Abstract The application describes improved techniques for correcting an output detection signal from an electron microscope for aberrant variations in the electron beam produced by the microscope. The preferred embodiment comprisea a monitor assembly for producing a reference signal proportional to the magnitude of the electron beam and a correction circuit for varying the magnitude of the detection signal in response to variations in the reference signal. The monitor assembly may comprise a diverting assembly for diverting a portion of the electron beam from its normal path to produce a flow of diverted electrons and a transducer assembly for producing a signal proportional to the number of diverted electrons so that a reference signal is produced. The correction circuit may comprise logarithmic amplifiers, a subtraction circuit, and an antilogarithmic amplifier for producing a signal which corresponds to the ratio of the detection signal and the reference signal. This corrected signal may be used to drive a cathode ray tube display of the specimen.
In an electron microscope comprising an electron source for producing an electron beam and comprising detection means for producing a detection signal corresponding to the flow of electrons from a specimen placed in the electron beam, improved apparatus for limiting variations in the detection signal due to variations in the electron beam comprising: monitor means for producing a reference signal having a magnitude determined by the magnitude of the electron beam, said monitor means comprising means for isolating an electric field produced by the monitor means from the electron beam; and correction means for producing a corrected signal corresponding to the ratio of the detection signal and the reference signal, whereby the corrected signal is free from changes in signal magnitude due to variations in the electron beam.
Claim 2
Dependent Claim
128 words
In an electron microscope comprising an electron source for producing an electron beam and comprising detection means for producing a detection signal corresponding to the flow of electrons from a specimen placed in the electron beam, improved apparatus for limiting variations in the detection signal due to variations in the electron beam comprising: monitor means for producing a reference signal having a magnitude determined by the magnitude of the electron beam, said monitor means comprising means for isolating an electric field produced by the monitor means from the electron beam; and correction means for producing a corrected signal corresponding to the ratio of the detection signal and the reference signal, whereby the corrected signal is free from changes in signal magnitude due to variations in the electron beam.
Claim 3
Dependent Claim
95 words
Apparatus, as claimed in claim 1, wherein the correction means comprises: a first logarithmic amplifier for producing a first signal corresponding to the logarithm of the detection signal; a second logarithmic amplifier for producing a second signal corresponding to the logarithm of the reference signal; a subtraction circuit for subtracting the second signal from the first signal to produce a remainder signal; an antilogarithmic amplifier for producing a corrected signal which corresponds to the antilogarithm of the remainder signal; and electronic means for instantaneously displaying an image corresponding to the corrected signal at electronic speed.
Claim 4
Dependent Claim
124 words
Apparatus, as claimed in claim 1, wherein the monitor means comprises: a first metal surface that defines a first aperture through which the electron beam is directed; a second metal surface that defines a second aperture smaller than the first aperture through which a portion of the electron beam may pass, whereby a portion of the electrons in the electron beam are diverted by the area of the second metal surface surrounding the second aperture; a porous metal structure that surrounds the electron beam between the first and second metal surfaces; a scintillator for receiving diverted electrons and for converting the diverted electrons to light; a light pipe connected to the scintillator; and a photomultiplier responsive to the light transmitted by the light pipe.
Claim 5
Dependent Claim
14 words
Apparatus, as claimed in claim 3, wherein the porous metal structure comprises a coil.