JPH03261846A - Infrared absorption enhanced spectrometer - Google Patents

Abstract

PURPOSE:To make the number of waves in a direction of a prism bottom coincide with the number of waves of surface electromagnetic waves to obtain a sufficient S/N ratio by uniformly pressing a film against a reflecting surface of a highly refractive prism and preventing divergence of incident light and outgoing light to the prism while an incident surface and an outgoing surface are made flat. CONSTITUTION:An object of analysis with this spectrometer is popolarization. In performing analysis, a crimp screw receiving jig 12, a crimp screw 13 and a crimp plate 14 are used to press a film 51 on which a thin film 53 being a specimen is deposited against a reflecting surface of a highly refractive prism 16. The film 51 is made of plastic such as PET and aluminum 52 has been deposited on it. The prism 16 is equipped with a flat reflecting surface while a reflecting mirror 17 and an angle adjusting mechanism 20 are used to adjust incident and outgoing angles with respect to a crystal. By thus constituting the spectrometer and turning the screw 13, the crimp plate 14 is lowered together with a cushion 41, and the PET film 51, the aluminum deposited film 52 and a specimen 53 are integrally pressed against the reflecting surface of the prism 16 so as to reduce a loss in infrared rays.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an infrared absorption enhanced spectrometer, and more specifically, to a high refractive index prism having an entrance surface, a reflection surface, and an exit surface. A thin layer of the sample to be analyzed is placed in the gap between the prism and the metal, which is a solid plasma made up of free electrons, and infrared light is incident on the incident surface of the prism, and the infrared light is totally reflected on the reflective surface. When analyzing the sample from the absorbance characteristics of the infrared light obtained by passing through the exit surface, the infrared light incident from the entrance surface excites electromagnetic waves on the surface of the metal. The present invention relates to an infrared absorption enhanced spectrometer that improves the absorbance characteristics and increases the analytical sensitivity.

[Prior Art] Materials in which electrons move freely, such as metals, can be considered solid plasma. Surface electromagnetic waves (surface plasmons) may exist near the surface of such solid plasma. For excitation of surface electromagnetic waves with light, use a high refractive index prism or
This is done by cutting a diffraction grating on the metal surface.

FIG. 5 is an explanatory diagram showing a surface electromagnetic wave excitation method proposed by Otto.

Reference numeral 1 denotes a high refractive index prism having a refractive index ηp, and a metal 3 having a dielectric constant ε(ω) is placed on the lower surface of the prism through a gap 2 having a dielectric constant η(ω). Note that ω is the angular frequency of light, and the dielectric constants η and ε are functions of ω.

Incident light 4 is totally reflected at the bottom of prism 1 and becomes reflected light 5, but the wave number (reciprocal of wavelength) of the light traveling through the prism is k
The component kpsinθ in the X direction of p = ηp ・ω/C (where C is the speed of light) is the wave number k of the excited surface electromagnetic wave.
If x matches, surface electromagnetic waves 6 are excited on the surface of the metal 3.

The dispersion relationship between the wave number kx of the surface electromagnetic wave 6 and the angular frequency ω of light is given by the following 2.

kx = ω/C-Jεη/(ε+η)...
・(1) For relatively low frequency light such as infrared rays, the absolute value of the permittivity of metal 1ε1 is much larger than the absolute value of the permittivity of general dielectric materials, and the above equation (1) can be approximated as follows. can.

kx = ω/Cr "...
(2) Low-frequency surface electromagnetic waves behave like photons guided by a highly conductive material within a gap.

According to the above principle, infrared rays can be transmitted in the plane direction to a thin layer as a sample on a metal surface, and analysis sensitivity can be improved by increasing the transmission distance of infrared rays to the thin film sample.

Now, surface electromagnetic waves have been studied for a long time, and the excitation method of surface electromagnetic waves using a high refractive index prism is also known as ○tto and Kretsc) + n + an
proposed by n.

Surface electromagnetic wave spectroscopy in the strict sense can be thought of as a method in which, for example, two prisms are placed at a fixed gap and the ratio of the intensity of light traveling on the surface between them and the intensity of incident light is calculated. However, even if a single prism is used, 0tto or K
It has been confirmed that surface electromagnetic waves are excited by Retschmann's method, which increases the absorption of a thin layer (sample) attached to a metal surface by passing light in the plane direction.
It is possible to increase analytical sensitivity.

