JPH06330300A - Formation of amino acid thin film and chemical sensor probe using thin film - Google Patents

Abstract

PURPOSE:To obtain the high polymer thin film which has a hydrophilic surface characteristic and is high in adhesion and has the basic structure of amino acids by using the platelike substrate stuck with amino acids as a sputtering target in a high-frequency current sputtering method. CONSTITUTION:For example, in forming a thin film, the sputtering target which is made by dropping the satd. aq. soln. of glutamic acid and phenylalanine on a polyethylene disk and evaporating water and drying is used. The amino acid thin film which has the hydrophilic surface characteristic and is high in adhesion is obtained by sputtering this sputtering target in high-frequency current discharge. Because the amino acid thin film has excellent and reproducible desorption function to an org. gas, by forming the amino acid thin film on a rock crystal vibrator, the chemical sensor probe which is high in sensitivity and has a wide object range is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film having an amino acid as a basic structure which is excellent in adhesion to a substrate, controllability of film thickness, etc., and its forming technique, and further to a chemical sensor probe using the amino acid thin film. .

[0002]

2. Description of the Related Art Among organic thin film forming technologies, those using vacuum or discharge technology have many excellent characteristics as compared with the wet method in terms of purity, adhesion, controllability of film thickness and substrate selectivity. Have. In particular, those obtained by utilizing the sputtering phenomenon have these characteristics. However, it is highly likely that the molecular structure of the base material will be significantly different from that of the base metal due to the cleavage of the bond due to ion bombardment or discharge. In particular, oxygen was easily lost, and it was difficult to introduce a hydroxyl group or a carbonyl group. Further, the vacuum vapor deposition method has a relatively low risk of breaking the structure of the base material, but has a very low possibility of being applicable to a substance having a small vapor pressure such as an amino acid. As a method of forming a sensitive film for a humidity sensor, there is a method of introducing hydrophilicity by introducing an amino group by chemically treating a plasma polymerized film. However, in this method, there is a risk of significantly disturbing the highly reactive membrane molecular structure. Especially, there is a high possibility of deactivating radicals. Further, a functional group containing oxygen cannot be introduced, and the effects involved in these cannot be expected.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a polymer thin film having hydrophilic surface properties and high adhesiveness, and having a high sensitivity and a wide target range formed by the thin film. To provide a chemical sensor probe.

[0004]

The present invention will be described in brief. The first invention of the present invention relates to a method for forming an amino acid thin film, which comprises forming a thin film by sputtering a sputtering target in a high frequency discharge. The high frequency sputtering method is characterized in that an amino acid solution is applied on a plate-shaped substrate and the solvent is evaporated to be used as a sputtering target. A second invention of the present invention relates to a chemical sensor probe, which is characterized in that an amino acid thin film is formed on a quartz oscillator.

The present invention relates to a sensitive film for chemical sensing, which is characterized by using an organic thin film having an amino acid as a basic structure in order to improve its sensitivity and target range.
Hereinafter, the present invention will be specifically described.

First, the first invention of the present invention will be described. As the type of amino acid used in the first invention, considering the solubility in a solvent for preparing a target,
In addition, it is necessary to consider the melting point or sublimability for use in the high frequency sputtering method, and as a result of examining various neutral, acidic and basic amino acids, it was found that glutamic acid and phenylalanine are suitable.

The high-frequency sputtering device, which is a thin film device used in the present invention, may be a conventionally known one, one example of which is shown in FIG. That is, FIG. 1 is a schematic diagram of an example of a high frequency sputtering apparatus for forming the amino acid thin film of the present invention. Reference numeral 1 is a vacuum container, 2 is a substrate holder, 3 is a thin film forming substrate, 4 is a sputtering target, 5 is a shutter, 6 is a high frequency electrode, 7 is a matching box, 8 is a high frequency power supply, 9 is an oil diffusion pump, and 10 is oil. Rotary pump, 1
1 is an exhaust system main valve, 12 is a roughing valve, 13
Is a suction valve for an oil diffusion pump, 14 is a variable valve for introducing gas, 15 is a stop valve, 16 is an argon gas cylinder, and 17 is a heater.

The molecular structure of the thin film was analyzed using a Fourier transform infrared spectrophotometer and an X-ray photoelectron spectrophotometer. The outermost surface structure of the thin film was analyzed by X-ray photoelectron spectroscopy (photoelectron escape depth: about 8 nm).

