You can possibly link up with the corresponding author(s). In some cases, similar methods may have been used in other papers previously. So if Supplementary information is not enough, the best thing is follow the authors through their email, or scholarly websites just like here on Research gate.

Note. I have keenly realised that many author(s) deliberately leave out some important information especially in methodology section for reasons best known to themselves

You may also check the references... sometimes, methods are just being adopted/followed from previous studies, especially if the authors have already published a similar paper...

well, its not about one or two papers from Nature journal, I have tried many papers, and all of them state that their "Methods" sections is available in online version of the paper, but I didn't find any such thing in online version, so my conclusion is that its about all the papers in Nature Nanotechnology, and its about the journal, its not that authors themselves hide the details.

its not mandatory that file with the name of supplementary information ar methods will available so just look you carefully you will find it. If not then put here details of paper so someone could help you.

For Nature Nanotechnology articles/letters that have you refer to the online version of the manuscript, the Methods are typically located in one of the sections located on the right sidebar of the website. The reason you are not seeing this section for your manuscript is because it is only available to users that have an active subscription with the journal or who are logged into a network with an active license.

If this is the case for you, my suggestion would be to reach out to the corresponding author of the manuscript and ask for the methods that were used for that article.

Thanks Michael. It seems that you are right, I am not authorized to download that methods part.