Classifications

• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y35/00—Methods or apparatus for measurement or analysis of nanostructures
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q30/00—Auxiliary means serving to assist or improve the scanning probe techniques or apparatus, e.g. display or data processing devices
  • G01Q30/08—Means for establishing or regulating a desired environmental condition within a sample chamber
  • G01Q30/12—Fluid environment
• • 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
  • G01Q60/32—AC mode
• • 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 invention relates to a probe for atomic force microscopy, an atomic force microscope comprising such a probe and an atomic force microscopy method.
• Atomic Force Microscopy or "AFM"
• Microscopy in English language is a scanning microscopy technique developed since the eighties and allowing to reach a resolution at the atomic scale.
• atomic force microscopy is not limited to image formation of conductive surfaces, making it particularly suitable for insulating, semiconductor materials, as well as biological nature.
• the dynamic technique is generally preferred for observations made in vacuum or in air. This technique is less suitable for observations in a liquid medium because the vibrations of the lever are strongly damped.
• Atomic force microscopy is today a very powerful experimental technique. Improvements in its performance, however, remain desirable.
• the invention aims to achieve at least some of the aforementioned objects. According to the invention, this is made possible by exploiting a volume oscillation mode of a micromechanical resonator, instead of a bending mode as in the case of probes of the prior art.
• Said probe may also comprise means for detecting oscillations of said micromechanical resonator according to said volume oscillation mode.
• Said means for detecting the oscillations of said micromechanical resonator may be chosen from a capacitive sensor and a piezoelectric sensor.
• Said means for selectively exciting a volume oscillation mode of said resonator may be chosen from a capacitive actuator and a piezoelectric actuator.
• Said micromechanical resonator may have a planar structure and said volume oscillation mode may be a plane deformation mode of said resonator.
• Said micromechanical resonator may have a thickness of between 0.01 ⁇ m and 10 ⁇ m, and preferably between 0.05 ⁇ m and 5 ⁇ m.
• Said micromechanical resonator may have a disk or ring shape.
• said volume oscillation mode can be an elliptical mode.
• said micromechanical resonator When said micromechanical resonator is disk-shaped, it may have an outer radius of between 0.1 ⁇ m and 200 ⁇ m.
• Said tip for atomic force microscopy can extend in the plane of said micromechanical resonator, from the contour of the latter.
• said tip for atomic force microscopy may form an angle with the plane of said micromechanical resonator.
• Said volume oscillation mode may have a natural frequency in the vacuum between 10 MHz and 20 GHz, and preferably between 50 MHz and 2 GHz.
• Said micromechanical resonator may have, for said oscillation mode volume, a quality factor in vacuum between 10 3 and 10 5, and preferably between 5-10 5-10 3 and 4.
• Said micromechanical resonator may have, for said volume oscillation mode, a quality factor in water of between 10 2 and 5-10 4 , and preferably between 10 3 and 10 4 .
• Said volume oscillation mode may have at least one nodal point on the contour of said micromechanical resonator, and the latter may have a means of attachment to a support structure positioned in correspondence of said nodal point.
• said probe may comprise a single fixing means, in the form of a beam.
• Said micromechanical resonator may have a symmetrical structure, said probe having at least one balancing element having a moment of inertia substantially equal to that of the tip, arranged so as to preserve the symmetry of said structure.
• Said micromechanical resonator may be disposed at the end of a beam constituting a support structure for the latter.
• Yet another object of the invention is a method of atomic force microscopy, comprising the steps of: approaching a surface to be imaged the tip for atomic force microscopy of a probe as described above; selectively exciting a volume oscillation mode of the micromechanical resonator of said probe using the means provided for this purpose, said volume oscillation mode having a natural frequency; and detecting the variations in the natural frequency of said volume-induced oscillation mode by forces exerted between said surface to be imaged and said tip for atomic force microscopy.
• Yet another object of the invention is a method of atomic force microscopy, comprising the steps of: approaching a surface to be imaged the tip for atomic force microscopy of a probe as described above; selectively exciting a volume oscillation mode of the micromechanical resonator of said probe using the means provided for this purpose, said volume oscillation mode having a natural frequency; and detecting the amplitude variations of said volume oscillation mode induced by forces exerted between said surface to be imaged and said tip for atomic force microscopy.
• at least said surface to be imaged and said tip for atomic force microscopy can be immersed in a liquid medium.
• FIG. 1A a probe for atomic force microscopy of a type known from the prior art
• Figure 1B the schematic diagram of a simplified mechanical model of the probe of Figure 1A;
• Figure 1C the resonance peaks of the probe of Figure 1A in air and water
• FIG. 2 is a plan view of a probe according to a first embodiment of the invention.
• FIG. 3 an elliptical vibration mode of the resonator of the probe of FIG. 2;
• Figure 4 is a side view of a probe according to a second embodiment of the invention.
• FIG. 1A shows the typical structure of a probe for atomic force microscopy known from the prior art, SM.
• SM atomic force microscopy
• Such a probe essentially consists of a built-in lever, or “cantilever” CL, which protrudes from a support structure STS. Near the distal end
