JP3536970B2 - Method for producing amino acid thin film and chemical sensor probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an amino acid thin film and a chemical sensor probe using the same.
Specifically, organic thin films made from amino acids as raw materials hold chemical information derived from the molecular structure of the raw amino acids, and provide a method for producing organic thin films that can identify chemical isomers. As a feature of the production method of the present invention, a thin film with high adhesion can be formed on any substrate by a simple method without changing the molecular structure of the raw material. Therefore, the present invention can be applied to a substrate having a complicated shape. The present invention can be expected to be applied to, for example, sensing technology, separation technology, concentration technology, sampling technology, and the like.

[0002]

2. Description of the Related Art A method of thinning an organic substance such as an amino acid is carried out by dipping a substrate in a solution dissolved in an organic solvent and then pulling it up by casting or spin coating, and then evaporating and removing the organic solvent. Generally, a wet method for forming a thin film is used.

[0003]

However, there is a problem that this method cannot be applied to an organic substance which is hardly soluble in a volatile organic solvent such as an amino acid. Further, even if a soluble solvent is present, solvent molecules remain in the formed thin film, and there is no fear that the expected physical properties of the film may be impaired. There is also a method of forming a thin film by a sputtering method which is a dry process without using an organic solvent. However, in this method, the problem of changing the structure of the raw material for forming a thin film is inevitable.

[0004] The present invention has been proposed in view of the above, and an object of the present invention is to change the structure of an organic substance that is hardly soluble in volatile organic solvents such as amino acids without changing its structure.
It is an object of the present invention to provide a technique for forming a thin film having high adhesion to a substrate while retaining physicochemical information resulting from the structure of a source molecule.

It is another object of the present invention to provide a chemical sensor probe having an optical isomer discriminating ability based on this film forming technique and capable of detecting an odor component gas at a ppm level with high sensitivity.

[0006]

In order to achieve the above object, a method for producing an amino acid thin film according to the present invention provides a molecular beam cell comprising vacuum-dried fine amino acid powder and a heater and a water cooling jacket. It is characterized in that it is heated in a vacuum using, sublimated and deposited on an arbitrary substrate.

[0007] In the above, the heating temperature is 15
It is characterized by a temperature of 0 ° C or higher and 240 ° C or lower.

Further, the method is characterized in that an inductively coupled plasma beam is irradiated when depositing the sublimated amino acid of the fine powder on an arbitrary substrate.

Further, in the chemical sensor probe of the present invention, the surface of the transducer-type weight detecting transducer is vacuum-dried using a molecular beam cell comprising a vacuum-dried fine powder of amino acid and a heater and a water-cooling jacket. Heated in
It is characterized by being covered with a thin film formed by sublimation.

In the chemical sensor probe, the surface of the transducer-type weight detection transducer is heated in a vacuum using a molecular beam cell composed of a heater and a water-cooled jacket, and vacuum dried amino acid fine powder. Then, when formed by sublimation, it is characterized in that it is covered with a thin film irradiated with an inductively coupled plasma beam.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method for forming a thin film without changing the molecular structure of an organic material which is hardly soluble in an organic solvent represented by amino acids. The method is characterized in that a raw material organic substance is filled in an organic molecular beam cell capable of precisely performing the above, and the temperature is controlled in the cell to sublimate the raw material in a high vacuum to form a thin film on an arbitrary substrate.

Further, the plasma flow generated by the inductively-coupled ion source capable of generating plasma in a high vacuum during the vapor deposition is made to act weakly, whereby the structural change of the source molecules is suppressed and the substrate flow is suppressed. This is a method for producing an organic thin film, which is characterized by improving the adhesion to the organic thin film.

