Table 1. Microfabrication techniques used for the primary patterning of nanostructures.

Note: relevant exemplars from the literature are cited against each technique. The minimum feature size and length of patternable area are highly equipment and facility dependent, these values are derived from the either manufacturer provided specifications at the time of writing, or from the literature, where available. Techniques are sorted loosely by their prevalence within the field, with the most common listed first. Most fabrication protocols include a combination of techniques, here we are referring to the process used to define the initial pattern.

Technique	Example applications	Minimum feature size [μm]	Diameter of patternable areaa) [mm]	Advantages	Disadvantages
Photolithography	Nanoneedles,[26,69,133] hollow nanoneedles/ nanotubes,[134,135] nanowires,[136]	~0.6 – 3[137]	≥300 (typically ≥100)[137]	Good resolution	Equipment expensive
				Parallel patterning	Tooling expensive and unmodifiable
				Well-established industry process	Complex protocols
					Sub-micron resolution challenging to achieve in many system
Electron-beam lithography	Nanowires,[138,139] nanopillars,[31] nanostructures,[140,141] nanopits / nanopores,[142,143] nanoelectrodes,[28,66,86,144]	~0.04 – 0.5[145]	≥300 (in theory, but in reality individual field size ~1 1)[146]	Best resolution	Expensive equipment
				Flexible design (no fixed tooling required)	Very slow, effectively limiting patternable area
					Complex protocols
					Limited resist choices
Track-etched membrane / nanopore templates	Nanoelectrodes,[147] spiky microstraws,[94] nanopillar arrays,[148] nanostraws,[90,91]	~0.1[89]	≥100[89]	Templates are highly affordable	Limited or no control over location of individual pores
				Large patternable areas
				No cleanroom required
Nanoimprint lithographyb)	Nanowires,[149] nanopillars,[148,150] nanostructures.[151]	≥0.04[153] - 25	≥150[153] (very large area roll-to-roll patterning reported)[151]	Parallel / quick patterning process	Requires expensive master stamp / shim
				Good resolution	Care required to optimize resist and surface treatments to ensure good demolding
				Excellent for reproducing existing designs
				Very large area patterning possible
Nanosphere / colloidal lithography	Nanowires,[27,154,155] nanoelectrodes,[136] nanopillars.[156]	~0.1 – 2[157,158]	1×103 (areas of up to 1 m2 reported)[158]	Affordable method	Challenging to align patterns to existing features
				Achievable with relatively simple equipment
					Strong interdependence between patterned particle and spacing
				Very large area patterning possible
Ion-beam lithographyc)	Nanoelectrodes,[62] nanoantennas,[159] nanotubes.[92]	~0.02 – 0.5[160]	~2.5[160]	High precision	Expensive equipment
				Best resolution	Very slow, effectively limiting patternable area
Interference lithography	Nanostructures;[161] nanoposts.[162]	~0.05 – 0.5[163]	≥200[163]	Good resolution	Limited design choices as pattern must be formed by interfering beams
				Relatively large areas possible
				Specific tooling required	Requires relatively specialist setup
				Parallel processing
Two-photon / multiphoton lithography	Nanopillars / ridges,[124,164] microneedles.[165]	~0.15 – 10 (2D patterning, in 3D resolution is lower)[166]	≥100 (individual field size ≥1)[166]	Good resolution	Expensive equipment
Flexible design (no fixed tooling required)				Highest resolution only possible in 2D, 3D structures more typically in micron scale
					Slow, hence limited write areas
Electroless depositiond)	Nanowires.[167,168]	~0.1 – 0.2[167–169]	≥100 (limited by wafer handling for acid etching)	Highly affordable	Stochastic – limited control over pattern density and size of features
				Achievable in chemistry lab, no cleanroom required	Challenging to align to existing features
Deposition of particulates from gas phase (e.g. aerosol deposited nanoparticles or sputtering)d)	Nanowires,[170,171] nanoneedles.[29,81]	~0.04 – 0.1[170,171]	≥100 (assuming wafer-based system)	Can be performed in-situ with growth mechanisms for efficient processing	Stochastic – limited control over pattern density and size of features
					Challenging to align to existing features
Direct (write) laser lithography	Nanoneedles[172]	1 – 50[173]	≥100[173]	Flexible design (no fixed tooling required)	Compromise on resolution due to larger laser beam spot size
Typically easier to pattern large areas (e.g. whole wafers) compared to multiphoton approaches	Requires relatively specialist equipment

^a)This is an estimate of the reasonable diameter over which a given technique can be used to define a pattern, assuming a circular write field;

^b)nanoimprint lithography requires a master stamp (also known as a shim) to define the pattern being imprinted. This stamp is frequently fabricated by other techniques, such as electron-beam lithography;

^c)this refers to using a focused-ion beam microscope to selectively mill (or deposit) a pattern of nanostructures;

^d)these techniques, while mainly used to deposit material and turn 2D structures into 3D, can also be used to define an initial pattern through the stochastic / partial deposition of another catalytic material onto a surface, which is subsequently used as a seed for further growth.