I’m working on a series of posts that will describe practical research objectives on paths toward advanced nanosystems. My main concern is progress in fabrication, and “Modular Molecular Composite Nanosystems” can be seen as first in the series.
This post, however, will be atypical. It’s about impractical research objectives that have received far too much attention. I want to get this topic out of the way at the beginning. Some widespread ideas about research objectives:
- are bad,
- seem absurd to most scientists,
- are inconsistent with my ideas and publications, and
- are nonetheless widely attributed to me.
I really dislike ideas like these, particularly when they’ve spawned a jumble of misconceptions that impede progress. Some ideas about diamond synthesis are in this category.
Why diamond synthesis is a bad objective
Contrary to popular opinion, diamond synthesis seems almost irrelevant to progress toward advanced nanosystems. At the current stage of research, it is both difficult and unnecessary. In a following post I’ll present some criteria and metrics for judging materials, praise cerium dioxide, and explain why humble fool’s gold is better than diamond.
At the outset, I should note that diamond is in many ways a true wonder-material: It simultaneously excels in hardness, strength, rigidity, thermal conductivity, electron mobility, and several other properties prized by engineers. This is why applications for diamond keep growing.
Diamond does, however, have a grave shortcoming: synthesis has been, and continues to be, difficult and expensive. Stubbornly so. The methods I’m familiar with require either high temperatures and ultrahigh pressures, or highly reactive gas-phase species interacting with a hot surface in a vacuum chamber. Neither process is suited to atomically precise control. Advanced mechanosynthetic methods (of the sort analyzed in Chapter 8 of Nanosystems) will eventually erase this problem, but the emphasis here is on the words “advanced” and “eventually”.
Diamond is a great material, but it’s hard to make, and there are other materials in the world that serve well in demanding tasks. In light of this, the intense focus on diamond nanotechnologies seems quite mysterious: How did the idea of molecular manufacturing — a general approach to organizing mechanosynthesis — become so closely identified with making diamond? And consider “mechanosynthesis” itself. The term means molecular synthesis directed by mechanical means, nothing more, and this is a concept broad enough to embrace the synthesis of proteins by ribosomes. How did such a basic and generic concept become equated with mechanosynthesis of diamond?
And most important: Considering the difficulties of diamond synthesis, why treat diamond mechanosynthesis as if it were a necessary first step toward molecular manufacturing? Building a tiny bit of diamond this way would of course be an impressive lab demo, but the plausible technologies for achieving this seem difficult to extend, and I doubt that they would be very useful in any general sense.
Indeed, a leading nanotechnology company, Zyvex, used computational modeling (density-functional based molecular dynamics) to study diamond mechanosynthesis and concluded that, although the physics would work, the present-day laboratory practicalities would not. They’ve chosen instead to pursue mechanosynthesis of silicon-surface structures, using a clever approach termed “patterned atomic-layer epitaxy”, a method in which the only mechanically directed operation is the removal of hydrogen atoms from a hydrogen-passivated surface.
About the confusion
Nanosystems discusses diamond and diamond-related materials at length, and the ideology of diamondism grew from my own words. It is, however, a mutant, alien growth. From my first paper forward (1981, 1986, 1992, 1994, 1999, 2005,…), I’ve advocated developing biomolecular nanosystems and building from there, and this is what’s been happening.
In Nanosystems, I discuss diamond synthesis not as an early step in development, but as a particularly difficult test-case for the application of advanced mechanosynthesis to high-performance materials. The confusion about this has been so annoying that I’ve posted the relevant paragraphs from Nanosystems here, just to set the record straight.
In short, there’s a huge difference between a practical, near-term objective and an attractive but distant aim point. It’s time to shift attention to aim points that are much closer. I’ll write soon about materials, criteria, metrics, and more appropriate materials. (Aqueous synthesis at room temperature, for example, is very nice.)
Title updated 10 Feb 09
- Modular Molecular Composite Nanosystems
Biomolecular engineering for atomically precise nanosystems
- Toward Advanced Nanotechnology: Nanomaterials (1)
Why I’ve never advocated starting with diamond
- Toward Advanced Nanotechnology: Nanomaterials (2)
Stiffness matters (and protein isn’t remotely like meat)
- Self-Assembly for Nanotechnology
The virtues of self-assembly and the benefits of external guidance
- From Self-Assembly to Mechanosynthesis
Mechanosynthesis begins with soft machines
- Toward Advanced Nanotechnology: Nanomaterials (3)
Mechanical engineering meets thermal fluctuations
- Toward Advanced Nanotechnology: Nanomaterials (4)
Nanostructures, Nanomaterials, and Lattice-Scaled Stiffness
- Toward Advanced Nanotechnology: Nanomaterials (5)
Nanomachines, Nanomaterials, and Klm