JPH0864170A - Extra fine region surface analyzing method and device therefor - Google Patents

Abstract

PURPOSE: To accurately conduct elemental analysis in an ultra fine region by taking up one atom or a plurality of atoms on the surface of a specimen to the surface of a probe, and conducting electrical separation of the atom from the probe to perform mass spectrometry from the time of flight of an ion for element identification. CONSTITUTION: A surface atom of a specimen is stuck to the tip of a probe 12, the probe 12 is let to go back, a specimen holder 14 is removed from a scanning tunnel microscope 1, and placed outside the time of flight of an ion. A switch 30 is switched, output voltages of a straight polarity high voltage power source 24 and a straight polarity pulse generator 25 are adjusted to generate a pulse. The pulse generated is picked up by a logos key coil 29, and a clock of a mass spectrometry system 26 using a time of flight method is started. When the ion is separated, the clock is stopped by a signal sent from an ion detector, and by the time difference between the stop signal and the start signal, the time of flight is recorded. An element is identified based on the time of flight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a surface of a microscopic area and an apparatus therefor. For more information,
The present invention relates to a method and apparatus for microscopic surface analysis, which is useful for elucidating the mechanism of surface microfabrication at the atomic level and for the creation of new materials and new materials, including elemental analysis of microscopic areas of solid substances. It is a thing.

[0002]

2. Description of the Related Art Conventionally, many solid surface analyzers based on various principles have been put to practical use, for example, a static secondary ion mass spectrometer (Static-SIMS),
A single molecule detection method by fluorescence, and a scanning probe microscope typified by a scanning tunneling microscope (STM) have been used as a typical example for surface analysis.

However, in the case of these conventional methods, it is difficult to select any one atom for elemental analysis, and the resolution of the analysis is poor. It has been a big issue for surface analysis. That is, for example, in the case of static secondary ion mass spectrometry, in which a solid sample is irradiated with a finely focused primary ion beam, and the ions of atoms emitted from the sample surface are identified by mass spectrometry, the detection sensitivity is Although it has characteristics that it has excellent mass resolution and that it can detect from hydrogen to heavy molecules, this method cannot select any one atom for elemental analysis and has a spatial resolution of 0. There were drawbacks such as staying above 2 μm.

A single molecule detection method in which a solid sample is irradiated with laser light in an ordinary atmosphere under an optical microscope and fluorescence emitted by one molecule is detected with high sensitivity by a photon counting method requires a vacuum environment. Without recognizing one molecule, the non-fluorescent molecule cannot be detected, and since the optical microscope is used, the accuracy of determining the position of the molecule remains in the μm order.

On the other hand, a scanning probe microscope is known as a device having a spatial resolution capable of directly looking at the atomic arrangement on the surface of a sample in real space. However, since it is not possible to identify the atomic species of the recognized atoms, a scanning probe microscope is used. The means cannot be called. Immediately after the development of the scanning tunneling microscope (STM), the work function of the surface was measured by changing the distance between the probe and the sample surface, and the possibility of identifying atomic species from the value was considered. Even if the work function on a specific atom can be measured by this method, the measured value is greatly influenced by the surrounding atomic arrangement, and the atomic species of the specific atom cannot be uniquely determined. However, there was a drawback that the element identification accuracy did not reach the practical level at all.

[0006]

SUMMARY OF THE INVENTION The present invention has been made as a solution to the problems of the prior art as described above, and in a scanning probe microscope having a conductive probe on its surface, After picking up one or more atoms on the sample surface on the needle surface, the atoms are desorbed from the probe by electric field, and the mass of the atom is analyzed from the flight time of the ion to identify the element. A method for analyzing a surface of a microscopic region is provided.

Further, according to the present invention, a scanning probe microscope having a probe whose surface is conductive and a means for applying a voltage to the probe,
An analyzer equipped with an ion detector, wherein one or more atoms on the sample surface are picked up on the probe surface,
A microscopic area characterized by element identification by analyzing the mass of atoms from the flight time until reaching the ion detector placed in front by applying a voltage to the probe to desorb these atoms as ions A surface analyzer is also provided.

