Diamond with Sp2-Sp3 composite phase for thermometry at Millikelvin temperatures

At a Glance

Metadata	Details
Publication Date	2024-05-08
Journal	Nature Communications
Authors	Jianan Yin, Yan Yang, Mulin Miao, Jiayin Tang, Jiali Jiang
Institutions	City University of Hong Kong, Chinese Academy of Sciences
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond for Millikelvin Thermometry

This document analyzes the research detailing the synthesis and performance of a novel sp²-sp³ Composite Phase Diamond (CPD) for cryogenic temperature sensing. The findings present a significant opportunity for 6CCVD to supply high-quality Polycrystalline Diamond (PCD) precursors and custom fabrication services to the quantum computing and low-temperature physics sectors.

Executive Summary

The development of the sp²-sp³ Composite Phase Diamond (CPD) represents a breakthrough in cryogenic thermometry, offering a stable, highly sensitive sensor capable of operating near absolute zero.

Unprecedented Measurement Limit: The CPD achieved a theoretical temperature measurement limit of 1 mK, significantly surpassing traditional cryogenic thermometers (e.g., RuO₂, Germanium).
Broad Operating Range: The sensor exhibits a highly fitted Negative Temperature Coefficient (NTC) characteristic across an exceptionally wide range, from 1 mK up to 400 K.
Extreme Environment Stability: The CPD demonstrated remarkably low sensitivity to strong magnetic fields, with a resistance shift rate of only -3% at 2 K under 9 T, making it ideal for use in superconducting magnets (MRI, quantum systems).
Enhanced Thermal Robustness: The composite structure increased the onset oxidation temperature to 1163 K (compared to 948 K for original diamond), ensuring excellent thermal stability and repeatability after severe thermal shocks.
High Conductivity: The material exhibits an exceptional room temperature conductivity of 1.2 S·cm⁻¹, crucial for minimizing self-heating and ensuring proper operation at ultra-low temperatures.
Scalability Demonstrated: Successful fabrication was shown across multiple scales, including micrometer-scale probes (Ø=1 µm via FIB) and centimeter-scale bulk structures, confirming manufacturing viability.

Technical Specifications

The following hard data points were extracted from the research paper, highlighting the performance metrics of the CPD material.

Parameter	Value	Unit	Context
Lowest Temperature Measurement Limit	1	mK	Theoretical detection limit achieved via Expdec3 function fit extrapolation.
Operating Temperature Range	1 mK to 400	K	Broad range with monotonic Negative Temperature Coefficient (NTC).
R-T Curve Goodness of Fit (3 K to 400 K)	0.99999	R²	Coefficient of determination for the Expdec3 fitted curve.
R-T Curve Goodness of Fit (< 1 K)	0.99775	R²	Coefficient of determination for the Expdec3 fitted curve below 1 K.
Room Temperature Conductivity	1.2	S·cm⁻¹	Exceptional conductivity achieved via the sp² conductive network.
Magnetic Field Sensitivity (Shift Rate)	-3	%	Maximum resistance shift rate observed at 2 K under a 9 T magnetic field.
Onset Oxidation Temperature (CPD)	1163	K	Measured via TGA/DSC, demonstrating enhanced thermal stability.
Onset Oxidation Temperature (Original Diamond)	948	K	Baseline comparison for thermal stability enhancement.
Resistance Stability (Thermal Shock)	< 0.4	%	Resistance change rate after 10 thermal shocks (400 K to 77 K).
Probe Diameter Demonstrated	1	µm	Micrometer-scale probe fabricated using Focused Ion Beam (FIB).

Key Methodologies

The CPD material was synthesized using a straightforward, cost-efficient heat-treatment approach on synthetic diamond powder, resulting in the controlled formation of the sp²-sp³ composite phase.

Starting Material: Commercially available synthetic Type 1b diamond powder (80 µm particle size).
Slurry Preparation: Diamond powder mixed with various polymers and photoinitiators (e.g., acrylic acid ammonium salt, acrylamide, N, N’-Methylenebisacrylamide) and water.
3D Printing (DIW): Direct Ink Writing (DIW) 3D printing was used to form complex or bulk structures (centimeter-scale) with a line width of 0.4 mm.
Curing and Drying: Preliminary curing was performed using a 365 nm ultraviolet lamp, followed by drying at 80 °C for 4 hours.
Sintering (Phase Conversion): The samples were sintered in a tube furnace at 1250 °C for 1800 minutes (30 hours) under atmospheric pressure in an Ar atmosphere.

6CCVD Solutions & Capabilities

The successful replication and extension of this groundbreaking cryogenic thermometry research requires highly controlled diamond materials and precision fabrication capabilities. 6CCVD is uniquely positioned to serve this market with our expertise in MPCVD diamond synthesis and customization.

Applicable Materials

The CPD material is derived from synthetic diamond powder and relies on the controlled introduction of sp² phases within the sp³ matrix. 6CCVD offers the ideal precursor material for scaling this technology:

Polycrystalline Diamond (PCD) Substrates: We supply high-purity MPCVD PCD plates and wafers, which serve as excellent, scalable precursors for the heat-treatment process described. Our PCD material ensures the necessary structural uniformity for consistent sp²-sp³ phase formation.
Boron-Doped Diamond (BDD): For researchers exploring alternative NTC thermometry methods, 6CCVD offers BDD materials. BDD’s tunable electrical properties and inherent radiation hardness make it a strong candidate for cryogenic sensors, particularly in high-radiation environments or where controlled doping is preferred over phase composites.

Customization Potential

The paper highlights the need for sensors across multiple scales, from 1 µm probes to centimeter-scale bulk structures. 6CCVD’s capabilities directly address these fabrication requirements:

Research Requirement	6CCVD Capability	Technical Advantage
Large-Scale Precursors	Custom PCD plates/wafers up to 125 mm diameter.	Enables industrial scaling of the CPD synthesis process beyond laboratory-scale powder batches.
Micrometer/Bulk Sensor Fabrication	Precision laser cutting and shaping services. Thickness control for PCD from 0.1 µm to 500 µm (wafers) and substrates up to 10 mm.	Supports the creation of custom geometries, including thin-film sensors or bulk elements, necessary for integration into dilution refrigerators.
Electrical Interfacing	In-House Metalization: Custom deposition of Au, Pt, Pd, Ti, W, and Cu.	Essential for creating robust, low-resistance electrical contacts required for accurate mK-level resistance measurements in cryogenic environments.
Surface Quality	Advanced polishing services achieving Ra < 5 nm (Inch-size PCD).	Provides the necessary surface quality for subsequent lithography or FIB processing of micrometer-scale sensor elements.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing diamond properties for extreme environments. We offer consultation services to assist researchers in:

Material Selection: Choosing the optimal PCD grade and thickness to maximize the thermal stability and NTC characteristics of the resulting CPD.
Process Optimization: Advising on precursor material preparation and post-processing techniques (e.g., metalization adhesion, surface preparation) for similar cryogenic thermometry and quantum sensing projects.
Global Logistics: Ensuring reliable, secure global shipping (DDU default, DDP available) of sensitive diamond materials directly to research facilities worldwide.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-024-48137-z