Various attempts have been made to achieve such effects. Sue Taka et al. observed that by depositing silver on the plane of a germanium semi-cylindrical prism, the infrared absorption of the thin film attached to the strapping surface was enhanced. In addition, I5hida et al. used a germanium prism with flat entrance and exit surfaces so that the incident angle was 75°, and attached a thin layer of the sample and step 5 to the reflecting surface, and then deposited silver on the top surface. An increase in infrared absorption is observed.

In all of these methods, the metal layer is formed by vapor deposition, and equipment such as a deposition device is required for use in normal analysis.

In addition, Sue Taka et al.'s method strengthens infrared absorption by island-shaped silver particles, and surface electromagnetic waves may also be involved, but the metal material used is silver and it is attached in island shapes. This is a very severe restriction for general use.

Note that the following documents can be cited as documents describing the prior art.

(1) Electromagnetic Wav
e S spectroscopy Surface
5science48 (1975) 253-287
0North-Holland Publishing
Company”lNTR0DUCTORY TH
EORY F○R5URFACE ELECTR
OMAGNETrCWA■E 5PECTRO3CO
PYJRobertJ, BELL R,W,ALE
XANDER Jr,, C, A, WARD and
r, L, TYLER (2) Zeitschri
ft fiir Physik 216°398
4 ■O (1968) 'Excitatio
n ofNonradiative 5urfac
e Plasma Waves 1nSilve
r by the Method of F
RustratedTotal Reflectio
n J ANDREAS OTT○ (Problem to be solved by the invention) The present invention provides a measurement method based on such a principle,
It can be easily installed in a state where the positional relationship between the metal surface, the thin sample layer on it, and the high refractive index prism can be measured, and the wave number of the light in the prism toward the bottom of the prism can be made to match the wave number of the surface electromagnetic waves. It is an object of the present invention to provide an infrared absorption enhanced spectrometer having an optical system with low infrared loss so that the angle of incident light can be easily adjusted and a sufficient S/N ratio can be obtained.

[Means to solve the problem]

A high-refraction prism is used to excite surface electromagnetic waves on the surface of a solid plasma that is protected from free electrons such as metals, and the light travels in the plane of the thin layer attached to the solid plasma surface. In surface electromagnetic wave spectroscopy, which increases light absorption and enhances analysis sensitivity, i) the shape allows the film to be held uniformly against the reflective surface with a high refraction 7" rhythm, so that the light entering and exiting the prism is as much as possible. In order to prevent divergence, the entrance and exit surfaces of the prism are flat, and ii) The thin film to be analyzed is a flexible film (for example, a polyethylene terephthalate film with a thickness of about 50 μm) with a metal deposited at about 500A (for example, aluminum). 1ii) has a mechanism for pressure-bonding the metallized film on which the thin film to be analyzed is attached to the reflective surface of the high refractive index prism; We have constructed an infrared absorption enhanced spectrometer based on surface electromagnetic waves G that has a changeable adjustment mechanism.

(Function) The absolute value of the metal dielectric constant ε=ε, +jε2 (where i is an imaginary number) increases as the frequency becomes lower.

In the infrared region, ε1>η summer (3), and the dispersion of surface electromagnetic waves can be approximated as shown in equation (2) above. This relationship may be any metal that satisfies Equation (3), but if we interpret it a little more broadly, it does not need to be a metal to ensure that light does not leak through the thin film of the sample (for example, if a material with a lower refractive index than the thin film is connected to the back surface of the thin film). ), but this relationship is satisfactory.

Expression (2) using the complex refractive index of the thin film is as follows.

kx = ω/C(ns −i ks)' −
(4) Here, (ns-4ks) is the complex refractive index of the thin film sample, ns is the real part of the complex refractive index, and ks is the imaginary part.
Also called extinction coefficient.

In order for the component kpsin θ of the wave number kp of light traveling inside the prism (refractive index np) in the direction of the prism surface to be equal to the wave number of the surface electromagnetic wave, assuming that each wave number is equal, kpsln θ= n p・( ω/C) sinθ=
ω / C (ns ~ 1ks) If we rearrange, sin θ = - (ns - iks)
-(5) np is obtained. If ks<ns, sin fl 'E ns/np
...(6) may be used.

