超高分解能用ポールピース

ultra-high-resolution polepiece

[目次：レンズ系]

ホルダの傾斜角を±(20°～25°)に抑えた高分解能用のポールピースでは加速電圧200kVに対してCs=0.5mm、Cc=1.0mmが得られており、電顕像の空間分解能は0.19nmである。高空間分解能像観察用はじめnmオーダーの微小領域の分析用に使われている。このポールピースでは対物絞りは、ホルダの傾斜角を制限しないように、下極の下に入れる。その場合、回折図形が絞りより上方にできる。そのために、絞りで一つの回折斑点だけを選ぶことが困難になり、正しい明視野、暗視野像が得られない場合がある。一つの回折斑点を選んで正しい明視野、暗視野を得る場合にはギャップ内に特別な絞りを挿入する。

The "ultra-high-resolution polepiece" makes it possible to obtain a Cs of 0.5 mm, a Cc of 1.0 mm and a spatial resolution for a TEM image of 0.19 nm at an accelerating voltage of 200 kV, in which the tilt angle of a specimen holder is limited to ±(20°to 25°). It is used for high spatial resolution microscopy and for analytical microscopy from nm diameter areas. This polepiece gives rise to a drawback which cannot be overlooked. That is, the correct bright and dark field images cannot be often obtained. The reason is as follows: The objective aperture is normally inserted into the lower part of the polepiece to prevent the objective aperture from contacting the specimen holder when it is tilted. In this case, the diffraction pattern is formed above the aperture plane. As a result, the aperture cannot often select one diffraction spot but takes influence of neighbor spots. Thus, the bright and dark field images are influenced by the effect of other diffraction. It is noted that there is option to insert a special aperture at the polepiece gap to obtain correct bright- and dark-field images.

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