Imaging thermal conductivity with nanoscale resolution using a scanning spin probe

At a Glance

Metadata	Details
Publication Date	2015-11-20
Journal	Nature Communications
Authors	Abdelghani Laraoui, Halley Aycock-Rizzo, Yang Gao, Xi Lu, Elisa Riedo
Institutions	City College of New York, Georgia Institute of Technology
Citations	106
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nanoscale Thermal Imaging via NV Centers

Reference: Laraoui, A. et al. Imaging thermal conductivity with nanoscale resolution using a scanning spin probe. Nat. Commun. 6:8954 (2015).

Executive Summary

This research successfully demonstrates a novel technique for imaging thermal conductivity with nanoscale spatial resolution (approaching 10 nm) by leveraging the unique properties of the Nitrogen-Vacancy (NV) center in diamond.

Core Achievement: Articulation of Atomic Force Microscopy (AFM) and confocal microscopy to use a diamond-nanocrystal-hosted NV center as a local, high-sensitivity temperature sensor attached to a heated silicon tip.
Material Advantage: The high thermal conductivity ($\kappa$) and minuscule mass of the diamond host are critical, enabling an exceptionally fast thermal time response ($\tau_a = 184$ µs), essential for probing transient heat dynamics.
Resolution & Sensitivity: The technique achieved nanoscale resolution, mapping the thermal conductivity of phantom microstructures (18 nm gold film on sapphire) and detecting subtle variations correlated with surface contamination.
Methodology: Thermal changes are monitored via Optically Detected Magnetic Resonance (ODMR), tracking the temperature-dependent shift of the NV spin resonance frequency.
6CCVD Value Proposition: Replication and extension of this high-resolution thermometry requires high-purity Single Crystal Diamond (SCD) with long spin coherence times ($t_{2NV}$) to maximize detection sensitivity, a core capability of 6CCVD.
Future Applications: The approach is highly promising for investigating phonon dynamics in nanostructures, characterizing heterogeneous phase transitions, and mapping hot spots in integrated semiconductor devices.

Technical Specifications

The following hard data points were extracted from the research paper, detailing the operational parameters and measured results of the NV-assisted thermal scanning probe.

Parameter	Value	Unit	Context
Spatial Resolution Limit	10	nm	Defined by the AFM tip radius
Heater Temperature ($T_h$) Range	300 - 550	K	Operational range tested
Maximum Tip Temperature ($T_t$)	500	K	Maximum temperature achieved
Contact Cooling Drop	~100	K	Observed $T_t$ drop when contacting bulk diamond at $T_h = 500$ K
Thermal Time Constant ($\tau_a$)	184	µs	Characteristic response time of the tip/nanocrystal system
NV Readout Time ($t_r$)	~1	µs	Ultimate time resolution limit for spin readout
Gold Film Thickness	18	nm	Thickness of the patterned test structure on sapphire
Measured Gold Film $\kappa_s$	230 ± 20	W m^-1 K^-1	Thermal conductivity measured for the 18 nm film
Bulk Gold $\kappa_{bulk}$	314	W m^-1 K^-1	Accepted value for comparison
Bulk Diamond $\kappa_{SCD}$	~2 x 10³	W m^-1 K^-1	Used as the highest thermal conductivity reference substrate
Optimal Heater Temperature ($T_{h}^{(opt)}$)	620 - 660	K	Calculated range for maximum sensitivity
Optimal Tip Temperature ($T_{t}^{(opt)}$)	~570	K	Corresponding tip temperature at optimal sensitivity

Key Methodologies

The experiment relies on precise material engineering and the integration of multiple high-resolution techniques.