[0008]

The present invention is characterized by the above-mentioned method and the apparatus therefor. The principle of the method will be described as follows. That is, in the method of the present invention, first, a probe of a scanning probe microscope capable of observing individual atoms on a solid surface is positioned above atoms in an arbitrarily specified microscopic region, and a voltage applied between the probe and the solid surface is applied. One or more of the specified atoms on the solid surface are extracted by a method such as electric field evaporation by
Attach the atom to the probe. Next, the probe is separated from the solid surface and a positive voltage is applied. Then, the atoms attached to the surface of the probe are desorbed from the electric field, become positive ions, and fly toward the front of the probe. Since the energy of this flight is determined by the magnitude of the applied voltage V, if the distance to the ion detector is l and the time to reach it is t,
The ratio between the mass m of the atom and the valence number n of the ion is represented by the following equation.

[0009]

[Equation 1]

Here, a is a constant. Thus, by measuring the arrival time t to the ion detector, the mass m of the atom can be obtained, and the element can be identified from the value. Therefore, in the method of the present invention, the time-of-flight method is used for mass spectrometry of the ions desorbed from the probe. By this, without missing one specific atom to be analyzed,
It is possible to measure the mass. That is, a mass spectrometer having a transmittance of 100% for atoms at any position is constructed.

Mass spectrometers of the type in which the intensity of an electric field or a magnetic field is swept to obtain a mass spectrum have been widely used so far, but in the conventional case, an ion having a mass deviated from the transmission condition is analyzed. There is a defect that it cannot pass through and does not reach the detector. However, the present invention eliminates such drawbacks and enables mass spectrometry with high accuracy and elemental identification by it.

According to the present invention, the apparatus structure for analysis has a scanning probe microscope having a probe, and an ion detector together with a means for applying a voltage to the probe. As a means for desorbing the electric field from the device, it is considered to have a counter electrode or to arrange a pulse laser device. Furthermore, by using a multi-anode for the ion signal extraction unit, and by providing an angle-focusing reflectron and a long-focus electrostatic lens for focusing ions, it is possible to perform analysis with higher accuracy.

Hereinafter, the analysis method and apparatus of the present invention will be described in more detail with reference to examples.

[0014]

EXAMPLE 1 FIG. 1 of the accompanying drawings schematically illustrates an analyzer of the present invention. In this example, the probe (12) of the scanning tunneling microscope (1) is, for example, a tip of a tungsten wire having a diameter of 0.5 mm, which is sharpened by electrolytic polishing, and the radius of curvature of the tip is about 50 nm. This probe (1
2) is controlled by the piezo drive mechanism (15) in the X, Y, and Z directions, and of the vibration isolation mechanism (16) using viton rubber so as to face the sample (13) attached to the sample holder (14). It is listed above. On the other hand, the probe (1
2) At a position separated by a distance l, for example, two stacked microchannel plate electron multiplier plates (hereinafter, MCP) (21) with an effective diameter of 75 mm and a fluorescent screen (2
Install the ion detector consisting of 2). More than that
Along with the sample back-and-forth moving mechanism (41) and the ion detector up-and-down moving mechanism (42), an ultra-high vacuum chamber (43) having a diameter of 25 cm and a length of 40 cm held in an ultra-high vacuum of, for example, 10 ⁻⁷ Pa or less. It is contained. In order to detect one or several ions that have been desorbed from the probe (12) by an electric field, an ultrahigh vacuum atmosphere in which the scattering of ions by a gas can be ignored.

The scanning tunneling microscope (1) is a scanning tunneling microscope controller (1) located outside the ultra-high vacuum chamber (43).
7). When the switch (30) is tilted to the controller side, the atomic arrangement on the surface of the sample (13) can be drawn, or the probe can be moved to rest on the designated atom. On the other hand, a positive DC high voltage power source (23) installed outside the ultra high vacuum chamber (43) and a high voltage dividing resistor (3)
According to 1), a voltage of 2 kV is applied between the front surface and the back surface of the two MCPs (21) of the ion detector, and a voltage of, for example, 3 kV is applied between the back surface of the MCP (21) and the fluorescent screen (22). When any element from one hydrogen atom to a heavy atom collides with the surface of MCP (21) with an energy of 1 keV or more, an electric pulse with a wave height of several mV or more is generated at the terminal connected to the fluorescent screen. This electrical pulse
After being amplified by the preamplifier (27) through the DC voltage blocking capacitor (33), it is detected in the time-of-flight mass spectrometry system (26).

