Can you provide a reference for the quantum dots? I'd guess this distance would be very close to that of graphene as the (average) diameter of the quantum dot gets larger

Actually I'm not discarding the possibility that the interlayer distance between graphene QDs be less than the interlayer distance in graphite. My answer was more in the sense that with AB stacking of QDs the interlayer distance could increase as the QD diameter increases, if it is indeed the number Dr. Patil quotes. What I meant is, I find it strange that this is a "magic number" valid for whatever QD size. There can be all kinds of effects that could make this number be smaller for QDs. First thing to know would be how the dangling bonds of the above mentioned QDs are: passivated with hydrogens, bare? Then see if this number is obtained for a particular QD size and shape, and only then try to obtain some rationale to explain the result. That's why I asked for the article(s) Dr. Patil is referring to.

Just wondering: for QDs with bare edges, if the stacking is AA between identically shaped dots, this could be due to a bond forming between dangling p orbitals, which coukd form a sigma bond slightly larger than the CC bond in graphene. If that were the case, there could be some bulging of the dot, due to repulsion between the pz orbitals that form the pi-bond network on each of the QDs. That could be interesting, albeit useless for practical applications :)

Thank you very much Dr. Alves and Dr. Roy,

As Dr. Alves asked for some references please find Fig. 3 c in the following article

http://www.sciencedirect.com/science/article/pii/S0008622313007185

Where it has been stated that "The measured lattice spacing is 0.213 nm, corresponding to the {1 1 0 0} lattice fringes of graphene"

Figure 3 b from following paper

http://pubs.acs.org/doi/ipdf/10.1021/nl302520m

0.2 nm is the distance between 2 atoms on the hexagonal graphene plane (x-y axis), also called the lattice constants. It is the same lattice constants in graphite crystal structure. On the other hand, the 0.34nm  is the distance between the the hexagonal planes (in z-axis) in graphite crystal structure. Interplanar distance only applied to graphite because graphene is single layer.

Average distance between 2 atoms on the hexagonal graphene es 0,14nm.

0,24nm is the lattice fringe. Lattice-fringe fingerprinting is the name given to the method of identifying nanocrystals using high-resolution phase-contrast TEM images.

Actually, the well-resolved crystal lattice fringes with a spacing of 0.21 nm which is very close to the (100) facet of graphite carbon.

For reading please go to this article

Article Direct demonstration of photoluminescence originated from su...

Reason 2: The crystallinity with a lattice parameter of 0.2136 nm corresponding to the (1100) lattice fringes of graphene providing that our GQDs were fabricated from graphene.

Read Articles:

1. Article Luminescent graphene quantum dots fabricated by pulsed laser synthesis

2. Article Uniform Graphene Quantum Dots Patterned from Self-Assembled ...

Thus we can easily distinguish that, if we synthesised CD's from other sources (except graphite of graphene), then the lattice spacing of 0.21 nm referred as (100) facets of graphitic carbon.

If the GQDs/CDs obtained from graphene or graphite source irrespective of method, then lattice spacing corresponding to 0.21 nm referred as {1100} plane of graphene.

Regards

Gaurav Kumar Yogesh