JP2014094881A - Method for manufacturing vanadium dioxide particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing vanadium dioxide particles capable of manufacturing vanadium dioxide particles having a high dispersibility and an inhibited oxidizing tendency and yielding, when deposited as a film, a film having a high transparency and to provide vanadium dioxide particles manufactured by using the method for manufacturing vanadium dioxide particles.SOLUTION: The provided method for manufacturing vanadium dioxide particles is a method for manufacturing vanadium dioxide particles having an average particle diameter of 50 nm or less including the steps of: gas-substituting, with an inert gas, a raw ingredient liquid including a raw vanadium dioxide ingredient and a solvent; and irradiating a laser beam onto the raw ingredient liquid wherein the fluence, per pulse, of the laser beam is 0.2 to 5 J/cm.

Description

The present invention relates to a method for producing vanadium dioxide particles capable of producing vanadium dioxide particles having high dispersibility, suppressing oxidation, and obtaining a highly transparent film when formed. Moreover, it is related with the vanadium dioxide particle manufactured using the manufacturing method of this vanadium dioxide particle.

Vanadium dioxide has been studied in many fields because of its high thermochromic properties. The thermochromic property refers to a property showing a thermochromic phenomenon in which optical properties such as transmittance and reflectance are reversibly changed by temperature change.
The crystal of vanadium dioxide shows a semiconductor phase below the phase transition temperature, but transitions to the metal phase above the phase transition temperature. The optical properties change significantly with the phase transition. Along with the transition from the semiconductor phase to the metal phase, the transmittance in the infrared region is remarkably reduced (the transmittance in the visible light region is hardly changed). Pure vanadium dioxide has a phase transition temperature of about 68 ° C., but this transition temperature is lowered by substituting some of the vanadium atoms with other metal atoms (W, Mo, Nb, Ta, Re, etc.). Can be shifted to the side.
Utilizing the thermochromic properties of vanadium dioxide, for example, it has been proposed to be used as an infrared blocking material that blocks infrared rays (heat rays) at a certain temperature or higher. When such an infrared shielding material is applied to a window of an automobile or a building, an effect of suppressing a temperature rise in the vehicle or the room and improving cooling efficiency is expected.

As a method for obtaining a thermochromic material using vanadium dioxide, for example, Non-Patent Document 1 discloses that a hydrosol in which vanadium and tungsten are dissolved in hydrogen peroxide solution is spin-coated on a substrate at several hundred degrees Celsius. A method for forming a glassy coating of vanadium dioxide by reduction firing has been proposed.
However, in this method, since it is necessary to heat the vanadium solution on the substrate and then heat it at a high temperature, it can be used only for a base material having heat resistance such as glass, its use is limited, and the area is increased. There is also a problem that it is difficult.

On the other hand, as a method capable of forming a film with a large area by a low-temperature process, a method of applying a dispersion containing nano-order particles has recently attracted attention. In particular, when a base material made of an organic material is used, such a method can be suitably used because a high temperature process cannot be applied. In addition, since thermochromic films are also required to have high transparency, production of nanometer-order vanadium dioxide particles is required.
On the other hand, in Patent Document 1, a material obtained by synthesizing vanadium oxide and tungsten oxide by a melting method is pulverized by a bead mill to obtain vanadium oxide fine particles, and a dispersion of the vanadium oxide fine particles is applied to a substrate. Thus, a method for producing a thermochromic material has been proposed.
However, in this method, since the vanadium oxide material is finely divided by mechanical pulverization, submicron-sized particles are easily obtained, but nanometer-sized particles are difficult to obtain. Further, the pulverization method such as a bead mill has a problem that the thermochromic characteristics are deteriorated because the particles are likely to be contaminated or defective.
Furthermore, as a method for producing fine particles having thermochromic properties, a method of supporting vanadium dioxide on inorganic particles such as silica has been proposed (see Patent Document 2).
However, with this method, the particle size of the core particles can be controlled to the nanometer order, but it is not easy to control the uniformity and thickness of the vanadium dioxide layer, and it is difficult to obtain a material with high thermochromic properties. It was.

