Make exponent style in Riche Text field
In craft/config/redactor you can either add your own setting file, or edit one of the ones already there. If you add the following JSON:

"formattingAdd": [
  {
    "tag": "sup",
    "title": "Superscript"
  }
]


You will have access to a Superscript choice under the Formatting buttons dropdown menu. This will wrap the selected text in a &lt;sup&gt; tag.

While I'm not sure if this is the correct way of adding stuff like this, I just tested it and it does work.