SINGLE CRYSTALS ISSUES TO ADDRESS -What is single crystal ? -Most widely used Crystal Growth methods -Single crystal materials and their industrial applications

“GRAINS ALIGN THEMSELVES WITH HEAT FLOW DIRECTION.” WHAT IS SINGLE CRYSTAL ? Single crystal is a crystalline solid material in which periodic and repeated arrangements of atom is perfect and extends throughout the entire sample with no interruption and grain boundaries . -----IMPORTANT FACTS------- Since grain boundaries have significant effect on material properties especially on mechanical, optical and electrical ones, grain boundaries are the main concern of studies in single crystals. Because of the thermodynamic effects of surrounding on the microstructure of materials, stress effects of impurities and mobility of crystallogrophich defects and dislocations, natural formation of single crystals in significance size are exceedingly rare in nature. Moreover single crystal growth is also diffucult in the under controlled laboratory conditions, because most of them are relied on emprical enginering and trial-error techniques due to influence of numerous interdependent parameter. Most of growth techniques are based on the fact: “GRAINS ALIGN THEMSELVES WITH HEAT FLOW DIRECTION.”

SINGLE CRYSTAL GROWTH METHODS Czochralski Method Flaot Zoning Bridgman Stockbarger Vapor Phase Epitaxy

Most Widely Used Single Crystal Materials

INDUSTRIAL APPLICATIONS SILICON: - Predictable , reliable electronic properties - Extensive usage in fabrication of semiconductor -Fundamental material of electronic circuits and devices. -microprocessors SAPPHIRE: Advanced light transmission property and good heat conductivity and resistivity. - First ever laser produced is based on the sapphire (ruby chromium impurity in saphire). - Vacuum equipments, windows in reaction furnaces, scanner windows and caps for optical communication . S.C. SUPPERALLOYS: -Advanced mechanical strength and enhanced creep resistance at high temperatures, good corrosion and oxidation resistance. -With single crystal super alloys operation temperature has advanced up to 1373 K from 973 K . - Turbine blades, jet engines, minature gas turbines (micro turbines).