A valid travel document is required to travel to Spain to attend IEEE NANO 2024. Spain is a member state of the Schengen Area, so that citizens of the Schengen Area only need a valid passport.
There are also countries whose nationals are not required to obtain a Schengen visa in order to enter any member country of the Schengen Area for tourism or business purposes for stays up to three months. The list of those countries can be found at www.schengenvisainfo.com/who-doesnt-need-a-visa/
The citizens of the rest of the countries (www.schengenvisainfo.com/who-needs-schengen-visa/) need to request a Schengen Visa, which is the most common visa for Europe. It enables its holder to enter, freely travel within, and leave the Schengen zone from any of the Schengen member countries.
The Schengen Visa can be requested at the Spanish embassies and consulates with territorial competence for the country in which the IEEE NANO 2024 participant resides (www.exteriores.gob.es/en/EmbajadasConsulados/Paginas/index.aspx).
If you need a personal letter of invitation for visa application to attend the Conference, please contact the IEEE NANO 2024 General Chair Prof. Montserrat Rivas (send an email to firstname.lastname@example.org indicating in the subject “IEEE NANO 24 Letter of Invitation”). It will be issued only after you have successfully completed your conference registration, so that, please, register as early as you can to make sure you have enough time to get your visa. Your name should be listed exactly in the registration as it appears on your passport in order to avoid a delay/denial of the visa. Please, note that such an invitation letter is not a certificate of participation or certificate of attendance.