Nanoscale electric field imaging with an ambient scanning quantum sensor microscope
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-09-09 |
| Journal | npj Quantum Information |
| Authors | Ziwei Qiu, Assaf Hamo, Uri Vool, Tony Zhou, Amir Yacoby |
| Institutions | Harvard University |
| Citations | 39 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Scanning NV Electrometry Demonstrated: The research successfully demonstrated nanoscale imaging of external Alternating Current (AC) and Direct Current (DC) electric fields using a single Nitrogen-Vacancy (NV) center embedded in a diamond scanning tip under ambient conditions.
- High AC Sensitivity: Achieved an AC E-field sensitivity of 26 mV ”m-1 Hz-1/2, representing a two-order-of-magnitude improvement in sensitivity compared to previous scanning NV electrometry work.
- Screening Effect Characterization: A strong low-frequency E-field screening effect, likely caused by mobile surface charges, was quantitatively measured. This screening follows a high-pass filter response with a resistive-capacitive (RC) time constant of approximately 30 ”s (cut-off frequency fc = 35.4 kHz).
- Motion-Enabled DC Imaging: To bypass low-frequency screening for DC field mapping, the diamond probe was mechanically oscillated at ~190 kHz. This technique upconverts the local DC E-field gradient into a T2-limited AC signal.
- High DC Gradient Sensitivity: The motion-enabled technique achieved a DC E-field gradient sensitivity of 2 V ”m-2 Hz-1/2, significantly improving DC sensing capability.
- Platform Integration: The system integrates a confocal microscope and an Atomic Force Microscope (AFM) in shear force mode, establishing a foundation for a scanning-probe-based multimodal quantum sensing platform.
- Resolution: Spatial resolution was achieved at sub-100 nm, limited primarily by the physical distance between the NV center and the sample surface.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| AC E-Field Sensitivity | 26 | mV ”m-1 Hz-1/2 | Achieved using Dynamical Decoupling (PDD) sequences. |
| DC E-Field Gradient Sensitivity | 2 | V ”m-2 Hz-1/2 | Achieved using motion-enabled imaging. |
| Spatial Resolution | Sub-100 | nm | Limited by NV-sample distance. |
| NV-Sample Distance (Typical) | ~100 | nm | Distance maintained during scanning. |
| Diamond Tip Diameter | 300 | nm | Diameter of the sensing nanopillar apex. |
| NV Depth | ~40 | nm | Location of the NV center below the diamond surface. |
| Bias Magnetic Field (Bâ„) | ~73 | G | Used for E-field sensing (working regime Bâ„ > 70 G). |
| Zero-Field Splitting (Dgs) | 2.87 | GHz | NV electron spin property. |
| Transverse E-Field Coupling (dâ„) | 0.17 ± 0.03 | MHz ”m V-1 | Measured coupling strength. |
| E-Field Screening Cut-off Frequency (fc) | 35.4 | kHz | Frequency where screening significantly diminishes. |
| RC Time Constant (Ï) | ~30 | ”s | Characteristic time constant of the diamond surface screening. |
| Probe Oscillation Frequency (DC Imaging) | ~190 | kHz | Frequency used for mechanical upconversion of DC gradients. |
| NV Coherence Time (T2) | ~1.5 | ”s | Moderate T2 used in the experiment. |
| MW Amplifier Power | 30 | W | Used for driving spin transitions (Amplifier Research 30S1G6). |
| DC Input Voltage (Vdc) | 16 | V | Voltage applied across the gold structure for DC imaging. |
Key Methodologies
Section titled âKey Methodologiesâ- Integrated Scanning Platform: A home-built system combining a confocal microscope (532 nm laser excitation, APD readout) and an Atomic Force Microscope (AFM) operating in ambient conditions, utilizing a quartz crystal tuning fork for frequency modulation (FM-AFM) in shear force mode.
- Diamond Probe Engineering: Used electronic-grade CVD diamond probes containing 15NV centers. The probe features multiple nanopillars, with the NV located at the apex of a sensing pillar (~40 nm deep) for close-proximity scanning.
- Qubit Initialization and Readout: NV spin was initialized to the |ms = 0> state and read out via spin-dependent photoluminescence (ODMR). A bias magnetic field B℠(~73 G) was applied perpendicular to the NV axis to maximize E-field sensitivity by splitting the |±> states.
- AC Electrometry (Lock-in Detection):
- Low Frequency (< 50 kHz): Used Ramsey-based pulse sequences synchronized with the AC reference signal to sample the E-field and extract amplitude/phase via sinusoidal fitting.
- High Frequency (> 200 kHz): Employed Periodic Dynamical Decoupling (PDD) sequences (e.g., XY4, XY8) to extend the NV coherence time (T2) and maintain high sensitivity.
- DC Electrometry (Motion-Enabled Imaging): To overcome low-frequency screening, the diamond probe was mechanically oscillated parallel to the sample surface at ~190 kHz. The quantum sensing pulse sequences (XY4) were synchronized with this motion, effectively converting the static DC E-field gradient (dE/dx) into a measurable AC signal.
- Electrostatics Simulation: Finite-element calculations (COMSOL) were performed using real device geometries (U-shaped gold structure) to model the expected AC and DC electric field distributions for comparison and validation against experimental data.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Sensing and Metrology: Development of next-generation multimodal scanning-probe platforms capable of simultaneous, nanoscale vector mapping of both magnetic and electric fields (vector electrometry).
- Advanced Materials Characterization: Non-invasive, quantitative analysis of charge dynamics, internal fields, and screening effects in novel materials, including 2D materials, multiferroics, and strongly correlated electron systems.
- Semiconductor Device Physics: High-resolution imaging of charge trapping states, near-surface band-bending, and potential distributions in microelectronic and quantum computing devices under ambient conditions.
- Chemical and Biological Sensing: Mapping local electric fields associated with molecular interactions, charge transfer processes, and biological signals (e.g., detecting action potentials or charge phenomena in living cells).
- Diamond Qubit Engineering: Providing tools to characterize and mitigate surface charge noise and screening effects in shallow NV centers, crucial for improving the performance and coherence of diamond-based quantum sensors.
View Original Abstract
Abstract Nitrogen-vacancy (NV) center in diamond is a promising quantum sensor with remarkably versatile sensing capabilities. While scanning NV magnetometry is well-established, NV electrometry has been so far limited to bulk diamonds. Here we demonstrate imaging external alternating (AC) and direct (DC) electric fields with a single NV at the apex of a diamond scanning tip under ambient conditions. A strong electric field screening effect is observed at low frequencies. We quantitatively measure its frequency dependence and overcome this screening by mechanically oscillating the tip for imaging DC fields. Our scanning NV electrometry achieved an AC E-field sensitivity of 26 mV ÎŒm â1 Hz â1/2 , a DC E-field gradient sensitivity of 2 V ÎŒm â2 Hz â1/2 , and sub-100 nm resolution limited by the NV-sample distance. Our work represents an important step toward building a scanning-probe-based multimodal quantum sensing platform.