Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
1998-11-23
2001-08-28
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
C250S307000, C073S105000
Reexamination Certificate
active
06281495
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to scanning probe microscopy (SPM) techniques using a noncontact atomic force microscope (AFM) which receives forces from a sample and produces a topographic image of the surface of the sample and which is also capable of detecting magnetic forces from the sample by magnetic force microscopy (MFM) utilizing the functions of the noncontact AFM.
DESCRIPTION OF THE PRIOR ART
Scanning probe microscopy has been heretofore developed which images the topography of the surface of a sample by the function of noncontact AFM by measuring a physical force produced between a tip and the sample and which can also detect the magnetic force from the sample by the functions of MFM. In this conventional SPM, the magnetic force is a long-range force and so the magnetic force is separated from the atomic force by moving the tip or cantilever away from the sample into a position where the atomic force no longer affects the tip or cantilever; in the topography mode, the atomic force dominates. This method of detection is generally known as lift mode operation. The tip is lifted for every point, every line, or every frame of image on the scanned sample surface. Thus, a topographic image and an atomic force image are both obtained.
In this lift mode operation, the topographic image and atomic force image seem to be separated completely. In practice, however, the spatial resolution is deteriorated because the distance between the sample and the tip is increased. Consequently, only large force variations, i.e., magnetic force variations, are imaged. Therefore, it seems as if the magnetic force image were completely separated from the topographic image. Accordingly, in this lift mode operation, it is difficult to improve the resolution of the magnetic force image further.
SUMMARY OF THE INVENTION
In view of the foregoing circumstances, the present invention has been made.
It is an object of the present invention to provide a scanning probe microscope (SPM) capable of providing a magnetic force image of a sample with improved resolution easily and reliably.
One embodiment of the present invention starts with obtaining a first kind of topographic data of a sample from the resonance frequency of a cantilever in noncontact mode by FM detection. This first kind of topographic data undergoes magnetic effects. A second kind of topographic data of the sample free of magnetic effects is derived from the amplitude of the cantilever by slope detection. The difference between these two kinds of topographic data is produced, thus giving rise to data about a magnetic force image.
Another embodiment of the invention starts with obtaining a first kind of topographic data of a sample from the resonance frequency of a cantilever in noncontact mode by FM detection. The topographic data undergoes magnetic effects. A second kind of topographic data of the sample free of magnetic effects is derived from the resonance frequency of the cantilever in contact mode by FM detection. The difference between these two kinds of topographic data is produced, thus giving rise to data about a magnetic force image.
A further embodiment of the invention provides a scanning probe microscope that images the surface of a sample by FM detection and images the surface by slope detection or contact-mode operation. In particular, an error amplifier produces a first output when the difference between the output from a frequency-to-voltage converter and a first reference voltage applied to the error amplifier is kept constant. A topographic image of the sample is obtained from the first output by FM detection. This topographic image undergoes magnetic effects of the sample. The error amplifier produces a second output when the difference between the output from an amplitude-to-voltage converter and a second reference voltage applied to the error amplifier is kept constant. Another topographic image is obtained from the second output by slope detection or contact-mode operation. This topographic image undergoes no magnetic effects of the sample. An arithmetic means calculates the difference between these two topographic images. As a result, the difference reflects only the magnetic effects. Hence, a high-resolution magnetic force image of the sample is derived from this difference.
Still other embodiments of the invention provide a scanning probe microscope that images the surface of a sample only by FM detection. Where the surface of the sample is imaged while a tip is not in contact with the sample, an error amplifier produces a first reference voltage when the difference between the output from a frequency-to-voltage converter and a first reference voltage applied to the error amplifier is kept constant. A topographic image of the sample surface is obtained from the first output from the error amplifier. This topographic image undergoes magnetic effects from the sample. Where the sample surface is imaged when the tip is closest to and contacts the sample, the error amplifier produces a second output provided that the difference between the output from the frequency-to-voltage converter and a second reference voltage applied to the error amplifier is kept constant. A topographic image of the sample surface is derived from the second output from the error amplifier. This topographic image undergoes no magnetic effects of the sample. In the same way as the embodiment described first, the difference between these two images is calculated. Consequently, a high-resolution magnetic force image of the sample can be obtained.
In one embodiment of the invention, plural reference voltages are established. In consequence, magnetic force images can be produced with higher resolution.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
REFERENCES:
patent: 5308974 (1994-05-01), Elings et al.
patent: 5519212 (1996-05-01), Elings et al.
“Separation of magnetic and topographic effects in force microscopy”,J. Appl. Phys., vol. 67. No. 12, Jun. 15, 1990, pp. 7278-7280.
Jeol Ltd.
Nguyen Kiet T.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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