**5. Fabrication**

Generally, there are two methods to synthesize nanomaterials including quantum dots, top-down and bottom-up (**Figure 3**). In the top-down synthesis approach, the bulk material is transferred to nanometer size using an electron beam or high-energy ions. The methods that fall into this category are electron beam lithography, reactive ion etching, focused beam lithography, and dip pen lithography [12]. However, these methods have limitations and disadvantages such as structural defects in the patterning and impurities in the quantum dots synthesized [13]. In the bottom-up methods, atoms or molecules are assembled step by step to produce nanomaterials. These synthesis approaches are highly diverse and generally

**Figure 3.**

*Various methods for the synthesis of nanomaterials.*

can be categorized as chemical, physical, and biological methods. The common bottom-up methods are derived from the development of atom or molecular selfassembly such as chemical reduction method, electrochemical method, microemulsion method, and physical/chemical vapor deposition techniques [14]. The main advantage of bottom-up approach is that they can generally synthesize homogenous nanostructures with perfect crystallographic and surface structures.
