JPS6363945A - Stabilization of optical property measurement - Google Patents

Abstract

PURPOSE:To measure photoabsorptivity of a thin film on a liquid surface accurately and sensitively, by making an excitation beam irradiate a measuring part of a sample intermittently while several probe beams irradiate it to detect deflection of the probe beam. CONSTITUTION:An excitation beam 5 emitted from an excitation light source 6 is modulated 7 into a light intermittent or varying in the intensity to irradiate a measuring part of a thin film 1 developed on a liquid surface 2 of a liquid tank 4, which causes an intermittent change in the refractive index of the thin film 1 near the beam. On the other hand, probe beams 8a and 8b are made incident into the liquid tank 4 and totally reflected at the irradiation part of the excitation beam 5 on the liquid surface 2 to leave the liquid tank 4. With such an arrangement, the beams 8a and 8b pass through the measuring part at which the refractive index varies intermittently by the irradiation with the beam 5. The optical paths of the beams 8a and 8b are deflected according to the distribution of refractive index thus changed. When the beams 8a and 8b are both made to pass through an area with the refractive index distribution symmetrical with respect to the center of the excitation beam irradiation area, the vector sum of deflection of the probe beam due to variations in the liquid surface is down to zero, thereby enabling the detecting 10 of deflection according to the refractive index.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for optically measuring the physical properties of solids, liquids, and gases, and in particular to optically measuring the properties of a thin film spread on a liquid surface. More specifically, it relates to the measurement of light absorption properties that are the basis of various characteristic analyzes of thin films, such as the characteristic analysis of monomolecular films spread on the liquid surface to be accumulated during the formation of monomolecular cumulative films. It is used for etc.

[Conventional technology]

Conventionally, as a device for measuring the light absorption characteristics of a measured object,
There is a device that determines light absorption characteristics from transmittance or reflectance.

However, when the object to be measured is irradiated with light, there is scattered light in the pool of transmitted light and reflected light, and in order to achieve even higher accuracy, it is important to directly measure the absorption component of light in evaluating light absorption characteristics. becomes.

A photoacoustic spectrometer (Photoacoustic 5 spectrometer) is a device that directly measures absorption components of light.
scope: PAS) and photothermal radiation spectrometer (Photo
thermal radiometry (PTR).

In addition, as a device that directly measures the absorption components of light,
Photothermal deflection spectrometer
m a IDeflection 5pectros
There is a device called copy: PDS). This P
In a DS device, the refractive index changes due to heat generation due to light absorption of the object to be measured, and a temperature distribution in and around the object to be measured.
This makes use of the fact that the light incident thereon is deflected.

That is, the measurement site of the object to be measured is irradiated with excitation light that generates temperature distribution due to heat generation when the light is absorbed and changes the refractive index, and probe light that measures the amount of deflection caused by the excitation light. The light absorption characteristics of the object to be measured are measured from the wavelength of the light and the amount of deflection of the probe light. This device is
The object to be measured and the detection system can be set independently, making it suitable for on-site measurement and remote measurement, and the basic principle of the present invention is the same as that of this PDS device.

Theoretical handling of this PDS device is to solve the heat conduction equation within the object to be measured, and the amount of deflection measured as the deflection angle φ is determined by the excitation light intensity, the temperature coefficient of the refractive index (δn/δT
), the temperature gradient in the region through which the probe light passes (δT/δ
X), etc. A term proportional to the light absorption coefficient of the object to be measured is included in δT/δX). Also (δn/
δT) can take either a positive or negative value depending on the object to be measured, which indicates that the deflection angle can also be positive or negative.

Further, a position sensitive detector (PSD) is often used as a detector for measuring the amount of deflection of the probe light of the PDS device.

FIG. 8 is a vertical sectional view showing an example of the structure of a PDS (position sensitive detector), and FIG. 9 shows its operating principle. PDS(
A position-sensitive detector) is a device that can continuously obtain a position signal that is unrelated to changes in light intensity, and can obtain position signals in both one-dimensional and two-dimensional cases.

Here, according to the operating principle of the PSD, when there are two or more points of light incidence, position signals weighted in proportion to the respective light intensities are obtained. Furthermore, even when the light beam is spread out, a position signal of the center of gravity of the light intensity can be obtained.

On the other hand, conventionally, a monomolecular cumulative film forming apparatus is known in which monomolecular films are layered one by one and transferred to a substrate by a monomolecular film cumulative method called the Langmuir-Prodgett method (hereinafter referred to as LB method) named after the inventor. (New Experimental Chemistry Course 1)
Vol. 8, pp. 498-507, Maruzen).

