A single crystal, also called monocrystal, is a crystalline solid in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.
Grain boundaries have a lot of significant effects on the mechanical, physical and electrical properties of materials.
Therefore, single crystals are demanded in many fields, such as microelectronics and optoelectronics, as well as structural and high temperature materials.
How does it work?
A number of methods to grow single crystal has been developed and employed:
Flame fusion: The raw materials are added to the top chamber of the furnace. Oxygen and hydrogen are blown into the cabin for combustion, where a high temperature is achieved. Liquid droplets of materials form single crystal at the tip. This method could provide a high growing speed. The quality of the crystal produced, however, is limited by the irregular temperature distribution and cooling velocity.
Czochralski: In the Czochralski method, a single crystal is pulled from the melt. This method has had nearly one hundred years’ history, whereas currently is still the most widely used method to fabricate single crystal materials, especially large semiconductor and metallic materials. It can produce very high quality crystals.
Bridgman-Stockbarger: In this method, the central chamber is turning as well as pushed down, from the high temperature region towards the low temperature region. The solid liquid interface is moved along the charge.
Floating Zone: Floating zone crystal growth is a method developed from Bridgman-Stockbarger method. It is most broadly utilized in growing cylindrical boules of very high purity Silicon single crystal. Its main advantage is the absence of crucible which is one of the sources of contamination in the other methods. It is arguably one of the most enabling techniques developed in the information era, to allow integrated circuits to be mass produced on smaller scales.
Solution growth: The basic idea of this method is to achieve an over-saturated solution first and then to have it crystallized. It is particularly adapted to non congruent materials and/or very high melting point compounds.
The limitation of this method lies in the choice of appropriate solvent. For each particular crystal that is demanded, there should be some certain solvent, either water, or molten salt or metals, to provide a stable crystallization.
Hydrothermal: Hydrothermal synthesis can be defined as a method of synthesis of single crystals which depends on the solubility of minerals in hot water under high pressure. The crystal growth is performed in an apparatus consisting of a steel pressure vessel called autoclave, in which a nutrient is supplied along with water. A gradient of temperature is maintained at the opposite ends of the growth chamber so that the hotter end dissolves the nutrient and the cooler end causes seeds to take additional growth.
Sublimation: When materials cannot be grown from the liquid phase, the sublimation method could be a good alternative. It uses solid in a powder state as a source. Generally the crystal quality is more difficult to control than when the growth is done from the liquid phase.
Applications of single crystal materials are broad.
Silicon single crystals and related materials have a large market in integrated circuits industry. Monocrystals of sapphire are highly demanded in laser devices.
For metallic materials, turbine blades can be made of single crystals of superalloys, which can achieve novel mechanical properties.
Sample handling requirements:
Suitable precursor/ Solid Form
Dr Ian Hancox, 024 76 150380 email i dot hancox at warwick dot ac dot uk
Typical results format, and sample:
|Warwick collect/analyse data|
|Warwick collect data|
|Available to user with expertise/ contribution|
|Spare capacity for collaborative research|