JP3671222B2 - Method and apparatus for analyzing radical species - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radical species analyzing method and analyzer capable of capturing unstable radical species such as peroxy radicals on a substrate and examining their chemical structures and reactions.
[0002]
[Prior art]
It is very important to study the chemical structure and reactions of peroxy radicals in the study of atmospheric environment. For example, HCFC134a (CF ₃ CH ₂ F), which is an alternative chlorofluorocarbon, is decomposed in the atmosphere to produce CF ₃ OO radicals. Examining the reaction of these radicals in the atmosphere is very important for evaluating the environmental effects of HCFC 134a. is there. In addition, other organic substances in the atmosphere react with oxygen in the atmosphere and always undergo a decomposition process that generates peroxy radicals. Therefore, such radical intermediates are extremely important in examining the branching ratio and decomposition mechanism.
[0003]
As a method for analyzing peroxy radicals, conventionally, a reaction starting material is confined in a rare gas matrix in advance, and then the matrix is irradiated with light to cause peroxy radicals to be generated and observed. Was taken. However, in this method, the reaction mechanism may be different from the actual gas phase reaction, and in order to trace the atmospheric reaction, a method capable of analyzing peroxy radicals generated in the gas phase reaction is necessary.
[0004]
[Problems to be solved by the invention]
However, since such a peroxy radical intermediate is very unstable, it could not be detected by an experimental method using a conventional atmospheric chamber. Matrix method has been used for the measurement of peroxy radical species, but in the conventional method, a reaction starting material was previously confined in the matrix to generate peroxy radical in the matrix. In this method, the reaction mechanism may be different from the actual atmospheric reaction, and in the case of a complicated reaction, it is difficult to generate a peroxy radical. (In this device, as will be described later, since a peroxy radical can be efficiently generated and detected by a gas phase reaction, a complicated reaction occurring in an atmospheric reaction can be handled.) It is desired to develop a technique capable of reliably detecting extremely unstable radical species in addition to such peroxy radicals.
[0005]
Therefore, the main object of the present invention is to provide a radical species analyzing method and analyzer capable of accurately and easily detecting radical species such as peroxy radicals.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the radical species analysis method according to the present invention fixes a cooled sample substrate in an ultra-high vacuum analysis chamber, and arranges argon gas, oxygen, and substrate gas in the proximity of the sample substrate. The concentrated gas is supplied to the position, the laser is irradiated to the concentrated portion of the gas, the gas reacts, and the radical species gas generated by the reaction is adsorbed and trapped on the sample substrate using argon gas as a matrix. The measured gas is measured with a high sensitivity reflection type infrared absorption spectrometer.
[0007]
Further, the radical species analyzer according to the present invention concentrates an ultra-high vacuum analysis chamber in which a sample substrate is fixed so as to be cooled, an argon gas, oxygen, and a substrate gas at a position close to the sample substrate. A gas supply device that supplies gas, a laser irradiation device that irradiates a laser to a concentrated portion of the gas, and reacts the gas; A reflection type infrared absorption spectrometer.
[0008]
In another radical species analyzer according to the present invention, the sample substrate is cooled by a liquid helium cryostat during an analysis operation in the radical species analyzer.
[0009]
The radical species analyzer according to the present invention is the radical species analyzer, wherein the concentrated gases intersect each other at a solid angle of 90 degrees, and the incident angle is 45 degrees with respect to the sample substrate. It is to be supplied.
[0010]
Still another radical species analyzer according to the present invention is such that in the radical species analyzer, the laser irradiated from the laser irradiation device is irradiated in parallel to the sample substrate.
