I write in sequence. You can grow graphene on Ni, Pd, Ru, Cu, Ir. Out of those, Ni and Cu were the choices because they are less expensive to others. If you grow on Ni, it is difficult to control the number of graphene layers due to the high solubility of carbon in Ni and graphene layers (single and multi layers) growth is limited to the microns region. Cu is the best substrate because of very low solubility of carbon in Cu(

As a very basic explanation, Copper forms hexagonal lattices, which are surmised to be beneficial for the growth of graphene, which also has a hexagonal structure. Again, this is a very basic explanation. For more information, you can read this article: https://pubs.rsc.org/en/content/articlelanding/2011/JM/C0JM02126A#!divAbstract

Copper substrate is one of many other transition metals that were used as catalyst in the reaction of graphene formation in the CVD. The structure of the produced graphene is highly affected by the surface features of the substrate materials including its composition, structure, morphology, etc....

For more details, please refer to:

https://www.intechopen.com/books/graphene-materials-advanced-applications/fundamentals-of-chemical-vapor-deposited-graphene-and-emerging-applications

Actually it act as substrate to hold nano catalyst

in fact it gives space to grow graphene

I write in sequence. You can grow graphene on Ni, Pd, Ru, Cu, Ir. Out of those, Ni and Cu were the choices because they are less expensive to others. If you grow on Ni, it is difficult to control the number of graphene layers due to the high solubility of carbon in Ni and graphene layers (single and multi layers) growth is limited to the microns region. Cu is the best substrate because of very low solubility of carbon in Cu(

i would add , Cu is easy to etch out and you can get the graphene sheet

The pioneers of CVD graphene have been using Cu and Ni because of their catalytic power, their price and their availability. As mentioned by Manisha, there are other alternatives as most transition metals can catalyze the cracking of methane (or other C precursors). The scientific community quickly realized it is more challenging to control the growth of graphene on Ni. Because of its higher C solubility and higher catalytic power, you are more prone to get multilayer regions (especially in the vicinity of the Ni grain boundary grooves). You can improve the control over the number of layers by using a thin film (instead of bulky foil) but it is not great compared to using Cu or Pt.

Ideally, it would be better to avoid Cu (due to the risk of Si contamination in industry) but not using a catalyst is more tricky. Directly growing graphene on an isolating substrate would be advantageous for practical applications (for obvious reasons, you cannot fabricate transistors using a metal as substrate). However, you then need growth temperatures above 1200°C to crack classic C gaseous sources (which means you cannot really use a quartz tube and cheap furnace anymore).

Finally, the relatively high mobility of C species on the Cu surface makes it more easy to produce large single crystalline domains (thus minimizing the density of defects induced by graphene grain boundary for C species). C species can diffuse to growing graphene domains rather than making new domains.

Dear Kambiz Hosseinpanahi ,

the key (to your Q:why Cu//...), as a rule[1], is the (quasi[1,2]-) epitaxial fast growth of (CVD) graphene, on single crystal [(Ni(111), Cu (111)[3] and Cu/Ni(111) alloy foil[4]] substrates.

1. Ideally, the epitaxial growth of graphene is possible in small substrates' parts having ideal (single) crystalline areas and low mismatch stain under the critical thickness[2].

2. Anomalies in thickness measurements of graphene and few layer graphite crystals by tapping mode atomic force microscopy https://www.sciencedirect.com/science/article/pii/S0008622308002856

3. see page 49, in "https://www.intechopen.com/books/graphene-materials-advanced-applications/fundamentals-of-chemical-vapor-deposited-graphene-and-emerging-applications"

Graphene can be grown with a preferred orientation on Cu(111), and even seamless sticking of graphene domains on Cu(111) substrates has been obtained. Thus, unidirectional alignment of nucleated graphene crystals on a single-crystal metal substrate can be the perfect solution to grow uniform graphene films. However, Synthesis of graphene on a single-crystal metal substrate is not suitable for large-scale production owing to the high cost and the difficulty of preparing single-crystal metal.

4. see Figure S4, in https://pubs.acs.org/doi/suppl/10.1021/acsnano.8b02444/suppl_file/nn8b02444_si_001.pdf https://pubs.acs.org/doi/pdf/10.1021/acsnano.8b02444#notes1

Cu and Ni are the best catalyst for graphene synthesis.