Tag: cbnnt

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Electron-Induced Formation of C2 on Si(100) from Acetylene and Ethylene

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).

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Towards Atom-by-Atom Fabrication: Mechanosynthetic Donation And Abstraction

Above: The molecular tool and general mechanosynthetic processes. (A) Overview of the probe and sample (above and below, respectively, not to scale) for IM-STM enabled mechanosynthesis. (B) Zoomed-in focus on the desired surface binding of the EAOGe–C2I molecular tool. (C) Chemical scheme for (B). (D) The deiodinated tool (EAOGe–C2
●). Approaching the tool to the probe surface and retracting may cause either mechanosynthetic (E) donation, yielding EAOGe● or (F) abstraction, yielding EAOGe–C2Si●.

Another part of the mechanosynthesis series from CBNNT, available at arxiv.org/abs/2606.13876 and focusing on efforts and molecular tool behavior on depassivated silicon surfaces. Still far too revolutionary to be called "more of the same."

And, for additional context, noting that long-time blogger and tracker of many things APM Brian Wang picked the paper up and processed notable items surrounding this and the previous paper in a short stack of posts on his nextbigfuture site:

Authors: Brandon Blue, Mathieu Morin, Alex Inayeh, Rosemary Cranston, Cameron J. Mackie, Marc Savoie, Adam Bottomley, Christian J. Imperiale, Zehra Ahmed, Rafik Addou, Aly Asani, Eduardo Barrera-Ramirez, Jeremy Barton, Doreen Cheng, Megan Cowie, Chris Deimert, Tyler Enright, James Zhangming Fan, Robert A. Freitas Jr., Alan T.K. Godfrey, Ryan Groome, Si Yue Guo, Kareem A. Clarcia, Aru Hill, Taleana Huff, Mark Jobes, Robert J. Kirby, Sam Lilak, Hadiya Ma, Adam C. Maahs, Oliver MacLean, Steven M. Maley, Michael Marshall, Terry McCallum, Ralph Merkle, Matthew Moses, Jonathan Myall, Ryan Plumadore, Adam Powell, Henry Rodriguez, Sam Rohe, Luis Sandoval, Khalil Sayed-Akhmad, Benjamin Scheffel, Kashif Tanveer, Bheeshmon Thanabalasingam, Denis A.B. Therien, Janice L. Wong, Reid Wotton, Cristina Yu, Damian G. Allis, Michael Drew, Matthew R. Kennedy, Tait Takatani, Marco Taucer, Dušan Vobornik, Ryan Yamachika, Mathieu Durand

CBN Nano Technologies, Inc. (CBNNT); Ottawa, K1Y 4W5, Canada

June 11, 2026

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.

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(Hetero)adamantane Synthesis: A Triple Alkylation Reaction

Above: Examples of subtractive and additive mechanosynthesis under IM-STM/UHV conditions. HAT between activated 19 (chemisorbed on a Si(100)-2×1 surface) and H:Si(100)-2×1 SPC apex (A) and possible reaction outcomes between activated 19 (chemisorbed on a Si(100)-2×1 surface) and Si(100)-2×1 SPC apex including additive (C2-transfer) and subtractive (Si-atom abstraction) mechanosynthesis (B). BDEs calculated using ωB97X-D/Def2-TZVPP of model compounds 1-ethynyl-1-germaadamantane (model of molecular tool) and ethynyl-tris(trimethylsilyl)silane (model of surface-bound acetylene). See the pre-print for more.

Available as a preprint: https://chemrxiv.org/doi/full/10.26434/chemrxiv.15002728/v2

I described it as "Prelude to Foundational" on an X post, as the entire process that resulted in "Atomically precise mechanosynthesis of carbon structures on hydrogenated Si(100) by inverted-mode STM" (APM-IM-STM) was long, involved, and exploratory — the ground-floor search for the most viable conditions for performing the reported work by our SPM experts, theoreticians, and synthetic chemists at CBN Nano Technologies (CBNNT). To that end, a considerable improvement in adamantane cage chemistry — including the generation of functionalized (hetero)adamantane cages containing carbon and germanium bridgehead atoms (with the option for more!) — was realized by the amazing CBNNT synthetic chemistry team in collaboration with Brilliant Matters.

