Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Dr. Chad Sosolik, Committee Chair
Dr. Endre Takacs
Dr. Catalina Marinescu
Dr. William R Harrell
As the dimensions of the smallest feature on the integrated circuit has minia-turized into the range of tens of nanometers, patterning of highly ordered nanos-tructures with tunable size and shape in large scale on the surface of substrate is highly demanding and increasingly challenges the limits of nanolithography. To over-come the conventional lithographic limitations, self assembled methods have been explored. While strain driven self assembly is widely viewed as a promising technique for patterning at the nanoscale, to follow this approach and create structures in a desired manner, a reliable means to engineer and characterize the shape and sizes of nanostructures during self assembly is essential. The work presented here describes a detailed analysis of the morphological and compositional evolution of patterns in Cu3Si strain-driven self assembles.
The ﬁrst project described in this thesis is the fabrication of self assembled copper silicide nanostructures on SiO2/Si(111) and SiO2/Si(100) with electron beam evaporation in ultrahigh vacuum. The copper silicide growth was determined to be defect assisted. In order to create defect sites or voids at the surface, the SiO2/Si substrates in this work were annealed at 500◦C for 10-12 hours in a vacuum sys-tem prior to the deposition of Cu. The development of these nucleation centers or voids at the surface is discussed along with the deposition of Cu at low temperatures (T < 450◦C) and the deposition of Cu and growth of nanostructures in an optimal temperature range (450◦C < T < 600◦C). The variation in the density of voids at the sample surfaces was investigated with SEM-EDS and XRD techniques. Copper silicide phase and orientation of nanostructures were investigated with SEM-EDAX techniques. For the growth of Cu3Si nanostructures on SiO2/Si(111), equilateral tri-angles of various sizes were found to grow up to a critical size, beyond which the shape transitioned from equilateral triangular to trapezoid. For Cu3Si nanostruc-tures on the SiO2/Si(100) surface, square islands were found to grow up to a critical size, beyond which rectangular islands and long nanowires were formed. A growth mechanisms for Cu3Si nanostructures based on the strain induced shape transition growth model is discussed.
The second project discussed in this thesis is the nanopatterning of self as-sembled copper silicide nanostructures on SiO2/Si(111) and SiO2/Si(100) with highly charged ion beams (HCIs) of argon. Since the void creation at surface using the ther-mal annealing technique requires long times, we investigated the use of highly charge ion beams to induce defect sites on the surface of the substrate. Arq+ ion beams of varying ﬂuence and charge state (q=1,4,8) were used to produce nucleation centers or voids at the surface of SiO2/Si substrates. This approach could provide an alternative method for probing the sputter yields of HCI irradiated oxides. The deposition of Cu and the growth of nanostructures at an optimal temperature of 600◦C are discussed. The variation in the density and orientation of Cu3Si nanostructures as a function of HCI charge state and ﬂuence were investigated with the SEM-EDS technique. For the growth of Cu3Si nanostructures on SiO2/p-Si(111) and on SiO2/p-Si(100) surfaces, square islands have been found to grow up to a critical size, beyond which rectangular islands and long nanowires were formed. In general, the growth results were similar to the previous study. However, the size and hence the growth rate was signiﬁcantly longer.
The ﬁnal project presented in this thesis is modiﬁcation of the surface prop-erties of polycarbonate with HCIs. Polycarbonate (PC, Lexan) has many industrial applications because of its excellent transparency and high impact resistance. How-ever, PC requires a surface modiﬁcation to improve adhesion for metallization and optical applications. The surface of PC samples were irradiated with highly charged ion beams of argon and oxygen in order to understand the role of low energy HCIs on the surface modiﬁcation. Surface characterization of PC prior to and after HCI irradiation was performed using the XPS technique. Chain scission and cross linking were determined to occur during the HCI polymer interaction. The change in the relative intensities of C-C,C-O and C=O functional groups with HCI species, charge state and ﬂuence were discussed. An increase in the relative intensities of C-O, C=O and a decrease in C-C bond intensities were discussed in terms of potential energy dependent sputtering.
Srinadhu, Endu Sekhar, "Defect Assisted Growth of Copper-Silicide Nanostructures on Si(100) and Si(111)" (2016). All Dissertations. 2305.