Lock-in Thermography Using Diamond Quantum Sensors

At a Glance

Metadata	Details
Publication Date	2022-12-12
Journal	Journal of the Physical Society of Japan
Authors	K. Ogawa, Moeta Tsukamoto, Kento Sasaki, Kensuke Kobayashi
Institutions	The University of Tokyo
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Lock-in Thermography using Diamond Quantum Sensors

Reference: Ogawa et al., Lock-in thermography using diamond quantum sensors (arXiv:2212.07616v1, 2022).

Executive Summary

This research successfully demonstrates the application of Nitrogen-Vacancy (NV) centers in nanodiamonds for non-contact, micrometer-scale lock-in thermography, a technique highly relevant to thermal management in nanoelectronics and quantum sensing.

Core Achievement: Visualization and quantitative measurement of thermal diffusion and diffusivity in materials (glass coverslip, Teflon) using NV-center Optically Detected Magnetic Resonance (ODMR).
High Sensitivity: Achieved a temperature sensitivity of (297 ± 53) mK/√Hz, demonstrating the viability of NV centers as highly sensitive quantum thermometers.
Quantitative Results: Thermal diffusivity values derived from temperature oscillation amplitude (e.g., 3.5 ± 1.5 x 10^-7 m²/s for glass) show quantitative agreement with established literature values.
Non-Contact Sensing: The method relies on spreading nanodiamonds on the sample surface, eliminating invasive physical contacts (like lead wires) and enabling analysis of diverse materials (insulators, semiconductors, metals).
Future Potential: The technique is scalable toward nanometer-scale spatial resolution and integration with advanced quantum control methods for high-frequency (kHz-GHz band) thermal dynamics visualization.
6CCVD Relevance: The limitations identified (non-uniformity, spatial resolution) directly highlight the need for 6CCVD’s high-quality Single Crystal Diamond (SCD) substrates and advanced fabrication services for next-generation quantum thermometry devices.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Nanodiamond Particle Size	50	nm	Used for surface dispersion
Spread ND Layer Thickness	212 ± 77	nm	Estimated thickness, approx. 4 layers
Excitation Laser Wavelength	515	nm	Green laser source
Laser Output Power	150	mW	Used for NV center excitation
Microwave Frequency (ZFS)	2.87	GHz	Zero-Field Splitting center frequency
AC Heating Voltage Amplitude	3.2	V	Applied to 10 Ω resistor heater
Thermal Oscillation Frequency	0.5	Hz	Resulting lock-in frequency
Temperature Sensitivity	297 ± 53	mK/√Hz	Estimated sensitivity per pixel (100x100 pixel region)
Thermal Diffusivity (Glass)	3.5 ± 1.5	10^-7 m²/s	Derived from amplitude fit
Thermal Diffusivity (Teflon)	1.1 ± 0.57	10^-7 m²/s	Derived from amplitude fit
Spatial Resolution (FOV)	106 x 140	µm	Field of View of the CMOS camera
DC Heating Temperature Rise	~27	K	Measured via ZFS shift (2 MHz shift)

Key Methodologies

The experiment utilized a combination of optical, microwave, and thermal control techniques integrated with phase-sensitive lock-in detection.

Sample Preparation: Nanodiamonds (50 nm particle size) were dispersed onto the sample surface (glass coverslip or Teflon) via spin coating at 1000 RPM, resulting in a non-uniform layer thickness of approximately 212 nm.
Thermal Setup: Heat was generated using a 10 Ω chip resistor (heater) placed on a Printed Circuit Board (PCB) with an 18 µm copper foil layer, ensuring thermal contact via thermal grease. The sample was placed in a central cavity.
Optical Detection: A 515 nm laser (150 mW) irradiated the nanodiamonds through a 100x objective (NA = 0.7). NV center fluorescence (650-800 nm) was collected and focused onto a CMOS camera (772 x 1032 pixels).
Microwave (MW) Control: A 2.87 GHz MW signal was amplified (45 dB) and delivered via a circular antenna (1 mm diameter) to perform ODMR measurements.
Four-Point Measurement Protocol: Instead of acquiring the full ODMR spectrum, the temperature deviation (δT) was calculated efficiently using the Photoluminescence (PL) contrast measured at four specific microwave frequencies (f₁, f₂, f₃, f₄) selected on the slopes of the ODMR spectrum.
Lock-in Thermography: An AC voltage (3.2 V amplitude, 0.25 Hz frequency) was applied to the heater, generating 0.5 Hz thermal oscillations. Time-resolved temperature data was fitted to a sinusoidal curve to extract the spatial distribution of the amplitude and phase.
Thermal Diffusivity Calculation: Thermal diffusivity (α) was deduced by fitting the exponential decay of the temperature oscillation amplitude and the linear evolution of the phase with distance (x) from the heater, based on the one-dimensional heat diffusion equation.

