Useful yields of organic molecules under dynamic SIMS cluster bombardment

Abstract

Useful yields have been measured for a series of organic compounds using Ar + , SF 5 + and Bi 3 + primary ion bombardment under high dose (>10 13 ions/cm 2 ) SIMS sputtering conditions on both magnetic sector and ToF-SIMS instruments. A precision inkjet deposition system was used to produce well defined arrays of microdrops on silicon with each deposit containing a known number of analyte molecules. The individual deposits were sputtered until consumed while monitoring the integrated characteristic molecular secondary ions for each analyte. The ratio of integrated counts to the number of molecules in the deposit defines the useful yield of the experiment. Measured useful yields varied from 1 × 10 −2 to less than 1 × 10 −8 depending on the compound examined, the probe beam used and the instrument configuration. Published in

Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

“…Precise measurements of these ion yields are difficult to obtain but estimates range from one parent ion per every 100 to 100 000 impacts. Recent measurements of useful yields for Ar + and SF 5 + bombardment [1] are consistent with this estimate. These yields seem incredibly small given that simulations of C 60 bombardment on molecular targets show that all the energy (10-120 keV) is deposited in the top 2-3 nm of the substrate in a time of 50-100 fs.…”

Estimation of useful yields for electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS)

“…The useful yield depends on the ionization probability as well as the transmission and detection efficiencies of the analytical instrument. The useful yield is thus a measure of the practical sensitivity obtainable for a given projectile, sample type and instrument configuration . In the present work, the crude assumptions (1) and (2) described above were made for the mixed samples of C 60 /rhodamine B and C 60 /Aerosol OT.…”

“…Gillen et al . measured the useful yields as 1.28 × 10 −3 and 5.83 × 10 −3 for ionic compounds of tetrabutyl ammonium bromide and tetrapentyl ammonium bromide, respectively, using SF 5 + as the projectile . These values are much smaller than the useful yield of 0.26 for K + from KBr using the same projectile.…”

“…Gillen et al measured the useful yields of KBr and organic molecules using Ar + , SF 5 + and Bi 3 + primary ion bombardment under high dose (>10 13 ions/cm 2 ) SIMS sputtering conditions on both magnetic sector and TOF-SIMS instruments. [20] A precision ink jet deposition system was used to produce well-defined arrays of microdroplets on silicon with each deposit containing a known number of analyte molecules. The individual deposits were sputtered until consumed while monitoring the integrated characteristic molecular secondary ions for each analytes.…”

Method for improved secondary ion yields in cluster secondary ion mass spectrometry

“…9 Therefore, for site-specific analysis where limited amounts of analyte material are available for detection, the overall secondary ion signals need to be increased to allow the detection of organic molecules without compromising sample integrity through degradation. Based on the current instrumentation (not including post-ionization techniques), there are two approaches to increase useful yields: sample modification and the use of cluster projectiles.…”