Physical Methods

Physical Methods

Inert-gas condensation

Physical Methods: (IGC) is a bottom-up approach to synthesize nanostructured materials, which involves two basic steps. The first step is the evaporation of the material and the second step involves a rapid controlled condensation to produce the required particle size.

Physical Methods

Physical Methods

Physical Methods

Electrical arc discharge
is based on laser vaporization; here an electric arc is used to vaporize the material directly, rather than indirectly through a laser pulse source. About 10% of the clusters formed are ions, and this avoids the need for a separate cluster ionization stage. Generally, cluster sizes of up to around 50 atoms are deposited on the target. Nanoshel uses the arc discharge heating to produce ultrafine powders of Fe, Si, SiC, and Al2O3. Gas pressure and arc current are the critical parameters that need to be controlled during evaporation to obtain the desired particle size.

Physical Methods: Nanoparticles are also synthesized by RF plasma method in Nanoshel. This plasma is generated by RF heating coils. The starting metal is contained in a pestle and this pestle is contained in an evacuated chamber. The metal is heated above its evaporation point by using high voltage RF coils wrapped around the evacuated chamber. Helium gas is allowed to enter the system and this gas forms high temperature plasma in the region of the coils. The metal vapor nucleates on the helium gas atoms and diffuses up to a cold collector rod, where nanoparticles are collected. Finally these nanoparticles are passivated by the introduction of appropriate gas (Oxygen).

Physical Methods

Pulsed Laser Method: This method is capable of high rate of production of 3gm/min. Nanoshel mainly uses this method in the synthesis of silver nanoparticles. Silver nitrate solution and reducing agent are allowed to flow into a blender like device. This device consists of a solid disc and this disc rotates with solution. Hot spots are created on the surface of the disc by subjecting it to pulses from a laser beam. Silver nitrate reacts with reducing agent at these hot spots and as a result, nano silver particles are formed. These particles can be separated by centrifuge. The size of the particles is controlled by the energy of the laser and angular velocity of the disc.

Ion Sputtering Method

Sputtering or Ion Sputtering involves vaporizing materials from a solid surface by bombarding a target with high-velocity ions of an inert gas, which causes ejection of atoms and clusters. Since high pressure hinders transportation of the sputtered material, sputter sources such as an ion gun or a hollow cathode plasma sputter source are normally used under vacuum. Positive, negative, as well as neutral charged clusters are produced. The clusters produced are hot and cool down by evaporation in flight.

Laser ablation (LA) is a process in which a laser beam is focused on a sample surface to remove material from the irradiated zone. Laser ablation has been considered and used for many technical applications, including: the production of nano materials, deposition of thin metallic and dielectric films, fabrication of superconducting materials, routine welding and bonding of metal parts, and micromachining of MEMS structures. Recently in Nanoshel laser ablation has been used for the production of various materials.

The laser pyrolysis technique is usually classified as a vapor-phase synthesis process which is also used in Nanoshel for the production of nanoparticles. In this class of synthesis routes, nanoparticles formation starts abruptly when a sufficient degree of super saturation of condensable products is reached in the vapor phase. Once nucleation occurs, fast particle growth takes place by coalescence/coagulation rather than further nucleation.

The ball milling method: A ball mill contains a stainless steel container and many small iron, hardened steel, silicon carbide, or tungsten carbide balls are made to rotate inside a mill (drum). The powder of a material is taken inside the steel container. This powder will be made into nanosize using the ball milling technique. Nanoshel uses this method for reducing the size of Nanoparticles.

Molecular Beam Epitaxy (MBE) can be considered as a special case of evaporation for single crystal film growth, with highly controlled evaporation of a variety of sources in Ultrahigh-vacuum of typically ̴10 -10 torr. Nanoshel uses MBE for synthesis of various thin films.

Chemical vapor Deposition (CVD) is chemical process used to give high quality, high performance, and solid materials. Here one or more volatile precursors are transported via the vapor phase to the reaction chamber, where they decompose on a heated substrate. Nanoshel have both vertical as well as horizontal CVD used to produce various materials.