Unit - 3 RPOCESSING of Nanomaterials Preparation

Nanomaterials and Preparation

1. OML353 – Nanomaterials and Applications Handled by Dr. M. Vinoth ASP/EEE Selvam College of Technology

2. UNIT III PROCESSING Bottom-up and top-down approaches for the synthesis of nanomaterials, mechanical alloying, chemical routes, severe plastic deformation, and electrical wire explosion technique.

3. Based on Synthesis Method: a. Bottom-Up Nanomaterials: Nanomaterials synthesized from atomic or molecular building blocks, often through chemical or physical processes. b. Top-Down Nanomaterials: Nanomaterials derived from bulk materials through processes like grinding, etching, or lithography. These classifications are not exhaustive, as nanomaterials continue to be a rapidly evolving field of research with new materials and structures being discovered and engineered.

4. TOP DOWN APPROACH The top-down approach in nanotechnology refers to a methodology where larger structures or devices are fabricated by reducing their size from bulk materials through various subtractive processes. It involves manipulating and sculpting materials at the nanoscale to create desired structures and functionalities. This approach is often used when working with well-established materials and technologies that can be manipulated at larger scales and then miniaturized.

5. Key characteristics and steps of the top-down approach in nanotechnology include: Lithography: Lithography is a central technique in the top-down approach. It involves using patterns to selectively remove or add material to a substrate. Etching: Etching techniques are used to selectively remove material from a substrate. Wet chemical etching and dry etching (e.g., reactive ion etching) are utilized to achieve high precision in pattern transfer from the mask to the substrate. Deposition: Deposition techniques are employed to add thin layers of material onto a substrate. Physical vapor deposition (PVD) and chemical vapor deposition (CVD) are examples of methods used to deposit materials atom by atom or molecule by molecule. Milling and Machining: In cases where direct patterning techniques are not suitable, milling and machining processes can be used to sculpt materials at the nanoscale.

6. Lithography:

7. Etching:

8. Milling and Machining

9. Some common bottom-up techniques for producing nanomaterials include: Chemical Synthesis: Chemical methods, such as sol-gel synthesis, hydrothermal synthesis, and chemical vapor deposition (CVD), are used to create nanomaterials by controlling the reaction conditions and precursor molecules. These techniques can produce a wide range of nanomaterials, including nanoparticles, nanowires, and nanotubes. Self-Assembly: Self-assembly is a process in which molecules or nanoparticles spontaneously organize themselves into ordered structures at the nanoscale. This approach relies on molecular interactions, such as van der Waals forces, hydrogen bonding, and electrostatic interactions, to form nanomaterials with specific arrangements.

10. Common wet chemical synthesis techniques include: Sol-Gel Method: This method involves the hydrolysis and condensation of metal alkoxides to form a colloidal solution, which is then transformed into solid nanomaterials. Co-precipitation: In this technique, two or more precursor salts are mixed in a solvent, and the desired nanomaterial precipitates out of the solution. Chemical Reduction: This method involves the reduction of metal ions in solution to form nanoparticles. Typically, a reducing agent is used to convert metal ions into metal atoms, which then nucleate and grow into nanoparticles.

11. Chemical vapor deposition  ( CVD ) Chemical vapor deposition  ( CVD ) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.