When people hear “diamond,” they often think of a sparkling gemstone. But in industry, diamond is a true “heavy hitter.” What many don’t realize is that diamond does not come in just one structural form. Subtle yet critical differences between single-crystal and polycrystalline diamonds lead to completely different performance profiles and application paths.

If you’re curious about their “microscopic secrets” and their real-world roles, this article walks you through their structures, properties, fabrication methods, and application domains to help you understand the distinct strengths of these two remarkably hard materials.

1. Microstructure: The Fundamental Distinction

Single-Crystal Diamond: A Crystal That Is Ordered From Start to Finish

In single-crystal diamond, carbon atoms are tightly bonded through highly directional covalent bonds. These atoms are arranged in a perfectly ordered three-dimensional lattice—like a rigorously aligned formation.

This high degree of structural uniformity gives single-crystal diamond its purity, homogeneity, and structural integrity.

Polycrystalline Diamond: A Large Team Built From Many “Small Units”

Polycrystalline diamond consists of a multitude of nanoscale grains, each with its own crystallographic orientation. Grain boundaries exist between these small crystals, and the internal alignment is not perfectly uniform, making its structure far more complex than that of a single crystal.

However, it is precisely these grain boundaries that impart excellent toughness and a form of “self-sharpening,” making polycrystalline diamond even more suitable than single-crystal diamond for certain applications.

2. Differences in Physical Properties Directly Shape Their Application Styles

3. Fabrication Methods

Single-Crystal Diamond: Grown Layer by Layer

Modern industry primarily uses Chemical Vapor Deposition (CVD) to fabricate single-crystal diamond. The basic process is:

Low-pressure, high-temperature chamber → activate carbon-containing gases using plasma or hot filaments → carbon atoms deposit layer by layer onto a substrate → gradually forming a high-purity, highly controlled single crystal.

This approach allows precise control over crystal orientation, impurity levels, and color. It is the dominant method for producing laboratory-grown gemstones.

Polycrystalline Diamond: Growing Many Crystal Nuclei at Once

Polycrystalline diamond is also grown by CVD, but the process conditions—pressure, temperature, gas flow—are adjusted to promote the simultaneous formation of numerous crystal nuclei.

Each nucleus grows into a grain, ultimately forming a polycrystalline “mosaic.”
By tuning grain boundaries and grain size, various functional polycrystalline diamond films or bulk materials can be produced.

4. Application Fields

Where Single-Crystal Diamond Excels

1. Semiconductor Devices

Wide bandgap enables high-frequency and high-voltage transistors

Applicable to 5G systems, power electronics, and EV power chips

2. High-End Optical Instruments

Used in laser windows, infrared detectors, precision lenses

Absence of grain boundaries makes it ideal for ultra-high-precision optics

3. Jewelry and Scientific Research

CVD single crystals are now an important part of the gem-grade diamond market

Also essential in advanced laboratory tools such as diamond anvil cells (DACs)

Where Polycrystalline Diamond Shines

1. New Energy and Energy-Saving Technologies

Thermal management for photovoltaic modules

Protective or functional coatings for PEM fuel-cell bipolar plates

2. Thermal Management in Electronic Packaging

Used as heat-spreading substrates to cool chips

A key material for improving performance in compact electronic devices

3. Semiconductor Heat-Spreader Substrates

Extremely high thermal conductivity enables rapid heat dissipation

Enhances device stability and lifespan

Conclusion: No Absolute “Better”—Only What’s More Suitable

Single-crystal diamond:
Highly pure and structurally uniform, offering extreme performance for high-end applications.

Polycrystalline diamond:
Tough, cost-effective, and self-sharpening—making it ideal for industrial machining and thermal management.

They are like two equally capable experts with very different strengths, each excelling in its own arena. As CVD technology continues to advance, the boundaries between their applications will keep expanding, and both forms of diamond will play increasingly important roles in electronics, energy, optics, and beyond.

JXT Technology Co., Ltd. supplies single-crystal diamond substrates, polycrystalline diamond substrates, and diamond films.