According to the present invention, a thin film can be formed with little change in the molecular structure of the amino acid (with a very small change in the structure), and thus the amino acid molecule has an active property with respect to various intermolecular interactions. A thin film can be obtained.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of the configuration of a plasma molecular beam deposition apparatus according to the present embodiment. As shown in FIG. 1, the plasma molecular beam deposition apparatus includes a vacuum vessel 1, a substrate holder 2 disposed above the vacuum vessel 1, a molecular beam deposition cell 3 disposed facing the lower side, and a vacuum vessel 1.
Inductively coupled plasma ion source 4 provided on the side of
And A quartz window 5 is provided at the outer end of the inductively coupled plasma ion source 4, and a copper loop antenna 6 is provided in the quartz window 5, and the copper loop antenna 6 is connected to a high-frequency power supply 8. Connected to box 7. The vacuum vessel 1 is provided with a vacuum valve 9, a turbo molecular pump 10, an oil rotary pump 11, a vacuum gauge 12, a vacuum valve 13, a mechanical booster pump 14, and an oil rotary pump 15.

Molecular beam deposition cell 3 provided in vacuum vessel 1
2 is shown in FIG. As shown in FIG. 2, the molecular beam deposition cell 3 comprises a crucible 2 in which amino acids are filled.
0, a heater 21 provided around the crucible 20 for heating the crucible 20, a water cooling jacket 22, and a thermocouple 2
3.

Next, a method for forming an amino acid thin film using the above-described plasma molecular beam deposition apparatus will be described. A vibrator-type weight detection transducer (not shown) for a chemical sensor is installed on the substrate holder 2. A typical example of the transducer-type weight detection transducer is a crystal resonator (QCR, fundamental frequency 9 MHz). Normally, AT having a small temperature dependence of the resonance frequency near room temperature
Using a QCR composed of cut surfaces. It is desirable that the QCR used as a substrate for forming an organic thin film be washed with an organic solvent such as acetone or alcohol and then sufficiently dried in a drying furnace. In some cases, a silicon wafer or a borosilicate glass plate is installed for film analysis. Next, a heater 2 provided in a molecular beam deposition cell 3 with an amino acid as a deposition material was used.
1. Fill the crucible 20 composed of the water cooling jacket 22 and the like. Here, it is preferable that the amino acid is sufficiently ground in a mortar to obtain fine powder and then sufficiently dried in a vacuum drying furnace. This time, D-phenylalanine (D
-Phe) will be described. The filling amount is adjusted depending on the desired film thickness to be formed, but by filling D-Phe in the range of 0.1 to 2 g, an amino acid film having a film thickness of 0.1 to 2 μm can be formed.

First, the vacuum vessel 1 is brought into a high vacuum state by a turbo molecular pump exhaust system. That is, the oil rotary pump 1
1 is operated, the vacuum valve 9 is opened, and the evacuation of the vacuum vessel 1 is started. When the degree of vacuum rises to about 10 ^-1 Torr, the turbo molecular pump 10 is operated to perform high vacuum evacuation. Evacuation is performed until a vacuum degree of 10 ⁻⁷ Torr is reached. At this time, it is desirable to perform a treatment of heating the vacuum vessel 1 with a heater (not shown) in order to supplement the vacuum evacuation.

After the high vacuum state is obtained, the temperature of the crucible 20 in the molecular beam deposition cell 3 is raised to 150 ° C. or more and 240 ° C. or less, preferably 200 ° C., and D-Ph
e is sublimated and vapor deposition is started. The lower limit of the temperature range is 15
The reason why the temperature is set to 0 ° C. is that below this, the desired sublimation of the deposition material is not performed. On the other hand, if the temperature is higher than 240 ° C., the deposition raw material is decomposed or deteriorated. The higher the temperature, the higher the deposition rate. However, it is desirable to deposit at a temperature of 220 ° C. or lower in order to obtain a high quality amino acid film. At the time of vapor deposition, the vacuum exhaust system is switched to a mechanical booster pump system by closing the vacuum valve 9 and opening the vacuum valve 13. Here, the oil rotary pump 15 and the mechanical booster pump 14 are operated in advance so that the pump can be evacuated. At this time, the degree of vacuum during the deposition is 10 ⁻⁴ T
It is common to be in orr. The end of the vapor deposition process is determined based on the change in the degree of vacuum. Usually, all the raw materials are completely evaporated within two hours.

