Modification on graphite due to helium ion irradiation

• Used an ingenious helium ion source to study irradiation induced transformation on graphite.
• OM, AFM and TEM analyses confirm the formation mostly rounded structures.
• SAED patterns confirm the retention of crystallinity of graphite even after exposure to larger helium ion fluences.
• XRD patterns confirm the development of new peaks that indicate structural rearrangement.

This paper studies the influence of helium ion irradiation on morphological and structural properties of graphite samples. The helium ions emanated from a plasma focus device have been used to irradiate graphite samples by varying the number of ion pulses. The effect of radiation induced changes in morphology and structure are examined by using optical microscopy, atomic force microscopy, transmission electron microscopy along with selected area electron diffraction and x-ray diffraction. A distinct change in the surface topography is marked in the case of the ion irradiated samples when viewed under the optical microscope. The micrographs of the ion irradiated samples confirm mostly rounded and sparely elongated type of structures arising due to intense melting and local ablation accompanied with ejection of graphite melts that depends upon the ion fluence. The atomic force microscopy images also reveal the formation of globules having sizes ∼50–200 nm which are the agglomeration of small individual clusters. Transmission electron micrographs of the ion irradiated samples furnish that the diameter of these individual small clusters are ∼10.4 nm. Moreover, selected area electron diffraction patterns corroborate that the ion irradiated sample retains its crystalline nature, even after exposure to larger helium ion pulses. It is noticed from the x-ray diffraction patterns that some new phases are developed in the case of ion irradiated sample.