JPH07244053A - Scanning force microscope - Google Patents

Abstract

PURPOSE:To provide a scanning force microscope capable of observing the arrangement of atoms not only in air but also in a vacuum. CONSTITUTION:A probe 1 is connected to a coarse adjustment mechanism 7 and a scanner 6 in a state floated from an electrode 3 or a magnetic pole electrostatically or magnetically to be arranged through a structure 5. A displacement measuring system 4 is provided on the side opposite to the probe 1 and allowed to approach a sample 2 in this state to detect force such as interatomic force. Therefore, the cantilever probe detection force on the surface of the sample 2 required in observation in a scanning force microscope is reduced as compared with conventional one to avoid the damage of the surface of the sample 2 or the leading end of a detection part and an image of an atomic scale can be observed not only in air but also in a vacuum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning force microscope (hereinafter referred to as SFM: Scanning Force Microscope) for observing the surface shape of atoms, organic substances and molecules of biological substances on a solid surface.
abbreviated as scope).

[0002]

2. Description of the Related Art The SFM is for obtaining various microscopic images as a scanning image by detecting various other forces, which are inferred by the invention of the atomic force microscope (AFM), by using some kind of probe. There are those that use ultrasonic waves and the like, and are used as a generic name here. Conventional A
In FM, Physical Review Letters Volume 56 (1
(866) page 930, the probe uses a cantilever type micro-cantilever type detection unit with one end fixed. The amount of displacement that balances the force received as a result of the interaction between the probe at the tip of the free end of the cantilever and the sample surface and the spring constant of the cantilever that opposes this is the displacement of the surface of the cantilever opposite to the probe. The amount is detected by STM, the interference method using a laser, the optical lever method, or the like. A fine movement mechanism such as a tripod type or a cylindrical type is used to perform two-dimensional scanning on either the sample side or the cantilever side.

[0003]

[Problems to be Solved by the Invention]
In the FM, the relationship between the force F applied to the cantilever and the displacement amount x can be regarded as a spring characteristic when the spring constant of the cantilever is k, as will be described later, and can be expressed as F = kx. 10 ^-11 N to detect adsorbed atoms
It is estimated that it must respond to a small force of (Newton) or less, and it is necessary to detect a displacement x of 0.1 nm or less. Therefore, the spring constant k is at least about 0.1 N / m. A value is required. This value is S
It is difficult to use a conventional cantilever (spring constant k to 1 N / m) made of a substance composed of iO ₂ or SiN ₂ . That is, it is difficult to improve it by selecting the material or changing the shape a little.

Further, it is considered that the lower limit of the force (force) that can be detected by the probe is too large in a vacuum or in air where no medium exists between the probe and the sample. There was a problem that we could not observe the atoms.

The object of the present invention is to determine the limit of the force that can be detected depending on the material and the shape, and without using the cantilever detection method whose size is not yet sufficiently small, without weakness between the sample and the probe. The detection of atomic forces provides an observable SFM of individual atoms in vacuum or in air.

[0006]

The above problems are caused by a nail-shaped probe, a structure having levitation means for holding and floating the probe, and a moving means for holding the structure and approaching the sample. The problem is solved by forming a scanning force microscope having a scanner having the above and a detecting means for detecting the displacement of the probe.

[0007]

The present invention is characterized in that the displacement caused by the interatomic force is directly detected by the probe which is held in a levitated state and is as light as possible.

Incidentally, Si having a radius of 10 μm and a length of 300 μm
The rod weighs approximately 3 × 10 ⁻⁷ g. That is, 3 × 10 ^-7 dyne, and therefore 3 × 1
Levitating with a force larger than 0 ^-12 Newton (N), the displacement can be detected. In addition, platinum of the same shape (P
At t), the force is about one digit larger (2 × 10 ^-11 N).
Will be detected.

The principle of the present invention will be described below with reference to FIG.
If the electric charge is applied to the electrode 3 in a state in which the nail-shaped micro probe 1 is passed through the hollow portion of the annular electrode 3 provided at the end of the structure 5 or the like and the probe 1 is a good conductor, it is hollow. Come to the center. (The levitation principle is used in basic experiments of physics, so that the same charge is applied to the surface of the probe 1 and the surface of the electrode 3 as in the case of a so-called electroscope. The probe will surface.)
In this state, when the gap between the sample surface and the sample surface is brought close to the distance d where the interatomic force works, the probe is displaced within the range of the above order. Furthermore, by relatively scanning the sample and the detection system, the probe is displaced so as to trace the sample surface so as to always receive a constant force. The displacement is measured by the displacement measuring means 4 using a laser or the like.

As a method of floating the probe, in addition to the electrostatic method, there is magnetic means as shown in FIG. In FIG. 3, a magnetic pole 8 is placed instead of the electrode 3 and the probe 1 is made of a magnetic material so that it is aligned with the magnetization direction of the magnetic pole 8. There is also a levitation method using a high frequency, but since the levitation principle is accompanied by heat generation due to eddy current loss, it is limited to the purpose of heating the probe.

By detecting a minute force by the floating probe as described above, it is possible to observe atoms in air or in vacuum without damaging the sample surface or the tip of the probe.

