM nanolithography for local depassivation of H:Si(100), which allowed us to probe GNR-Si interactions and revealed a semiconducting-to-metallic transition. The results of STM measurements were shown to be in good agreement with first-principles computational modeling.

Articles you may be interested inOptimal design and fabrication of three-dimensional calibration specimens for scanning probe microscopy Rev. Sci. Instrum. 83, 053708 (2012); 10.1063/1.4719661 TSP based Evolutionary optimization approach for the Vehicle Routing Problem AIP Conf.We describe the development and application of an imaging protocol, which evolves a scanning probe's atomic structure in parallel with automated optimization of the scan parameters. Our protocol coerces the system into a state that produces a specific atomic resolution image type without human involvement.

To better understand the specifics of nuclear magnetic resonance and spin relaxation in systems with magnetic nanoparticles and test the limits of the outer sphere model for the diffusion-related relaxation, iron oxide nanoparticle suspensions are studied in dependence on the particle concentration and size (5-40 nm). The model is modified to account for aggregation of the particles into clusters with an enlarged effective radius. For liquid suspensions containing small particles or clusters, both the longitudinal and transverse spin relaxation rates, T(1)(-1) and T(2)(-1), correspond well to the theory, which predicts passing of T(1)(-1) through a maximum and monotonic increase in T(2)(-1) with increasing particle size. For the largest particle sizes, as well as in the case of strong aggregation, the relaxation rates are significantly lower than theoretical predictions. An abrupt change in both the relaxation rates is observed in a narrow temperature range around the melting point of paraffin wax doped with magnetic nanoparticles. The applicability of fast-motion and fast-diffusion approximations is discussed for large effective sizes and limiting molecular motion cases.