Synthesis and Properties of Electrically Conductive/Nitrogen Grain Boundaries Incorporated Ultrananocrystalline Diamond (N-UNCD) Thin Films Grown by Microwave Plasma Chemical Vapor Deposition (MPCVD)
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-09-11 |
| Journal | Applied Sciences |
| Authors | Michelle Salgado-Meza, Guillermo MartĂnez-RodrĂguez, Pablo Tirado-CantĂș, Eliel Eduardo Montijo Valenzuela, Rafael GarcĂa |
| Institutions | Universidad de Hermosillo, Universidad Estatal de Sonora |
| Citations | 8 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research focuses on optimizing Microwave Plasma Chemical Vapor Deposition (MPCVD) parameters to maximize the electrical conductivity of Nitrogen-incorporated Ultrananocrystalline Diamond (N-UNCD) thin films.
- Record Conductivity Achieved: The highest electrically conductive N-UNCD films produced to date exhibited a resistivity of approximately 1 Ohm.cm. This is five to six orders of magnitude lower than undoped UNCD films (â„106 Ohm.cm).
- Optimal Growth Parameters: Maximum conductivity was achieved using a total plasma pressure of 100 mbar and a microwave power of 4500 W.
- Mechanism of Conduction: Electrical conductivity is induced by the incorporation of Nitrogen (N) atoms into the grain boundaries, which chemically react with C-atom dangling bonds, resulting in the release of free electrons.
- Temperature Correlation: Increased pressure and power resulted in a maximum substrate temperature of ~880 °C, which is critical for efficient N atom incorporation and enhanced conductivity.
- Structural Integrity: X-ray Diffraction (XRD) and Raman spectroscopy confirmed that the films consist primarily of crystalline nanodiamond grains (7-9 nm) with no detectable graphite impurity phase.
- Grain Boundary Chemistry: Raman analysis showed that optimal conditions reduced the intensity of Transpoliacetilene (TPA) bands, indicating a shift in grain boundary chemistry toward more sp2 bonded carbon and C-N bonds, favoring conductivity.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum Electrical Resistivity | ~1 | Ohm.cm | Optimal N-UNCD film (100 mbar, 4500 W) |
| Undoped UNCD Resistivity | â„106 | Ohm.cm | Standard insulating UNCD films |
| Optimal Microwave Power | 4500 | W | Power setting for highest conductivity |
| Optimal Total Pressure | 100 | mbar | Pressure setting for highest conductivity |
| Optimal Substrate Temperature | ~880 | °C | Correlated with maximum N incorporation |
| Microwave Frequency | 915 | MHz | Used in the IPLAS MPCVD system |
| Calculated Grain Size Range | 7 to 9 | nm | Determined via Scherrer-Debye equation |
| Film Thickness (Optimal) | 200 | nm | Measured by SEM cross-section (100 mbar, 4500 W) |
| Diamond XRD Peak (111) | 43.9 | ° (2Ξ) | Primary preferential orientation |
| Raman G Band | 1550 | cm-1 | Attributed to sp2 carbon bonds |
| Raman D Band | 1350 | cm-1 | Attributed to disorder-induced sp2 carbon bonds |
| Raman TPA Bands | 1130, 1450 | cm-1 | C=C and C-H bonds in transpoliacetilene (TPA) molecules |
Key Methodologies
Section titled âKey MethodologiesâThe N-UNCD films were grown using the Microwave Plasma Chemical Vapor Deposition (MPCVD) technique in an IPLAS system (915 MHz).
- Substrate Preparation: SiO2/Si and Si substrates were used.
- Chamber Environment: The chamber was evacuated to a base pressure of approximately 10-7 Torr.
- Gas Mixture and Flow: A fixed gas mixture was used: Ar (78 sccm), CH4 (2 sccm), and N2 (20 sccm).
- Growth Duration: All films were grown for a fixed period of 2 hours.
- Parameter Variation (Experimental Series):
- Total pressure was varied across 70, 80, 90, and 100 mbar.
- Microwave power was maintained constant within three series: 3000 W (Series 1), 4000 W (Series 2), and 4500 W (Series 3).
- Temperature Monitoring: Substrate surface temperature (ranging from 717-880 °C) was measured using a pyrometer.
- Characterization Techniques:
- Electrical Conductivity: Four-point probe measurements.
- Crystalline Structure/Grain Size: X-ray Diffraction (XRD).
- Morphology/Thickness: Scanning Electron Microscopy (SEM).
- Chemical Bonding/N Presence: X-ray Photoelectron Spectroscopy (XPS).
- Grain Boundary Chemistry: Raman Spectroscopy.
Commercial Applications
Section titled âCommercial ApplicationsâThe unique combination of high electrical conductivity, corrosion resistance, and mechanical hardness makes N-UNCD films suitable for next-generation electrochemical and electronic devices.
- Energy Storage (Li-ion Batteries - LIBs):
- Corrosion-resistant, electrically conductive coatings for anodes (e.g., natural graphite/copper) and cathodes.
- Safety and Longevity: The coating eliminates the uncontrollable development of the Solid Electrolyte Interface (SEI) dendritic layer, which is responsible for capacity degradation and potential explosive failure in commercial LIBs.
- Enables LIBs with â„10 longer charge/discharge life and improved safety.
- Electrochemical Systems:
- Corrosion-resistant, electrically conductive electrodes for electrolysis-based water purification systems (e.g., Diamonoxâą).
- High-Power Electronics:
- Used in high-power electronic devices requiring robust, conductive materials.
- Emission Devices:
- Suitable for thermionic and field emission devices due to negative electron affinity and low work function.
View Original Abstract
Research and development have been performed to investigate the effect of total pressure and microwave power on the electrical conductivity of nitrogen (N) atomsâ grain boundaries incorporated ultrananocrystalline diamond (N-UNCD) films grown by microwave plasma chemical vapor deposition (MPCVD). Insertion of N atoms into the UNCD filmâs grain boundaries induces N atoms chemical reaction with C-atoms dangling bonds, resulting in release of electrons, which induce electrical conductivity. Four-point probe electrical measurements show that the highest electrically conductive N-UNCD films, produced until now, exhibit electrical resistivity of ~1 Ohm.cm, which is orders of magnitude lower than the â„106 Ohm.cm for undoped ultrananocrystalline diamond (UNCD) films. X-ray diffraction analysis and Raman spectroscopy revealed that the growth of the N-UNCD films by MPCVD do not produce graphite phase but only crystalline nanodiamond grains. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nitrogen (N) in the N-UNCD films and the high conductivity (no electrical charging is observed during XPS analysis) shown in electrical measurements.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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