Burning and graphitization of optically levitated nanodiamonds in vacuum
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-02-22 |
| Journal | Scientific Reports |
| Authors | A. T. M. A. Rahman, A. C. Frangeskou, Kim Ms, S. Bose, G.W. Morley |
| Institutions | Imperial College London, University College London |
| Citations | 81 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Levitated Quantum Systems
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Levitated Quantum SystemsâExecutive Summary
Section titled âExecutive SummaryâThis research investigates the thermal stability and degradation mechanisms (burning and graphitization) of optically levitated Nitrogen-Vacancy (NV) nanodiamonds under vacuum, identifying critical material limitations for quantum applications.
- Thermal Degradation: Levitated nanodiamonds absorb 1064 nm trapping laser light, leading to high internal temperatures ($T_i$) reaching up to $\approx 800$ K at 20 mB pressure.
- Material Failure Modes: In air, nanodiamonds burn ($T_i \approx 750$ K). In a nitrogen environment, burning is prevented, but graphitization occurs below $\approx 10$ mB ($T_i \approx 800$ K).
- Root Cause: The excessive heating and subsequent degradation are primarily attributed to the presence of amorphous carbon and impurities on the surface of the commercial HPHT nanodiamonds used.
- Quantum Impact: Internal temperatures exceeding 625 K severely degrade the NV- center spin coherence time, rendering the material unsuitable for high-vacuum quantum sensing and superposition experiments.
- Solution Requirement: The authors explicitly suggest that purer nanodiamonds are necessary to mitigate laser absorption and thermal instability, directly pointing toward the advantages of high-purity MPCVD diamond.
- Methodological Advance: A novel technique is demonstrated for in situ determination of nanoparticle size by exploiting the measured damping rate ($\gamma$CM) of the levitated object.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results regarding the levitated nanodiamonds and operating conditions:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Wavelength | 1064 | nm | Optical trapping source |
| Numerical Aperture (NA) | 0.80 | - | Microscope objective |
| Nanodiamond Type | ND-NV-100 nm | - | HPHT synthesized, nominal 100 nm size |
| NV- Center Count | $\approx 500$ | centers | Per nanodiamond |
| Internal Temperature ($T_i$) (Air, 380 mW) | $\approx 750$ | K | Maximum measured $T_i$ in air at 20 mB |
| Internal Temperature ($T_i$) (N2, Max Power) | $\approx 800$ | K | Maximum measured $T_i$ in nitrogen at 20 mB |
| Graphitization Onset Pressure (N2) | $\approx 10$ | mB | Pressure threshold for size reduction in nitrogen |
| NV- Coherence Degradation Onset | 625 | K | Temperature where spin coherence time decreases |
| Diamond Melting Point | $\ge 4000$ | K | Required temperature (rules out melting as failure mode) |
| Estimated Diameter (Air, 180 mW, 10 mB) | $\approx 41$ | nm | Calculated ultimate size after burning/evaporation |
| Damping Rate ($\gamma$CM) (180 mW, 20 mB) | $2.18 \times 10^{5}$ | radian/s | Used for in situ size calculation |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized an optical tweezer setup combined with vacuum control and spectral analysis to monitor the thermal and physical behavior of the levitated nanodiamonds.
- Optical Tweezer Setup: A 1064 nm laser beam was focused using a NA = 0.80 microscope objective to create a diffraction-limited dipole trap within a vacuum chamber.
- Sample Preparation: HPHT nanodiamonds (nominal 100 nm, $\approx 500$ NV- centers) were sonicated for $\approx 10$ minutes to prevent agglomeration, then injected into the chamber via a nebulizer.
- Environmental Control: Experiments were conducted by gradually evacuating the chamber from atmospheric pressure down to $\approx 2$ mB, comparing behavior in standard air versus a high-purity nitrogen environment (purged 15 times).
- Internal Temperature Determination: The internal temperature ($T_i$) was extracted using a Brownian motion-based technique involving the analysis of the Power Spectral Density (PSD) of the particleâs motion, assuming full thermal accommodation ($T_i = T_{em}$).
- Size Determination: The in situ size of the levitated particle was calculated using the measured damping rate ($\gamma$CM) as a function of pressure, combined with Rayleigh scattering intensity measurements.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights a critical need for ultra-high purity diamond materials to overcome thermal instability in levitated quantum systems. 6CCVDâs expertise in MPCVD growth directly addresses the limitations of the HPHT materials used in this study.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and ExtensionâThe primary requirement is diamond material with minimal amorphous carbon and metallic impurities to reduce 1064 nm absorption.
| Application Context | Recommended 6CCVD Material | Key Material Specification |
|---|---|---|
| High-Coherence Quantum Sensing | Optical Grade Single Crystal Diamond (SCD) | Ultra-low nitrogen (N) and boron (B) content; Ra < 1 nm polish; minimal defects/impurities to prevent laser absorption and heating. |
| Mesoscopic Superpositions | High-Purity Polycrystalline Diamond (PCD) | Plates/wafers up to 125mm size; high thermal conductivity; suitable for large-scale processing into uniform nanoparticles. |
| Controlled NV- Doping | Custom Doped SCD/PCD | Precise nitrogen incorporation during MPCVD growth to control NV- center density ($\approx 500$ centers/particle) and optimize spin coherence time above 625 K. |
Customization Potential for Levitated Systems
Section titled âCustomization Potential for Levitated Systemsâ6CCVD offers specialized processing capabilities essential for advancing levitated quantum experiments beyond the limitations of commercial HPHT powders.
| Research Requirement | 6CCVD Customization Capability | Benefit to Researcher |
|---|---|---|
| Uniform Particle Size | Precision Laser Cutting & Milling | Enables the creation of highly uniform micro- or nanoparticles from SCD/PCD wafers, eliminating the polydispersity noted in the paper (Fig. 4a). |
| High-Vacuum Integration | Custom Metalization (Au, Pt, Ti, W, Cu) | Internal capability to deposit thin metal films for electrical gating, charge control, or integration into micro-electromechanical systems (MEMS) required for advanced levitation control. |
| Substrate Thickness | SCD/PCD Substrates up to 10 mm | Provides robust, high-purity diamond platforms for building the vacuum chamber optics and mechanical supports, leveraging diamondâs superior thermal and mechanical properties. |
| Surface Quality | Ultra-Smooth Polishing | SCD polished to Ra < 1 nm, ensuring minimal surface defects that could contribute to charge instability or scattering losses in the optical trap. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in optimizing MPCVD growth parameters for specific quantum applications. We can assist researchers in selecting the ideal material specifications (purity, doping level, dimensions) required to replicate or extend this research, specifically focusing on materials that maintain $T_i$ below the critical 625 K threshold necessary for stable NV- spin coherence.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract A nitrogen-vacancy (NV â ) centre in a nanodiamond, levitated in high vacuum, has recently been proposed as a probe for demonstrating mesoscopic centre-of-mass superpositions and for testing quantum gravity. Here, we study the behaviour of optically levitated nanodiamonds containing NV â centres at sub-atmospheric pressures and show that while they burn in air, this can be prevented by replacing the air with nitrogen. However, in nitrogen the nanodiamonds graphitize below â10 mB. Exploiting the Brownian motion of a levitated nanodiamond, we extract its internal temperature ( T i ) and find that it would be detrimental to the NV â centreâs spin coherence time. These values of T i make it clear that the diamond is not melting, contradicting a recent suggestion. Additionally, using the measured damping rate of a levitated nanoparticle at a given pressure, we propose a new way of determining its size.