STM Atom Manipulation 2D: Assembling a Quantum Corral

Tip Controls

Drag inside the top-down view to move the STM tip laterally. Lower the tip into the manipulation gap to grab the nearest atom, then drag it onto an empty ring site.

Tip-sample gap d 6.0 Å

Sample bias V 100 mV

Thermal jitter T 0.0

Tunneling Junction

Current I

— pA

Regime

Imaging

Atoms placed in corral 0 / 10

How it works

A scanning tunneling microscope holds a metal tip a few ångströms above a conducting surface. Electrons tunnel quantum-mechanically across the vacuum gap, and the current depends exponentially on the gap distance:

I(V,d) ∝ V · exp(-2κd)
κ = √(2mΦ) / ħ  ≈ 1 Å⁻¹  for a typical work function Φ

d ≈ 6-8 Å  → normal, non-perturbing imaging
d ≲ 6 Å    → tip-adsorbate force exceeds the surface
             diffusion barrier: the atom hops with the tip

Pull mode — lowering the gap below ~6 Å lets the attractive van der Waals / chemical-bond force between tip and adatom drag the atom sideways as the tip moves, one lattice hop at a time.
Push mode — the tip instead shoves a nearby atom directly away from itself, useful for nudging a misplaced atom out of the way.
Raising the gap back above the manipulation threshold restores the weak-coupling imaging regime and drops the atom at its current lattice site — if that site is one of the ten empty ring markers, it locks into place.
Thermal jitter — raising the surface "temperature" adds a small random walk to every free adatom each frame, modelling ordinary thermal diffusion on the lattice between manipulations.

The lower panel plots the same I(V,d) law on a log scale across the full gap range, with a dot marking where the tip sits right now and a dashed line at the manipulation threshold — the exponential becomes a straight line on this scale, exactly as tunneling theory predicts.

This is the exact technique Don Eigler and Erhard Schweizer used at IBM Almaden in 1990 to arrange 35 xenon atoms on nickel into the letters "IBM" — the first time individual atoms were deliberately positioned one by one.

Free adatom Captured by tip Locked in corral site

I(V,d) — log scale, current gap marked