JP2021110676A - Molybdenum cluster membrane containing element, sensor, device and measurement method for temperature, humidity and light using them - Google Patents

Abstract

To provide an element for measuring three physical quantities of temperature, humidity, and light with one element.SOLUTION: Disclosed is an element for measuring the physical quantity, which includes a pair of opposed electrodes and a sensitive membrane disposed between the electrodes. The sensitive membrane is a complex of an eight tetrahedral structure and contains the complex consisting of fourteen ligands which stabilize six molybdenum atoms and the complex of the eight tetrahedral structure and a molybdenum cluster which has at least one hydronium ion as a counterion.SELECTED DRAWING: Figure 1

Description

The present invention relates to a Mo ₆ cluster film-containing element, a sensor including the element, a device including the sensor, and a method for measuring temperature, humidity, and light (for example, illuminance and ultraviolet intensity) using the sensor. Here, "Mo ₆ " means that the number of molybdenum atoms is six.

Conventionally, a measuring device (so-called multi-sensor) capable of measuring two or more physical quantities such as temperature, humidity, and light with one unit has been known.

T. K. N. Nguyen, F.M. Grasset, B. et al. Dierre, C.I. Matsunaga, S.M. Cordier, P.M. Lemoine, N.M. Ohashi, and T. et al. Uchikoshi, ECS Journal of Solid State Science and Technology, 5 (2016) 178-186

Generally, when measuring a plurality of physical quantities, an element corresponding to each physical quantity to be measured is required. That is, when a plurality of physical quantities are measured by one measuring device, a number of elements corresponding to the number of physical quantities to be measured is required in the measuring device. Moreover, it is necessary to prepare and arrange a circuit board corresponding to each element. For example, when designing a device that measures three types of physical quantities of temperature, humidity, and light with one measuring device, three elements (specifically, an element for temperature measurement, an element for humidity measurement, and an element for measuring humidity, and An element for optical measurement) and three circuit boards (specifically, a circuit board corresponding to an element for temperature measurement, a circuit board corresponding to an element for humidity measurement, and a circuit corresponding to an element for optical measurement). It is necessary to prepare and arrange the substrate). In this way, when designing a device that measures a plurality of physical quantities (particularly temperature, humidity, light) with one measuring device, a plurality of elements and a circuit board are prepared and arranged in the measuring device. There must be. As a result, the design of the above-mentioned device becomes complicated, it is difficult to reduce the size and weight of the device, and there are problems such as an increase in manufacturing cost.

Therefore, an object of the present invention is to provide an element for measuring three physical quantities of temperature, humidity, and light with one element. Specifically, it is intended to provide an element that returns an electrical response regardless of whether temperature, humidity, or light is input.

We (the present inventors) are recognized as multifunctional building blocks for the design of nanomaterials for the purpose of designing new smart devices (eg sensors) that utilize optical electronic and optical ionic properties. We focused on metal atom clusters.

For Mo ₆ atomic clusters, light-related physical properties such as light emission, absorption or photocatalytic properties have already been reported due to their individual electronic structures. However, their electrical properties have not been studied.

_{Recently, Mo 6} cluster film formation using the EPD method has been reported (Non-Patent Document 1). However, even in that report, no studies have been conducted on the electrical properties. The functional property shown in the report is only to absorb ultraviolet rays and near-infrared rays due to the optical _{property of the Mo 6 cluster, and it is a physical property related to light as before.}

Thus, the electrical properties of the Mo ₆ cluster have not been known so far. This is difficult to measure the electrical properties of Mo ₆ clusters, Mo ₆ clusters are said to have the electrical properties were well known presumed.

For the first time, we have succeeded in measuring the temperature, humidity, and its unique electrical properties that change with light irradiation by using the _{Mo 6} cluster film formed by the EPD method.
These data show that this material can sense temperature, humidity and light at the same time.

As a result, they have found that the above-mentioned problems can be solved by _{a predetermined Mo 6 cluster film-containing device, and have completed the present invention.}

Specifically, the present invention is as follows.
[1]
A pair of opposing electrodes and
A sensitive film placed between the electrodes and
It is an element having
The sensitive film is
A complex having an octahedral structure consisting of 6 molybdenum atoms and 14 ligands that stabilize the octahedral structure of the complex, and at least one hydronium ion as a counterion.
Contains molybdenum clusters,
element.
[2]
The device according to the above [1], wherein the ligand consists of a halogen atom or contains both a halogen atom and at least one hydroxy group.
[3]
The device according to the above [1] or [2], wherein the counterion is essentially composed of one or more hydronium ions.
[4]
The element according to any one of [1] to [3] above, which exhibits an electrical response to any input of temperature, humidity, and light.
[5]
The element according to any one of the above [1] to [4] and
Power supply and
A detector for detecting the electrical response from the element,
Sensor with.
[6]
The sensor according to the above [5], wherein the power supply is selected from a DC power supply, an AC power supply, and a power supply that can be switched between DC and AC.
[7]
A sensing device including the sensor according to the above [5] or [6].
[8]
A method for measuring at least one of temperature, humidity, and light using the element according to any one of [1] to [4] above.
[9]
A method for measuring three types of temperature, humidity, and light using the element according to any one of the above [1] to [4].

