Manipulating and Probing the Distribution of Excess Electrons in an Electrically Isolated Self-Assembled Molecular Structure

Atomically Precise Manufacturing of Silicon Electronics

Atomically precise manufacturing (APM) is a key technique that involves the direct control of atoms in order to manufacture products or components of products. It has been developed most successfully using scanning probe methods and has received particular attention for developing atom scale electronics with a focus on silicon-based systems. This review captures the development of silicon atom-based electronics and is divided into several sections that will cover characterization and atom manipulation of silicon surfaces with scanning tunneling microscopy and atomic force microscopy, development of silicon dangling bonds as atomic quantum dots, creation of atom scale devices, and the wiring and packaging of those circuits. The review will also cover the advance of silicon dangling bond logic design and the progress of silicon quantum atomic designer (SiQAD) simulators. Finally, an outlook of APM and silicon atom electronics will be provided.

Energy Dissipation from Confined States in Nanoporous Molecular Networks

Crystalline nanoporous molecular networks are assembled on the Ag(111) surface, where the pores confine electrons originating from the surface state of the metal. Depending on the pore sizes and their coupling, an antibonding level is shifted upward by 0.1-0.3 eV as measured by scanning tunneling microscopy. On molecular sites, a downshifted bonding state is observed, which is occupied under equilibrium conditions. Low-temperature force spectroscopy reveals energy dissipation peaks and jumps of frequency shifts at bias voltages, which are related to the confined states. The dissipation maps show delocalization on the supramolecular assembly and a weak distance dependence of the dissipation peaks. These observations indicate that two-dimensional arrays of coupled quantum dots are formed, which are quantitatively characterized by their quantum capacitances and resonant tunneling rates. Our work provides a method for studying the capacitive and dissipative response of quantum materials with nanomechanical oscillators.

Tunable Single-Atomic Charges on a Cleaved Intercalated Transition Metal Dichalcogenide

Control of a single ionic charge state by altering the number of bound electrons has been considered as an ultimate testbed for atomic charge-induced interactions and manipulations, and such subject has been studied in artificially deposited objects on thin insulating layers. We demonstrate that an entire layer of controllable atomic charges on a periodic lattice can be obtained by cleaving metallic Co_1/3NbS₂, an intercalated transition metal dichalcogenide. We identified a metastable charge state of Co with a different valence and manipulated atomic charges to form a linear chain of the metastable charge state. Density functional theory investigation reveals that the charge state is stable due to a modified crystal field at the surface despite the coupling between NbS₂ and Co via a_1g orbitals. The idea can be generalized to other combinations of intercalants and base matrices, suggesting that they can be a new platform to explore single-atom-operational 2D electronics/spintronics.

Real Space Visualization of Entangled Excitonic States in Charged Molecular Assemblies

Entanglement of excitons holds great promise for the future of quantum computing, which would use individual molecular dyes as building blocks of their circuitry. Studying entangled excitonic eigenstates emerging in coupled molecular assemblies in the near-field with submolecular resolution has the potential to bring insight into the photophysics of these fascinating quantum phenomena. In contrast to far-field spectroscopies, near-field spectroscopic mapping permits direct identification of the individual eigenmodes, type of exciton coupling, including excited states otherwise inaccessible in the far field (dark states). Here we combine tip-enhanced spectromicroscopy with atomic force microscopy to inspect delocalized single-exciton states of charged molecular assemblies engineered from individual perylenetetracarboxylic dianhydride (PTCDA) molecules. Hyperspectral mapping of the eigenstates and comparison with calculated many-body optical transitions reveals a second low-lying excited state of the anion monomers and its role in the exciton entanglement within the assemblies. We demonstrate control over the exciton coupling by switching the assembly charge states. Our results reveal the possibility of tailoring excitonic properties of organic dye aggregates for advanced functionalities and establish the methodology to address them individually at the nanoscale.

Ionic charge distributions in silicon atomic surface wires

Using a non-contact atomic force microscope (nc-AFM), we examine continuous dangling bond (DB) wire structures patterned on the hydrogen terminated silicon (100)-2 × 1 surface. By probing the DB structures at varying energies, we identify the formation of previously unobserved ionic charge distributions which are correlated to the net charge of DB wires and their predicted degrees of freedom in lattice distortions. Performing spectroscopic analysis, we identify higher energy configurations corresponding to alternative lattice distortions as well as tip-induced charging effects. By varying the length and orientation of these DB structures, we further highlight key features in the formation of these ionic surface phases.

Imaging Charge Localization in a Conjugated Oligophenylene

Polaron formation in conjugated polymers has a major impact on their optical and electronic properties. In polyphenylene, the molecular conformation is determined by a delicate interplay between electron delocalization and steric effects. Injection of excess charges is expected to increase the degree of conjugation, leading to structural distortions of the chain. Here we investigated at the single-molecule level the role of an excess charge in an individual oligophenylene deposited on sodium chloride films. By combining sub-molecular-resolved atomic force microscopy with redox-state-selective orbital imaging, we characterize both structural and electronical changes occurring upon hole injection. While the neutral molecule exhibits a delocalized frontier orbital, for the cationic radical the excess charge is observed to localize, inducing a partial planarization of the molecule. These results provide direct evidence for self-trapping of the excess charge in oligophenylenes, shedding light on the interplay of charge localization and structural distortion.