The thin film produced by the method of the present invention exhibits surface properties which are hydrophilic and excellent in biocompatibility because of its molecular structure containing oxygen and nitrogen, and these surfaces are promising as a necessary coating technique. In addition, it also contains a high concentration of active sites for hydrophobic intermolecular interactions such as radicals and unsaturated bonds in the molecular skeleton having a large atomic number density characteristic of plasma-derived organic thin films. Due to these properties, the thin film forming method of the present invention enables highly sensitive sensing of a wide range of chemical substances.

Next, the second invention of the present invention will be specifically described. The amino acid thin film according to the second invention has an excellent adsorption / desorption function that is reproducible with respect to organic gases, and it is possible to detect gas molecules with high sensitivity using these thin films. The amino acid to be used is selected from this viewpoint because it is necessary. The method for forming the amino acid thin film may be a conventional method, for example, a method of coating an amino acid solution on a crystal oscillator and evaporating a solvent, a vacuum vapor deposition method, a sputtering method, or the thin film according to the first aspect of the present invention. A forming method and the like are exemplified. However, from the viewpoints of adhesion, durability, sensitivity, etc. between the amino acid thin film and the crystal oscillator, the thin film forming method is preferably the method of the first invention, and the amino acid used is preferably glutamic acid and phenylalanine. I found that.

As described above, the chemical sensor probe of the present invention needs to have good adsorption characteristics for organic gases, and the measuring device is schematically shown in FIG. That is, FIG. 4 is a schematic view of an apparatus for measuring the gas adsorption characteristics of the chemical sensor probe of the present invention. Reference numeral 21 is a sensitive film-coated crystal oscillator, 22 is a measuring cell, 23 is a three-way cock, and 2
4 is a gas source cell, 25 is a constant temperature bath, 26 is a stop valve, 27 is a mass flow controller, 28 is a pure air cylinder, 29 is a stop valve, 30 is a mass flow controller, 31 is a pure air cylinder, 32 is an oscillator, 33 is a frequency The counter 34 is a computer. The measuring method is described below. First, pure air is sent from the pure air cylinder 28 to the measuring cell 22 in which the sensitive film-coated crystal oscillator 21 is set at a flow rate of about 0.2 liter / min, and the frequency of the oscillator is stabilized. Thereafter, the flow path from the gas source cell 24 filled with the solution to be measured is switched by the three-way cock 23, and pure air is similarly introduced through 31, 29 and 30,
The gas is sent from the gas source to the measuring cell 22 to perform the measurement. The weight change due to the adsorption of the crystal unit is read by the frequency counter 33 and displayed on the computer 34.

[0012]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 As an example of a method for forming an amino acid thin film according to the present invention, a thin film formation of glutamic acid and phenylalanine will be described. First, a saturated aqueous solution of glutamic acid and phenylalanine was dropped on a polyethylene disc (diameter: 135 mm, thickness: 10 mm), water was evaporated overnight at room temperature, and the product was further dried at 70 ° C for 1 hour as a sputter target. Prepare in advance prior to thin film formation. Next, a specific procedure for forming a thin film of an amino acid using the device shown in FIG. 1 on a crystal oscillator to obtain a chemical sensor probe will be described.
A crystal disk (AT cut,
A fundamental frequency: 9 MHz) and a silicon wafer for analysis are attached. This crystal disk has a thickness of 0.1 mm and a diameter of 10 m.
m, a gold electrode having a thickness of several microns and a diameter of 5 mm is formed on both sides. A polyethylene disk coated with glutamic acid or phenylalanine as the sputter target 4 is fixed to the high frequency electrode 6. After operating the oil rotary pump 10 and opening the oil diffusion pump suction valve 13, the heater of the oil diffusion pump 9 is operated to start the pump.
After closing the valve 13, the roughing valve 12 is opened to start evacuation. When the degree of vacuum rises to about 10 ^-2 Torr, the valve 12 is closed, the valve 13 is opened, and the main valve 11 is opened to evacuate high vacuum by the oil diffusion pump to raise the degree of vacuum to about 10 ^-6 Torr. Wait for Variable valve 1 for gas introduction when exhausting to a specified vacuum level
4 is gradually opened, and argon is introduced from the argon gas cylinder 16 so that the degree of vacuum is adjusted to the level of 10 ^-2 Torr. Here, 1.2 k is applied to the high frequency electrode 6 by the high frequency power source
A high frequency voltage of about V is applied to cause discharge. A capacitor is adjusted in the matching box 7 to make a stable discharge state. Once the discharge is generated, the supply of argon gas is stopped and the main valve 11 is adjusted to keep the pressure inside the vacuum container 1 at 5 × 10 ⁻² Torr or more. After discharging for several minutes to remove the contaminated layer on the surface of the sputter target, the shutter 5 is opened and the amino acid thin film is deposited on the crystal oscillator. The film thickness to be deposited is adjusted by the opening time of the shutter. Glutamic acid and phenylalanine thin films formed on silicon wafers at 22 ° C and 54% humidity
The contact angles of water measured under the atmosphere are 57.3 degrees and 66.9 degrees, respectively, which is much smaller than the sputtered thin film of the hydrophobic fluoropolymer showing about 100 degrees. From this, it can be confirmed that the surface of these amino acid thin films is hydrophilic.

