An ultrafast diamond nonlinear photonic sensor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-09-25 |
| Journal | Nature Communications |
| Authors | Daisuke Sato, Junjie Guo, Takuto Ichikawa, Dwi Prananto, Toshu An |
| Institutions | Keio University, Japan Advanced Institute of Science and Technology |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces an ultrafast diamond nonlinear photonic sensor, leveraging Nitrogen-Vacancy (NV) centers to achieve unprecedented spatio-temporal resolution for electric field sensing.
- Core Achievement: Developed a nanoscopic electro-optic (EO) sampling technique that breaks the diffraction limit of light and the nanosecond time resolution limit of conventional NV sensing (ODMR).
- Resolution Metrics: Achieved spatial resolution potentially †500 nm and temporal resolution †100 fs.
- Sensing Mechanism: Utilizes the Pockels EO effect in a diamond nanotip. NV defects locally break the crystalâs spatial inversion symmetry, resulting in a non-zero second-order nonlinear susceptibility (Ï(2) â 0).
- Demonstration: Successfully measured the dynamics of the surface electric field (carrier screening and relaxation) on a prototypical semiconductor (n-GaAs) and a two-dimensional material (WSe2 monolayer and bulk).
- Key Finding in WSe2: Observed distinct double exponential relaxation dynamics in bulk WSe2 (t1 â 0.3 ps, t2 â 2.2 ps), attributed to intervalley scattering followed by trapping by surface defect states.
- Value Proposition: Provides a critical tool for developing next-generation nanometer-scale quantum devices by enabling high-resolution sensing of electric, magnetic, and thermal fields.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spatial Resolution (Potential) | †500 | nm | Limited by NV tip apex size and EO enhancement |
| Temporal Resolution (Achieved) | †100 | fs | FWHM of shortest EO response |
| Pump Laser Pulse Length | †10 | fs | Ti: sapphire oscillator |
| Pump Laser Wavelength | 795 | nm | Center wavelength (1.56 eV) |
| Pump Fluence (WSe2) | 215 | ”J cm-2 | Generates carrier density ~1.35 x 1013 cm-2 |
| NV Implantation Energy | 30 | keV | 14N+ ions |
| NV Implantation Depth | ~40 | nm | Deduced from SRIM simulation |
| NV Annealing Temperature | 900 | °C | 1 hour in Ar atmosphere |
| GaAs Relaxation Time (Macroscopic) | ~1.1 | ps | Carrier relaxation/diffusion |
| GaAs Relaxation Time (Local, NV Tip) | ~0.5 | ps | Faster due to surface effects |
| WSe2 Bulk Relaxation Time (t2) | 2.2 ± 0.1 | ps | Attributed to trapping by surface defect states |
| WSe2 1ML Relaxation Time | 0.2 ± 0.1 | ps | Strong coupling to SiO2 substrate |
| Estimated Electric Field Sensitivity | ~100 | V cm-1 Hz-1/2 | Based on n-GaAs EO signal and noise level |
| GaAs Macroscopic ÎE | ~-3.1 x 106 | V m-1 | Maximum experimental EO response |
Key Methodologies
Section titled âKey Methodologiesâ-
Diamond NV Probe Fabrication:
- Material: (100)-oriented CVD-grown electronic-grade bulk diamond (< 5 ppb initial N impurities).
- NV Creation: 14N+ ion implantation at 30 keV, followed by annealing at 900 °C for 1 hour in an Argon (Ar) atmosphere.
- Tip Shaping: Laser cutting and Gallium ion (Ga+) Focused Ion Beam (FIB) milling used to define the nanotip geometry.
- Integration: Probe attached to a self-sensing cantilever for Atomic Force Microscopy (AFM) force detection.
-
WSe2 Sample Preparation:
- Monolayer (1ML) and bulk WSe2 prepared from a single crystal.
- Substrate was Si covered with a 100-nm SiO2 layer.
- Au-assisted transfer method used to place WSe2 onto the substrate.
-
Ultrafast Electro-Optic (EO) Sampling Setup:
- Technique: Reflective pump-probe scheme combined with AFM (Scanning Probe Microscopy).
- Light Source: Ti: sapphire femtosecond oscillator (†10 fs pulse length, 795 nm center wavelength, 75 MHz repetition rate).
- Optics: Reflective (Schwarzschild) objective lens used to inject the probe beam from the back side of the tip to minimize dispersion.
- Time Delay: Modulated by an oscillating retroreflector (shaker) in the pump path at 10 Hz.
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Sensing Mode (Pin-Point AFM):
- The AFM system operated in âpin-point mode,â vertically approaching and retracting the diamond NV probe at designated points.
- This ensures the diamond probe maintains a quasi-zero distance (typically 0.1-0.3 nm) from the sample surface during measurement.
- The EO signal (anisotropic reflectivity change) was detected by a 1 GHz high-speed Si-PIN photodetector, with noise reduction achieved via signal integration (5000 accumulations).
Commercial Applications
Section titled âCommercial Applicationsâ| Industry/Field | Application Area | Relevance to Technology |
|---|---|---|
| Quantum Sensing & Metrology | Next-generation quantum sensors and electrometers. | Provides the necessary spatio-temporal resolution (nm/fs) to characterize localized electric fields in single-spin systems and quantum devices, surpassing ODMR limits. |
| 2D Materials Research | Characterization of Transition Metal Dichalcogenides (TMDCs) and topological insulators. | Enables direct, nanoscopic measurement of ultrafast carrier dynamics (Mott transition, scattering, defect trapping) crucial for optimizing 2D material performance. |
| High-Speed Photonics | Optical switches, modulators, and integrated circuits. | The EO effect is fundamental to these devices. The technique allows for high time-resolution testing of components operating in the sub-picosecond regime. |
| Semiconductor Device Engineering | Power device materials (e.g., SiC) and compound semiconductors (GaAs). | Allows for the measurement of electric field distribution and carrier transport dynamics near surfaces and interfaces, critical for device reliability and performance. |
| Nanoscopy Tool Development | Advanced Scanning Probe Microscopy (SPM) systems. | The diamond NV probe concept can be integrated into commercial SPM platforms (e.g., QZabre, Qnami) to create hybrid tools offering combined AFM, ultrafast spectroscopy, and quantum sensing capabilities. |