Generally, you will find many of the forementioned aircraft operating single pilot under the Part 135 operations of the FAA in America. In Europe, these seem aircraft tend to be operated with First Officers. For example, in the US you could charter a flight on a Beech KingAir 200 with 1 pilot. In Europe the company chartering the B200 would have a pilot and co-pilot operating the charter.
I think in the US the term "First Officer" is bit more applicable to the position, whereas "intern" is the correct term for a First Officer in the EU (this is how airline mgmnt views the FO)This was not always the case; however things have changed in the last couple of years.
Best of luck with your article.