Scanning tunnelling microscopy resolves the electronic structure of surfaces atom by atom, and across 2026 it is simultaneously the default characterisation tool for quantum materials and an early-stage fabrication tool being pushed towards positionally controlled atom-by-atom synthesis.
Summary
Scanning tunnelling microscopy (STM) brings a sharp conductive tip within a fraction of a nanometre of a conductive surface and measures the current that tunnels across the gap. Because that current depends exponentially on the gap width, a feedback loop holding it constant while the tip raster-scans produces a map with atomic lateral resolution. Sweeping the bias instead of scanning gives scanning tunnelling spectroscopy (STS), which reads out the local density of electronic states at a chosen point, so the instrument returns both structure and local electronic structure from the same measurement. Variants extend this: spin-polarised STM uses a magnetic tip to read spin contrast and to couple magnetically to the sample, the field-emission regime accesses image potential states above the surface, and quasiparticle interference (QPI) mapping around defects converts real-space standing waves into momentum-space information.
The manufacturing claim is separate and much younger. Inverted-mode STM with functionalised molecular tools has been used to demonstrate positionally controlled donation of carbon atoms and abstraction of silicon atoms at a model build site on an atomically clean, cryogenic silicon surface. That is a chemistry demonstration at single-site scale, not a process.
The parameters that decide STM’s usefulness are: sample conductivity (insulating films need workarounds, which is why photoexcitation sensing on dielectric films has been moved to AFM instead); vacuum and cryogenic stability; the unknown and drifting state of the tip; serial single-tip throughput; and the human labour of labelling and interpreting the images, which is now being attacked with few-shot and unsupervised segmentation and with machine-learning regression of physical parameters directly from image data.
Evidence base
- 15 June 2026: inverted-mode STM with functionalised molecular tools demonstrated positionally controlled donation of carbon and abstraction of silicon atoms at a model build site on an atomically clean, cryogenic surface.
- 8 May 2026: low-temperature STM and STS visualised quantised collective modes of a Tomonaga-Luttinger liquid in mirror twin boundary segments of monolayer WSe2 as short as one nanometre.
- 30 June 2026: spin-polarised STM with an Fe-coated tip induced an energy shift of up to 10 meV in the spin-polarised surface state of Cr(001), switchable by external magnetic field.
- 4 June 2026: ARPES showed complete suppression of long-range charge density wave order in flat regions of a TiSe2-NbSe2 heterostructure while high-resolution STM resolved a curvature-driven revival.
- 19 June 2026: few-shot plus unsupervised segmentation of STM images removed the need for large manually annotated datasets and transferred across Si(001), Ge(001) and TiO2(110), including adsorbed AsH3.
- 17 June 2026: photoexcitation detection in single molecules on non-conductive dielectric films was implemented with laser-synchronised AFM rather than STM, achieving angstrom-scale sub-molecular contrast.
Open questions
- What are the per-operation yield and error rate of mechanosynthetic donation and abstraction, and does either scale beyond a single model build site?
- Can the coupled sample-and-instrument digital twin framework, demonstrated for amplitude-modulation scanning probe microscopy, be transferred to STM where tip state is unknown and drifts?
- Does the proposed QPI tomography of the density matrix and quantum geometric tensor with unpolarised tips survive experimental test, and on which materials?
- Is THz-STM able to resolve Floquet gaps and edge states experimentally, as the nonequilibrium Green’s function treatment predicts?
Assessment drafted 2026-08-31 from up to 18 KB sources using the technology-scorecard framework; scores are a draft read pending review.