"some beaches of chemistry or material sciences"
What the heck is that? Sounds like you are calling those dirty some beaches names.
Just make an effort and don't go so over the top you look like some kind of smooth operator. Maybe a step up from your usual attire. Maybe a step up for your peer group. What you mention should be fine this time of year.
The most important thing is the suggested research. I have researched every faculty member and administrator I have ever met with to some degree. And if it was an important meeting, I read their publications, at least their abstracts. You need to be able to keep the conversation at least a little bit moving as they blather on about whatever cool thing they are doing. This is an absolute necessity. Why would I even bother to take time to talk with someone about working with me who doesn't know what I do!
And, be prepared to answer questions like "Why are you interested in this?" "What are your career plans?" "How will this work help you?" "What can you contribute to the project?" or put another way "What can you do for me?" even if these are not asked, you should answer most of them.
And above all, convey the idea that you can follow instructions while also making a project your own. The students that have most impressed me are those that when I "suggested" they do A, they did it well, then went on to develop a follow up B, and came up with C, D, ... that might be worth pursuing. The latter part of that is what distinguishes a scientist/scholar from a technician.