According to the present invention, it is possible to provide an element that exhibits an electrical response regardless of whether temperature, humidity, or light is input. Therefore, according to the present invention, there are provided sensors and devices (eg, sensing devices) that enable measurement of temperature, humidity, and light with a single element.
That is, according to the present invention, when a single measuring device measures a plurality of physical quantities of temperature, humidity, and light, the number of elements required by the device can be one. As a result, according to the present invention, it is expected that the design of a device for measuring temperature, humidity, and light with one device can be simplified, the device can be easily miniaturized, and the manufacturing cost of the device can be significantly reduced. can.

^{_{[Mo 6 L i 8 L a}} 6] 2- ( wherein, ^{L i} (inner ligand) = Cl, Br, I, L a ( apical ligand) = Cl, Br, I, F, OH) It is a figure which shows the schematic diagram of the _{Mo 6} cluster represented by the chemical formula of. It is a figure which shows one schematic diagram of the sensing apparatus of this invention. It is a figure which shows the characteristic of the cluster film made by EPD. a shows an SEM image of a cross section of a film deposited on an anode substrate coated with an ITO layer by EPD. b _{is, [Mo 6 Br 14-n} (OH) n] 2- ions (here, n = 0, 1 and 2), and associated monitoring and simulation electrospray ionization mass spectra of _{H 2} O adduct Is shown. c indicates the ATD recorded for the deposited membrane [Mo ₆ Br _14-n (OH) _n ] ^2- (where n = 0, n = 1, n = 2). Here, the drift condition of the drift tube is helium at 298 K and a pressure of 4.0 torr, and a drift voltage of 450 V. Collision break measured in helium at 298K for AuNCs [Mo ₆ Br _14-n (OH) _n ] ^2- (function of n, number of exchanged Br / OH, accuracy of CCS value values ± 2%) It is a figure which shows the area ( ^DT CCS _He). It is the electrospray ionized mass spectrum of the MoBr precursor, and is the figure which shows that only one peak corresponding to _{[Mo 6} Br ₁₄ ] ^{2- exists.} It is the electrospray ionization mass spectrum of the membrane peeled off from the anode substrate, and is the figure which shows that there are peaks of two groups (A and B). A is a divalently charged species and _{is attributed to [Mo 6} Br _14-n (OH) _n (H ₂ O) _m ] ^2- (0 ≦ n ≦ 2 and 0 ≦ m ≦ 2). It is a monovalently charged species and is attributed to _{[Mo 6} Br ₁₂ (OH)] ^- and [Mo ₆ Br ₁₃ ] ^-. It is a figure which shows the schematic diagram of the experimental apparatus of conductivity measurement with and without irradiation with LED light. It is a figure which shows the conduction property of an amorphous octahedral molybdenum cluster thin film. FIG. A is a diagram showing the temperature dependence of the conductivity of the cluster film due to the difference in humidity. b is a diagram showing the humidity dependence of the conductivity at 300 K. c is a diagram showing the frequency dependence of M ″ at each temperature. d is a diagram showing the frequency dependence of M ″ at each humidity. It is a figure which shows the impedance spectrum of the cluster film measured at different temperature under a constant humidity of 80RH%. It is a figure which shows the impedance spectrum of the cluster film measured at different relative humidity of a temperature of 300K. It is a figure which shows the humidity dependence of the conductivity of the cluster film prepared by the deposition time of 20 seconds. It is a figure which shows the temperature dependence of the relaxation time of a cluster membrane. It is a figure which shows the electric characteristic change of the cluster film by light irradiation. FIG. A is a diagram showing an It curve when a DC voltage of 2 V is applied to the cluster film. FIG. b is a diagram showing an It curve of the cluster film by irradiation with UV-A (395 nm), blue (465-475 nm) and red light (660 nm). c is a diagram showing the increase in current due to the light intensity of different UV-A. (The inserted figure shows ΔI / average ΔI _{360 lx} .) D is an impedance diagram of the cluster membrane before, during, and after UV-A irradiation. e is a figure which shows the resistance change of a cluster film under UV-A, blue, and red light irradiation. It is a schematic diagram of the structure of a cluster membrane. FIG. A is a diagram showing octahedral molybdenum clusters in a cluster membrane. b is a diagram showing a structure assumed for a cluster film at high humidity and low humidity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate.

