Electrostatic lens system

Referring again to Figure 2.4, the slow positrons emitted from the boron were accelerated and focussed by the electrostatic lens system... 

The passage of electrons or other particles with charge q and mass m through an electrostatic lens system is governed by their motion under the action of the electric field. In the case considered here, cylindrical symmetry around the optical axis (z-axis) and paraxial rays will be assumed. Of the cylindrical coordinates only the transverse radial coordinate p and the distance coordinate z are of relevance, and the electrostatic potential of the lens is given by q>(p, z). As shown in Section 10.3.1, in the paraxial approximation the potential q>(p, z) is fully determined by the potential symmetry axis. Hence, the equations of motion and the fundamental differential equation of an electrostatic lens depend only on this potential. The fundamental lens equation is given by (see equ. (10.38))... 

R radius of the first aperture of the electrostatic lens system... 

XPS Equipment Operated with an Electrostatic Lens System... 

FIGURE 5 XPS equipment with electrostatic lens system. 

The ion beam is produced in the following way U atoms are evaporated from an oven at a temperature of typically 400 C, and are ionized and excited to the metastable 2 5 state by electron impact, when leaving the oven aperture. The electrons are emitted from a little ring-shaped tungsten wire cathode which is placed horizontally several millimeters above the oven exit. The cathode is held at ground potential, the oven at +200 V. The electrons are accelerated directly onto the oven aperture thus counterpropa-gating to the ions which are accelerated in the same electric field. The ions pass the cathode loop and are formed into a well-collimated beam by an electrostatic lens system. 

Fig. 5.2 Schematics of the atmospheric pressure orifice leak inlet system attached to the lithium ion attachment mass spectrometer. The sampling of the inlet probe is shown for polymer pyrolysis. RC reaction chamber, ELS electrostatic lens system, QMS quadrupole mass spectrometer. (Reprinted with permission from [26]. 2001, Elsevier)...

Fig. 6.11 A schematic drawing of new ion attachment mass spectrometer with the capillary sample inlet and a vacuum envelope with a wall separating ELS chamber fiom mass analyzer chamber. This capillary inlet is fixed on the front flange of the vacuum envelope. 1C ionization chamber, ELS electrostatic lens system, QMS quadrupole mass spectrometer, TMP turbomolecular pump, RP rotary pump. The vacuum envelope is pumped by a single 230 L sec" turbomolecular pump with two ISO-100 inlet flanges (Pfeiffer-Vacuum TMH 261-250-010) plus a 250 mL min" rotary pump. Ionization chamber is closed-type, with a 1 mm < ) aperture through which ionic species are passed. The typical operating conditions are IS pressure with nitrogen gas used as a buffer gas, 40 Pa pressure of ELS chamber, 8x10" Pa, pressure of the QMS chamber, 8 xlO"" Pa. (Reprinted with permission from Ref. [93]. 2012, Springer)...

A compact ion attachment mass spectrometer was designed that is simple and small and fulfills all the basic requirements for lAMS the system can be used to obtain only molecular ions by detecting any chemical species in real time [93]. This custom-made apparatus (Fig. 6.11) consists of a Li+ ion attachment ion source into which a stream of gas from a capillary leak inlet is directed, an electrostatic lens system (ELS), and a quadrupole mass spectrometer and detector, all of which are installed in a vacuum-separated envelope. The system employs a single tuibomo-lecular pirmp on the vacuum envelope instead of a differential pumping system. 

Salmeron M, Schlogl R (2008) Ambient pressure photoelectron spectroscopy A new tool for surface science and nanotechnology. Surf Sd Rep 63 (4) 169-199 Ogletree DF, Bluhm H, Lebedev G, Fadley CS, Hussain Z, Salmeron M (2002) A differentially pumped electrostatic lens system fen photoemission studies in the millibar range. Rev Sci Instr 73 (ll) 3872-3877... 

Ogletree, D., Bluhm H., Lebedev G., et al. (2002). A Differentially Pumped Electrostatic Lens System for Photoemission Smdies in the Millibar Range, Rev. Sci. Instrum., 73, pp. 3872-3877. 

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