A monomolecular film is formed using the above device and transferred to a substrate. The above apparatus is as shown in FIGS. 6 and 7.

[Problem that the invention seeks to solve]

In this way, even if a monomolecular film is formed by the above method,
Due to the unique environment of a thin film such as a monomolecular film spread on the liquid surface, the optical properties of this extremely thin object can be measured using PAS@ff, PTR equipment, or PDS instrument T as is. If you try, it will be impossible. Problems arise in that the measurement itself becomes difficult and accuracy and sensitivity tend to decrease.

PAS devices can be divided into microphone type and piezoelectric element type depending on the type of detector, but the microphone type requires the sample to be placed in a sealed sample chamber, and the piezoelectric element type has restrictions on the arrangement of the detector and sample. Therefore, both methods are unsuitable for measuring thin films spread on the liquid surface as they are.

In addition, in the vertical type of PDS device, the probe light passes through the thin film that is the object to be measured, and is simultaneously affected by both the liquid phase and the gas phase, whose refractive index changes based on the thin film's absorption of excitation light. There is a problem with this.

In addition, in the case of a lateral type PDS device, in order to pass through a region where the refractive index change is as large as possible,
It is necessary to bring the probe light close to the thin film on the liquid surface. In particular, since the detector of the PDS device has the property of detecting the position of the center of gravity of the received light intensity, it is preferable that the center of the probe light beam, where the light intensity is strong, be close to the thin film. but,
The center of the probe beam cannot be brought closer to the thin film than the radius of the probe beam, and the center of the probe beam, where the light intensity is strong,
There is a problem that the refractive index tends to pass through a region far away from the thin film where the change in refractive index is weak, making it difficult to measure with high accuracy and sensitivity.

Therefore, it is an object of the present invention to make it possible to accurately and sensitively measure the light absorption characteristics of a thin film spread on a liquid surface, which is extremely thin and under a unique environment.

[Means for solving problems]

The means taken in the present invention to solve the above problems is to intermittently irradiate the measurement site of the sample with excitation light, and irradiate the measurement site or its vicinity with probe light, so that the intermittent excitation light is When measuring the optical physical properties of a sample from the amount of deflection of the corresponding probe light, in a stabilizing method that makes the measurement independent from fluctuations in the sample, two or more probe lights are used, and with respect to the center of the excitation light irradiation area, If a pair of probe lights is irradiated at positions symmetrical to each other, and the amount of variation obtained as a result is due to sample variation, the amount of variation will always be such that the vector sum is always equal to the reference point on the detection surface. If the amount of variation in the probe light due to the change in refractive index due to the excitation light is zero, the deflection direction of the amount of variation is
A method for stabilizing optical physical property measurement is characterized in that optical systems are set so that all the optical systems are oriented in the same direction with respect to a reference point on a detection surface.

[Effect]

When the excitation light is absorbed by the thin film that is the sample, the refractive index of the measurement site and its vicinity changes between when the excitation light is irradiated and when it is not irradiated. By detecting this as the amount of deflection of the probe light, the light absorption can be detected. Characteristics can be measured. This P
A feature of the principle of the DS method is that the PDS output ultimately obtains a signal at the center of gravity of the light intensity distribution.

FIG. 1 is a coordinate diagram illustrating the basic principle of the stabilization method according to the present invention. In FIG. 1(a), mutually orthogonal X-Y coordinate axes are set on a plane perpendicular to the average emission direction of the light beam reflected from the sample surface, and the amount of deflection of the reflected light is indicated by arrow 112. has been done.

If the above coordinate system is inverted using the required optical system, the projected diagram will be X'-Y as shown in Figure 1(b).
', and the amount of deflection of the reflected light also becomes as shown by arrow 113. When these mutually inverted light beams are irradiated onto the target irradiation surface, their coordinates become point symmetrical (112a, 113a) with respect to the origin O, as shown in FIG. 1(C), and the intensity of both light beams increases. are equal, the light beam and
The center of gravity of energy always coincides with the origin O. Therefore, if an optical system that satisfies the above conditions is used, even if sample surface fluctuations occur due to external factors, the center of intensity of the irradiation beam will be compensated for without being affected.

FIG. 2 is a schematic configuration diagram of a basic device for one-dimensionally verifying the effect based on the above principle, in which two laser light sources 9a
, 9b are irradiated onto areas close to each other on the sample surface 1, and the separated two pairs of light beams are sent to mirrors 26, 9b.
27, 28, etc., respectively, to the optical position detector 10 to record the fluctuation of the sample surface l. FIG. 3 is a graph showing the measurement results of the amount of positional deviation of the light beam with the above configuration, where the vertical axis indicates the detection position P of the light beam,
The horizontal axis indicates time t.