JP 2000-233929 A JP 2004-346261 A

I. Takahashi et al. , Jpn. J. et al. Appl. Phys. , Vol. 35 (1996), pp. L438-L440

The present invention provides a method for producing vanadium dioxide particles that can produce vanadium dioxide particles that are highly dispersible, have low oxidation, and can produce highly transparent films when deposited. For the purpose. Moreover, it aims at providing the vanadium dioxide particle manufactured using the manufacturing method of this vanadium dioxide particle.

The present invention is a method for producing vanadium dioxide particles having an average particle diameter of 50 nm or less, the step of replacing a raw material liquid containing a vanadium dioxide raw material and a solvent with an inert gas, and a laser in the raw material liquid The method includes the step of irradiating light, and the laser beam is a method for producing vanadium dioxide particles having a fluence per pulse of 0.2 to 5 J / cm ² .
Hereinafter, the present invention will be described in detail.

As a result of intensive studies, the present inventors perform a step of replacing a raw material liquid containing a vanadium dioxide raw material and a solvent with an inert gas, and a step of irradiating the raw material liquid with laser light having a predetermined intensity. In order to complete the present invention, it is possible to produce vanadium dioxide particles having a high dispersibility, suppressing oxidation, and obtaining a highly transparent film when formed, by a simple method. It came.

The method for producing vanadium dioxide particles according to the present invention includes a step of replacing a raw material liquid containing a vanadium dioxide raw material and a solvent with an inert gas (hereinafter also referred to as a gas replacement step), and applying laser light to the raw material liquid. An irradiation step (hereinafter also referred to as a laser irradiation step).
An example of a liquid phase laser ablation apparatus for carrying out the method for producing vanadium dioxide particles of the present invention is shown in FIG. The liquid phase laser ablation apparatus includes a laser oscillator 100, a mirror 101, a processing vessel 102, a solvent 103, a vanadium dioxide raw material 104, a stirrer table 105, a stirrer 106, and a gas cylinder 107. In FIG. 1, the symbol M indicates laser light.

In the method for producing vanadium dioxide particles according to the present invention, first, a step of replacing the raw material liquid containing the vanadium dioxide raw material 104 and the solvent 103 with an inert gas is performed. The gas replacement step may be performed before the laser light irradiation step or may be performed during the laser light irradiation step.
Specifically, a method of venting an inert gas from a gas cylinder 107 through a gas pipe 108 to a raw material liquid containing the vanadium dioxide raw material 104 and the solvent 103 in the processing vessel 102 and then exhausting it through the exhaust port 109 is provided. Can be used.

By performing such a gas replacement step, dissolved oxygen in the raw material liquid is removed, and oxidation of the obtained vanadium dioxide particles can be suppressed. In particular, in the case of vanadium dioxide particles, it has been found by the present inventors that the ratio of oxidation derived from dissolved oxygen is larger than that derived from solvent. Therefore, the oxygen content can be effectively reduced by performing the gas replacement step.

Although the time which performs the said gas replacement process is not specifically limited, 1-120 minutes are preferable, More preferably, it is 5-60 minutes.
Further, the gas flow rate during the gas replacement step is preferably 10 to 1000 ml / min.

Examples of the inert gas include noble gases such as helium, neon, argon, krypton, and xenon, and nitrogen, and a mixed gas thereof may be used. Especially, it is preferable to use argon from a viewpoint of reducing oxygen content and a viewpoint of cost.

Specific examples of the gas replacement step include a method of directly introducing the inert gas described above.
Moreover, it is preferable to perform the said gas substitution process in the state which disperse | distributed the said vanadium dioxide raw material.
Thereby, dissolved oxygen can be removed efficiently. Specifically, a method of introducing an inert gas while stirring using the stirrer 106 may be used.

Next, in the method for producing vanadium dioxide particles of the present invention, a step of irradiating the raw material liquid with laser light is performed. By performing such a process, it becomes possible to reduce the vanadium dioxide raw material into vanadium dioxide particles having an average particle diameter of 50 nm or less.

Specifically, as shown in FIG. 1, the laser beam M generated from the laser oscillator 100 is reflected by a mirror 101 and irradiated to the vanadium dioxide raw material 104 in the processing container 102.
In addition, by rotating the mirror 101, the angle of the reflection surface can be changed, and the irradiation position of the laser beam M can be moved so that the same position of the vanadium dioxide raw material 104 is not repeatedly irradiated.

