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Claims  |
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What is claimed is:
1. An apparatus for measuring a magnetic field in a sample using a scanning
tunneling microscope having a tip comprising:
drive means for controlling the distance between the tip and a surface of
the sample and a position of the tip for enabling scanning of the surface
and for providing a signal indicative of the position of the tip relative
to the sample;
generator means coupled to said tip for providing a current signal at a
frequency substantially equal to the resonance frequency of said tip for
generating a current between said tip and the surface for causing the tip
to undergo vibratory motion in the presence of a magnetic field;
detector means disposed for measuring the motion of the tip in a direction
substantially parallel to the plane of the surface of the sample and
providing a signal indicative of such motion, and
computer means coupled to said detector means and said drive means for
providing an output signal indicative of a position of the tip and a
magnetic field magnitude corresponding to the position.
2. An apparatus as set forth in claim 1 further comprising output device
means coupled to said computer means for providing an image of the
magnetic field magnitude at corresponding positions of the tip.
3. An apparatus as set forth in claim 2, wherein said output device means
comprises a screen.
4. An apparatus as set forth in claim 2, wherein said output device means
comprises a plotter.
5. An apparatus as set forth in claim 1, wherein said drive means comprises
piezoelectric drive means for positioning the tip relative to the surface.
6. An apparatus as set forth in claim 5, wherein said piezoelectric drive
means positions the tip relative to a stationary surface.
7. An apparatus as set forth in claim 5, wherein said piezoelectric drive
means position the surface relative to a stationary tip.
8. An apparatus as set forth in claim 1, wherein said computer means
provides another output indicative of the topography of the surface of the
sample.
9. An apparatus as set forth in claim 1, wherein said detector means is an
optical heterodyned interferometer.
10. A method for measuring a magnetic field in a sample using a scanning
tunneling microscope having a tip comprising the steps of:
disposing the tip in close proximity to a surface of a sample and scanning
the surface;
providing to the tip a current signal at a frequency substantially equal to
the resonance frequency of the tip for generating a current between the
tip and the surface for causing the tip to undergo vibratory motion in the
presence of a magnetic field;
measuring the motion of the tip in a direction substantially parallel to
the plane of the surface of the sample and providing a signal indicative
of such motion, and
computing the position of the tip and a magnetic field magnitude
corresponding to the position.
11. A method as set forth in claim 10, further comprising the step of
displaying the position of the tip and the magnetic field magnitude
corresponding to the tip position.
12. A method as set forth in claim 10, further comprising the step of
simultaneously measuring the topography of the surface of the sample.
13. A method as set forth in claim 12, further comprising the step of
simultaneously displaying the topography of the surface of the sample.
14. A method as set forth in claim 10, wherein said measuring the motion is
optically measuring the motion.
15. An apparatus for measuring a magnetic field in a sample using a
scanning tunneling microscope having a tip comprising:
piezoelectric drive means for controlling the distance between the tip and
a surface of the sample and a position of the tip for enabling scanning of
the surface and providing a signal indicative of the position of the tip;
generator means for providing a current at a frequency substantially equal
to the resonance frequency of the tip for generating a current signal
between the tip and the surface of the sample for causing the tip to
undergo vibratory motion in the presence of a magnetic field;
optical heterodyned interferometric means disposed for measuring the motion
of the tip in a direction substantially parallel to the plane of the
surface of the sample and providing a signal indicative of such motion;
computer means coupled to said optical heterodyned interferometric means
and said piezoelectric drive means for providing an output signal
indicative of a position of the tip and a magnetic field magnitude
corresponding to the position, and
output device means for providing a display responsive to said output
signal.
16. An apparatus as set forth in claim 15 said computer means providing
another output signal indicative of the topography of the surface of the
sample.
17. An apparatus for measuring a magnetic field in a sample using a
scanning tunneling microscope having a tip comprising:
drive means for controlling the distance between the tip and a surface of
the sample and a position of the tip for enabling scanning of the surface
and for providing a signal indicative of the position of the tip relative
to the sample;
generator means coupled to the tip for providing a current signal at a
first predetermined frequency for generating a current between the tip and
the surface for causing the tip to undergo vibratory motion in the
presence of a magnetic field;
means coupled to said drive means for causing the tip to undergo vibratory
motion relative to the surface at a second predetermined frequency along
an axis substantially normal to the plane of the surface of the sample;
detector means disposed for measuring the motion of the tip in a direction
substantially parallel to the plane of the surface of the sample and
providing a signal indicative of such motion, and
computer means coupled to said detector means and said drive means for
providing an output signal indicative of a position of the tip and a
magnetic field magnitude corresponding to the position.
