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Graphene preparation

Guidelines for Crafting Graphene Grids The objective involves overlaying a layer of hexagonally distributed single-layer graphene (2D carbon) onto a perforated or Quantifoil grid to enhance particle adsorption onto the grid.

Required Materials: • Copper etchant (Alfa Aesar, cat# 44583): Liquid solution that dissolves copper, acidic nature. • 1% Collodion (Parlodion) in Amyl acetate: Light-sensitive, flammable plastic material dissolved in organic solvent (resembles acetone). • Graphenea Graphene on copper: Purchased as a graphene layer atop copper. • Cutter • Western blotting filter paper (Thermo Scientific, ref# 88600) • Glass petri dish • Solutions: 10%, 1%, 0.1%, 0.01% HCl, and deionized water • Pump • Grids

Graphene, procured as a layer atop copper sheet from Graphenea, demands careful handling due to its fragility. It should be stored under vacuum in a desiccator. Trim it within its container to a ~2*3 cm rectangle using a cutter. Proceed as follows:

  • Fill a glass petri dish with H2O.

  • Gently add 60-100 ul of collodion solution to the water's surface. This volatile plastic layer dries quickly, exhibiting a sweet spot with rainbow hues and partial dryness. At this point, place the graphene/copper sheet on the water surface, ensuring graphene contacts the plastic. Be cautious not to let the copper side touch the plastic.

  • As the plastic solidifies, delicately trim excess plastic around the graphene/copper sheet, leaving a small margin.

  • Transfer the sheet to filter paper (copper down, graphene-plastic up), forming a "sandwich" configuration.

  • For copper dissolution, carefully introduce a portion of copper etchant into the glass petri dish. Place the sandwich onto the etchant with the copper side facing downward. Over time, observe the copper dissolve, leaving the sheet transparent, with only the graphene and plastic layers remaining.

  • After copper dissolution, employ the pump to facilitate a gradual wash of the sheet. Begin by gradually introducing 250 ml of a 10% HCl solution. Repeat this process with 250 ml portions of 1% HCl, 0.1% HCl, and 0.01% HCl solutions, consecutively. Conclude by rinsing with deionized water.

  • Before the water level in the petri dish decreases significantly, place the pre-cut filter paper into the dish. Carefully position the grids on top of the filter paper, facing upwards. This step can be performed while temporarily pausing the pump. Maintain a slight spacing between the grids to facilitate later cutting.

  • Delicately adjust the position of the filter paper along with the graphene sheet within the petri dish until the filter paper aligns precisely beneath the graphene sheet. Continue using the pump to extract water from the dish, ensuring careful handling to avoid dislodging the alignment. Gradually, the graphene will adhere to the filter paper and grids, with the plastic coating remaining on the surface. As the water reduces, cautiously tilt the dish to promote secure attachment of the graphene to the filter paper and grids. Once nearly all water has been removed, extract the filter paper from the petri dish and place it onto a paper towel, allowing for gradual and complete drying. Utilize the petri dish and tweezers to shield the upper side of the graphene (with the plastic facing upwards).

  • Once fully dry, store the filter paper with grids in a desiccator for several months.

To prepare the graphene-coated grids for sample application, follow these steps: Immerse the grids in the following solutions sequentially, with approximately 15 dips for each chemical.

Transfer the washed grids onto a clean filter paper. Place the grids onto a glass slide and bake at 150 degrees Celsius for one hour. After cooling down, the grids can undergo typical plasma cleaning/glow discharge processes and will be ready for sample application.

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