Metallic clusters, ranging from 1 to 2 nm in size, have emerged as promising candidates for creating nanoelectronic devices at the single-cluster level. With the intermediate quantum properties between metals and semiconductors, these metallic clusters offer an alternative pathway to silicon-based electronics and organic molecules for miniaturized electronics with dimensions below 5 nm. Significant progress has been made in studies of single-cluster electronic devices. However, a clear guide for selecting, synthesizing, and fabricating functional single-cluster electronic devices is still required. This review article provides a comprehensive overview of single-cluster electronic devices, including the mechanisms of electron transport, the fabrication of devices, and the regulations of electron transport properties. Furthermore, we discuss the challenges and future directions for single-cluster electronic devices and their potential applications.

The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level, but also brings opportunities for the development of single-molecule optoelectronic devices. Understanding the interaction mechanisms between molecules and nanocavities is essential to obtain on-demand properties in devices by artificial design, since molecules in junctions exhibit unique behaviors of excited states benefited from the structures of metallic nanocavities. Here, we review the excitation mechanisms involved in the interplay between molecules and plasmonic nanocavities, and reveal the influence of nanostructures on excited-state properties by demonstrating the differences in excited state decay processes. Furthermore, vibronic transitions of molecules between nanoelectrodes are also discussed, offering a new single-molecule characterization method. Finally, we provide the potential applications and challenges in single-molecule optoelectronic devices and the possible directions in exploring the underlying mechanisms of photophysical and photochemical processes.

Recent years have witnessed the fabrication of various non-covalent interaction-based molecular electronic devices. In the non-covalent interaction-based molecular devices, the strength of the interfacial coupling between molecule and electrode is weakened compared to that of the covalent interaction-based molecular devices, which provides wide applications in fabricating versatile molecular devices. In this review, we start with the methods capable of fabricating graphene-based nanogaps, and the following routes to construct non-covalent interaction-based molecular junctions with graphene electrodes. Then we give an introduction to the reported non-covalent interaction-based molecular devices with graphene electrodes equipped with different electrical functions. Moreover, we summarize the recent progress in the design and fabrication of new-type molecular devices based on graphene and graphene-like two-dimensional (2D) materials. The review ends with a prospect on the challenges and opportunities of non-covalent interaction-based molecular electronics in the near future.