Heat-induced transformation of nickel-coated polycrystalline diamond film studied in situ by XPS and NEXAFS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-12 |
| Journal | Beilstein Journal of Nanotechnology |
| Authors | Olga V. Sedelnikova, Yu. V. Fedoseeva, Dmitriy V. Gorodetskiy, Yuri N. Palyanov, Elena V. Shlyakhova |
| Institutions | Freie UniversitÀt Berlin, Siberian Branch of the Russian Academy of Sciences |
| Analysis | Full AI Review Included |
As an expert material scientist, I have analyzed the provided research paper, âHeat-induced transformation of nickel-coated polycrystalline diamond film studied in situ by XPS and NEXAFS,â and structured the findings for an engineering audience.
Executive Summary
Section titled âExecutive Summaryâ- Catalytic Graphitization: Nickel (Ni) coating significantly lowers the temperature required for diamond surface transformation, promoting the formation of sp2 carbon layers (graphite-like films) on polycrystalline diamond (PCD) and single-crystal diamond (SCD) at 1100-1150 °C in ultrahigh vacuum (UHV). Bare PCD surfaces were highly resistant to transformation at these temperatures.
- Structural Ordering: Ni-coated SCD (110) face produced highly ordered graphitic layers (Raman ID/IG ratio of 0.15), while Ni-PCD resulted in structurally disordered, multilayer graphitic stacks (I2D/IG ratio of ~0.6).
- Anisotropic Texture: Angle-resolved NEXAFS confirmed that the sp2 carbon layers formed on the Ni-SCD (110) face exhibit a strong vertical orientation (upright) relative to the diamond surface.
- Mechanism Confirmation: XPS data confirmed the presence of Ni-C states and sp2 carbon, supporting the model where Ni etches the diamond, and the released carbon atoms saturate the etched surface bonds, forming the graphitic layer.
- Face Dependence: While the morphology of Ni particles varied significantly between the (110) (etched pits) and (111) (agglomerates) faces of PCD, the chemical state of the resulting sp2 carbon was largely insensitive to the crystallite orientation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| PCD Film Thickness | ~500 | ”m | Grown by PE CVD |
| Ni Coating Thickness | ~40 | nm | Deposited by thermal evaporation |
| PCD Annealing Temperature | 1100 | °C | High vacuum (10-9 mbar), 15 min |
| SCD Annealing Temperature | 1150 | °C | High vacuum (10-9 mbar), 15 min |
| PCD Crystallite Size | ~100 | ”m | Mixed (110) and (111) orientations |
| Raman G Band (Ni-PCD) | 1584 | cm-1 | Characteristic sp2 carbon stretching vibration |
| Raman ID/IG Ratio (Ni-SCD) | 0.15 | - | Low defectiveness in sp2 layer |
| Raman I2D/IG Ratio (Ni-PCD) | ~0.6 | - | Suggests formation of multilayer graphitic stacks |
| NEXAFS C K-edge (Ï* resonance) | 285.3 | eV | Unoccupied Ï* states of sp2 carbon |
| XPS Excitation Energy 1 | 830 | eV | Probing depth ~3 nm |
| XPS Excitation Energy 2 | 330 | eV | Probing depth ~2 nm (more surface sensitive) |
| NEXAFS IÏ*/IÏ* (90° incidence) | 0.67 | - | Ni-SCD (110) face, indicates vertical sp2 orientation |
| NEXAFS IÏ*/IÏ* (50° incidence) | 0.44 | - | Ni-SCD (110) face, confirms anisotropic texture |
| Ni Surface Concentration | 0.1 | atom % | Measured by Survey XPS after annealing |
Key Methodologies
Section titled âKey Methodologiesâ- Substrate Preparation:
- Polycrystalline Diamond (PCD) films (~500 ”m thick) were synthesized via Plasma-Enhanced Chemical Vapor Deposition (PE CVD) using hydrogen/acetone/air plasma.