This deposited film has insufficient adhesion to the substrate,
There were problems in durability and handling. Therefore, it is necessary to devise a method of applying a plasma flow during the deposition of amino acids to improve the adhesion to the substrate. However, at this time, by the action of plasma particles mainly composed of high energy electrons,
May alter the structure of amino acids. It is important to obtain a desired thin film by controlling the power applied to the plasma. If the power is suppressed, a structural change can be avoided, but a certain amount of power is required from the viewpoint of adhesion to the substrate and increasing the density of the thin film.

A method for generating a plasma flow will be described. 13.56 MH in the inductively coupled plasma ion source 4 through the quartz window 5 from the copper loop antenna 6 by the high frequency power supply 8
A high frequency of z is applied at a power of 30 W or less to generate inductively coupled plasma (ICP). In order to optimize the input power, the power is adjusted by a variable condenser in the high-frequency matching box 7 so that the reflected wave power is minimized.

The molecular structure of the amino acid thin film formed on an arbitrary substrate is a Fourier transform infrared spectroscopy (FTIR, FT / IR-5M manufactured by JASCO Corporation) equipped with a mercury-cadmium tellurium (MCT) detector. X-ray photoelectron spectroscopy using an Mg-Kα ray as an excitation source (XPS, ESCA-34 manufactured by Shimadzu Corporation)
00).

FIG. 3 shows an FTIR spectrum. DP
He's standard sample was prepared by the KBr pellet method.
The deposited film and the deposited & ICP film were formed on a gold electrode of a quartz oscillator and measured by a regular reflection method. At this time, evaporation & I
The CP film was formed with a power of 10 W. The standard sample and the deposited film in FIG. 3 show almost the same signal pattern up to the fine structure of the spectrum.
In particular, weak absorption due to a carboxyl group having a peak at 2150 cm ⁻¹ characteristic of an amino acid is clearly apparent in the deposited film, and the deposited film is composed of a material retaining the molecular structure of the raw material D-Phe. It is suggested that

Next, in the case of vapor-deposited & ICP film, a signal is observed in a region where an elemental molecular species such as a hydroxyl group, a carbonyl group, an amino group, a hydrocarbon, etc. constituting an amino acid is likely to be expressed. The peak position is different as compared with. In particular, microstructures characteristic of the standard sample and the vapor-deposited film were found at places where the vapor-deposited & ICP film was not observed, suggesting a slight change in molecular structure due to the action of the plasma flow.

Next, FIG. 4 shows an XPS spectrum of a Cls region by carbon atoms. As a standard sample, D-Phe finely powdered in a mortar was compression-molded into a pellet using a tablet molding machine. Regarding the deposited & ICP films, those formed with input powers of 10 W and 30 W were examined. The spectrum pattern of the deposited film is more similar to the standard sample than the two types of deposited & ICP films, and it is supported that the molecules constituting the deposited film retain the structure of the raw material D-Phe. Is done. On the other hand, in the case of the deposited & ICP film, the signal was unclear in the standard sample and the deposited film.
A sub-band having a peak at 8.9 eV is clearly recognized, and this is a characteristic effect of plasma irradiation. This sub band on the high energy side is a signal originating from carbon bonded to oxygen or nitrogen.
The peak position of the main band of eV also slightly shifts to the high energy side, reflecting the increase of the constituent elements.

Table 1 summarizes the element ratios among carbon, oxygen and nitrogen, which are samples, detected by XPS (X-ray photoelectron spectroscopy).

[Table 1]

The three types of D-Phe films prepared using the molecular beam deposition cell according to the present invention with respect to the standard sample show a decrease in oxygen concentration of about 3%. This suggests that a peptide bond may have been generated by evaporation or dehydration of water due to heating. Also, among the D-Phe films, IC
Deposition & ICP created by irradiating P plasma
In the film, the nitrogen concentration is increased by about 2% as compared with the vapor-deposited film, while the carbon concentration is decreased. The reason for this is that the nitrogen molecules of the air components remaining and mixed commonly found in the plasma product are decomposed in the plasma, become reactive nitrogen atoms, and are taken into the film.

