Graphene sensors find subtleties in magnetic fields

Cornell researchers used an ultrathin graphene “sandwich” to create a tiny magnetic area sensor that may function over a better temperature vary than earlier sensors, whereas additionally detecting miniscule modifications in magnetic fields that may in any other case get misplaced inside a bigger magnetic background.

Corridor-effect sensor Supplied

Researchers led by Katja Nowack, assistant professor of physics, created this micron-scale Corridor-effect sensor by sandwiching graphene between sheets of hexagonal boron nitride, leading to a tool that operates over a better temperature vary than earlier Corridor sensors.

The group’s paper, “Magnetic Area Detection Limits for Ultraclean Graphene Corridor Sensors,” revealed Aug. 20 in Nature Communications.

The group was led by Katja Nowack, assistant professor of physics within the Faculty of Arts and Sciences and the paper’s senior creator.

Nowack’s lab makes a speciality of utilizing scanning probes to conduct magnetic imaging. One in every of their go-to probes is the superconducting quantum interference gadget, or SQUID, which works properly at low temperatures and in small magnetic fields.

“We wished to develop the vary of parameters that we are able to discover by utilizing this different sort of sensor, which is the Corridor-effect sensor,” stated doctoral scholar Brian Schaefer, the paper’s lead creator. “It may work at any temperature, and we have proven it might probably work as much as excessive magnetic fields as properly. Corridor sensors have been used at excessive magnetic fields earlier than, however they’re often not in a position to detect small magnetic area modifications on high of that magnetic area.”

The Corridor impact is a well known phenomenon in condensed matter physics. When a present flows by a pattern, it’s bent by a magnetic area, making a voltage throughout either side of the pattern that’s proportional to the magnetic area.

Corridor-effect sensors are utilized in a wide range of applied sciences, from cellphones to robotics to anti-lock brakes. The gadgets are typically constructed out of standard semiconductors like silicon and gallium arsenide.

Nowack’s group determined to strive a extra novel strategy.

The final decade has seen a increase in makes use of of graphene sheets — single layers of carbon atoms, organized in a honeycomb lattice. However graphene gadgets usually fall in need of these comprised of different semiconductors when the graphene sheet is positioned immediately on a silicon substrate; the graphene sheet “crumples” on the nanoscale, inhibiting its electrical properties.

Nowack’s group adopted a lately developed approach to unlock graphene’s full potential — sandwiching it between sheets of hexagonal boron nitride. Hexagonal boron nitride has the identical crystal construction as graphene however is an electrical insulator, which permits the graphene sheet to lie flat. Graphite layers within the sandwich construction act as electrostatic gates to tune the variety of electrons that may conduct electrical energy within the graphene.

The sandwich approach was pioneered by co-author Lei Wang, a former postdoctoral researcher with the Kavli Institute at Cornell for Nanoscale Science. Wang additionally labored within the lab of co-senior creator Paul McEuen, the John A. Newman Professor of Bodily Science and co-chair of the Nanoscale Science and Microsystems Engineering (NEXT Nano) Process Pressure, a part of the provost’s Radical Collaboration initiative.

“The encapsulation with hexagonal boron nitride and graphite makes the digital system ultraclean,” Nowack stated. “That permits us to work at even decrease electron densities than we might earlier than, and that is favorable for enhancing the Corridor-effect sign we’re fascinated about.”

The researchers have been in a position to create a micron-scale Corridor sensor that features in addition to the perfect Corridor sensors reported at room temperature whereas outperforming some other Corridor sensor at temperatures as little as four.2 kelvins (or minus 452.11 levels Fahrenheit).

The graphene sensors are so exact they will select tiny fluctuations in a magnetic area towards a background area that’s bigger by six orders of magnitude (or one million instances its dimension). Detecting such nuances is a problem for even high-quality sensors as a result of in a excessive magnetic area, the voltage response turns into nonlinear and due to this fact tougher to parse.

Nowack plans to include the graphene Corridor sensor right into a scanning probe microscope for imaging quantum supplies and exploring bodily phenomena, comparable to how magnetic fields destroy unconventional superconductivity and the ways in which present flows in particular lessons of supplies, comparable to topological metals.

“Magnetic area sensors and Corridor sensors are necessary components of many real-world functions,” Nowack stated. “This work places ultraclean graphene actually on the map for being a superior materials to construct Corridor probes out of. It would not be actually sensible for some functions as a result of it is exhausting to make these gadgets. However there are totally different pathways for supplies progress and automatic meeting of the sandwich that individuals are exploring. After you have the graphene sandwich, you’ll be able to put it anyplace and combine it with current know-how.”

Co-authors embrace doctoral scholar Alexander Jarjour, and researchers from the Nationwide Institute for Supplies Science in Tsukuba, Japan.

The analysis was supported by the Nationwide Science Basis and the Cornell Heart for Supplies Analysis, an NSF Supplies Analysis Science and Engineering Heart. The researchers made use of the Cornell NanoScale Science and Expertise Facility, and the Columbia Nano Initiative Clear Room.