Electron microscopy in the 1980s

by Tim Palucka

During the 1980s TEM resolutions were further reduced to 1.0 to 1.5Å, making imaging of atoms in lattice planes possible. SEM resolutions went from 3 nm (30Å) at the beginning of the decade to 1.5 nm (15Å) at the end. Microprocessor control of microscopes and computerized analysis of data became common due to the emergence of the personal computer in the early 80s. This microprocessor control brought about such features as an auto-stigmator and auto-focus, freeing the microscope operator from the mundane tasks that had always been involved in using the instrument. Electron energy loss spectroscopy (EELS) detectors were incorporated in STEMs and AEMs, allowing detection of low atomic number elements that could not be seen using x-ray techniques. Micron markers began to be placed automatically on micrographs, making determination of feature size easier. Specialty instruments continued to appear, with high resolution instruments specifically designed for clinical pathologists and other life science workers being offered next to models designed specifically for the physical sciences. The demands of the fast-growing integrated circuits industry produced electron microscopes designed for non-destructive testing of semiconductor wafers and for functional testing of ICs. Smaller electron beam sizes made it possible to switch from microprobe to nanoprobe technology. Elemental mapping of a sample's surface could now be done on a nanometer level.

In 1988 a company called Electroscan produced the first commercial environmental scanning electron microscope (ESEM) to allow researchers to work with samples in a more natural environment. Innovations included a new secondary-electron detector that could obtain topographical images in the presence of water vapor; for the first time it was possible to examine wet samples without dehydration of the sample. This enabled studies of biological samples closer to their natural state. Pressure-limiting apertures placed in the path of the electron beam effectively separated vacuum regions around the gun and lenses from pressurized chambers containing the sample. Observations could now also be made at elevated and low temperatures, and in atmospheres containing gases, eliminating the high vacuum requirements of previous microscopes.

TEMs

Low-cost, easy-to-use TEMs

Development of low cost instruments was not a priority in the 1980s. Some that were developed in the 1970s continued to be sold, but development was focused on high-performance, high-resolution, microprocessor-controlled instruments.

High resolution, high-performance TEMs and AEMs

JEOL produced 7 new TEM units between 1980 and 1986. These included the JEM-1200 EX (1981), which added microprocessor control to the JEM-100 CX (1976). The same model equipped with an EDS x-ray spectrometer was called the JEM-1200 EX/Analytical microscope. The 1984 model JEM-2000 FX/Analytical had a maximum voltage of 200 kV and a resolution of 2.8 Å; this instrument marked the switch from a microprobe beam to a nanoprobe. The JEM–4000 FX/Analytical microscope introduced in 1986 raised the acceleration voltage to 400 kV, which produced a beam probe size only 2 nm in diameter. After years of a standard 100 kV accelerating voltage with a few ultrahigh voltage units thrown in, these medium-voltage microscopes finally became popular.

Philips led the way in specialized-market microscopes with the introduction in 1982 of three TEMs designed for:

1. the life sciences (100 kV)
2. applied research (20 to 120 kV)
3. fundamental research (300 kV).

They followed this with three more TEMs released in 1985 featuring the “microprocessor-based MICROCONTROLLER system”:

1. the CM 10 (40 to 100 kV)
2. the CM 12 (20 to 120 kV)
3. the CM 12 STEM (the scanning version of CM 12).

Hitachi's 1983 model H-600FE TEM/STEM  had a field emission gun and an EELS detector. The resolution was 1.4Å in TEM mode, and 10Å in STEM mode.

SEMs

High-performance SEMs

JEOL developed 12 new SEMs between 1980 and 1986. Of particular interest are the four units produced for the IC industry in 1982 and 1983:

• the JSM-35CFS
• JSM-840
• JSM-IC845
• JSM-IC848.

The JSM-IC 845 had a sample stage capable of holding 6 inch semiconductor wafers, while the JSM-IC848 cold handle 9 inch wafers. This is a clear case of the instrument manufacturer responding to the changing needs of his customer. The JSM-T220 and JSM-T330, both launched in 1986, featured the auto-stigmator and auto-focus functions.

Philips introduced a new doped-yttrium silicate scintillator for the detection of backscattered electrons in its 1980 model SEM 505; this new detector was 200 times more sensitive to backscattered electrons than previous scintillators. The 1984 model SEM 515 improved on the 505 by adding computer-controlled automatic focussing and astigmation correction. Continuing with the IC industry specialization theme, the SEM 525 IC (1985) was designed for the non-destructive testing of semiconductor wafers, and the SEM 525 EB (1985) was created for functional testing of ICs.

Ultrahigh Voltage EMs

Hitachi returned one more time to the Ultrahigh Voltage EM market with the H-1300S (1982), a 1300 kV microscope based on ion radiation. In 1983, JEOL produced a one-of-a-kind Ultrahigh Voltage EM for the Lawrence Berkeley Laboratories in California, where scientists were interested in atomic resolution. This instrument, the JEM-ARM-1000 had an acceleration voltage of 400 to 1,000 kV.

• Electron microscopy in the 1960s
• Electron microscopy in the 1970s
• Electron microscopy in the 1980s
• Electron microscopy in the 1990s