how to/can i apply to these tech startups?

I found 3-4 tech startups in the field of 'carbon accounting' (linkedin says they have max 14 employees each) doing things I find interesting but I don't explicitly see jobs available for positions I can apply for (non computer science related). Im currently getting a phd in chem and i study different co2 removal technologies and i was wondering if I should still apply to them.

They all have emails listed where I have to provide: my resume, position im interested in, and an additional info piece/document.

Can I use my research knowledge in the field they work in to write something convincing in the additional info section?

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