18. An apparatus as set forth in claim 17 further comprising output device
means coupled to said computer means for providing an image of the
magnetic field magnitude at corresponding positions of the tip.
19. An apparatus as set forth in claim 18, wherein said output device means
comprises a screen.
20. An apparatus as set forth in claim 18, wherein said output device means
comprises a plotter.
21. An apparatus as set forth in claim 17, wherein said drive means
comprises piezoelectric drive means for positioning the tip relative to
the surface.
22. An apparatus as set forth in claim 21, wherein said piezoelectric drive
means positions the tip relative to a stationary surface.
23. An apparatus as set forth in claim 21, wherein said piezoelectric drive
means position the surface relative to a stationary tip.
24. An apparatus as set forth in claim 17, wherein said detector means is
an optical heterodyned interferometer means.
25. An apparatus as set forth in claim 17, wherein said detector means
measures the motion of the tip at a sum frequency substantially equal to
the sum of said first predetermined frequency and said second
predetermined frequency and the sum frequency is substantially equal to
the resonance frequency of the tip.
26. An apparatus as set forth in claim 25 wherein said detector means is an
optical heterodyned interferometer means.
27. An apparatus as set forth in claim 17, wherein said detector means
measures the motion of the tip at a difference frequency substantially
equal to the difference of said first predetermined frequency and said
second predetermined frequency and the difference frequency is
substantially equal to the resonance frequency of the tip.
28. An apparatus as set forth in claim 27 wherein said detector means is an
optical heterodyned interferometer means.
29. An apparatus as set forth in claim 17, wherein said computer means
provides another output indicative of the topography of the surface of the
sample.
30. A method for measuring a magnetic field in a sample using a scanning
tunneling microscope having a tip comprising the steps of:
disposing the tip in close proximity to a surface of a sample and scanning
the surface;
providing to the tip a current signal at a first predetermined frequency
for generating a current between the tip and the surface for causing the
tip to undergo vibratory motion in the presence of a magnetic field;
simultaneously vibrating the tip at a second predetermined frequency along
an axis substantially normal to the plane of the surface of the sample;
measuring the motion of the tip in a direction substantially parallel to
the plane of the surface of the sample and providing a signal indicative
of such motion, and
computing the position of the tip and a magnetic field magnitude
corresponding to the position.
31. A method as set forth in claim 30 further comprising the step of
displaying the position of the tip and the magnetic field magnitude
corresponding to the tip position.
32. A method as set forth in claim 30, further comprising the step of
simultaneously measuring the topography of the surface of the sample.
33. A method as set forth in claim 32, further comprising the step of
simultaneously displaying the topography of the surface of the sample.
34. A method as set forth in claim 32 wherein said measuring is optical
measuring.
35. A method as set forth in claim 30 wherein said measuring measures the
motion of the tip at a sum frequency substantially equal to the sum of
said first predetermined frequency and said second predetermined frequency
and the sum frequency is substantially equal to the resonance frequency of
the tip.
36. A method as set forth in claim 35 wherein said measuring is optical
measuring.
37. A method as set forth in claim 30 wherein said measuring measures the
motion of the tip at a difference frequency substantially equal to the
difference between said first predetermined frequency and said second
predetermined frequency and the difference frequency is substantially
equal to the resonance frequency of the tip.
38. A method as set forth in claim 37 wherein said measuring is optical
measuring.
39. An apparatus for measuring a magnetic field in a sample using a
scanning tunneling microscope having a tip comprising:
piezoelectric drive means for controlling the distance between the tip and
a surface of the sample and a position of the tip for enabling scanning of
the surface and providing a signal indicative of the position of the tip;
generator means coupled to the tip for providing a current signal at a
first predetermined frequency for generating a current between the tip and
the surface for causing the tip to undergo vibratory motion in the
presence of the magnetic field;
means coupled to said piezoelectric drive means for causing the tip to
undergo vibratory motion at a second predetermined frequency along an axis
substantially normal to the plane of the surface of the sample;
optical heterodyned interferometric means disposed for measuring the motion
of the tip in a direction substantially parallel to the plane of the
surface of the sample and providing a signal indicative of such motion;
computer means coupled to said optical heterodyned interferometric means
and said piezoelectric drive means for providing an output signal
indicative of a position of the tip and a magnetic field magnitude
corresponding to the position, and
output drive means for providing a display responsive to said output
signal.