In Fig. 3, one light beam is directly transmitted to the optical position detector 1.
When irradiating to 0, the fluctuation of the sample surface l is recorded as shown in Fig. 3(a), and when compensated by the present invention, the fluctuation of the sample surface is removed and stable as shown in Fig. 3(b). I can see that you are doing it.

On the other hand, it has been theoretically and experimentally confirmed that the PDS signal is as follows depending on the relationship between the excitation light irradiation area and the probe light irradiation position.

If the excitation light is intermittent and the excitation light modulation of the amount of deflection of the probe light and the synchronous component are synchronously detected using a lock-in amplifier, etc., as shown in Fig. An amplitude signal is obtained that is symmetrical and reaches a nearly maximum at the edge of the excitation light irradiation region, and then decreases exponentially thereafter. Note that the phase signal is inverted (shifted by 180°) at the center of the excitation light irradiation area.

Therefore, in the present invention, a pair of probe light beams are irradiated symmetrically with respect to the center of the excitation light irradiation area and are deflected toward each other. Since variations in the sample surface cause both probe beams to be deflected in the same direction, if the above-mentioned sample surface variation compensating optical system is used, only the sample surface variations can be removed.

In this way, the present invention absorbs the effects caused by fluctuations in the sample into the vector sum by irradiating the sample with multiple light beams from the probe light source, and the greater the number of probe lights, the greater the effect. becomes certain.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a configuration diagram showing an example of a monomolecular cumulative film forming apparatus in which the present invention is implemented.

In FIG. 4, reference numeral 4 denotes a liquid tank containing a liquid 3, and a thin film 1, which is an object to be measured, is spread on the liquid surface 2 of the tank. The illustrated thin film 1 is a schematic representation of a monomolecular film.

Probe light sources 9a and 9b are located slightly below the side of the liquid tank 4.
is provided. From the probe light sources 9a and 9b, probe lights 8a and 8b are emitted from the liquid 3 side toward the measurement site of the thin film 1 at an angle at which the probe lights 8a and 8b are totally reflected by the liquid surface 2 on which the thin film 1 is spread.

Further, a detector 10 is provided at a position facing the probe light sources 9a and 9b with the liquid tank 4 in between, for detecting the position of the probe light 8 sent thereto. The probe beams 8a and 8b are arranged by mirrors 26, 27, 28 so as to mutually compensate for fluctuations in the liquid level 2 caused by external factors on the light receiving surface of the detector 10 based on the aforementioned principle. The signal from this detector IO is sent to a lock-in amplifier 12 via a driver 11.

An excitation light source 6 is provided above the liquid tank 4.

The excitation light source 6 irradiates excitation light 5 toward the measurement site of the thin film 1 . A light intensity modulator 7, such as a chopper or a variable filter, is provided at a position along the optical path of the excitation light 5 to make the excitation light 5 into intermittent light or to irradiate the light with varying intensity. Further, the excitation light 5 is further focused by a lens 13 and irradiated onto the measurement site of the thin film 1. FIG. 4(B) is an enlarged view of the excitation light and probe light irradiation parts in FIG. 4(A). In the diagram (b) in FIG. 4 (B) viewed from the direction perpendicular to the film surface, it is shown as an oval shape elongated in the direction of the probe light incident surface.

The light intensity modulator 7 is connected to a lock-in amplifier 12, and uses the signal from the light intensity modulator 7 indicating intermittent or strong/weak edges of the excitation light 5 as a reference signal to synchronously detect the signal from the detector 10. It is now possible to do so. Probe light sources 9a and 9b, excitation light source 6, optical intensity modulator 7, and lock-in amplifier 12 are each connected to measurement controller 14. The measurement controller 14 controls the optical path and wavelength of the probe lights 8a and 8b and the excitation light 5, as well as the intermittent or intensity interval of the excitation light 5 by the optical intensity modulator 7, and also controls the optical absorption characteristics by a signal from the lock-in amplifier 12. is calculated.

The liquid tank 4 does not need to be entirely transparent as long as a transparent window is provided in the optical path of the probe lights 8a and 8b and the excitation light 5. If the absorption is small for 5, the probe light 8
It is preferable that the material be transparent, although it will not have much of an adverse effect on the measurement even if it has a direct effect on the material.