• a laser beam FLI is directed towards the lever CL to be reflected by the latter; any deflection of the lever results in a deflection of the reflected beam FLR, which can be detected by a four-quadrant photodetector.
• the lever CL is generally made of silicon by means of photolithographic processes and has a width of between a few tens and a few hundred micrometers, a width also a few tens of micrometers and a thickness of a few micrometers.
• a "volume mode” can be defined as a mode of vibration characterized by a proper form (deformed of the resonator oscillating at a natural frequency) symmetrical with respect to the (x) plane (s) of the neutral fibers. This is for example a compression mode, as opposed to bending or torsion modes that do not have such a symmetry.
• Using a volume mode is advantageous in many ways.
• the elastic constant k associated with the volume modes is much higher than that associated with the bending modes.
• the resonance frequency is therefore also higher, and can reach the MHz, or even the GHz, without the need to excessively reduce the dimensions of the resonator.
• a resonance frequency of several MHz makes it possible to reach a temporal resolution of the order of a microsecond ( ⁇ s); however, many phenomena of biophysical interest take place on this time scale.
• volume swing modes the most important benefit that results from the use of volume swing modes is the reduction of hydrodynamic losses in liquid applications.
• a plane deformation mode of the latter ie a mode of oscillation or displacement is mainly in the plane of the resonator.
• the hydrodynamic forces exert essentially on the edge of the resonator, whose thickness is typically of the order of one micrometer.
• Micromechanical resonators having volume oscillation modes that may be suitable for producing a probe for atomic force microscopy are known from the prior art, mainly for use as electromechanical filters in the field of telecommunications.
• Figure 2 shows a probe for atomic force microscopy according to a first embodiment of the invention.
• This resonator has a mode of plane deformation, said elliptical type;
• Figure 3 shows the RMM ring in its equilibrium state (line hatched) and in its deformed state corresponding to the maximum amplitude of an oscillation according to this volume mode (continuous line).
• the resonance frequency of the elliptical mode is 7.3 MHz and the quality factor in the vacuum is 1000.
• the oscillations can typically have an amplitude at the ventral points of the order from 30 to 50 nm.
• FIG. 3 shows that the elliptical mode of oscillation of the ring RMM has four PN1, PN2, PN3, PN4 nodal points distributed regularly along the contour C of the latter, as well as four ventral points PV1, PV2, PV3 , PV4, also distributed regularly around the contour C and offset by 45 ° with respect to said nodal points.
• Two points P1 and P2 are arranged in correspondence of two diametrically opposed ventral points, PV1 and PV2.
• One of these points, P1 is intended to be oriented towards the surface to be imaged SI, while the other is intended to make the symmetrical structure vis-à-vis the vibration mode used.
• the tip P1 When the elliptical mode is excited, the tip P1 is reciprocated in a radial direction, which leads it to move towards and away from the surface SI. Under these conditions, the interaction forces between the tip and the surface modify the resonance frequency and the quality factor of the resonator.
• a selective excitation means of the elliptical oscillation mode is provided in the form of an arcuate electrode EL1, with a width typically between 1 .mu.m and 200 .mu.m located outside the ring RMM opposite the ventral point PV3, and spaced from the contour C of said ring by an interval ES1.
• an alternating electric signal whose frequency corresponds to the resonance frequency of the elliptical mode is applied to the electrode EL1
• said elliptical mode is excited selectively by electrostatic effect.
• electrostatic type actuation in a micromechanical system is known, see for example the article by H. Camon, J.-Y. Fourniols, S. Muratet and B.
• the oscillation detection is performed capacitively using a second electrode EL2, arranged symmetrically with respect to the excitation electrode EL1.
• a constant potential difference is applied between the electrode EL2 and the resonator RMM, the oscillations of the latter determine a variation of the width of the gap ES2, and thus of the capacity of the system, which generates an electrical signal alternative.
• probe SM 'of the invention can be entirely realized in integrated or "monolithic" form, including as regards the means of excitation and detection of oscillations, and this using only techniques classic lithography. This is another advantage of the invention over the prior art.
• the micromechanical resonator RMM may be ring-shaped, with an outside radius R ex of between 0.1 ⁇ m and 200 ⁇ m and a width which depends at the same time on the need to obtain a resistance sufficient mechanical and technological limitations posed by lithographic manufacturing processes (currently of the order of 8 nm).
• the resonator may also have a disk shape; this generally results in a higher resonant frequency than in the case of an annular resonator.
• a circular shape is not essential, because one can for example consider polygonal plate resonators, possibly with rounded corners. Similarly, the elliptical mode is only one possible choice among others.
• the aforementioned articles provide examples of resonators that can be used for the implementation of the invention.

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• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• General Physics & Mathematics (AREA)
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• Chemical & Material Sciences (AREA)
• Nanotechnology (AREA)
• Power Engineering (AREA)
• Analytical Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Micromachines (AREA)

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• 2007
  • 2007-05-02 FR FR0703161A patent/FR2915803B1/fr active Active
• 2008
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  • 2008-04-23 EP EP08805499A patent/EP2150799A1/de not_active Withdrawn
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