Characterization of a hybrid BEEQ instrument for the study of polyatomic ion-surface collision phenomena
Abstract
The design, construction and characterization of a hybrid mass spectrometer for the study of ion-surface collision processes is described. A general overview of previous ion-surface collision studies is provided, with special emphasis given to those works which use polyatomic ions as the primary projectile. In addition, the various characteristics of previous Aston laboratory ion-surface instruments which led to the development of the hybrid design are outlined. The principal characteristics of the hybrid instrument include the ability to select the primary ion's mass energy and incident angle of collision while the mass, energy and angle of emergence of the scattered/sputtered ions can be measured. In order to obtain the desired versatility, several complex mechanical systems are incorporated into the instrument. These features, which include the rotable analyzer system and the target transfer system are discussed in detail. Also, the complex vacuum system which allows one to maintain ultra-high vacuum in the main scattering chamber, is discussed. Several new ion optical elements are incorporated in the development of the analysis chamber. The various elements are designed based on ion trajectory calculations using an available ion simulation program. For quantitative information on the final location of the ion optical elements, the image aberrations and the beam cross sections at various locations, a simulation program based on transfer matrix calculations is used. Since the energy of the primary projectile is variable from 1 to 3000 eV, the corresponding scattered or sputtered ions can only be analyzed if the analyzers are floated at the appropriate potential. The design and operational characteristics of special power supplies used for deceleration and for floating the electrostatic analyzer and quadrupole mass analyzer are given in detail. Experimental performance is characterized and representative experiments are presented which depict its capabilities and limitations. For example, energy distribution measurements of ions sputtered from a surface using polyatomic projectiles as well as polyatomic elastic and inelastic scattering experiments are presented. Ion-surface reactive collisions of ions such as pyrazine and benzene with a C$\sb{16}$ deuterated thiol (CD$\sb3$(CD$\sb2)\sb{15}$SH) covalently bound to a polycrystalline gold surface results in the production of (M + CD$\sb3$)$\sp+$ and (M + CD$\sb3$ - D$\sb2$)$\sp+$, respectively.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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