A low-voltage electron microscope ( LVEM ) is operated at relatively low electron accelerating voltage between 5 25 kV . Some of these can be a combination of SEM, TEM and STEM in a single compact instrument.
22.
The accelerating voltage for a television cathode ray tube may be described as " extra-high voltage " or " extra-high tension " ( EHT ), compared to other voltage supplies within the equipment.
23.
Since the phosphors were relatively opaque, the system required very high accelerating voltages, between 25 and 40 kV . An improved version was introduced that used transparent phosphor layers and thin insulating layers between them that reduced the required voltages.
24.
The slower ions with less kinetic energy stay closer to a surface of the target electrode or pulsed electrode when the accelerating voltage is applied and therefore start being accelerated at a greater potential compared to the ions farther from the target electrode.
25.
To prevent charging of non-conductive specimens, operating conditions must be adjusted such that the incoming beam current is equal to sum of outcoming secondary and backscattered electrons currents a condition that is more often met at accelerating voltages of 0.3 4 kV.
26.
The grid voltage sends the electrons flowing into the open area between the emitters at the back and the screen at the front of the display, where a second accelerating voltage additionally accelerates them towards the screen, giving them enough energy to light the phosphors.
27.
Where the exit wavefunction ? is a function of both r in the plane of the sample, and z perpendicular to the plane of the sample . \ tau _ o represents the wavefunction incident on the top of the sample . \ lambda is the wavelength of the electron beam, which is set by the accelerating voltage.
28.
The advantage of the cyclotron design over the existing " electrostatic " accelerators of the time such as the Cockcroft-Walton accelerator and Van de Graaff generator, was that in these machines the particles were only accelerated once by the voltage, so the particles'energy was equal to the accelerating voltage on the machine, which was limited by air breakdown to a few million volts.
29.
(2 ) Power density ( focusing of the beam ) The power density at the spot of incidence of the beam with the workpiece depends on factors like the size of the electron source on the cathode, the optical quality of the accelerating electric lens and the focusing magnetic lens, alignment of the beam, the value of the accelerating voltage, and the focal length.
30.
Thus for an ion which traverses a 1 m flight path, across a time of 2000 ns, given an initial accelerating voltage of 5000 V ( V in Si units is kg . m ^ 2 . s ^-3 . A ^-1 ) and noting that one amu is 1?0 " 27 kg, the mass-to-charge ratio ( more correctly the mass-to-ionisation value ratio ) becomes ~ 3.86 amu / charge.
