Application-driven synthesis and characterization of hexagonal boron nitride deposited on metals and carbon nanotubes

At a Glance

Metadata	Details
Publication Date	2021-07-02
Journal	2D Materials
Authors	Victoria Chen, Yong-Cheol Shin, Evgeny Mikheev, Qing Lin, Joel Martis
Citations	4
Analysis	Full AI Review Included

Technical Analysis and Documentation: Application-Driven Synthesis of Hexagonal Boron Nitride

Executive Summary

This research demonstrates the scalable synthesis of high-quality hexagonal Boron Nitride (h-BN) films via Low-Pressure Chemical Vapor Deposition (LPCVD) on various substrates, highlighting critical material properties and advanced applications.

Diamond-Grade Insulation: h-BN is confirmed as an exceptional electrical insulator (Band Gap ~6 eV) and thermal conductor (>400 W m⁻¹ K⁻¹), second only to diamond among insulators, making it ideal for high-power electronics and heat spreading.
Substrate Quality Impact: Growth on single crystal Pt(111) yielded significantly smoother and more spatially uniform h-BN (RMS roughness 0.80 nm) compared to polycrystalline Pt (1.70 nm), emphasizing the necessity of high-quality, crystalline substrates for 2D material synthesis.
Ultrathin Protection Barrier: Monolayer h-BN (3.33 Å thick) successfully protected monolayer MoS₂ from degradation during high-temperature (up to 450°C) annealing in H₂/Ar atmosphere, demonstrating its utility as an ultra-thin, high-temperature passivation layer.
Scalable & Reusable Methods: An electrochemical bubbling transfer method was utilized, enabling the reuse of expensive single crystal Pt substrates for hundreds of subsequent CVD growths without measurable degradation.
Target Applications: The resulting h-BN films are positioned for use in advanced electronic devices, including gate dielectrics, resistive random-access memory (RRAM) switching layers, and interlayer dielectrics for 3D integrated circuits (ICs) requiring directional heat dissipation.

Technical Specifications

Parameter	Value	Unit	Context
h-BN Band Gap	~6	eV	Electrical insulator performance
h-BN Thermal Conductivity (In-Plane)	>400	W m⁻¹ K⁻¹	High thermal management capability
Monolayer Thickness	3.33	Å	Interlayer spacing of bulk material
Growth Temperature (Pt/CNTs)	1100	°C	LPCVD synthesis condition
Growth Temperature (Cu)	1050	°C	LPCVD synthesis condition
Growth Pressure	~900	mTorr	LPCVD operating condition
Precursor Heating Temperature	100	°C	Ammonia Borane decomposition
RMS Surface Roughness (Single Crystal Pt(111))	0.80	nm	Smoother, more uniform h-BN film
RMS Surface Roughness (Polycrystalline Pt)	1.70	nm	Less uniform h-BN film
h-BN Monolayer Raman Peak (E’ peak)	~1370	cm⁻¹	Characteristic signature
MoS₂ Protection Temperature	Up to 450	°C	Protected by h-BN capping layer

Key Methodologies

The large-area h-BN films were prepared using Low-Pressure Chemical Vapor Deposition (LPCVD) in a 2” diameter furnace, followed by specialized transfer techniques.

Substrate Preparation: Metal substrates (Polycrystalline Pt, Single Crystal Pt(111), Cu foil) were annealed at their respective growth temperatures (1050°C or 1100°C) for 40 minutes to remove impurities and smooth the surface.
Precursor Introduction: The air-stable, solid-source precursor, Ammonia Borane (H₃NBH₃), was placed in an ampoule and heated independently to 100°C, decomposing into borazine [(HBNH)₃] and hydrogen.
CVD Growth: H₂ carrier gas diffused the borazine onto the substrates inside the furnace chamber, maintained at a pressure of ~900 mTorr. Growth on Pt was limited to a single monolayer, while growth on Cu and CNTs resulted in multilayer films.
Electrochemical Transfer (Pt Substrates): A room-temperature electrochemical bubbling method was used to delaminate the h-BN/PMMA stack from the Pt substrates in a 1M NaOH solution. This non-etching process allows the expensive Pt substrates to be reused.
Wet Etching Transfer (Cu Substrates): A wet etching method was used to transfer h-BN films from the Cu substrate onto a target substrate (typically 300 nm SiO₂ on Si) for characterization.
Characterization: Films were analyzed using Atomic Force Microscopy (AFM) for thickness and roughness (Ra < 1 nm for single crystal growth), Raman spectroscopy (E’ peak at ~1370 cm⁻¹), Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and cross-sectional Transmission Electron Microscopy (TEM).

