Plasmonic nanolithography

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Plasmonic nanolithography (also known as plasmonic lithography or plasmonic photolithography) [1] is a nanolithographic process that utilizes surface plasmon excitations such as surface plasmon polaritons (SPPs) to fabricate nanoscale structures. SPPs, which are surface waves that propagate in between planar dielectric-metal layers in the optical regime, can bypass the diffraction limit on the optical resolution that acts as a bottleneck for conventional photolithography.

Contents

Theory

Schematic representation of a surface plasmon polariton Electron density wave - plasmon excitations.png
Schematic representation of a surface plasmon polariton

Surface plasmon polaritons are surface electromagnetic waves that propagate in between two surfaces with sign-changing permittivities. They originate from coupling of photons to plasma oscillations, quantized as plasmons. SPPs result in evanescent fields that decay perpendicularly to the interface where the propagation occurs. The dispersion relation for SPPs permits the excitation of wavelengths shorter than the free-space wavelength of the inbound light, additionally ensuring subwavelength field confinement. Nevertheless, the excitation of SPPs necessitate momentum mismatch; prism and grating coupling methods are common. [2] For plasmonic nanolithography processes, this is achieved through surface roughness and perforations. [1]

Methods

A general scheme for photomask lithography Mask illustration.svg
A general scheme for photomask lithography

Plasmonic contact lithography, a modification on the evanescent near-field lithography, uses a metal photomask, on which the SPPs are excited. Similar to common photolithographic processes, photoresist is exposed to SPPs that propagate from the mask. Photomasks with holes enable grating coupling of SPPs; the fields only propagate for nanometers. [1] [3] Srituravanich et al. has demonstrated the lithographic process experimentally with a 2D silver hole array mask; 90 nm hole arrays were produced at 365 nm wavelength, which is beyond diffraction limit. [4] Zayats and Smolyaninov utilized a multi-layered metal film mask to enhance the subwavelength aperture; such structures can be realized by thin film deposition methods. Bowtie apertures and nanogaps were also suggested as alternative apertures. [1] A version of the method, named as surface plasmon interference nanolithography by Liu et al., uses SPP interference patterns. [5] Despite offering high resolution and throughput, plasmonic contact lithography is regarded as an expensive and complex method; contamination due to contact is also a limiting factor. [1]

Optical trapping via plasmon-assisted etching. In this scheme, etching is achieved through LSP resonances in gold nanoantennas. [6]

Planar lens imaging nanolithography uses plasmonic lenses or negative-index superlenses, which were first proposed by John Pendry. Many superlens designs, such as Pendry's thin silver film or Fang et al.'s superlens, benefit from plasmonic excitations to focus Fourier components of incoming light beyond the diffraction limit. [1] Chaturvedi et al. has demonstrated the imaging of a 30 nm chromium grating through silver superlens photolithography at 380 nm, [7] while Shi et al. simulated a 20 nm lithography resolution at 193 nm wavelength with an aluminum superlens. [8] Srituravanich et al. has developed a mechanically adjustable, hovering plasmonic lens for maskless near-field nanolithography, [9] whereas another maskless approach by Pan et al. uses a "multi-stage plasmonic lens" for progressive coupling. [10]

Plasmonic direct writing is a maskless form of photolithography that is based on scanning probe lithography; the method uses localized surface plasmon (LSP) enhancements from embedded plasmonic scanning probes to expose the photoresist. [1] [11] Wang et al. experimentally demonstrated 100 nm field confinement with this method. [12] Kim et al. has developed a ~50 nm resolution scanning probe with a patterning speed of ~10 mm/s. [13] Gold nanoparticles and other plasmonic nanostructures such as nanogaps have been used as masks for lithography; [6] [14] etching in this case can be achieved through either through photomasking principles [14] or enhanced local heating in the vicinity of the nanostructure due to the LSP resonances. [6] [15] [16] Lin et al. also used localized thermal excitations in gold nanoparticles to fabricate two-dimensional structures such as patterned graphene and molybdenum disulfide monolayers in a process termed as "optothermoplasmonic nanolithography." [17] Photochemical effects of LSP resonances were also used as a catalyst in lithographic processes: [18] Saito et al. demonstrated selective etching of silver nanocubes on titanium dioxide substrates by the means of plasmon-induced charge separation. [19]

See also

Related Research Articles

In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect selected areas of it during subsequent etching, deposition, or implantation operations. Typically, ultraviolet light is used to transfer a geometric design from an optical mask to a light-sensitive chemical (photoresist) coated on the substrate. The photoresist either breaks down or hardens where it is exposed to light. The patterned film is then created by removing the softer parts of the coating with appropriate solvents, also known in this case as developers.