40. An apparatus as set forth in claim 39 said computer means providing
another output signal indicative of the topography of the surface of the
sample.
41. An apparatus as set forth in claim 39 wherein said optical heterodyned
interferometric means measures the motion of the tip at a sum frequency
substantially equal to the sum of said first predetermined frequency and
said second predetermined frequency and said sum frequency is
substantially equal to the resonance frequency of the tip.
42. An apparatus as set forth in claim 39 wherein said optical heterodyne
means measures the motion of the tip at a difference frequency
substantially equal to the difference between said first predetermined
frequency and said second predetermined frequency and said difference
frequency is substantially equal to the resonance frequency of the tip.
43. An apparatus for measuring a magnetic field in a sample using a
scanning tunneling microscope having a tip comprising:
drive means for controlling the distance between the tip and a surface of
the sample and a position of the tip for enabling scanning of the surface
and for providing a signal indicative of the position of the tip relative
to the sample;
generator means coupled to said tip for providing a signal for generating a
current between said tip and the surface;
detector means disposed for measuring the motion of the tip in a direction
substantially parallel to the plane of the surface and providing a signal
indicative of such motion, and
computer means coupled to said detector means and said drive means for
providing an output signal indicative of a position of the tip and a
magnetic field magnitude corresponding to the position.
44. An apparatus as set forth in claim 43 further comprising output device
means coupled to said computer means for providing an image of the
magnetic field magnitude at corresponding positions of the tip.
45. An apparatus as set forth in claim 43, wherein said computer means
provides another output indicative of the topography of the surface of the
sample.
46. An apparatus as set forth in claim 43, wherein said detector means is
an optical heterodyned interferometer.
47. A method for measuring a magnetic field in a sample using a scanning
tunneling microscope having a tip comprising the steps of:
disposing the tip in close proximity to a surface of a sample and scanning
the surface;
providing to the tip a signal for generating a current between the tip and
the surface;
measuring the motion of the tip in a direction substantially parallel to
the plane of the surface and providing a signal indicative of such motion,
and
computing the position of the tip and a magnetic field magnitude
corresponding to the position.
48. A method as set forth in claim 47, further comprising the step of
displaying the position of the tip and the magnetic field magnitude
corresponding to the tip position.
49. A method as set forth in claim 47, further comprising the step of
simultaneously measuring the topography of the surface of the sample.
50. A method as set forth in claim 49, further comprising the step of
simultaneously displaying the topography of the surface of the sample. |
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Description |
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BACKGROUND OF THE INVENTION
The present invention concerns Lorentz force microscopy and in particular
concerns imaging magnetic structures in a sample with high resolution by
measuring Lorentz force-induced deflection of the tip in a scanning
tunneling microscope (STM).
Several approaches exist for imaging magnetic field distributions on a
microscopic scale. For moderate resolutions optical techniques based upon
the Kerr effect are adequate and provide spatial resolution of
approximately 0.5 micron which is limited by the optical wavelength.
Another approach is to use the Bitter pattern technique which requires the
spreading of a magnetic particle suspension over the surface to be imaged
and subsequently obtaining an image using light. In order to achieve
higher spatial resolution, it is necessary to resort to the use of
electron beam imaging techniques such as spin polarized imaging and
Lorentz microscopy.
Presently, leading techniques for high-resolution imaging of magnetic
structures include the use of magnetic force microscopy (MFM) as is
described in the article by Y. Martin and H.K. Wickramasinghe entitled
"Magnetic Imaging by "Force Microscopy" with 1000 .ANG. Resolution", Appl.
Phys. Lett Vol. 50, No. 20, May 18, 1987, pp. 1455-1457, in which the
lateral resolution is limited by the tip size, typically 1000 angstroms.
Another technique is the use of scanning electron microscopy with
polarization analysis (SEMPA) as is described in the article by R.T.
Celotta and D.T. Pierce entitled "Polarized Electron Probes of Magnetic
Surfaces", Science, Vol. 234, Oct. 17, 1986, pp. 333-340, which in
principle is limited in resolution to the far-field electron beam spot
size. The SEMPA technique also suffers from the difficulties associated
with surface preparation and in the reliability of the
polarization-sensitive detector. To date, the SEMPA technique has been
demonstrated with a resolution of 1000 angstroms, but the potential exists
of achieving 100 angstroms resolution.