Further, in the example of FIG. 1, another positive voltage source (24) and a positive pulse voltage generator (2) are used.
5) is provided so that the output in which these outputs are superimposed can be given to the probe (12) by switching the switch (30). For example, the output voltage from the positive DC high voltage power supply (24) can be varied in the range of 0 to +10 kV, and the output pulse waveform of the positive pulse voltage generator (25) can be varied in the range of +0.4 kV to +4 kV. ing. A voltage signal proportional to each of the DC high voltage and the pulse wave height is sent to the mass spectrometry system (26) by the time-of-flight method and used to calculate the mass of the atom. Generation of the pulse voltage is detected by the Rogowski coil (29) and the constant fraction waveform discriminator (28), and a time-of-flight measurement start signal is issued to the time-of-flight mass spectrometry system (26).

The procedure for analyzing an arbitrary monoatomic element present on the surface of the sample (13) in the configuration of the above apparatus will be described below. That is, first, the sample holder (14) on which the sample (13) is placed is attached to the scanning tunneling microscope (1).
Attached to the sample holder receiver, switch (30) to the scanning tunneling microscope controller side, set the tunnel current to a small value within the allowable range, and observe it while not disturbing the atomic arrangement on the surface of the analytical sample. To do. Based on this observation result, the sample (1
The atom (12) is attached to the tip of the probe by a method such as moving the probe (12) onto the surface atom of (3) and instantaneously increasing the bias voltage and the tunnel current more than when observing the atomic arrangement.

Next, the probe (12) is fully retracted to avoid collision with the sample, and the sample holder (14) is removed from the scanning tunneling microscope (1) and placed outside the ion flight space. The switch (30) is switched to adjust the output voltage of the positive DC high voltage power supply (24) and the positive pulse generator (25) (for example, the ratio of the pulse voltage to the DC voltage is 1: 5 to 1: 9). Select the range of, and fix this ratio) Generate a pulse. Each time a pulse is generated, the Rogowski coil (29) picks it up and causes the time-of-flight mass spectrometry system (26) to start timing. If the sample atoms attached to the probe (12) are not desorbed by the electric field, the ion detector does not generate a signal, but when desorbed, the signal sent from the ion detector stops the timing, and the stop signal and start signal Is recorded as the flight time of the desorbed ions. For example, the mass spectrometry system of this embodiment can measure the flight times of up to eight desorbed ions with one start signal. Since there is a clear correlation between the ease of electric field desorption of attached atoms, the electric field strength at the tip of the probe, and the applied voltage to the probe,
By first lowering the voltage applied to the probe and gradually increasing the voltage applied while generating a pulse, it is possible to prevent detection failure of attached atoms. Actually, the ratio of the pulse voltage to the DC voltage may be out of the above range without any problem, but if the attached atoms are desorbed only by the DC voltage during the pulse pause, the flight time cannot be measured, and this atom is Analysis will be missed. The electric field is not desorbed only by the DC voltage (that is, while the pulse is stopped), and the desorption is caused only when the pulse voltage is superimposed.

In the apparatus of this example, the longer the flight distance 1 or the shorter the pulse width of the pulse current applied to the probe (12) for desorbing the attached atoms, the higher the mass resolution. For example, when the flight distance 1 is set to 10 cm and the pulse width is set to 5 ns, and Δm is the half width of the peak at mass m, the obtained mass resolution m / Δm is about 30. Example 2 FIG. 2 exemplifies an analyzer using a method of desorbing the surface atoms of a sample picked up by a probe using an opposing electrode. In this example, the smaller opening diameter is 4m
m, the larger opening diameter is 25 mm, and the height of the truncated cone is 23
A movable counter electrode (51) made of a hollow frustoconical metal electrode having a size of mm is installed. The angle of the side surface of the truncated cone is adjusted so that the ions desorbed from the tip of the probe fly into the detection effective range of the ion detector. The counter electrode (51) is a counter electrode moving mechanism (5
The position is controlled by 2), and it is several meters in 3 directions of X, Y and Z.
Fine adjustment is made with a stroke of m.

In Example 1, a positive high voltage was applied to the probe (12), but in this example, a negative high voltage is applied to the counter electrode (51) while maintaining the ground potential. Therefore, the first embodiment
The positive polarity DC high voltage power supply (24) and the positive polarity pulse voltage generator (25) of
4) and a negative pulse voltage generator (55). The characteristics such as the variable range of the output voltage are the same. As a result, there is no need to switch the circuit to the probe (12), the switch (30) of the first embodiment is unnecessary, and the original configuration of the scanning tunneling microscope (1) is always maintained.

