SSMS

Now, making only the change in notation of SSM for SST to indicate the total deviation from the mean and changing from upper to lower case r, we have... 

SRM. selected reaction monitoring SSMS. spark source mass spectrometry... 

Spark Source Mass Spectrometry (SSMS) is a method of trace level analysis—less than 1 part per million atomic (ppma)—in which a solid material, in the form of two conducting electrodes, is vaporized and ionized by a high-voltage radio frequency spark in vacuum. The ions produced from the sample electrodes are accelerated into a mass spectrometer, separated according to their mass-to-charge ratio, and collected for qualitative identification and quantitative analysis. 

SSMS provides complete elemental surveys for a wide range of sample types and allows the determination of elemental concentrations with detection limits in the range 10-50 parts per billion atomic (ppba). 

GDMS is slowly replacing SSMS because of its increased quantitative accuracy and improved detection limits. Like SNMS and SALI, GDMS is semiquantitative without standards ( a factor of 3) and quantitative with standards ( 20%) because sputtering and ionizadon are decoupled. GDMS is often used to measure impuri-des in metals and other materials which are eventually used to form thin films in other materials applications. 

Table 1 lists some of the materials typically analyzed by SSMS and some of the forms in which these materials may exist. The basic requirement is that two conducting electrodes be formed of the material to be analyzed. Details of the analysis of each type of sample will be discussed in a later section. 

Figure 2 Ion-sensitive plate detector showing the species produced by the SSMS analysis of a Y203 Eu203 mixture compacted with gold powder.

Although SSMS cannot be considered a surface technique due to the 1-5 rm penetration of the spark in most materials, few other techniques can provide a trace elemental survey analysis of surfaces consisting of films or having depths of interest... 

The SSMS point-to-plane surface technique has been shown to be particularly useful in the survey analysis of epitaxial films, heavy metal implant contamination, diflRision furnace contamination, and deposited metal layers. 

Due to the relative uniformity of ion formation by the RF spark (although its timing is erratic), the most widely used method of quantitation in SSMS is to assume equal sensitivity for all elements and to compare the signal for an individual element with that of the total number of ions recorded on the beam monitor. By empirically calibratii the number of ions necessary to produce a certain blackness on the plate detector, one can estimate the concentration. The signal detected must be corrected for isotopic abundance and the known mass response of the ion-sensitive plate. By this procedure to accuracies within a factor of 3 of the true value can be obtained without standards. 

Figure 4 SSMS surface analysis. The point-to-plane technique allows ppma elemental surveys over a depth of 1-5 xm.

GDMS cannot be used instead of SSMS. As GDMS source designs are developed to allow clean, thin-film analyses, and some limitations are accepted for the analysis of insulators, GDMS instrumentation will replace more and more of the older SSMS installations. For the present, however, there are exceUent laboratories having SSMS instrumentation and services, and SSMS should be used when it proves to be the technique of choice. 

Because GDMS can provide ultratrace analysis with total elemental coverage, the technique fills a unique analytical niche, supplanting Spark-Source Mass Spectrometry (SSMS) by supplying the same analysis with an order-of-magnitude better accuracy and orders-of-magnitude improvement in detection limits. GDMS analy-... 

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