Diamond phase in space and the possibility of its spectroscopic detection
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-02-01 |
| Journal | Physics-Uspekhi |
| Authors | A. A. Shiryaev |
| Institutions | Frumkin Institute of Physical Chemistry and Electrochemistry |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Spectroscopic Detection Focus: This review evaluates Infrared (IR) absorption and Photoluminescence (PL) spectroscopy as the most promising methods for detecting the diamond phase of carbon (nanodiamonds, NDs) in space, particularly focusing on features observed in meteoritic samples.
- Key Spectroscopic Signature (Luminescence): The negatively charged Silicon-Vacancy (SiV-) defect, peaking at 7370 A, is the only luminescing point defect reliably observed in real meteoritic nanodiamonds. Its stability and high quantum yield make it ideal for astronomical detection, provided the grains are cooler than ~450 K.
- Key Spectroscopic Signature (IR): IR spectroscopy detects C-H bonds on the surface of ND grains (bands at 3.43 and 3.53 ”m). This method is effective for observing relatively large, hot grains (800-1000 K) in protoplanetary disks, but less suitable for smaller, cold grains.
- Nanodiamond Characteristics: Meteoritic nanodiamonds are extremely small (median size 2.6-2.8 nm) and contain high concentrations of impurities, notably Nitrogen (1-4 at.%) and surface-bound Hydrogen (20-40 at.%).
- Formation Mechanism: Gas-phase deposition (CVD-like process) is considered the most efficient formation mechanism in space, requiring non-equilibrium conditions and extremely rapid cooling (tens of milliseconds) to prevent the newly formed diamond from graphitizing.
- NV Defect Limitations: Nitrogen-Vacancy (NV) centers, popular in laboratory diamond, are deemed unlikely targets for astronomical detection due to their strong size dependence, low probability of formation in small grains (<50 nm), and absence in studied meteoritic samples.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nanodiamond Grain Size (Median) | 2.6-2.8 | nm | Extracted from meteorites (range 1-10 nm) |
| Macrodiamond Density | 3.51 | g/cm3 | Crystallographic density of diamond |
| Nitrogen Concentration (Bulk ND) | 1-4 | at.% | Routinely found in meteoritic nanodiamonds |
| Hydrogen Concentration (Bulk ND) | 20-40 | at.% | Primarily surface-bound impurity |
| SiV- Luminescence Peak (ZPL) | 7370 | A | Zero-phonon line of the silicon-vacancy defect |
| SiV- Maximum Operating Temperature | ~450 | K | Constraint for observable luminescence intensity |
| Hot ND Emission Temperature | 800-1000 | K | Temperature range for detectable IR C-H emission |
| C-H Vibration Band (IR) | 3.43 and 3.53 | ”m | Surface C-H vibrations detected in protoplanetary disks |
| Graphite-Diamond Conversion Pressure | ~18 to ~33 | GPa | Required for shock-induced transformation of sp2-carbon |
| Required Cooling Time (Gas Phase) | Tens of | milliseconds | Necessary to cool NDs from >2000 °C to <600 °C |
| A-Defect Formation Activation Barrier | ~4.5 | eV | Nitrogen diffusion barrier required for A-defect formation |
Key Methodologies
Section titled âKey MethodologiesâThe study reviews four primary mechanisms for diamond formation and two key spectroscopic methods for characterization:
Diamond Formation Mechanisms
Section titled âDiamond Formation Mechanismsâ- High Pressure-High Temperature (HPHT) Synthesis:
- Conditions: High static pressures (typically 4-5 GPa) and high temperatures (T > 900 °C).
- Relevance: Used for industrial diamond synthesis; less plausible for presolar nanodiamonds, except possibly for microdiamonds found in ureilites (shock transformation is favored).
- Dynamic PT-parameters (Shock Waves):
- Conditions: High dynamic pressures (18-33 GPa) causing direct conversion of sp2-carbon (graphite).
- Requirement: Requires extremely rapid cooling (tens of milliseconds) to prevent newly formed diamond from reverting to graphite.
- Deposition from Gas Phase (CVD/PVD):
- Conditions: Metastable growth from gaseous hydrocarbons (e.g., CH4, C2H2) activated by plasma or heat, often requiring atomic hydrogen/oxygen to etch sp2-carbon.
- Relevance: Considered the most efficient mechanism for nanodiamond formation in space, consistent with the structural features of meteoritic NDs. High growth rates facilitate high nitrogen incorporation.
- Radiation-Induced Transformation:
- Mechanism: Irradiation of carbonaceous material (like carbon onions) by heavy ions, electrons, or high-energy photons (UV/X-rays).
- Result: Internal layers shrink, creating pressure sufficient to stabilize the diamond phase.
Spectroscopic Detection Methods
Section titled âSpectroscopic Detection Methodsâ- Infrared (IR) Spectroscopy:
- Target: Surface-bound functional groups, primarily C-H bonds (3.43 and 3.53 ”m).
- Application: Detection of hot (800-1000 K), relatively large ND grains in astronomical objects (e.g., Herbig stars).
- Limitation: Lattice absorption (nitrogen defects) is generally absent or masked in nanodiamonds.
- Photoluminescence (PL) Spectroscopy:
- Target: Point defects within the diamond lattice.
- Key Finding: Only the SiV- defect (7370 A) is observed in meteoritic NDs.
- Application: Detection of cold nanodiamonds (T < 450 K) in space, offering a phase-specific, narrow-line signature.
Commercial Applications
Section titled âCommercial ApplicationsâThe fundamental understanding of nanodiamond structure, defects, and synthesis mechanisms derived from this research supports several high-tech commercial applications:
- Quantum Sensing and Computing: The SiV- defect is a leading candidate for solid-state quantum emitters. Its confirmed presence and photostability in small NDs (even <2 nm) are critical for developing nanoscale quantum sensors (e.g., magnetometers, thermometers) and quantum memory devices.
- Advanced Coatings and Films (CVD): Insights into gas-phase deposition and the role of impurities (N, H) are directly applicable to optimizing Chemical Vapor Deposition (CVD) processes for manufacturing high-quality, defect-engineered diamond films for electronics and optics.
- High-Performance Materials: Nanodiamonds are used commercially as superior additives in lubricants, polishing slurries, and composite materials due to their extreme hardness and small size (1-10 nm range).
- Biomedical Imaging and Drug Delivery: The ability to functionalize the surface of NDs with hydrogen-containing groups (C-H bonds) is essential for creating biocompatible nanocarriers used in targeted drug delivery and fluorescent bioimaging.
- High-Power Electronics: Control over nitrogen incorporation (1-4 at.%) and defect formation is crucial for producing diamond substrates used in high-power, high-frequency electronic devices where thermal management is paramount.
View Original Abstract
The eventual presence of the diamond carbon allotrope in space is discussed\nin numerous theoretical and experimental studies. The review summarizes the\nprincipal mechanisms of nanodiamond formation and experimental results of\nspectroscopic and structural investigations of nano- and microdiamonds from\nmeteorites. The size dependence of diamond spectroscopic properties is\ndiscussed. Infrared spectroscopy allows detection of C-H bonds on surfaces of\nhot nanodiamond grains. Spectroscopic observation of nitrogen-related point\ndefects in nanodiamonds is very challenging; moreover, such defects have never\nbeen observed in nanodiamonds from meteorites. At the same time,\nphotoluminescence and, eventually, absorption of some impurity-related defects,\nin particular, of the silicon-vacancy (SiV) center, observed in real meteoritic\nnanodiamonds opens the possibility of diamond detection in astronomical\nobservations.\n