The surface of the MCP (21) is, for example,
In order to set the fluorescent screen (22) at 5 kV to the ground potential, the positive DC high voltage power supply (23) of Example 1 is replaced with the negative DC high voltage power supply (53). As a result, the preamplifier (27) can be directly connected to the fluorescent screen (22) of the ground potential, and the DC voltage blocking capacitor (3
Since 3) is unnecessary, improvement of high frequency characteristics can be expected. Furthermore, regardless of the desorption voltage of the atom on the probe surface, that is, the potential of the counter electrode, the energy of the ions incident on the ion detector is always 5 keV, which greatly contributes to the operational stability of the device.

However, in this embodiment, the space in which the ions of the attached atoms desorbed from the probe (12) fly is not an electric field-free space, and the above formula for calculating m / n is assumed, assuming uniform velocity motion. Will not do. Therefore, in this example, the computer simulation of the behavior of the charged particles in the electrostatic field is performed to change the m / n value and the counter electrode potential V variously, and the flight time t in that case is obtained to create a correspondence table, From the flight time t and the counter electrode potential V of the analysis result, the value of m / n is determined in reverse by the correspondence table. In addition, since no magnetic field is used in the device, if the potential, time, mass, etc. are described by the normalized dimensionless quantity due to the property of the electrostatic field, the normalized time obtained by simulation for one case can be obtained. Just by multiplying by a constant, the flight time of ions of any mass can be obtained at once.

Therefore, the procedure for elemental analysis of arbitrary atoms existing on the surface of the sample (13) will be described below. That is, first, the sample holder (14) on which the sample (13) is placed is attached to the sample holder receiver of the scanning tunneling microscope (1), and the tunnel current value is set small within the allowable range.
Observe with care not to disturb the atomic arrangement on the surface of the analytical sample. Based on this observation result, the probe (12) is moved onto the surface atom for which element identification is desired, and the bias voltage or tunnel current is instantaneously increased by a method such as that when observing the atomic arrangement. Pick up on the tip of the needle.

Next, the probe (12) is fully retracted to avoid collision with the sample, and then the sample holder (14) is removed from the scanning tunneling microscope (1) and placed outside the ion flight space. The counter electrode (51) is inserted into the opening from which the sample holder (14) has been removed by the counter electrode moving mechanism (52) and fixed at a position several mm in front of the probe (12). Since the counter electrode (51) applies a high voltage for desorbing the attached atoms to the electric field, it should not come into contact with the sample holder opening at ground potential.

While adjusting the output voltage of the negative DC high voltage power supply (54) and the negative pulse generator (55) (for example, the ratio of the pulse voltage to the DC voltage is selected in the range of 1: 5 to 1: 9, Generate a pulse (fix this ratio).
The flight time of the ions desorbed by the electric field by the counter electrode (51) is measured based on the generation of the pulse, and the mass spectrometry is performed based on the flight time t in the same manner as in Example 1 to identify the element.

In this example, the counter electrode potential is actually -1.
At 2 kV, trivalent ions of tungsten and silicon 2
The median time of flight of valence ions is 510 ns,
It was 240 ns. The mass resolution determined by the breadth of the flight time distribution was the same as in Example 1. Embodiment 3 FIG. 3 shows an example of the device of the present invention which uses a pulse laser having a short pulse width to desorb sample surface atoms picked up by a probe. That is, different from the first and second embodiments, two mutually independent changes are added. These two changes are: -a pulse laser with a short pulse width was used-a signal output part of the ion detector was changed. By making these changes, the effect of improving the mass resolution becomes more remarkable.

In this example, when the atoms picked up on the surface of the probe (12) are desorbed by the electric field for the time-of-flight mass spectrometry, the third harmonic (wavelength 355 nm) of the Nd-YAG laser is detected. Only the tip of the needle (12) is focused and irradiated. Therefore, the positive pulse voltage generator (25) of the first embodiment is removed, and only the positive DC high voltage power supply (24) is connected to the probe (12) via the switch (30). On the other hand, outside the ultra-high vacuum chamber (43), a pulse laser (61) (Nd-YAG, pulse width 35 ps,
An energy (5 mJ per pulse of triple harmonic) is installed, and a pinhole (62), a convex lens (63) and a sapphire vacuum window (64) are used to probe a laser beam (12).
Irradiate the tip of. Then, the laser light that is focused on the tip of the probe (12) and diverges again is an ultra-high vacuum chamber (43).
Instead of being reflected and scattered by the inner wall of the, the other sapphire vacuum window (65) escapes to the outside of the ultra-high vacuum chamber. The pinhole (62) is for reducing the power of the laser with which the probe (12) is irradiated. The slight reflection of the laser light on the surface of the sapphire window (64) on the incident side is captured by the biplanar discharge tube (66), and the output signal is used for the time-of-flight mass spectrometry system (26).
Start timing.

