Investigation of evaporation of sessile droplets using luminescent nano-probes and other applications of NV centers in diamond

At a Glance

Metadata	Details
Publication Date	2018-01-01
Journal	EPJ Web of Conferences
Authors	Taras Plakhotnik, Haroon Aman
Institutions	The University of Queensland
Analysis	Full AI Review Included

6CCVD Technical Analysis and Documentation

Research Paper: Investigation of evaporation of sessile droplets using luminescent nano-probes and other applications of NV centers in diamond (Plakhotnik and Aman, EPJ Web of Conferences 190, 02008 (2018))

Executive Summary

The research validates the critical role of diamond-based Nitrogen-Vacancy (NV) centers as robust, ultra-local probes for complex micro-fluidic and thermal environments, directly aligning with advanced sensor and bio-imaging applications.

Core Value Proposition: Diamond nanocrystals containing NV-centers function as highly stable, luminescent nano-probes capable of tracking dynamic processes (e.g., fluid flow) in small droplets (< 1 mm) with high fidelity.
Achieved Resolution: Demonstrated high spatial resolution, tracing a 35-nm diamond probe with approximately 20-nm accuracy.
Contradictory Fluid Dynamics: Experimental results contradicted established theoretical models, showing a constant velocity (11.4 µm/s) followed by constrained diffusion near the droplet rim, necessitating high-resolution diamond probes for accurate modeling.
Thermal Sensing Capability: Highlights the extreme sensitivity of NV centers to temperature, utilizing the ODMR frequency shift with a thermal gradient of 75 kHz/K, essential for ultra-local thermometry.
Application Relevance: The sessile droplet system serves as a reliable proxy for complex intracellular measurements, addressing the need for stable, non-photobleaching labels and sensitive local temperature sensors.
Market Need: This work supports the growing demand for high-ppurity diamond substrates required for scalable, high-yield fabrication of NV-center ensembles for next-generation quantum and biological sensors.

Technical Specifications

Parameter	Value	Unit	Context
Droplet Characteristic Dimension	< 1	mm	Across evaporating droplets
Nano-probe Material	NV-center Diamond	N/A	Used as luminescent label/thermometer
Nano-probe Size	35	nm	Diameter of tracked diamond crystal
Tracing Accuracy	≈ 20	nm	Spatial resolution of experimental method
Observed Constant Velocity	11.4	µm/s	Drift speed towards the droplet rim
Distance to Rim at Constrained Flow	≈ 2	µm	Velocity decrease observed within this distance of the rim
Position of Rim (Displacement)	≈ 21	µm	Displacement x corresponding to the rim position
NV Thermal Sensitivity (ODMR)	75	kHz/K	Gradient of resonance shift with crystal temperature
Simple Model Temp Difference (Cell)	< 1	mK	Estimated temperature gradient on a 100-nm scale
Experimental Local Temp Rise (Cell)	1	K	Reported local temperature rise (the “10⁵ gap”)

Key Methodologies

The investigation relied on the unique physical properties of diamond NV-centers embedded in nanocrystals to study micro-scale fluid dynamics and potential temperature effects.

Probe Synthesis and Selection: Utilizing ultra-small diamond nanocrystals (tens of nanometers or less) embedded with highly stable Nitrogen-Vacancy (NV) centers to prevent photo bleaching and function as robust luminescent labels.
Model System Setup: Depositing sessile micro-droplets (less than 1 mm across) on a solid substrate, incorporating the NV nano-probes into the fluid phase.
High-Resolution Tracking: Tracing the movement and position of individual 35-nm diamond nanocrystals over time to high accuracy (20 nm) to analyze fluid velocity profiles near the rim of the evaporating droplet.
NV Center Utilization for Dynamics: Exploiting the diamond lattice stability and NV center luminescence to obtain precise tracking data on constrained diffusion and liquid flow dynamics in steady liquid flow.
NV Center Utilization for Thermometry: Proposing the use of NV centers as ultra-local thermometers by measuring the thermal shift of either the ODMR frequency (75 kHz/K gradient) or the zero-phonon line (ZPL) in the luminescence spectra.

6CCVD Solutions & Capabilities

This research underscores the critical need for high-purity, low-defect diamond material, whether for bulk NV generation (SCD) or robust substrate integration (PCD). 6CCVD is positioned as the ideal partner to supply the necessary foundational diamond material and custom processing services required to advance this research from nano-probes to integrated diamond sensors.

Applicable Materials

To achieve high-yield, high-coherence NV centers required for reliable quantum sensing and bio-imaging applications, high-quality MPCVD diamond substrates are essential:

Research Requirement	6CCVD Recommended Material	Material Justification
High NV Center Coherence & Yield	Optical Grade Single Crystal Diamond (SCD)	SCD offers the lowest strain and highest purity necessary for deterministic NV-center implantation and annealing, maximizing thermal sensitivity and quantum coherence time.
Robustness & Large Area Integration	High Purity Polycrystalline Diamond (PCD)	Suitable for large-area heat spreading, sensor integration, or bulk mechanical support for micro-fluidic chips built upon the diamond platform (Plates up to 125mm).
Integrated Sensors (Future Work)	Boron-Doped Diamond (BDD)	For integration of electrochemical or micro-electrode sensors alongside NV thermometry in microfluidic systems. 6CCVD offers custom BDD resistivity.

Customization Potential

The advancement of micro-fluidic NV systems relies heavily on precision fabrication, which 6CCVD provides in-house:

Precision Substrates: 6CCVD provides SCD and PCD plates/wafers with custom dimensions and thickness (SCD/PCD from 0.1 µm to 500 µm), allowing researchers to select optimal thermal dissipation and optical clarity characteristics.
Ultra-Low Roughness Polishing: Achieving high-resolution optical access and reproducible fluid dynamics requires exceptional surface quality. 6CCVD guarantees ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for large-area PCD.
Integrated Device Metalization: Should the research move toward integrated on-chip ODMR sensing or micro-heater elements for thermal control, 6CCVD offers internal, high-tolerance metalization services, including Ti/Pt/Au, W, Cu, Pd, and others, deposited directly onto the diamond surface.

Engineering Support

NV-center integration and optimal substrate selection are highly complex, application-specific problems. 6CCVD provides comprehensive technical support:

Material Consultation: Our in-house PhD team specializes in material selection for quantum sensing applications, ensuring the chosen SCD or PCD grade meets the necessary purity and strain requirements for robust NV center generation and optimal thermal management.
Advanced Fabrication: We offer engineering assistance for researchers needing customized geometry (e.g., laser cutting or etching features) and precise thickness control required for micro-droplet or micro-fluidic experimentation.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The paper describes application of diamond nano crystals to research on dynamic processes in small (less than 1 mm across) evaporating droplets deposited on a solid substrate. Such droplets are used as a model system for testing proposed bio applications of nitrogen-vacancy centers in diamond. We demonstrate that a high spatial resolution of our methods reveals unexpected features of the evaporation and fluid mechanics in such droplets.

Tech Support

Original Source

DOI: https://doi.org/10.1051/epjconf/201819002008