[0011]
The analysis apparatus for radical species according to the present invention will be described more specifically. The analysis apparatus is roughly classified into an ultra-high vacuum analysis chamber, a load lock chamber section, a sample substrate cooling mechanism (liquid helium type cryostat), and a high sensitivity for surface analysis. It consists of five: a reflection type Fourier transform infrared spectrophotometer and an excimer laser irradiation system. In the present invention, “ultra-high vacuum” refers to a range of 10 ⁻⁵ to 10 ⁻⁸ Pa in which this term is usually used. Radiation source gas such as substrate gas, oxygen, etc., and argon gas are respectively incident on the cooling substrate from three gas introduction pipes installed at such an ultra-high vacuum chamber and intersecting at a solid angle of 90 degrees. At the same time, a laser beam having a wavelength of about 245 nm is irradiated to a portion where these gases are concentrated below the substrate, and a reaction is performed in the analysis chamber. The reacted gas is trapped on the cooling substrate using argon gas as a matrix. Analysis of the reaction gas adsorbed on the substrate is performed using reflection-absorption spectroscopy (IR-RAS).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
More specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing main components in an embodiment of a peroxy radical analyzing apparatus 1 according to the present invention. This apparatus as a whole has a sample substrate 2 such as Cu inside as a gas in the lower part of the figure. An ultra-high vacuum analysis chamber 3 fixed with the capture surface facing, a load lock chamber 4 capable of supplying a plurality of samples, a sample substrate cooling device 5 using a liquid helium cryostat or the like for cooling the samples, red Infrared light emitted from the external light source 6 and reflected by the sample substrate 2 is received by the infrared detector 7, and the signal is computer processed to analyze the surface of the sample substrate. An excimer laser irradiation device (not shown) that irradiates a laser beam 7 having a wavelength of, for example, 245 nm, which is irradiated in a direction perpendicular to the paper surface in FIG. It is composed mainly by a gas supply apparatus provided with three nozzles for supplying three kinds of gases to be described later in the chamber 3.
[0013]
The ultra-high vacuum analysis chamber 3 can be set to an ultra-high vacuum of about 7 × 10 ⁻⁸ Pa, and is equipped with nozzles as three gas introduction pipes intersecting each other at a solid angle of 90 degrees, In the figure, argon gas is supplied from the first nozzle 10, radical source gas such as oxygen gas having a purity of 99.9999% is supplied from the second nozzle 11, and a substrate such as CF ₃ I is further supplied from the third nozzle 12. Gas is being supplied. Although schematically shown in the drawing, these nozzles are all blown at 45 degrees to the sample substrate 2.
[0014]
The laser beam 7 as described above is irradiated at a position where the gases supplied from the nozzles as described above are concentrated and collide with each other, so that these gases react in the analysis chamber 3. In the illustrated apparatus, the load lock chamber 4 and the analysis chamber 3 are communicated with each other through a communication path 13, an isolation valve 14 is provided in the communication path 13, the isolation valve 14 is released, and a sample transfer rod 15 is provided. As a result, the sample substrate in the load lock chamber 4 maintained in a vacuum similar to that of the analysis chamber 3 can be transferred into the analysis chamber 3 and transferred into the analysis chamber 3. The sample substrate is transported to a predetermined position and fixed by a conveying means (not shown), and in the illustrated embodiment, the sample substrate cooling device 5 is placed thereon so that it can be cooled.
[0015]
In the apparatus as described above, the present inventors conducted the following analytical experiment and confirmed that peroxy radicals can be detected by this apparatus. That is, argon gas as a matrix gas is supplied from the first nozzle 10 to the analysis chamber 3 with a background vacuum of 7 × 10 ⁻⁸ Pa while adjusting with a variable leak valve, and the pressure in the analysis chamber 3 is 5.0. It introduce | transduces until it becomes * 10 <^-6> Pa. Next, 99.9999% oxygen gas was introduced from the second nozzle 11 until the pressure in the analysis chamber 3 reached 5.0 × 10 ⁻⁵ Pa, and finally CF ₃ I as a substrate gas was introduced into the third nozzle. 13 until the pressure in the analysis chamber 3 reached 1.3 × 10 ⁻⁴ Pa. In this way, the sample substrate 2 is irradiated in parallel with the excimer laser 7 having a pulse period of 50 Hz and a wavelength of 245 nm so that the laser strikes a portion where the gases ejected from the three nozzles are mixed. The gas was allowed to react.
[0016]
Thereby, the gas reacted as described above is trapped as Ar gas as a matrix on the surface of the sample substrate 2 that has been cooled to about 4 degrees K in advance with a liquid helium cryostat, and the spraying time is further increased. By doing so, the peroxy radical produced | generated in trace amount can be concentrated. The product thus adsorbed and trapped on the sample substrate 2 was measured with a reflection type infrared absorption spectrometer conventionally used. By using such a reflection type infrared absorption spectrometer (RAS), it is possible to measure a low concentration product with high sensitivity.