[element]
The "element" of the present invention is an element having a pair of opposing electrodes and a sensitive film arranged between the electrodes, and the sensitive film is a complex having an octahedral structure and has six elements. It contains a molybdenum cluster having a complex composed of a molybdenum atom and 14 ligands for stabilizing the octahedral structure of the complex, and at least one hydronium ion as a counter ion.
Here, the "sensitive film" in the present invention is a film whose electrical characteristics change depending on any input of temperature, humidity, and light.
The "molybdenum cluster" in the present invention comprises a "complex" and a "counterion".
The "complex" is an octahedral complex consisting of 6 molybdenum atoms and 14 ligands that stabilize the octahedral structure of the complex. Normally, six Mo atoms are present at the octahedral vertices.
The "14 ligands" are preferably composed of a halogen atom or contain both a halogen atom and at least one hydroxy group. However, there is no particular limitation as long as it stabilizes the octahedral structure of the complex.
Usually, the "molybdenum cluster", through the inner ligands covering the octahedra mainly through the Mo-L ⁱ bonds with covalent (L ^i), a Mo-L ^a bond having a strong ionic character It is stabilized by six further bonded apical ligand (L ^a). Therefore, in _general, can be represented by the chemical formula of _{^{[Mo 6 L i 8 L a}} 6] 2- ( wherein, ^{L i} = inner ligand, ^{L a} = apical ligand). The inner ligand ^{(L i),} for example, Cl, Br, may I, as the apical ligand ^{(L a),} for example, Cl, Br, I, F, is OH. FIG. 1 shows an outline of the structure.
FIG 12a, an inner ligand ^{(L i)} is Br, apical ligand ^{(L a)} is shown the structure of a molybdenum octahedral cluster complex is Br and OH.
The "complex" may be H 2 _O adduct.
The "counterion" comprises at least one hydronium ion. The "counterion" preferably consists of only hydronium ions. However, as long as the object of the present invention can be achieved when used as an element, at least one or more substances other than hydronium ions may be contained as the "counterion". For example, it may contain impurity ions below the detection limit together with hydronium ions. Therefore, in the present application, "essentially" of "the counterion is essentially composed of one or more hydronium ions" means hydronium ions as long as the object of the present invention can be achieved when used as an element. It means that it may contain substances other than.
The "electrode" constituting the "element" of the present invention is not particularly limited as long as it can achieve the object of the present invention when used as an element. For example, examples of the "electrode" include an anode substrate (anode electrode) of ITO glass and a cathode electrode of a stainless steel sheet, respectively.
By setting the force per contact area between the "electrode" and the "sensitive film" to an appropriate force, the electrical characteristics of the "element" of the present invention are effectively exhibited. Therefore, it is preferable that the "electrode" is brought into contact with the "sensitive film" with an appropriate force capable of measuring the electrical characteristics of the element. Specifically, it is preferable that the force per contact area between the electrode and the sensitive film is 0.5 (N / cm ^{2) or more.} Further, from the viewpoint of the strength of the sensitive film and the like, it is also preferable that ^{the force per contact area is 50 (N / cm 2) or less.}
The "element" of the present invention is also characterized in that it "shows an electrical response to any input of temperature, humidity, and light." Here, "showing an electrical response to any input of temperature, humidity, and light" in the present application means that the electrical characteristics change regardless of any physical quantity of temperature, humidity, or light. However, it means that this is output as an electric signal corresponding to the physical quantity.
As for the light input means, there are light irradiation means using UV-A or blue LED light. However, the means are not limited as long as the object of the present invention can be achieved.

[Sensor]
The "sensor" in the present invention includes the element, a power source, and a detection unit for detecting an electrical response from the element.
Here, the "detector for detecting an electrical response from the element" is a portion that detects and outputs the electrical signal as the corresponding physical quantity, and is a so-called "detector" or "detector". "And so on.
Unless otherwise specified, the "power supply" means a power supply provided for measuring the electrical characteristics of the "elements" constituting the "sensor". Further, the "power supply" may be a DC power supply, an AC power supply, or a power supply capable of switching between DC and AC, or may be a combination thereof.

[Sensing device]
The "sensing device" of the present invention includes the sensor.
The "sensing device" in the present invention means a device that performs measurement / measurement using a sensor. For example, a detection unit of the sensor including a display unit (display) that digitizes and displays an electric signal detected and output as a physical quantity can be mentioned as an example.

FIG. 2 shows a schematic view of the “sensing device” of the present invention.

[Measuring method]
As described above, by using the "element" of the present invention, at least one of temperature, humidity, and light can be measured. Moreover, temperature, humidity, and light can all be measured by one "element".
In the present invention, the above measurements may be performed simultaneously or one by one.

The outline of the present invention will be supplemented and described below.

