Boron Doped Ultrananocrystalline Diamond Films on Porous Silicon - Morphological, Structural and Electrochemical Characterizations
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-11-20 |
| Journal | Materials Research |
| Authors | Lilian Mieko da Silva, Marta dos Santos, MaurĂcio Ribeiro Baldan, A.F. Beloto, N.G. Ferreira |
| Institutions | National Institute for Space Research |
| Citations | 10 |
| Analysis | Full AI Review Included |
Technical Documentation and Analysis: Boron Doped Ultrananocrystalline Diamond Films
Section titled âTechnical Documentation and Analysis: Boron Doped Ultrananocrystalline Diamond FilmsâExecutive Summary
Section titled âExecutive SummaryâThis study successfully demonstrates the fabrication and characterization of Boron-Doped Ultrananocrystalline Diamond (BDUND) films deposited onto Porous Silicon (PS) substrates via Hot Filament Chemical Vapor Deposition (HFCVD). The core findings drive immediate interest for high-performance electrochemical applications:
- Exceptional Capacitance Achieved: BDUND/PS electrodes exhibit a high electrochemical capacitance of up to $6500 \mu\text{F}\cdot\text{cm}^{-2}$ (geometric area basis) at $0.8 \text{ V} \times \text{Ag/AgCl}$.
- Performance Benchmark: This capacitance value is confirmed to be more than 20 times higher than that of standard planar BDD/Si electrodes and approximately 30 times greater than comparable nanohoneycomb diamond structures.
- Material Morphology: Structural analysis (FEG-SEM, XRD, Raman) confirms the formation of ultrananocrystalline diamond (UNCD) with a fine average grain size of $\sim 5 \text{ nm}$.
- Substrate Conformation: The BDUND film successfully coated the highly porous PS substrate, covering the pore walls and bottom surfaces while maintaining the critical high-surface-area porous morphology.
- Application Potential: The demonstrated high capacitance strongly confirms that BDUND/PS composites are highly promising candidates for next-generation, high-density electrochemical capacitors (supercapacitors).
- Process Parameters: Films were synthesized using a high boron doping ratio (20000 ppm B/C in solution) under low pressure (30 Torr) HFCVD, demonstrating a robust recipe for producing conductive, high-surface-area UNCD structures.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the synthesis and characterization of the BDUND/PS electrodes.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Type | n-type Monocrystalline Silicon (100) | N/A | Resistivity: $1\text{-}20\ \Omega\cdot\text{cm}$ |
| CVD Technique | Hot Filament CVD (HFCVD) | N/A | Used Tungsten filaments, $125\ \mu\text{m}$ diameter |
| Boron Doping Ratio | 20000 | ppm (B/C in solution) | Used $\text{B}{2}\text{O}{3}$ dissolved in methanol bubbler |
| Reactor Pressure | 30 | Torr | Constant pressure during growth |
| Filament Current | 15 | A | Applied to linear tungsten filaments |
| Growth Time (Sample 1) | 3 | h | Optimized for highest capacitance |
| Growth Time (Sample 2) | 4 | h | Showed slight capacitance decrease vs. 3h sample |
| Gas Flow (3h Sample) | $18 / 1.5 / 80$ | sccm | $\text{H}{2} / \text{CH}{4} / \text{Ar}$ ratio |
| Gas Flow (4h Sample) | $18.5 / 1.0 / 80$ | sccm | $\text{H}{2} / \text{CH}{4} / \text{Ar}$ ratio |
| Average Grain Size | $\sim 5$ | nm | Calculated from X-ray $\lt 111\gt$ peak broadening |
| Grain Agglomerate Size | $\sim 240$ | nm | Observed via FEG-SEM |
| Electrolyte | $0.5 \text{ mol/L } \text{H}{2}\text{SO}{4}$ | N/A | Used for Cyclic Voltammetry (CV) |
| CV Scan Rate | 50 | $\text{mV/s}$ | Used for electrochemical characterization |
| Maximum Capacitance (3h) | 6500 | $\mu\text{F}\cdot\text{cm}^{-2}$ | At $0.8 \text{ V} \times \text{Ag/AgCl}$ (geometric area) |
| Capacitance Improvement | 20x | Factor | Relative to planar BDUND/Si control |
| Raman D Band Peak | 1345 | $\text{cm}<sup>-1</sup>$ | Associated with $\text{sp}^{2}$ disorder (UNCD feature) |
| Raman G Band Peak | 1550 | $\text{cm}<sup>-1</sup>$ | Associated with $\text{sp}^{2}$ amorphous carbon |
Key Methodologies
Section titled âKey MethodologiesâThe synthesis involved a critical two-step process: preparation of the porous substrate followed by boron-doped ultrananocrystalline diamond growth.
-
Porous Silicon (PS) Substrate Preparation:
- Starting Material: n-type monocrystalline silicon wafers (100) with $1\text{-}20\ \Omega\cdot\text{cm}$ resistivity.
- Ohmic Contact: Silicon backside covered with Indium to ensure good ohmic contact.
- Etching Process: Electrochemical etching performed using HF-acetonitrile solution as the electrolyte.
- Anodization: Samples polarized under galvanostatic conditions at a current density of $56.5\ \text{mA/cm}^{2}$ for 120 minutes, enhanced by a 50 W dichroic lamp.
- Cleaning: Rinsed in deionized water and dried using nitrogen gas.
-
BDUND Seeding (Pretreatment):
- The PS substrates were pretreated using a self-assembly seeding method.
- Substrates were immersed in a solution containing PDDA polymer, KCl colloidal solution, and $4 \text{ nm}$ diamond particles.
-
BDUND Film Growth (HFCVD):
- Reactor Type: Hot Filament Chemical Vapor Deposition (HFCVD).
