Tungsten

Zero-Valent Reaction:

Synthesis Setup:

Chemicals:

Tungsten hexacarbonyl, octadecene

Note: The procedure below is the published procedure. However, it is possible to intercalate W using acetone rather than octadecene and heating to only 52C following a similar procedure as iron intercalation.

Degassing Octadecene

• Freeze-Pump-Thaw: On a Schlenck line, place octadecene in a heavy-walled (critical) single-neck round bottom flask or a sealed Schlenk flask. Freeze it by immersing in liquid nitrogen. Once frozen, open the flask to high vaccum and pump for about 5 minutes. Keep the octadecene in liquid N2. Place solvent back under N2 and let thaw. Repeat 3 times. Remove solution using a needle and syringe into a N2 filled septa vial.

• Purging: So, this is what I do for octadecene. This is really hard on a vacuum pump so use a robust pump (Varian DS Rotary Vane Pump). Place octadecene in a round bottom flask. Heat to 110°C and place under vacuum for about 30 minutes. Refill with N₂. Keeping under N₂ atmosphere, bubble N₂ or Ar into the flask using a long needle. Bubble for about an hour or two.

Store degassed octadecene in a glovebox.

Procedure:

Much like Co, Mn, Mo, and Fe, tungsten is intercalated by the decomposition of tungsten carbonyl in a solution under inert atmosphere. Again, either use a Schlenk line or use the procedure and setup explained for Cr above. Tungsten carbonyl requires a lot higher temperature than the others to decompose the carbonyl groups and it does not decompose as well under light. Thus, octadecene is used rather than acetone.

Setup the reaction as above. Place the 2D material in the round-bottom flask, evacuate and flush with N₂ gas. In a glovebox, create two stock solutions. Stock solution 1 should be 5 mL of degassed octadecene. Stock solution 2 should be 10 mM of tungsten hexacarbonyl in 20 mL of degassed octadecene. This is approximately from 0.07 g of tungsten carbonyl dissolved in 20 mL of degassed octadecene. Inject the first stock solution of octadecene into the round-bottom flask and heat to 150-170°C. Dropwise, inject in the tungsten (solution 2) over the course of 2-3 hours. After all solution has been injected, allow the mixture to sit just below reflux for 1 more hour. Remove the substrate and rinse repeatedly with acetone to remove excess octadecene.

How much can be intercalated into Bi₂Se₃ nanoribbons:

W(CO)₆	Octadecene	Time	~ Intercalated in Bi₂Se₃
0.01 g	25 mL	3 hours	4 atm % ± 2%

Relevant Publications:

M. Wang, D. Williams, G. Lahti, S. Teshima, D. Dominguez-Aguilar, K. J. Koski, Chemical intercalation of heavy metal, semimetal, and semiconductor atoms into 2D layered chalcogenides. 2D Materials, 5, 045005 (2018)

Supported by NSF DMR-1658019