JPS6058820B2 - Surface analysis method for transparent materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface analysis method in a total reflection Raman method that utilizes the phenomenon of total reflection of light at the interface between two transparent materials having different refractive indexes.

Figure 1 is a diagram showing the principle of total internal reflection. Conventionally, when a ray of light enters a substance A with a large refractive index into a substance B with a small refractive index at the interface between two transparent substances, the angle is larger than the critical angle. It is known that light incident on an interface is totally reflected without being refracted.

Furthermore, during this total reflection, from a microscopic perspective, it is also known that the incident light is not completely reflected at the interface between two materials, but enters material B, which has a lower refractive index, by a certain depth from the interface. .

The light beam that passes through substance B (the part shown by the dotted line in Figure 1) generates scattered light originating from the molecules or molecular aggregates that constitute substance B, so if this scattered light is spectrally measured, it is possible to A Raman spectrum is measured depending on the type or structure, and the molecular type or molecular state of the portion near the surface of substance B can be determined.

Here, the high refractive index material A that enables total reflection of light at the contact interface with material B due to close contact is called an internal reflection element plate. The distance that light passes through is much larger than that in substance B, which is the object of analysis.

Therefore, in the case of Raman spectroscopy, the Raman scattering of the internal reflective element plate and its background must be sufficiently small in order for the internal reflective element plate to not become a hindrance.

A conventional total internal reflection Raman method is a surface analysis method for transparent materials that utilizes this principle.

Regarding this conventional total internal reflection Raman method, for example, Applied Optics
, Vol. T, page 197, page 2236.

According to this description, the light source has a wavelength of 632.8 nm (7)
A He-Ne laser is placed on an internal reflection element plate with a refractive index of 1.
．． Measurements of total reflection Raman spectra of carbon disulfide have been reported using No. 713 flint glasses.

The purpose of this report is to investigate whether the Raman spectrum of substance B can be measured by the total reflection phenomenon of light, and carbon disulfide, which is a liquid, is used as a sample.

However, in this report, as described in the comparative example below, the Raman peak due to the sample is
This result was at a level that could be recognized as a signal, and the results suggested that the total internal reflection Raman method could not be used as a surface measurement method. The main reason for this is thought to be that flint glass, which has relatively strong background scattering, was used for the internal reflection element plate.

Therefore, in order to improve such conventional drawbacks, the present inventors conducted extensive studies and completed the present invention by focusing on the use of sapphire as a high refractive index material.

An object of the present invention is to provide an accurate method for analyzing the surface of a material that can be applied to a wide range of transparent materials.

The method of the present invention for achieving such an object includes: closely contacting an internal reflection element plate made of sapphire to a transparent material; A laser beam is incident on the internal reflection element plate, and the laser beam is totally reflected at the contact interface. At this time, the scattered light generated by the laser beam that enters the transparent material is separated to obtain the Raman spectrum of the transparent material. This is a method for analyzing the surface of a transparent material, which is characterized by recording.

Hereinafter, the method of the present invention will be specifically explained with reference to the drawings.

FIG. 2 is a schematic diagram of the method of the invention. First, an internal reflection element plate 2 made of sapphire is closely attached to a transparent substance 1,
Laser light 3 is incident on internal reflection element plate 2.

At this time, the laser beam is incident at an angle of incidence such that it is totally reflected at the interface between the internal reflection element plate 2 and the transparent material 1. When the laser beam 3 is incident, it is refracted and reaches the contact interface 4 between the internal reflection element plate 2 and the transparent material 1 at an angle larger than the critical angle, and is totally reflected at point C.

As shown in FIG. 1, since the point C penetrates the transparent material 1 to a certain depth microscopically, the molecules constituting the transparent material 1 or Scattered light 5 containing Raman light from molecular aggregates is generated.

This scattered light 5 is separated by a Raman spectrometer 7 through a condensing lens 6, and the Raman spectrum of the transparent material 1 is recorded.
From this spectrum, it is possible to know the molecular species or molecular state of the portion of the transparent material 1 that is close to the surface.

