A novel atom probe is described which can determine the mass‐to‐charge ratios of all ion species produced during a single desorption event or of individual species at several preselected crystallographic locations during each desorption event. This is accomplished without tip movement in an instrument no larger than a conventional field ion microscope by using a new channel plate photomultiplier detector. Alignment, aiming, and pulse stability problems common to all previous designs have been eliminated. Although the present mass resolution is 4 amu at m/n = 184/3, single isotope resolution, if desired, seems possible.
REFERENCES
1.
E. W. Müller and J. A. Panitz, 14th Field Emission Symposium, Washington, D.C., 1967.
2.
E. W.
Müller
, J. A.
Panitz
, and S. B.
McLane
, Rev. Sci. Instrum.
39
, 83
(1968
).3.
4.
5.
6.
7.
As in all other atom probe designs, field evaporation will continue for the duration of the applied pulse unless its nominal amplitude is carefully adjusted so that a field evaporated end‐form is reached early in the pulse. The effect of continual evaporation during the applied pulse is to broaden the detected ion peaks and thereby limit resolution unless the evaporation event is terminated in a time shorter than the separation in time of the adjacent species one wishes to resolve. One therefore has two options. Either gently field evaporate to reach an end‐form quickly or adjust the pulse duration to be smaller than the required time resolution.
8.
In previous instruments the ion kinetic energy was determined by a dc bias and the amplitude of the evaporation pulse. Their sum had to be increased as the tip radius increased (to maintain a constant evaporation field), requiring constant recalculation to obtain each value. Since each recalculation required another accurate measurement of ion travel time for each species, data reduction time soon became excessive.
9.
Electro‐Optical Instruments, Inc., Pasadena, Calif., model CU60/A.
10.
J. A.
Panitz
, S. B.
McLane
, and E. W.
Müller
, Rev. Sci. Instrum.
40
, 1321
(1969
).11.
12.
CPS, Inc., Sunnyvale, Calif., model 100R.
13.
A product of the Bendix Corp., Electro‐Optical Division, Sturbridge, Mass.
14.
15.
The advantages of using stacked channel plates as a detector in a conventional atom probe were mentioned previously by
E. W.
Müller
, S. V.
Krishnaswamy
, and S. B.
McLane
, Rev. Sci. Instrum.
44
, 84
(1973
).16.
Bendix Corp., Electro‐Optical Division, Sturbridge, Mass., Chevron CEMA array. Dark current count rate less than at gains greater than
17.
The ratio of tip to shield potential is restricted by the simple electrode configuration described when atom‐by‐atom probing is being conducted. For the present instrument, if severe image distortion results and single atomic sites are no longer distinguishable.
18.
In practice, the shield potential during imaging is made as close as possible to This permits the extent of the image shift by the subsequent evaporation pulse to be seen. The detector is positioned over the shifted image spot, the shield potential reduced to and the desorption pulse, applied.
19.
20.
A desorption field‐ion microscope using a single channel plate and an image intensifier was recently described by
R. J.
Walko
and E. W.
Muller
, Phys. Status Solidi A
9
, K9
(1972
).21.
J. A. Panitz, Ph.D. thesis, The Pennsylvania State University, 1969.
22.
This number may be too large since the occurrence of possible spurious “after pulses” produced by ion feedback in the multiplier array has been neglected. This problem was recently considered in detail by
S. S.
Brenner
and J. T.
McKinney
, Rev. Sci. Instrum.
43
, 1264
(1972
).
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© 1973 The American Institute of Physics.
1973
The American Institute of Physics
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