JPH0760658B2 - Brightness control device for transmission electron microscope - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transmission electron microscope, and more particularly, to a brightness of a transmission electron microscope that always obtains a projected image of a desired brightness regardless of magnification. The present invention relates to a control device.

[Prior Art] Generally, in an electron microscope, in the past, automatic brightness control (Automatic Bright
htness Control, hereinafter simply referred to as ABC. ) Is done. Fig. 3 shows the outline of ACB in a transmission electron microscope. The electron beam emitted from the electron gun 21 passes through the condenser lens 22 and hits the sample 20. An electron beam transmitted through the sample is imaged on a projection surface 25 via an objective lens 23 and a projection lens 24. Since the projection surface is usually a fluorescent surface, the operator can see the projection surface through an observation window (not shown). Also, by placing a film on the projection surface,
You can also take pictures. The above is the structure of a well-known transmission electron microscope.

Now, in such a transmission electron microscope, the brightness of the projection surface is adjusted by controlling the exciting current of the condenser lens to focus or diffuse the electron beam on the sample. , Conventionally, when the exciting current scanning circuit 27 scans the exciting current from the maximum value to the minimum value and the current value of the projection surface obtained by the current amplifier 26 reaches a predetermined value corresponding to a predetermined brightness. Then, the scanning of the exciting current was stopped.

What takes the invention Problems to be Solved] conventional above described arrangement, the brightness of the relationship to the exciting current of the condenser lens, as in the Figure 2, excitation current I _c (hereinafter, this The maximum is when the point is crossover, and even if it becomes larger (hereinafter, this region is called the strong excitation side), it becomes smaller (hereinafter, this region is called the weak excitation side). Is reduced, and this characteristic is not known in advance. That is, the current value of the exciting current is I ₁ in FIG. 2, and even if the exciting current is changed to obtain an appropriate brightness, the characteristic curve is unknown, so if the value is larger than the value of I _1. I couldn't decide whether to make it smaller or smaller, so I had to scan the entire range of the exciting current and adjust to the optimum brightness.

Since the conventional ACB is as described above, it takes time to adjust the brightness, which is not practical.

The present invention is to solve the above-mentioned problems, and it is possible to shorten the scanning time of the exciting current by distinguishing whether the current exciting current is on the weak exciting side or the strong exciting side. An object is to provide a brightness control device for an electron microscope.

[Means for Solving the Problems] In order to achieve the above object, a brightness control device for a transmission electron microscope according to the present invention is a transmission electron that changes an exciting current of a condenser lens to obtain an image having a desired brightness. In the microscope brightness control device, compare the crossover excitation current value of the condenser lens with the current excitation current value of the condenser lens, and check if the current excitation current value is on the strong excitation side of the crossover excitation current value. If the output of the comparison circuit and the comparing circuit that identifies whether the current is on the weak excitation side indicates that the current excitation current value is on the strong excitation side of the crossover excitation current value, the excitation current of the condenser lens is If only the strong excitation side is scanned and the output of the comparison circuit indicates that the current excitation current value is on the weak excitation side of the crossover excitation current value, the capacitor Excitation current scanning means for scanning the excitation current of the lens only on the weak excitation side is provided.

[Operation] Conventionally, the reason why the entire range of the exciting current has to be scanned is that the characteristics shown in FIG. 2 have not been measured in advance as described above. If the current is known, it can be discriminated whether the current exciting current is on the strong exciting side or the weak exciting current side, and it can be understood that the scanning range can be limited to which side.

Therefore, in the present invention, from the pre-measured exciting current at the time of crossover and the present exciting current, it is discriminated whether it is currently on the strong exciting side or the weak exciting side, and if it is on the strong exciting side, only the strong exciting side is identified. The scanning is performed, and if it is on the weakly excited side, only the weakly excited side is scanned.