The present inventors have discovered that titanium dioxide, strontium titanate,
Many materials, including various types of flint glass, were considered for the internal reflective element plate, but these were approximately 15
00c "It had the drawback of having strong Raman scattering in the wave number region below 1, and was not sufficient.

As a result of continued careful consideration, the sapphire was determined to be 760 cm.
It was discovered that there was almost no Raman scattering above -1, and the background was very weak, and the present invention was succeeded for the first time by using this as an internal reflection element plate. A feature of the method of the invention is therefore the use of internal reflective element plates made of sapphire.

As shown in Figure 3, sapphire is a single-crystal alumina belonging to a hexagonal crystal system, is colorless and transparent, and has a refractive index of 1.76-1.
The range is 78. Furthermore, because of the polarization of sapphire's own Raman spectrum and the ability to use the Raman peak of sapphire as a standard, it is desirable that the internal reflection element plate be a sapphire plate cut in the direction of a specific crystal axis. The shape of the internal reflection element plate made of sapphire is not particularly limited, but to give an example, the fourth
A flat plate with one end cut at a specific angle as shown in Figures A and B, and the L, M, N, and P surfaces other than the side surfaces optically polished, or Figure 4 C
, D has a semi-cylindrical shape with optically polished Q and R surfaces.

For cutting out the axes and planes, for example, the major axis direction in the two examples shown in FIG. (see figure), but is not limited to this. The smoothness of the M or Q surface that is brought into close contact with the sample is particularly important. The cut angle at one end of the flat internal reflection element plate is not limited to a specific value, but can be selected as an appropriate angle depending on the refractive index of the transparent material for analysis.

Usually, total reflection Raman spectra measured by the method of the present invention include the material of the internal reflection element plate, and the like. In other words, the Raman spectra of sapphire are measured in an overlapping manner.

However, sapphire has its main Raman peak at 760 cm
80, which is important for measuring normal transparent materials.
There are almost no Raman peaks in the 0 to 3100 cm-1 region. In addition, the background in this region is very weak, so the background of sapphire itself hardly poses any problem in measurement. However, in order to use the total internal reflection Raman method as a surface measurement method, the background scattering of sapphire as an internal reflection element must be made sufficiently smaller than the signal of the actual sample.

Suitability of the internal reflection element is determined by relative comparison of the Raman signal of the sample and background scattering.
Actually, as described in Examples 1 to 5 described later, 800
In the ~4000 cm region, the background scattering of sapphire is so small that the signal from the 60A thick polystyrene thin film can be sufficiently separated and measured (Example 3, Figure 10), and the internal scattering for surface measurement is small. It was recognized that it is fully suitable as a material for reflective elements.

Also, Ar5l4.5nm! Approximately 1700 in Noza Hikari
cm-1 or more, Ar'488.0 nm laser light has a background due to fluorescence originating from sapphire at about 3100 cm-1 or more, but by further shortening the wavelength of the laser light, it can be reduced to 4000 cm-1. It becomes possible to measure the wavenumber range of .

In addition, as mentioned above, if the direction of the cutting axis of the internal reflection element plate and the polarization direction of the laser beam as a light source are clearly defined, the Raman peak of sapphire can be adjusted to the standard peak (intensity, wave number) in the total reflection Raman spectrum. ) can be used as

In addition, since the refractive index of sapphire is 1.76 to 1.78, which is larger than that of most organic and inorganic substances, the incident angle is larger than the critical angle determined from the refractive index of sapphire and these organic and inorganic substances. Laser light can be incident on the interface between the two at the corner, causing total internal reflection.

Furthermore, the transparent substance in the method of the present invention is an analytical sample to be measured, and its refractive index is 0. The material may be either solid or liquid as long as it is small in size and transparent, but a material that does not contain a coloring component, especially a fluorescent material, is preferable.

When the transparent substance is a liquid, the Raman spectrum of the solid-liquid interface can be measured by using a sapphire internal reflection element plate in the liquid cell. In the method of the present invention, close contact between the internal reflection element plate and the analysis sample is particularly important.

