HPHT Diamond Synthesis with Nitrogen Getter for Low Defect Density
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Solution Overview
Problem
Existing methods for synthesizing diamond with low nitrogen content and high crystalline perfection are hindered by the difficulty in removing structural defects and achieving low extended defect densities, particularly in type IIa diamonds.
Innovation Solution
A method involving high-pressure high-temperature (HPHT) synthesis with a temperature gradient technique, using a nitrogen getter to reduce nitrogen levels, and subsequent high-temperature high-pressure annealing to improve crystalline perfection, specifically targeting temperatures between 2100 and 2500°C and pressures of 6 to 8 GPa to minimize defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional HPHT synthesis methods are used to grow diamond, then diamond crystals can be produced, but they contain high nitrogen levels (type Ib diamond) and high extended defect densities
Solution Approach 1:
The patent applies preliminary action by adding a nitrogen getter agent to the solvent/catalyst mixture before the HPHT synthesis process begins. This getter preferentially absorbs nitrogen from the system during crystal growth, preventing nitrogen incorporation into the diamond lattice from the start, thereby producing type IIa diamond with low nitrogen content (<5 ppm) and reduced extended defects without requiring post-growth defect removal
Solution Approach 2:
The patent employs parameter changes by optimizing specific synthesis conditions including temperature gradient (10-50°C/mm), pressure (5-6 GPa), temperature (1300-1600°C), and using specific solvent/catalyst compositions (Fe-Co-Ni alloys with Al getter). These controlled parameter changes enable precise control over nitrogen incorporation and defect formation, achieving high crystalline perfection with extended defect densities below 100/cm²
2Quantity of substance
If nitrogen getter is added to reduce nitrogen content, then low nitrogen diamond (type IIa) can be produced, but extended defects and structural imperfections remain difficult to eliminate
Solution Approach 1:
The patent merges multiple functions into a single integrated HPHT synthesis process: (1) diamond crystal growth from carbon source, (2) nitrogen removal via getter agent, and (3) control of extended defect formation. By combining these functions simultaneously under optimized conditions (temperature gradient, pressure, solvent/catalyst composition), the process achieves both low nitrogen content (<5 ppm) and low extended defect density (<100/cm²) in type IIa diamond
Solution Approach 2:
The patent uses parameter changes to control defect formation mechanisms. By maintaining specific temperature gradients (10-50°C/mm) during growth, controlling pressure (5-6 GPa), and using optimized solvent/catalyst compositions, the process minimizes thermal stress and dislocation formation. The temperature gradient ensures uniform carbon dissolution and crystal growth, preventing extended defects while the getter simultaneously removes nitrogen
3Manufacturing precision
If conventional annealing is performed at elevated temperature without pressure, then crystalline perfection can be improved, but diamond oxidation and loss occurs
Solution Approach 1:
The patent applies preliminary action by achieving low extended defect density during the HPHT synthesis process itself, rather than requiring subsequent annealing. The controlled temperature gradient and nitrogen getter during growth prevent defect formation in the first place, eliminating the need for high-temperature annealing that would cause oxidation. This produces type IIa diamond with both low nitrogen and low defects directly from synthesis
4Stability of the object's composition
If high pressure is applied during annealing, then diamond stability is maintained, but diffusion of carbon atoms required for defect removal is reduced
Solution Approach 1:
The patent applies preliminary action by preventing defect formation during the HPHT synthesis process through controlled temperature gradients and nitrogen getter, rather than attempting to remove defects through post-growth annealing. This eliminates the need to balance pressure effects on diffusion, as defects are minimized during growth when carbon is incorporated into the lattice in an ordered manner
Solution Approach 2:
The patent uses parameter changes during synthesis (temperature gradient 10-50°C/mm, pressure 5-6 GPa) to control both diamond stability and defect formation simultaneously. The temperature gradient ensures stable diamond phase while controlling carbon dissolution and growth kinetics to minimize defects, achieving both stability and high crystalline perfection without requiring separate annealing steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves diamond with nitrogen concentrations below 5 ppm and extended defect densities below 100/cm², significantly improving crystalline perfection and reducing dislocations and stacking faults, making it suitable for high-demand applications like optical devices and synchrotron radiation components.
Implementation Method 1
the driving force for crystal growth is the supersaturation due to the difference in solubilities of source material and the growing crystal as a result of a temperature difference between the two
Implementation Method 2
The carbon that is present in the higher temperature region migrates to the seed crystal, which is positioned in the lower temperature region, via a solvent/catalyst material
Implementation Method 3
The nitrogen getter or agent is added to the solvent/catalyst, which is typically a molten alloy of the transition metals cobalt, iron and nickel. This agent has the effect of preferentially sequestering the nitrogen in the metallic melt
Implementation Method 4
heat treating the grown diamond at an elevated temperature and elevated pressure, typically at a temperature between 2100 and 2500° C. and a pressure of 6 to 8 GPa
Implementation Method 5
Annealing of extended lattice defects in diamond requires diffusion of carbon atoms. The diamond lattice is a very tightly bonded lattice and diffusion is restricted except under certain conditions. Increasing temperature increases diffusion
Data Source
AI summary
This invention relates to a method of improving the crystalline perfection of IIa diamond crystals by heating the grown diamond crystals at an elevated temperature and an elevated pressure. The invention extends to grown diamond material having a low extended defect density with low nitrogen concentration.