We have developed a new environmental sensing device based on optical ion-electron phenomena using octahedral molybdenum metal (Mo _{6) clusters.
When Mo 6} clusters are deposited on a transparent electrode in an organic solvent containing trace amounts of water using an electrochemical method, the water is incorporated into the deposited membrane. During this process, _{some types of ligands that stabilize the skeletal structure of Mo 6} clusters are partially substituted with hydroxyl (OH) groups and _{negatively charged skeletal structures of Mo 6} cluster units (units). It is stabilized by hydronium ions as counter ions _(H 3 ^{O +).}
As a result, _{the transparent film of the Mo 6} cluster produced by this method exhibits hydronium ion-electron mixed conductivity.
Ion conductivity changes greatly depending on the temperature and humidity in the atmosphere, and electron conductivity changes greatly depending on the wavelength and intensity of the irradiation light. This unique multi-sensing property opens up new possibilities for environmental sensor applications.

Functional materials based on metals, semiconductors, ceramics, polymers, composites, etc. have provided solutions to social problems and developed new technologies for industry. In particular, materials that convert thermal, chemical, optical, mechanical, or electrical energies to each other are widely used on a daily basis. Nevertheless, devices such as piezoelectric elements, thermoelectric elements, gas sensors, and photodiodes require more advanced material properties to achieve a sustainable and safe society.
In recent years, the miniaturization of equipment has made innovative technological advances in various fields.
The development of multifunctional materials that can simultaneously detect different types of information using a single material will further expand its application in sensing, miniaturization, and weight reduction devices.
As recently reported on halide perovskite and LiNbO ₂ , the effect of light on the electrical properties of ionic conductors near room temperature has become one of the new and striking topics.
We focused on metal atomic clusters, which are recognized as multifunctional building blocks for the design of nanomaterials, for the purpose of designing new smart devices (eg sensors) that utilize optical electronic and optical ionic properties. ..
Metal Atom Cluster "A finite number of metal atoms that are held together, or at least to a large extent, primarily together by direct bonds between metal atoms, even though some non-metal atoms may be closely related to the cluster. "Flocks" have various interesting properties that result from their simple and unique structure consisting of a limited number of elements.
Among the metal clusters, the general formula A ₂ Mo ₆ X ⁱ ₈ L ^a ₆ (A = Cs ⁺ , n- (C ₄ H ₉ ) ₄ N ⁺ and X = Cl, Br or I and L = Cl, Br, Molybdenum octahedral cluster compounds) having i = inner ligand, a = apical ligand, such as I, F, OH) have photochemical properties and photochemical properties due to the delocalization of valence electrons on the metal center. Shows redox characteristics.
The Mo ₆ cluster consists of an inner ligand (Br ⁱ ) that covers the octahedron mainly via a covalent Mo-Br ⁱ bond, and six additional ^{Mo-Br a} bonds with strong ionic properties. It is stabilized by the bound apical ligand (Br ^a).
It is well known that these cluster compounds dissociate in a solvent to form a rigid {Mo ₆ Br ⁱ ₈ } ⁴⁺ block-based [Mo ₆ Br ⁱ ₈ Br ^a ₆ ] ^{2-anion unit.
In solution, the Br a} atom at the apical position on the cluster can be exchanged with a functional group.
Previous studies of Mo ₆ cluster materials have revealed phosphorescence, photovoltaic, and photocatalytic properties under light irradiation.
Recently, proton conductivity has been proposed for compressed pellets of _{Cs 2} Mo ₆ Br ₁₄ and Cs ₂ Mo ₆ Cl ₁₄ powders due to the difference in resistance at room temperature between moist and dry air. , The origin of the carrier and the conduction mechanism have not been clarified.
Apart from their work, Nguyen et al. Succeeded in developing a method for producing homogeneous and transparent membranes based _{on Nb 6} , Mo ₆ and Ta _{6 clusters using electrophoretic deposition (EPD).} It provides an important combination of cost effectiveness, long-term consistency of film thickness and surface morphology, size expandability, high deposition rate, and regioselectivity (eg, Non-Patent Document 1).
The resulting cluster film exhibits high transmittance in the visible region, strong absorption in the UV and NIR regions, and is accompanied by emission of red fluorescence generated from _{the Mo 6 cluster.}
X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), from of X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) analysis, Nguyen et al., Mo ₆ film formed by EPD process Has an amorphous structure and has the following properties.
^{-All Cs +} ions in the original cluster block cannot be found, and H ₃ O ⁺ exists as a counter cation instead.-Apical ligand of ^{Br −} is partially replaced by ^{OH −.} A small amount of is incorporated into the membrane during the EPD process.
_{Therefore, proton conductivity is expected for Mo 6} cluster membranes formed by the EPD process, but their electrical properties have not yet been evaluated.

In this study, the humidity and temperature dependence of the electrical properties of the _{translucent Mo 6 cluster film prepared by EPD was investigated.} Furthermore, the conductivity under light irradiation was also examined. Based on the obtained results, the conduction mechanism of the membrane was considered.
Mass spectrometry was used to accurately determine the chemical composition of _{the Mo 6} cluster membrane prepared by EPD.
Furthermore, the electrical characteristics of the film were evaluated in detail by the AC impedance measurement method and the DC measurement method, and the effects of light irradiation were investigated for the electronic and ionic characteristics.