However, since sapphire has high hardness and excellent mechanical strength, for example, if a solid transparent substance is brought into contact with the optically polished surface of an internal reflection element plate made of sapphire, and this is appropriately tightened, the element plate and the transparent Can be in complete contact with substances. In addition, since the beam diameter of the laser beam is small (4). 3 mfn or less), a relatively small adhesion area (10 mfn or less) is sufficient, and there are no measurement difficulties caused by the degree of adhesion. As mentioned above, the laser light enters the transparent material during total reflection, but the depth of penetration depends on the incident angle at which the laser light enters the interface between the transparent material and the internal reflection element plate and the wavelength of the laser light used. do.

Therefore, by changing this angle of incidence, it is possible to measure Raman spectra from the surface to layers at different depths, and it is possible to analyze from the surface of a transparent material to a depth of 0.01 μm to several 0.1 μm. be.

Furthermore, by reducing the spread angle of the laser beam and setting the incident angle accurately, the depth from the surface can be defined more clearly, and by taking the difference spectrum between the spectra for each incident angle. Thus, spectra can be obtained for various layers at different depths from the surface. According to the theory of total reflection of light, a laser beam of wavelength λ is incident at an angle of incidence θ at the interface with a transparent substance for analysis (refractive index Rl2) in an internal reflection element plate (refractive index n1), and total reflection occurs. When reflection occurs, the intensity I of the laser light entering the transparent material for analysis is 1=IOe-2γ at the depth z from the interface.
7)(1)
2 red γ = 27rn1 [Sin2θ-(N
2/n1)] /λ.

The intensity of the scattered light is proportional to the intensity of the laser beam as excitation light and the length of the optical path passed through it. Therefore, the depth Z1 from the interface
The contribution of the intensity of the Raman scattered light of the layers up to the intensity of the total Raman scattered light is given by.

From these relationships, it is possible to quantitatively determine the dependence of the Raman scattering intensity on the incident angle and the wavelength of the laser beam up to layers of different depths. In particular, when there is a very thin layer on the surface of a transparent material for analysis that can be identified by its Raman spectrum, equation (2) becomes R = 2γZ1, and since the relative intensity is proportional to the thickness, the total reflection Raman spectrum is By measuring, the thickness Z1 of the surface layer can be easily determined.

The laser beam used as a light source can be any of the lasers used for normal Raman measurements, Ar, Kr, etc. However, each signal in the pre-reflection Raman spectrum is inherently weak, and the scattering intensity increases as the fourth power of the wavelength. It is desirable to use a laser beam with a short wavelength because it is inversely proportional and the spectrum from a position closer to the surface can be measured with a shorter wavelength.

Although a normal Raman spectrometer used in the method of the present invention can be used as is, a special accessory device designed to measure total internal reflection Raman spectra is provided in the sample chamber. This accessory device brings the transparent substance of the analysis sample into close contact with the internal reflection element plate. It is possible to maintain the direction and surface of the top plate at a constant angle to the incident laser beam, and to change the incident angle of the laser beam to the sample surface with high precision, effectively concentrating scattered light due to total internal reflection. It has the ability to

According to the analysis method of the present invention, the spectrum of the layer from the surface of the measurement sample to the same depth can be measured in almost the entire wave number range of the Raman spectrum, and since the laser beam as the light source is completely polarized, By appropriately selecting the polarization direction of the incident laser beam and the cut-out crystal axis and plane of the internal reflection element plate, an easy-to-analyze spectrum that is not affected by the polarization of the incident laser beam on the sapphire reflection element plate can be obtained. Obtainable. By narrowing down the laser beam diameter, surface microanalysis becomes possible.

Furthermore, the sapphire used as the internal reflection element plate in the method of the present invention is easy to obtain as it has an established industrial manufacturing method as a synthetic sapphire, and has excellent hardness and mechanical strength, so it does not scratch the polished surface. Without a doubt,
It has particularly excellent light transmittance and is not attacked by water or organic solvents.

