To cite package sf in publications use:

Pebesma, E., 2018. Simple Features for R: Standardized Support for Spatial Vector Data. The R Journal, https://journal.r-project.org/archive/2018/RJ-2018-009/

Corresponding BibTeX entry:

  @Article{,
    author = {Edzer Pebesma},
    title = {{Simple Features for R: Standardized Support for Spatial
      Vector Data}},
    year = {2018},
    journal = {{The R Journal}},
    url =
      {https://journal.r-project.org/archive/2018/RJ-2018-009/index.html},
  }