We present a detailed investigation of the spring behavior of carbon nanotu
be caps. We show that the caps act as harmonic springs, responding linearly
to axial forces for appreciable displacements. Interestingly, we find the
spring constant to be essentially independent of diameter and number of lay
ers, but the maximum harmonic displacement increases with tube diameter and
especially with number of layers. This spring effect is significant when t
he tubes are sufficiently short so that buckling does not occur before cap
compression. [S0163-1829(98)05340-5].