The laser oscillator 100 is not particularly limited as long as it can generate the laser light M. For example, the laser oscillator 100 includes a YAG laser device and an excimer laser device, and among these, the YAG laser device is used. Those are preferred.

The mirror 101 is not particularly limited, and a known reflector or the like (for example, a mirror) can be used as appropriate. The mirror 101 is preferably used in a rotatable state so that the angle of the reflecting surface can be changed from the viewpoint of more uniformly irradiating the target with laser light.

The processing container 102 is not particularly limited as long as it can transmit the laser beam M, and examples of the material include quartz, sapphire, and glass. As the shape of the processing container 102, for example, a cup-shaped one, a round bottom flask, an eggplant-shaped flask, a pear-shaped flask, a test tube, or the like can be used as appropriate.

The solvent 103 is not particularly limited, and water, an organic solvent, a mixed solution of water and an organic solvent, and an inorganic solvent can be appropriately used. Especially, it is preferable to use water and an organic solvent.
Examples of the organic solvent include hydrocarbons, ketones, alcohols, glycols and derivatives thereof, nitrile solvents, amine solvents, thiols, xylene, kerosene, ionic liquids, and the like. Examples thereof include supercritical carbon dioxide and liquid nitrogen. Of these, water is preferable from the viewpoint of preventing organic contamination, and ketones, alcohols, glycols and derivatives thereof are preferable from the viewpoint of dispersibility and crystallinity after the treatment.
Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, and amyl methyl ketone. Examples of alcohols include ethanol, methanol, 1-propanol, 2-propanol, butanol, and pen. Examples of the glycols include ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol. Examples of these derivatives include triethylene glycol di-2- Ethyl hexanoate (3GO), triethylene glycol di-2-ethylbutyrate (3GH), dihexyl adipate (DHA), tetraethylene glycol diheptanoate (4G7), or Tiger ethylene glycol di-2-ethylhexanoate (4GO), and the like.
Moreover, as a liquid mixture of the said water and an organic solvent, the liquid mixture of water and acetone, the liquid mixture of water and alcohols, and the liquid mixture of water and glycols are preferable.

The vanadium dioxide raw material 104 may be in the form of powder or particles, or may be in the form of a rod, plate or pellet. From the viewpoint of reducing the particle size, powders and particles are preferable. In the case of powder or granular form, the vanadium dioxide raw material may be dispersed throughout the solvent as shown in FIG. 1, and in the case of plate or pellet form, it may be disposed on the inner surface of the processing vessel.

The case where a plate-shaped material is used as the vanadium dioxide raw material 104 is shown in FIG. The vanadium dioxide raw material 104 is arrange | positioned at the inner surface of a processing container.

As the vanadium dioxide raw material 104, a material in which a part of vanadium atoms is substituted with at least one atom selected from tungsten, molybdenum, niobium and tantalum (hereinafter also referred to as substituted vanadium dioxide) may be used. .
The vanadium dioxide constituting the vanadium dioxide raw material 104 has various crystal phases, but a monoclinic crystal and a tetragonal crystal (rutile type) undergo a phase transition reversibly. Its phase transition temperature is about 68 ° C., but the phase transition temperature is adjusted by replacing some of the vanadium atoms in vanadium dioxide with at least one atom selected from tungsten, molybdenum, niobium and tantalum. be able to. Therefore, by appropriately selecting vanadium dioxide particles or substituted vanadium dioxide particles, or by appropriately selecting the atomic species and substitution rate to be substituted in the substituted vanadium dioxide particles, the performance of the obtained thermochromic film can be controlled. it can.

The substituted vanadium dioxide preferably has a metal atom substitution rate of 0.1 atomic% at the lower limit and 10 atomic% at the upper limit. When the substitution rate is within this range, the phase transition temperature of the substituted vanadium dioxide can be easily adjusted, and excellent thermochromic properties can be exhibited. The metal atom substitution rate is a value indicating the percentage of the number of substituted atoms in the total of the number of vanadium atoms and the number of substituted atoms.

The vanadium dioxide constituting the vanadium dioxide raw material 104 preferably has a half width at 2θ = 27.8 ° of 0.270 or less in the X-ray diffraction method (XRD). When the half width is 0.270 or less, crystallinity is suitable and good thermochromic properties can be ensured.
More preferably, the lower limit of the half width is 0.05 and the upper limit is 0.5.