If a sapphire internal reflection element plate is used in a liquid cell, it is possible to measure the Raman spectrum at the solid-liquid interface. In addition, when used in high-pressure cells, it can also be used to elucidate interfacial phenomena between solids or liquids under high pressure.

Next, examples of the present invention will be described.

jExample 1 FIG. 5 specifically shows one example of the internal reflection element plate.

Sapphire (manufactured by Kyoto Ceramic Co., Ltd.) is subjected to force in the crystal axis direction, shape and size of C and a shown in Fig. 5,
The L, M, N and P surfaces were optically polished. Next, toluene solutions with polystyrene concentrations of 0.3 and 33% were prepared, spread uniformly on a 30 μm thick polyethylene film as thinly as possible, and evaporated to form two types of polystyrene/polyethylene. A layered sample was prepared. Here, the thickness of the polystyrene film was measured using a stylus-type film thickness meter and was found to be 0.05 μm for the former and 1.1 μm for the latter.
As shown in FIG. 6, the total reflection Raman spectrum was measured with the polystyrene film A side in close contact with the internal reflection element plate S. In FIG. 6, A is a polystyrene film and B is a polyethylene film. In addition, a silicone rubber plate C1 and a stainless steel plate D are placed on the back of the polyethylene.
The inner reflective element plate and the polystyrene film surface were brought into close contact by tightening with a certain amount of force.

The Raman spectrometer is Spex's RamalOg5 (photomultiplier tube RCAC3lO34), and the laser light source is CO2.
The measurement was carried out using a CR-3 argon ion laser manufactured by herentRadiatiOn, Inc., and an Ar''488.0r1m laser beam. The total reflection Raman spectra are shown in FIG. 7A and FIG. 8A.

Figures 7B and 8B show Raman spectra measured by transmitting a laser beam through these two-layer samples as usual, with both incident angles being critical angle +3.7.

In these figures, S is a peak derived from polystyrene, SP is a peak derived from sapphire, and R is a peak derived from silicone rubber. All unmarked peaks in FIGS. 7 and 8B originate from polyethylene, and all peaks in FIG. 8A originate from polystyrene. Figure 7 A and B for a 0.05 μm thick film sample
, and from a comparison of FIGS. 8A and 8B for a sample of a film with a thickness of 1.1 μm, it is clear that the method of the present invention is an extremely effective surface analysis method.

Example 2 Toluene solutions with polystyrene concentrations of 0.2, 0.3, 0.6, 1.0 and 1.7% were prepared, and these solutions were applied to the M side of a sapphire internal reflection element plate (Fig. 5). (see ), spread it to an appropriate thickness, and evaporated the toluene to form a film.

After the spectrum measurement, the thickness of the film was measured using a stylus-type film thickness meter in the same manner as in Example 1. The film thickness is 0, respectively.
．． 013, 0.034, 0.064, 0.16 and 0
．． It was 35 μm.

Next, a polycarbonate film (thickness 11.5 μm) was closely attached to the polystyrene film to form a polystyrene/polycarbonate double layer sample, and the total reflection Raman spectrum was measured by varying the thickness of the polystyrene film in the same manner as in Example 1. The depth from the surface that can be analyzed was actually measured.

In this measurement, the incident angle of the laser beam to the internal reflection element plate was set using a goniometer that can be set with an accuracy of 0.1 real.

The incident angle of the laser beam on the sample is 68.5 plates (critical angle 13.7
FIG. 9A shows the total reflection Raman spectrum in the 860 to 1160 cm −1 wave number region in the case of .

Here, in Figure 9A, the polystyrene film thickness is 0.013 μm.
M. ．． B is 0.034 μM. ．． C is 0.064 μM. ．．
D is 0.16pm. ．． E indicates the case of 0.35 μm.

In the spectrum, the 1002an-1 peak originates from polystyrene, and the 890 and 1112crfi-1 peaks originate from polycarbonate. As is clear from the top of Figure 9A,
As the thickness of the polystyrene film decreases (E→A)
, polystyrene 1002C77! -1 peak The intensity is weaker than the two peaks of polycarbonate.

