Seeing the Invisible
How Scanning Tunneling Microscopes Reveal the Atomic World
The tool that transformed our vision from the microscopic to the atomic.
Visualizing the Atomic World
Imagine having a microscope so powerful that you could not only see individual atoms but also pick them up and move them to spell out the name of your company. This is not science fiction; it is the reality made possible by the scanning tunneling microscope (STM), an instrument that forever changed our relationship with the atomic world.
By feeling surfaces rather than looking at them, the STM exploits the quirky rules of quantum mechanics to create stunning images of the atomic landscape, enabling today's scientists to do the once-unthinkable, from mapping magnetic fields beneath surfaces to watching the heart of an atom switch in real time.
The Quantum Magic of Feeling Atoms
The scanning tunneling microscope, invented by Gerd Binnig and Heinrich Rohrer at IBM Zürich in 1981, is a revolutionary type of microscope that images surfaces at the atomic level. Its development earned them the Nobel Prize in Physics in 1986, just five years later.
Unlike optical microscopes or even electron microscopes, the STM does not use lenses or light waves. Instead, it works by scanning an extremely sharp, atomically fine metal tip incredibly close to the surface of a sample.
Fundamental Components of a Scanning Tunneling Microscope
| Component | Function | Key Details |
|---|---|---|
| Scanning Tip | Sources the tunneling current | Often made of tungsten or platinum-iridium; must be atomically sharp 3 |
| Piezoelectric Scanner | Precisely controls tip position | Moves the tip in x, y, and z directions with sub-atomic precision 3 9 |
| Vibration Isolation System | Protects measurement from external vibrations | Uses mechanical springs, magnetic levitation, or eddy currents 3 |
| Feedback Loop Electronics | Maintains tunneling current or tip height | Translates current changes into a digital image 3 9 |
A Deeper Look: The Experiment That Saw Beneath the Surface
For decades, a significant limitation of conventional STM was that it could only investigate the uppermost atomic layer of a material. However, a team of researchers from the University of Münster has recently shattered this barrier.
Methodology: A Resonant Revelation
In July 2025, Prof. Anika Schlenhoff and Dr. Maciej Bazarnik announced they had successfully modified the STM technique to image properties buried beneath the surface. Their experiment followed a meticulous procedure 1 :
Sample Preparation
The team created a layered system, growing an ultra-thin magnetic film of iron and covering it with a single, two-dimensional layer of graphene.
Resonant Tunneling
Instead of relying solely on electronic states on the sample's surface, the team used a variant called resonant scanning tunneling microscopy.
Magnetic Sensing
These image-potential states penetrate beneath the graphene layer and interact with magnetic iron atoms underneath.
Data Acquisition
By carefully measuring the tunneling current in this resonant mode, the researchers could extract information about the structural and magnetic properties of the buried iron layer.
Results and Analysis
The results, published in ACS Nano, were groundbreaking. The team demonstrated that their modified STM could achieve two key objectives 1 :
Mapping Buried Magnetism
They successfully detected the local magnetic properties of the iron film lying beneath the graphene cover.
Visualizing Stacking Sequences
The researchers found that image-potential states were sensitive to tiny local variations in how graphene atoms positioned relative to underlying iron atoms.
Comparison of STM Operational Modes
| Mode | How It Works | Advantages | Disadvantages |
|---|---|---|---|
| Constant-Current | Feedback loop adjusts tip height to maintain a set tunneling current. | Safer on rough surfaces; provides both topographic and electronic data. | Slower due to feedback loop adjustment at every point 3 . |
| Constant-Height | Tip travels at a fixed height; variations in tunneling current are mapped. | Much faster imaging speed. | High risk of tip crashing on rough or uneven surfaces 3 . |
| Resonant | Utilizes image-potential states to probe subsurface electronic and magnetic structure. | Can investigate buried interfaces and properties beneath the top layer. | More complex setup and interpretation; not for all material systems 1 . |
The Scientist's Toolkit: Essentials for Atomic Exploration
Working at the atomic frontier requires a carefully curated set of tools and materials. Below is a list of essential "reagent solutions" for STM research, gleaned from the methods used in the featured experiments and standard practices in the field.
| Item | Function in STM Research |
|---|---|
| Highly Oriented Pyrolytic Graphite (HOPG) | A commonly used substrate prized for its large, atomically flat surfaces 6 . |
| Gold on Mica | A substrate providing large, ultra-smooth, conductive terraces ideal for scanning 6 . |
| Tungsten or Platinum-Iridium Wire | The material used to fabricate the STM tip sharpened to achieve a single atom at the apex 3 . |
| Ultra-High Vacuum (UHV) Chamber | A pristine environment that prevents contamination from air molecules 3 6 . |
| Piezoelectric Scanner (e.g., PZT) | The heart of the STM's motion control for sub-atomic precision 3 9 . |
| Iron Film & Graphene | Key materials in subsurface experiments for investigating buried magnetic interfaces 1 . |
The Atomic Frontier: Recent Breakthroughs and Future Visions
The capabilities of STM continue to expand at a breathtaking pace, pushing the boundaries of what we can observe and control.
Watching a Single Atom's Heart Switch
In a stunning feat of measurement, researchers at Delft University of Technology announced they had observed the nuclear spin—the magnetic heart—of a single atom switching back and forth in real time.
Using an STM tip to read out the spin via the atom's electrons, they found the nuclear spin remained stable for several seconds, a veritable eternity in the quantum world. This "single-shot readout" of a nuclear spin opens exciting paths for quantum sensing and computing at the atomic scale 2 .
Identifying an Atom's Chemical Signature
In a landmark achievement, scientists combined the spatial resolution of STM with the analytical power of X-rays.
Using a technique called synchrotron X-ray scanning tunneling microscopy (SX-STM), they captured the unique X-ray fingerprint of a single atom for the first time. This allows researchers to not only see an atom but also identify its chemical element and state, a capability with profound potential for medicine, materials science, and environmental research 8 .
STM Evolution Timeline
1981
STM invented by Gerd Binnig and Heinrich Rohrer at IBM Zürich
1986
Nobel Prize in Physics awarded to Binnig and Rohrer for their invention
1990
First manipulation of individual atoms using STM
2024
First chemical identification of a single atom using SX-STM 8