Hereinafter, the present invention will be described in detail with reference to specific examples. However, the present invention is not limited to this example.

1. 1. Preparation, morphological observation, and structural evaluation of Mo _{6 cluster film The production, morphological observation, and structural evaluation of the Mo 6} cluster film used for the device according to one embodiment of the present invention were carried out as follows.

[Preparation of cluster membrane by EPD]
Cs ₂ Mo ₆ Br ₁₄ powder was _{synthesized from MoBr 2} and CsBr reagents at high temperature by the solid phase method.
_{Cs 2} Mo ₆ Br ₁₄ powder was dissolved in reagent grade MEK (99.5%, Kishida Chemistry) at a concentration of 5 g / L with stirring on a magnetic stirrer until a clear solution was obtained.
ITO glass and a stainless steel sheet were connected to a DC power supply (PD56-10AD, KENWOOD) as an anode substrate and a cathode electrode, respectively.
Prior to use, ITO glass was washed with distilled water and ethanol by sonication. EPD was carried out at a constant voltage of 15 V for 30 seconds.
_{The Mo 6} cluster film deposited on the ITO glass substrate was dried in air for 24 hours and then characterized.

Here, MEK refers to methyl ethyl ketone.
ITO is indium tin oxide.
EPD is an electrophoretic volume method.

[Observation of thin-film film morphology]
An SEM image of a cross section of the film deposited on the anode substrate coated with the ITO layer by EPD is shown in FIG. 3a.
The sedimentary membrane exhibits a homogeneous morphology with a relatively flat surface. Its thickness was about 1.6 μm.

[Membrane structure evaluation (1)]
Structural evaluation of the prepared membrane was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) analysis.

From X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), fluorescent X-ray (XRF) and X-ray photoelectron spectroscopy (XPS) analysis, the Mo ₆ film formed by the EPD process has an amorphous structure. And confirmed to have the following characteristics.
^{-All Cs +} ions in the original cluster block cannot be found, and H ₃ O ⁺ exists as a counter cation instead.-Apical ligand of ^{Br −} is partially replaced by ^{OH −.} A small amount of is incorporated into the membrane during the EPD process.

[Membrane structure evaluation (2)]
The chemical composition of the prepared membrane was also evaluated by mass spectrometry (ISO-MS: Ion mobility spectroscopy-mass spectrometry). Specifically, it was carried out as follows.

[Mass spectrometry]
IMS-MS measurements were performed using a homemade tandem drift tube in combination with a quadrupole time-of-flight mass spectrometer (Maxis Impact Bruker, Bremen, Germany) described in detail elsewhere.
To perform IMS-MS measurements, the cluster membrane was first scraped from the ITO substrate and then dissolved in 1 mL of acetonitrile and then diluted to a final concentration of 50 μmol / L in the same solvent.
For comparison, a solution from the precursor powder was prepared in acetonitrile at the same concentration.
The solution was injected directly into the electrospray source using a syringe pump (120 μL / h) and analyzed in anion mode.
Electrosprayed ions were periodically injected into a helium-filled 79 cm long drift tube maintained at 298 K at a pressure of 4 torr.
A drift voltage in the range of 250-500 V was applied to the tube to allow mobility separation.
The mass decomposition ATD (Arrival Time Distribution) was finally obtained by recording the mass spectrum as a function of the arrival time of the ions at the end of the drift tube.
Absolute CCS (Collision Cross Section) was obtained without calibration by measuring the arrival time as a function of the inverse drift field based on the Mason-Schamp equation.
According to this procedure, the uncertainty of the absolute value of CCS was estimated to be 2%.

The results are described below.

[Ionic Mobility Spectroscopy-Mass Spectrometry (IMS-MS)]
The mass spectrum dominated by the precursor solution _{showed a single peak corresponding to [Mo 6} Br ₁₄ ] ^2- (see FIG. 5a). The mass spectrum of the membrane is more complex. As highlighted in FIG. 3b, even if a small amount of corresponding monovalently charged ions are detected, they are dominated by the divalently charged anions (see FIG. 5b).
The next section focuses on the dominant divalently charged species.
From the simulation of the isotope pattern, the characteristics of the different spectra _{are the ions whose general formula is [Mo 6} Br _14-n (OH) _n ] ^2-and whose n is in the range of 0 to 2, and the water adducts of the latter ions. caused by.
As shown in FIG. 3c, all arrival time frequency distributions (ATDs) are dominated by a single peak, even if the signal-to-noise ratio is _{relatively low for [Mo 6} Br ₁₂ (OH) ₂ ] ^2-anions. Will be done.
The width of the peaks observed for [Mo ₆ Br ₁₂ (OH) ₂ ] ^2- and [Mo ₆ Br ₁₃ (OH)] ^2- anions has limited resolution, which is a single for those ions. It is understood that it is due to the presence of isomers.
In contrast, the [Mo ₆ Br ₁₄ ] ^2- anion shows a slightly broader peak. This can result from the coexistence of different isomers with similar structures.
However, it was difficult to separate different populations by operating our device in tandem IMS mode and by selecting only some of the broad ATD peaks. This can be a coexisting species of signal hidden under a broad ATD characteristic and undergoing rapid interconversion in the gas phase (<ms).
Collision cross sections (CCSs) were determined for the three observed complexes and listed in FIG.
Interestingly, the [Mo ₆ Br _14-n (OH) _n ] ^2- species CCS is _{similar to the [Mo 6} Br ₁₄ ] ^2- CCS, and the overall structure of the cluster is preserved during Br / OH exchange. It suggests that it has been done.
These results, Br of apical position during EPD process ^- are clearly supports our speculation that is replaced with ^- part of ions OH.

