SURFACE-MORPHOLOGY AND OPTICAL-PROPERTIES OF MEV-ENERGY HEAVY-ION IRRADIATED CRYSTALLINE SI AND CRYSTALLINE GE - POSSIBILITY OF FORMATION OF POROUS MATERIAL

The effect of bombardment of crystalline Si (c-Si) and crystalline Ge (c-Ge) with 75 MeV Ni+, Ge+ and Ag+ ions at room temperature and liqui d-nitrogen temperature (LNT) at fluences in the range of 1 x 10(13) - 1 x 10(14) ions cm(-2) has been investigated. The ion-induced damage b rought about by electronic and nuclear energy losses on the surface an d deep inside the bulk, has been monitored by scanning electron micros copy and optical spectroscopy. In an optical study, the effect has bee n studied by measuring the reflectivity R and transmittance T in the s pectral range 200-2500 nm and by determining the optical constants, na mely the absorption coefficient alpha and refractive index n. These st udies indicate that the surface morphological changes depend strongly on the temperature of bombardment and the nature of the projectile ion . The most striking effect in both the crystals is seen with Ni+-ion b ombardment at LNT, while no appreciable effect is observed with Ag+ io ns. The possibility of the formation of electronic energy-loss-induced porous Si and Ge on the surface of the irradiated c-Si and c-Ge is re vealed in this study.