The polystyrene thickness in Figure 9A is 0.013 μm.
The fact that the polystyrene peak of 1002C7I-1 has an intensity comparable to that of polycarbonate and is clear even in the case of 1002C7I-1 indicates that the method of the present invention is sufficiently applicable to the analysis of the thin surface layer of about 100 people.

Example 3 The minimum analyzable thickness was determined using a polystyrene/polycarbonate bilayer as a model.

Similar to Example 2, a 0.1% toluene solution of polystyrene was spread as thinly as possible on the internal reflection element plate, and the toluene was evaporated to form a film. Although it was difficult to measure the thickness of the film, it was estimated to be 0.006 μm1, or 60A, since the thickness of a film made in the same manner from a 0.2% toluene solution of polystyrene was 0.013 μm. The total reflection Raman spectrum was measured in the same manner as in Example 2 for a double layer sample of this film and a 11.5 μm polycarbonate film.

The results are shown in FIG. 10A. Further, the total reflection Raman spectrum of the polycarbonate single layer is shown in FIG. 10B.

In Figures 10A and B, the 1002cm-1 peak and 890 and 1112c derived from polycarbonate.
Comparing the relative intensity with the m-1 peak, it is clear that the 1002 cm-1 peak in FIG. 10A originates from polystyrene.

Next, the validity of the estimated thickness of this polystyrene film was examined from the correlation between the thickness of the film and the intensity of the 1002 cm-1 peak of polystyrene.

The results are shown in FIG. The 1002 cm-1 peak intensity was expressed as the relative intensity to the 576CTfL-1 peak of sapphire.

In addition, the 100
The relative intensity of the 2Crfi-1 peak was used.

In addition, the 1002cjn-1 peak intensity was corrected for the contribution of polycarbonate and sapphire.

l As is clear from Figure 11, there is a good linear relationship between the relative intensity of the polystyrene peak in the total reflection Raman spectrum and the thickness in the thickness range of 0 to 0.1 μm, and this Since it can be estimated theoretically as described in the text, the estimated thickness of 0.006 μm is considered appropriate.

In other words, it is shown that the method of the present invention can sufficiently analyze a surface layer with a thickness of 60A.

Example 4 Thickness of polystyrene is 0.006, 0.013
,0.034,0.064,0.16,0.35,0.
Polystyrene/polycarbonate double layer samples of 43, 0.56, 0.65 and 0.93 μm were measured in the same manner as in Example 2 with the incident angle set to the critical angle +3.7-, and the 1002 cm-1 peak derived from polystyrene was measured. of,
The relationship between the relative intensity of the 576c peak derived from sapphire and the thickness of the polystyrene film layer was actually measured.

The results are shown in FIG. In the figure, the solid line is λ = 0.488 μm 1θ = critical angle + 3.72, n1 from equation (2) in the main text.
The theoretical value curve obtained as = 1.775 (sapphire) and 1.606 (polystyrene), and the mark O is the actual measured value, and it is clear that the actual measured value corresponds well to the theoretical value curve.

Example 5 For a polystyrene (0.064 μm thick)/polycarbonate double layer, the incident angle θ of the laser beam on the polystyrene sample surface was set to +1.
1, +1.2, +1.4, +1.9, +2.4 and +
86 measured in the same manner as in Example 2, changing to 3.7
Total reflection Raman spectra in the 0 to 1160 cm −1 region are shown in FIGS. 13A to 13F, respectively.

However, when the laser beam was incident on the internal reflection element plate, the polarization direction of the laser beam was set to be perpendicular to the plane of incidence. As is clear from FIGS. 13A to 13F, the closer the incident angle is to the critical angle, the higher the 890 and 1112 cm peaks of polycarbonate are compared to the 1002 cm peaks of polystyrene.
The intensity of one peak becomes significantly stronger. In other words, the penetration depth of the laser beam into the analysis sample side during total reflection becomes deeper.
In this way, we can measure Raman spectra from the surface to various depths by changing the incident angle. can. Therefore, by changing the angle of incidence of the laser beam on the analysis sample surface using the method of the present invention and taking spectra between the total reflection Raman spectra at each angle, Raman spectra for layers at various depths can be obtained. One can be measured.

