We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.
This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.
Optisk litografi er av sentral betydning i fabrikasjon av nanoskala strukturer og enheter. Økte fremskritt i romanen litografi teknikker har evnen til å aktivere nye generasjoner av nye enheter. 8-11 i denne artikkelen, en anmeldelse er presentert av en klasse av optiske litografiske teknikker som oppnår dyp sub-bølgelengde oppløsning ved hjelp av nye photoswitchable molekyler. Denne tilnærmingen kalles Mønstring via optisk-mettes Transitions (POST). 1-3
POST er en ny teknikk som nanofabrication unikt kombinerer ideene til metting optiske overganger av fotokromatiske molekyler, spesielt (1,2-bis (5,5'-dimetyl-2,2'-bithiophen-yl)) perfluorocyclopent-1-en. Colloquially er denne forbindelsen refereres til som BTE, figur 1, slik som de som brukes i stimulert emisjon-uttømming (STED) mikroskopi 12, med forstyrrelser litografi, noe som gjør det til et kraftig verktøy for large-område parallelt nanopatterning av dype Subwavelength funksjoner på en rekke ulike overflater med potensiell forlengelse til 2- og 3-dimensjoner.
Fotokromatet laget er opprinnelig i en homogen stat. Når dette lag er utsatt for en jevn belysning av λ 1, konverterer det til den andre isomer tilstand (1c), Figur 2. Deretter ble prøven blir utsatt for en fokusert node ved λ 2, som omdanner prøven inn i den første isomer tilstand ( 1o) overalt unntatt i umiddelbar nærhet av noden. Under styreeksponeringsdosen, kan størrelsen av uomdannet region gjøres vilkårlig små. En etterfølgende fikseringstrinn av en av isomerene kan selektivt og irreversibelt omdannet (låses) i en 3 rd tilstand (sort) for å låse mønster. Deretter blir sjiktet eksponeres jevnt til λ 1, som omdanner alt bortsett fra den låste region tilbake til den opprinnelige tilstand. Denrekkefølge av trinn kan bli gjentatt med en forskyvning av prøven i forhold til optikken, som resulterer i to låste regioner som avstanden er mindre enn fjernfelts diffraksjonsgrensen. Derfor kan en vilkårlig geometri være mønstret i en "dot-matrix" fashion. 1-3
The fabrication, experimental setup and related operational procedures of Patterning via Optical Saturable Transitions (POST) have been described. By exploiting the linear switching properties of thermally stable photochromic molecules, POST offers new perspectives on circumventing the far-field diffraction limit.1-2,4
Previously long-term storage requirement of the samples was solved by storing the samples under N2, directly after the initial evaporation.2 How…
The authors have nothing to disclose.
Thanks to Michael Knutson, Paul Hamric, Greg Scott, and Chris Landes for helpful discussions and assistance related to the custom inert atmosphere sample holder and assistance in the University of Utah student machine shop. P.C. acknowledges the NSF GRFP under Grant No. 0750758. P.C. acknowledges the University of Utah Nanotechnology Training Fellowship. R.M. acknowledges a NSF CAREER Award No. 1054899 and funding from the USTAR Initiative.
Name of Material/ Equipment | Company | Catalog Number | Comments/Description |
Isopropanol | Fisher Scientific | P/7500/15 | CAUTION: flammable, use good ventilation and avoid all ignition sources. |
Buffered Oxide Etch | |||
Methanol | Ricca Chemical | 48-293-2 | CAUTION: flammable, use good ventilation and avoid all ignition sources. |
Ethylene Glycol | Sigma-Aldrich | 324558 | CAUTION: Harmful if swallowed |
Silicon wafer | |||
Diamond Scribe | |||
Glass Beakers | |||
Tweezers | Ted Pella | 5226 | |
Reactive Ion Etching System | Oxford | Plasma Lab 80 Plus | |
Inert Atmosphere Sample Holder | Proprietary In-house Designed | ||
Polarizing beamsplitter cube | Thorlabs | PBS052 | |
HeNe Laser | Melles Griot | 25-LHP-171 | CAUTION: Wear safety glasses |
Half-wave plates | Thorlabs | WPH05M-633 | |
Thermal Evaporator | Proprietary In-house Designed | ||
TMV Super | TM Vacuum Products | TMV Super | |
Voltammograph | Bioanalytical Systems | CV-37 | |
Shortwave UV lamp 365nm | UVP Analytik Jena Company | UVGL-25 | CAUTION: Wear UV safety glasses |