As described above, the molecular structure of the thin film was analyzed using a Fourier transform infrared spectrophotometer and an X-ray photoelectron spectrophotometer. FIG. 2 shows specular reflection infrared spectroscopy spectra of the phenylalanine thin film and the glutamic acid thin film formed on the crystal oscillator. That is, FIG. 2 shows a Fourier transform infrared spectroscopic spectrum of the amino acid thin film of the present invention measured by the specular reflection method, in terms of the relationship between wave number (cm ⁻¹ , horizontal axis) and transmittance (arbitrary unit, vertical axis). It is a figure. Both amino acids (N-
A signal due to stretching vibration of H) and hydroxyl group (OH) is recognized around 3400 cm ^-1 . Also, C-H
Stretching vibration is observed near 3000 cm ^-1 . Furthermore,
Stretching vibration of C = O of the carboxyl group is observed as a strong absorption band centered at 1670 cm ^-1 . In the case of phenylalanine thin film, the skeletal vibration of the benzene ring is presumed to be included in this strong absorption band.

As described above, the outermost surface structure of the thin film is X
Line photoelectron spectroscopy (photoelectron escape depth: about 8 nm)
Was analyzed by. The constituent element ratio of the thin film calculated from the signal intensity of each element is carbon: 7 in the phenylalanine thin film.
7.6%, oxygen: 13.2%, nitrogen: 9.2%, glutamic acid thin film carbon: 64.0%, oxygen: 19.4%,
Nitrogen: 16.6%. However, these values are calculated excluding undetectable hydrogen. The concentrations of oxygen and nitrogen, which contribute to hydrophilicity, at the outermost surface were higher in glutamic acid, and this result is reflected in the contact angle of water being smaller than that of the phenylalanine thin film. An X-ray photoelectron spectroscopy (XPS) spectrum in the Cls region is shown in FIG. That is, FIG. 3 shows X of Cls region of the amino acid thin film of the present invention.
It is a figure which shows a line photoelectron spectroscopy spectrum by the relationship between the binding energy (eV, abscissa) and photoelectron intensity (arbitrary unit, ordinate). The Cls-XPS spectrum of the phenylalanine thin film shows a main peak due to a hydrocarbon (CxHy) around 285 and its high binding energy side (286 to 289e).
A weak signal attributed to a functional group such as a carboxyl group or an amino acid having a bonding mode with oxygen and nitrogen spreading in V) is observed. On the other hand, Cls-X of glutamic acid thin film
In the PS spectrum, the signal intensity of these functional groups is greatly increased, which corresponds to the fact that the relative element ratio of oxygen and nitrogen in the film is larger than that in the phenylalanine thin film. After sputter etching this surface with 0.5 kV argon ions for 3 minutes, the phenylalanine thin film had carbon: 89.1%, oxygen: 3.9%, nitrogen: 7.0%,
In the glutamic acid thin film, carbon: 73.8%, oxygen: 8.9
%, Nitrogen: 17.3%. In both cases, the oxygen concentration is reduced by ion etching, which is particularly remarkable in the phenylalanine thin film. It is presumed that this reflects the result that oxygen in the surface contaminated layer in the atmosphere was removed in addition to oxygen contained in the functional group constituting the film.

