Electric lamp and discharge devices – Photosensitive – Secondary emitter type
Reexamination Certificate
1999-08-18
2001-07-24
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Photosensitive
Secondary emitter type
C313S1050CM, C313S532000, C313S528000
Reexamination Certificate
active
06265812
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a device applicable, for example, to electron microscopes; and, in particular, to an electron multiplier for multiplying incident electrons and outputting thus multiplied electrons.
2. Background Art
As conventional electron microscopes, those of reflection type and transmission type have been known. To these electron microscopes, an electron multiplier equipped with a microchannel plate (hereinafter referred to as MCP) having a plurality of channels for electron multiplication is applicable as electron multiplying means.
Here, the reflection type electron microscope is an apparatus which detects secondary electrons from a sample generated by an electron beam emitted toward the sample, and processes the resulting signal, so that an image of the sample is observed. On the other hand, the transmission type electron microscope is an apparatus which detects electrons transmitted through a sample irradiated with an electron beam, so that an image of the sample is observed.
The electron beam apparatus disclosed in Japanese Patent Application Laid-Open No. 2-275368 and the like, for example, have been known as the prior art related to the above-mentioned reflection type electron microscope, whereas the electron beam apparatus disclosed in Japanese Patent Application Laid-Open No. 6-310076 and the like, for example, have been known as the prior art related to the above-mentioned transmission type electron microscope.
DISCLOSURE OF THE INVENTION
As a result of studies of conventional electron microscopes, the inventors have found the following problems. Namely, with the reflection type electron microscope, transmitted electron images formed by electrons transmitted through a sample cannot be observed. In other words, though a surface of the sample can be observed therewith, the inner structure of the sample and the like cannot be observed, whereby separate transmission type viewing equipment is necessary for observing such an inner structure and the like.
With the transmission scanning electron beam apparatus, on the other hand, while a transmitted electron image formed by electrons transmitted through a sample can be observed by an electron detector installed below the sample (in a space opposing the space where an electron source is installed with respect to the sample), and a reflected electron image formed by secondary electrons from the sample can be observed by an electron detector located above the sample, the dedicated electron detectors are necessary for obtaining the respective electron images. Also, a signal selecting circuit for selecting the respective signals of the electron detectors is necessary along therewith. Consequently, the apparatus becomes complicated, thereby increasing the size and cost thereof.
For example, in cases where a voltage to an MCP (electron multiplying means) of an electron multiplier employed in such an electron microscope is selectively supplied and stopped, so that the reflected electron image and transmitted electron image can be observed alternately, an electric field may leak to the front side of the MCP when the voltage is supplied thereto, whereby the electron beam incident on the sample may be bent by the leakage electric field. Due to this phenomenon, each part of the resulting transmitted electron image shifts to a position different from that of the reflected electron image. According to the experiments conducted by the inventors, such electron image shifting occurred by about 3 &mgr;m when a voltage of 700 V was applied to the MCP, whereby the amount of shift between the electron images would not be negligible anymore when observed at a high magnification (e.g., 1 &mgr;m×1 &mgr;m).
In addition, when it comes to the handling of the electron multiplier equipped with the MCP, it has conventionally been necessary for a skilled person to take considerable care in replacing the MCP in the electron multiplier in order to prevent the MCP from being damaged or contaminated. In particular, the conventional structure for mounting the electron multiplier has such a configuration that the MCP unit is hard to remove therefrom, whereby it has been necessary to replace the whole electron multiplier in its already mounted apparatus.
In order to overcome the problems such as those mentioned above, it is an object of the present invention to provide an electron multiplier comprising a structure which effectively prevents an electric field from leaking to the vicinity of an MCP due to a voltage applied to the MCP, facilitates an operation of attaching/detaching the MCP, and prevents the MCP from being damaged and so forth during the operation.
Namely, the present invention relates to an electron multiplier equipped with a microchannel plate (MCP) having a plurality of channels for multiplying an incident electron and outputting thus multiplied electron, the MCP being provided with a first electrode on a first surface positioned on a side where the electron is incident, and a second electrode on a second surface opposing the first surface. The plurality of channels extend along a predetermined reference axis from the first surface toward the second surface.
In particular, in order to prevent an electric field from leaking due to a voltage supplied to the MCP acting as an electron multiplying means, the electron multiplier according to the present invention comprises an electric field shield cap (outer electric field shield member) accommodating the MCP. The electric field shield cap has a body portion surrounding at least a side face of the MCP while being separated therefrom by a predetermined distance. Further, in order for the electric field to be more effectively restrained from leaking to the front side of the MCP, the electric field shield cap preferably comprises a support portion (outer support portion) extending from a first end part of the body portion toward the reference axis and supporting the MCP. This support portion has an opening for exposing the first surface of the MCP, and this electric field shield member having this support portion realizes an MCP support structure and an electric field shield function at the same time.
Also, the electron multiplier according to the present invention comprises a base for mounting the electric field shield cap accommodating the MCP therein, thereby realizing a structure which can effectively restrain the MCP from being damaged and so forth during an operation of replacing the MCP and attain a sufficient electric field shield effect. Namely, a second end of the electric field shield cap opposing a first end thereof (an end part provided with the support portion) is detachably mounted to the base, thereby realizing a structure in which the base and the electric field shield cap are electrically connected to each other.
In this configuration, as the electric field shield cap is grounded while being electrically insulated from the first electrode formed on the first surface of the MCP or while being electrically in contact with the first electrode through a predetermined insulating member, it is shielded from the electric field occurring when a voltage is supplied to the MCP, whereby the electric field can be effectively restrained from leaking to the front side of the MCP (the space on the side where the electron source is installed with respect to the MCP) (i.e., the influence of the electric field on the electron beam orbit can be eliminated). When the electric field shield cap and the first surface of the MCP (or the first electrode formed on the first surface) are electrically insulated from each other, the first electrode can be set to a potential other than the ground potential.
The electron multiplier according to the present invention may further comprise an intermediate member (inner electric field shield member) accommodated within a space defined by the electric field shield cap while being electrically insulated from the electric field shield cap while being electrically in contact with the second surface of the MCP. This m
Iguchi Masahiko
Kusuyama Yutaka
Watanabe Hiroyuki
Hamamatsu Photonics K.K.
Morgan & Lewis & Bockius, LLP
Patel Ashok
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