Probe Fabrication: A diamond nanocrystal hosting a single NV center was attached (grafted via AFM scanning and Van der Waals forces) to the apex of a thermal AFM cantilever.
Cantilever Design: The thermal cantilever was constructed from n-doped, electrically conductive silicon, featuring an intrinsic (undoped) silicon section above the tip apex to serve as a localized heater.
Heating Mechanism: An electrical current (up to 1 mA) was circulated through the cantilever arms using an external voltage source ($V_o$) and series resistor ($R_s = 2$ kΩ) to set the heater temperature ($T_h$).
Optical Setup: A high-numerical-aperture objective was used in a two-sided geometry to excite the NV center (Green laser, 1 µs pulse) and collect the fluorescence.
Thermal Sensing (ODMR): Microwave (MW) pulses (500 ns) were applied via a wire on the sample surface. The NV spin state was read out via fluorescence, monitoring the shift in the NV resonance frequency (near 2.8 GHz) to determine the local tip temperature ($T_t$).
Thermal Imaging: The AFM tip was scanned across the substrate (e.g., 18 nm Au film on sapphire). The contact-induced drop in $T_t$ was recorded at each position to generate a thermal conductivity map.
Transient Measurement: A sharp voltage pulse (4 ns rise/decay time) was applied to the heater to measure the system’s thermal response time ($\tau_a$).

6CCVD Solutions & Capabilities

This research highlights the critical role of high-quality diamond material in achieving high-sensitivity nanoscale thermometry. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom fabrication services required to replicate, optimize, and extend this groundbreaking work.

Applicable Materials

The paper explicitly notes that improved sensitivity requires diamond crystals of higher purity and longer NV spin transverse relaxation times ($t_{2NV}$).

Research Requirement	6CCVD Solution	Technical Advantage
High-Purity NV Host	Optical Grade Single Crystal Diamond (SCD)	Ultra-low nitrogen content ensures long $t_{2NV}$ (approaching 200 µs), significantly enhancing the signal-to-noise ratio and detection sensitivity ($\eta_{\kappa_s}$) for thermal sensing.
Integrated Tip Platforms	SCD Substrates & Thin Films	SCD films (0.1 µm - 500 µm) can be overgrown or bonded onto customer-supplied silicon cantilevers, providing a robust, high-thermal-conductivity platform for precision NV implantation (as suggested for future work).
Electrothermal Applications	Boron-Doped Diamond (BDD)	For extending the technique to characterize hot spots in conductive materials or semiconductor junctions, BDD offers tunable electrical conductivity combined with superior thermal and chemical stability.

Customization Potential

The success of this technique relies on precise material dimensions and interface engineering. 6CCVD offers full customization capabilities to meet the demands of advanced scanning probe research.

Custom Dimensions: We provide SCD and PCD plates/wafers up to 125 mm, and substrates up to 10 mm thick, allowing for the fabrication of custom AFM cantilever bodies or robust reference substrates.
Precision Polishing: Achieving reliable thermal contact requires ultra-smooth surfaces. 6CCVD guarantees polishing to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, minimizing interface thermal impedance.
Custom Metalization: The experiment required metal contacts (e.g., Au on Al₂O₃) for the MW source and heater connections. 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu for creating reliable ohmic contacts or patterned test structures (like the 18 nm gold film used in the study).
Laser Cutting & Shaping: We offer precision laser cutting services for creating custom geometries, such as the V-shaped cantilever arms or specific substrate shapes required for two-sided optical access.

Engineering Support

The observed discrepancies between bulk and thin-film thermal conductivity (e.g., 18 nm gold film measured at 230 W m^-1 K^-1 vs. bulk 314 W m^-1 K^-1) highlight the complexity of nanoscale heat transport. 6CCVD’s in-house PhD team specializes in diamond material science and thermal management. We can assist researchers with:

Material selection and optimization for similar Nanoscale Thermal Transport projects.
Designing diamond films for optimal NV center integration, maximizing $t_{2NV}$ and photon collection efficiency ($\alpha(T)$).
Consultation on interface engineering to minimize thermal resistance between the diamond probe and the cantilever body.

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

View Original Abstract

Abstract The ability to probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. The small mass and high thermal conductivity of the diamond host make the time response of our technique short, which we demonstrate by monitoring the tip temperature upon application of a heat pulse. Our approach promises multiple applications, from the investigation of phonon dynamics in nanostructures to the characterization of heterogeneous phase transitions and chemical reactions in various solid-state systems.

Tech Support

Original Source

DOI: https://doi.org/10.1038/ncomms9954