Further, in the ion detector of this example, the structure of the ion detection signal extracting portion is different from those of the first and second embodiments, and a multi-tube having the concentric annular aluminum vapor deposition electrode shown in FIG. 4 is used instead of the fluorescent screen. Anode (6
7) is used. The width of each of the eight rings is determined so that the anode areas are the same for convenience. The signals output from the respective annular parts pass through a DC voltage blocking capacitor (33) and a preamplifier (27) which are independent of each other,
The time-of-flight mass spectrometry system (26) is stopped. The mass spectrometry system (26) by the time-of-flight method of this device is such that the ion on which annular anode on the detector is
It can recognize when it is incident.

The procedure for analyzing an element of an arbitrary atom existing on the surface of the sample (13) is as follows. That is, first, based on the result of observing the sample (13) with the scanning tunneling microscope (1), the sample (1
The probe (12) is moved onto the surface atom of 3), and this atom is attached and picked up on the tip of the probe. Then the probe (1
The sample holder (14) is removed from the scanning tunneling microscope (1) after the 2) is fully retracted to avoid collision with the sample, and is placed outside the ion flight space.

Next, the switch (30) is switched to the positive DC high voltage power supply (24). The process of irradiating the probe (12) with a laser pulse and gradually increasing the DC voltage applied to the probe (12) and repeating the process of confirming the arrival of ions by measuring the flight time is repeated. When the voltage of the probe (12) reaches the detachment voltage of the attached atom (it depends on the type of attached atom and other factors), the ionization and desorption of the attached atom occurs and the ion detector detects it. You can

In this example, the mass resolution in element identification is improved as compared with Examples 1 and 2. The reason can be considered as follows. In mass spectrometry by the time-of-flight method, the shorter the pulse width, the higher the mass resolution, but it is difficult to make the pulse width shorter than 5 ns with a high-voltage electric pulse. Therefore, it is easy to generate a strong optical pulse of picosecond or less. A laser beam that can be generated is used. of course,
Applying a DC voltage to a metal probe of tungsten, etc.
The mechanism of electric field desorption upon irradiation with a pulse is based on the rise in the probe temperature due to the absorption of laser energy, so even if the pulse width becomes short, the mass resolution is simply improved by that proportion. It doesn't.

Further, in this embodiment, a DC voltage is applied to the extent that electric field desorption does not occur at normal temperature,
The absorption of the laser light causes the temperature of the probe to rise, and the electric field desorption occurs only when the applied DC voltage exceeds the electric field desorption voltage value at that temperature. With this arrangement, after the pulse irradiation, the temperature of the tip of the probe returns to the normal temperature due to the heat dissipation to the shaft of the probe, but the temperature of the tip of the probe rises and falls by the laser beam with the pulse width of 35 ps, and it takes 1 ns.
It is considered that it takes some time, and there is a possibility that the electric field will be desorbed at any time during this period. In order to rapidly raise and lower the temperature, laser light is irradiated only on the smallest possible area at the tip of the probe.

In the mass spectrometry by the time-of-flight method, it is premised that the flight distance l is constant, but as in the embodiments shown so far, the effective diameter 7 is set at the position where the flight distance is 10 cm.
With a structure with a 5 mm ion detector, it is possible to detect all the atoms attached to a large area on the probe surface.
Flight distance of ions incident on the center of the ion detector (10c
There is a difference of 6.8% between m) and the flight distance (10.68 cm) of the ions incident on the outermost periphery of the ion detector. In Examples 1 and 2, there is a variation of 6.8% in the flight time between the ions having the same mass entering the center of the detector and the ions entering the outermost part of the detector, which is a factor that reduces the mass resolution. It was one, but in this example,
The radius of the incident point on the detector is recognized by the multi-anode (67), and the value of the flight distance l is calculated for each annular anode in the mass calculation formula m / n = a · V · (t / l) ^2. Changing.

