Atomic force microscope and method for imaging surfaces with atomic resolution
First Claim
1. A method for generating a topographical image of a surface of a sample with a resolution better than 100 nm, comprising the steps of:
- moving a sharp point (5) which is fixed to one end of a spring-like cantilever (7) toward the surface of the sample (4) to be inspected to a distance where the forces occurring between the atoms at the apex of said point (5) and on the sample'"'"'s surface are larger than 10-20 N and the resulting force deflects said cantilever (7);
detecting the deflection of said cantilever (7) by means of a tunnel tip (8) disposed adjacent said cantilever (7);
maintaining the tunnel current flowing across the tunnel gap between said cantilever (7) and said tunnel tip (8) at a substantially constant preselected value by using any detected variations of the tunnel current from said preselected value to generate a correction signal;
using said correction signal to maintain the point-to-sample distance substantially constant; and
moving the sample relative to said point (5).
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Accused Products
Abstract
A sharp point (5) is brought so close to the surface of a sample (4) to be investigated that the forces occurring between the atoms at the apex of the point (5) and those at the surface cause a spring-like cantilever (7) to deflect. The cantilever (7) forms one electrode of a tunneling microscope, the other electrode being a sharp tip (8). The deflection of the cantilever (7) provokes a variation of the tunnel current, and that variation is used to generate a correction signal which can be employed to control the distance between said point (5) and the sample (4), in order, for example, to maintain the force between them constant as the point (5) is scanned across the surface of the sample (4) by means of an xyz-drive (3). In certain modes of operation, either the sample (4) or the cantilever (7) may be excited to oscillate in z-direction. If the oscillation is at the resonance frequency of the cantilever (7), the resolution is enhanced.
85 Citations
26 Claims
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1. A method for generating a topographical image of a surface of a sample with a resolution better than 100 nm, comprising the steps of:
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moving a sharp point (5) which is fixed to one end of a spring-like cantilever (7) toward the surface of the sample (4) to be inspected to a distance where the forces occurring between the atoms at the apex of said point (5) and on the sample'"'"'s surface are larger than 10-20 N and the resulting force deflects said cantilever (7); detecting the deflection of said cantilever (7) by means of a tunnel tip (8) disposed adjacent said cantilever (7); maintaining the tunnel current flowing across the tunnel gap between said cantilever (7) and said tunnel tip (8) at a substantially constant preselected value by using any detected variations of the tunnel current from said preselected value to generate a correction signal; using said correction signal to maintain the point-to-sample distance substantially constant; and moving the sample relative to said point (5). - View Dependent Claims (2, 3, 4, 5, 6)
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7. An atomic force microscope for evaluating the surface of a sample (4), said microscope comprising:
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means including first and second tunnel electrodes and associated electronics for measuring the distance between said tunnel electrodes and for generating a correction signal in response to deviations of said distance from a predetermined value; said first tunnel electrode including a cantilever (7) having at one end thereof a pint (5) adjacent which the sample surface is disposed; said second tunnel electrode (8) being disposed adjacent and spaced distance from said first tunnel electrode (7); means (9) for moving said second electrode relative to said first electrode; means responsive to said correction signal for maintaining the distance between the sample and point constant; and means for moving the sample relative to said point. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for generating a topographical image of a surface of a sample with a resolution better than 100 nm, comprising the following steps:
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moving a point (5) which is fixed to the free end of a spring-like cantilever (7) toward the surface of the sample (4) to be inspected to a distance where the forces occurring between the atoms at the apex of said point (5) and on the sample'"'"'s surface ar larger than 10-20 N and the resulting force deflects said cantilever (7); detecting the deflection of said cantilever (7) by means of a detector (8) which is disposed adjacent said free end of said cantilever (7) and provides an output signal indicative of the distance between the cantilever (7) and said sample (4); using variations in the output signal of the detector (8) to generate a correction signal; maintaining said distance substantially at a constant value by using said correction signal in a servo-like system; and moving the sample relative to said point (5). - View Dependent Claims (17)
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18. A method for examining a surface of a sample, comprising the following steps:
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providing relative motion in a z direction between a point on a deflectable cantilever of an atomic force microscope and a surface of said sample to be inspected, said point and said surface being brought sufficiently close that the interatomic force between atoms at the apex of said point and at a first area on said sample surface cause a deflection of said cantilever; detecting and using the deflection of said cantilever to produce a signal indicative of a property of said area of said sample; producing relative lateral motion between said sample and said point to scan said point with respect to said sample surface; and detecting and using the deflection of said cantilever when it is scanned across said sample surface to produce further signals indicative of a property of other areas of said sample surface, thereby examining said surface. .Iaddend. .Iadd. - View Dependent Claims (19, 20, 21)
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22. oscillated in the z direction. .Iaddend. .Iadd.25. An atomic force microscope for evaluating the surface of sample, comprising:
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a spring-like cantilever including a pointed tip; a sample holder for holding said sample in a position where said surface faces said pointed tip; first means for producing relative motion in the z direction between said pointed tip and said sample surface to bring said pointed tip and said sample surface sufficiently close that the interatomic force between atoms on said tip and at a first area on said sample surface causes a deflection of said cantilever; second means for producing relative motion in the lateral directions between said pointed tip and said sample surface to scan said pointed tip across other areas on said sample surface; and means including detector means for detecting the deflections of said cantilever during said scanning of said areas to produce signals indicative of a property of said sample surface, thereby evaluating said
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- 25. to said sample surface. .Iaddend. .Iadd.29. The microscope of claim 25, where said first means includes means for moving said sample in said z direction. .Iaddend. .Iadd.30. The microscope of claim 25, further including means for oscillating said cantilever in the z direction.
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26. Iaddend. .Iadd.31. An atomic force instrument, comprising:
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a deflectable member including a pointed tip; means for bringing closely together said pointed tip and a region of a surface, the distance between said tip and said surface being sufficiently small that interatomic forces exist between atoms on said tip and at a first area on said surface of sufficient magnitude to cause a deflection of said deflectable member; means responsive to deflection of said deflectable member to detect changes in a control parameter between said tip and surface; means for producing relative lateral motion between said pointed tip and other areas on said surface; and means responsive to said control parameter during said lateral motion to provide a series of signals indicative of a property of said surface, thereby evaluating said surface. .Iaddend.
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Specification