Crystal Growth Support Thermal Expansion Gap Control
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Solution Overview
Problem
Early vapour phase crystal growth systems face challenges in controlling crystal growth due to sensitivity to temperature differentials and vapour flow, with limitations in precise control of vapour properties and risk of support damage during positioning and removal.
Innovation Solution
The apparatus employs a support with a higher coefficient of thermal expansion than the growth chamber, allowing for precise calibration of the gap between them, enabling accurate control of vapour properties and easy positioning/removal, with the support's relative expansion reducing the gap at higher temperatures for precise flow restriction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the support is made sufficiently smaller than the growth chamber at ambient temperature to allow easy positioning and removal, then the gap between the support and growth chamber is large enough for safe handling, but at high temperatures the gap becomes too large to provide precise flow restriction control
Solution Approach 1:
The support is made of a material with a higher coefficient of thermal expansion than the growth chamber. When heated to high temperatures, the support expands more than the growth chamber, automatically reducing the gap between them to provide precise flow restriction control. At ambient temperature, the support remains smaller, allowing easy positioning and removal with sufficient clearance.
2Manufacturing precision
If the gap between the support and growth chamber is reduced to improve flow restriction control, then vapour properties are better controlled, but the support may impact against the growth chamber during positioning and removal
Solution Approach 1:
The differential thermal expansion between the support and growth chamber ensures that the gap is large at ambient temperature (preventing impact during handling) and small at high temperatures (providing precise flow restriction). This temperature-dependent gap adjustment resolves the contradiction between safety during positioning and precision during operation.
3Manufacturing precision
If the support is made larger to improve flow restriction control at high temperatures, then vapour properties are better controlled, but positioning and removal become more difficult and risky
Solution Approach 1:
By selecting a support material with higher thermal expansion than the growth chamber material, the support automatically adjusts its size relative to the chamber based on temperature. At ambient temperature, the support is smaller and easier to handle; at high temperature, it expands to provide the desired flow restriction control.
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
This approach allows for precise control of vapour properties and crystal growth conditions, facilitating easy support placement and removal while minimizing the risk of damage, and enabling adjustment of the crystal's position within the temperature profile, particularly beneficial for growing thick crystals.
Implementation Method 1
By providing a support having a coefficient of thermal expansion which is greater than that of the growth chamber, when the apparatus including the support and the growth chamber is heated to the high temperatures required for vapour phase crystal growth, the relative expansion of the support will be greater than that of the growth chamber.
Implementation Method 2
By creating a temperature difference between the source zone and the sink zone where the seed is provided, a vapour pressure difference will be created between the source and sink zones which acts as the driving force for crystal growth.
Implementation Method 3
The gap between the support and the growth chamber can therefore play an important role in defining the vapour properties and hence growth conditions of a crystal growth apparatus.
Data Source
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AI summary
Crystal growth apparatus having a source chamber (20) configured to contain a source material, a growth chamber (50), a passage (40) for transport of vapour from the source chamber (20) to the growth chamber (50), and a support (70) provided within the growth chamber (50) and configured to support a seed crystal (60). The coefficient of thermal expansion of the support (70) is greater than the coefficient of thermal expansion of the growth chamber (50).