The present invention provides for accurate measurement of the force
between a tip and a sample as a function of the spacing between the tip
and sample surface. A tip is vibrated in close proximity to &he surface
and an optical heterodyned interferometer is employed to accurately
measure the vibration of the tip. The technique provides a sensitive and
flexible arrangement for measuring the force. As a result, it is possible
to image the magnetic field by noncontact profiling on a scale of a few
angstroms.
Specifically, the measuring technique of the present invention is
theoretically capable of attaining resolution which is limited only by the
near-field beam size, i.e. better than 5 angstroms lateral resolution, as
demonstrated using high-resolution images of a scanning tunneling
microscope.
In accordance with the teachings of the present invention, a scanning
tunneling microscope is operated using a long, thin tip. In such a
configuration the tip is stiff in a direction normal to the plane of the
sample surface but is flexible in a direction parallel to the plane of the
sample surface. In the presence of a magnetic field in a plane parallel to
the sample surface, and with a tunneling current passing between the tip
and the sample, there will be a static deflection of the tip. When
applying a first alternating current bias voltage at a first frequency
between the tip and sample, the oscillatory current causes the tip to
undergo vibratory motion at the first frequency in a direction parallel to
the sample surface. The oscillatory motion is detected by means of an
optical heterodyned interferometer by measuring the laser phase
variations.
The motion of the tip may be detected in two orthogonal planes, which as
will be described hereinafter determine the magnitude and direction of the
component of the magnetic field parallel to the sample surface. The
detection is accomplished, for example, either by using two, independent
interferometers or by using a simple interferometer and measuring both the
amplitude and phase of the detected optical signal. By scanning the tip
across the sample surface, an image of the vector magnetic field
throughout the sample is thus obtainable.
Scanning tunneling microscopes are well known and are described, for
example, in U.S. Pat. No. 4,343,993 entitled "Scanning Tunneling
Microscope", issued to G. Binnig et al and assigned to the same assignee
as the present invention, which patent is incorporated herein by
reference.
SUMMARY OF THE INVENTION
A principal object of the present invention is therefore, the provision of
an apparatus for and a method of imaging magnetic structures in a sample
with high resolution by measuring the Lorentz force-induced deflection of
the tip in a scanning tunneling microscope.
Another object of the invention is the provision of an apparatus for and a
method of imaging magnetic structures in a sample in which the resolution
is in the order of approximately several angstroms.
A further object of the invention is the provision of an apparatus for and
a method of simultaneously measuring the topography and lateral field
strength of a sample.
Further and still other objects of the invention will become more clearly
apparent when the following description is read in conjunction with the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic representation of the essential components of a
conventional scanning tunneling microscope, and
FIG. 2 is a schematic representation of an apparatus useful for practicing
the present invention.
DETAILED DESCRIPTION
Referring now to the figures and to FIG. 1 in particular there is shown
schematically the essential components of a conventional scanning
tunneling microscope. A sample 10 to be imaged acts as an electrode above
which and in close proximity thereto a tip 12 is disposed. The sample and
tip are capable of undergoing motion relative to each other in each of the
three coordinate axes designated x, y and z. The sample and/or the tip are
also provided with three piezoelectric drives 14, 16, 18. Piezoelectric
drives 14 and 16 operate in the lateral directions x and y respectively.
The drives may act either on the tip 12, the sample 10 or a combination of
both to cause relative motion between the tip and sample along the x and y
axes. Vertical piezoelectric drive 18 adjusts the spacing between the tip
12 and surface of sample 10 in the z-axis direction, in the vertical
direction as shown. A measuring device 20 is coupled to sample 10 and tip
12 as well as to piezoelectric drives 14, 16 and 18. Controller 22 is
coupled both to measuring device 20 and z-axis piezoelectric drive 18 for
controlling the separation distance between the sample 10 and tip 12.
Measuring device 20 is connected to analyzer 24 which in turn is connected
to an output device such as a plotter 26 or a viewing screen 28. The
electrodes are drawn schematically in exaggerated size. The actual
mechanical dimensions of the electrodes, sample and tip, as well as their
possible range of adjustment are extraordinarily small because of the
delicate nature of the tunneling effect. The controller 22 must be able to
operate very precisely and the measuring device 20 must be extremely
sensitive.
