Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
  • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
  • G01Q60/26—Friction force microscopy
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q20/00—Monitoring the movement or position of the probe
  • G01Q20/04—Self-detecting probes, i.e. wherein the probe itself generates a signal representative of its position, e.g. piezoelectric gauge
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
  • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
  • G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders

Definitions

• the present invention relates generally to surface forces measurement instrumentation, and more particularly is a cantilever spring assembly used in probe
• SPM's Scanning Probe Microscopes
• SPM's such as AF 's (Atomic Force Microscope) and STM's (Scanning Tunneling Microscope) generally consist of a sample surface and a fine round "tip" that is supported at the end of a force-measuring cantilever spring. They operate by first bringing (positioning) the tip near the surface and then moving the tip or surface vertically (contact
• tapping mode or tapping mode
• laterally scanning mode
• the force is calculated by measuring the deflection of the cantilever spring supporting the tip.
• the most common method is the optical or beam deflection method (bouncing a laser
• the tip can in principle be measured by any of these methods. In cases where friction
• Friction Force Microscope When making "force measurements” at different locations of a surface (i.e., on
• Fig. 1A shows a "simple cantilever" spring of length L, width b, and thickness t.
• the spring is clamped at one end, with a rigid tip of length h at the free end.
• This is the basic design of a typical AFM or FFM cantilever, although other versions, for example, triangular
• the angular deflections ⁇ at Q may be determined according to
• resistive elements must be placed along the compliant length of the cantilever, as in the Kirk et al. reference, U.S. Patent # 5,444,244.
• the cantilever bends into arcs of circles whose relevant angles of curvature are given by the following equations (cf. Fig. 1 A):
• Equations (4) and (6) are proportional to Equations (1) and (3), the expression for the twist-bending deflection, Equation (5), is different from Equation (2), the
• the sensitivity to measuring friction forces in the twist mode using the OPTICAL method will be less than the sensitivity to measuring normal
• a further limitation of the simple cantilever constructions illustrated in Fig. 1 is that it is not'obvious that purely vertical or lateral forces provide pure and independent bending along the different cantilever axes even when the tip length h is small. This is because of the complicated triangular or rectangular geometries of these commonly-used cantilevers.
• the present invention is a dual- and triple- mode cantilever suitable for simultaneously measuring both normal (adhesion) and lateral (friction) forces independently in three orthogonal directions.
• the cantilever design allows the
• the cantilever is useful in Scanning Probe Microscopes (SPM's) and other force-measuring devices, such as the Atomic Force Microscope (AFM), the Friction Force Microscope (FFM) and in probe attachments for the Surface Forces Apparatus (SFA) where both normal and lateral forces acting on a tip need to be accurately and unambiguously measured.
• SPM Scanning Probe Microscopes
• AFM Atomic Force Microscope
• FFM Friction Force Microscope
• SFA Surface Forces Apparatus
• the resistive cantilever structure may also be used for optical detection of tip deflections.
• Another advantage of the present invention is that it provides a system that has a higher general sensitivity to measuring forces than the prior art devices by making use of a full-bridge configuration, rather than a half-bridge construction. This doubles the intrinsic
• the present invention also effectively eliminates differential thermal drifts because all four resistance elements are located in close
• a still further advantage of the present invention is that it enables a symmetrical design of the cantilever system that ensures that all force-detecting modes (bending, twisting, buckling, and twist-bending) will respond independently to tip forces acting along the x, y, and z directions.
• the new cantilever may also be used with the optical method of detecting displacement, wherein a light beam reflects off the cantilever surface at some suitable point (not necessarily the center).
• Figs. 1 A-C show three basic "simple cantilever" constructions known in the prior art.
• Fig. 2 illustrates the bending deflections of a cantilever with a long rigid tip at one
• Fig. 3 is a schematic view of a preferred "symmetrical" design of the present
• Fig. 4 is a perspective view of the preferred embodiment of the present invention.
