Who is Who — Nanotechnology

Scanning Probe Microscopy is the tradition of techniques that image and manipulate surfaces at atomic resolution by raster-scanning a sharp probe a few angstroms above the surface. Gerd Binnig and Heinrich Rohrer invented the scanning tunnelling microscope (STM) in 1981, which images conducting surfaces by quantum tunnelling. Binnig later developed the atomic force microscope (AFM), which can image insulators. Together, SPM techniques made atomic-scale imaging and manipulation routine, enabled the demonstration of single-atom positioning by Don Eigler, and became the primary characterisation tool of nanotechnology.

Can help you with: How STM and AFM work, the physics of quantum tunnelling at surfaces, atomic-resolution imaging of conducting and insulating surfaces, the distinction between imaging and manipulation modes, the development of SPM from 1981 to the present, and SPM as a tool for nanotechnology characterisation and fabrication.

Molecular Assembly Theory, originating in K. Eric Drexler’s Engines of Creation (1986) and Nanosystems (1992), proposes that molecular-scale machines (assemblers) could be built to position reactive molecules with atomic precision, enabling the synthesis of any structure consistent with physical law. The theory envisions a manufacturing technology of unlimited scope operating at room temperature with near-zero waste. It generated both the most optimistic claims about nanotechnology’s potential and the sharpest criticism (Smalley’s fat fingers and sticky fingers objections). The debate clarified what molecular nanotechnology can and cannot mean.

Can help you with: Drexler’s molecular assembler concept, the theoretical limits of bottom-up fabrication, the Smalley-Drexler debate and its resolution, Engines of Creation as a text, molecular machine design principles, the gap between current nanotechnology and Drexlerian nanotechnology, and the relationship between molecular biology and molecular machinery.

Single-Atom Engineering is the tradition that demonstrates precise positioning of individual atoms using an STM tip as a tool. Don Eigler’s team at IBM Almaden spelled “IBM” in thirty-five xenon atoms on a nickel surface in 1989 — the first deliberate manipulation of individual atoms for a specified purpose. Subsequent work produced quantum corrals (rings of atoms that trap electron waves) and demonstrated that single atoms could function as switches, logic gates, and memory elements. The tradition proves that atomic-scale fabrication is physically possible, whatever the engineering challenges of scaling it.

Can help you with: How individual atoms are positioned with an STM, the IBM xenon experiment, quantum corrals and electron confinement, atomic-scale switches and logic, the physics of surface diffusion that constrains manipulation, and the relationship between single-atom demonstrations and practical nanotechnology.

Mechanical Bond Chemistry is the tradition of designing molecules in which components are linked not by covalent bonds but by mechanical interlocking — rings threaded onto axles (rotaxanes) or rings linked through each other (catenanes). Jean-Pierre Sauvage synthesised the first catenane by a template-directed method in 1983. The mechanical bond creates molecules with fundamentally new properties: the components are constrained but mobile, and controlled motion between them is possible. Sauvage, Stoddart, and Feringa shared the Nobel Prize in Chemistry in 2016 for developing molecular machines based on these principles.

Can help you with: Catenanes and their synthesis, rotaxanes and how they work, the mechanical bond as a new chemical concept, template-directed synthesis, the relationship between topology and molecular properties, and the 2016 Nobel Prize and the three traditions it recognised.

Mechanically Interlocked Architecture, developed principally by Fraser Stoddart, takes the mechanical bond and designs it into functional devices. A molecular shuttle: a ring threaded onto a dumbbell-shaped axle, able to shuttle between two stations depending on external stimuli (chemical, electrochemical, optical). These are bistable switches at the molecular scale — the components of molecular logic. Stoddart’s group synthesised molecular rotors, molecular elevators, and molecular muscles. The extension to memory and computing applications at the molecular scale remains the long-term horizon.