- Filaments: Five linear tungsten wires ($125\ \mu\text{m}$ diameter) spaced $7\ \text{mm}$ apart, operating at 15 A.
- Doping Method: Boron introduction via an additional hydrogen line passing through a bubbler containing $\text{B}{2}\text{O}{3}$ dissolved in methanol. The target $\text{B/C}$ ratio in solution was $20000\ \text{ppm}$.
- Recipe 1 (3h): $\text{H}{2}/\text{CH}{4}/\text{Ar}$ flow rates: $18 / 1.5 / 80\ \text{sccm}$.
- Recipe 2 (4h): $\text{H}{2}/\text{CH}{4}/\text{Ar}$ flow rates: $18.5 / 1.0 / 80\ \text{sccm}$.
- Pressure: Maintained at 30 Torr.
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Characterization:
- Morphology: Scanning Electron Microscopy (SEM) and Field Emission Gun (FEG)-SEM were used to confirm uniform UNCD coalescence and the preservation of the PS porous structure.
- Structure/Quality: Raman spectroscopy and high-resolution X-ray diffraction (XRD) were used to confirm diamond crystallinity ($\lt 111\gt$, $\lt 220\gt$, $\lt 311\gt$ peaks) and ultrananocrystalline features (D and G bands).
- Electrochemical: Cyclic Voltammetry (CV) performed using a standard three-electrode system (sample, platinum counter, $\text{Ag/AgCl}$ reference) in $0.5 \text{ mol/L } \text{H}{2}\text{SO}{4}$ to determine capacitance.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research validates high-surface-area, heavily boron-doped diamond as a superior material platform for energy storage devices. 6CCVD is uniquely positioned to supply and enhance the materials required to replicate and scale this highly successful research endeavor.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the high conductivity and electrochemical activity demonstrated in this paper, 6CCVD recommends materials with tailored dopant levels and crystalline structure control:
- Heavy Boron-Doped Polycrystalline Diamond (BDD PCD): Suitable for large-scale electrode manufacturing where a very high surface area and conductivity are paramount. 6CCVD offers PCD wafers up to 125mm in diameterâideal for scaling capacitor prototypes beyond lab-bench dimensions.
- Ultrananocrystalline Diamond (UNCD) Services: While the paper used HFCVD, 6CCVDâs advanced MPCVD reactors allow precise control over gas mixtures ($\text{H}{2}/\text{Ar}/\text{CH}{4}$ ratios) and growth conditions necessary to synthesize highly uniform UNCD or Nanocrystalline Diamond (NCD) layers with controlled grain sizes (as small as $5\ \text{nm}$).
- Custom Porous Substrate Growth: Although the paper utilized pre-etched PS, 6CCVD can perform MPCVD growth directly onto customer-supplied substrates (including patterned or porous structures) to maintain the delicate morphology required for maximum capacitance.
Customization Potential
Section titled âCustomization PotentialâThe optimization of BDUND/PS systems requires precise dimensional control, controlled thickness, and potential integration with external circuits.
| Research Requirement | 6CCVD Custom Capability | Engineering Advantage |
|---|---|---|
| Film Thickness | SCD or PCD layers from $0.1\ \mu\text{m}$ up to $500\ \mu\text{m}$ | Precise control over penetration depth and pore filling (key challenge noted in the paper). |
| Boron Doping | Precise, reproducible BDD doping control (B/C ratio) | Ability to match the critical 20000 ppm level or explore specific electrochemical regimes. |
| Substrate Size | PCD wafers available up to $125\ \text{mm}$ in diameter | Enables scaling of electrochemical devices from research coupon size to full wafer production. |
| Electrode Contact | Internal metalization capability: Au, Pt, Pd, Ti, W, Cu | Essential for reliable electrode integration and achieving stable ohmic contacts, often required after CVD growth. |
| Surface Finish | Polishing services available (Ra < 5 nm for Inch-size PCD) | While porous structure is desired here, 6CCVD can provide ultra-smooth finishes for adjacent layers or reference electrodes used in testing. |
Engineering Support
Section titled âEngineering SupportâThe challenges noted in the paperâsuch as obtaining a BDUND layer that promotes a uniform film while maintaining porous morphologyârequire sophisticated CVD expertise.
6CCVDâs in-house PhD team can provide expert consultation on material selection, recipe optimization (e.g., precise $\text{H}{2}/\text{CH}{4}/\text{Ar}$ flow ratios for UNCD synthesis), and process design to prevent excessive pore filling. We specifically assist clients working on similar electrochemical capacitor (supercapacitor) and high-surface-area electrode projects, leveraging our deep experience in tailored diamond growth on complex substrates.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) for seamless delivery of critical research materials.
View Original Abstract
Boron doped ultrananocrystalline diamond (BDUND) films were grown and characterized on porous silicon (PS) substrates. PS samples were prepared from n-type monocrystalline silicon wafers (100) with 1-20 Ω.cm of resistivity, by electrochemical etching, using HF-acetonitrile solution as electrolyte. BDUND films were grown by Hot Filament Chemical Vapor Deposition using CH4, H2 and Ar. The doping process consisted of an additional hydrogen line, passing through a bubbler containing B2O3 dissolved in methanol, with boron/carbon ratio of 20000 ppm in solution. Raman spectroscopy and X-Ray diffraction were used to evaluate the quality of the films. Scanning electron microscopy was used for morphological characterization, and confirmed that the films covered the pores without filling them. Electrochemical response and capacitance behavior of the electrodes were explored, by cyclic voltammetry. Samples presented high capacitance, confirming that BDUND/PS electrodes are promising for application as electrochemical capacitors.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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