The present invention provides a measurement resolution of better than 5
angstroms in a lateral direction. As shown in FIG. 2, a scanning tunneling
microscope is operated using a long thin tip 40 supported by support 42.
The tip 40 is rigid in a direction along the longitudinal axis of the tip,
i.e. in a direction substantially normal to the surface 44 of a metallic
sample 46, and is flexible in a direction substantially parallel to the
sample surface 44. The tip, preferably fabricated from tungsten, is
dimensioned approximately 200 microns in length with a diameter tapering
from 10 microns at the base to a final point approximately 20 nanometers
in diameter.
When a magnetic field is manifest in the plane of the sample and a current
from source 48 is passed between the tip 40 and sample 46, there will be a
static deflection in the direction r=I.times.B. When applying an a.c. bias
voltage at a frequency .omega..sub.1 from a voltage generator 50 between
the tip 40 and sample 46, the operating current causes the tip 40 to
undergo vibratory motion in a direction substantially parallel to the
plane of the sample surface 44. The motion of the tip 40 is detected and
measured using an optical heterodyned interferometer 51 comprising laser
probe 52 and lens 54.
Optical heterodyned interferometers are known. A preferred interferometer
which has been used successfully in applications with a scanning force
microscope is described in detail in the article "Atomic Force
Microscope-Force Mapping and Profiling on a sub 100-.ANG. Scale" by Y.
Martin, C.C. Williams and H.K. Wickramasinghe, J. Appl. Phys., Vol. 61,
No. 10, May 15, 1987, pages 4723-4729, which article is incorporated
herein by reference. The tip 40 and holder 42 are coupled to x, y and z
piezoelectric drives shown schematically as elements 56, 58, and 60
respectively. The position of the tip relative to a point on the
stationary sample 46 in the x, y and z directions respectively is provided
along conductors 62, 64, and 66 to a computer 68. While the tip is scanned
over the sample in the x-axis and y-axis direction, the position
calculated by computer 68 from the piezoelectric drive signals received
from each of the element 56, 58 and 60 along conductors 62, 64 and 66
respectively and the magnetic field strength B provided from the
interferometer 51 along conductor 70 to the computer 68 are combined to
generate at an output device 72 a representation of the magnetic field
along the surface of the sample 46 as the tip is scanned over the surface.
The output device 72 may be a screen presentation, plotter, recorder or
any other device capable of providing a graphical or tabular
representation of the magnetic field as a function of position along the
surface 44 of the sample 46.
In operation, the tip is located at a distance in the order of one
nanometer from the surface of the sample. The amplitude of the vibratory
motion is in the range between 0.1 to 10 nanometers. The computer 68 is
preferably an IBM PC/AT or a computer of equal or better capability for
data acquisition.
While the above description discloses motion of the tip relative to a
stationary sample, it will be apparent to those skilled in the art that
relative motion between a stationary tip and moving sample or between a
moving tip and moving sample, as described in conjunction with the
description of the STM shown in FIG. 1, will perform equally as well.
The magnitude of the magnetic field effect is calculable by the computer 68
as follows. In a material with a magnetic field B located just outside of
the sample which decreases over a characteristic length scale l exhibiting
a tunnel current I, and where the spring constant of the tip 40 is k, the
static deflection of the tip is in the order of IBl/k. For the case of an
alternating current current having a frequency .omega..sub.1 of the bias
voltage selected to be approximately equal to the mechanical resonance
frequency of the tip, the amplitude a of the tip motion is Q multiplied by
the static deflection or a=QIBl/k. In the case of high spatial frequency
components of the magnetic field, the length l over which the magnetic
field B decays is approximately equal to the spatial wavelength of B.
Therefore, in order to resolve 100 angstrom fluctuations of the tip in the
field B, l is set to 100 angstroms. For a typical Q of 100, B=1W/m.sup.2,
k=10.sup.-2 N/m, an alternating current of 1.mu.A and l=100 angstroms, the
tip will oscillate at a peak-to-peak amplitude of 1 angstrom. The
intrinsic limit of resolution of the microscope for magnetic field imaging
will be similar to that of a scanning tunneling microscope, possibly being
limited by increased tunneling area and gap distance due to field emission
from the tip. Both of these effects are known to be several orders of
magnitude below the resolution available with currently known techniques.
