Information on SIMS Relative Sensitivity Factors

Secondary Ion Mass Spectrometry is per se not a quantitative analytical method. As the material that is to be analyzed has to be removed from the surface, its ionization efficiency and bonding state affect the amount of material that ultimately forms the ion intensity images. Only the use of standards allows quantitative statements.

This poses a problem for the impact residue analysis done on LDEF surfaces: With practically all impact parameters (velocity, size, density, composition, direction) and the precise impact dynamics on the MOS detectors unknown, it is practically impossible to define the state of the impact residue in the feature. LDEF's surface contamination adds to this problem.

In general, impact residue can exist in two forms:

as a surface deposit in the form of thin films and/or small particles composed primarily of impactor material, and

as a thin or thick film and/or large or small particle of intermixed impactor and substrate materials. We decided to use two relative sensitivity factors for

Material implanted in a silicon matrix (as should be the case for residue that melted and became intermixed with the substrate)
Material in a lunar analog glass (as should be the case for "pure" meteoritic residue as it may be suspected to be the case in some of the tiny spheres found close to the discharge site)

Neither of these assumptions is correct. Also, many meteorites are expected to be Fe based (very little silicate "glass" characteristic), and manmade orbital debris detectable on the Al/Si substrates is composed of paint particles or metal alloys.

Following is a list of the two sets of RSF's used for the most common species:

+------+---------+--------------------+----------------+
|      |	 |	RSF for       |     RSF for    |
| Mass | Species | Lunar Analog Glass | Silicon Matrix |
+------+---------+--------------------+----------------+
|  12  |  C+	 |		      |        0.007   |
|  23  |  Na+	 |	  6	      |      139       |
|  24  |  Mg+	 |	  7.9	      |       18       |
|  27  |  Al+	 |	  6.15	      |       36       |
|  28  |  Si+	 |	  1	      |        1       |
|  30  |  Si+	 |	  1	      |        1       |
|  39  |  K+	 |	 12	      |      125       |
|  40  |  Ca+	 |	 11.05	      |       38.5     |
|  48  |  Ti+	 |	  3.8	      |       13.9     |
|  52  |  Cr+	 |	  2.8	      |        7.69    |
|  56  |  Fe+	 |	  3.6	      |        1.85    |
|  58  |  Ni+	 |	  2.42	      |        1.35    |
|  63  |  Cu+	 |		      |        1.61    |
+------+---------+--------------------+----------------+

Klaus G. Paul, 6-15-1994

Klaus G. Paul, 4-30-1994