Browsing by Author "Jerome J. Cuomo, Committee Chair"

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Applications of Atmospheric Plasmas
(2009-11-08) Oldham, Christopher John; Mohamed A. Bourham, Committee Member; Jerome J. Cuomo, Committee Chair; J. Michael Rigsbee, Committee Member; Mark A.L. Johnson, Committee Member
Surface modification techniques using plasmas have generally been completed in a low pressure environment due to Pd (pressure x gap distance) considerations influencing the behavior of plasma generation. Generally, plasmas produced in a low pressure environment are of a non-thermal or cold nature. The basic feature of non-thermal plasmas is the majority of electrical energy used to generate the plasma is primarily used to produce energetic electrons for generating chemical species. Low pressure plasmas serve many purposes for materials processing. Since the plasma environment is contained within a closed vessel, the plasma can be controlled very easily. Low pressure plasmas have been used in many industries but the complexity associated with the large pumping stations and limitation to batch processing has motivated new work in the area of atmospheric plasmas. Atmospheric plasmas offer both economic and technical justification for use over low pressure plasmas. Since atmospheric plasmas can be operated at ambient conditions, lower costs associated with continuous processing and a decrease in the complexity of equipment validate atmospheric plasma processing as a next generation plasma-aided manufacturing processes. In an effort to advance acceptance of atmospheric plasma processing into industry, a process was developed, the dielectric barrier discharge (DBD), in order to generate a homogeneous and non-thermal plasma discharge at ambient conditions. The discharge was applied to the reduction of known food borne pathogens, deposition of thin film materials, and modification of lignocellulosic biomass.
Growth Optimization and Characterization of Reactively Sputtered Zirconium Nitride Thin Films for III-V Buffer Layer Applications
(2002-11-07) McGregor, David Ross Jr.; Jerome J. Cuomo, Committee Chair; Mohamed A. Bourham, Committee Member; Dennis M. Maher, Committee Member
Zirconium nitride (ZrN) thin films were deposited by reactive dc magnetron sputtering to assess the effects of processing conditions upon film properties. Processing conditions and parameters were optimized to generate films of completely oriented (111) ZrN on silicon to be used as buffer layers for the growth of gallium nitride A single and double Langmuir probe were used to determine trends in electron temperature, ion density, ionization fraction, and floating potential during reactive sputtering of zirconium in argon and nitrogen. Reactive gas concentration, deposition pressure, deposition temperature, cathode current, film thickness and substrate orientation were investigated as variable processing conditions. Four-point probe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and x-ray diffraction (XRD) were used to characterize thin films produced. The optimum growth conditions for the (111) oriented growth of ZrN, for this work, were found to occur during reactive magnetron sputtering at a deposition temperature of 500°C, a constant cathode current of 0.5 ampere, a deposition pressure of 15 mTorr, a reactive nitrogen gas concentration of 4% in argon, deposited on (111) oriented silicon, with a thickness on the order of 600 nanometers. Gallium nitride was then deposited on films of ZrN to assess the crystallinity of films produced. The lattice mismatch between (111) oriented ZrN and c-axis oriented GaN was calculated at 1.6%. Microscopic evaluation showed the films to be of columnar structure with dense grains and smooth surfaces. A change in preferred orientation was noticed as a function of increasing film thickness and cathode current and was determined to be due to an increase in ion channeling and bombardment energy.
Pulsed DC reactive magnetron sputtering of aluminum nitride thin films
(2003-08-29) Cho, Jung Won; Dennis Maher, Committee Member; Jagdish Narayan, Committee Member; Jerome J. Cuomo, Committee Chair; Mohamed Bourham, Committee Member
Aluminum nitride thin films have been deposited by pulsed DC reactive magnetron sputtering. The pulsed DC power provides arc-free deposition of insulating films. Two types of pulsed DC (unipolar and asymmetric bipolar) were studied with respect to characteristics and properties of resultant films. The unipolar power supply generates a series of 75 kHz DC pulses modulated with 2.5 kHz frequency. The frequency of asymmetric power supply can be varied from 50 kHz to 250 kHz. The duty cycle, which is a ratio of negative pulse time to total time, can be varied from 60% to 98%. Very fast oscillation and overshoot were observed when the polarity of the target voltage was changed. The control of crystal orientation of deposited film is important since the properties of AlN film is related with the orientation. For example, the acoustic velocity is high along the c-axis. The electromechanical coupling coefficient is large in a-axis direction. The crystal orientation and microstructure of the AlN films were strongly affected by the deposition conditions such as sputtering power, growth temperature, sputtering gas pressure and frequency/duty cycle. The crystal orientation of AlN films was closely related with the energy of sputtered atoms and mobility of adatoms on substrate. The c-axis oriented films were obtained when the target power and growth temperature were high. This provided higher energy of sputtered atoms and mobility of adatoms. The deposited AlN films have a columnar structure. The crystal orientation of the AlN films was changed from (101) to (002) by applying an RF bias was applied to the substrate in unipolar pulsed DC sputtering. The columnar structure disappeared when the RF bias was applied to the substrate. Applying bias was thought to increase mobility of adatoms by ion bombardment. MIM (aluminum-AlN-aluminum or molybdenum) structure was fabricated to measure electric properties of AlN films. Dielectric constants of 8.5 to 11.5 were obtained at 100 kHz. The relation of the current density and electric field of the AlN film followed ohmic conduction. The broad photoluminescence spectrum in the range of 300 nm and 650 nm was observed for the aluminum nitride thin films regardless of the deposition conditions. This spectrum might be due to the defects related with oxygen. The thermal conductivity of AlN films was evaluated by the 3omega method. The values in the range of 12 and 30 W/mK was obtained. Those values are very low compared to those of bulk. The reason might be attributed to the oxygen incorporation as well as the unique microstructure of the sputtered films. The plasma parameters such as electron temperature and charge density were obtained by the Lagmuir probe. The electron temperature in argon and nitrogen plasma increased from 2.7 to 5.3 eV when the frequency increased from 75 kHz to 250 kHz in asymmetric bipolar pulsed DC sputtering. The electron and ion densities were found to increase with frequency. The stochastic heating due to the fast oscillation in the target voltage waveform may be attributed to the increased electron temperature and electron/ion densities. The measured plasma characteristics were correlated with properties of the AlN film. The ion and energy flux were believed to increased as the frequency increased. The intensity of the (002) peaks was found to increase with the increase in the ion flux and energy flux.