Ultrahigh Voltage TEMs
- Practical Electron Microscopy and Database -
- An Online Book -

http://www.globalsino.com/EM/  



 

This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.

 

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High voltage TEMs (transmission electron microscopy) have several advantages. The most important advantages are: i) The observation of internal structures in thick specimens and ii) The high spatial resolution.

Before creation and applications of aberration corrections, a method to improve the capability of electron microscopes (EMs) is to increase the accelerating voltage of the electron gun to ultrahigh voltages in order to penetrate more deeply into thicker samples as listed in Table 4175. These ultrahigh-voltage EMs were so large that they typically occupied two-story building. The electron guns and their associated high voltage electronics were located near the ceilings of the second stories, while the operators sat at the bottom of the microscope column observing the images through the fluorescent screens. Figure 4175a shows the 1 MeV Atomic Resolution Microscope (ARM) at the Lawrence Berkeley Laboratory.

Table 4175. Ultrahigh voltage TEMs without aberration corrections.

Year
Spatial Resolution (Å)
Spatial Frequency (Å-1)
Model
Voltage
Location
Reference
1964
Hitachi HU-500
500 kV
1965
CEMES-LOE/CNRS
3 MeV
Toulouse, France
1966
JEOL JEM-1000
1 MeV
1968
HU-650
650 kV
1969
HU-1000
1 MeV
1970
HU-3000
3 MeV
1976
H-1250
1.25 MeV
1976
2.50
0.40
Horiuchi
1 MeV
[1]
1979
2.00
0.50
Cambridge
500 keV
[2]
1984
1.60
0.63
JEOL ARM-
1000
1 MeV
[3]
1985
1.70
0.59
4000EX
400 keV
[2]
1991
1.10
0.91
Hitachi H-
1500
1.3 MeV
[4]
1994
1.08
0.93
Ichinose
1250 keV
[5]
1996
1.05
0.95
Stuttgart
1.25MeV
[6]
1999
0.98
1.02
Ichinose
1.25MeV
[7]

The 1 MeV Atomic Resolution Microscope (ARM) at the Lawrence Berkeley Laboratory

Figure 4175a. The 1 MeV Atomic Resolution Microscope (ARM) at the Lawrence Berkeley Laboratory [8].

Figure 4175b shows the dependence of the appearance of electron diffraction and Kikuchi patterns on the TEM sample thickness and the accelerating voltages of the incident electron beam for molybdenite crystals. Diffraction patterns can be observed in the region below Curve A, while Kikuchi patterns can be observed between Curves A and B. Both diffraction and Kikuchi patterns can be simultaneously observed in the region slightly below and above Curve A. In general, the Curve B gives the maximum thickness for which dislocations can be observable.

The dependence of appearance of diffraction and Kikuchi patterns on the TEM sample thickness and the accelerating voltages of the incident electron beam

Figure 4175b. The dependence of the appearance of diffraction and Kikuchi patterns on the TEM sample thickness and the accelerating voltages of the incident electron beam for molybdenite crystals. Adapted from [9]

Manufacturers have attempted to use van de Graaff generators to supply high voltages to TEM systems, but the favorite voltage source is still Cockcroft–Walton voltage generator. Such voltage generators may be either air-insulated or confined in a tank filled with an insulating gas (e.g. freon, nitrogen, SF6) under pressure. For such systems, a large room or even a separate building is required to provide enough clearance against spark-over. Note that some systems have both generator and accelerator in a common tank; others use two separate tanks to minimize electrical interaction and make the service more convenient.

 

 

 

 


 

 

 

[1] R.M. Fisher, T. Imura, Ultramicroscopy 3 (1978) 3.
[2] D.J. Smith, Rep. Prog. Phys. 60 (1997) 1513.
[3] K.H. Downing, Hu. Meisheng, H.-R. Wenk, M.A. O’Keefe, Nature, 348 (1990) 525.
[4] S. Horiuchi, Y. Matsui, Y. Kitami, M. Yokoyama, S. Suehara, X.J. Wu, I. Matsui, T. Katsuta, Ultramicroscopy 39 (1991) 231.
[5] H. Ichinose, International Workshop on HVEM & HREM, Stuttgart, 1994.
[6] F. Phillipp, Adv. Solid State Phys. 35 (1996) 257.
[7] H. Ichinose, H. Sawada, E. Takuma, M. Osaki, J. Electron Microsc. 48 (1999) 887.
[8] www.caltech.edu
[9] Uyeda, Ryozi; Nonoyama, Minoru, The Observation of Thick Specimens by High Voltage Electron Microscopy. Experiment with Molybdenite Films at 50-500 kV, Japanese Journal of Applied Physics, 6(5), pp. 557 (1967).

 

 

 

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