arXiv subjects

Ralph C. Merkle

Publications and source records attributed to Ralph C. Merkle.

4 recordsLinked to original sources

arXiv2026

Atomically precise mechanosynthesis of carbon structures on hydrogenated Si(100) by inverted-mode STM

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, C$_2$ units are donated from surface-deposited molecules to pre-patterned reactive sites on a hydrogen-passivated Si(100) surface. We demonstrate single-site C$_2$ donation, spatially patterned multi-site C$_2$ 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.

cond-mat.mtrl-sci↗

arXiv2025

Inverted-Mode Scanning Tunneling Microscopy for Atomically Precise Fabrication

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.

cond-mat.mes-hall↗

arXiv2025

Design of a molecular Field Effect Transistor (mFET)

Field Effect Transistors (FETs) are ubiquitous in electronics. As we scale FETs to ever smaller sizes, it becomes natural to ask how small a practical FET might be. We propose and analyze an atomically precise molecular FET (herein referred to as an "mFET") with 7,694 atoms made only of hydrogen and carbon atoms. It uses metallic (4,4) carbon nanotubes as the conductive leads, a linear segment of Lonsdaleite (hexagonal diamond) as the channel, Lonsdaleite as the insulating layer between the channel and the gate, and a (20,20) metallic carbon nanotube as the surrounding gate. The (4,4) nanotube leads are bonded to the channel using a mix of 5- and 6-membered rings, and to the gate using 5-, 6- and 7-membered rings. Issues of component design assessment and optimization using quantum chemical methods are discussed throughout. A 10 watt sugar-cube-sized computer made with $10^{18}$ such mFETs could deliver $\sim 10^{25}$ switching operations per second.

cs.ET↗

arXiv2019

Mechanical Computing Systems Using Only Links and Rotary Joints

A new model for mechanical computing is demonstrated that requires only two basic parts: links and rotary joints. These basic parts are combined into two main higher level structures: locks and balances, which suffice to create all necessary combinatorial and sequential logic required for a Turing-complete computational system. While working systems have yet to be implemented using this new approach, the mechanical simplicity of the systems described may lend themselves better to, e.g., microfabrication, than previous mechanical computing designs. Additionally, simulations indicate that if molecular-scale implementations could be realized, they would be far more energy-efficient than conventional electronic computers.

cs.ET↗