Face-centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra-wide bandgap
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-07-02 |
| Journal | Communications Materials |
| Authors | I. Konyashin, Ruslan Muydinov, Antonio Cammarata, Andrey Bondarev, Marin Rusu |
| Institutions | Helmholtz-Zentrum Berlin fĂŒr Materialien und Energie, Technische UniversitĂ€t Berlin |
| Citations | 6 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Face-Centered Cubic Carbon on MPCVD Diamond Substrates
Section titled âTechnical Documentation & Analysis: Face-Centered Cubic Carbon on MPCVD Diamond SubstratesâThis document analyzes the research paper detailing the synthesis and characterization of face-centered cubic (fcc) carbon films grown epitaxially on single-crystal diamond (SCD) substrates via Plasma-Assisted Chemical Vapor Deposition (PACVD). This breakthrough confirms the existence of a new carbon allotrope with ultra-wide bandgap (UWBG) semiconductor properties, positioning 6CCVDâs high-purity MPCVD diamond as the critical enabling platform for next-generation carbon electronics.
Executive Summary
Section titled âExecutive Summaryâ- Novel Material Discovery: Successful synthesis and comprehensive characterization of face-centered cubic (fcc) carbon, proposed as the fourth basic carbon allotrope.
- Enabling Platform: Epitaxial films of fcc-carbon were grown on high-quality, single-crystal diamond (SCD) substrates using PACVD, validating SCD as the essential foundation for this advanced material science.
- Ultra-Wide Bandgap (UWBG): Fcc-carbon exhibits an ultra-wide bandgap ($E_{g} \approx 6.1$ eV optical), placing it firmly in the UWBG semiconductor class, suitable for extreme environment electronics.
- Intrinsic Semiconductor: The material shows intrinsic semiconductor behavior, characterized by a low electrical conductivity ($\approx 10^{-3}$ S·m-1 at RT) that increases with temperature, resolving previous contradictions regarding its metallic nature.
- Negative Electron Affinity (NEA): Fcc-carbon possesses a negative electron affinity ($E_{A} \approx -0.96$ eV), a highly desirable property for high-efficiency electron emitters, deep-UV optoelectronics, and vacuum microelectronics.
- Application Potential: This material opens a new pathway for âcarbon electronics,â targeting high-power/high-frequency devices, transparent electronics, and quantum memory applications, fields where 6CCVDâs SCD and PCD materials are foundational.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the characterization of the synthesized fcc-carbon films and the SCD substrate used.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Crystal Structure | Face-Centered Cubic (fcc) | N/A | Space Group Fm3m |
| Lattice Constant ($a_{0}$) | 3.551 | Ă | Conventional unit cell (Calculated) |
| Optical Bandgap ($E_{g, opt}$) | $\approx 6.1$ | eV | Determined via VUV reflection/Tauc plot |
| Calculated Bandgap ($E_{g, calc}$) | $\approx 7.1$ | eV | Ab initio DFT calculation |
| Electrical Conductivity ($\sigma$) | $\approx 10^{-3}$ | S·m-1 | At Room Temperature (RT) |
| Activation Energy ($E_{a}$) | $\approx 230$ | meV | Measured from temperature dependence |
| Work Function ($\Phi$) | 4.60 | eV | Measured by Kelvin Probe (KP) |
| Ionization Energy ($E_{i}$) | 5.14 | eV | Measured by PYS |
| Electron Affinity ($E_{A}$) | $\approx -0.96$ | eV | Calculated ($E_{A} = E_{i} - E_{g}$) |
| Fcc-Carbon Film Thickness | $\approx 1$ | ”m | Average thickness |
| Substrate Material | Single Crystal Diamond (SCD) | N/A | (100) orientation |
| Substrate RMS Roughness | < 20 | nm | Prior to deposition |
Key Methodologies
Section titled âKey MethodologiesâThe fcc-carbon films were obtained via Plasma-Assisted Chemical Vapor Deposition (PACVD) on single-crystalline diamond substrates under highly specific, non-standard conditions designed to favor the formation of the fcc-carbon phase over conventional diamond growth.
- Substrate Selection: Single-crystalline diamond (SCD) plates (3.8 x 3.8 x 0.3 mm, (100) orientation) were utilized.
