Enabling room temperature ferromagnetism in monolayer MoS2 via in situ iron-doping
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-04-27 |
| Journal | Nature Communications |
| Authors | Shichen Fu, Kyungnam Kang, Kamran Shayan, Anthony Yoshimura, Siamak Dadras |
| Institutions | Rensselaer Polytechnic Institute, University of Rochester |
| Citations | 176 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a scalable method for creating room-temperature (RT) ferromagnetic two-dimensional (2D) dilute magnetic semiconductors (DMS), overcoming major limitations of previous extrinsic doping techniques.
- Core Achievement: Enabling robust ferromagnetism in monolayer Molybdenum Disulfide (MoS2) at 300 K via in situ substitutional Iron (Fe) doping during Low-Pressure Chemical Vapor Deposition (LPCVD).
- Scalable Synthesis: The Fe atoms substitute Molybdenum (Mo) sites, achieving a doping concentration of 0.3 to 0.5% using a contact-growth LPCVD method, which is highly scalable compared to mechanical exfoliation or ion implantation.
- RT Ferromagnetism Confirmation: Ferromagnetism is confirmed at ambient conditions (300 K) using both spatially integrating Superconducting Quantum Interference Devices (SQUIDs) and spatially resolving Nitrogen-Vacancy (NV-) center magnetometry.
- Local Magnetic Field: NV- center magnetometry measured a significant local magnetic field up to 0.5 ± 0.1 mT at room temperature, providing clear evidence of preserved magnetization.
- Spectroscopic Signature: An unambiguous Fe-related photoluminescence (PL) emission peak was discovered at 2.28 eV, which is stable up to RT and displays pronounced ferromagnetic hysteresis in Magnetic Circular Dichroism (MCD) measurements.
- Defect Control: Fe doping was found to suppress native sulfur vacancies, resulting in a lower native point defect density compared to undoped CVD-grown MoS2.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Curie Temperature (Tc) | >300 | K | Ferromagnetism confirmed at ambient conditions (RT). |
| Fe Doping Concentration | 0.3 to 0.5 | % | Atomic concentration determined by X-ray Photoelectron Spectroscopy (XPS). |
| Local Magnetic Field (RT) | 0.5 ± 0.1 | mT | Measured via NV- center magnetometry. |
| Fe-Related PL Emission Peak | 2.28 | eV | Stable up to RT; exhibits strong MCD hysteresis. |
| Magnetic Circular Dichroism (CD) | ~40 | % | Observed for the Fe-related emission at 4 K and RT. |
| Monolayer Thickness | 0.8 | nm | Measured via Atomic Force Microscopy (AFM). |
| MoS2 Raman Mode (E12g) | 385.4 | cm-1 | In-plane vibration mode. |
| MoS2 Raman Mode (A1g) | 405.8 | cm-1 | Out-of-plane vibration mode. |
| STEM Intensity Ratio (Fe/Mo) | 0.38 | (unitless) | Consistent with the atomic number ratio (ZFe=26, ZMo=42). |
| SQUID Coercive Field (5 K) | ~3 | T | Pronounced M-H hysteresis loop at cryogenic temperature. |
Key Methodologies
Section titled âKey MethodologiesâThe Fe:MoS2 monolayers were synthesized using a Low-Pressure Chemical Vapor Deposition (LPCVD) contact-growth method.
1. Precursor Preparation and Setup
Section titled â1. Precursor Preparation and Setupâ- Mo Source: A thin MoO3 layer was prepared via Physical Vapor Deposition (PVD) onto a Si substrate with 300 nm thermal oxide.
- Fe Source: Fe3O4 particles were evenly cast onto a separate SiO2/Si substrate.
- Contact Growth: The MoO3-deposited substrate and the Fe3O4-coated SiO2/Si substrate were contacted face-to-face.
- Pre-Annealing: The Fe3O4-coated substrate was annealed at 110 °C for 5 min on a hot plate prior to growth.
2. LPCVD Growth Parameters
Section titled â2. LPCVD Growth Parametersâ- Ramping: Furnace heated with a ramping rate of 18 °C min-1.
- Hold Conditions: Held at 850 °C for 15 min.
- Gas Flow (Initial): Argon (Ar) gas (30 s.c.c.m.) supplied starting at 300 °C.
- Gas Flow (Reduction): Hydrogen (H2) gas (15 s.c.c.m.) delivered starting at 760 °C.
- Sulfurization: Sulfur (S) was supplied when the furnace temperature reached 790 °C.
3. Characterization Techniques
Section titled â3. Characterization Techniquesâ- Structural/Compositional:
- High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) confirmed substitutional Fe incorporation at Mo sites.
- X-ray Photoelectron Spectroscopy (XPS) determined the Fe atomic concentration (0.3-0.5%).
- Optical/Electronic:
- Raman and Photoluminescence (PL) spectroscopy confirmed lattice incorporation and identified the 2.28 eV Fe-related emission.
- Density Functional Theory (DFT) calculations corroborated the microscopic origin of the 2.28 eV transition.
- Magnetic:
- SQUID Magnetometry: Measured bulk magnetization (M-H loops) at 5 K and 300 K, confirming RT ferromagnetism.
- NV- Center Magnetometry: Nanodiamonds containing NV- centers were spin-coated onto the Fe:MoS2 surface to perform optically detected magnetic resonance (ODMR) measurements, quantifying the local magnetic field (up to 0.5 mT) at RT.
Commercial Applications
Section titled âCommercial ApplicationsâThis development of a scalable, RT ferromagnetic 2D semiconductor opens doors for integration into advanced electronic and quantum systems.
- Spintronics and Data Storage:
- Development of ultra-low power, high-density non-volatile magnetic memory (MRAM) utilizing spin-polarized charge carriers.
- Minimizing bit storage size in next-generation computing architectures.
- Quantum Information Science:
- Enabling on-chip magnetic manipulation and control of quantum states in 2D heterostructures.
- Integration into quantum devices requiring localized, stable magnetic fields at ambient conditions.
- Flexible Electronics:
- The atomically thin nature of the material allows for potential use in flexible spintronic devices and wearable technology.
- Advanced Sensors:
- Creation of highly sensitive magnetic field sensors based on the integration of the ferromagnetic Fe:MoS2 with other 2D materials.