6CCVD Solutions & Capabilities

The research highlights the critical need for materials that combine extreme electrical insulation with high thermal conductivity, and the necessity of ultra-smooth, high-crystallinity substrates for advanced 2D material synthesis. 6CCVD’s expertise in MPCVD diamond directly addresses these requirements, offering materials and services that can replicate, enhance, and scale the applications demonstrated in this paper.

Applicable Materials for Extreme Performance

The paper positions h-BN as a material “second only to diamond” for its combined insulating and thermal properties. 6CCVD provides the ultimate material solution for applications requiring Diamond-Grade Performance.

6CCVD Material	Relevance to h-BN Research & Applications
Optical Grade SCD (Single Crystal Diamond)	Ideal for high-power heat spreading (Fig. 6d) and gate dielectric applications (Fig. 6b). SCD offers thermal conductivity (up to 2200 W m⁻¹ K⁻¹) far exceeding h-BN, providing superior thermal management for 3D ICs and high-frequency devices.
Polycrystalline Diamond (PCD)	Excellent, cost-effective alternative for large-area heat spreading substrates. PCD wafers up to 125mm are available, suitable for scaling up the thermal management solutions discussed.
Boron-Doped Diamond (BDD)	While h-BN is an insulator, BDD offers a chemically inert, conductive platform. Useful for electrochemical applications or as a robust, conductive substrate where the h-BN is grown or transferred.

Customization Potential & Engineering Services

The success of the h-BN growth was highly dependent on the quality and crystallinity of the Pt substrate. 6CCVD provides the necessary precision and customization to meet the stringent demands of 2D material research.

Research Requirement	6CCVD Capability	Value Proposition
High-Quality Substrates	SCD/PCD plates and wafers up to 125mm in diameter. Substrate thickness up to 10mm.	Provides large-area, ultra-stable, and highly crystalline platforms for subsequent CVD growth of h-BN or other 2D materials.
Surface Finish	SCD polishing to Ra < 1nm; Inch-size PCD polishing to Ra < 5nm.	Directly addresses the finding that smoother substrates (like single crystal Pt(111)) yield higher quality, smoother h-BN films (Ra 0.80 nm).
Integrated Device Fabrication	Internal metalization capabilities: Au, Pt, Pd, Ti, W, Cu.	Allows researchers to integrate metal contacts (MIS contacts, RRAM electrodes, Fig. 6a, 6c) directly onto the diamond substrate or h-BN film stack, streamlining device prototyping.
Custom Dimensions	Precision laser cutting and shaping services.	Enables the creation of custom-sized plates or wafers required for specific furnace sizes (like the 2” furnace used in the study) or unique device geometries.

Engineering Support

The successful integration of h-BN as a gate dielectric or heat spreader requires deep materials expertise. 6CCVD’s in-house PhD team specializes in extreme material properties and can assist with material selection for similar 2D Material Encapsulation, Thermal Management, and High-K Dielectric projects. We offer consultation on optimizing diamond properties (crystallinity, doping, surface termination) to serve as the ideal foundation for next-generation electronic stacks.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery to your research facility.

View Original Abstract

Hexagonal boron nitride (h-BN) is unique among two-dimensional materials, with a large band gap (~6 eV) and high in-plane thermal conductivity (>400 W m<sup>-1</sup> K<sup>-1</sup>), second only to diamond among electrical insulators. Many studies to date have relied on exfoliated h-BN, however, for large-scale applications the material must be synthesized by methods such as chemical vapor deposition (CVD). Here, we first investigate single-layer h-BN synthesized by CVD on single crystal platinum (Pt), comparing these films with h-BN deposited on more commonly used polycrystalline Pt and Cu. The h-BN film grown on single crystal Pt has the lowest surface roughness and best spatial homogeneity, and our electrochemical transfer process allows the Pt to be reused with no measurable degradation. Additionally, we also demonstrate direct capping of carbon nanotubes (CNTs) with as-grown h-BN, but we find that the direct growth partly degrades the CNT electrical conductivity. On the other hand, we show that transferred monolayer h-BN can serve as an ultrathin barrier which protects MoS2 from damage at high temperatures and discuss other applications that take advantage of the conformal h-BN deposition.

Tech Support

Original Source

DOI: https://doi.org/10.1088/2053-1583/ac10f1

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