It's one half-step, or one semitone.
The A harmonic minor scale uses 1 sharp on the seventh degree, that would be a G♯, and you play the G♯ both when ascending and descending. The sequence of tones and semitones in a harmonic minor scale are as follows: Tone Semitone Tone Tone Semitone, Tone-and a half, Semitone. In A minot this is A (up a tone), B (up a semitone), C (up a tone), D (up a tone), E (up a semitone), F (up a tone-and-a-half), G♯ (up a semitone), A.
C-sharp to D, or C to D-flat would be a semitone.
All harmonic minor scales have the pattern of tone-semitone-tone-tone-semitone-tone-tone (raised 7th)-semitone. Therefore, D harmonic minor has the notes of D, E, F, G, A, B flat, C# (raised 7th), D.
C sharp/D flat
D sharp and E flat
Tone Tone Semitone Tone Tone Tone Semitone, is always the gap between notes in any major scale, which is why most scales need sharps or flats. For example, C major is: C - up a tone - D - up a tone - E - up a semitone - F - up a tone - G - up a tone - A - up a tone - B - up a semitone - C.
Tone and semitone are two words to describe differences in pitch between two notes. A semitone is the difference between F and F#, that is, only a bit. A tone is the difference between F and G, twice as much as a semitone.
It would be a sharp/flat. Like A would be A#/Bb
F major is F - G - A - B flat - C - D - E the A and B flat are a semitone apart. (3rd and 4th) the E and F are a semitone apart (7th and 8th (1st)) It is the same in all major scales (3-4 and 7-8 are always a semitone apart)
This interval is an example of a tone (as opposed to a semitone).
The leading tone in any key is one half-step below the tonic. In the key of D-sharp, the leading tone is C-double-sharp (it can't be spelled as D-natural, because the letter D is already used for the tonic).
The diatonic semitone for F is E. In the context of the diatonic scale, the semitone refers to the smallest interval between two notes within that scale. In the key of C major, for example, the notes are C, D, E, F, G, A, and B, with F and E being a semitone apart.