6CCVD Solutions & Capabilities

The research highlights the immense potential of NV-center thermometry but also exposes limitations related to material quality, specifically the non-uniformity of nanodiamond layers and the resulting spatial resolution constraints. 6CCVD provides the advanced diamond materials and fabrication services necessary to overcome these hurdles and transition this technology into robust, integrated quantum devices.

Applicable Materials for Advanced Quantum Thermometry

To replicate this research with superior performance (higher spatial resolution, better uniformity, and enhanced quantum coherence), 6CCVD recommends transitioning from dispersed nanodiamonds to engineered thin films and substrates:

6CCVD Material	Application & Advantage	Specifications
Optical Grade SCD	Ultimate Resolution & Coherence. Ideal for creating highly uniform, shallow NV layers via ion implantation or delta-doping. Essential for achieving nanometer-scale spatial resolution and integrating quantum control structures.	Thickness: 0.1 µm - 500 µm. Polishing: Ra < 1 nm (essential for high-fidelity optical setups).
High-Purity PCD Wafers	Large-Area Sensor Arrays. Suitable for scaling up the lock-in thermography technique across large samples (e.g., 100 mm wafers). Offers excellent thermal properties (high thermal conductivity) for heat management studies.	Dimensions: Plates/wafers up to 125 mm. Thickness: 0.1 µm - 500 µm. Polishing: Ra < 5 nm (Inch-size).
Boron-Doped Diamond (BDD)	Integrated Heating/Sensing. BDD films can serve as integrated resistive heaters or electrodes, eliminating the need for external copper foil/resistors, simplifying the experimental setup, and improving thermal contact uniformity.	Custom doping levels (p-type semiconductor). Thickness: 0.1 µm - 500 µm.

Customization Potential for Integrated Devices

The experimental setup relies on external components (PCB, copper foil, MW antenna). 6CCVD’s fabrication capabilities enable the integration of these functions directly onto the diamond substrate, leading to more stable and scalable quantum sensors.

Custom Metalization: The research requires precise microwave delivery (2.87 GHz). 6CCVD offers in-house deposition of standard and custom metal stacks (Au, Pt, Pd, Ti, W, Cu) for fabricating on-chip microwave antennas (e.g., coplanar waveguides) directly on SCD or PCD substrates, crucial for advanced quantum control (kHz-GHz band sensing).
Precision Dimensions: 6CCVD provides custom plates and wafers up to 125 mm in diameter, allowing researchers to scale the lock-in thermography method from small lab samples to industrial-sized wafers. Substrates up to 10 mm thick are available for robust thermal studies.
Surface Engineering: Achieving Ra < 1 nm polishing on SCD is critical for minimizing optical scattering and ensuring high-quality imaging necessary for improving the Signal-to-Noise Ratio (SNR) and spatial resolution beyond the current micrometer scale.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD growth and post-processing optimization for quantum applications. We can assist researchers in optimizing material selection for similar NV-Center Thermometry projects, specifically addressing the challenges of:

NV Density Control: Tailoring nitrogen concentration during growth or post-growth implantation to maximize PL contrast and sensitivity.
Uniformity: Providing highly uniform SCD films to eliminate the non-uniformity issues observed with spin-coated nanodiamonds, thereby improving the accuracy of thermal diffusivity measurements derived from phase analysis.
Integrated Device Design: Consulting on the design and fabrication of metalized structures for efficient microwave delivery and integrated heating elements on diamond substrates.

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

View Original Abstract

Precise measurement of temperature distribution and thermal behavior in\nmicroscopic regions is critical in many research fields. We demonstrate lock-in\nthermography using nitrogen-vacancy centers in diamond nanoparticles. We\nsuccessfully visualize thermal diffusion in glass coverslip and Teflon with\nmicrometer resolution and deduce their thermal diffusivity. By spreading\ndiamond nanoparticles over the sample surface, temperature variation can be\nmeasured directly without any physical contact, such as lead wires, making it\npossible to visualize the micrometer-scale thermal behavior of various\nmaterials.\n

Tech Support

Original Source

DOI: https://doi.org/10.7566/jpsj.92.014002

References

2001 - Electrons and Phonons: The Theory of Transport Phenomena in Solids [Crossref]
2010 - Lock-in Thermography: Basics and Use for Evaluating Electronic Devices and Materials [Crossref]