Design and evaluation of a radio frequency-powered glow discharge (RF-GD) source for atomic emission spectroscopy

• Main Author: Lazik, Christopher S
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1994
• Subjects: Analytical chemistry
• ISBN: 9798209077923

Radio Frequency powered glow discharges (rf-GD's) are finding increasing applications as atomization/excitation sources for atomic spectroscopy. Although rf-GD's have served an important role in the sputter etching and semiconductor processing industries for over thirty years, their true analytical potential has only recently been realized. This has been fueled in large part due to the increasing demands of an expanding technological industry for improved analytical techniques that can assist in the direct analysis of specialty materials, including alloys, ceramics, glasses, and semiconductors. With the development of modern rf-GD systems for various optical (OES) and mass spectroscopies (MS), these demands are being met with a high degree of success, and the rf-GD has rapidly been established as a premier technique for the direct analysis solid materials. In the present work, the development and a systematic parametric evaluation of an external sample mount-rf-GD source, designed in this laboratory for Atomic Emission Spectrometry (AES) is discussed. Much of the initial work involved the optimization of the sputtering and emission characteristics of the system with respect to source geometry, with the intention of employing the optimized system in future analytical work. These studies have also extended into the development of a "flow assisted" source modification that was intended to inhibit sputter material redeposition onto the cathode surface. The present rf-GD system also has the advantage of operating interchangeably with both conducting and insulating materials, which was not an option with most of the early rf-GD analytical source designs. The rf-GD-AES source has demonstrated a suitable potential for these important nonconductor applications; however, some limitations as to sample size and plasma energy have been observed. The operating rf frequency has been shown to have a strong influence on the sputtering and emission characteristics of the rf-GD-AES source. The primary effect of employing higher rf frequencies (${>20}$ MHz) are an enhancement in excitation of analyte material within the discharge negative glow. At lower frequencies, sputtering rates are improved and emission from high energy transitions is favored. These results stress the necessity of a thorough, comprehensive line selection procedure for the evaluation of atomic spectroscopic techniques.