First, the excitation light 5 emitted from the excitation light source 6 is modulated by the light intensity modulator 7 into intermittent or variable intensity light to measure the thin film 1 spread on the liquid surface 2 of the liquid tank 4. Irradiate the area. In the area on the measurement site where the excitation light 5 is irradiated, the thin film 1 on the liquid surface 2 absorbs the light and generates heat intermittently or with varying degrees of intensity due to a non-radiative radiation process.
Changes in the refractive index in the vicinity occur intermittently.

On the other hand, the probe lights 8a and 8b emitted from the probe light sources 9a and 9b are incident on the liquid 3 with an incident angle larger than the critical angle of the liquid 3, are totally reflected at the excitation light 5 irradiation site on the liquid surface 2, and are totally reflected in the liquid 3. It passes through the inside and exits to the outside of the liquid tank 4. Therefore, the probe lights 8a and 8b pass through a measurement site whose refractive index changes intermittently due to the irradiation with the excitation light 5. The probe light 8a emitted from the probe light sources 9a and 9b defines the region where the refractive index changes intermittently.
and 8b pass, depending on the changed refractive index distribution,
The optical path will be deflected. If the probe beams 8a and 8b are passed through regions with refractive index distributions that are very close to each other and symmetrical about the center of the excitation light irradiation region, the mirrors 26, 27, and 28 will prevent the probe beams from changing due to changes in the liquid level. The vector sum of the amount of variation becomes zero, and the amount of deflection corresponds only to the refractive index distribution due to excitation light irradiation.

The detector 10 continuously receives the probe lights 8a and 8b, and adjusts the receiving position of the probe lights 8a and 8b to the driver 11.
The signal is sent to the lock-in amplifier 12 via. The lock-in amplifier 12 receives the signal from the detector 10 and the signal from the optical intensity modulator 7 at the same time, and by synchronizing both signals, the lock-in amplifier 12 receives the signal from the optical intensity modulator 7, and by synchronizing both signals, the lock-in amplifier 12 receives the signal from the optical intensity modulator 7. The difference between the light receiving position signals of 8a and 8b and the light receiving position signals of probe lights 8a and 8b when the excitation light 5 is not irradiated or when the intensity is low is converted into an S/N ratio (sent to the measurement controller 14).

Based on this sent signal, the measurement controller 14 adjusts the probe lights 8a and 8 for the wavelength of the excitation light 5 at that time.
The amount of deflection of b is determined, and the light absorption characteristics are calculated based on this. Further, by performing similar measurements while sequentially changing the wavelength of the excitation light 5, the spectral absorption characteristics of the thin film 1 can be obtained.

In this measurement, the measurement site can be freely selected by adjusting the optical path of the excitation light 5 with the measurement controller 14, and the probe light 8 can be selected with the measurement controller 14 depending on the position of the liquid surface 2.
The optical paths of a and 8b can be adjusted for accuracy.

Also, probe light sources 9a and 9b.

It is also possible to automatically make all necessary adjustments to the excitation light source 6 and the light intensity modulator 7 by the measurement controller 14, thereby simplifying the operation.

The light energy absorbed by the thin film 1 is determined from the light intensity distribution of the excitation light 5 at the measurement site, the characteristics of the refractive index change due to heat of the liquid 3, the incident beam positions of the probe lights 8a and 8b, and the amount of deflection at that time. Therefore, the thin film 1 of the excitation light 5
By monitoring the irradiation energy with a photosensor or the like, the absolute light absorption characteristics of the thin film 1 can be obtained from both. Then, by changing the wavelength of the excitation light 5,
Absolute spectral absorption characteristics are obtained. Moreover, the relative spectral absorption characteristics can be obtained by simply determining the relative intensity of the excitation light 5 at each wavelength in advance and determining the amount of deflection of the probe lights 8a and 8b corresponding to the wavelength. The relative value and absolute value of the light absorption characteristic may be appropriately selected depending on the purpose of measurement.

Incidentally, the structure around the liquid tank 4 is similar to that of a conventional monomolecular cumulative film forming apparatus using the LB method, and this will be explained with reference to FIGS. 6 and 7.

