Single-Atom Sensor Offers New View of the Nanoscale

A so-called nitrogen-vacancy defect sensor provides superb image resolution of minute phenomena

2 min read
A black and white micrograph show protruding rows of closely spaced needle-like tips.
Image: Quantum Sensing and Imaging Group/UC Santa Barbara

It was a eureka moment when IBM researchers first realized that they were imaging the surface of an atom with what came to be known as the scanning tunneling microscope (STM). Many believe that invention triggered the field of nanotechnology. Now researchers at the University of California Santa Barbara (UCSB) have created a next-gen microscope that can image phenomena like magnetism on the atomic scale across a huge range of temperatures. The heart of the microscope is a single atom or, perhaps more accurately, the absence of a single atom.

In research described in the journal Nature Nanotechnology, the researchers fabricated a new kind of microscope sensor based on something called a nitrogen–vacancy (NV) defect in diamond. In these NV defects, a nitrogen atom replaces a carbon atom at one point in the diamond’s molecular lattice. This disrupts the structure of the lattice and leaves empty a normally-occupied location adjacent to the nitrogen atom.

This defect in the diamond lattice makes possible the sensing of certain physical phenomenon, most notably magnetism. In operation, a NV-based magnetic sensor detects this magnetism by measuring the defect’s spin-dependent photoluminescence. To actually build a microscope, the UCSB researchers created a sensor that resembles a toothbrush. Each bristle in this toothbrush-like structure has one of these NV defects at the tip.

“This is the first tool of its kind,” said Ania Jayich, a professor and leader of the research, in a press release. “It operates from room temperature down to low temperatures where a lot of interesting physics happens. When thermal energy is low enough, the effects of electron interactions, for instance, become observable, leading to new phases of matter. And we can now probe these with unprecedented spatial resolution.”

To test their NV-based sensor, the researchers imaged a superconductor that contained magnetic structures known as vortices, which are areas of changing magnetic flux. The new sensor was able to discern individual vortices.

In continuing research, the UCSB team is exploiting this excellent resolution to look at the world of skyrmions, which are swirling magnetic spin patterns in thin films. Skyrmions may sound obscure but they more form the basis a new kind of data storage.  With this new NV-based sensor, the researchers believe that its high resolution will make it possible to image all the interactions that occur in a material that lead to skyrmions.

Jayich added: “There are a lot of different interactions between atoms and you need to understand all of them before you can predict how the material will behave.”

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD

A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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