Integration of 2D materials in biomimetic photonic structures
Abstract
Today's society lives in constant dependence on electricity. It is common sense to look for sources that produce electricity with a minimal ecological footprint such as solar energy. The state-of-the-art of solar energy conversion is a very optimistic but uninspiring scenario since the highest efficiency research cell does not exceed 47.1%. Using bioinspired photonic nanostructures, it is possible to improve light-matter interactions of additional light-harvesting layers from volumes as reduced as two-dimensional materials on top of these cells, through techniques available in cleanroom-free environments. This allows a simpler and lower-cost way to increase the performance of the final device without increasing its footprint. The reproduction of sinusoidal optical diffraction gratings (nanowrinkles) inspired in epidermal cells' walls of angiosperms to enhance light-matter interactions of adjacent graphene was studied. A reproducible process was developed for the manufacture of nanowrinkles with periodic features of 600, 800, and 1000 nm composed of PDMS activated bran oxygen plasma treatment showing a sinusoidal profile with R² of 85.94%, 78.76%, and 97.00% respectively. Almost all fabricated samples behaved as optical diffraction gratings in angular spectrophotometry measurements. A method for integrating graphene grown by chemical vapor deposition into the aforementioned nanostructures was developed, based on a wet transfer. Fabricated samples with transferred graphene maintained the same periodicity, showing a sinusoidal profile with R² of 80,41%, 62.60%, and 43,32% respectively. Optically, the combination of the nanostructure with the material kept the behavior of a diffraction grating. Raman’s spectroscopy measurements on transferred graphene onto oxygen plasma-treated PDMS showed a 2D/G bands ratio and G band spectral position expected from a monolayer. Due to the material's brittleness resulting from the oxygen plasma treatment of PDMS, consistently oriented cracks appeared across the entire surface, inhibiting electrical conduction in transferred graphene. An implementation of gold contacts by sputtering with a copper adhesion layer spaced by 200 µmwas developed so that crack-free continuous areas of graphene connected side-by-side contacts. This technique allowed the injection of electric current when voltage was applied between contacts. Resistance was measured with values R ~ 10¹ — 10² kΩ.
Full text
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GRAPHENE WET TRANSFER International Iberian Nanotechnology Laboratory Created by José Gama (![email protected]) on November 29th, 2021 Edited by José Gama (![email protected])on October 26th, 2022 Last edit October 26, 2022 Protocol purpose: This protocol aims to guide the user in the wet transfer process of Graphene grown on copper (Cu) with acrylic support film (PMMA) to sample surfaces of different dimensions. EQUIPMENT 2 Aquariums 1 Lab Tub 1 Goblet Scissors Tweezer Lab Paper CHEMICALS FeCl3H2O 2% HCl C3H6O (Acetone) C3H8O (IPA) DANGERS Chemical Exposure ○ ○ ○ ○ ○ Physical Injury ○○○○○ Environmental Harm ○○○○ ○ Fire Hazards ○○ ○ ○ ○ Electrical Hazards ○○○○○ PROTECTIVE GEAR Laboratory Coat Gloves Safety Goggles PROTOCOL Step A[Time required 65 minutes] Copper substrate removal •Cut a piece of the supply material with the desired dimension. It’s fine to touch the material without a tweezer. Just make sure it stays the most flat possible. [1] [2] •Fill an aquarium with FeCl3.[3] •Put the cut piece into a FeCl3bath making sure it stays afloat with the PMMA surface faced-up for 1 straight hour. [4] Step B[Time required 35 minutes] Distilled Water Surface Cleaning •Fill another aquarium with distilled water. •Scoop the graphene over a stiff flat material. It was used Si+SiO2due to its high resistance to FeCl3and HCl corrosion and low reflectance (dark), which leads to a better positioning when catching the sample. [5] •Gently dive the stiff material with the sample adhered onto distilled water expecting the sample to stay afloat. Let it rest for at least 30 minutes. [6] Step C[Time required 15 minutes] Graphene Acid Purifying •Fill the lab tub with a 2% HCl solutiuon. The tub makes it easier to dispose the acid. •Repeat the previous step but from the distilled water to a HCl 2% (V) bath for a 10 minutes basis. The amount of exposure time depends on the desired properties of the graphene. [7] (View in Notes) Step D[Time required 5 minutes] Transfer into the sample •Once again, using the same catch and release technique of the previous steps, pass the graphene from the HCl bath to a renewed distilled water bath. •Now, repeat the scooping technique but with the target sample instead of the stiff flat material. [8] •Let the sample naturally dry overnight tilted into lab paper. [9] Step E[Time required 95 minutes] PMMA removal •Take the dried sample into an acetone bath for 90 minutes. That will depend on the PMMA film thickness of the supply. The sample can now sink in freely, the graphene should stay adhered to its surface. •Take the sample out and rinse it with Isopropyl Alcohol and lastly with distilled water. Let it dry out. [10]
WARNINGS #Corrosive Chemicals HCl 2% (V) and FeCl3are corrosive chemicals !Drippy Containers The liquids might drip off the aquariums if not handled carefully NOTES Take notice that in the original Cu/Graphene/PMMA supply, the borders DO NOT have any graphene since it was where the duct tape was when depositing the PMMA support layer on the Cu/Graphene sample by spin-coating. Those borders should then also be cut off. The FeCl3used can be stored on its aquarium for following transfers but remind that it should be filtered in order to maintain the most "variable-free" environment in the whole process. Typically the filtering is done after 5 transfers. The filtering should be something simple using some lab fibre diapers or even coffee filters. The amount of exposure time of graphene in HCl influences its current chemical structure. For better optical properties, thus, more neat graphene is achieved after a higher exposure time since the acid will attack external bonds with, for example, remains of copper attached. On the other hand, higher exposure times also mean more carbon bonds damaged so the structure will deteriorate over time leading to less stability regarding mechanical and electrical properties. PEOPLE TO CONTACT Martin Lopez-Garcia for NAPS lab access. Francisca Guedes about chemicals usage. Vítor Silva for graphene supply. SOURCES References •Chen, Yi, Xiao Lei Gong, and Jing Gang Gai (Aug. 2016). “Progress and Challenges in Transfer of Large-Area Graphene Films”. In: Advanced Science 3 (8). ISSN: 21983844. DOI: 10.1002/advs.201500343. IMAGE APPENDIX
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