Scanning auger electron microscopy pdf

In Auger electron spectroscopy AES , we bombard a sample surface with a focused beam of high-energy 2- to kV electrons. The incident electrons lose energy to the sample atoms, generating Auger electrons that have discrete kinetic energies characteristic of the emitting atoms. This technique is particularly useful for determining the elemental composition of the surface because Auger electrons have a limited escape depth.

A key capability of the field emission Auger electron spectroscopy FE-AES is its ability to focus the electron beam to a small spot, with resolutions similar to an electron microscope. An Auger electron microscope is equipped with a field-emission tip maintained at an essentially constant distance above the surface of the specimen.

Auger electrons emitted from the surface of the specimen are collected by an electron energy analyzer for conventional processing.

Mutual scanning displacement between the tip and specimen is obtained through use of an xyz-drive module, which is also responsible for adjusting the working distance of the tip.

The entire microscope setup is mounted on vibration damping means and may be inserted into a vacuum system by means of an appropriate flange, if desired. Field of the Invention. This invention relates to scanning Auger electron microscopes that are useful for spatially resolved investigation of elemental distributions, viz. When a focused electron beam impinges on a specimen surface, a number of interactions with the atoms on or below the surface can occur.

More specifically, if the incident electrons have enough energy, they ionize atoms by dislodging an inner shell electron. The atom spontaneously returns to its ground state by transferring an outer shell electron into the vacancy created in the inner shell.

Since the electrons are at discrete energy levels, the emitted Auger electrons will also have a discrete energy equal to the energy difference between the initial and final states of the atoms. The energy level of the emitted Auger electrons is characteristic of the emitting element. Therefore, the Auger electron microscope is well suited to investigate the chemical composition of the material of the specimen, at least at its surface. Since the electron beam impinging on the specimen under investigation is narrowly focused, as is the detector, the information provided is always related to the composition at the focal point.

In order to obtain composition information over a larger area, the electron beam and detector are raster-scanned across the area of interest and information is recorded for each point in the scan in accordance with the chosen resolution. Scanning Auger electron microscopes are well known and commercially available. Usually, Auger microscopes employ an electron gun to generate the electron beam to be directed at the specimen, with the smallest beam diameter being about 35 nm.

The resolution of the Auger analysis, however, is determined by the volume from which the electrons are emitted. The depth resolution normal to the surface of the specimen is determined by the effective escape depth which, in turn, is a function of the electron mean free path and of the takeoff angle.

Because of the relatively low kinetic energy of the electrons, the depth resolution is only a few monolayers. If the spatial resolution were to be improved much further, the elemental resolution would be substantially degraded due to a degradation of the signal-to-noise ratio which is a function of the primary beam current, typically below 1 nA for such resolution.

Auger microscopes employing electron guns are described by L. Goldstein and H. Auger microscopes are also known in which the filament in the electron gun is replaced by a field-emission electron source. Representative of the prior art in this area are D. Tuggle, L. Swanson and J. Todokoro, Y. Sakitani, S. Fuku- hara and Y.

Electron Microsc. Japan , Vol. The Auger microscope of the Tuggle et al. The working distance of the field emission source from the specimen is about 13 cm. In the Todokoro et al. Browning, P. Bassett, M. El Gomati and M. El Gomati, M. Prutton and R. The Browning et al. High voltages and working distances above 5 cm are characteristic of the prior art Auger microscopes.

Besides the danger usually involved with high voltage, these microscopes have the disadvantage of possibly causing damage on the specimens due to the high current densities at which they must be operated. Also, finefocus i. Another disadvantage of the prior art Auger microscopes is their size, in particular the size of the vacuum system which needs to be pumped down to, and maintained at, about 10 -8 Pa.

The microscope of the invention may be distinguished over the prior art in that the field-emission source consists of a sharply pointed tip having a tip radius of about 50 nm and being maintained at an essentially constant distance on the order of about 1 mm from the surface of the specimen, and in that an electrical potential exists between said tip and said specimen.

Details of an embodiment of this invention will hereafter be explained by way of example with reference to the attached drawings, in which:. Flange 1 carries a support 2 on which a frame 3 is suspended. The suspension is, for simplicity of the drawing, shown as springs 4 and 5 but may consist of a more elaborate vibration absorber. Arranged on frame 3 is an xyz drive module 6, for example one of the conventional type employing piezoelectric elements.

The specimen 7 to be investigated is supported on the top of drive module 6. Authors Authors and affiliations Richard P. Gunawardane Christopher R. This process is experimental and the keywords may be updated as the learning algorithm improves. This is a preview of subscription content, log in to check access.

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