Nitrogen-vacancy magnetometry of CrSBr by diamond membrane transfer
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-09-07 |
| Journal | npj 2D Materials and Applications |
| Authors | Talieh S. Ghiasi, Michael Borst, Samer Kurdi, Brecht G. Simon, Iacopo Bertelli |
| Institutions | Parc CientĂfic de la Universitat de ValĂšncia, Delft University of Technology |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the development and application of a deterministic âdry-transferâ technique for integrating Nitrogen-Vacancy (NV) diamond sensors directly onto two-dimensional (2D) magnetic materials, overcoming the critical challenge of achieving nanoscale proximity.
- Core Innovation: A pick-and-place dry-transfer method, compatible with standard 2D material assembly, was developed to place 50 ”m diamond micro-membranes containing shallow NV centers onto Chromium Sulfur Bromide (CrSBr) flakes.
- Proximity Achieved: The technique resulted in an intact interface and a measured NV-sample stand-off distance (Z0) of 0.13 ± 0.04 ”m, crucial for detecting weak magnetic stray fields.
- Monolayer Magnetization Quantified: By measuring the stray field generated at the edge of an uncompensated CrSBr layer, the saturated monolayer magnetization (MCSB) was extracted as 0.46 ± 0.02 T.
- Magnetic Order Confirmation: Spatially resolved Electron Spin Resonance (ESR) measurements confirmed that stray fields only arise from CrSBr regions corresponding to an odd number of layers, consistent with its interlayer antiferromagnetic stacking order.
- Phase Transition Detection: The temperature dependence of the stray field amplitude was used to accurately determine the Néel temperature (Tc) of the CrSBr flake at 130 ± 1 K.
- Engineering Advantage: The method enables the integration of high-density NV ensemble sensors onto arbitrary substrates (e.g., SiO2/Si with Au striplines) with micron lateral precision, facilitating fast, large-area magnetic readout.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Monolayer Magnetization (MCSB) | 0.46 ± 0.02 | T | Extracted from stray field fit at 10 K. |
| Néel Temperature (Tc) | 130 ± 1 | K | Determined by ESR signal decay vs. temperature. |
| NV-Sample Stand-off Distance (Z0) | 0.13 ± 0.04 | ”m | Extracted from stray field fit, greater than expected SRIM depth (~70 nm). |
| NV Implantation Depth | 70 ± 10 | nm | Estimated depth using 54 keV Nitrogen ions. |
| NV Density (Estimated) | 103 | NVs/”m2 | Resulting density after 800 °C vacuum anneal. |
| Diamond Membrane Size | 50 x 50 x 5 | ”m3 | Fabricated via RIE etching. |
| ESR Stray Field Detected (dBNV) | ~60 | ”T | Measured at the 2.4 nm CrSBr step edge. |
| External Bias Field (Bex) | 5.6 | mT | Used for selective driving of NV ESR transition. |
| PMMA Melting Temperature | 180 | °C | Used for final diamond membrane release from the PDMS stamp. |
| Microwave Stripline Thickness | 100 | nm | Gold (Au) layer thickness (with 5 nm Ti adhesion layer). |
| CrSBr Monolayer Thickness | 1.1 ± 0.23 | nm | Measured by AFM characterization. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on precise diamond membrane fabrication and a multi-step dry-transfer process adapted from 2D material assembly techniques.
1. NV Diamond Membrane Fabrication
Section titled â1. NV Diamond Membrane Fabricationâ- Implantation: Electronic-grade diamond was implanted with Nitrogen ions (54 keV, 1013/cm2 density) to create a shallow NV layer at ~70 nm depth.
- NV Creation: Vacuum annealing was performed, ramping up to 800 °C for 2 hours, resulting in an estimated NV density of 103 NVs/”m2.
- Membrane Etching: A Ti mask (defined by e-beam lithography) was used for Reactive Ion Etching (RIE).
- The Ti mask was etched using SF6/He plasma (30 W RF power).