<span class="mw-page-title-main">Plasmon</span> Quasiparticle of charge oscillations in condensed matter

In physics, a plasmon is a quantum of plasma oscillation. Just as light consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantization of plasma oscillations, just like phonons are quantizations of mechanical vibrations. Thus, plasmons are collective oscillations of the free electron gas density. For example, at optical frequencies, plasmons can couple with a photon to create another quasiparticle called a plasmon polariton.

<span class="mw-page-title-main">Electron-beam lithography</span> Lithographic technique that uses a scanning beam of electrons

Electron-beam lithography is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist (exposing). The electron beam changes the solubility of the resist, enabling selective removal of either the exposed or non-exposed regions of the resist by immersing it in a solvent (developing). The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching.

Masklesslithography (MPL) is a photomask-less photolithography-like technology used to project or focal-spot write the image pattern onto a chemical resist-coated substrate by means of UV radiation or electron beam.

Nanolithography (NL) is a growing field of techniques within nanotechnology dealing with the engineering of nanometer-scale structures on various materials.

<span class="mw-page-title-main">Dip-pen nanolithography</span> Scanning probe lithographic technique

Dip pen nanolithography (DPN) is a scanning probe lithography technique where an atomic force microscope (AFM) tip is used to create patterns directly on a range of substances with a variety of inks. A common example of this technique is exemplified by the use of alkane thiolates to imprint onto a gold surface. This technique allows surface patterning on scales of under 100 nanometers. DPN is the nanotechnology analog of the dip pen, where the tip of an atomic force microscope cantilever acts as a "pen," which is coated with a chemical compound or mixture acting as an "ink," and put in contact with a substrate, the "paper."

A superlens, or super lens, is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is a feature of conventional lenses and microscopes that limits the fineness of their resolution depending on the illumination wavelength and the numerical aperture NA of the objective lens. Many lens designs have been proposed that go beyond the diffraction limit in some way, but constraints and obstacles face each of them.

Contact lithography, also known as contact printing, is a form of photolithography whereby the image to be printed is obtained by illumination of a photomask in direct contact with a substrate coated with an imaging photoresist layer.

Nanophotonics or nano-optics is the study of the behavior of light on the nanometer scale, and of the interaction of nanometer-scale objects with light. It is a branch of optics, optical engineering, electrical engineering, and nanotechnology. It often involves dielectric structures such as nanoantennas, or metallic components, which can transport and focus light via surface plasmon polaritons.

Scanning probe lithography (SPL) describes a set of nanolithographic methods to pattern material on the nanoscale using scanning probes. It is a direct-write, mask-less approach which bypasses the diffraction limit and can reach resolutions below 10 nm. It is considered an alternative lithographic technology often used in academic and research environments. The term scanning probe lithography was coined after the first patterning experiments with scanning probe microscopes (SPM) in the late 1980s.

<span class="mw-page-title-main">Surface plasmon</span>

Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface. SPs have lower energy than bulk plasmons which quantise the longitudinal electron oscillations about positive ion cores within the bulk of an electron gas.

A spaser or plasmonic laser is a type of laser which aims to confine light at a subwavelength scale far below Rayleigh's diffraction limit of light, by storing some of the light energy in electron oscillations called surface plasmon polaritons. The phenomenon was first described by David J. Bergman and Mark Stockman in 2003. The word spaser is an acronym for "surface plasmon amplification by stimulated emission of radiation". The first such devices were announced in 2009 by three groups: a 44-nanometer-diameter nanoparticle with a gold core surrounded by a dyed silica gain medium created by researchers from Purdue, Norfolk State and Cornell universities, a nanowire on a silver screen by a Berkeley group, and a semiconductor layer of 90 nm surrounded by silver pumped electrically by groups at the Eindhoven University of Technology and at Arizona State University. While the Purdue-Norfolk State-Cornell team demonstrated the confined plasmonic mode, the Berkeley team and the Eindhoven-Arizona State team demonstrated lasing in the so-called plasmonic gap mode. In 2018, a team from Northwestern University demonstrated a tunable nanolaser that can preserve its high mode quality by exploiting hybrid quadrupole plasmons as an optical feedback mechanism.

