Microscope sees light from an atomic scale for the first time

Scientists achieved a nanometer optical resolution in a microscope, which could see light interacting with individual atoms and molecules.

This technology, called Ultra Large-Tip Oscillation Amplitude Scattering Near-Field Optical Microscopy (ULA-SNOM), represents our ability to study materials at the smallest possible scale.

The international team combines atomic force microscopes with visible laser illumination and specially prepared silver tips to create a narrow light field of only one cubic nanometer in the volume. This breakthrough made optical imaging of atomic scale structures, including individual defects and molecules – previously impossible with conventional optical methods.

Break the diffraction barrier

Traditional optical microscopy reaches a basic limit called a diffraction barrier, limiting the resolution to about 200 nanometers, which is half the wavelength of visible light. New technology undermines this limitation by confining light to a smaller space than the atom itself.

The key innovation involves oscillating precisely fabricated silver tips, with an amplitude of just one nanometer and approximately three atoms wide – on the sample surface. This creates what researchers call “plasma cavity”, in which light is captured and exacerbated in tiny gaps between the tip and the sample.

Working at ultra-high vacuum and low temperatures at 8-open Kelvin (-265°C), the team achieved unprecedented stability in maintaining the nanoscale gap required for atomic resolution imaging. Extreme conditions can prevent vibration and pollution, which can otherwise damage delicate light limitations.

See a thick atom in the Silicon Islands

To prove their technique, the researchers imaged the Silicon Islands on a silver surface with only one atom. Despite the small thickness, the material contrast is clearly visible, and the light signal shows a significant difference between the silicon and silver regions.

Key technical achievements include:

• 1 nm spatial resolution in optical imaging
• Detecting material differences in individual atomic layer
• Electrical, mechanical and optical measurements are performed simultaneously
• Stable operation under extremely low temperature vacuum conditions

The team used a focused ion beam polish to mold its silver tip to nanoprecision, ensuring repeatable optical properties. This careful tip preparation is crucial to the extreme light limits required to achieve atomic-level resolution.

Three views of the same atom

What makes Ula-snom particularly powerful is its ability to measure conductivity through scanning tunneling microscopy, atomic force microscopy and light scattering. This triple view provides unprecedented insight into how atoms and molecules behave.

The researchers found that different harmonic frequencies at its oscillation tip reveal different aspects of the sample. Lower harmonics are primarily topographical features, while higher harmonics (especially the fourth harmonic) present true optical contrast between different materials.

By analyzing the curves approaching the surface as the tip moves, the team can distinguish electrical, mechanical and optical signals, confirming that each measurement technique provides independent information about the characteristics of the sample.

Open new boundaries

This technology promises to change our understanding of how photoatomic scales behave. Potential applications include the study of photovoltaic materials, study of quantum dots, and examining biological molecules at unprecedented resolution.

For materials science, ULA-SNOM provides the possibility of optical properties at the atomic level by precisely controlling defects and interfaces. This could lead to new optical devices and more efficient solar cells.

The study shows that by combining multiple advanced technologies (mass enhancement, atomic force microscopy and cryogenic conditions), testamentists can push through possible boundaries in microscopy. The ability to observe how individual atoms interact with light opens up completely new research directions in physics, chemistry and materials science.

Although the current setup requires specialized equipment and extreme conditions, fundamental principles can ultimately be used for a wider range of scientific and industrial applications, bringing atomic-level optical analysis closer to conventional laboratory use.

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