Nanoscale electric-field imaging based on a quantum sensor and its charge-state control under ambient condition
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-04-28 |
| Journal | Nature Communications |
| Authors | Ke Bian, Wentian Zheng, Xianzhe Zeng, Xiakun Chen, Rainer Stöhr |
| Institutions | Peking University, University of Stuttgart |
| Citations | 108 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a significant advancement in quantum sensing by achieving nanoscale electric-field imaging and charge-state control using Nitrogen-Vacancy (NV) centers in diamond under ambient conditions.
- Nanoscale Electrometry: Achieved quantitative imaging of external electric-field contours from a sharp AFM tip, overcoming the challenge of weak NV-electric field coupling.
- High Spatial Resolution: Demonstrated a spatial resolution of ~17 nm for electric-field gradient imaging, limited by the sensor size and sensitivity.
- Ultra-Precise Charge Control: Realized electric control of the NV charge state (NV-, NV0, NV+) with sub-5 nm precision (4.6 nm resolution) using the high local field gradient of the tip.
- Enabling Technology: The system utilizes a qPlus-based Atomic Force Microscope (AFM) sensor, allowing for stable operation at tip-surface distances below 1 nm with extremely small oscillation amplitudes (100-300 pm), minimizing electric noise.
- Charge Stabilization Mechanism: The NV charge state (specifically NV+) is stabilized by a built-in electric field generated through photon-ionization and subsequent electron trapping at surface defects.
- Future Impact: This work establishes the first step towards nanoscale scanning electrometry based on a single quantum sensor, enabling quantitative mapping of local charge, electric polarization, and dielectric response in functional materials.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth | 5-10 | nm | Shallow NVs used as quantum probes. |
| E-Field Imaging Resolution | ~17 | nm | Best spatial resolution achieved for field gradient imaging. |
| Charge Control Resolution | ~4.6 | nm | Spatial precision for NV charge-state transition edge (NV+/NV0). |
| AFM Tip-Surface Distance | < 1 | nm | Required for achieving strong local electric fields. |
| AFM Oscillation Amplitude | 100-300 | pm | Used by the qPlus sensor to minimize electric noise. |
| Maximum Local E-Field | ~14 | MV cm-1 | Largest field strength reachable by the system. |
| Minimum Detectable E-Field | ~17.6 | kV cm-1 | Determined by the spectral resolution of pulsed-ODMR. |
| Magnetic Field (BL) | ~9.6 | G | Transverse magnetic field applied perpendicular to the NV axis. |
| NV Coherence Time (T2) | 15-30 | ”s | Typical T2 measured using spin-echo sequence on Sample A. |
| Microwave Pi-Pulse Duration | ~5.4 | ”s | Used in pulsed-ODMR measurements. |
| Diamond Material | Electronic-grade | N/A | Single-crystal chips with intrinsic N concentration below 5 ppb. |
| N15 Implantation Energy | 5 | keV | Used for creating shallow NVs. |
| Tip Bias Voltage Range | -150 to +150 | V | Supplied to the conductive tungsten tip. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment integrates a home-built scanning probe microscope (SPM) with NV center quantum sensing technology, utilizing a qPlus AFM sensor for precise tip positioning and field generation.
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NV Sample Preparation:
- Electronic-grade single-crystal diamond chips (N concentration below 5 ppb) were milled into membranes (20-30 ”m thickness).
- Shallow NVs were created via 5-keV N15 ion implantation, followed by high-temperature annealing to facilitate vacancy diffusion.
- Sample surfaces were treated (piranha solution/acid boiling) to reduce background fluorescence and revive NVs.
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AFM Setup and Operation:
- A qPlus sensor (high stiffness, low oscillation amplitude) with a sharpened tungsten tip was used for non-contact AFM operation in Frequency Modulation (FM) mode.
- The tip was positioned below 1 nm from the diamond surface to maximize the electric field gradient while maintaining small oscillation amplitudes (100-300 pm) to minimize electric noise.
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Quantum Sensing (Pulsed-ODMR):
- NV spin states were initialized (532-nm laser) and read out (red fluorescence, 650-nm LP filter).
- A transverse magnetic field (~9.6 G) was applied to align the NV eigenstates into |±> states.
- Electric field strength was measured via the Stark effect, observing the frequency shift (Îf) of the |±> states using the highly sensitive pulsed-ODMR scheme (Ï-pulse duration ~5.4 ”s).
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Electric Field Imaging:
- The microwave frequency was fixed slightly off-resonant, and fluorescence intensity was monitored while scanning the biased tip, allowing a single Îf (field gradient) to be probed.
- Quantitative field strength was estimated from the preset microwave frequency and the observed ring structure line width.
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Charge State Control and Imaging:
- The tip bias was ramped (e.g., +150 V to -150 V) while monitoring NV fluorescence to induce charge state transitions (NV- â NV0 â NV+).
- The mechanism involves photon-ionization of deep donors (P1 centers) by the excitation laser, followed by electron trapping at surface defects, creating a stable, built-in electric field that stabilizes the NV+ state.
- Charge-state transition imaging was performed by continuously recording fluorescence while scanning a positively biased tip, yielding a spatial resolution of 4.6 nm at the transition edge.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a fundamental tool for characterizing materials at the nanoscale, particularly those where charge dynamics and local electric fields dictate performance.
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Quantum Computing and Information:
- Constructing complex qubit networks and quantum processors by enabling precise control and stabilization of solid-state qubits (NV centers, SiV centers, SiC defects).
- Enhancing spin coherence and contrast of shallow NVs by controlling the local electrostatic environment and depleting surrounding charges.
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Advanced Materials and Device Characterization:
- Quantitative mapping of local charge, electric polarization, and dielectric response in functional materials.
- Characterization of ferroelectrics, multiferroics, and 2D magnetic materials.
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Energy Storage and Conversion:
- Probing local charge dynamics and electric fields in solar cells, ion batteries, and electronic devices.
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Semiconductor Industry:
- Nanoscale inspection and characterization of semiconductor devices, including mapping band bending and charge distribution in integrated circuits.
- Potential for high-speed charge carrier transfer studies vital for nuclear-based quantum storage and spin-to-charge readout.
View Original Abstract
Abstract Nitrogen-vacancy (NV) centers in diamond can be used as quantum sensors to image the magnetic field with nanoscale resolution. However, nanoscale electric-field mapping has not been achieved so far because of the relatively weak coupling strength between NV and electric field. Here, using individual shallow NVs, we quantitatively image electric field contours from a sharp tip of a qPlus-based atomic force microscope (AFM), and achieve a spatial resolution of ~10 nm. Through such local electric fields, we demonstrated electric control of NVâs charge state with sub-5 nm precision. This work represents the first step towards nanoscale scanning electrometry based on a single quantum sensor and may open up the possibility of quantitatively mapping local charge, electric polarization, and dielectric response in a broad spectrum of functional materials at nanoscale.