These amino acid thin films were formed on an AT-cut quartz crystal disk (QCM) having a diameter of 1 cm and a thickness of 0.1 mm, and the gas adsorption characteristics were examined. This QCM has a fundamental frequency of 9 MHz, and a frequency change of 1 Hz corresponds to a weight change of 1 ng. As described above, the outline of the measuring device is shown in FIG.
Shown in. A crystal unit coated with a thin film of about 0.36 μm amino acid was exposed to 20 ppm concentration of primary alcohol vapor at 25 ° C.
FIG. 5 shows the amount of gas adsorbed at the time of exposure in Table 1 as the volume of alcohol molecules. That is, FIG. 5 is a diagram showing the amount of adsorption of the amino acid thin film of the present invention with respect to alcohol gas having a concentration of 20 ppm, in terms of the relationship between the molecular volume (Å ³ , abscissa) and the number of adsorbed molecules (nmol, ordinate). Such a low-concentration alcohol vapor has an extremely small amount of adsorption in a hydrophobic thin film such as a fluorine-containing plasma polymer, and cannot be clearly detected. However, as shown in FIG. 5, it was clearly detected in the amino acid thin film, and a particularly large adsorption amount was confirmed in the phenylalanine thin film. These are the averages of three measurements using the same thin film, and each film showed reproducible adsorption / desorption characteristics. It is presumed that hydroxyl groups, which are responsible for the strong intermolecular interaction located at the ends of the linear carbon chains, make a large contribution to the adsorption of these alcohol molecules, and the contribution of the hydrocarbon part is small. This hydrocarbon part mainly controls only the volume and mass of the molecule, and this molecular parameter increases from methyl alcohol to n-pentyl alcohol. The adsorption amount of both membranes decreases as the volume of alcohol molecules increases. This tendency is remarkable especially in the phenylalanine thin film. Since small volumes of methyl alcohol and ethyl alcohol show a large adsorption amount, it is considered that these small molecules have an adsorption mechanism that permeates into the thin film. Particularly, in the phenylalanine thin film, it is suggested that the adsorption amount is saturated with alcohol molecules having a carbon number of n-propyl alcohol or more. The fact that the amount of adsorption of n-pentyl alcohol is slightly higher than that of n-butyl alcohol means that alcohol molecules aggregate and accumulate near the film surface rather than permeate into the film at this size. It is highly possible that this reflects the fact that the process of going about becomes dominant. In addition to these alcohols, ketones represented by acetone, aromatics represented by benzene, halogenated carbons represented by carbon tetrachloride, aliphatic hydrocarbons represented by hexane, etc. As a result of gas adsorption measurement, it was also revealed that it has a reproducible adsorption / desorption function equivalent to or better than that of the fluorine-containing plasma polymer.

Finally, this amino acid-coated crystal oscillator is left in a thermo-hygrostat (temperature: 60 ° C., relative humidity: 85%) for 10 days, and then left in the atmosphere for 1 day to evaporate water to evaporate the same alcohol. Even when the gas adsorption measurement was carried out, the change in the characteristics was within a few percent, and it was revealed that these thin films have hydrophilicity but excellent durability against humidity.

[0018]

Industrial Applicability As described above, the amino acid thin film according to the present invention has a reproducible and excellent adsorption / desorption function with respect to an organic gas. Can be detected. In addition, the sensor probe composed of these thin films has excellent durability, low noise and high sensitivity in the atmosphere, so it can be used for everything from familiar things such as detection of various gases and fires to global pollution monitors. Environmental sensing becomes possible. Furthermore, these thin films have a hydrophilic surface derived from amino acids, and are expected as a promising coating technology particularly in the biological field, which requires these surfaces.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a high-frequency sputtering apparatus for forming an amino acid thin film of the present invention.

FIG. 2 is a diagram showing a Fourier transform infrared spectroscopy spectrum of the amino acid thin film of the present invention measured by a specular reflection method.

FIG. 3 is a diagram showing an X-ray photoelectron spectroscopy spectrum in the Cls region of the amino acid thin film of the present invention.

FIG. 4 is a schematic view of an apparatus for measuring gas adsorption characteristics of the chemical sensor probe of the present invention.

FIG. 5 is a graph showing the amount of adsorption of the amino acid thin film of the present invention to alcohol gas having a concentration of 20 ppm.

[Explanation of symbols]

1: vacuum container, 2: substrate holder, 3: thin film forming substrate,
4: sputter target, 5: shutter, 6: high frequency electrode, 7: matching box, 8: high frequency power supply, 9:
Oil diffusion pump, 10: Oil rotary pump, 11: Main valve for exhaust system, 12: Roughing valve, 13: Suction valve for oil diffusion pump, 14: Variable valve for gas introduction, 15: Stop valve, 16: Argon gas cylinder , 17: heater, 21: sensitive film-coated crystal unit, 22: measuring cell,
23: 3-way cock, 24: gas source cell, 25: constant temperature bath,
26: Stop valve, 27: Mass flow controller, 28: Pure air cylinder, 29: Stop valve, 3
0: Mass flow controller, 31: Pure air cylinder,
32: oscillator, 33: frequency counter, 34: computer

Claims (2)

[Claims] 1. A high-frequency sputtering method for forming a thin film by sputtering a sputter target in a high-frequency discharge, wherein the amino acid solution is applied onto a plate-shaped substrate and the solvent is evaporated to obtain a sputter target. Method for forming thin film. 2. A chemical sensor probe having an amino acid thin film formed on a quartz oscillator.