These effects are described, for instance, in the article entitled "The
Topografiner: An Instrument for Measuring Surface Microtopography" by R.
Young, J. Ward and F. Scire, Rev. Sci. Instr., Vol. 43, No. 7, July 1972,
pages 999-1011.
The signal-to-noise ratio of the measurement is determined by the noise
limit of the optical interferometer and by thermally excited oscillation
of the tip. Tests have shown that the optical interferometer described in
the Martin et al article supra is able to measure tip displacements as low
as approximately 5.times.10.sup.-5 .ANG./.sqroot.Hz for 100.mu.W of laser
power and therefore does not represent a severe limitation. For a spring
constant of 10.sup.-2 N/m, the root-mean-square fluctuation in tip
position is approximately 12.ANG. at room temperature. The amplitude in a
bandwidth .beta. is given by the expression N=(4R.sub.B
TQ.beta./k.omega..sub.1).sup.1/2. When attempting to achieve 100 angstroms
resolution (i.e., a=1) with the parameters set forth hereinabove, the
bandwidth .beta. and the resonant frequency .omega..sub.1 of the tip 40
are related as follows: .omega..sub.1 /.beta.=1.6.times.10.sup.4 in order
to achieve a signal-to-noise ratio of 1. Typically, .omega..sub.1 is
approximately 50 kHz, so that .beta. is approximately 4 Hz. The practical
limit to measurement resolution will then be due to drift in the scanning
tunneling microscope, which sets a lower bound on .beta. of approximately
0.1 Hz to 1 Hz, or roughly 15.ANG. resolution.
Further immunity from environmental noise sources is achievable by
vibrating the tip at a second frequency .omega..sub.2 in a direction along
the z-axis, substantially normal to the plane of the surface 44 of the
sample 46. The tip is made to undergo vibratory motion by applying a
suitable a.c. voltage signal to the z-axis piezoelectric drive. The
frequency .omega..sub.2 is not at the resonant frequency of the tip and
.omega..sub.2 so that the sum or difference frequency, which ever is
detected, is at the resonance frequency of the tip. A typical value for
.omega..sub.2 is between 10 kHz and 100 kHz. Detection of the tip motion
by the optical heterodyned interferometer at a difference or sum frequency
of the two applied motions (.omega..sub.1 .+-..omega..sub.2) results in
the interaction of only the tip 40 and sample 46 being detected and
measured. In addition to rejecting low resolution components of the force
interaction with the tip, the described heterodyned scheme eliminates
spurious signals resulting from Joule heating-induced modulation of the
sample height. Either a single interferometer, as shown, capable of
measuring laser phase variations or two interferometers, each measuring
motion along one of the axes of motion, measure the tip motion.
While the above refers to motion of the tip, it will be apparent to those
skilled in the art that the relative motion between the tip and sample is
important. Therefore, motion of the tip, sample or both the tip and sample
may be used in practicing the present invention.
The tip motion and x, y and z axes position are provided to the computer as
described above. The computer, in turn, calculates the magnetic field
strength at each associated tip position relative to the sample surface,
using the above described equation relating tip vibration amplitude and
field strength and provides an output signal responsive to the calculated
values.
The above described invention offers unique advantages over the prior
methods. First, the apparatus operates independently as a conventional
scanning tunneling microscope. Thus, the topography and lateral magnetic
field strength are measured simultaneously. Since the static deflection of
the tip (for topographical measurement) is quite small compared to the
length scales of interest, the topography and magnetic field image is
readily separated. Therefore, an independent measure of magnetic field
strength, apart from the topographic measurement, is conveniently
achieved. Second, the resolution is much better than that achieved using
either magnetic force microscopy or scanning electron microscopy with
polarization analysis since the better high resolution obtainable with the
scanning tunneling microscope determines resolution of the magnetic field
measurement. Tip shape affects resolution in the same manner as in a
conventional scanning tunneling microscope, particularly when measuring
rough surfaces. Also, secondary election emission will not play a large
role in the resolution limit. Finally, by detecting the tip oscillation in
two orthogonal directions, the direction of magnetization in the sample
can be determined.
While there has been described and illustrated a method and preferred
embodiment of an apparatus for measuring the magnetic field strength of a
sample, it will be apparent to those skilled in the art that modifications
and variations thereof are possible without deviating from the broad
spirit of the invention which shall be limited solely by the scope of the
claims appended hereto.
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