For general samples (samples to be analyzed), n5=1
．． There are many things in the 5th place, so np like germanium
= 4 prism, θ = 22.5° and KR3-
In a prism with np=2.4 as in No. 5, θ=about 39°, so that the angle of incidence can be finely adjusted in accordance with the refractive index of the sample.

It is extremely difficult to narrow the gap between the high-refractive-index prism reflective surface and the metal plane to the extent that magnetic waves are excited on the metal surface by the ehanescent wave from the prism surface. In order to effectively excite a metal plane with an exponential wave (electromagnetic wave that decays exponentially) from a prism surface with a high refractive index, even in the infrared wavelength region, it is necessary to
They must be brought close to each other at a distance on the order of μm.

First, both the prism and the metal surfaces must be finished with flatness on the order of 0.1 μm.

Next, even if the surface is finished with such flatness, there must be no adhesion of particles with a diameter of 0.1 μm or more on both surfaces. This means that if there is even one particle of that size, the prism and the metal plane can be separated by it.

A similar degree of cleanliness has been achieved in the semiconductor VLSI manufacturing process, but this is achieved in an extremely controlled environment. Even in such an environment, one of the surfaces must be flexible and follow the other surface in order to always achieve a state in which more than several tens of percent of the area is in contact within 0.1 μm. No.

Since prisms generally use crystals, flexibility cannot be expected. On the other hand, metals are usually hard and cannot be expected to be flexible, but a thickness of several hundred angstroms is sufficient for the optical role of metals.

Therefore, a flexible plastic film with, for example, 500 metals deposited on its surface behaves optically in the same way as a semi-infinite metal surface.

Contact between the reflective surface of the prism and the metal surface (within 0.1 μm or less can be achieved by evaporating about 500 metals onto a flexible film and press-bonding it to the reflective surface.If the flexible film If the surface of the pressure bonding plate, which is thin and pressure is applied from behind, is affected, it is sufficient to provide a cushion layer on the pressure bonding plate so that the pressure is uniform on the surface.

In a spectrophotometer using this device, the sample chamber in which the sample is placed and various accessories for measurement are placed has a fixed optical path and a center focus (the focus is in the center of the optical path of the sample chamber). There is - boat fishing. Therefore, it is desirable that the incident side and the output side of this device be symmetrical and that the focal point be at the reflection point of the prism. This device has an optical system that allows the angle of incidence to be varied and focuses on the reflection point.

[Example] The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a front view showing one embodiment of the present invention, and FIG. 2 is a side view of the same.

In these figures, 11 is a base plate, 12 is a crimp screw receiver, 13 is a crimp screw, 4 is a crimp plate, 41 is a cushion, 51 is a PET (polyethylene terephthalate) film, 52 is an aluminum vapor deposited film, and 53 is an analysis target 16 is a high refractive index prism, ■7
is a reflecting mirror, 18 is incident light, 19 is output light, 20 is incident light,
This is an output angle adjustment mechanism.

The tank bottom will be briefly explained below. Reference numeral 11 denotes a base plate, on which the main parts of the device are arranged. Incident light 18 and output light 1
An adjustment mechanism 20 is provided externally to align the optical axis of the device 9 with that of an external device.

In addition, a polarizer is placed on the optical axis other than this device so that P-polarized light can be selected for incident light or reflected light of this device, so that P-polarized light can be selected. The analysis is performed for general P-polarized light.

Crimp screw receiver 12. Crimp screw 13. A pressure-bonding plate 14 is a mechanism for pressure-bonding a film 51 on which a thin film 53 of a sample is attached and a metal vapor-deposited film 51 is attached to a reflective surface of a high refractive index prism 16. 5
1 is a film for supporting a sample 53, which is different from a Z plastic film such as PET, and has a metal such as aluminum vapor-deposited 52 thereon. Reference numeral 16 denotes a high refractive index prism, with a flat reflective surface that joins the flexible metal vapor deposition surface 52, and a prism with a refractive index of 4 where the incident light and reflected light are approximately 22.5 degrees, and the refractive index is 2.4. In prism, 3
It has a shape that allows light to enter the crystal at an incident angle of about 9 degrees.

Reference numeral 17 is a reflecting mirror for allowing horizontally incident and emitted light to pass through the crystal at the required angle, and the angle adjustment mechanism 20 allows adjustment of the angle of light entering and exiting the crystal.

