Structural and Physical Characterization of Nanodiamond Composite Thin Films Synthesized by Pulsed-Laser Ablation Method (A Review)
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-10-21 |
| Journal | Proceedings of International Exchange and Innovation Conference on Engineering & Sciences (IEICES) |
| Authors | Lama Osman, Abdelrahman Zkria, Tsuyoshi Yoshitake |
| Institutions | Kyushu University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Structural and Physical Characterization of Nanodiamond Composite Thin Films (A Review)
Section titled âStructural and Physical Characterization of Nanodiamond Composite Thin Films (A Review)âThis analysis summarizes the synthesis and characterization of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite (NDC) thin films fabricated using Pulsed-Laser Ablation (PLD).
Executive Summary
Section titled âExecutive Summaryâ- Material System: Nanodiamond Composite (NDC) films, consisting of diamond crystallites (< 10 nm) embedded in an amorphous carbon (a-C) matrix.
- Synthesis Advantage: PLD was utilized to synthesize high-quality NDC films at a relatively low substrate temperature (550 °C), enabling deposition on diverse solid-state substrates, unlike high-temperature Chemical Vapor Deposition (CVD).
- Structural Quality: Undoped films exhibited a high sp3 bonding fraction (68%) and sharp sp3 peak FWHM (0.91 eV), confirming the presence of dense, homogeneous nanodiamond crystallites (~5 nm).
- Electronic Properties: The films displayed a large direct optical band gap of 2.2 eV, attributed to the grain boundaries between the NDCs and the a-C matrix.
- Doping Effects (Boron): Boron incorporation successfully enhanced the sp3 bonding fraction up to 74%, correlating with an enlargement of the NDC grain sizes.
- Doping Effects (Nitrogen): Nitrogen incorporation increased the sp2 fraction (reducing sp3 content to 60%), primarily integrating into the grain boundaries (C-N and C=N bonds).
- Method Efficacy: The review validates PLD as an advanced physical vapor deposition technique for controlling the structural and electronic properties of NDC films through ambient gas (hydrogen) and doping.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimum Substrate Temperature | 550 | °C | PLD deposition condition |
| Ambient Hydrogen Pressure | 53.3 | Pa | PLD deposition (equivalent to 4 Torr) |
| Laser Type | ArF Excimer | N/A | Used for ablation |
| Laser Wavelength | 193 | nm | ArF Excimer Laser |
| Laser Pulse Duration | 24 | ns | ArF Excimer Laser |
| Laser Fluence | 5 | J/cm2 | Target irradiation |
| Undoped Crystallite Diameter | 5 | nm | Observed via TEM |
| Undoped Film Thickness | 2 | ”m | Deposited on sapphire (0001) |
| Direct Optical Band Gap | 2.2 | eV | Undoped NDC film |
| Indirect Optical Band Gap | 1.0 | eV | Undoped NDC film (attributed to a-C matrix) |
| Undoped sp3/(sp2+sp3) Ratio | 68 | % | Determined by XPS |
| N-Doped sp3/(sp2+sp3) Ratio | 60.4 | % | 7.9 atm.% N-doped film |
| B-Doped sp3/(sp2+sp3) Ratio | 74 | % | 13 atm.% B-doped film (highest sp3 content) |
| Undoped sp3 FWHM (XPS) | 0.91 | eV | Indicates high crystallite homogeneity |
| Characteristic Raman Peak | 1149 | cm-1 | Specific to NDCs |
Key Methodologies
Section titled âKey MethodologiesâThe NDC films were synthesized and characterized using the following procedures:
-
Pulsed-Laser Ablation (PLD) Synthesis:
- Target: Graphite target was irradiated by an ArF excimer laser (193 nm, 24 ns).
- Environment: Deposition occurred under an ambient hydrogen pressure (53.3 Pa) at 550 °C. Hydrogen was critical for selectively etching sp2 bonds, promoting sp3 diamond growth, and improving film morphology (surfactant effect).
- Doping: Nitrogen and Boron were incorporated to tune electronic properties. Nitrogen content was controlled by gas inflow ratio (up to 7.9 atm.%), while Boron was incorporated via doped targets (up to 13 atm.%).
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Structural and Morphological Characterization:
- Transmission Electron Microscopy (TEM): Used in dark-field and high-resolution modes to confirm the presence and size (~5 nm) of diamond crystallites within the amorphous matrix.
- Selected Area Electron Diffraction (SAED): Confirmed diamond phases ((111), (220), (311)) without evidence of graphite rings.
-
Chemical Bonding and Electronic Characterization:
- X-ray Photoemission Spectroscopy (XPS): Measured the C1s core level spectra. Decomposition of the C1s peak into sp3, sp2, and C-O/C=O components allowed precise determination of the sp3/(sp2+sp3) ratio.
- Near-Edge X-ray Absorption Fine Structure (NEXAFS): Utilized synchrotron radiation to probe the local atomic bonding configuration (Ï* and Ï* transitions), confirming the sp3 fraction and revealing specific doping-induced bonds (e.g., Ï* C-B and Ï* C=N).
- Fourier Transform Infrared Spectroscopy (FTIR): Examined CHn vibration peaks, confirming hydrogen termination at the grain boundaries, especially the intense sp3-CH peak in NDC films.
-
Optical Characterization:
- UV-Vis Spectroscopy: Measured transmittance (T) and reflectance (R) to calculate the absorption coefficient (α), leading to the determination of direct (2.2 eV) and indirect (1.0 eV) optical band gaps.
Commercial Applications
Section titled âCommercial ApplicationsâThe unique combination of high hardness, smoothness, high thermal conductivity, and tunable electronic properties makes NDC films suitable for advanced engineering applications:
| Application Area | Relevant NDC Property | Specific Use Cases |
|---|---|---|
| Advanced Electronics | Tunable wide band gap, high thermal conductivity | High-power/High-frequency transistors, heat spreaders, passive components. |
| Field Emission Technology | Low electron affinity, high conductivity (when doped) | Cold cathodes, flat panel displays, electron sources for vacuum microelectronics. |
| Biomedical Devices | Bio-compatibility, chemical inertness, smoothness | Protective coatings for medical implants, biosensors, drug delivery platforms. |
| Mechanical/Tribology | Extreme hardness, low friction | Wear-resistant coatings for micro-tools, MEMS components, protective layers in harsh environments. |
| Optics and Sensors | Wide optical transparency, doping-induced defects | UV detectors, optical windows, quantum sensing platforms (if NV centers are formed). |
View Original Abstract
Ultrananocrystalline diamond/hydrogenated amorphous carbon composite (so called Nanodiamond composite) thin films were deposited on diverse substrate materials at optimum substrate temperature of 550â and ambient hydrogen pressure of 53.3 Pa by pulsed-laser deposition technique. The structural and physical characterization of the undoped, nitrogen-doped and boron-doped films were well-discussed through this review.