Smoothly Varying Injected Neutral Beam Voltage and Current Provides New Capability on the DIII-D Tokamak

J. T. Scoville; B. J. Crowley; D. C. Pace; J. M. Rauch

doi:10.1109/tps.2017.2784765

SEM at Low Beam Voltage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100112245 ◽

1984 ◽

Vol 42 ◽

pp. 440-443

Author(s):

James Pawley

Keyword(s):

Low Voltage ◽

Probe Diameter ◽

Small Probe ◽

Beam Voltage ◽

Practical Constraints

Operation of the SEM with V0 = l-3kV (LVSEM) was early recognized to reduce charging artefacts and increase topographic contrast. This early promise was not pursued because several theoretical and practical considerations made it difficult to produce a small probe diameter (d0) at low voltage. Recently, the necessity of using low V0 to image uncoated semiconductors without damaging them has prompted a re-evaluation of LVSEM. This re-evaluation has taken the form of efforts to eliminate the practical constraints and to alleviate the theoretical ones. In the process, some heretofore neglected theoretical advantages of LVSEM have emerged. These problems and possibilities will now be discussed in more detail.

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LVSEM: Past Present and Future

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180574 ◽

1990 ◽

Vol 48 (1) ◽

pp. 364-365

Author(s):

James B. Pawley

Keyword(s):

Field Emission ◽

Line Width ◽

Time Scales ◽

Silicon Oxide ◽

Beam Current ◽

High Brightness ◽

High Beam ◽

Fixed Charges ◽

Beam Voltage ◽

Deposited Metal

Past: In 1960 Thornley published the first description of SEM studies carried out at low beam voltage (LVSEM, 1-5 kV). The aim was to reduce charging on insulators but increased contrast and difficulties with low beam current and frozen biological specimens were also noted. These disadvantages prevented widespread use of LVSEM except by a few enthusiasts such as Boyde. An exception was its use in connection with studies in which biological specimens were dissected in the SEM as this process destroyed the conducting films and produced charging unless LVSEM was used.In the 1980’s field emission (FE) SEM’s came into more common use. The high brightness and smaller energy spread characteristic of the FE-SEM’s greatly reduced the practical resolution penalty associated with LVSEM and the number of investigators taking advantage of the technique rapidly expanded; led by those studying semiconductors. In semiconductor research, the SEM is used to measure the line-width of the deposited metal conductors and of the features of the photo-resist used to form them. In addition, the SEM is used to measure the surface potentials of operating circuits with sub-micrometer resolution and on pico-second time scales. Because high beam voltages destroy semiconductors by injecting fixed charges into silicon oxide insulators, these studies must be performed using LVSEM where the beam does not penetrate so far.

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Design of a Spectroscopic Low-Energy Emission Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180549 ◽

1990 ◽

Vol 48 (1) ◽

pp. 358-359

Author(s):

Lee H. Veneklasen

Keyword(s):

Parallel Imaging ◽

Objective Lens ◽

Energy Window ◽

Flat Surfaces ◽

Beam Voltage ◽

New Instrument ◽

Real Time Image ◽

Image Planes ◽

Backscatter Diffraction ◽

Time Image

This paper discusses some of the unique aspects of a spectroscopic emission microscope now being tested in Clausthal. The instrument is designed for the direct parallel imaging of both elastic and inelastic electrons from flat surfaces. Elastic contrast modes of the familiar LEEM include large and small angle LEED, mirror microscopy, backscatter diffraction contrast (for imaging of surface structure), and phase contrast (for imaging of step dynamics)(1). Inelastic modes include topology sensitive secondary, and work function sensitive photoemission. Most important, the new instrument will also allow analytical imaging using characteristic Auger or soft X-ray emissions. The basic instrument has been described by Bauer and Telieps (2). This configuration has been redesigned to include an airlock, and a LaB6 gun, triple condensor lens, magnetic objective lens, a double focussing separator field, an imaging energy analyzer, and a real time image processor.Fig. 1 shows the new configuration. The basic beam voltage supply Vo = 20 KV, upon which separate supplies for the gun Vg, specimen Vs, lens electrode Vf, and analyzer bias Vb float. The incident energy at the sample can be varied from Vs = 0-1 KV for elastic imaging, or from Vg + Vs = (3 + Vs) KV for inelastic imaging. The image energy window Vs±V/2 may be varied without readjusting either the illumation, or imaging/analyzer optics. The diagram shows conjugate diffraction and image planes. The apertures defining incoming Humiliation and outgoing image angles are placed below the separator magnet to allow for their independent optimization. The instrument can illuminate and image 0.5-100 μm fields at 0-1 keV emission energies with an energy window down to 0.2 eV.

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