A plasmonic-enhanced solar cell, commonly referred to simply as plasmonic solar cell, is a type of solar cell that converts light into electricity with the assistance of plasmons, but where the photovoltaic effect occurs in another material.

<span class="mw-page-title-main">Surface plasmon polariton</span> Electromagnetic waves that travel along an interface

Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric or metal–air interface, practically in the infrared or visible-frequency. The term "surface plasmon polariton" explains that the wave involves both charge motion in the metal and electromagnetic waves in the air or dielectric ("polariton").

A plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve optical properties not seen in nature. Plasmons are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs). Once launched, the SPPs ripple along the metal-dielectric interface. Compared with the incident light, the SPPs can be much shorter in wavelength.

<span class="mw-page-title-main">Localized surface plasmon</span>

A localized surface plasmon (LSP) is the result of the confinement of a surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. When a small spherical metallic nanoparticle is irradiated by light, the oscillating electric field causes the conduction electrons to oscillate coherently. When the electron cloud is displaced relative to its original position, a restoring force arises from Coulombic attraction between electrons and nuclei. This force causes the electron cloud to oscillate. The oscillation frequency is determined by the density of electrons, the effective electron mass, and the size and shape of the charge distribution. The LSP has two important effects: electric fields near the particle's surface are greatly enhanced and the particle's optical absorption has a maximum at the plasmon resonant frequency. Surface plasmon resonance can also be tuned based on the shape of the nanoparticle. The plasmon frequency can be related to the metal dielectric constant. The enhancement falls off quickly with distance from the surface and, for noble metal nanoparticles, the resonance occurs at visible wavelengths. Localized surface plasmon resonance creates brilliant colors in metal colloidal solutions.

In nano-optics, a plasmonic lens generally refers to a lens for surface plasmon polaritons (SPPs), i.e. a device that redirects SPPs to converge towards a single focal point. Because SPPs can have very small wavelength, they can converge into a very small and very intense spot, much smaller than the free space wavelength and the diffraction limit.

<span class="mw-page-title-main">Plasmonics</span>

Plasmonics or nanoplasmonics refers to the generation, detection, and manipulation of signals at optical frequencies along metal-dielectric interfaces in the nanometer scale. Inspired by photonics, plasmonics follows the trend of miniaturizing optical devices, and finds applications in sensing, microscopy, optical communications, and bio-photonics.

<span class="mw-page-title-main">Electromagnetic metasurface</span>

An electromagnetic metasurface refers to a kind of artificial sheet material with sub-wavelength thickness. Metasurfaces can be either structured or unstructured with subwavelength-scaled patterns in the horizontal dimensions.

Spoof surface plasmons, also known as spoof surface plasmon polaritons and designer surface plasmons, are surface electromagnetic waves in microwave and terahertz regimes that propagate along planar interfaces with sign-changing permittivities. Spoof surface plasmons are a type of surface plasmon polariton, which ordinarily propagate along metal and dielectric interfaces in infrared and visible frequencies. Since surface plasmon polaritons cannot exist naturally in microwave and terahertz frequencies due to dispersion properties of metals, spoof surface plasmons necessitate the use of artificially-engineered metamaterials.