With the above-mentioned improvement, in this example, the mass resolution m / Δm for elemental identification could be increased to 100 without changing the flight space length that affects the compactness of the ultra-high vacuum chamber. Example 4 FIG. 5 shows a secondary ion mass spectrometer (SIM) having the highest mass resolution among surface analyzers currently in practical use.
3 is a schematic view of a monoatomic elemental analyzer according to the present invention having a mass resolution equivalent to that of S).

In this example, a long focus type electrostatic lens (72) is arranged immediately before the probe (12), and ions desorbing from the tip of the probe (12) with a wide angular spread are narrowed down to converge the angle. It is sent to the incident point of the mold reflectron (71). FIG. 6 illustrates the structure of the long-focus electrostatic lens (72) used in this example. This is a single lens (Einzel lens) built into the sample holder (14) of the scanning tunneling microscope (1).
It was made compact with the goal of being as lightweight and highly rigid as possible so as not to impair the atomic resolution in observation by. The sample holder (14) made of tantalum has two sample fixing claws (87) and a fixing screw (88), and the sample (1
3) Immediately near the position where the sample is fixed, an annular protrusion (8 mm in this case) having a height (0.4 mm in this case) that becomes the surface position of the sample surface.
1) is integrally processed. On the back surface of the sample holder (14), a ring-shaped insulating plate (83) made by Macor is sandwiched,
The stainless steel plate ring (84) which becomes the central electrode of the single lens and the stainless steel plate ring (85) which becomes the end electrodes are fixed by three stainless steel screws (86) for fixing the electrode, and the ion passage opening (82). Is running through. When a single lens is used, the sample holder (14) and the end electrode ring (85) are set to the ground potential, and a voltage that is about half the probe applied voltage and that is linked to this is applied to the center electrode ring (84). Central electrode ring (8
The outer diameter of 4) is smaller than that of the other rings because the central electrode ring (8
This is because the effect of the voltage of 4) is effectively shielded by the end electrode ring (85).

As described above, this embodiment is characterized in that the angle focusing reflectron (71) and the ion focusing long focus electrostatic lens (72) are provided. The reflectron (71) used in the present invention is different from the reflectron used in the conventional time-of-flight SIMS in that no grid is used in the electrostatic mirror section.
Unlike SIMS in which a very large number of sample surface atoms are destructively released and mass spectrometry is performed, in the present invention, it is essential to detect and mass detect one desired atom picked up at the tip of the probe. Therefore, it is not allowed to reduce the transmittance of the reflectron (71) by the grid electrode. Also, if the ions that have left the probe (12) do not enter so as to pass in a predetermined direction, the reflectron (7
Although 1) does not work by design, these conditions will be satisfied by the axis alignment function of the device. However, other consideration is required only for the allowable angle spread, and since the angle spread that can guarantee good time convergence is limited to about 10 degrees even with the angle convergence type reflectron (71),
A long focus electrostatic lens (72) is arranged immediately before the probe (12) to focus the ions desorbed from the tip of the probe (12) with a wide angle spread at the incident point of the reflectron (71). ing.

Also, an angle-converging reflectron (71)
Since the ions are focused by the long focus electrostatic lens (72) for focusing the ions, the ions should ideally be focused at one point. In order to accommodate flexibility, an ion detector having a detection effective diameter of 50 mm is used. Actually, in order to analyze an element of an arbitrary monatom existing on the surface of the sample (13), first, it is desired to identify the element based on the result of observing the sample (13) with a scanning tunneling microscope (1). The probe (12) is moved onto the surface atom, and this atom is attached and picked up on the tip of the probe, and then the sample holder (1
4) is moved laterally to move the probe (12) from the surface of the sample (13) to the center of the ion passage opening (82) of the single lens. The procedure thereafter is the same as that of the other embodiments.

By such an operation, in this embodiment, the mass resolution of m / Δm = about 1000 is actually obtained even by the ionization desorption by the voltage pulse having the pulse width of 5 ns. The isotopes of the elements could be clearly identified. Combining ionization and desorption by a laser pulse with a short pulse width and stable kinetic energy of ions, which is determined only by a direct current voltage, further improves mass resolution, and ²⁹ Si (m / n =
It is considered possible to discriminate between 28.976) and ²⁸ SiH (m / n = 28.985) (mass resolution m / Δm = 3000 is required).