- Surface Preparation: Substrates were polished to an RMS roughness of < 20 nm and subjected to acid cleaning.
- Deposition Technique: Microwave PACVD reactor operating at 2.45 GHz.
- Gas Mixture: $\text{CH}{4}-\text{H}{2}$ gas mixture.
- Gas Composition: Hydrogen content: 98 vol%; Methane content: 2 vol%.
- Substrate Temperature: $\approx 600$ °C.
- Total Pressure: 29.33 kPa.
- Microwave Power: Nearly 2.2 kW.
- Deposition Rate Control: The process was maintained at an unusually low deposition rate ($\approx 0.14$ nm/min), which is critical for achieving the narrow window where fcc-carbon formation dominates over diamond etching.
- Post-Growth Treatment: Samples were treated in diluted $\text{HNO}_{3}$ for 24 hours to eliminate surface hydrogen termination and associated surface conductivity effects.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful synthesis of this groundbreaking UWBG material relies entirely on the quality and precision of the SCD substrate. 6CCVD is uniquely positioned to supply the foundational materials and custom engineering services required to replicate, scale, and advance this research into commercial applications.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| High-Purity Epitaxial Substrates | Optical Grade Single Crystal Diamond (SCD) wafers. | Guaranteed (100) orientation, high purity, and low defect density required for reliable epitaxial growth of novel carbon allotropes. |
| Film Thickness Control | SCD Thin Films (0.1 ”m - 500 ”m). | We provide SCD substrates and thin films with precise thickness control, enabling researchers to optimize the platform for the $\approx 1$ ”m fcc-carbon active layer. |
| Scaling and Custom Dimensions | Custom Dimensions & Large Area PCD. | While the study used small 3.8 mm plates, 6CCVD offers SCD substrates up to 10 mm thick and Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, crucial for transitioning research to wafer-scale production. |
| Ultra-Smooth Surface Finish | Precision Polishing Services. | Internal capability to achieve SCD surface roughness of Ra < 1 nm (and PCD Ra < 5 nm for inch-size wafers), ensuring the pristine surface quality necessary for demanding epitaxial growth and minimizing scattering losses in optical applications. |
| Device Integration & Contacts | Custom Metalization Services. | We offer in-house deposition of standard and custom metal stacks (Au, Pt, Pd, Ti, W, Cu), essential for fabricating ohmic or Schottky contacts required for electrical characterization and device prototyping. |
| Comparative Material Studies | Boron-Doped Diamond (BDD) Materials. | BDD is available in both SCD and PCD forms for comparative studies, addressing the paperâs discussion on the challenges of conventional diamond doping and providing a pathway for developing p-type contacts. |
Engineering Support
Section titled âEngineering SupportâThe discovery of fcc-carbon as an intrinsic UWBG semiconductor with Negative Electron Affinity (NEA) is highly relevant to next-generation electronics. 6CCVDâs in-house PhD team specializes in MPCVD growth parameters and material selection for UWBG, NEA, and high-power applications. We offer consultation to assist engineers and scientists in optimizing substrate specifications (orientation, thickness, roughness) to maximize the yield and quality of novel material synthesis, such as the fcc-carbon allotrope.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).
View Original Abstract
Abstract Carbon is considered to exist in three basic forms: diamond, graphite/graphene/fullerenes, and carbyne, which differ in a type of atomic orbitals hybridization. Since several decades the existence of the fourth basic carbon allotropic form with the face-centered cubic ( fcc ) crystal lattice has been a matter of discussion despite clear evidence for its laboratory synthesis and presence in nature. Here, we obtain this carbon allotrope in form of epitaxial films on diamond in a quantity sufficient to perform their comprehensive studies. The carbon material has an fcc crystal structure, shows a negative electron affinity, and is characterized by a peculiar hybridization of the valence atomic orbitals. Its bandgap (~6 eV) is typical for insulators, whereas the noticeable electrical conductivity (~0.1 S m â1 ) increases with temperature, which is typical for semiconductors. Ab initio calculations explain this apparent contradiction by noncovalent sharing p -electrons present in the uncommon valence band structure comprising an intraband gap. This carbon allotrope can create a new pathway to âcarbon electronicsâ as the first intrinsic semiconductor with an ultra-wide bandgap.