Field acceleration voltage

Figure Bl.17.8. Iron oxide particles coated with 4 nm of Pt in an m-planar magnetron sputter coater (Hennann and Mtiller 1991). Micrographs were taken in a Hitachi S-900 in-lens field emission SEM at 30,000 primary magnification and an acceleration voltage of 30 kV. Image width is 2163 nm.

If only ions with a single charge (z = 1) are considered, then with a constant magnetic field strength and constant accelerating voltage, the radius of arc depends on mass and, from Equation 24.3, Equation 24.4 is obtained. 

V = accelerating voltage at the ion source E = electric-sector voltage B = magnetic-field strength. 

The accelerating voltage V for ions leaving the source and the electric-sector voltage E for energy focusing are the two electric ones. The field B is the magnetic one. 

Accelerating voltage (high voltage) scan. An alternative method of producing a momentum (mass) spectrum in magnetic-deflection instruments. This scan can also be used, in conjunction with a fixed radial electrical field, to produce an ion kinetic energy spectrum. 

Operation of the high-field ZAB spectrometer at 7-kV accelerating voltage extends the mass range to nearly 3800 without a significant loss in sensitivity. Above that point, there is a steady decline in sensitivity. When V is lessened... 

The integral is taken along a trajectory I parallel to the optical axis, passing inside and outside the specimen, and which must include stray fields V(f, z) and Az(r, z) are the electrostatic potential and the z component of the magnetic vector potential A(f,z), respectively E a factor that becomes the accelerating voltage in the non-relativistic... 

V Accelerating voltage (V) B Magnetic field strength (Tesla) B2 Square of magnetic field strength (Tesla2) r2 Square of electron beam path radius (m2) e/m ratio (c/kg)... 

Bright field electron micrographs and electron diffraction (ED) patterns were taken with a Hitachi H-500 electron microscope, which was operated at an acceleration voltage of 75 kV and... 

Finally, the instrument can be operated in the peak-matching mode, which provides optimum mass resolving power and mass accuracy. Here the magnetic field strength is kept constant and the electric sector and acceleration voltages are scanned over a relatively small m/z range. This mode of operation is suitable when two ions that are very close in mass need to be separated or when the elemental composition of a molecule is to be determined at high resolution. 

How can metastable ions be registered with a classic magnetic sector mass spectrometer (See Chapter 2, Section 2.2.2) Let ion mj+ leave the ion source and after acceleration with accelerating voltage V fragment, with formation of ion m2+ and a neutral particle m3° between the source and magnetic analyzer (first field-free region, 1 FFR). 

Nevertheless, a resolution of 80,000 for a sector instrument does not mean that this mass spectrometer allows one to obtain separate peaks of the singly charged ions of masses 79,999 and 80,000. The registered mass is proportional to B2/V. An unlimited increase of magnetic field B is technically unreasonable, while decrease of accelerating voltage V decreases the resolving power. 

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