[0017]
FIG. 2 shows a spectrum without light irradiation indicated by a broken line and a spectrum with light irradiation indicated by a solid line, respectively. In the figure, in the infrared spectrum without light irradiation, the absorption of the stretching vibration of CF ₂ I appears at 1192 cm ⁻¹ and 1085 cm ^−1, and the absorption of the deflection vibration appears at 741 cm ⁻¹ .
[0018]
Each infrared spectrum of CF ₂ measured in the gas phase ^is, 1187cm ^-1, 1075cm ^-1, the peak respectively appears at 743cm ^-1, when the matrix as described above, the peak of the stretching vibration shifts as described above I found out that In the infrared spectrum when irradiated with light, the peaks at 1192 cm ⁻¹ and 1085 cm ⁻¹ disappeared, and new peaks apparently appearing as photooxidative decomposition products appeared. CF ₂ I is expected to generate CF ₃ O ₂ .radicals through a decomposition process of the following formula in the analysis chamber.
λ = 245nm
CF ₃ I → CF ₃ · + I (1)
CF ₃ + O ₂ → CF ₃ O ₂ (2)
[0019]
According to literature, it has been reported that CF ₃ O ₂ .radical has specific infrared absorption at 1173 cm ⁻¹ and 1094 cm ⁻¹ . This document is data measuring CF ₃ O ₂ .radicals generated by thermal decomposition and photolysis in a matrix, respectively. When these documents are qualitative infrared spectrum when irradiated with light as a ^{reference, 1263cm -1, 1172cm -1, 1093cm} -1, respectively ^{_{883cm -1, CF 3, FCF 2}} , O-O, stretching the CO bond Attributed to. Thus, it was confirmed that peroxy radicals (CF ₃ O _2. ) Generated by gas phase decomposition could be detected using this apparatus.
[0020]
【The invention's effect】
In the method and apparatus for analyzing radical species according to the present invention, an unstable decomposition product generated by a low-concentration gas phase reaction having a gas concentration of about 1 ppb or less and a total gas pressure of about 1/3 × 10 −4 Pa. Even small radical species can be analyzed in trace amounts.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an apparatus for analyzing radical species according to the present invention.
FIG. 2 is a diagram showing experimental data of infrared absorption of an Ar matrix of CF ₃ I and an Ar matrix of a photooxidation product obtained by the analyzer according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Analyzer 2 Sample substrate 3 Analysis chamber 4 Load lock chamber 5 Sample substrate cooling device 6 Infrared light source 7 Infrared detector 8 Infrared spectrophotometer 9 Laser light 10 First nozzle 11 Second nozzle 12 Third nozzle 13 Station Passage 14 Isolation valve 15 Sample transfer rod

Claims (5)

Fix the cooled sample substrate in the ultra-high vacuum analysis chamber,
Argon gas, oxygen, and substrate gas are concentrated and supplied to the vicinity of the sample substrate,
Irradiate a laser to the concentrated portion of the gas to react the gas,
The radical species gas generated by the reaction is adsorbed and trapped on the sample substrate using argon gas as a matrix,
A method for analyzing radical species, wherein the adsorbed and trapped gas is measured with a high-sensitivity reflective infrared absorption spectrometer. An ultra-high vacuum analysis chamber in which the sample substrate is fixed so that it can be cooled;
A gas supply device that supplies argon gas, oxygen, and substrate gas in a concentrated manner in the vicinity of the sample substrate;
A laser irradiation device for irradiating a laser to the concentrated portion of the gas and reacting the gas;
An apparatus for analyzing radical species, comprising: a high-sensitivity reflection-type infrared absorption spectrometer that measures radical species gas using argon gas as a matrix adsorbed and captured on the sample substrate. 3. The radical species analyzer according to claim 2, wherein the sample substrate is cooled during an analysis operation with a liquid helium cryostat. 3. The radical species analyzer according to claim 2, wherein each of the concentrated gases crosses each other at a solid angle of 90 degrees and is supplied to the sample substrate at an incident angle of 45 degrees. 3. The radical species analyzer according to claim 2, wherein the laser irradiated from the laser irradiation apparatus is irradiated in parallel to the sample substrate.

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