Range.Characters (Excel)

Returns a Characters object that represents a range of characters within the object text. You can use the Characters object to format characters within a text string.

The Characters object isn't a collection.

Characters (Start, Length)

With Worksheets("Sheet1").Range("A1") 
 .Value = "abcdefg" 
 .Characters(3, 1).Font.Bold = True 
End With

Arguments

The following arguments are optional

Start (Long) - The first character to be returned. If this argument is either 1 or omitted, this property returns a range of characters starting with the first character.

Length (Long) - The number of characters to be returned. If this argument is omitted, this property returns the remainder of the string (everything after the Start character).