The size of the vanadium dioxide raw material 104 is not particularly limited, but in view of the conversion rate to nanoparticles, those having an average particle diameter of 500 μm or less are preferable. More preferably, it is 250 μm or less.
The amount of the vanadium dioxide raw material 104 added is preferably 0.001 to 10% by weight of the raw material liquid. When the amount is less than 0.001% by weight, the productivity is extremely deteriorated. When the amount exceeds 10% by weight, long-time laser light irradiation is required to convert all the raw materials to be charged into nanoparticles.

The raw material liquid containing the vanadium dioxide raw material 104 and the solvent 103 may contain an oxidation inhibitor. By containing an oxidation inhibitor in the raw material liquid, oxidation of the generated vanadium dioxide nanoparticles can be further suppressed.
As the oxidation inhibitor, for example, substances having reducibility such as ascorbic acid, isoascorbic acid, hydroquinone, hydrazine, hydrazide, propyl gallate, butylhydroxyanisole, dibutylhydroxytoluene, thiosulfate and the like are suitable.

As the laser beam M, a laser having an arbitrary wavelength and an arbitrary energy can be used according to the type of material of the container, the type of solvent, the type of vanadium dioxide raw material, and the like. In addition, the irradiation surface shape of the laser light M when the vanadium dioxide raw material 104 is irradiated with the laser light M (condensing shape when condensing with a lens or the like), energy density (fluence) conditions, etc. are mixed with impurities. In order to prevent this, there is no particular limitation as long as the conditions are such that the processing container 102 is not damaged, and known conditions can be appropriately employed. Note that such conditions strongly depend on the type of processing vessel 102 and the type of each material in the vanadium dioxide raw material 104. Therefore, the preferable conditions are not general, and the type of vessel material, solvent According to the type of vanadium dioxide, the type of vanadium dioxide raw material, etc., the conditions may be appropriately changed so as to obtain target vanadium dioxide particles.

As the laser beam M, a pulse laser beam is preferable, and a pulse width is preferably 100 femtoseconds to 100 nm.
The wavelength of the laser beam M is preferably 190 to 5000 nm. More preferably, it is 300-4000 nm.
Furthermore, the output of the laser beam M is preferably 0.1 to 10 W.

The fluence (energy density) per pulse of the laser beam M when performing the laser beam irradiation process is 0.2 to 5 J / cm ² .
If the fluence per pulse of the laser beam M is less than 0.2 J / cm ² , the particle size reduction is insufficient, and if it exceeds 5 J / cm ² , oxidation is promoted and the purity of vanadium dioxide is increased. Decreases.
Preferable lower limit is 0.3 J / cm ² fluence per pulse of the laser beam M, a preferred upper limit is 4J / cm ^2, still more preferred lower limit 0.4 J / cm ^2, still more preferred upper limit 3J / cm ² It is. Moreover, the irradiation surface shape of the laser beam M is not particularly limited, but a diameter of about 0.5 to 10 mm is preferable.
Furthermore, although the temperature condition at the time of irradiating the said laser beam is not restrict | limited, In order to prevent the temperature rise of a raw material liquid, it is preferable that it is below room temperature (25 degreeC). The temperature control of the raw material liquid can be performed by installing the processing container 102 in FIG. 1 in a thermostatic chamber capable of controlling the temperature.

By using the method for producing vanadium dioxide particles of the present invention, the average particle diameter is 50 nm or less, the particle diameter is small, the dispersibility is high, the oxidation is suppressed, and a highly transparent film can be obtained when the film is formed. Vanadium particles are obtained.
The vanadium dioxide particles thus obtained are also one aspect of the present invention. The vanadium dioxide particles of the present invention are useful as a raw material for thermochromic coating films and interlayer films for laminated glass.

In the vanadium dioxide particles of the present invention, the content of vanadium atoms having a valence other than +4 is preferably 10 mol% or less of the total vanadium atoms in measurement using X-ray photoelectron spectroscopy (XPS). . If it exceeds 10 mol%, the properties of the vanadium dioxide particles may change.