Can help you with: Molecular shuttles and their design, bistable molecular switches, the extension from chemistry to molecular devices, how molecular machines might be integrated into functional systems, Stoddart’s contributions to the 2016 Nobel, and the gap between molecular machine demonstrations and practical molecular electronics.

Molecular Motor Chemistry is the tradition of designing molecules that convert energy into directed, controlled rotary motion at the nanoscale. Ben Feringa’s first light-driven molecular motor (1999) used a chiral double bond that isomerises under UV light, producing unidirectional rotation. Subsequent motors achieved millions of rotations per second. The challenge is doing useful work: a motor that spins freely does nothing. Feringa’s group has attached molecular motors to surfaces, used them to propel molecular “cars,” and driven the rotation of microscale objects. The Nobel recognised the demonstration of controllable molecular motion.

Can help you with: How light-driven molecular motors work, the design principles of unidirectional rotation, the difference between a motor and a switch, interfacing molecular motors with macroscopic systems, Feringa’s contributions and the 2016 Nobel, and the long-term vision of molecular machinery doing mechanical work.

Molecular Machine Design, developed in David Leigh’s group at Manchester and Edinburgh, extends the mechanical bond tradition toward functional devices that perform specified tasks. His group built a molecular machine that tied a knot in a single polymer chain, a molecular “robot” that could walk along a track and pick up, carry, and deposit molecular cargo, and a molecular pump that moves rings along an axle against a concentration gradient. Each demonstrates a principle of machine operation — directed motion, mechanical work, information processing — at the molecular scale.

Can help you with: Molecular machines and their operating principles, how to design directed motion at the nanoscale, the molecular knot synthesis, molecular robots and cargo transport, the transition from chemistry to engineering at the nanoscale, and what molecular machines need to do before they constitute a technology.

Soft Matter Fabrication is the tradition of nanofabrication that uses polymers, gels, and self-assembling molecules rather than hard silicon and clean-room photolithography. George Whitesides invented soft lithography — using patterned PDMS (polydimethylsiloxane) stamps to print micron-scale patterns rapidly and cheaply — which democratised the fabrication of microfluidic devices. His group also pioneered self-assembly as a fabrication principle, showed that biological molecules could be used to pattern surfaces, and developed laboratory-on-a-chip technologies for diagnostics. The approach is slower and lower resolution than conventional lithography but vastly cheaper and accessible outside clean rooms.

Can help you with: Soft lithography and microcontact printing, PDMS and its properties, microfluidics design and fabrication, self-assembly as a manufacturing principle, lab-on-a-chip technologies, the economics of fabrication (cheap vs. precise), and the relationship between materials choice and accessible nanotechnology.

DNA Origami, developed by Paul Rothemund in 2006, is the technique of folding a long single-stranded DNA scaffold into arbitrary two-dimensional shapes by hybridising it with hundreds of short “staple” strands whose sequences are designed to hold specific parts of the scaffold in contact. The result is a flat DNA nanostructure of any desired shape — smiley faces, maps of the Western hemisphere, molecular pegboards for positioning other molecules. The technique extended Seeman’s structural DNA nanotechnology from simple lattices to arbitrary shapes, and has been extended to three-dimensional structures, dynamic structures, and functional scaffolds for drug delivery.

Can help you with: How DNA origami works, scaffold and staple strand design, what shapes can be made, the extension from 2D to 3D structures, dynamic and switchable DNA origami, DNA origami as a platform for positioning molecules at specified locations, drug delivery applications, and the relationship between DNA origami and Seeman’s structural DNA nanotechnology.

Based on the published writings of K. Eric Drexler. His Engines of Creation (1986) introduced the idea of molecular-scale manufacturing to a wide audience, and his technical work Nanosystems (1992) provided the engineering analysis of nanoscale mechanical systems. He is the founder of molecular nanotechnology as a design discipline.

Can help you study: Molecular nanotechnology and its engineering principles, Nanosystems and the design of molecular machines, the Drexler-Smalley debate, and the history of bottom-up nanotechnology as a discipline.