Examples Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of a brightness control device for a transmission electron microscope according to the present invention, in which 1 is a condenser lens, 2 is a projection plate, 3 is a current amplifier, and 4 is an exciting current setting. Means, 5 is a comparison circuit, 6 is a scanning drive circuit, 7, 8, 11
And 14 are switches (hereinafter, the switches are referred to as SW),
9 is a weak excitation side scanning circuit, 10 is a strong excitation side scanning circuit, 12 is a crossover excitation current setting means, 13 is a comparison circuit, 15 is a condenser lens control circuit, and 16 is a manual adjustment circuit.

The condenser lens 1, the projection plate 2, and the current amplifier 3 are the third
It is similar to that described in the figure. The exciting current setting means 4 is
The current value in the projection plate 2 corresponding to the proper brightness when directly observing the projection plate 2 and the current value in the projection plate 2 corresponding to the proper brightness for each film when film-shooting are set in advance. For example, these current values may be stored in a table, the type of film may be input, and the corresponding current value may be called. This current value is set on the strong excitation side and the weak excitation side for each appropriate magnification. This is because, as can be seen from FIG. 2, the current value for a given brightness exists on the strong excitation side and the weak excitation side, respectively. Further, it goes without saying that a means for manual adjustment may be provided so that the operator can set the brightness to an arbitrary value. The comparison circuit 5 is a current amplifier 3
And the output of the exciting current setting means 4 are compared and the difference is obtained. The scanning drive circuit 6 drives the two scanning circuits 9 and 10 by obtaining the output of the comparison circuit 5 and the output of the comparison circuit 13, and the details of the operation of this circuit will be described later.
SWs 7 and 8 are SWs that operate complementarily, and when one is closed, the other is open. Such SW is a relay,
It can be configured with an electronic switch or the like. Weak excitation side scanning circuit 9
Is for scanning the exciting current of the condenser lens only within the range on the weak excitation side, and similarly, the strong excitation side scanning circuit 10 is for scanning only within the range on the strong excitation side. SW11 is switched by the output of the comparison circuit 13. The crossover exciting current setting means 12 stores the preset exciting current value of the crossover, and becomes the reference value when the comparing circuit 13 compares with the current exciting current value. The comparison circuit 13 compares the value of the crossover excitation current setting means 12 and the value of the current excitation current, which is the output of the lens control circuit 15, to determine whether the current excitation current is on the strong excitation side or on the weak excitation side. Whether it is present or not is discriminated and, for example, "1" is output when it is on the strong excitation side, and "0" is output when it is on the weak excitation side. This output controls the scan drive circuit 6 and also controls the connection states of the SWs 7, 8 and 11. Further, based on this output, the excitation current setting means 4 determines whether to adopt the strong excitation side value or the weak excitation side value of the set current values. SW14 selects whether to perform brightness adjustment automatically or manually. The lens control circuit 16 is a circuit for supplying an exciting current to the condenser lens 1. The manual adjustment circuit 16 is a well-known circuit for manually adjusting the brightness.

The operation in the case of performing ACB by setting SW14 to the connection state shown in FIG. 1 with such a configuration is as follows. We are now observing at a certain magnification, and the characteristic of the excitation current vs. brightness at that magnification is the second
Suppose it was like curve 17 in the figure. In addition, the current excitation current is I ₁ and the brightness is L ₁ (point P _{1 in} FIG. 2), the proper brightness is
At L ₀ , the exciting current at that time is I ₂ (point P _{2 in} FIG. ₂ ). In this state, the comparison circuit 13 compares the exciting current value I _{c of the} crossover with the current value I ₁ , identifies that the current value is on the strong excitation side, and outputs “1”. As a result, the exciting current setting means 4 sets the current value I ₂ on the strongly excited side, the SWs 7, 8 and 10 are in the state shown in FIG. 1, and the scan drive circuit 6 scans the strongly excited side.

