How Scientists Study Friction at the Atomic Scale
Explore the NanoworldAt the nanoscale (typically 1 to 100 nanometers, where a nanometer is a billionth of a meter), the ordinary rules of physics we experience daily begin to change. The familiar squeak of a door hinge or the wear on car tires manifests completely differently when viewed at the atomic level. Here, quantum effects dominate, and materials exhibit properties dramatically different from their bulk counterparts. Nanotribology—a term first introduced in a 1991 paper by Krim, Solina, and Chiarello on atomic-scale friction—has emerged as the field dedicated to understanding friction, wear, and lubrication at these minute scales 1 .
The development of microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS)—the tiny devices that power our smartphones, fitness trackers, and medical diagnostics—has made understanding nanoscale interactions essential 1 .
The components in these systems are incredibly light and operate under very light loads, making them highly susceptible to surface forces that would be negligible at larger scales 1 . As we continue to shrink technological devices, the behavior of materials at the nanoscale becomes increasingly important.
At the macroscopic level, friction often correlates with weight and surface roughness. But at the nanoscale, this relationship changes dramatically. Atomic-scale friction is governed by different principles, including quantum effects, atomic bonding, and surface energies 5 .
This explains why materials like graphite and graphene exhibit such low friction at the nanoscale. Their atomic structure allows layers to slide with minimal resistance, a property known as superlubricity that scientists are attempting to harness for future technologies 1 .
Just as with friction, wear processes operate differently at small scales. Instead of the visible material loss we see in mechanical parts, nanoscale wear involves the gradual removal of atomic layers or molecular clusters.
To combat this, researchers have developed molecularly thin films that serve as lubricants. Certain carbon-based materials like diamond-like carbon (DLC) have shown exceptional tribological behavior, enabling the creation of surfaces with extremely low friction and wear rates 1 .
At the nanoscale, adhesive forces—the stickiness between surfaces—often overwhelm other forces like gravity. This is because the surface-to-volume ratio increases dramatically as objects shrink, making surface forces increasingly dominant 8 .
When two surfaces come into close contact at the nanoscale, they may spontaneously adhere through various intermolecular forces. This presents significant challenges for NEMS devices, where components may permanently stick together, a phenomenon known as stiction 5 .
How do researchers investigate phenomena they can't directly see? Nanotribology relies on sophisticated instruments and techniques that can probe atomic-scale interactions:
| Technique | What It Measures | Key Applications in Nanotribology |
|---|---|---|
| Atomic Force Microscopy (AFM) | Surface topography and interaction forces | Mapping surface features, measuring friction forces at nanoscale, manipulating nanoparticles 1 5 |
| Friction Force Microscopy (FFM) | Lateral forces during scanning | Quantifying friction at atomic scale, studying friction anisotropy on different crystal surfaces 4 |
| Transmission Electron Microscopy (TEM) | Internal structure and crystal defects | Imaging atomic arrangements, analyzing wear mechanisms at nanometer scale 3 7 |
| UV-Visible Spectroscopy | Light absorption and scattering | Determining nanoparticle size, concentration, and agglomeration state 3 |
| Molecular Dynamics (MD) Simulations | Atomic motion and interactions | Theoretical modeling of friction processes, predicting material behavior under stress 5 |
These tools have revealed that carbon-based materials like diamond, graphene, and carbon nanotubes take a prominent role in nanotribology due to their exceptional tribological properties, including low friction and high wear resistance 1 . Their unique carbon bonding structures allow them to form interfaces that minimize adhesion and wear at the nanoscale.
A compelling example of how nanotribology explores biologically relevant systems comes from a 2025 study that investigated the adhesion and movement of viruses on surfaces 9 . This research provides insights into how viruses spread and infect hosts, with significant implications for public health and antiviral strategies.
Researchers selected two model viruses—brome mosaic virus (BMV) and murine polyoma virus (MPyV)—along with synthetic gold nanoparticles (AuNPs) for comparison. The viruses were prepared through biological methods, while the gold nanoparticles were synthesized chemically to achieve near-perfect spheres 9 .
The particles were deposited on two different atomically flat surfaces: polar mica and nonpolar highly-oriented pyrolytic graphite (HOPG). This allowed scientists to study how surface chemistry affects adhesion and movement 9 .
Using the AFM tip, researchers carefully pushed individual virus particles and nanoparticles across the surfaces while measuring the resistance forces. This was done in liquid to mimic physiological conditions 9 .
The team measured both the static adhesion (force required to initiate movement) and dynamic friction (resistance during movement) by monitoring the torsion of the AFM cantilever as it pushed the particles 9 .
The experiments revealed fascinating differences between biological particles and synthetic nanoparticles:
| Particle Type | Primary Motion | Force Required for Movement | Lateral Force Work | Particle Behavior |
|---|---|---|---|---|
| Virus Capsids | Predominantly rolling | 4 times less than AuNPs | ~10⁴ kT | Mechanically compliant, deforms to increase contact area |
| Gold Nanoparticles | Combined rolling and sliding | 4 times more than viruses | ~10 times more than viruses | Rigid, maintains shape under stress |
The most significant finding was that viruses tend to roll rather than slide on surfaces, requiring substantially less energy to move compared to rigid gold nanoparticles of similar size. This rolling motion resembles how soccer balls roll across a field rather than slide. The researchers attributed this difference to the mechanical compliance of viruses—their proteinaceous shells can deform to increase contact area with surfaces, yet they move more easily once set in motion 9 .
These findings challenge the traditional view that adhesion is governed primarily by geometrical factors like size and contact area. Instead, they highlight the importance of mechanical properties and deformability in understanding how biological nanoparticles interact with surfaces. This knowledge could inform the development of antiviral surfaces that prevent virus adhesion and spread, as well as improve our understanding of how viruses infect cells by moving along cell membranes.
Nanotribology has evolved from a niche interest to a vibrant interdisciplinary field. A comprehensive analysis of research output between 1996 and 2010 reveals fascinating patterns in how this science has developed 4 :
| Aspect | Findings | Implications |
|---|---|---|
| Publication Growth | Increased from 34 papers in 1996 to 161 in 2010 | Rapidly expanding field with growing scientific interest |
| International Collaboration | 30% of papers involved international cooperation | Highly interdisciplinary nature requiring diverse expertise |
| Most Productive Country | United States led in publications and citation impact | Significant research investment and output in the US |
| Key Research Topics | Molecular dynamics, MEMS/NEMS, hard disk technology, diamond-like carbon | Focus on both theoretical and application-driven research |
The data reveals that internationally collaborative papers had the highest citation impact, with an average of 11.71 citations per paper compared to 9.0 for the field overall 4 . This suggests that the complex challenges in nanotribology benefit from diverse expertise and resources from multiple countries and disciplines.
Nanotribology and nanomechanics represent more than just scientific curiosity about the atomic world—they are essential disciplines enabling technological progress across numerous fields. From the magnetic hard disks that store our data to the MEMS sensors in our vehicles and smartphones, applications of nanotribology are all around us, yet largely invisible to the naked eye.
Current research focuses on materials that can adapt their properties in response to environmental changes.
Materials that mimic nature's efficient solutions are being developed for various applications.
As we continue to engineer devices at smaller scales and tackle challenges in energy, healthcare, and information technology, understanding and controlling interactions at the nanoscale will become increasingly crucial. The invisible world of atoms and molecules, once the pure domain of physicists, has become an essential playground for engineers, materials scientists, and biologists alike—all working together to solve some of our most pressing technological challenges by thinking small.