[0039]

As described in detail above, the present invention enables elemental identification of a desired one or a small number of atoms selected by looking directly at the atomic arrangement on the surface of a solid sample in real space. Furthermore, it will contribute not only to elemental analysis of ultrafine areas of materials, but also to elucidation of the mechanism of atomic level surface ultrafine processing and creation of new materials and new materials through such analysis.

[Brief description of drawings]

FIG. 1 is a block diagram showing a single atom elemental analysis device of the present invention.

FIG. 2 is a block diagram showing a monatomic element analyzer according to the present invention using a counter electrode.

FIG. 3 is a block diagram showing a monatomic element analyzer according to the present invention with improved mass resolution.

FIG. 4 is a diagram showing an electrode pattern shape of a multi-anode used in the elemental analysis device shown in FIG.

FIG. 5 is a block diagram showing a monatomic elemental analyzer according to the present invention having extremely high mass resolution.

6 is a view showing the structure of a sample holder incorporating an electrostatic lens for ion focusing used in the elemental analysis device shown in FIG.

[Explanation of symbols]

1 Scanning Tunneling Microscope 12 Tip 13 Sample 14 Sample Holder 15 Piezo Drive Mechanism 16 Vibration Isolation Mechanism 17 Scanning Tunneling Microscope Controller 21 Micro Channel Plate Electron Multiplier (MC
P) 22 Fluorescent screen 23 Positive DC high voltage power supply 24 Positive DC high voltage power supply 25 Positive pulse voltage generator 26 Time-of-flight mass spectrometry system 27 Preamplifier 28 Constant fraction waveform discriminator 29 Rogowski coil 30 switch 31 high resistance for voltage division 32 high resistance for pulse blocking 33 capacitor for DC voltage blocking 34 load resistance 41 sample back-and-forth moving mechanism 42 ion detector up-and-down moving mechanism 43 ultra-high vacuum chamber 51 counter electrode 52 counter electrode moving mechanism 53 Negative DC high voltage power supply 54 Negative DC high voltage power supply 55 Negative pulse voltage generator 61 Pulse laser 62 Pinhole 63 Convex lens 64 Sapphire vacuum window 65 Sapphire vacuum window 66 Biplanar discharge tube 67 Multi-anode 68 Insulating substrate 69 Signal Take-out part 7 1 Angle Converging Reflectron 72 Long Focus Electrostatic Lens 81 Circular Protrusion 82 Ion Passing Opening 83 Circular Insulating Plate 84 Central Electrode Ring 85 End Electrode Ring 86 Electrode Fixing Screw 87 Sample Fixing Claw 88 Fixing Screw

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01J 37/28 Z

Claims (8)

[Claims] 1. In a scanning probe microscope having a conductive probe on its surface, one or more atoms on the sample surface are picked up on the probe surface, and these atoms are desorbed from the probe by an electric field to remove the ions. A method of analyzing a surface of a microscopic area, which is characterized by mass spectrometric analysis from flight time to identify elements. 2. The method for analyzing a surface of a microscopic region according to claim 1, wherein one or a plurality of the picked-up atoms are desorbed by an electric field by a counter electrode. 3. The method for analyzing a surface of a microscopic region according to claim 1, wherein the picked-up one or a plurality of atoms are subjected to electric field desorption by a pulse laser. 4. An analyzer equipped with a scanning probe microscope having a conductive probe on its surface, a means for applying a voltage to the probe, and an ion detector, wherein one surface of the sample is the probe surface. Alternatively, a plurality of atoms are picked up, a voltage is applied to the probe, the atoms are desorbed as an ion by electric field, and the mass of the atom is analyzed from the flight time until it reaches the ion detector arranged in front, and the element identification is performed. An analyzer for a surface of a microscopic area, which is characterized by: 5. The analyzer according to claim 4, further comprising a counter electrode for desorption of an electric field. 6. The analyzer according to claim 4, further comprising a pulse laser device for desorption of the electric field. 7. The analyzer according to claim 4, wherein the ion signal extracting portion is provided with a multi-anode having concentric annular aluminum vapor deposition electrodes. 8. The analyzer according to claim 4, further comprising an angle-focusing reflectron and a long-focusing electrostatic lens for focusing ions.