• Fig. 1 A shows the four different types of deflection modes (bend, twist, buckle and twist-bend) that can occur when normal or lateral forces (F z , F x and F y ) are applied to a tip supported at the free end of a "simple cantilever" that is rigidly clamped at the other end.
• Equations 1 to 6 The corresponding deflection angles along different directions are given by Equations 1 to 6.
• Other simple cantilever constructions are also commonly employed in the prior art as in the Kirk, et al. reference, U.S. Patent # 5,444,244. Two of these devices are shown in Figs. 1 B and 1C, for which the same equations of motion apply (with minor
• Fig. 2 shows why a "simple cantilever" cannot provide high resolution for both normal and lateral forces at the same time as these forces are measured independently.
• the main problem is that by extending the tip length (or, more correctly, the length of the rigid pillar or base supporting the tip) the tip bends and no longer moves in the z-direction when a force F z is applied along this direction.
• a preferred embodiment design of the present invention includes two simple cantilevers 10 in series.
• the cantilevers 10 are fixed symmetrically
• the cantilevers 10 may be either solid or split cantilevers as desired by the user.
• the rigid base 12 of the tip 13 is located at the center of the cantilevers 10. In this case
• Equations 1-3 apply to OPTICAL measurements of displacements by reflecting a laser light beam from the top surface of the cantilever at Q or Q', i.e., not necessarily at the center Q.
• Equations 3-6 apply to RESISTIVE measurements, as when resistance elements 14 are placed at strategic points on the upper or lower faces of the cantilever surface as
• Fig. 4 shows the preferred embodiment of the invention that makes use of the above equations and principles to optimize the performance of the system for high resolution in both normal and lateral force-measuring modes.
• the arms of the clamping means 11 act
• the arms of the clamping means 11 do move slightly inwards, towards each other, when the cantilever spring 10 bends, buckles or twists.
• the tip 13 and its rigid base 12 are shown on the underside of the cantilever 10, but may also be positioned to protrude upward from the top surface.
• the entire unit may be micro-fabricated from a single starting block.
• the magnitudes of L, h, and b may be optimized to obtain the highest sensitivity in bending, buckling and/or twist-bending modes, depending on the specific application.
• the cantilever width b can be split into two or more parts (as illustrated in the broken area in
• the resistance strain gauges 14 may be placed as shown, but also at other positions on the cantilever 10, including both the top and bottom sides of the cantilever 10. By having the strain gauges 14 spaced well apart on the two sides of the cantilevers 10 as shown, unwanted electrical interference and noise is further minimized.
• the four resistive elements 14 and their connective wires 15 allow for a full-bridge operation which is more sensitive and less susceptible to thermal drift than a half-bridge or single-gauge construction as is known in the art.
• the present invention presents three possible full-bridge configurations, instead of the two configurations possible with prior art devices.
• the bridge can be configured to measure the four resistances in three combinations which involve adding the currents from two resistors and subtracting the currents from the two remaining resistors. There are three ways of doing this. The output currents from these three combinations are in turn independently proportional to the three orthogonal forces as given by the following equations:
• the present invention allows for three orthogonal forces to be measured independently at the same time.
• Prior art devices only allow the simultaneous measurement of two orthogonal forces.
• the device can certainly be used to measure only one or two modes, if so desired by the user.
• the present invention has a higher general sensitivity to measuring forces than
• optical method of detecting displacement whereby the light beam reflects off the cantilever surface at some suitable point (not necessarily the center).

Landscapes

• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Radiology & Medical Imaging (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=32852246

Family Applications (1)

Country Status (3)

Families Citing this family (2)

Citations (3)

Family Cites Families (2)

• 2003
  • 2003-03-13 WO PCT/IB2003/000913 patent/WO2004070765A1/en not_active Application Discontinuation
  • 2003-03-13 AU AU2003212557A patent/AU2003212557A1/en not_active Abandoned
  • 2003-03-13 EP EP20030708379 patent/EP1609164A4/de not_active Withdrawn

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events