fullerenes within a nanotube are only stabilized at a diameter difference of 0.34 nm or less, and when the diameters are nearly identical, the interacting energy heightens to such a degree (comparable to 0.1 gpa) that the fullerenes become unable to be extracted from the swnt even under high vacuum. the encapsulated fullerenes have diameters close to that of c and form a chain inside the tube.