Extraordinary Alignment of Nb Films with Sapphire And The Effects of Added Hydrogen

The current method of growing large-area graphene on polycrystalline Cu surfaces (foils or thin films) and its transfer to arbitrary substrates is technologically attractive. However, the quality of graphene can be improved significantly by growing it on single-crystal Cu surfaces. Here we show that high quality, large-area graphene can be grown on epitaxial single-crystal Cu thin films on reusable basal-plane sapphire  substrates for transfer to another substrate. While enabling graphene growth on Cu single-crystal surfaces, this method has the potential to avoid the high cost and extensive damage to graphene associated with sacrificing bulk single-crystal Cu during graphene transfer.

We present the results of high-resolution x-ray scattering studies of the structural coherence of niobium  films grown by molecular-beam epitaxy on sapphire substrates. In transverse scans of the out-of-plane Bragg peak we find two components, the sharper of which implies mosaicities an order of magnitudes better than bulk single-crystal Nb, and transverse structural coherence lengths exceeding 104 Å. In addition, we observe that the planes associated with the sharp component are exactly aligned with the sapphire planes. Upon hydrogen loading of the Nb film, we find evidence for a dramatic increase of the lateral coherence length.


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