Phase transition observation of nanoscale water on diamond surface
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Acta Physica Sinica |
| Authors | Zhiping Yang, Xi Kong, Fazhan Shi, Jiangfeng Du |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the use of shallow Nitrogen-Vacancy (NV) centers in diamond as a dual quantum sensor for simultaneous nanoscale Nuclear Magnetic Resonance (NMR) and in situ thermometry, focusing on the dynamics of confined water.
- Core Achievement: Successful measurement of proton NMR signals from a nanoscale water layer (6-7 nm thick) adsorbed on the diamond surface under ambient pressure.
- Phase Transition Observation: The solid-liquid phase transition of the nano-water was observed by monitoring the change in the nuclear spin correlation time (T2*), which increased significantly upon solidification (from 12 ”s to 46 ”s).
- Dynamic Differentiation: The technique clearly distinguished liquid water (broad NMR linewidth, 53 kHz, dominated by molecular diffusion away from the sensor) from solid ice (narrower linewidth, 33 kHz, dominated by static magnetic dipole interactions).
- In Situ Thermometry: The NV center zero-field splitting (D) was utilized as a local temperature sensor, providing a sensitivity of -87 ± 12 kHz/K to track the sample temperature during the phase change.
- Confinement Effects: The observed solid-liquid transition point occurred at a temperature slightly higher than 0 °C, suggesting that surface confinement or hydrophilicity influences the phase behavior of nanoscale water.
- Technological Advancement: This work validates NV-based nano-NMR as a powerful, non-invasive method capable of probing the structure and dynamics of confined materials and biological systems at the nanoscale, overcoming sensitivity limitations of traditional NMR.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth (Average) | 6-7 | nm | Proximity required for nanoscale NMR sensitivity. |
| Diamond Film Dimensions | 2 x 2 x 0.05 | mm | Sample size used in the experimental setup. |
| Implantation Energy | 5 | keV | Used for 14N+ ion creation of shallow NV centers. |
| Annealing Temperature | 800 | °C | Vacuum annealing post-implantation. |
| External Magnetic Field (B) | 42.2 | mT | Used for polarizing and sensing proton spins. |
| Proton Resonance Frequency | 1.8 | MHz | Corresponds to the 42.2 mT field. |
| Liquid Water Linewidth | 53 ± 9 | kHz | Measured at 11.1 °C (broadened by diffusion). |
| Solid Ice Linewidth | 33 ± 5 | kHz | Measured at -8.8 °C (dominated by dipole interaction). |
| Liquid Water Correlation Time (T2*) | 12 ± 3 | ”s | Measured via correlation spectroscopy (11.1 °C). |
| Solid Ice Correlation Time (T2*) | 46 ± 11 | ”s | Measured via correlation spectroscopy (-8.8 °C). |
| NV Zero-Field Splitting (D) (Room Temp) | 2870.26 | MHz | Measured at 19 °C. |
| NV Zero-Field Splitting (D) (Low Temp) | 2871.53 | MHz | Measured at 11.1 °C. |
| Temperature Sensitivity (dD/dT) | -87 ± 12 | kHz/K | Used for in situ temperature monitoring. |
| Estimated Detection Volume Sensitivity | 2.2 x 10-22 | L | Sensitivity for free water at 6 nm depth (approx. 7000 molecules). |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a specialized quantum sensing setup combining NV center initialization, microwave control, and cryogenic cooling to probe the nanoscale water layer.
- NV Center Fabrication: Shallow NV centers were created in a diamond thin film using 5 keV 14N+ ion implantation, followed by high-vacuum annealing at 800 °C to activate the defects.
- Surface Functionalization: The diamond surface was chemically treated using a three-acid mixture (concentrated sulfuric, nitric, and perchloric acids) and piranha solution to oxidize the surface groups to hydroxyls, ensuring a highly hydrophilic surface for stable water adsorption.
- Experimental Setup: The diamond was mounted adjacent to a coplanar waveguide and sealed with a glass sheet, creating a small gap (approx. 10 ”m) filled with sample water. The assembly was placed on a copper heat sink connected to a semiconductor cooler.
- Cryogenic Control: The sample temperature was actively controlled using the semiconductor cooler, allowing the temperature to be reduced below -10 °C within a protective nitrogen gas environment.
- In Situ Thermometry (ODMR): The local temperature was monitored non-invasively by measuring the NV center zero-field splitting (D) via Optically Detected Magnetic Resonance (ODMR), leveraging its known temperature dependence (dD/dT = -87 kHz/K).
- Nanoscale NMR Acquisition: Proton NMR spectra were acquired using the NV center electron spin coherence. The periodic dynamic decoupling (PDD) pulse sequence was applied to the NV spin, transferring coherence to the nuclear spins, and the resulting signal was read out optically.
- Phase Dynamics Measurement (Correlation Spectroscopy): The solid and liquid phases were differentiated using correlation spectroscopy, which measures the nuclear spin correlation time (T2*). This sequence involves two PDD periods separated by a free evolution time t, allowing the measurement of how quickly the nuclear spins decouple from the NV sensor due to molecular motion (diffusion in liquid, static dipole interaction in solid).
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to perform non-invasive, high-resolution sensing of molecular dynamics and temperature simultaneously at the nanoscale opens doors for several high-value engineering and scientific applications.
- Quantum Sensing and Metrology:
- Development of highly localized, multi-parameter quantum sensors capable of measuring magnetic fields, temperature, and strain simultaneously within confined volumes.
- Creating robust, room-temperature sensors for complex environments (e.g., high pressure, corrosive media).
- Nanoscale Fluid Dynamics and Tribology:
- Studying the behavior and phase transitions of confined fluids (e.g., lubricants, coolants, or electrolytes) at solid interfaces, critical for micro-electromechanical systems (MEMS) and advanced bearing design.
- Biological and Biomedical Research:
- Probing the dynamics of water and other molecules near biological interfaces, such as cell membranes or protein surfaces, providing insight into hydration shells and biological function where traditional NMR is insufficient.
- Catalysis and Surface Chemistry:
- Investigating the structure and dynamics of adsorbed reactants and intermediates on catalytic surfaces under realistic operating conditions, aiding in the design of more efficient catalysts.
- Microfluidics and Lab-on-a-Chip Devices:
- Integrating NV sensors into microfluidic platforms to monitor chemical reactions, mixing, and phase separation in real-time within confined channels.
View Original Abstract
Water is one of the most important substances in the world. It is a crucial issue to study the dynamics of water molecules at interfaces or in the confined systems. In recent years, the emerging magnetic resonance technique based on nitrogen-vacancy (NV) center has allowed us to observe the nanoscale nuclear magnetic signal and temperature simultaneously. Here we succeed in measuring the nuclear magnetic resonance (NMR) signals of nanoscale solid and liquid water on diamond surface by NV center, and observing the solid-liquid phase transition of these nano-water by temperature control. This work demonstrates that the nano-NMR technique based on NV centers can probe the dynamics behavior of nanoscale materials effectively, providing a new way for studying the nanoscale confined systems.