How to form nanoparticlesNanoparticles which are chemicals or objects with dimensions of 1-100nm can be synthesized through top down and bottom up processes [1, 2]. The top down approach dealing with large piece of material and process it into smaller size by milling, grinding or electron beam machining. The mechanical process usually yield particle of various size distributions in the range of (10 -1000nm) of different particle shape [5]. The method has the advantage for the application of nanocomposite due to its superior possibility of interconnection and integration to improve the particular property of a material [6]. For bottom up approach it involves the use of single atoms and molecules for building block of structures [2]. The methods can be further classified into vapor phase and liquid phase fabrication. Pyrolysis and solvothermal reaction are the examples for the synthesis method in each phase where the pyrolysis happens in vapor phase while the latter occurs in liquid phase [5]. Pyrolysis will result in aggregates and agglomerates through thermodecompostion of vaporous precursor at high pressure and elevated temperature. The oxide particles will then be recovered by air classified the resulting solid. For solvothermal reaction, the precursor mainly dissolved in hot non aqueous solvents for growing nanocrystal. Both the methods promised low cost, simple, continuous operation and high yield [3]. Refer to Figure 1 and 2 in appendix for the detail synthesis process. In comparison with both the top down and bottom up approach, top down methods are good for structures that make macroscopic connections and possess the property of long range order. Whereas, bottom up approaches are good for fabricate and establishing short range order at nanoscale dimensions [4]. References [1] Kennedy, Chris. 2014. What are nanoparticles. http://www.csiro.au/Organisation-Structure/Divisions/CMSE/Nanosafety/What-are-nanoparticles.aspx

[2] Kulkarni, Lokesh. 2009. Synthesis And Characterization of Nanoparticles. http://ise.tamu.edu/metrology/Group%20Seminars/Synthesis%20and%20Characterization%20of%20Nanoparticles.pdf[3] Mandal, Ananya. 2015. Synthesis of Nanoparticle. Accessed March 3, http://www.news-medical.net/health/Synthesis-of-Nanoparticles.aspx

[4] Picraux, Tom. 2014. Nanotechnology. http://www.britannica.com/EBchecked/topic/962484/nanotechnology/236451/Communications#toc236452 [5] Overney, Rene. 2010. Nanoparticle Synthesis. Accessed March 3, http://courses.washington.edu/overney/NME498_Material/NME498_Lectures/Lecture4-Overney-NP-Synthesis.pdf [6] Public Health. 2015. Nanotechnologies. Accessed March 3,http://ec.europa.eu/health/scientific_committees/opinions_layman/en/nanotechnologies/l-3/4-nanoparticle-formation.htm#0p0

Appendix

Figure 1: Vapor phase fabrication process [3]

Figure 2: Liquid phase fabrication process [3]

Top-down approaches are good for producing structures with long-range order and for making macroscopic connections, while bottom-up approaches are best suited for assembly and establishing short-range order at nanoscale dimensions.simple process, low cost, continuous operation and high yield.are the example of methods that used to build the nanoparticle atom-by atom through chemical reaction.

In pyrolysis, a vaporous precursor (liquid or gas) is forced through a hole or opening at high pressure and burned. The resulting solid is air classified to recover oxide particles from by-product gases. Pyrolysis often results in aggregates and agglomerates rather than singleton primary particles.Precursors are dissolved in hot solvents (e.g., n-butyl alcohol) and solvent other than water can provide milder and friendlier reaction conditions If the solvent is water then the process is referred to as hydrothermal method. growth and self assembly from single atoms or molecules for Take a large hunk of material and drill/blast/mechanically process it into tiny nano-sized pieces. This is thetop-down approach. Another way to think about this is making big stuff smaller.2. Take a molecule, or a simple salt , that has the right atoms, and perform a chemical reaction to build the nanoparticle atom-by-atom. This is thebottom-up approach. Another way to think about this is making small stuff bigger.Nanotechnologyis dependent onnanostructuresthat require creation and characterization. Two fundamentally different approaches for the controlled generation of nanostructures have evolved. On one hand there is growth and self assembly, from the bottom up, involving singleatomsandmolecules. On the other hand there is the top- down approach in which the powerful techniques of lithography and etching start with large uniform pieces of material and generate the required nanostructures from them. Both methods have inherent advantages. Top down assembly methods are currently superior for the possibility of interconnection and integration, as in electronic circuitry.Bottom-upassembly is very powerful in creating identical structures withatomicprecision, such as the supramolecular functional entities in living organisms. In many different fields ofnanoscalescience, e.g. the production of semiconductor quantum dots for lasers, the production ofnanoparticlesby self organization, and the generation of vesicles from lipids, self organization is used for the generation of functionalnanometresized objects. To date, man made self organised structures (Niemeyer 2001) remain much simpler than natures complex self organised processes and structures