My small contribution (to v2) provided additional context for the applications in our current hardware setup – the one that provided the data for both inverted-mode STM (IM-STM) and additive mechanosynthesis. Folks with a history tracking the technical studies in the MNT/AMM/APM community likely have seen papers exploring molecular tool designs for, specifically, carbon dimer transfers. This simple C₂ feedstock was the basis for proposing fabrication of diamond and related materials based on mechanosynthetic principles, from basic tool designs all the way through what became 1:40–2:40 of the famed Nanofactory Animation.

Whereas playing with the electronic structure of strained π-bonds to promote dimer transfer was key to the predicted behavior of DC10c (I now host a local copy of the PDF, since the journal version is no longer retrievable), most of the molecular transfer tool papers employed germanium bridgehead atoms for this task. The Ge–C bond is a fair bit weaker than the C–C bond, making dimer transfer highly favorable in configurations where the in-process build is ready to accept those dimers into an extended carbon lattice through basic radical coupling. While tin and lead would appear to be reasonable candidates based on their placement in the periodic table (C–Si–Ge–Sn–Pb), they were computationally demanding (and certainly were back in the early 2000s to get right), were prone to much more interesting chemistry owing to their large, polarizable electron shells (which risks the chemistry becoming more involved, including possible intramolecular reactions on delivery), and were certainly not the favorite elements to do organic chemistry with whenever the conversation came up with our chemists or with potential collaborators (which, as a chemical grandchild of John Verkade, I get). For many of the details on the use of germanium, see the bibliography and available papers at molecularassembler.com/Nanofactory/AnnBibDMS.htm. And, from this paper:

"Herein lies the significance of the functionalized germanium bridgehead as a first synthetic target for exploring additive mechanosynthesis through molecular transfer: bridgehead germaadamantanes provide a position for covalent bonding of species that can be activated for chemical transformations with far greater chemical tractability and stability than a comparable tin or lead analogue."

Fast-forward nearly 20 years, and the Ge bridgehead has survived a number of assessments of candidate tools to remain the delivery atom of choice, from Rob and Ralph's A Minimal Toolset for Positional Diamond Mechanosynthesis all the way to synthesis and first demonstrations. From all that work, this paper reports the significant improvements in yield and significant reduction in reaction steps for a convergent, triple-alkylation route to (hetero)adamantanes with interchangeable bridgeheads under mild conditions, turning two decades of Ge-bridgehead tool design into quantities sufficient for our mechanosynthetic exploration.

Things did get interesting on the long path to the first demonstrations. As is apparent from the APM-IM-STM paper, we are clearly jogging before running (from a purely diamondoid perspective, anyway) by working with a more tractable material in the form of Si(100) instead of diamond or any other carbon surface.

And here is the issue awaiting sufficient address. Bond-dissociation enthalpies for Ge–C and Si–C become uncomfortably close across an ethynyl (our C₂ dimer) fragment. As a result, every factor affecting bond strength at either position — dopant identity and placement on either side of the junction, current, defects, angle, and the residual theoretical uncertainty in the bonds themselves — becomes a variable driving the scission outcome. That, in turn, hints that additional levels of control are needed if the bridgehead, feedstock, and workpiece are to behave as they do in ongoing work and the desired outcomes (perhaps more philosophical than chemical — demonstrating a capability more than a specific product) are to be achieved.

Upcoming work (already discussed in presentations at conferences; I won't disclose details here prior to preprints being available, but am pleased to report such disclosures are imminent) explores just how uncomfortably close the bonds relevant to mechanosynthesis are in the current material/molecular-tool combination. Lessons learned from that process to follow.

Authors: Terry McCallum, Sam Rohe, Mathieu Morin, Hsin Yao Su, Samuel W. J. Shields, Kashif Tanveer, Marius Mamone, Nicolas Zindy, Damian G. Allis, Aru Joy Hill, and Michael Drew

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.