Editing Bottom-up and top-down design (section)

=== Nanotechnology ===
{{Main article|Nanotechnology}}
[[File:Nanoparticle synthesis techniques.jpg|thumb|right|Nanoparticle synthesis techniques]]

Top-down and bottom-up are two approaches for the manufacture of products. These terms were first applied to the field of nanotechnology by the [[Foresight Institute]] in 1989 to distinguish between molecular manufacturing (to mass-produce large atomically precise objects) and conventional manufacturing (which can mass-produce large objects that are not atomically precise). Bottom-up approaches seek to have smaller (usually [[Molecule|molecular]]) components built up into more complex assemblies, while top-down approaches seek to create nanoscale devices by using larger, externally controlled ones to direct their assembly. Certain valuable nanostructures, such as [[Silicon nanowire#Synthesis|Silicon nanowires]], can be fabricated using either approach, with processing methods selected on the basis of targeted applications.

A top-down approach often uses the traditional workshop or microfabrication methods where externally controlled tools are used to cut, mill, and shape materials into the desired shape and order. [[Micropatterning]] techniques, such as [[photolithography]] and [[inkjet printing]] belong to this category. Vapor treatment can be regarded as a new top-down secondary approaches to engineer nanostructures.<ref>{{cite journal|last1=Saghaei|first1=Jaber|last2=Fallahzadeh|first2=Ali|last3=Saghaei|first3=Tayebeh|title=Vapor treatment as a new method for photocurrent enhancement of UV photodetectors based on ZnO nanorods|journal=Sensors and Actuators A: Physical|date=June 2016|volume=247|pages=150–155|doi=10.1016/j.sna.2016.05.050|bibcode=2016SeAcA.247..150S }}</ref>

Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to (a) self-organize or self-assemble into some useful conformation, or (b) rely on positional assembly. These approaches use the concepts of [[molecular self-assembly]] and/or [[molecular recognition]]. See also [[Supramolecular chemistry]]. Such bottom-up approaches should, broadly speaking, be able to produce devices in parallel and much cheaper than top-down methods but could potentially be overwhelmed as the size and complexity of the desired assembly increases.