Studies of ion beam nanopatterning on silicon and polymer thin film
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Ion bombardment can lead to a spontaneous formation of a range of nanopatterns on surfaces, including nanodots, nanoscale ripples, and nanoscale pits or holes. Research in this thesis is mainly focused on the behavior of ripple patterns on silicon surfaces as a function of the ion incidence angle. A preliminary study of ion beam nanopatterning of polymer thin ﬁlms is also presented in this thesis. The research on ion beam nanopatterning of Si is largely motivated by a recent theory predicting the development of well ordered ripples when the ion incidence angle is close to the critical angle. For this study of silicon nanopatterning, initially ﬂat samples were bombarded by a broad beam of 250 eV Ar+ ions with a range of angles (65° - 41°) close to the critical angle, leading to the spontaneous formation of nanoscale ripples. Atomic Force Microscopy (AFM) topographs show the change of ripples as the function of ion incidence angle. The ripple wavelength and crest length are measured from AFM topographs to quantify the degree of order. The ripple peak width in the AFM Power Spectral Density is also examined. In general, the ripples achieve higher degree of order close to critical angle. However, the behavior of ripple formation close to critical angle is more complicated than the theory’s prediction. More studies need to be done to further understand this complex behavior. For the preliminary study of polymer thin ﬁlm nanopatterning, initially ﬂat samples were bombarded by 250 eV Ar+ ions at the incidence angle of 0°, 45°, and 65° to study the interaction of ion beams with polymers based on diﬀerent proposed pattern forming mechanisms. Scanning Electron Microscopy (SEM) and AFM topographs show that several types of interesting patterns formed on the surface of diﬀerent polymer thin ﬁlms.