Patterning par Transitions Optical saturable - Fabrication et caractérisation
Summary
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.
Abstract
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.
Introduction
Lithographie optique est d'une importance clé dans la fabrication de structures et dispositifs à l'échelle nanométrique. Progrès accrus dans de nouvelles techniques de lithographie a la capacité de permettre à de nouvelles générations de nouveaux dispositifs. 8-11 Dans cet article, un examen est présentée d'une classe de techniques lithographiques optiques qui permettent d'atteindre une résolution sub-longueur d'onde profonde en utilisant de nouvelles molécules photoswitchable. Cette approche est appelée Modélisation via optique saturable Transitions (POST) 1-3.
POST est une nouvelle technique de nanofabrication qui combine de façon unique les idées de saturer transitions optiques de molécules photochromiques, spécifiquement (1,2-bis (5,5'-diméthyl-2,2'-bithiophen-yl)) perfluorocyclopent-1-ène. Familièrement, ce composé est appelé BTE, Figure 1, tels que ceux utilisés dans l'émission stimulée appauvrissement (STED) microscopie 12, avec une interférence lithographie, ce qui en fait un outil puissant pour large-zone nanostructuration parallèle de fonctions de Subwavelength profondes sur une variété de surfaces avec extension potentielle à 2 et 3 dimensions.
La couche photochromique est à l'origine dans un état homogène. Lorsque cette couche est exposée à un éclairage uniforme de λ 1, on convertit en le second état d'isomères (1c), la figure 2. Ensuite, l'échantillon est exposé à un noeud ciblé à λ 2, qui convertit l'échantillon dans le premier état d'isomères ( 1o) partout, sauf dans le proche voisinage du noeud. En commandant la dose d'exposition, la taille de la région ne ayant pas réagi peut être rendue arbitrairement faible. Une étape de fixation ultérieure de l'un des isomères peut être sélectivement et irréversiblement transformée (verrouillé) dans un 3 ème Etat (en noir) pour verrouiller le motif. Ensuite, la couche est exposée uniformément à λ 1, qui convertit tout sauf la région verrouillée à l'état d'origine. Leséquence d'étapes peut être répétée avec un déplacement de l'échantillon par rapport à l'optique, résultant en deux régions verrouillées dont l'écartement est inférieur à la limite de diffraction en champ lointain. Par conséquent, ne importe quelle géométrie arbitraire peut être modelée de façon "matricielle". 1-3
Protocol
Representative Results
Discussion
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…
Disclosures
The authors have nothing to disclose.
Acknowledgements
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.
Materials
| 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 |
References
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