[0012]

【Example】

(Embodiment 1) FIG. 1 shows an embodiment of the present application. Probe 1,
The electrodes 3 and the structure 5 holding them are manufactured by using a microfabrication technique as in the case of semiconductor devices, but can be manufactured without the need of the latest technology required for those devices. The structure 5 is bonded to the cylindrical scanner 6, but the structure 5 and the scanner may be connected with appropriate rigidity depending on the sizes of the structure and the scanner. The scanner is connected to a coarse movement structure 7 such as a moving mechanism for bringing the probe and the sample close to each other. After the displacement detection system 4 such as an interference method using an optical laser or an optical lever method is put into an operating state, a potential is applied to the electrode 3 to give an electric charge and the probe 1 is levitated. After that, the probe 1 is brought closer to the sample 2 until displacement occurs. When two-dimensional scanning is performed by the scanner 6, the probe 1 is displaced according to the unevenness of the sample surface, and the displacement is measured by the displacement measuring means 4. If the unevenness of the sample surface exceeds the displacement area of the probe, set the displacement range of the probe, and if it displaces more, control using the servo mechanism of the scanner and add that amount on the display system. To do.

Regarding the point of levitating by electrostatic force,
It is conceivable that the electric charge possessed by the probe moves to the sample surface during scanning of the probe, and as a result, the floating effect from the electrode 3 is lost. However, first of all, it is immediately levitated when the probe touches the electrode 3, and secondly, it is light enough to be always levitated by the atomic force regardless of whether the probe is levitated from the electrode 3. From each of the points of being, it is a matter of melancholy.

(Embodiment 2) FIG. 4 shows another embodiment of the probe portion. 3 shows a practical implementation method of the magnetic levitation method shown in FIG. 3, in which the permanent magnet 3 of FIG. 3 is replaced with a coil that operates as a magnet by passing an exciting current or a coil with a core such as ferrite, The probe is levitated by using a magnetic substance. That is, the probe current is magnetized in the same direction as the magnetic field generated by the coil, but the probe magnetizes and the coils and the same poles approach each other, so that they repel each other and levitate. If the sample is a non-magnetic material, the operation is similar to that of the first embodiment, but in the case of a magnetic material, the so-called
It can be applied as a magnetic force microscope (MFM). Moreover, since the reverse magnetic field can be immediately realized by passing the exciting current in the opposite direction, it is very effective as an MFM.

The strength of the magnetic field required for magnetic levitation is approximately 10 ^-10 AT when the gap between the probe and the electrode 3 is extremely small (10 μm or less) with respect to the 3 × 10 ^-7 g probe.
(Ampere turn), 2 × 10 ⁻⁶ g of the probe is of the order of 10 ⁻⁸ AT when the gap with the electrode 3 is ˜100 μm, and can be levitated with a sufficiently small current.

(Embodiment 3) FIG. 5 shows another embodiment of the present invention. The floating principle of the probe is the same as in the other embodiments,
The structure 5 holding the probe 1 is held by another structure 11. On the side opposite to the observation surface of the sample 2, the scanner 6 and the coarse movement structure 7 are connected to each other, and
It is connected to the probe side via 2, 13, and 14. The coarse movement structure 7 and the scanner 6 are controlled to bring the sample close to the probe, and when the displacement measuring means 4 detects the displacement of the probe, the coarse movement structure 7 is stopped and the scanner 6 performs control corresponding to the displacement amount. Although the probe is displaced by the two-dimensional scanning of the scanner, servo is performed by the scanning control system 15 so that the displacement amount is always kept constant, and the surface shape is displayed on the display system 16.
Represent. In this embodiment, it is important to manufacture the structures 11, 12, 13, and 14 as rigid as possible, which is the same as the conventional apparatus of the same kind, and it is also effective to integrally manufacture the structures.

[0017]

As described above, according to the present invention, the surface force of the sample and the tip of the detection part are damaged by making the force required between the detection part and the sample necessary for observation with the scanning force microscope smaller than before. This made it possible to observe the arrangement of atoms in air and in vacuum.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention. (Levitation of electrostatic force)

FIG. 3 is a diagram for explaining the operation of the present invention. (Magnetic levitation)

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a third embodiment of the present invention.

[Explanation of symbols]

1 ... Probe, 2 ... Sample, 3 ... Electrode (cantilever), 4 ...
Displacement measuring system, 5 ... Structure, 6 ... Scanner, 7 ... Coarse movement structure, 8 ... Magnetic pole, 9 ... Coil, 10 ... Core, 11, 1
2, 13, 14 ... Structures constituting the apparatus, 15 ... Scan control system, 16 ... Display system.

Claims (3)

[Claims] 1. A nail-shaped probe, a structure having a levitation means for holding and floating the probe, a scanner having a moving means for holding the structure and bringing it closer to a sample, and the probe. A scanning force microscope comprising a detection means for detecting displacement of a needle. 2. The scanning force microscope according to claim 1, wherein the levitation means floats the probe by electrostatic force, magnetic force or high frequency current. 3. The scanning force microscope according to claim 1, wherein the detecting means detects the displacement of the probe by irradiating the upper part of the probe with light.