Multiple local probe measuring device and method

Details Multiple local probe measuring device and method Multiple local probe measuring device and method

2000-09-13

2003-06-24

Lee, John R. (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

C250S307000, C250S309000, C250S310000, C250S311000

Reexamination Certificate

active

06583411

ABSTRACT:

The present invention concerns a multiple local probe measuring device for effecting local measurements referring to a sample, a multiple local probe measuring method and a multiple local probe manipulation method. One application field of the novel device and the novel methods is the scanning force microscopy (SFM), also known as atomic force microscopy (AFM). However, the invention is not restricted to such an application. The basic concept is applicable to the whole range of local probe techniques developed so far, especially all other scanning probe microscopy (SPM) techniques which require stabilization of measurement conditions, e.g. distance relations, for microscope probes, possibly cantilevers, for high-resolution measurements. Since it is hardly possible to give a complete list of scanning probe microscope techniques to which the invention can be applied, only some important techniques are given: scanning tunneling microscopy (STM), magnetic force microscopy (MFM), scanning near-field. optical microscopy (SNOM), lateral force microscopy (LFM), electrical field/force microscopy (EFM), magneto-tunneling microscopy and spin sensitive tunneling microscopy.
An object of the invention is to allow measurements with well defined measurement conditions. To this end, the invention provides for at least one of a stabilization of measurement conditions and a calibration and detection of measurement conditions.
In many local probe microscopy techniques, a distance of a local probe with respect to a sample or a reference surface is an essential parameter defining the measurement conditions. Accordingly, at least one of a stabilization, calibration, and detection of a distance associated with a local probe with respect to a sample or a reference surface is a central field to which the invention can be applied. As will be explained in more detail, the invention proposes providing a plurality of local probes to allow at least one of a calibration, detection, and stabilization of measurement conditions for at least one local probe on the basis of measurement effected with respect to at least one other local probe. For many applications, it will be sufficient to provide two local probes, one of the local probes being used for at least one of calibration, detection, and stabilization of the measurement conditions of the other local probe.
In the following the background and concept of the present invention will be exemplified with reference to the scanning force microscopy technique on the basis of two local probes in the form of cantilevers, as commonly used for scanning force/atomic force microscopy. According to the invention, there is provided a detector arrangement allowing independent detection of first measurement data referring to local measurements effected by first local probe and independent detection of second measurement data referring to local measurements effected by a second local probe. In the following, it will be assumed that this detection arrangement is realized by a double sensor system.
The concept of the invention can easily be extended to multiple local probe measurement devices having more than two local probes by providing a corresponding detection arrangement adapted to independently detect measurement data for each local probe with respect to the sample or the reference surface. Such a detection arrangement may be realized by a multiple independent sensor system. The provision of more local probes than a first probe and a second local probe allows a further increase of the stability and well defined measurement conditions possibly comprising a well defined orientation of a local probe in three-dimensional space.
BACKGROUND OF THE INVENTION
Scanning force microscopes (SFM) were in developed in 1986 by Binnig et al. (compare: Binnig, G. et al., PhysRev Letters, 1986, Vol. 56(9), p. 930-933) for imaging non-conducting surface with atomic resolution. They have since become a widely used tool in the semi-conductor industry, biological research and surface science. The first SFM was basically a thin metal foil acting as a cantilever, which was jammed between an STM-tip and the sample surface. Since the cantilever was a conducting metal, it become possible to measure the surface corrugation of non-conducting samples by monitoring how the foremost tip of the cantilever pointing towards the sample was deflected while moving across the sample surface on the basis of a tunneling current between the cantilever and a probing tip according to the scanning tunneling microscopy principle. Today, the registration of a laser's deflection from the back of the cantilever on a segmented photodiode is commonly used for this task (compare: Meyer, G. et al., Physics Letters, 1988, Vol. 53, p. 1045-1047).
Just as Binnig and Rohrer were originally interested in doing local spectroscopy on superconductors while developing the scanning tunneling microscope (STM) in 1981 (compare: Binnig, G. et al., ApplPhys Letters, 1982, Vol. 40, p. 178-180), the SFM was soon applied to local measurements of forces between different materials in vacuum, gaseous atmospheres, and in liquid. For many researches in different fields, the SFM has become an instrument for measuring local force-distance profiles on the atomic and molecular scale. Measurements that have been performed recently were concerned with ligand-receptor binding forces (compare: Florin et al., Science 1994, Vol. 264, p. 415-417), the unfolding and refolding of proteins (compare: Rief et al., Science, 1997, Vol. 276, p. 1109-1112), stretching of DNA as well as monitoring charge migration on semiconductors and conductor/insulator surfaces (compare: Yoo, M. J., et al., Science, 1997, Vol. 276, p. 579-582).
In the context of e.g. atomic force microscopy it is known, that the optical beam deflection detection method allows simultaneous measurement of height displacements and torsion (induced by lateral forces) of the cantilever used as local probe (compare: Kees. O. van der Werf, Constant A. J. Putman, Bart G. de Grooth, Frans B. Segerink, Eric H. Schipper, Niek F. van Hulst, and Jan Greve, Review of Scientific Instruments, October 1993, Volume 64, Issue 10, p. 2892-2897, “Compact stand-alone atomic force microscope”).
Local measurements of forces between tip and surface suffer from the following problems: 1) drift of the positioning arrangement, generally a piezo (immediately after the piezo has been extended or compressed); 2) hysteresis of the positioning arrangement or piezo; 3) mechanical drift; 4) thermal drift between sensor and sample on time scales ranging from seconds to hours; and 5) general mechanical instability resulting from the fact that the sensors' mechanical “feedback” on the sample is typically realized via a mechanical arm of much larger dimensions and mass than the sensor itself.
These problems can be alleviated to some degree if the force between tip and surface and, therefore, the distance between substrate and sample surface is kept constant, for instance, by keeping the deflectionangle of the cantilever constant (constant force mode). This is restricted to cases, though, where the lever (cantilever) is actually in contact with the sample surface and the normal force on the tip is large enough so as to be well distinguishable from any background noise.
A minimal force-level in the range of a hundred pN is generally required to provide a stable feedback control. Many interactions, especially of biological molecules under physiological conditions, are in the range well below 100 pN down to the level of thermally induced fluctuation forces of the cantilever. Presently available instruments are not capable of locally stabilized measurements at well-defined distances from the sample in this important force range of thermally fluctuating sensors (few pN).
Furthermore, data often need to be sampled locally over time periods of seconds to hours. Stability problems (as enumerated above) of instruments available to date ultimately render such measurements impossible.
OVERVIEW OF THE INVENTION
One object of the inve

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