First create as many sheets as you want (using Sheets.Add()).
Then loop through your plots, calling
Sheet1 = get(Sheets, 'Item', ctr);
where I have assumed ctr is the loop variable. Sheet1 (or call it something else if you like) will then be a reference to the ctr-th Worksheet.
So you could do something like:
for ctr = 1:N
Sheet1 = Sheets.Item(ctr);