Every material is composed of building blocks known as atoms, which can be arranged in a number of different configurations. The physical properties of a solid material are largely determined by its atomic arrangement, which in turn is influenced by the growth or synthesis conditions. Solid materials can be identified as crystalline or amorphous, depending upon their atomic configuration. Crystalline materials can be further divided into single crystal, microcrystalline, and nanocrystalline categories.
A crystal is a solid material that has a regular pattern of atoms or molecules that repeats across all dimensions. The repeating lattice pattern in some materials is continuous throughout an entire solid; these are known as single-crystal materials. Many elements and compounds can exist in a number of different forms, depending on their growth conditions. Silicon, which is used throughout the electronics industry, can exist in single-crystal as well as other forms.
Microcrystalline materials consist of millions of tiny crystals that have dimensions in the micro- range (one millionth of a meter). The crystals can point in random directions, giving the material distinctly different properties compared to single crystals. The areas between the micro-crystal-lites are known as grain boundaries and these are often visible under a microscope. Examples of microcrystalline materials include quartz and silicon.
Nanocrystalline materials consist of billions of small crystals that have length scales less than 100 nanometers (one ten millionth of a meter). As the crystallite size approaches the nanometer scale, a larger proportion of the material consists of grain boundaries leading to distinct properties. For example, nanocrystallite materials with crytallite sizes in the 10-20 nanometer range are often found to have a dramatically increased hardness. In some applications, an increased hardness can be useful. For example, nanocrystalline materials are being exploited in the production of super-hard steels.
Amorphous materials have no definite crystal structure and instead the atoms are arranged randomly within the solid. Amorphous materials occur naturally and can be synthesized in the laboratory. Either way, they are usually formed when liquids are cooled quickly below the melting temperature. When this occurs the atoms or molecules do not have sufficient time to arrange themselves into a crystalline structure. Examples of amorphous materials include sand, colloids, foam and glass.
- Iowa State University: Solid State Structure
- ASM International: Crystalline Structure
- PV Education: Single Crystalline Silicon
- The Free Dictionary: Microcrystalline
- National Board: Grain Boundaries
- Quartz Page: Types of Quartz
- Solar Energy Materials and Solar Cells: Microcrystalline materials and cells deposited by RF glow discharge
- Toosi University of Technology: Nanocrystalline Materials
- University of California Berkeley: Amorphous materials
- Cambridge University Press: Microcrystalline and Nanocrystalline Semiconductors: T. Leigh et. al.
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