[0027] Among the deposited & ICP films, the 30W film is 1 better.
Compared to the 0W film, the concentration of oxygen and nitrogen is slightly smaller than that of the 0W film, while the concentration of carbon is increased. As a result of electron spin resonance (ESR) analysis, very weak ESR signals due to dangling bonds were observed in both films. Spin concentration is 2.5 × 10 ⁴ spins / cm ³ , 10 W for a 30 W film
It was 1.9 × 10 ⁴ spins / cm ³ for the membrane. Since the amount of oxygen and nitrogen is slightly reduced in the 30 W film from the element ratio in Table 1, the bond dissociation is promoted by increasing the power of the plasma, so that oxygen and nitrogen are desorbed and carbon radicals are generated. It is suggested that

The difference in the constituent elements between the samples has been discussed above, but the degree of the difference is generally extremely small, and the change between the reference sample and the deposited film as well as the deposited & ICP film is very small. It can be said that there is.

Next, the sensing function of the chemical sensor probe comprising the amino acid thin film according to the present invention for an organic gas which is a typical odor component will be described. By passing high-purity air gas at a constant flow rate and constant temperature through a container holding a glass bottle (opening) filled with organic material,
A sample gas was prepared by a gas diffusion tube method capable of stably generating an organic gas stream having a constant concentration. This sample gas was installed with a chemical sensor probe.
1 was introduced into the sensor cell and evaluated. At this time, the sensor cell and the gas pipe are installed in a constant temperature bath maintained at 25 ° C., so that highly reliable measurement is considered.

As a sample gas, 16 ppm of limonene was used. Limonene is one of the typical odorants. The (+) body (d body) is the main component of lemon odor, and the (-) body (l body) is mainly contained in pine needles and oranges. It is an odor component. The difference in gas absorption between the two optical isomers was examined.

FIGS. 5 and 6 show the resonance frequency variation (sensor response) of the QCR coated with the deposited film and the deposited & ICP film. Here, the resonance frequency was measured with an accuracy of 0.1 Hz, and the deposition & ICP film used was a film formed by applying a power of 10 W. The operation procedure in these figures will be described along the time axis (horizontal axis). Sample gas ON from the beginning
Until (approximately 30 minutes later), only pure air is flown to keep the background level. To obtain this background level, the sensor cell is cleaned by continuously flowing pure air until the frequency variation falls within the variation of 1 Hz / 10 minutes or less. Switching between the pure air line and the sample gas line is performed by a four-way valve. Next, until the sample gas is turned off (after about 3 hours and 30 minutes), the sample gas is continuously introduced into the sensor cell for about 3 hours to obtain a sensor response curve. This shows the desorption process of the sample gas after switching to the pure air line again after the sample gas is turned off.

The vapor deposition film shown in FIG. 5 is the vapor deposition & IC shown in FIG.
The absorption amount is larger than that of the P film, and limonene can be detected with high sensitivity. As the time elapses, the amount of change in the resonance frequency tends to increase, and the amount of change after 3 hours reaches about 30 Hz in the (-) body. By using this chemical sensor probe, it is possible to detect limonene at a low concentration of ppm or less.

In addition, for both the deposited film and the deposited & ICP film,
The (-) body (1 body) absorbs more than the (+) body (d body). It is considered that this is because both the thin films use D-Phe as a raw material, and if the optical activity information is held in a thin film state, the affinity for the (-) form is larger than that for the (+) form. . In particular, for the deposited & ICP film, the (+) body could hardly be detected,
(-) A sufficient detection function can be confirmed for the body.