As is already clear, the operation of this device is as follows: by turning the crimp screw 13, the crimp plate 14 is lowered together with the bonding plate 41, and the PET film 51, Al≧Nium evaporation #52,
, the sample 53 is pressed as one body against the reflective surface of the high refractive index prism 16, and the incident angle of the incident light 18 is adjusted using the incident/output angle adjustment mechanism 20.

We will introduce an example of analysis using this device.

A base material in which about 500 layers of aluminum was deposited on a polyester film having a thickness of 75 μm was used, and an alkyd resin was applied to the aluminum-deposited surface to a thickness of 1000 layers. An alkyd resin was dissolved in toluene at 1 wt %, a certain amount of the solution was measured with a microsyringe, and the solution was spread uniformly over the aluminum evaporated surface.

FIG. 3 shows the spectrum of this sample measured by a general specular reflection method using a 4 cm-'32 scan DTGS detector.

FIG. 4 shows the spectrum of the same sample measured using this apparatus under the same conditions.

The spectrum obtained by this device clearly has less noise and small peaks are clearly visible, but the conventional spectrum obtained by the specular reflection method has a lot of noise and the presence of small peaks cannot be determined. Comparing the absorbance at the maximum peak near 1734 cm-', the 1734 cm obtained with this device is
-' peak has an absorbance 65 times that of the peak obtained by the specular reflection method. If we compare the sensitivity based on absorbance alone, this device improves the sensitivity by 65 times.

[Effects of the Invention] As explained above, according to the present invention, the surface of the metal,
It can be easily set up in a state where the positional relationship between the thin sample layer on top of the sample and the high refractive index prism can be measured, and the wave number of the light in the prism direction toward the bottom of the prism can be easily made to match the wave number of the surface electromagnetic waves. Adjustable light angle and sufficient S
This has the advantage that it is possible to realize an infrared absorption enhanced spectrometer with low infrared loss and a high /N ratio.

[Brief explanation of drawings]

Fig. 1 is a front view showing one embodiment of the present invention, Fig. 2 is a side view of the same, Fig. 3 is a spectrum diagram showing the analysis results measured by the conventional general specular reflection method, and Fig. 4 is a diagram showing the present invention. FIG. 5 is an explanatory diagram showing a method of excitation of surface electromagnetic waves. Explanation of symbols 11...Base plate, 12...Crimp screw receiver, 13...
- Crimping screw, 14... Crimping plate, 41... Ri, John, 51... PET (polyethylene terephthalate) film, 52... Aluminum vapor deposited film, 53...
Sample as analysis target, 16... High refractive index prism, 17... Reflecting mirror, 18... Incident light, 1
9... Outgoing light, 20... Incoming and outgoing angle adjustment mechanism, Fig. 5

Claims (1)

[Scope of Claims] 1) A sample to be analyzed is placed in a gap provided between the reflective surface of a high refractive index prism having an incident surface, a reflective surface, and an exit surface and the metal as a solid plasma composed of free electrons. is arranged as a thin layer, and infrared light is incident from the entrance surface of the prism,
When analyzing the sample based on the absorbance characteristics of the infrared light obtained by total reflection on the reflecting surface and passing through the output surface, the infrared light incident from the incident surface is transmitted to the surface of the metal and the sample. In an infrared absorption enhanced spectrometer that improves the absorbance characteristics and increases analytical sensitivity by exciting electromagnetic waves on the surface, the sample is placed on a flexible film such as a polyethylene terephthalate film, A metal such as aluminum as the solid plasma is deposited on the metal evaporation surface, and the reflective surface of the prism is formed by applying a pressure bonding mechanism to the metal evaporation surface of the film to which the sample is attached evenly. It has a shape that can hold what is pressed against it,
The entrance surface and the exit surface are made flat so that the incident light on the entrance surface of the prism and the exit light from the exit surface do not diverge, and the incident angle is such that the incidence angle of the infrared light with respect to the reflective surface of the prism can be adjusted. An infrared absorption enhanced spectrometer characterized by being equipped with an adjustment mechanism. 2. In the infrared absorption enhanced spectroscopy device according to claim 1, the point where the incident light incident from the entrance surface of the prism reaches the sample on the metal-deposited surface of the film that is pressed against the reflective surface of the prism. An infrared absorption enhanced spectrometer characterized by making incident light incident so that it is focused at .