2. Temperature and Humidity Dependence of Electric Conductivity of Mo _{6 Cluster Membrane The temperature and humidity dependence of electric conductivity of the Mo 6} cluster film produced in this example were measured and evaluated as follows.

[AC (alternating current) impedance measurement and DC (direct current) measurement]
The conductivity of the cluster film was measured by the potentiometer galvanostat (IVIUMSTAT, Ivium Technologies) AC impedance method which is implemented in the frequency range of 1 to 10 ⁶ Hz at an applied voltage of a 0.1V using.
The electrical circuit was assembled using a micrometer. The electrodes were brought into contact with the cluster membrane with a constant force of 5.2 N with a contact area of ^{0.33 cm 2.}
In addition, to keep the test environment constant, measurements were taken in a constant temperature and humidity chamber (SH-222, ESPEC CORPORATION) at a fixed temperature in the range of 300-350K and a fixed relative humidity in the range of 20-80RH%. (Fig. 6).

The DC measurement was performed with an applied voltage of 2 V and a shunt resistance of 2.72 kΩ. A regulated DC power supply (manufactured by Kenwood Corporation: PA-18-3A) was used to apply the DC voltage, and a digital multimeter (Hewlet-Pacard: 34401A) was used to drop the voltage of the shunt resistor. The test environment was the same as the AC impedance method described above.

FIG. 6 shows a schematic view of an experimental device for measuring conductivity with and without LED light irradiation.

The results are described below.

[Temperature and humidity dependence of electrical conductivity of _{Mo 6 cluster membrane]}
The impedance spectrum of the cluster film measured at different temperatures under a constant humidity of 80 RH% is shown in FIG. 8a. It was found that the electrical resistance of the cluster film showed temperature dependence, and as the temperature increased, the semi-arc became smaller, corresponding to the decrease in electrical resistance.
An Arrhenius plot of the conductivity of the cluster membrane at 50 RH% and 80 RH% humidity is shown in FIG. 7a. The conductivity changes linearly with increasing temperature.
Generally, the conductivity (σ) is expressed by the following equation.
σT = Aexp (-E _a / RT) (1)
Here, A is a constant, T is a temperature, R is a gas constant, and E _a is an activation energy.
The activation energies at relative humidity of 50 RH% and 80 RH% were estimated to be about 68 kJ / mol and 50 kJ / mol, respectively.
_{Similar activation energies were obtained for Mo 6} cluster membranes prepared at different deposition times, suggesting that electrical properties are not affected by the film thickness of this sample size.

The impedance spectra of the cluster membranes measured at different relative humidity are shown in FIG. 8b. The temperature was fixed at 300 K for all measurements.
The electrical resistance of the cluster film is humidity-dependent, and as the relative humidity decreases, the semicircle becomes larger and the electrical resistance increases.
The relationship between the conductivity of the cluster film and the relative humidity at 300 K is shown in FIG. 7b. Membranes were prepared with a deposition time of 30 seconds.
The conductivity of the sample prepared with a deposition time of 20 seconds is shown in FIG.
The conductivity of the cluster membrane changed exponentially with increasing humidity, and the conductivity of the two samples prepared by EPD over 30 and 20 seconds showed similar values.

[Relaxation frequency dependence of _{Mo 6} cluster membrane by electrical modulus analysis]
The conductivity (σ) is given by the following equation.
σ = neμ (2)
Here, n is the carrier concentration, e is the carrier charge, and μ is the mobility.
The carriers in the cluster membrane should be cations introduced during the deposition process to compensate for the negative charge on a cluster-by-cluster basis. If so, the carrier species and carrier density in the membrane do not change. Therefore, the temperature and humidity dependence of conductivity should be caused by the different mobility of carriers.
In this study, the electroelastic modulus M ^* was calculated using the following relational expression.
In the relational expression of the equation (3), j is √-1, ω (= 2πf) is the angular frequency, and C ₀ is the geometric capacitance.
M ^* can be divided into a real part and an imaginary part, the imaginary part M'' is given by the equation (4), and f represents the frequency.
M ^* = jωC ₀ Z ^* = M'+ jM'' (3)
M'' = 2πfC ₀ Z'(4)
The frequency dependence of the parameter M'' is shown in FIGS. 7c and 7d.
A plot of the relationship between the value of M'' and frequency is often used to evaluate ionic conductivity.

