Scanning probe microscopy, method of producing the probe,...

Details Scanning probe microscopy, method of producing the probe,... Scanning probe microscopy, method of producing the probe,...

2002-05-17

2004-05-04

Lee, John R. (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

C250S307000, C250S42300F, C436S501000, C436S518000, C436S524000, C436S525000, C436S527000, C436S531000, C436S532000, C435S006120, C435S007100, C435S291400, C073S105000

Reexamination Certificate

active

06730905

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a probe for use in an “intermolecular force microscope” which analyzes/processes a surface of a solid substance by utilizing a chemical reaction, and a production method of such a probe. The present invention further relates to a scanning probe microscope incorporating such a probe, and a molecule processing method using such a scanning probe microscope.
BACKGROUND ART
A measurement apparatus called a “scanning probe microscope” examines information over a surface of a solid substance by scanning a predetermined range of the surface of the solid substance with a sharp-tip probe placed in the close vicinity of the surface of the solid substance at the accuracy of angstroms, and measuring an interaction caused between the probe and the surface of the solid substance during the scanning operation. There are various scanning probe microscope proposed in accordance with the type of interaction to be measured. For example, when the interaction is a tunneling current, a scanning tunneling microscope is employed; when the interaction is interatomic force, an atomic force microscope is employed; and when the interaction is magnetic force, a magnetic force microscope is employed.
There are proposed “intermolecular force microscopes”, where a molecule having a chemical sensor function, or a molecule of a catalyst, is fixed at the tip of a probe of a scanning probe microscope, and a chemical interaction or catalysis caused between the molecule at the tip of the probe and the molecule to be measured is utilized to examine or process chemical information of the molecule to be measured (Japanese Patent No. 2653597; Japanese Patent No. 2561396; Nakagawa, “Shokubai (catalyst)”, Vol 39, pp. 628-635, 1997). The principle of an intermolecular force microscope composed by fixing a sensor molecule to a probe of an atomic force microscope is described below. Herein, a “chemical sensor function” refers to a function of analyzing a chemical characteristic of an organic molecule. In general, a chemical characteristic of a molecule is determined by the three-dimensional structure of the molecule or a functional group included in the molecule. A sensor molecule having a chemical sensor function can specifically examine such a structure or functional group.
FIG. 11
illustrates the principle of an atomic force microscope. A sample
153
is fixed on a piezoelectric element
154
extendable in X-, Y-, and Z-directions. A probe
114
, which includes a tip having the radius of curvature of several tens of nanometers, is present above the sample
153
. The probe
114
is fixed at the tip of a lever portion
152
. When force is applied between the sample
153
and the probe
114
, the lever portion
152
is deflected. This deflection can be evaluated by measuring with two photodiodes
155
the variation in the reflection angle of a laser beam
151
reflected by the lever portion
152
. Therefore, force caused between the sample and the probe can be calculated from the product of the amount of deflection and the spring constant of the lever portion. Thus, force caused between the sample and the probe is measured while scanning a specific region of the sample on an X-Y plane with the piezoelectric element, whereby information on the surface of the sample can be examined.
For example, an X-Y region is scanned while applying feedback to the movement of the piezoelectric element in the Z-direction such that force caused between the sample and the probe is maintained to be constant, whereby the relationship of the movement of the piezoelectric element in the X-, Y-, and Z-directions is examined. Through such an examination, concaves/convexes of the sample can be evaluated. Herein, a sensor molecule is fixed to the tip of the probe for measuring a surface of a base material on which other types of molecules are present, so that the position of a specific molecule can be examined. That is, in the case where the sensor molecule is a molecule that causes strong attractive force only with a molecule (molecule A), the position of molecule A can be examined at a resolution of a molecular level by measuring the surface of the base substance on which the other types of molecules are present, with a probe having such a sensor molecule. Further, if a catalyst molecule is fixed to the probe, a specific molecule can be processed with such a probe.
A base sequence of a DNA can also be determined by using an intermolecular force microscope. In the case where adenine, which constitutes a DNA, is fixed to a probe, and a single stranded DNA fixed on the base material is measured, the position of thymine can be specified because adenine causes large attractive force with thymine in a DNA. The base sequence in the DNA can be examined by conducting a measurement in a similar manner using probes having thymine, guanine, and cytosine attached thereto.
In a conventional intermolecular microscope, a molecule is fixed to a probe such that the molecule covers an entire surface of the probe. Thus, without correct control of the distance between the probe and a sample, a large number of molecules on the probe come into contact with the molecule to be examined during an examination process, so that the measurement resolution is poor. Similarly, also in molecular processing using an intermolecular force microscope, it is difficult to process only a single molecule because a large number of molecules fixed on the probe cause interaction with the large number of molecules to be processed. Hereinafter, problems involved in conventional intermolecular force microscope are described in detail.
FIG. 12
diagrammatically illustrates an example where the position of molecule A
163
, which is fixed on a surface of a solid substance, is examined using an intermolecular force microscope. When a probe is pressed against the surface of the solid substance, the surface of the solid substance is elastically deformed, so that two neighboring molecules, molecule A
163
and molecule B
164
, cause an interaction, and as a result, the positions of these two molecules cannot be identified.
FIG. 13
is a conceptual diagram which illustrates an example of determining the position of adenine
174
, which is a base included in a single stranded DNA
173
, by using an intermolecular force microscope. Thymine
172
, which causes a specific interaction with adenine, is fixed to a probe
171
. In principle, the position of adenine
174
in a DNA can be examined by examining the position of adenine which causes an interaction with thymine
172
on the probe. However, if the probe
171
is too close to the sample, two or more thymine molecules
172
are specifically interacted with two or more adenine molecules
174
of the DNA strand
173
. As a result, it becomes difficult to identify the position of adenine in the DNA strand
173
.
FIG. 14
illustrates an example where a protein thin film fixed onto a base material is processed using an intermolecular force microscope. Peptidases, which are enzymes for decomposing a protein, are fixed to a probe
181
. In this case, if force caused between the probe and a sample is too large, a large number of peptidases come into contact with the protein thin film. As a result, it becomes difficult to process the protein to a precision of a single molecule size.
It is readily appreciated that the above problems can be solved by fixing a sensor molecule or a catalyst onto a probe having the radius of curvature of angstroms. A proposed candidate for a probe having the smallest radius of curvature is a carbon nanotube. In recent years, there has been proposed a method for fixing a carbon nanotube to a probe of an AFM (atomic force microscope) and fixing an organic molecule to the carbon nanotube (D. Hongjie, et al., Nature; vol. 384, p.147, 1996). However, even a carbon nanotube has a radius of curvature of 2.6 nm at the tip thereof, and accordingly, the number of molecules formed in the region (tip surface) at the tip of the probe which faces a sample is about several hundreds. Thus, simila

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