Browsing by Subject "Silicon--Effect of lasers on"
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Item Experimental studies of high energy density silicon using ultra-fast lasers(2007) Grigsby, Will Robert, 1978-; Ditmire, Todd R.Understanding material behavior under extreme conditions is an important area of research in physics and material science. One method to study the behavior of materials under these conditions is to drive a strong shock wave through a material and watch its response. In many cases the material response is complicated by phase transitions such as lattice restructuring (Barker 1975; Mabire and Hereil 2000; Swift, Tierney et al. 2005) and melting (Asay 1975; Elias, Chapron et al. 1988; Werdiger, Eliezer et al. 1999; Mabire and Hereil 2000; Swift, Tierney et al. 2005). To study these dynamics we are using lasers in high time resolution pump-probe experiments to develop a real time diagnostic on the phase of a shocked material. This technique enables probing of the entire phase history of a material as it shock compresses and releases. In addition to linear reflectivity and ultra-fast 2D displacement interferometry, we developed a melting diagnostics based on the non-linear optical technique of third harmonic generation (THG) using a circularly polarized laser pulse. This diagnostic resolves the less than 300 fs melting transition of laser excited Si and GaAs, and it also detects a response in shock compressed silicon. Our results show that Si remains crystalline during compression of an elastic 100 kbar shock wave. Results from Si shocked to higher pressures (> 300 kbar) indicate a decrease in THG, suggesting some level of disordering or unexplained phase change.Item Laser micro/nano scale processing of glass and silicon(2006) Theppakuttai Komaraswamy, Senthil Prakash; Chen, ShaochenItem Laser micro/nano scale processing of glass and silicon(2006-05) Theppakuttai Komaraswamy, Senthil Prakash, 1977-; Chen, ShaochenThe revolutionary progress in semiconductor, communication, and information industries based on electronic and photonic technologies demands for the development and enhancement of new laser processes to support micro and nanotechnologies. This dissertation is aimed at exploring the use of lasers for micro and nano scale processing of glass and silicon, the most commonly used materials in the IC industry. The objective of the dissertation is two fold: a) use lasers for locally micro bonding glass and silicon wafers, and b) use lasers for nanopatterning glass and silicon substrates by circumventing the diffraction limit of light. In the first part of the thesis, glass and silicon wafers are bonded locally in microscale by a pulsed Nd:YAG laser. Glass is transparent to the wavelength used and hence the laser beam passes through the glass wafer and is absorbed by silicon. As a result, silicon is melted and upon resolidification bonding is realized between the two substrates. The transient melting and resolidification of the substrates is studied experimentally and compared to the simulation results of a finite element numerical model. The bonded areas are studied in detail using a scanning electron microscope and a chemical analysis is done to understand the bonding mechanism. In the second part of the thesis, nanopatterns are created on glass and silicon substrates by circumventing the diffraction limit of light. The nanofeatures are created by irradiating silica and gold nanospheres deposited on a substrate. In case of silica spheres, features approximately half the diameter of the sphere were obtained by utilizing the optical field enhancement around the spheres. In case of gold spheres, features as small as 40 nm were realized by the excitation of coherent resonant electron plasma oscillations. The effect of sphere size, laser wavelength, polarization, incident angle, and energy were studied experimentally. Finally, these experimental results are compared with the numerical results from a multidimensional, heat transfer model.