JPH0616403B2 - High-resolution non-interferometric image observation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high resolution observation method of an electron microscope, and particularly to metal particles and a dispersion state on a light element amorphous supporting film such as a replica sample or a biological section sample. The present invention relates to a method for observing a high-resolution non-interference image suitable for observing a shape.

BACKGROUND OF THE INVENTION In a general transmission electron microscope, a circuit that superimposes a quasi-triangular wave on a lens exciting current to give a variation is provided as an accessory mechanism for adjusting an electron beam to pass through the center of an objective lens. Is provided (for example, in 1975, published by Kyoritsu Shuppan Co., Ltd., co-authored by Koichi Adachi and others, see [Basics of Using Electron Microscope], page 66, column c.), But the amount of fluctuation is too large for different purposes However, it is impossible to obtain a high-resolution non-interference image because of the drawbacks that the influence of aberration on the image is large and the phase difference contrast cannot be effectively reduced by the pseudo triangular wave.

[Object of the Invention]

An object of the present invention is to provide a method for observing a high-resolution non-interfering image composed of only scattering contrast by removing phase contrast which adversely affects fine structure determination when observing a high-resolution image with an electron microscope. And even
By properly controlling the phase difference contrast intensity and the frequency, an image that matches the purpose is obtained.

[Outline of Invention]

The phase difference contrast in the electron microscope image is mainly caused by the transfer function of the objective lens, and the periodic structure corresponding to a specific frequency at which this function has a peak appears emphasized. In order to reduce the phase difference contrast, the amplitude of the transfer function may be reduced over the entire period.

In the present invention, the defocus amount, which is one variable of the transfer function, is changed by slightly changing the lens exciting current, and the transfer function is smoothed by adding the transfer functions at various defocus amounts. Turn into. Defocus amount Δ when observing T (ΔF) shown in FIG. 1 (a)
Assuming that the transfer function corresponds to F, when the transfer function T (ΔF + Δf ₁ ) (FIG. 1 (b)) in the defocus amount ΔF + ΔFf _{1 which} has the relationship of the opposite phase is added,
A transfer function with a reduced amplitude of T (ΔF) + T (ΔF + Δf ₁ ) shown in FIG. 1 (c) is obtained. At this time, since a phase difference contrast has a problem in a large periodic structure of several Å or more, a transfer function that reduces the amplitude of the periodic structure to about 20% or less is used. Further, since it is not possible to attenuate all the amplitudes by adding only one transfer function, a plurality of transfer functions that respectively attenuate the amplitudes in each cycle are used.

The defocus amount corresponding to each transfer function as described above is (ΔF +
It can be written as Δf ₁ ), (ΔF + Δf ₂ ), (ΔF + Δf ₃ ) .... The focus fluctuations of Δf ₁ , Δf ₂ , Δf ₃ ... Are obtained by superimposing a minute fluctuation of the exciting current in an amount proportional thereto as a pulse on the exciting current giving ΔF.

Example of Invention

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3. When a pulse that gives a slight variation Δf of the focal length as shown in FIG. 2 is superimposed on the objective lens exciting current, which is the focus condition of the defocus amount ΔF, the transfer function of the objective lens is the transfer function when the pulse is not superimposed. Expression (2) can be written for expression (1). For example, ΔF = 0Å, Δf ₁ = 1000
Å, Δf ₂ = 2500Å, Δf ₃ = −500Å, Δf ₄
== − 2000Å, as shown in Fig. 3, (1)
The transfer function (a) with respect to the equation changes as shown in (b), and the peak, that is, the phase difference contrast that appears for a specific frequency decreases over all frequencies. The degree of disappearance of the phase difference contrast with respect to the minute fluctuation of the exciting current can be made more effective by appropriately selecting the defocus amount ΔF and the waveform of the pulse to be superimposed.

λ: Wavelength of electron beam C _s : Spherical aberration coefficient α: Scattering angle of electron beam [Effect of the Invention] According to the present invention, when high-resolution observation is performed by a transmission electron microscope, non-interference or partial It can be observed as an image that is an interference, by appropriately reducing the phase difference contrast, which has been a major obstacle in determining the fine structure of metal particles on an amorphous support film, according to the purpose.
The fine structure can be analyzed accurately. Further, according to the present invention, the device can be configured relatively easily and at a low cost simply by adding an electric circuit for superimposing a pulsed modulation current to the conventional electron microscope.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining how to reduce the amplitude by adding transfer functions having different defocus amounts, FIG. 2 is a pulse waveform diagram which gives a slight fluctuation to the objective lens exciting current, and FIG. 3 is FIG. 4 is a diagram showing a transfer function of an objective lens.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-139458 (JP, A) Adachi, Ishihara, Ono, Tanabe, Shimoto Co-authored "Basics of Using Electron Microscope" Kyoritsu Publishing (Sho 51-8-1) ), P. 347-352

Claims (1)

[Claims] 1. When observing a transmission electron microscope image of a sample by using a transmission electron microscope using a magnetic field type objective lens, a pulse having a portion where the defocus amount linearly changes in the exciting current of the lens. A method for observing a high-resolution non-interferometric image, which comprises superimposing a modulation current so as to give a change in the amount of defocus, and reducing the phase contrast in the obtained transmission electron microscope image.