The vanadium dioxide particles of the present invention are extremely excellent in dispersibility, and a highly transparent film can be obtained when formed. Therefore, by using this, a thermochromic coating film excellent in thermochromic properties and an intermediate for laminated glass Membranes can be manufactured.

INDUSTRIAL APPLICABILITY The present invention can provide a method for producing vanadium dioxide particles that can produce vanadium dioxide particles that have a high dispersibility, suppress oxidation, and provide a highly transparent film when formed. Moreover, the vanadium dioxide particle manufactured using the manufacturing method of this vanadium dioxide particle can be provided.

It is a schematic diagram which shows an example of the liquid phase laser ablation apparatus for performing the manufacturing method of the vanadium dioxide particle of this invention. It is a schematic diagram which shows another example of the liquid phase laser ablation apparatus for performing the manufacturing method of the vanadium dioxide particle of this invention.

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

Example 1
(Gas replacement process)
After weighing 20 mg of VO ₂ powder with an average particle diameter of 50 μm into a glass vial with a volume of 30 ml, 20 g of pure water was added. Thereafter, the rubber stopper of the vial was sealed with an aluminum cap and sealed. Subsequently, an injection needle was inserted into the rubber stopper, and the gas was replaced by introducing argon gas in a gas cylinder into the vial for 10 minutes while stirring.

(Laser irradiation process)
The solution subjected to gas replacement was irradiated with an Nd: YAG laser (wavelength 1064 nm, pulse width 8 nm, fluence per pulse of 1.5 J / cm ² ) generated from a laser oscillator for 15 minutes. A black colloidal solution was obtained after irradiation.

(Example 2)
In the (laser irradiation step), the colloidal solution was obtained in the same manner as in Example 1 except that the wavelength of the irradiation laser was changed to 532 nm and acetone was used as the solvent.

(Example 3)
Instead of 20 mg of VO ₂ powder having an average particle size of 50 μm, vanadium dioxide (V _0.98 W _0.2 O ₂ ) substituted with 2.0 mol% of tungsten (W) was used, and acetone was used as a solvent. Obtained a colloidal solution in the same manner as in Example 1.

(Example 4)
A colloidal solution was obtained in the same manner as in Example 1 except that ethanol was used instead of pure water as a solvent.

(Example 5)
A colloidal solution was obtained in the same manner as in Example 1 except that ethylene glycol (EG) was used instead of pure water as a solvent.

(Example 6)
A colloidal solution was obtained in the same manner as in Example 1 except that triethylene glycol di-2-ethylhexanoate (3GO) was used as a solvent instead of pure water.

(Example 7)
In the laser irradiation step, a colloidal solution was obtained in the same manner as in Example 5 except that the fluence per pulse of the laser was changed to 4.5 J / cm ² .

(Example 8)
In the laser irradiation step, a colloidal solution was obtained in the same manner as in Example 5 except that laser light having a wavelength of 355 nm was used.

Example 9
A colloidal solution was obtained in the same manner as in Example 1 except that a mixed solution of water and acetone (water: acetone = 1: 1) was used as the solvent.

(Comparative Example 1)
A colloidal solution was obtained in the same manner as in Example 1 except that argon gas was not substituted.

(Comparative Example 2)
In the laser irradiation step, a colloidal solution was obtained in the same manner as in Example 5 except that the fluence per pulse of the laser was changed to 0.1 J / cm ² .

(Comparative Example 3)
In the laser irradiation step, a colloidal solution was obtained in the same manner as in Example 5 except that the fluence per pulse of the laser was changed to 5.5 J / cm ² .

(Comparative Example 4)
After weighing ₂ g of VO ₂ powder with an average particle size of 50 μm and 50 g of zirconia beads with an average particle size of 50 μm in a dedicated vessel having a volume of 100 ml, 15 g of ethanol was added. Thereafter, the vessel was set in a vertical bead mill (RMB, manufactured by Imex) and treated at 20000 rpm for 2 hours.
When the treated particles were measured by particle size distribution, the average particle size was about 150 nm. Further, in the X-ray diffraction measurement, in addition to vanadium dioxide, a peak derived from zirconia was also observed.

(Evaluation)
(Average particle size)
The average particle size of the obtained colloidal liquid or powder was measured using a particle size distribution meter (manufactured by NICOMP, NICOMP 380DLS).