7c and 7d show the frequency dependence of M'' at various temperatures (FIG. 7c) and humidity (FIG. 7d).
The frequency at the M'' _max position is known as the relaxation frequency. It shifts to higher frequencies as temperature or humidity increases, indicating that the relaxation process in the cluster membrane is affected by temperature and humidity.
f _max and relaxation time (τ) have a relationship of _{τ = 1 / 2πf max.} That is, as the temperature and humidity increase, τ decreases.
The temperature dependence of the relaxation time is shown in FIG.
The temperature dependence of relaxation time is expressed by the following equation.
τ = τ ₀ exp (-E _a / RT) (5)
Here, τ ₀ is a material-dependent pre-exponential factor.
The estimated activation energy is about 48 kJ / mol, which is about the same as the activation energy obtained from the Arrhenius plot of conductivity.
The relationship between conductivity and dielectric relaxation is expressed by the following equation.
σ ＝ ε ₀ ε _s / τ (6)
Here, ε ₀ is the permittivity of the vacuum, and ε _s is the static permittivity.
It is clear that reducing τ in this equation increases the conductivity.

3. 3. _{Electrical Properties of Mo 6} Cluster Film Under Light Irradiation The electrical properties of the Mo ₆ cluster film produced in this example under light irradiation are as follows by the DC impedance (DC) method and the AC impedance (AC) method. Evaluated to.

[Irradiation conditions]
Both DC and AC impedance methods were applied to measure the conductivity of cluster films under UV-A or visible light irradiation.
The AC impedance method was performed under the above-mentioned conditions.
The DC measurement was performed at an applied voltage of 2 V (V1) using the measurement system assembled as shown in FIG.
For light irradiation, LEDs having fixed wavelengths of 390 to 395 nm (UV-A), 465 to 475 nm (blue), and 660 nm (red) were used.
In FIG. 6, R1 is a shunt resistor and V2 is a voltage applied to the LED.
The illuminance was measured using an illuminometer (MT-912, URCERI).
The measurement was performed at 300 K and 50 RH%.

[Electrical properties _{of Mo 6} cluster membrane under light irradiation characterized by DC measurement]
The It curve when 2 V DC is applied to the cluster film is shown in FIG. 11a.
When a DC voltage was applied, the current reached its maximum immediately and then decreased over time. Moreover, even after the decrease in the current almost stopped, the current continued to flow slightly at a certain value.
When the current became constant, the application of voltage was stopped.
After recording the flowing current as a negative value, it reached zero. Considering the polarization behavior of ions, it is suggested that the membrane acts as an ionic conductor.
In addition, the low current continues to flow even after the initial rapid current decrease when a DC voltage is applied to the film, suggesting that it is due to electron conduction.
In cold amorphous systems, their (charge) transport is often dominated by hopping conduction.
Electrical conduction in such systems is generally achieved through incoherent transitions of charge carriers between spatially localized states.
FIG. 11b shows the It curve of _{the Mo 6} film under irradiation with UV-A, blue and red LED light when DC is applied.

In each case, after 270 seconds had passed from the start of applying the DC voltage, light irradiation was performed only for 30 seconds.
In the case of UV-A and blue light, a temporary increase in current was observed, but not in the case of red light.
In order to clarify this behavior, as shown in FIG. 11c, the phenomenon caused by the above light irradiation was investigated by changing the illuminance of UV-A.
As shown in the inset of FIG. 11c, the current value was clearly increased by about 2.6 times when irradiating with strong light of 950 lpx as compared with the case of irradiating with weak light of 360 lpx.

[Electrical properties _{of Mo 6} cluster membrane under light irradiation characterized by AC impedance measurement]
Impedance measurements of the cluster membrane were performed under UV-A, blue and red light irradiation at 280 xl, 100 klx and 35 klx illuminances, respectively. The photon flux densities of these illuminances are approximately the same under these conditions.
FIG. 11d shows an impedance plot for UV-A LED light irradiation.
The impedance semi-arc is recorded slightly larger than before irradiation, which represents a decrease in conductivity.
FIG. 11e shows the rate of increase in impedance when irradiated with UV-A, blue and red LED light.
An increase in impedance was clearly observed during irradiation with UV-A and blue light, but as expected, no significant change was observed with red light.

The findings obtained from the above results are summarized below as "discussion".

