Quantum microscopy leads to nanoscale detection

A prototype quantum microscope developed by an Australian team - a "spin sensor" - has been shown to create high-resolution maps of different physical quantities. The research results, titled "Quantum Microscopy Using Van der Waals Heterostructures" [1], were published in "Nature-Physics".

The work was led by Professor Igor Aharonovich from the University of Technology Sydney (UTS) and Dr Jean-Philippe Tetienne from the Royal Melbourne Institute of Technology (RMIT).

01Quantum Microscopy: Probing material properties, physical processes with high precision

The microscope has come a long way since its invention.

We don't know exactly who made the first microscope, but Dutch eyeglass maker Zacharias Janssen is thought to have built one of the first microscopes, which used two lenses around 1600. The earliest microscopes could magnify an object 20 or 30 times its normal size.

Microscopes have gotten better at magnifying tiny objects as technology has developed, but they are limited by the wavelengths of light used. Objects smaller than one micrometer (one millionth of a meter) are too close in size to the wavelengths of visible light to be seen in conventional microscopes.

Entering the age of electron microscopes, electrons have wavelengths of about ten billionths of a meter: the best electron microscopes can show noticeable detail. But, unlike quantum microscopes, they can't tell us much about physical properties, such as electric and magnetic fields.

Solid-state spin sensors have the ability to act as quantum microscopes to probe material properties and physical processes. Quantum microscopes exist, but they rely on defects that exist in bulky, three-dimensional crystals like diamond. In these materials, spin sensors are limited in access to the sample under study. So in experiments, the team demonstrated a versatile quantum microscope using "point" defects embedded in thin layers of the van der Waals material hexagonal boron nitride (hBN).

Hexagonal Boron Nitride (hBN) Thin Layers

02Quantum microscopy based on van der Waals materials: utility extends to two dimensions

According to Prof. Aharonovich [2], the ingenuity of this new method lies in the use of a single-atom thin layer of a crystal called hexagonal boron nitride (hBN), which is known as a van der Waals material.

Van der Waals materials have strong bonds in two dimensions and weaker forces in a third dimension, which means that individual layers, graphene layers, can be exfoliated and used in many different applications. "This van der Waals material consists of strongly bonded two-dimensional layers that can be made very thin and conform to arbitrarily rough surfaces, enabling high-resolution sensitivity," Aharonovich said.

"These properties led us to the idea of ​​using 'quantum active' hBN foils for quantum microscopy, which is essentially an imaging technique - using an array of quantum sensors to create a spatial map of the quantities to which they are sensitive," Tetienne added. "So far, quantum microscopy has been limited in terms of spatial resolution and flexibility of application by interface issues inherent in the use of bulky three-dimensional sensors. By utilizing van der Waals sensors, we hope to extend the utility of quantum microscopy to previously unattainable into the field.”

The team tested their prototype on a ferromagnetic van der Waals material: a thin sheet of chromium ditelluride (CrTe2) crystals. The hBN-based quantum microscope is capable of imaging the magnetic domains of ferromagnets, approaching the sensor at nanometer-scale distances at room temperature. The unique properties of hBN allowed the researchers to record temperature maps as well, confirming that microscopy can link images between two different physical quantities. The direct integration of hexagonal boron nitride quantum sensors with other van der Waals materials will bring enormous practical benefits to the design and measurement of 2D devices.

Quantum microscopy with hBN spin defects

03Achieve nanoscale resolution for remote sensing, imaging

The authors note that the resolution of their quantum microscope is limited by the diffraction of light, which is about 1 micrometer in their results; but they add that this could in principle be sharpened to around 10 nanometers. "At this point, we're no longer talking about microscopes, but nanomirrors."

"This new generation of quantum microscopes has enormous potential," said UTS senior researcher Dr Mehran Kianinia. "Not only can it operate at room temperature and simultaneously provide information on temperature, electric and magnetic fields, but it can be seamlessly integrated down to the nanoscale. devices and can withstand very harsh environments because hBN is a very hard material."

"Key future applications include high-resolution MRI (magnetic resonance imaging) and NMR (nuclear magnetic resonance), which can be used to study chemical reactions and identify molecular origins, as well as applications in space, defense and agriculture, where remote sensing and imaging are key ."

Reference link:

[1]https://cosmosmagazine.com/science/physics/quantum-microscope-prototype/

[2]https://cosmosmagazine.com/science/physics/quantum-microscope-prototype/