Although the effect of the inductively coupled plasma has been described in the above embodiment, the same effect can be obtained by using a plasma source capable of discharging in a high vacuum and generating a weak plasma beam. Can be It is a plasma source such as helicon wave plasma, electron cyclotron resonance plasma, or ion beam plasma.

[0035]

As described above, according to the method for producing an amino acid thin film of the present invention, a thin film can be formed while suppressing the structural change of the amino acid-based raw material and maintaining the function of separating optical isomers. In addition, a stitch (crosslinking) structure at an atomic level characteristic of the plasma film forming technology is developed, and an amino acid thin film having excellent adhesion to a substrate and high durability can be produced.

The present invention is extremely effective for sensing of chemical substances and separation techniques typified by liquid and gas chromatography. In particular, this technology is required in the field of separating and identifying optical isomers, and is an important technology in sensing and separation of odor substances.

Environmental monitoring in living spaces and workplaces,
It can be expected to be used in a wide range of fields, such as gas sensing and quality control in production facilities, and the acquisition of environmental chemistry information such as security systems such as fire detection and dangerous substance detection. In addition, there is a great possibility that it will be effectively used in the amenity and medical fields, which are closely related to human physiological phenomena such as contamination, sensory (odor), diagnosis and prescription.

[Brief description of the drawings]

FIG. 1 shows a structure of a plasma molecular beam deposition apparatus exemplified in an embodiment of the present invention.

FIG. 2 shows the structure of the three molecular beam deposition cell of FIG. 1 exemplified in the embodiment of the present invention.

FIG. 3 is a Fourier transform infrared spectrum of a D-phenylalanine film exemplified in an example of the present invention.

FIG. 4 is an X-ray photoelectron light spectrum diagram in the Cls region of the D-phenylalanine film exemplified in the example of the present invention.

FIG. 5 is an adsorption / desorption response curve of a deposited film exemplified in an example of the present invention with respect to limonene (16 ppm).

FIG. 6 is an adsorption / desorption response curve for limonene (16 ppm) of a deposition & inductively coupled plasma film exemplified in an example of the present invention.

[Explanation of symbols]

1 vacuum container 2 Board holder 3 Molecular beam deposition cell 4 Inductively coupled plasma ion source 5 Quartz window 6 Copper loop antenna 7 High frequency matching box 8 High frequency power supply 9 Vacuum valve 10 Turbo molecular pump 11 Oil rotary pump 12 Vacuum gauge 13 Vacuum valve 14 Mechanical booster pump 15 Oil rotary pump 20 crucibles 21 heater 22 Water cooling jacket 23 Thermocouple

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-253518 (JP, A) JP-A-6-330300 (JP, A) JP-A-61-66160 (JP, A) JP-A-63-63 243835 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 5/02 C23C 14/00-14/32 JICST file (JOIS)

Claims (5)

(57) [Claims] 1. An amino acid fine powder that has been vacuum-dried,
A method for producing an amino acid thin film, comprising heating in a vacuum using a molecular beam cell composed of a heater and a water-cooling jacket, sublimating it, and depositing it on an arbitrary substrate. 2. The heating temperature according to claim 1, wherein the heating temperature is 150 ° C.
A method for producing an amino acid thin film, wherein the temperature is not less than 240 ° C. 3. An amino acid fine powder dried in a vacuum,
Production of an amino acid thin film characterized by irradiating an inductively coupled plasma beam when heating in a vacuum using a molecular beam cell composed of a heater and a water cooling jacket, sublimating it and depositing it on an arbitrary substrate Method. The surface of the transducer-type weight detection transducer is heated in a vacuum using a molecular beam cell composed of a heater and a water-cooled jacket to sublimate the vacuum-dried fine powder of amino acid. A chemical sensor probe characterized by being coated with a formed thin film. 5. A method in which the surface of a transducer-type weight detection transducer is heated in a vacuum using a molecular beam cell composed of a heater and a water-cooled jacket to sublimate fine vacuum-dried amino acid powder. A chemical sensor probe characterized by being coated with a thin film irradiated with an inductively coupled plasma beam when formed.