At this time, by reducing the spread angle of the laser beam and making it a parallel beam, it becomes possible to measure the depth with even higher precision. Example 6 Similar to Example 2, M of the sapphire internal reflector element
A polystyrene film was formed on the surface (see FIG. 5), a 30 μm thick polyethylene film was adhered to this to form a polystyrene/polyethylene double layer, and the total reflection Raman spectrum was measured.

For comparison, a Raman spectrum of polyethylene was also measured using a conventional method.

These results are shown in Figures 14A-C.

FIG. 14A is a total reflection Raman spectrum of a polyethylene bilayer sample prepared using conventional polyethylene, and FIGS. 14B and 14C are polystyrene/polyethylene bilayer samples with polystyrene thicknesses of 0.045 and 0.32 μm, respectively.

In FIGS. 14B and 14C, S indicates a peak derived from polystyrene, PE indicates polyethylene, and SP indicates a peak derived from sapphire. From a comparison of these spectra, it is clear that the method of the present invention is an excellent surface analysis method for determining molecular species or atomic groups on the surface of a substance.

Comparative Example The results of measuring the total reflection Raman spectrum of carbon disulfide by the conventional total reflection Raman method described above are shown in FIG.

This FIG. 15 shows measurement examples at six incident angles ψ, but all of these signals are extremely weak, the signal/noise ratio is small, and the spectra are not of a quality that can be used for analysis.

A measurement example of the present invention under conditions corresponding to this comparative example is shown in FIG. 8A, for example, in which a very clear spectrum with a high signal/noise ratio is obtained.

From the comparison between FIG. 15 and FIG. 8, it is clear that the measuring method according to the present invention is superior to the conventional method.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing total internal reflection, Fig. 2 is a schematic diagram of the method of the present invention, Fig. 3 is an explanatory diagram of the crystal axis and crystal plane of sapphire, and Fig. 4 is an explanatory diagram of a sapphire internal reflection element plate. A is a plan view, B and C are a side view, and D is a perspective view.
Fig. 5 is a diagram showing an embodiment of an internal reflection element plate made of sapphire, Fig. 6 is a schematic diagram showing an embodiment of the method of the present invention, and Figs. 7 and 8 are diagrams showing a polystyrene/polyethylene double layer film. Figure 9 shows the Raman spectrum of a polystyrene/polycarbonate double layer film, Figure 10A shows the total reflection Raman spectrum of a polystyrene/polycarbonate double layer film, and Figure 10B shows the total reflection Raman spectrum of a polycarbonate single layer film. Figure 11 shows the reflection Raman spectra and the polystyrene film thickness and 1002
Figure 12 shows the relationship between the relative intensity of the 1002 cm-1 peak of polystyrene and the film thickness. Figures 13A-G show the relationship between the relative intensity of the 1002 cm-1 peak of polystyrene and the film thickness. Diagram showing the reflection Raman spectrum when changing the light incidence angle, 1st
Figure 4A is a diagram showing the Raman spectrum of polyethylene obtained by the conventional method, Figures 14B and C are diagrams showing the total reflection Raman spectrum of polystyrene/polyethylene double layer, Figure 1
FIG. 5 is a diagram showing an example of measurement of carbon disulfide by the conventional total internal reflection Raman method. 1... Transparent substance, 2... Sapphire internal reflection element plate, 3... Loser light, 5...
...scattered light.

Claims (1)

[Claims] 1. A sapphire internal reflection element plate is brought into close contact with a transparent substance, and a laser beam is incident on the internal reflection element plate at an angle such that the laser beam is totally reflected at the contact interface between the internal reflection element plate and the transparent substance. The laser beam is totally reflected at the contact interface between the internal reflection element plate and the transparent material, and the scattered light generated by the laser beam that enters the transparent material is analyzed to record the Raman spectrum of the transparent material. A method for analyzing the surface of a transparent substance.