References

  1. 1 2 3 4 5 6 7 Xie, Zhihua; Yu, Weixing; Wang, Taisheng; et al. (31 May 2011). "Plasmonic nanolithography: a review". Plasmonics. 6 (3): 565–580. doi:10.1007/s11468-011-9237-0.
  2. ↑ Maradudin, Alexei A.; Sambles, J. Roy; Barnes, William L., eds. (2014). Modern Plasmonics. Amsterdam: Elsevier. p. 1–23. ISBN   9780444595263.
  3. ↑ Shao, D. B.; Chen, S. C. (2005). "Surface-plasmon-assisted nanoscale photolithography by polarized light". Applied Physics Letters (86): 253107. doi:10.1063/1.1951052.
  4. ↑ Srituravanich, Werayut; Fang, Nicholas; Sun, Cheng; et al. (2004). "Plasmonic nanolithography". Nano Letters . 4 (6): 1085–1088. Bibcode:2004NanoL...4.1085S. doi:10.1021/nl049573q.
  5. ↑ Liu, Zhao-Wei; Wei, Qi-Huo; Zhang, Xiang (2005). "Surface plasmon interference nanolithography". Nano Letters . 5 (5): 957–961. Bibcode:2005NanoL...5..957L. doi:10.1021/nl0506094. PMID   15884902.
  6. 1 2 3 Chen, Hao; Bhuiya, Abdul M.; Ding, Qing; Johnson, Harley T.; Toussaint Jr., Kimani C. (2016). "Towards do-it-yourself planar optical components using plasmon-assisted etching". Nature Communications (7): 10468. doi: 10.1038/ncomms10468 . PMC   4737853 .
  7. ↑ Chaturvedi1, Pratik; Wu, Wei; Logeeswaran, VJ; et al. (25 January 2010). "A smooth optical superlens". Applied Physics Letters . 96 (4): 043102. Bibcode:2010ApPhL..96d3102C. doi:10.1063/1.3293448.
  8. ↑ Shi, Zhong; Kochergin, Vladimir; Wang, Fei (2009). "193nm superlens imaging structure for 20nm lithography node". Optics Express . 17 (3): 11309–11314. Bibcode:2009OExpr..1711309S. doi: 10.1364/OE.17.011309 . PMID   19582044.
  9. ↑ Srituravanich, Werayut; Pan, Liang; Wang, Yuan; Sun, Cheng (12 October 2008). "Flying plasmonic lens in the near field for high-speed nanolithography". Nature Nanotechnology . 3 (12): 733–737. Bibcode:2008NatNa...3..733S. doi:10.1038/nnano.2008.303. PMID   19057593.
  10. ↑ Pan, Liang; Park, Yongshik; Xiong, Yi; Ulin-Avila, Erick (29 November 2011). "Maskless plasmonic lithography at 22 nm resolution". Scientific Reports . 1 (175). doi: 10.1038/srep00175 . PMC   3240963 . PMID   22355690.
  11. ↑ Heltzel, Alex; Theppakuttai, Senthil; Chen, S.C.; Howell, John R. (6 December 2007). "Surface plasmon-based nanopatterning assisted by gold nanospheres". Nanotechnology . 19 (2): 025305. doi:10.1088/0957-4484/19/02/025305. PMID   21817542.
  12. ↑ Wang, Yuan; Srituravanich, Werayut; Sun, Cheng; Zhang, Xiang (2008). "Plasmonic nearfield scanning probe with high transmission". Nano Letters . 8 (9): 3041–3045. Bibcode:2008NanoL...8.3041W. CiteSeerX   10.1.1.862.5284 . doi:10.1021/nl8023824. PMID   18720976.
  13. ↑ Kim, Yongwoo; Kim, Seok; Jung, Howon; et al. (2009). "Plasmonic nano lithography with a high scan speed contact probe". Optics Express . 17 (22): 19476–19485. Bibcode:2009OExpr..1719476K. doi: 10.1364/OE.17.019476 . PMID   19997168.
  14. 1 2 Ueno, Kosei; Takabatake, Satoaki; Nishijima, Yoshiaki; et al. (2010). "Nanogap-Assisted Surface Plasmon Nanolithography". The Journal of Physical Chemistry Letters . 1 (3): 657–662. doi:10.1021/jz9002923.
  15. ↑ Fedoruk, Michael; Meixner, Marco; Carretero-Palacios, Sol; Lohmüller, Theobald (2013). "Nanolithography by Plasmonic Heating and Optical Manipulation of Gold Nanoparticles". ACS Nano . 7 (9): 7648–7653. doi:10.1021/nn402124p.
  16. ↑ Wang, Shuangshuang; Ding, Tao (2019). "Plasmon-assisted nanojet lithography". Nanoscale . 11: 9593–9597. doi:10.1039/C8NR08834A.
  17. ↑ Lin, Linhan; Li, Jingang Li; Li, Wei; Yogeesh, Maruthi N.; et al. (2018). "Optothermoplasmonic Nanolithography for On‐Demand Patterning of 2D Materials". Advanced Functional Materials . 28 (41): 1870299. doi:10.1002/adfm.201803990.
  18. ↑ Tan, Che; Qin, Chu; Sadtler, Bryce; Sadtler, Bryce (2017). "Light-directed growth of metal and semiconductor nanostructures". Journal of Materials Chemistry C . 5: 5628–5642. doi:10.1039/C7TC00379J.
  19. ↑ Saito, Koichiro; Tanabe, Ichiro; Tatsuma, Tetsu (2016). "Site-Selective Plasmonic Etching of Silver Nanocubes". The Journal of Physical Chemistry Letters . 7 (21): 4363–4368. doi:10.1021/acs.jpclett.6b02393.
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