Applied Materials interview questions

My PhD advisor knows an upper exec at AMAT, so I emailed them directly. He forwarded me to one of his Senior Directors. I mentioned that I was graduating soon and would be visiting the Bay Area, so he asked me to come in and speak with some people. It wasn't officially an interview, but it felt similar. I spoke with 4 senior directors for 30 min each, mostly about technical issues.

After 30 minute phone interview, was called in for serial interview: first with HR then with 4 engineers, each 30 minutes. Questions were general and friendly, and each interviewer asked a technical question, a simple physics problem on paper, asking "how would you approach this?" Overall it seemed to go well.