(Dispersion stability)
Dispersibility was evaluated using a centrifugal sedimentation / light transmission type dispersion stability analyzer (LUMiSize 612, manufactured by LUM Co.). Specifically, about 1 ml of a dispersion obtained by mixing 10 parts by weight of vanadium dioxide nanoparticles obtained in Examples and Comparative Examples, 1 part by weight of polyvinylpyrrolidone (PVP), and 89 parts by weight of isopropanol was used as a glass analysis cell. Then, the supernatant was irradiated with light, and the integrated value of the amount of change in the amount of light transmitted per hour was determined to evaluate the dispersibility.
In Table 1, the amount of change in the amount of transmitted light in Comparative Example 4 was set to 1.00, and other Examples and Comparative Examples listed relative values with respect to Comparative Example 1.

(V content other than tetravalent [XPS measurement])
The vanadium dioxide particles obtained in the examples and comparative examples were vacuum-dried and then put into an aluminum cap having a diameter of 5 mm, and pellets were produced by pressurization. The binding energy of 2p electrons of V was measured for this pellet using X-ray photoelectron spectroscopy. The binding energy of 2p electrons of V shifts to the higher energy side as the valence increases. By performing curve fitting on the obtained 2p spectrum of V, the area of the peak corresponding to V of each valence can be obtained. The content (%) of V other than +4 valence (V ⁵⁺ , V ³⁺ etc.) was evaluated by the ratio of the sum of the areas of V peaks other than +4 valence to the total area of 2p of V. The detection sensitivity of the device is 0.1%.

(Visible light transmittance of thin film)
A dispersion obtained by mixing 10 parts by weight of the vanadium dioxide particles, 1.0 part by weight of polyvinylpyrrolidone (PVP) and 89 parts by weight of isopropanol was formed on a glass substrate by spin coating, and then dried at 120 ° C. for 1 hour. A thermochromic thin film was prepared.
The transmittance of the obtained thermochromic thin film in the visible light region was measured using a spectrophotometer (manufactured by Hitachi High-Tech).

According to the present invention, it is possible to provide a method for producing vanadium dioxide particles, which can produce vanadium dioxide particles having high dispersibility, suppressing oxidation, and obtaining a highly transparent film when formed. it can. Moreover, the vanadium dioxide particle manufactured using the manufacturing method of this vanadium dioxide particle can be provided.

DESCRIPTION OF SYMBOLS 100 Laser oscillator 101 Mirror 102 Processing container 103 Solvent 104 Vanadium dioxide raw material 105 Stirrer base 106 Stirrer 107 Gas cylinder 108 Gas pipe (In)
109 Exhaust port

Claims (8)

A method for producing vanadium dioxide particles having an average particle size of 50 nm or less,
A step of gas-substituting a raw material liquid containing a vanadium dioxide raw material and a solvent with an inert gas; and
Irradiating the raw material liquid with laser light,
The laser beam is method for producing a vanadium dioxide particles fluence per pulse is characterized by a 0.2~5J / cm ^2. 2. The method for producing vanadium dioxide particles according to claim 1, wherein a part of the vanadium atom in the vanadium dioxide raw material is substituted with at least one atom selected from tungsten, molybdenum, niobium and tantalum. The method for producing vanadium dioxide particles according to claim 1 or 2, wherein the solvent is at least one selected from the group consisting of water, an organic solvent, and a mixture of water and an organic solvent. The method for producing vanadium dioxide particles according to claim 3, wherein the organic solvent is a ketone or an alcohol. The method for producing vanadium dioxide particles according to claim 4, wherein the organic solvent is a glycol or a derivative thereof. The method for producing vanadium dioxide particles according to claim 1, 2, 3, 4, or 5, wherein the raw material liquid contains an oxidation inhibitor. The method for producing vanadium dioxide particles according to claim 1, 2, 3, 4, 5, or 6, wherein the wavelength of the laser light is 190 to 5000 nm. Vanadium dioxide particles obtained by using the method for producing vanadium dioxide particles according to claim 1, 2, 3, 4, 5, 6 or 7,
Vanadium dioxide particles, wherein the content of vanadium atoms having a valence other than +4 is 10 mol% or less of all vanadium atoms in measurement using X-ray photoelectron spectroscopy (XPS).

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