Above: Tunneling-electron-induced molecular displacements of acetylene. All STM images are filled-state, and visualizations below show the position of the acetylene features on the Si lattice. (a,b) A switch from the OD (a) to ID (b) configuration induced by a +3.2 V pulse (average current >10 nA) over the center of the OD feature. (c,d) Long-range migration of OD-C2H2 induced by a +3.6 V pulse (4.6 nA). (e,f) Presumed desorption of OD-C2H2 induced by a +3.6 V pulse (2 nA). No new acetylene was observed within a radius of 6 nm. In each image, vertical lines indicate the center of the dimer rows and horizontal lines show the positions of three adjacent dimers. Imaging parameters: (a,b) –2.0 V, 100 pA (c,d) –2.0 V, 50 pA (e) –2.8 V, 50 pA (f) –2.9 V, 50 pA.
Now available: arxiv.org/abs/2607.19488
A simple question: how do you know what you know? In the cases of C2 on two chemically distinct surfaces – passivated (arxiv, local) and depassivated (arxiv, local) Si(100) – some confidence comes immediately from knowledge of the hardware, chemistry, and reaction design. But then the discovery that mechanosynthetic behavior is different (enough) on both surfaces is made, for which greater confidence then comes from statistics, analysis, and theoretical assessment. Even higher confidence in assignments and the underlying chemistry comes from employing complementary experimental methods to reach the same end, ideally with generation conditions and failure modes as orthogonal as possible to the ones being explored in the other work (links above).
The importance of the work in this study lies in that complementarity. Additionally, this study discusses in some detail just how well molecular proxies are as bases for STM simulations of small carbon structures on depassivated silicon, for which Mackie, Ou, and Yamachika deserve an awful lot of credit for getting that workflow standing upright.
Authors: Oliver MacLean, Marc Savoie, Damian G. Allis, Rafik Addou, Ryan Groome, Si Yue Guo, Aru Joy Hill, Alex Inayeh, Hadiya Ma, Cameron J. Mackie, Sheena Ou, Marco Taucer, Denis A. B. Therien, Finley Van Barr, Ryan Yamachika
CBN Nano Technologies, Inc. (CBNNT); Ottawa, K1Y 4W5, Canada
Hydrogen Desorption Lithography on Si(100) demonstrates the ability of the Scanning Tunneling Microscope (STM) to create functional atomic-scale structures and devices. The dehydrogenation of adsorbed molecules represents a potential complementary technique that has received little attention. For example, formation of C2 could introduce local strain or act as centers for subsequent reactions and would inform positionally controlled mechanosynthesis, an approach with vast potential in surface patterning and functionalization. Here, we studied the electron-induced dehydrogenation of acetylene and ethylene on Si(100) at 4 K using STM. Excitation of acetylene at ≥+3.2 V induces configurational switching, including to a new sublayer-bonded geometry previously predicted to be an adsorption precursor, as well as migration and desorption. Excitation also induces dehydrogenation to C2. Switching between three observed C2 configurations can be induced by excitation at ≥+4.2 V. Simulations using density functional theory reproduced the experimental images based on choice of functional, dimer-buckling averaging, and inclusion of diffuse basis functions. In addition, dehydrogenation could be induced using field-emitted electrons on a scale ranging from a single molecule to a radius of >10 nm. These observations highlight the potential of carbon dehydrogenation as an additional tool in Atomically Precise Fabrication (APF).