Thursday, February 26, 2009

Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition

Alfonso Reina, Xiaoting Jia, John Ho, Daniel Nezich, Hyungbin Son, Vladimir Bulovic, Mildred S. Dresselhaus, Jing Kong (2009). Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition Nano Letters, 9 (1), 30-35 DOI: 10.1021/nl801827v

A very nice CVD paper where the graphene is transferred to a device friendly substrate (SiO2). The authors used chemical vapor deposition (CVD, also discussed here) on a polycrystalline nickel film, pumping hydrogen and methane gases at ambient pressure and 900-1000 C temperatures. The graphene grown was varied in the number of layers, with the larger number of layers occuring at the step edges of the Ni substrate. The graphene was transfered to SiO2 (although it could have been any other substrate) by protecting graphene with the polymer PMMA, etching the nickel away, and then placing it on the SiO2 surface. The transfer doesn't introduce many more defects, which is quite nice. They mention that some of the multilayers they saw on the nickel might have been electronically disconnected, meaning that they will still act like single-layer graphene (this is also seen sometimes with epitaxial graphene). Here's the stats on their graphene:

Sheet resistance: 770-1000 ohms/cm2
Optical transmittance: around 90% in the 500-1000nm range
On/off ratio at high voltage: between 1.3 and 2
Mobility for e's and holes: between 100-2000 cm2/V (huge range)

Moral of the story: This paper makes decent-quality graphene by CVD at ambient pressure, and they come up with a very nifty way to transfer their graphene to a useable substrate, an approach that overcomes a large disadvantage of using CVD to make graphene.


Brian Kessler said...

Nice blog you've got going here. Thought I would just point out that sheet resistance is in ohms/square not ohms/cm^2. Since its the resistivity (ohm-m) times the thickness (m) it doesn't depend on the size of the sample.

Sonam said...

I believe I read the paper a while back and I was bit disappointed that they glossed over some very important facts. If you want to make a transistor out of graphene, it is absolutely essential that there should be no Ni(metal) left over in graphene layers after etching. More analysis should have been done to characterize the elemental composition of graphene.

tonyon said...

maglev&zipper for space elevator future

tonyon said...
This comment has been removed by the author.
tonyon said...

(1a)... ☼ ← O ♦▬↔▬▬▬▬▬▬→▬▬▬☺ → ☼ (railroad to the moon)...a hyper-speed vertical electric train of Magnetic Levitation with Moon receiving from nuclear electric generator on Moon...with only emergency brake rockets...((from Earth, passengers in rocket to space-elevator of Moon located between 20,000 and 70,000 kms high...or...)) awaits passengers almost each perigee in the gyratory World´s around in 27.55 days Pendant♦Station, size as an aircraft carrier, located between 9 and 43,638 kms, "50000 + 9 - 6371" (by elliptic Moon orbit) from Earth surface, and by 1 track (1 train monorail, half length above half length below through Station´s floor, with thin sheet lead anti-radiations), carbon nanotubes track made in hinge joint sections, such as a bike chain drive (so, also the Station can modify its own height with 10 kms/hour speed, starting each perigee to preparing the height for the next (10 kms/h*24h*27.55 days = 6,612 kms max. height adjustment capacity for next perigee), staying almost all perigees at 9 kms height from Earth´s surface, going due to the continuous changes of Moon´s perigee, upwards for avoid Station crash against ground!!...or downwards, by the zipper track carrying the track´s excess... Track with 387,883 kms in total length ((347,883 kms minimum length (356000 "approx. minimum distance between Earth/Moon centers" - 6371 "Earth med. radius" - 9 - 1737 "Moon radius") + 20,000 kms over Station + other 20,000 kms by security over Moon Station reserves length for Moon´s perigee changes, with situation lights along, little mirrors reflecting Sun light, and radar´s reflectors making well visible the Track for spacecrafts...) at the upper end attached to the Moon surface...