The gap made the current sensitive
Binnig and Rohrer’s lecture traces local tunneling spectroscopy into scanning tunneling microscopy. A conducting tip brought very close to a conducting specimen permits tunneling at an applied bias. The strong distance dependence turns tiny changes of the junction into measurable current changes.
The development needed vibration isolation, stable approach, sharp tips and scanning control; Christoph Gerber and Edmund Weibel also contributed. A barrier-transmission equation alone does not supply a working microscope.
A barrier estimate explains sensitivity
For a simple constant vacuum barrier, low-bias current decays approximately exponentially with gap. The decay parameter depends on electron mass and an effective barrier energy. A one-electronvolt-scale change of barrier or a change of tip state can therefore alter the current without the surface moving.
The expression is only a distance-sensitivity limit. It neglects detailed tip and sample densities of states, voltage-dependent barrier shape and lateral structure. It must not be fitted to every pixel as if the barrier were known and uniform.
Sources: [1]
The silicon traces retained a reconstruction pattern
The lecture presents the silicon (111) seven-by-seven reconstruction as both a relief assembled from original recorder traces and a processed top view. Keeping those representations together shows the passage from measured scan lines to an interpreted surface image.
The pattern constrained competing surface models; it did not directly reveal all subsurface atomic coordinates. Bias dependence and the electronic character of tunneling mean that bright features need not coincide with a simple geometrical atom center.
Sources: [1]
Feedback adds a bandwidth limit
Constant-current scanning adjusts height to maintain a setpoint. If the scan outruns the feedback, slopes and edges can be distorted; multiple tip apexes can repeat structures. Constant-height scanning instead retains current variations and has a different risk of collision.
At different biases the accessible sample states and tip response change. A contrast reversal can therefore be electronic rather than a physical inversion of the surface. Quantitative interpretation needs junction conditions and a tunneling model.
Sources: [1]
Use the barrier model without calling it an STM
The existing tunneling Lab tests transmission through a prescribed barrier. It contains no complete raster, current feedback or local-density-of-states imaging. The historical article is complete as a reading path; the independently planned STM instrument remains a separate implementation task.
Sources: [1]