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Focused Electron Source using Novel Magnetic Microlens

IP.com Disclosure Number: IPCOM000110404D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 97K

Publishing Venue

IBM

Related People

Rugar, D: AUTHOR [+2]

Abstract

Disclosed is a very simple design for a focused electron beam source. The design uses a novel type of lens, a magnetic microlens (1,2,3). The magnetic microlens consists of a field emission type located in close proximity to the surface of a permanent magnet, thus achieving a low-aberration focused beam.

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Focused Electron Source using Novel Magnetic Microlens

       Disclosed is a very simple design for a focused electron
beam source.  The design uses a novel type of lens, a magnetic
microlens (1,2,3).  The magnetic microlens consists of a field
emission type located in close proximity to the surface of a
permanent magnet, thus achieving a low-aberration focused beam.

      One implementation of the magnetic microlens is shown in the
figure.  The microlens consist of a field-emission tip mounted
between the poles of two permanent magnets preferably made of a hard
magnetic material such as NdFeB or CoSm, separated by a gap short
enough, relative to the areas of the magnetic poles, that a
substantially uniform magnetic field is produced.  The magnets are
mounted on an iron loop for magnetic flux closure, and the entire
assembly is on linear motion vacuum feedthrough.   By moving the
magnets with respect to the tip, the field could be turned for
focusing.  It is possible to tilt the magnetic axis to align it with
the tip axis as well as translate the magnets perpendicular to the
tip to adjust the field strength.  To produce images, the sample is
scanned by a piezolectric tube scanner, and the current in the sample
as well as the transmitted current are recorded.  The sample may be
moved in two directions, x and z, by means of suitable mechanical
means such as inch-worm motors.  The entire apparatus is preferably
operated in vacuum.

      This design, in which the magnetic polegap is 1 inch, the
magnetic field is 3000 gauss and a 10-9 torr vacuum is produced, has
achieved a focused spot size as small as 150 nm.  Short focusing
distances with small aberrations can be provided.  The low aberration
permits a high beam current to be focused on a small spot.  For a
tip-sample distance of 1 mm, this aberration-limited focused spot
size corresponds to an emission angle of 5o.  Further improvement in
the resolution of the microlens can be obt...