Cluster projectiles for ToF-secondary ion mass spectrometry /
Surface analysis of nonvolatile, thermally labile organic molecules presents challenges. Difficulties arise in achieving adequate production of molecular ions without depositing excessive energy which often leads to fragmentation. Of all the surface techniques, SSIMS (static secondary ion mass spect...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1998.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=732843341&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Surface analysis of nonvolatile, thermally labile organic molecules presents challenges. Difficulties arise in achieving adequate production of molecular ions without depositing excessive energy which often leads to fragmentation. Of all the surface techniques, SSIMS (static secondary ion mass spectrometry) provides the molecular information needed to perform organic surface analysis. Although other desorptionionization methods have certain advantages, SSIMS can limit the energy deposited by the probing mechanism to the upper few manslayers. This study combined efficient monatomic or ''cluster'' projectiles with event-by- event embarkment and detection. The advantages of SSIMS were enhanced with the use of cluster projectiles. [C60+] produced -58 times more (M-H)- from leucine enkephalin than [Cs':] monatomic projectiles when compared at 20 keV. The increase in secondary ion yields allowed virtually nondestructive analysis of organic and bioorganic molecules, e.g. polypropylene glycol and phosphatidylcholine, with a total projectile dose of [105 - 106] impacts/[cm2]. In contrast, molecular ions from polypropylene glycol and phosphatidylcholine were not detected using [Cs':] monatomic projectiles. At the same time, cluster projectile impacts also increased the yields of ''manufactured'' ions resulting from fragmentation or rearrangement reactions. [CK+] projectiles produced the highest molecular ion yields, but also increased, to a much greater extent, the amount of nonspecific [(CxH)-] fragment ions. To improve analysis and ultimately limit of detection, it is necessary to use efficient projectiles that will maximize production of molecular ions, while minimizing the degradation of molecular information due to excessive fragmentation. Projectiles containing three large mass constituent atoms like [(CsI)Cs+] produced higher efficiency ratios than projectiles comprised of smaller mass constituents such as [SiF5-] or [C60+]. |
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| Item Description: | Vita. |
| Physical Description: | xvi, 149 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references: pages 143-148. |