[Discussion]
A schematic diagram of the structure of _{the Mo 6} cluster in the membrane proposed from these results is shown in FIG. 12a.
By dispersing the Cs ₂ Mo ₆ Br ₁₄ powder in methyl ethyl ketone (MEK)), it ^{dissociates into Cs +} and [Mo ₆ Br ₁₄ ] ^2- ions, with up to two Br apical ligands simultaneously OH. Replaced by.
The site of the substituted Br apical ligand will be random. Water molecules present in the MEK solvent electrolyze on the surface of the electrode during application of an electric field to generate ^{H +} and then combine with _{H 2} O molecules to form _{H 3} O ^+. Thus, H ₃ O ⁺ ions act as counter cation to neutralize the negatively charged Mo ₆ cluster units deposited on the substrate.
As a result, new amorphous networks will be formed by the chaotic arrangement of _{modified Mo 6 clusters.}
Further, H ₃ O ⁺ counter cation to coordinate with substituents OH group of Br ^a site by hydrogen bonds, and many water molecules will become to be coupled in the same manner by hydrogen bonds surrounding it. In fact, previous experimental and simulation results ^{clearly demonstrate the existence of HO-H *} -OH crosslinks between adjacent cluster units, which seems to support the "vehicle diffusion model". ..

Based on temperature- and humidity-dependent conductivity, it was revealed that the conduction mechanism is related to the content and mobility of water molecules.
According to _{E a} value of Mo ₆ clusters film is about 50~70kJ / mol, powertrain cluster _film, it is proposed that H 3 ^{O +} is a "vehicle mechanism" that moves. A schematic diagram of the proposed conduction mechanism is shown in FIG. 12b.
Under high humidity conditions, the membrane contains more water molecules. They surround the hydronium ions coordinated to the OH apical ligands of the Mo ₆ cluster, weaken hydrogen bonds, and allow the hydronium ions to move easily through the network. As a result, the activation energy decreases at higher humidity.
From a temperature point of view, it is clear that the conductivity increases with increasing temperature corresponding to the increase in mobility of _{H 3} O ^{+ ions.}
As a result of DC measurement, a significant increase in current due to light irradiation was confirmed.
From the measurement of photoluminescence excitation (PLE) of the cluster membrane, _{it is disclosed that the Mo 6} cluster is excited by light in the wavelength range of 370 to 470 nm, resulting in red emission.
From these facts, it is confirmed that the electrical characteristics of the cluster film can be changed by irradiation with UV-A and blue light.
_{The Mo 6} cluster excited by light irradiation emits one electron, and as a result, the Mo ₆ cluster having 23 electrons becomes a strong oxidant. Excited electrons probably become free electrons and flow through the membrane by applying an electric field.
As a result of AC impedance measurement, the increase in impedance due to UV-A and blue irradiation was 6% and 7%, respectively.
These highly reproducible phenomena are reversible as observed in FIG. 11d for UV-A irradiation.
The conduction characteristics deteriorated by light irradiation are restored to the initial state after equilibration for 1 hour.
Given that the Mo ₆ clusters exhibit photocatalytic properties, the water molecules and / or hydronium ions contained in the membrane will be degraded by the photoreaction, resulting in reduced ionic conductivity.
This mechanism is presumed to be possible due to the statistical distribution of ions located between the hydroxyl groups at the apical position of adjacent clusters.
Furthermore, when carrier reduction occurs, the negative charge per cluster is reduced and Mo ₆ Br ₁₂ (H ₂ O) ₂ can be locally formed.

Based on these experiments, the dependence of humidity, irradiation light intensity and irradiation wavelength on _{the electrical properties of the Mo 6} cluster film was demonstrated for the first time.
_{Taking into account the most advantageous features of Mo 6} clusters, such as large Stokes shift with high red emission efficiency and long life, EPD films are promising multifunctional devices for humidity and UV light sensing.

The present invention has industrial applicability for applications in sensing, miniaturization, and weight reduction devices (eg, portable multi-sensors).

Claims (9)

A pair of opposing electrodes and
A sensitive film placed between the electrodes and
It is an element having
The sensitive film is
A complex having an octahedral structure consisting of 6 molybdenum atoms and 14 ligands that stabilize the octahedral structure of the complex, and at least one hydronium ion as a counterion.
Contains molybdenum clusters,
element. The device according to claim 1, wherein the ligand consists of a halogen atom or contains both a halogen atom and at least one hydroxy group. The device according to claim 1 or 2, wherein the counterion is essentially composed of one or more hydronium ions. The device according to any one of claims 1 to 3, which exhibits an electrical response to any input of temperature, humidity, and light. The element according to any one of claims 1 to 4,
Power supply and
A detector for detecting the electrical response from the element,
Sensor with. The sensor according to claim 5, wherein the power source is any one selected from a DC power source, an AC power source, and a power source switchable between DC and AC. A sensing device comprising the sensor according to claim 5 or 6. A method for measuring at least one of temperature, humidity, and light using the element according to any one of claims 1 to 4. A method for measuring three types of temperature, humidity, and light using the element according to any one of claims 1 to 4.

Images