Alton D. Romig

Electron Energy Loss Spectrometry

The aim of this laboratory session is to demonstrate the use of a magnetic prism electron spectrometer to perform electron energy loss spectrometry (EELS). The main characteristics of the energy loss spectrum will be discussed as well as the effect of instrumental and specimen parameters on the spectrum. Quantitative elemental analysis will be demonstrated and if time permits an example of EELS imaging will be shown. More details can be found in PAEM, Chapters 7 and 8.

Electron Channeling Contrast

The objective is to acquaint the microscopist with the crystallographic and contrast effects of electron channeling. The initial emphasis is on channeling experiments which can be performed on any conventional scanning electron microscope: large area channeling patterns of single crystals and channeling contrast images to reveal the crystalline microstructure of polycrystalline materials. The optional advanced experiments on covering area electron channeling patterns can only be carried out on an SEM which is equipped with special scanning and/or electron optical modifications. More detail on this topic may be found in ASEMXM, Chapter 3.

Bulk Specimens for SEM and X-Ray Microanalysis

The purpose of this laboratory is to prepare samples of metallic, ceramic, polymeric, and biological specimens for examination and analysis in the SEM. The organization is such that under each type of material sample preparations are discussed for surface topography (e.g., fracture surface), microstructural analysis (e.g., phase morphology), and x-ray microanalysis. Special procedures for semiconductor devices, polymers, and biological samples are also considered. The objective is to provide a brief outline and enough general references to enable the reader to produce all of the specimens used in this workbook. The outlined methods should not be considered comprehensive, however, and the reader is strongly urged to consult the references listed. For further discussion, see SEMXM, Chapters 9–12.

Backscattered Electron Imaging

Experiment 8.1: E-T Detector Collection Efficiency. The solid angle and efficiency of a specific E-T detector for direct collection of BSEs is: (a) Area, A, of scintillator (cm2) = 1.5 cm2. (b) Distance, r, from specimen to scintillator (cm) = 4 cm. (c) Solid angle, Ω = A/r2 = 1.5/16 = 0.094 steradians. (e) For a specimen set normal to the beam (0° tilt), approximate take-off angle = 45°.

Electron Beam Parameters

This laboratory demonstrates: (1) election gun saturation and alignment; (2) the measurement of beam current, beam size, and beam convergence; (3) the concept of electron gun brightness; and (4) the effects of these parameters on depth-of-field and resolution. More details and references can be found in SEMXM, Chapter 2.

Voltage Contrast and EBIC

The purpose of this laboratory is to understand voltage contrast (VC) and electron beam induced contrast (EBIC) as important tools for the examination of semiconductor materials which aid in the production of microcircuit devices. More details may be found in ASEMXM, Chapter 2.

Energy-Dispersive X-Ray Microanalysis

The modern energy-dispersive x-ray spectrometer (EDS) coupled with a computer-based multichannel analyzer (MCA) provides a powerful analytical facility in the SEM lab. The purpose of this laboratory is to introduce the student to the wide range of analytical capabilities of the EDS/MCA system and to illustrate the basic appearance and characteristics of electron-excited x-ray spectra. Procedures for both qualitative and quantitative analysis will be examined. More detail on these subjects can be found in SEMXM, Chapters 6, 7, and 8.

Scanning Transmission Imaging in the AEM

The aim of this laboratory session is to introduce the scanning transmission electron microscope (STEM), used in this and other analytical electron microscopy (AEM) laboratory sessions, and to demonstrate the various imaging modes available. The experimental control that the operator has over the information in the image will be emphasized. More details may be obtained in PAEM, Chapter 3 and D. B. Williams, Practical Analytical Electron Microscopy in Materials Science, Philips Electron Optics, Mahwah, New Jersey, 1984.

SE Signal Components

The SE signal collection efficiency of the conventional E-T detector is limited by the asymmetry of the collection field resulting from the detector position and from the surface potential of rough specimens. Specimen biasing should be routinely applied to optimize signal collection for a given specimen and imaging situation. The voltage supply must be of extreme stability which can be provided by dry batteries such as 45-V farm batteries. Two batteries connected in series provide for an easy change of polarity. There is no rule to predict the effect of specimen biasing on signal collection. The bias modifies only the accelerating voltage of the probe and the collection field of the collector. Thus, SE components will still be collected. (Note: Only a grounded specimen grid which shields the specimen from all other biased surfaces allows establishment of a positive field between the grid and the specimen for the absorption of SE-I+II as described in experiments of Section 12.3.)