MM ethods for ethods for single crystal single crystalgrowthgrowth

SS . UMEET S . UMEET SCCHAVANHAVAN

. .- -M SC II SEM III. .- -M SC II SEM III

CC ontent ontent

1.1. CC .RYSTAL GROWTH FROM LIQUID SOLUTION .RYSTAL GROWTH FROM LIQUID SOLUTION

- FLUX GROWTH- FLUX GROWTH

- .TEMPERATURE GRADIENT METHODS- .TEMPERATURE GRADIENT METHODS

2. 2. CC .RYSTAL GROWTH FROM VAPOUR PHASE .RYSTAL GROWTH FROM VAPOUR PHASE

- .EPITAXIAL GROWTHMETHODS- .EPITAXIAL GROWTHMETHODS

FLUX GROWTH FLUX GROWTH

- - IIn contrast to the other methods in which melted n contrast to the other methods in which melted solid substance that have the same composition as the solid substance that have the same composition as the melt.melt.

- - FFlux growth method involves the growth of crystals lux growth method involves the growth of crystals from solvent of different compositon to give crystals.from solvent of different compositon to give crystals.

- - TThe solvent may be the one of the constituents of the he solvent may be the one of the constituents of the desired crystal. desired crystal. E.g. : crystalization of salt hydrate crystals using E.g. : crystalization of salt hydrate crystals using water as a solvent.water as a solvent. - - TThe solvent may be entirely seperate liquid element or he solvent may be entirely seperate liquid element or compound in which the crystal of intrest are partially compound in which the crystal of intrest are partially soluble. soluble. EE.g : SiO.g : SiO22 and various high melting silicates may be and various high melting silicates may be precipitated from low melting borate or halide melts.precipitated from low melting borate or halide melts.

- - IIn these cases, the solvent melts are sometimes n these cases, the solvent melts are sometimes reffered to as fluxes, since they effectively reduce the reffered to as fluxes, since they effectively reduce the M.P. M.P. OOf the crystals by the considerable amount.f the crystals by the considerable amount.

- The method has been used to grow crystals of - The method has been used to grow crystals of beta-allumina and acid electrolytes using borax flux.beta-allumina and acid electrolytes using borax flux.

TEMPERATURE GRADIENT METHODTEMPERATURE GRADIENT METHOD (HYDROTHERMAL TECHNIQUE)(HYDROTHERMAL TECHNIQUE)

-- Hydrothermal synthesis involves heating reactants in Hydrothermal synthesis involves heating reactants in water/steam at high pressures and temperatures.water/steam at high pressures and temperatures.

- - TheThe water has two functions, as a pressure-water has two functions, as a pressure-transmitting medium and as a solvent, in which the transmitting medium and as a solvent, in which the solubility of thesolubility of the reactants is Preactants is P..TT..-dependent.-dependent.

- R- Reacteactaant and water are placed nt and water are placed inside a PTFE-lined cylinderinside a PTFE-lined cylinder oror‘bomb’ which is either sealed or‘bomb’ which is either sealed orconnected to an externalconnected to an externalpressure control.pressure control.

- - The The cylindercylinder is placed in an oven, is placed in an oven,usually at a temperature in the range usually at a temperature in the range 100–500 ◦C.100–500 ◦C.

- - Pressure is controlledPressure is controlled either externally or by the either externally or by the degreedegree ofof filling in a sealed filling in a sealed cylinder. cylinder.

Pressure–temperature relations for water at constant volume.Pressure–temperature relations for water at constant volume.

- - Dashed curves represent pressuresDashed curves represent pressures developed inside a closed developed inside a closed vessel;vessel;- N- Numbers represent the percentage filling of the vessel by umbers represent the percentage filling of the vessel by water at ordinarywater at ordinary P,T. P,T.

- B- By making use of the P–T ‘phase diagram’y making use of the P–T ‘phase diagram’curve AB is the saturatedcurve AB is the saturated steam curve and separates steam curve and separates water (above) from steam (below)water (above) from steam (below)..

- A- At temperatures above 374 ◦C, t temperatures above 374 ◦C, point B, waterpoint B, wateris in the supercritical condition and there is no is in the supercritical condition and there is no distinction between liquid and vapour statesdistinction between liquid and vapour states..

- - FFor the growth of single crystal by hydrothermal or the growth of single crystal by hydrothermal method, it is neccessary to add a mineralizer. method, it is neccessary to add a mineralizer. MMineralizer is any compound that speeds up to its ineralizer is any compound that speeds up to its crystalization.crystalization.

- It is usually operates by increasing the solubility of - It is usually operates by increasing the solubility of the solute through the formation of soluble species that the solute through the formation of soluble species that would not usually be present in water.would not usually be present in water.

CRYSTAL GROWTH FROM VAPOUR PHASECRYSTAL GROWTH FROM VAPOUR PHASE (EPITAXIAL GROWTH METHOD)(EPITAXIAL GROWTH METHOD)

-- Single crystal in the form of thin layers are often Single crystal in the form of thin layers are often required for application in electronic devices and special required for application in electronic devices and special methods may be needed for their applications.methods may be needed for their applications.

- The use of seed crystal in other methods implies on - The use of seed crystal in other methods implies on orientation relationship between two growing crystals orientation relationship between two growing crystals and seed.and seed.

- The crystal may grow epitaxially or topotaxially.- The crystal may grow epitaxially or topotaxially.

Vapour-phase transport Vapour-phase transport

- - The essential feature of this method is the formation The essential feature of this method is the formation of a volatile, unstable intermediate that contains at leastof a volatile, unstable intermediate that contains at least one of the elements in the desired final product. The one of the elements in the desired final product. The method may be used to grow single crystals. method may be used to grow single crystals.

-- The method consists of a tube, usually of silica glass, The method consists of a tube, usually of silica glass, with the reactantswith the reactants A, at oneA, at one end, which is sealed either end, which is sealed either under vacuum or with a small amount of the under vacuum or with a small amount of the transporting agenttransporting agent BB..

- - IIn the epitaxial growth of thin layers, oriented growth n the epitaxial growth of thin layers, oriented growth of crystals occurs on the surface of the substrate. of crystals occurs on the surface of the substrate. TThe he substrate may be crystal of the same or similar substrate may be crystal of the same or similar composition or it may be an entirely different material composition or it may be an entirely different material whoes lattice parameters at its surface, match those of whoes lattice parameters at its surface, match those of the growing crystals to within few percent.the growing crystals to within few percent.

- The chemical reaction may or may not be takes place - The chemical reaction may or may not be takes place in vapour phase.in vapour phase.

- - IIn this deposition it is carried out on a substrate two n this deposition it is carried out on a substrate two dimentionally hence, it is known as epitaxial growth.dimentionally hence, it is known as epitaxial growth.

E.g – deposition of silicon from silane or chlorosilane.E.g – deposition of silicon from silane or chlorosilane.

SiHSiH44(g) carrier gas Si(s) + 2H(g) carrier gas Si(s) + 2H22(g)(g)

SiClSiCl44(g) + 2H(g) + 2H22(g) Si(s) + 4HCl(g) Si(s) + 4HCl

RReferenceeference

Solid State Chemistry and its Solid State Chemistry and its Applications, 2nd Edition by Applications, 2nd Edition by A.R. WestA.R. West..