https://arxiv.org/abs/2605.27250
Abstract
The ability to build atomically precise structures on surfaces with complete control over both atomic placement and chemical bonding remains a central challenge in nanoscale fabrication. Here, we demonstrate simultaneous spatial and chemical control over the mechanosynthetic fabrication of carbon structures. Using inverted-mode STM, C2 units are donated from surface-deposited molecules to pre-patterned reactive sites on a hydrogen-passivated Si(100) surface. We demonstrate single-site C2 donation, spatially patterned multi-site C2 donation, and the stepwise assembly of polyyne structures through successive C-C bond formation. Together, these results establish controlled mechanosynthetic donation as a foundational capability for programmable atomically precise fabrication.
From the conclusion:
Together, these results establish atomic-scale control over composition, bonding, and spatial placement, opening avenues to the assembly of bespoke, three-dimensional carbon architectures on silicon and providing a foundation for integration of mechanosynthetic APF with molecular scale electronics and silicon-based quantum devices.
https://arxiv.org/abs/2606.13876v1
Abstract
Enabled by inverted-mode scanning tunneling microscopy (IM-STM) and the use of functionalized molecular tools, we demonstrate positionally-controlled mechanosynthetic addition (donation) of carbon and subtraction (abstraction) of silicon atoms on a model build site: atomically clean and crystalline Si(100). The resulting structures represent the first demonstrations of an emerging ability to manipulate radical chemistry with positional control of specific atoms and moieties in 3D. Furthermore, by comparing the behavior of molecular tools designed for atomic donation versus abstraction, we highlight general principles governing molecular tool design for selective and reliable mechanosynthetic functionality.
https://arxiv.org/abs/2512.24431
Abstract
Scanning Tunneling Microscopy (STM) enables fabrication of atomically precise structures with unique properties and growing technological potential. However, reproducible manipulation of covalently bonded atoms requires control over the atomic configuration of both sample and probe - a longstanding challenge in STM. Here, we introduce inverted-mode STM, an approach that enables mechanically controlled chemical reactions for atomically precise fabrication. Tailored molecules on a Si(100) surface image the probe apex, and the usual challenge of understanding the probe structure is effectively solved. The molecules can also react with the probe, with the two sides of the tunnel junction acting as reagents positioned with sub-angstrom precision. This allows abstraction or donation of atoms from or to the probe apex. We demonstrate this by using a novel alkynyl-terminated molecule to reproducibly abstract hydrogen atoms from the probe. The approach is expected to extend to other elements and moieties, opening a new avenue for scalable atomically precise fabrication.
https://arxiv.org/abs/2508.16798v1
Abstract
Scanning probe microscopy (SPM) investigations of on-surface chemistry on passivated silicon have only shown in-plane chemical reactions, and studies on bare silicon are limited in facilitating additional reactions post-molecular-attachment. Here, we enable subsequent reactions on Si(100) through selectively adsorbing 3D, silicon-specific "molecular tools". Following an activation step, the molecules present an out-of-plane radical that can function both to donate or accept molecular fragments, thereby enabling applications across multiple scales, e.g., macroscale customizable silicon-carbon coatings or nanoscale tip-mediated mechanosynthesis. Creation of many such molecular tools is enabled by broad molecular design criteria that facilitate reproducibility, surface specificity, and experimental verifiability. These criteria are demonstrated using a model molecular tool tetrakis(iodomethyl)germane (Ge(CH2I)4; TIMe-Ge), with experimental validation by SPM and X-ray photoelectron spectroscopy (XPS), and theoretical support by density functional theory (DFT) investigations. With this framework, a broad and diverse range of new molecular engineering capabilities are enabled on silicon.
https://chemrxiv.org/doi/full/10.26434/chemrxiv.15002728/v2
Abstract
(Hetero)adamantanes containing tetrel bridgeheads are important structures in surface and chemical sciences. Syntheses of diamondoid structures generally occur in a linear fashion, often using harsh conditions. These limitations make it difficult to access diverse (hetero)adamantane-based molecules with interchangeable functional groups for broad applications. The discovery of an expedient and convergent methodology for the synthesis of diamondoid scaffolds is described. The convenient synthetic route proceeding via a triple alkylation reaction represents a breakthrough in accessing the adamantane molecular class. Applications of this transformation to diamondoid tripods containing tetrel bridgeheads (C- and Ge-) were explored.