- The diamond was etched using O2 plasma RIE (90 W RF, 1100 W ICP) at a rate of 0.25 ”m/min to define 50 x 50 x 5 ”m3 squares connected by small holding bars.
2. CrSBr Sample Preparation
Section titled â2. CrSBr Sample Preparationâ- Substrate: SiO2/Si substrate was prepared with an Au stripline (100 nm Au / 5 nm Ti) defined by e-beam lithography and evaporation.
- Exfoliation: CrSBr bulk crystals were cleaved and exfoliated onto a PDMS layer.
- Transfer: CrSBr flakes were transferred from the PDMS onto the target substrate, positioned within 5 ”m of the Au stripline.
3. Deterministic Dry-Transfer Process
Section titled â3. Deterministic Dry-Transfer Processâ- Membrane Detachment (Step 1): A metallic tip was used to break the holding bars and detach a single 50 ”m diamond membrane onto a flexible Polydimethylsiloxane (PDMS 1) layer.
- Pick-up (Step 2): A PMMA-PDMS stamp (PDMS 2) was brought into contact with the diamond membrane. The strong adhesion between PMMA and diamond allowed the membrane to be picked up upon retraction (optional annealing up to 80 °C).
- Alignment and Contact (Step 3): The diamond/PMMA stack was aligned over the target CrSBr flake and brought into contact while heating the stage to 100 °C.
- Release (Step 4): The stage temperature was increased to 180 °C to melt the PMMA, ensuring the diamond membrane was released and adhered directly onto the CrSBr flake and SiO2 substrate.
- Cleanup (Step 5): PMMA surrounding the region of interest was removed via e-beam lithography to minimize optical scattering during NV readout.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology enables the integration of high-performance quantum sensors with emerging 2D material systems, facilitating the development and characterization of next-generation spintronic and quantum devices.
- 2D Spintronic Device Development:
- Quantitative, non-invasive characterization of magnetization, domain walls, and localized defects in atomically thin magnets (e.g., CrSBr, CrI3).
- Enables fast readout of magnetic configurations in 2D spin-logic and memory devices.
- Quantum Sensing and Metrology:
- Fabrication of integrated quantum sensors for large-area magnetic imaging with diffraction-limited resolution.
- Used for high-sensitivity detection of weak static and dynamic magnetic fields generated by nanoscale structures.
- Heterostructure Engineering:
- Provides a robust, inert-atmosphere compatible method for stacking complex 2D material heterostructures with integrated NV sensors, minimizing interface contamination (e.g., dust particles).
- Cryogenic and High-Temperature Research:
- NV magnetometry is effective across a wide temperature range (0.35 K to 600 K), allowing for the study of magnetic phase transitions in novel materials.
View Original Abstract
Abstract Magnetic imaging using nitrogen-vacancy (NV) spins in diamonds is a powerful technique for acquiring quantitative information about sub-micron scale magnetic order. A major challenge for its application in the research on two-dimensional (2D) magnets is the positioning of the NV centers at a well-defined, nanoscale distance to the target material required for detecting the small magnetic fields generated by magnetic monolayers. Here, we develop a diamond âdry-transferâ technique akin to the state-of-the-art 2D-materials assembly methods and use it to place a diamond micro-membrane in direct contact with the 2D interlayer antiferromagnet CrSBr. We harness the resulting NV-sample proximity to spatially resolve the magnetic stray fields generated by the CrSBr, present only where the CrSBr thickness changes by an odd number of layers. From the magnetic stray field of a single uncompensated ferromagnetic layer in the CrSBr, we extract a monolayer magnetization of M CSB = 0.46(2) T, without the need for exfoliation of monolayer crystals or applying large external magnetic fields. The ability to deterministically place NV-ensemble sensors into contact with target materials and detect ferromagnetic monolayer magnetizations paves the way for quantitative analysis of a wide range of 2D magnets assembled on arbitrary target substrates.