Further, in the comparison circuit 5, the difference between the current value corresponding to the exciting current I ₁ which is the output of the current amplifier 3 and the value corresponding to the exciting current I ₂ from the exciting current setting means 4 is obtained. The calculation of the comparison circuit 5 is based on the value of the exciting current setting means 4 and the current amplifier
If the value of is subtracted, then a positive output is obtained. The scan drive circuit 6 drives the strong excitation side scanning circuit 10 from the positive output from the comparison circuit 5 and the output of “1” from the comparison circuit 13 so as to increase the excitation current. If the output of the comparison circuit 5 is negative, driving is performed so as to reduce the exciting current. The same applies when the output of the comparison circuit 13 is "0", that is, on the weak excitation side. Obviously, such a circuit can be constructed by an appropriate logic circuit.

Now, when the strongly exciting side scanning circuit 10 increases the exciting current in this way, the point P ₁ in FIG. ₂ approaches the point P ₂ ,
When the point P ₂ is reached, the difference becomes 0 in the comparison circuit 5, so that the scanning drive circuit 6 stops the scanning of the strong excitation side scanning circuit 10. With this, proper brightness is obtained.

Next, it is assumed that the magnification is increased from this state and the observation is made with the characteristics shown by the curve 18 in FIG. In this case, since the proper brightness is at the point P ₄ , the exciting current setting means 4 is set to a value corresponding to the exciting current I ₃ at that time. Since it is currently at the position of point P ₃ , and therefore the output of the current amplifier 3 has a value corresponding to I ₂ , the comparison circuit 5 has a negative output, and the scan drive circuit 6 is strongly excited to reduce the exciting current. Side scanning circuit 10
To drive. As a result, the point P ₃ reaches the point P ₄ , and proper brightness is obtained.

In the above description, the case where the brightness is controlled on the strong excitation side has been described, but it will be clear that the same can be done on the weak excitation side. Further, it will be apparent from the above description that the same operation is performed when observing with a reduced magnification. Further, it is apparent that the present invention is not limited to the above embodiment and various modifications can be made.

[Effects of the Invention] As is apparent from the above description, according to the present invention, it is possible to always observe at a desired brightness regardless of the magnification, and whether the current excitation current is on the strong excitation side or the weak excitation side. It is possible to limit the scanning of the exciting current to the strongly excited side or the weakly excited side by distinguishing whether or not it is present, so that the time required to obtain the desired brightness can be shortened as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a brightness control device for a transmission electron microscope according to the present invention, FIG. 2 is a diagram showing a relationship between an exciting current of a condenser lens and brightness, and FIG. It is a figure which shows the example of a brightness control apparatus. 1 ... Condenser lens, 2 ... Projection plate, 3 ... Current amplifier, 4 ... Excitation current setting means, 5 ... Comparison circuit, 6
...... Scanning drive circuit, 7,8,11,14 ...... Switch, 9 ...... Weak excitation side scanning circuit, 10 ...... High excitation side scanning circuit, 12 ...... Crossover excitation current setting means, 13 ...... Comparison circuit , 15 ……
Lens control circuit, 16 ... Manual adjustment circuit.

Claims (1)

[Claims] 1. A brightness control device for a transmission electron microscope which obtains an image of a desired brightness by changing an exciting current of a condenser lens, wherein a crossover exciting current value of the condenser lens and a current exciting current value of the condenser lens. The output of the comparison circuit compares the current excitation current value with the comparison means that identifies whether the current excitation current value is on the strong excitation side or the weak excitation side of the crossover excitation current value. If it indicates that the current is on the strong excitation side of the overexcitation current value, the excitation current of the condenser lens is scanned only on the strong excitation side, and the output of the comparison circuit shows that the current excitation current value is greater than the crossover excitation current value. In the case of indicating that the excitation current is on the weak excitation side, an excitation current scanning means for scanning the excitation current of the condenser lens only on the weak excitation side is provided. Brightness control apparatus of an electron microscope.