- Synthetic Single-Crystal Diamond (SCD) was grown via the High-Pressure High-Temperature (HPHT) method and polished to expose the (110) face.
- Coating Deposition:
- A thin nickel film (~40 nm) was deposited onto both PCD and SCD (110) substrates using thermal evaporation.
- In Situ Annealing:
- Samples were annealed simultaneously in ultrahigh vacuum (UHV, 10-9 mbar) for 15 minutes.
- PCD and Ni-PCD were annealed at 1100 °C.
- SCD and Ni-SCD were annealed at 1150 °C.
- In Situ Synchrotron Analysis:
- X-ray Photoelectron Spectroscopy (XPS): Measured C 1s and Ni 3p core levels using two excitation energies (330 eV and 830 eV) to achieve variable depth sensitivity (probing depths of ~2 nm and ~3 nm, respectively).
- Near-Edge X-ray Absorption Fine Structure (NEXAFS): Measured C K-edge and Ni L-edge spectra in Total Electron Yield (TEY, probing bulk, ~10 nm) and Auger Electron Yield (AEY, probing surface, ~3 nm) modes.
- Orientation Determination:
- Angle-resolved NEXAFS was performed on the annealed Ni-SCD (110) face at 90° (normal incidence) and 50° (tilted incidence) to determine the spatial orientation of the sp2 carbon Ï orbitals.
- Ex Situ Characterization:
- Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) spectroscopy were used to analyze surface morphology and elemental distribution.
- Raman Spectroscopy (514 nm laser) was used to assess the crystalline quality and defect concentration (ID/IG and I2D/IG ratios) of the graphitic layers.
Commercial Applications
Section titled âCommercial Applicationsâ- Power Electronics: Fabrication of thin, highly conductive electrodes on diamond, which serves as a superior dielectric and heat dissipation substrate for high-power devices.
- Graphene-on-Diamond Heterostructures: Controlled synthesis of sp2/sp3 interfaces for advanced microelectronic devices, utilizing the unique electronic properties of graphene integrated with diamondâs wide bandgap.
- Thermal Management: Creating integrated conductive pathways or contacts on diamond heat spreaders and thermal interface materials (TIMs) where localized conductivity is required.
- High-Frequency/RF Components: Developing anisotropic conductive coatings where the vertical orientation of graphitic layers (as observed on SCD) could be leveraged for specific electrical or thermal transport requirements.
- Electrochemical Sensors: Utilizing the chemically stable and conductive graphitic surface layers formed on diamond substrates.
View Original Abstract
Controlling high-temperature graphitization of diamond surfaces is important for many applications, which require the formation of thin conductive electrodes on dielectric substrates. Transition metal catalysts can facilitate the graphitization process, which depends on the diamond face orientation. In the present work, the role of a nickel coating on the electronic structure and chemical state of graphite layers formed on the surface of a polycrystalline diamond (PCD) film with mixed grain orientation was studied. A synthetic single-crystal diamond (SCD) with a polished (110) face was examined for comparison. The samples were coated with a thin nickel film deposited by thermal evaporation. The graphitization of diamond with and without a nickel coating as a result of high-vacuum annealing at a temperature of about 1100 °C was studied in situ using synchrotron-based X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) methods. XPS data revealed the formation of a thin graphite-like film with low-ordered atomic structure on the surface of the nickel-coated PCD film. The chemical state of sp 2 -hybridized carbon atoms was found to be insensitive to the face orientation of the diamond micro-sized crystallites; however, the layer defectiveness increased in areas with fine-dispersed crystallites. According to NEXAFS and Raman spectroscopy data, the most ordered atomic structure of graphitic layers was obtained by annealing nickel-coated SCD. The angular dependence of NEXAFS C K-edge spectra of nickel-coated (110) face after annealing discovered the vertical orientation of sp 2 -hybridized carbon layers relative to the diamond surface. The observed behavior suggests that sp 2 carbon layers were formed on the diamond surface due to its saturation by released carbon atoms as a result of etching by nickel.