The liquid tank 4 has a wide and shallow rectangular shape, and an inner frame 16 made of polypropylene or the like is suspended horizontally inside the tank 4 to partition the liquid level 2. As the liquid 3, pure water is usually used. Inside the inner frame 16, a film forming frame 17 made of, for example, polypropylene is floated. Film forming frame 1
7 is a rectangular parallelepiped whose width is slightly shorter than the inner width of the inner frame 16;
The piston is capable of two-dimensional movement in the left and right directions in the figure. A weight 18 is connected to the film forming frame 17 via a pulley 19 for pulling the film forming frame 17 to the right in the figure. Further, there are provided a magnet 20 fixed on the film forming frame 17 and counter magnets 21 which are movable from side to side in the figure above the film forming frame 17 and repel each other when approaching the magnet 20. Accordingly, the film forming frame 17 can be moved from side to side in the figure and stopped. Instead of such a weight 18 or a set of magnets 20, 21, there is also a method in which a rotary motor or a pulley is used to directly move the film forming frame 17.

Suction nozzles 2 are connected to a suction pump (not shown) via a suction pipe 22 on both sides of the inner frame 16.
3 are lined up. This suction nozzle 23 quickly removes unnecessary monomolecular films from the previous process on the liquid surface 2 in order to prevent impurities from being mixed into the monomolecular film or monomolecular cumulative film. It is used for. In addition, 15
is a substrate attached to the substrate holder 24 and vertically moved up and down.

The principles of forming a monomolecular film and obtaining the cumulative film using the above-described monomolecular cumulative film forming apparatus are basically the same as those of the conventional method.

First, the film forming frame 17 is moved to sweep up unnecessary monomolecular films and the like on the liquid surface 2 while sucking them out from the suction nozzle 23 to purify the liquid surface 2. Next, the film forming frame 17 is placed in the liquid tank 4.
After dropping the film constituent material on the liquid surface 2, moving the film forming frame 17 to narrow the development area and forming a solid film, the substrate 15 is moved up and down to spread the formed monomolecular film. Just transfer it.

By the way, in the apparatus according to this embodiment, as explained in FIG. 4, the physical properties of the thin film 1, which is a monomolecular film spread on the liquid surface 2, can be directly measured on the spot optically. .

Therefore, if the movement of the counter magnet 21, that is, the movement of the film forming frame 17, is controlled by the measurement controller 14 based on this measurement from the formation of the monomolecular film to the completion of its transfer,
A monomolecular film having desired physical properties can be reliably accumulated on the substrate 15.

〔Effect of the invention〕

According to the present invention, the physical properties of a thin film developed on the liquid surface can be accurately known by measuring the light absorption characteristics with high precision and high sensitivity. It is possible to obtain a monomolecular cumulative film with extremely high To provide a method for stabilizing optical physical property measurement by controlling the system or light source to obtain stable measurement results that are not affected by sample fluctuations caused by, for example, fluctuations in the liquid surface in which a monomolecular film as a sample is developed. Can be done.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a block diagram of a basic device based on the principle, Fig. 3 is a graph of measurement results, Fig. 4 is a block diagram of an embodiment of the present invention, and Fig. 5 is the irradiation light position and PD
FIGS. 6 and 7 are diagrams showing the relationship between S signals, FIGS. 6 and 7 are explanatory diagrams of a monomolecular cumulative film forming apparatus, and FIGS. 8 and 9 are diagrams explanatory of a PSD element. l: object to be measured, 2: liquid level, 3: liquid, 4. liquid tank, 5: excitation light, 6: excitation light source, 7: light intensity modulator, 8 niblob light, 9 niblob light source, 10: detector, lt driver, 12: lock-in amplifier, 13: lens, 14: measurement controller, 15: substrate, 17: film forming frame, 2・l: substrate holder, 25: optical path adjuster, 26, 27, 28, 29 ,30
:Mira.

Claims (2)

[Claims] (1) When excitation light is intermittently irradiated onto the measurement site of the sample and probe light is irradiated onto the measurement site, and the optical properties of the sample are measured from the amount of deflection of the probe light corresponding to the intermittent excitation light. A stabilization method that makes measurements independent of sample fluctuations uses two or more probe lights and irradiates pairs of probe lights at symmetrical positions with respect to the center of the excitation light irradiation area. Among the amount of variation, if the amount of variation is due to the variation of the sample, the amount of variation is an optical physical property characterized by having an optical system set so that the vector sum is always zero with respect to a reference point on the detection surface. Measurement stabilization method. (2) The stabilization method for optical physical property measurement uses two or more probe lights to irradiate pairs of probe lights at symmetrical positions with respect to the center of the excitation light irradiation area, and the amount of fluctuation obtained as a result. Among them, if the amount of variation in the probe light due to a change in the refractive index due to the excitation light, the optical system is set so that the deflection direction of the amount of variation is all in the same direction with respect to the reference point on the detection surface. A method for stabilizing optical physical property measurement according to claim 1.