(tubular neighbourhood theorem)
Every embedding does admit a tubular neighbourhood.
For instance (DaSilva, theorem 3.1).
Moreover, tubular neighbourhoods are unique up to homotopy in a suitable sense:
This appears as (Godin, prop. 31).
Basics on tubular neighbourhoods are reviewed for instance in
Ana Cannas da Silva, section 3 of Prerequisites from differential geometry (pdf)
Stanley Kochmann, section 1.2 of Bordism, Stable Homotopy and Adams Spectral Sequences, AMS 1996
The homotopical uniqueness of tubular neighbourhoods is discussed in
For an analogue in homotopical algebraic geometry see