Techniques for Synthesis of Nano-materials Akshay Tiwari and Rushabh Shah B.Tech Electrical
What are Nano-Particles • In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. • Particles are further classified according to size: in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. • Fine particles are sized between 2,500 and 100 nanometers. • Ultrafine particles, or nanoparticles are sized between 100 and 1 nanometers.
Synthesis Method • Top Down Approach: • Begins with a pattern generated on a larger scale, then reduced to nanoscale • Relatively expensive and time consuming technique • The approach use larger (macroscopic) initial structures • The structures can be externally-controlled in the processing of nanostructures • Bottom Up Approach: • Start with atoms or molecules and build up to nanostructures • Fabrication is much less expensive • Includes the miniturization of materials components (atomic level) leading to formation of nano structures. • During Self assembly the physical forces operating at nanoscale are used to combine basic units into larger stable structure
Top-Down Approach: Lithography Coat Protect Expose Etch Repeat Multiple Patterned Layer of Different Materials
Bottom Up: Molecular Assembly • Nature uses self-assembly in infinitely subtler ways; indeed, the whole of the natural world is self assembled • Spontaneous organization of molecules into stable, structurally well-defined aggregates (nanometer length scale). • Molecules can be transported to surfaces through liquids to form self-assembled monolayers (SAMs). Polythiophene wires
Bottom Up Method: Inert-gas Condensation • An inorganic material is vaporized inside a vacuum chamber into which an inert gas (typically argon or helium) is periodically admitted. • Once the atoms boil off, they quickly lose their 23 energy by colliding with the inert gas. • The vapor cools rapidly and supersaturates to form nanoparticles with sizes in the range 2–100 nm that collect on a finger cooled by liquid nitrogen.
Molecular Beam Epitaxy (MBE) A molecular beam epitaxy (MBE) machine is essentially an ultrahigh-precision, ultra clean evaporator, combined with a set of in-situ tools, such as Auger electron spectroscopy (AES) and/or reflection high energy electron diffraction (RHEED), for characterization of the deposited layers during growth.
Methods for making 1-D and 2-DNanomaterials • The production route for 1-D rod-like nanomaterials by liquidphase methods is similar to that for the production of nanoparticles. • CVD methods have been adapted to make 1-D nanotubes and nanowires. Catalyst nanoparticles are used to promote nucleation. • Nanowires of other materials such as silicon (Si) or germanium (Ge) are grown by vapor-liquid-solid (VLS) methods.
Chemical Vapour Deposition • A process involving deposition of a solid material from gaseous phase. • Precursor gases diluted in carrier gases are delivered into the reaction chamber at ambient temperatures. • As they pass over or come into contact with a heated substrate, they react or decompose forming a solid phase which and are deposited onto the substrate. • Precursors for CVD processes must be volatile, but also stable enough to be able to be delivered to the reactor. • Physical Vapour Deposition is different from cvd as it uses solid precursors whereas cvd uses gases.
Conclusions • Two approaches used for nano-particle synthesis • Bottom-up and • Top-Down Approach • Common Methods Used include: • Optical Lithography (Top-Down) • Inert Gas Condensation (Bottom-up) • Chemical Vapour Deposition( Bottom-up)