Flood guns, electron

Because polymers are typically non-conductive, sample charging can occur and has to be compensated carefully, e. g. by use of a low-energy electron-flood gun, to avoid line-shape distortion and misinterpretation of the measurements. 

Figure 2.10. An example of electron flood gun treatment of XPS charging shifts of O (Is) lines from a silica specimen. The effect of increasing flood gun current is shown. (After Barr, 1983.)...

TOF analyzer it is critical for the mass resolution that the secondary ions are ejected at a precisely defined time. This means that the primary ion pulse should be as narrow in time as possible, preferably < 1 ns. At the same time maximum lateral resolution is desired. Unfortunately, there is a trade-off between these two parameters if the primary ion intensity is not to be sacrificed [122], Therefore, TOF-SIMS instruments have two modes of operation, high mass resolution and high lateral resolution. An advantage with the pulsed source is that an electron flood gun can be allowed to operate when the primary ion gun is inoperative. Thus, charge-compensation is effectively applied when analyzing insulating materials. 

For the TOF SIMS analysis, only slides treated with a natural pH HAPS solution were used. These were subsequently extracted with warm and hot water. They were mounted into a grid sample holder for transportation into a VG IX23S time-of-flight (TOF) SIMS instrument operating at a vacuum of < 10 Torr with a microfocused liquid Ga metal ion primary beam source (30 keVx 1.0 nA). For charge compensation, an electron flood gun was used. The working resolution of the spectrometer was determined from a lead phthalocyanine spectrum for Pb+ at mlz = 208 and the molecular ion at mlz = 720, it was 500 and 1000, respectively. 

Figure 4. The electrostatic quadrupole triplet lens and target chamber used for micro PIXE showing the 30 sq mm Si(Li) X-ray detector and the absotber ladder at 135 the RBS detectors which are at 158 above and below the lens the Ge(Li) PIGE detector and collimator the electron flood gun and the movable zoom microscope used for focusing and alignment of the beam.

A Perkin Elmer Physical Electronics Model 550 spectrometer was used for XPS, Relative amounts of eJements were obtained without corrections for depth sensitivities from the data processing sysLem associated with the spectrometer. Sample charging was neutralized by an electron flood gun, and peak energy was calibrated against the Al(2p) peak at 74.4 eV and the C ls) peak at 284 6 eV from the contamination overlayer. 

Figure 7.19 Comparison of XPS spectra of plastic tape with a monochromatic X-ray source (a) spectrum with electron flood gun off (b) spectrum with the flood gun on, but with incorrect electron compensation and (c) spectrum with the flood gun on and proper electron compensation. (Reproduced with permission from D. Briggs and J.T. Grant, Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications and Surface Spectra Ltd, Chichester. 2003 IM Publications.)...

The transmission electron microscopy was done with a 100-kV accelerating potential (Hitachi 600). Powder samples were dispersed onto a carbon film on a Cu grid for TEM examination. The surface analysis techniques used, XPS and SIMS, were described earlier (7). X-ray photoelectron spectroscopy was done with a Du Pont 650 instrument and Mg K radiation (10 kV and 30 mA). The samples were held in a cup for XPS analysis. Secondary ion mass spectrometry and depth profiling was done with a modified 3M instrument that was equipped with an Extranuclear quadrupole mass spectrometer and used 2-kV Ne ions at a current density of 0.5 /zA/cm2. A low-energy electron flood gun was employed for charge compensation on these insulating samples. The secondary ions were detected at 90° from the primary ion direction. The powder was pressed into In foil for the SIMS work. 

---