RU163672U1 - OPTICAL THERMOMETRIC DEVICE ON THE POLYMERIC BASIS - Google Patents

Abstract

An optical thermometric device that provides temperature measurement by changing the diffraction pattern of light, containing a substrate with a diffraction periodic microstructure embedded in its surface, the elements of which are regions subjected to ion irradiation and characterized by a different dielectric constant relative to the substrate material, characterized in that the substrate is made of optically transparent polymer, and the diffraction structure contains ion-synthesized metal nanoparticles, dispersed in the near-surface region of the substrate at a layer thickness of 10 to 600 nm at a metal concentration of 2.0 · 10-8.0 · 10 atoms / cm.

Description

The proposed technical solution relates to optical thermometric devices in which the temperature of a substance is measured by recording by a non-contact method a change in the diffraction of a probe light beam (usually laser) interacting with the analyzed material [1], namely, to optical thermometric devices for the visible range, made on the basis of thin-film periodic microstructured layers of various substances.

Such devices find their application for temperature monitoring and control in vacuum technological processes of microelectronics (deposition of thin films, etching of microstructures, etc.), the interaction of gas-discharge plasma and charged particle beams, for measuring temperature in difficult conditions (high electrical potentials, electromagnetic interference, background nonequilibrium radiation, when working in aggressive environments, etc.) [1].

Known "Device for measuring temperature", USSR copyright certificate No. 932285, published 02.06.1982. Bull. No. 20, selected as an analogue, where the Brega optical diffraction grating, consisting of parallel strips, and located at a Bregu angle to the axis of the light source, is introduced into the heat-sensitive element. The sensitive element is made of a transparent material, which can be used as lithium niobate, lithium tantalate, galium arsenide, quartz, glass, etc. The Brega diffraction grating can be formed, for example, during crystal growth by periodically changing the growth conditions that affect the value of the refractive index of the crystal or by recording the periodic distribution of light intensity in crystals with a photostructural effect. When the temperature of the material of which the Brega grating is made changes, the physical parameters of the heat-sensitive element change, leading to its expansion or contraction. This leads to a change in the period of the diffraction grating of the thermally sensitive element and, as a consequence, to the redistribution of light passing through the Bragg grating in the diffraction pattern.

A disadvantage by analogy is that it provides for the formation of a thermometric device only on a strip type of diffraction gratings, namely, consisting of parallel structures (Bragg gratings), not allowing the formation of a thermometric device on diffractive periodic structures with its components of various shapes (square, triangular etc.), which, of course, narrows the design options and the variety of thermometric devices.

It is known [2] an optical thermometric device that provides temperature measurement by changing the Fraunhofer diffraction by reflection from special silicon two-dimensional periodic structures [3]. Diffraction gratings are formed as a result of implantation of the surface of single-crystal silicon by phosphorus ions through a mask - a thin metal grid. As a result, amorphous cells bounded by a single-crystal silicon network are formed on the silicon surface. The implantation energy of 40 keV, the implantation dose of 3.12-10 ¹⁵ ion / cm ² and the type of ion were chosen so that an amorphous layer is formed, starting from the irradiated silicon surface. When such a periodic diffraction structure is probed by a beam of a cw He-Ne laser (wavelength 632.8 nm), a diffraction pattern is observed.

The functioning of the thermometric device (measuring the temperature of the material) based on periodic silicon microstructures (gratings) is carried out by detecting under optical reflection changes in the Fraunhofer diffraction pattern from the grating due to thermal expansion or contraction of the semiconductor substrate. For this, the angular redistribution of diffraction maxima that occurs when the geometric dimensions of the grating during its heating or cooling is monitored is monitored. The magnitude of the deflection angle of the diffraction beam determines the change in the lattice period, which allows you to set the temperature of the sample according to well-known formulas [1].

This optical thermometric device, based on periodically-structured ion implantation of silicon [2], is the closest to the claimed technical solution and therefore is selected as a prototype.

The disadvantages of the prototype are:

- a thermometric device based on a periodic diffraction microstructure obtained on an opaque silicon substrate in the visible region by ion implantation can only be used for optical reflection;

- the sensitivity of the thermometric device based on silicon is not large due to the low value of its coefficient of thermal expansion (α _Si = 4 · 10 ^-6 K ^-1 ).

The technical problem to be solved in the claimed technical solution consists in providing the possibility of obtaining an optical thermometric device containing periodic diffraction microstructures in the surface volume of various polymer substrates (polymethyl methacrylate - PMMA, polyimide, epoxy resins, etc.), for the use of such thermometric devices as for reflected, so for transmitted light. Such an approach will also make it possible to increase the sensitivity of a thermometric device that provides temperature measurement in a certain range by changing the Fraunhofer diffraction from special two-dimensional periodic structures, due to a higher thermal expansion coefficient of the polymer substrate containing the lattice. For example, the thermal expansion coefficient of PMMA is α _PMMA = 5 · 10 ^-5 K ^-1 [4], which is an order of magnitude higher than that for silicon (α _Si = 4 · 10 ^-6 K ^-1 ).

The problem in the proposed technical solution in an optical thermometric device that provides temperature measurement by changing the diffraction pattern of light, consisting in the formation on the surface of the initial substrate of the elements of a given periodic diffraction microstructure by ion implantation through a surface mask, is achieved by using an optically transparent substrate polymer, and the formed diffraction structure contains ion-synthesized metal nanoparticles eggs dispersed in the near-surface region of the substrate at a layer thickness of 10 to 600 nm at a metal concentration of 2.0 · 10 ²⁰ -8.0 · 10 ²² atoms / cm ³ .

In figure 1. shows a general diagram (drawing) of the use of an optical thermometric device (product). Elements of the scheme are: a light source, for example, a laser 1, an optical thermometric device 2, consisting of an optically transparent polymer substrate 3 with a diffraction periodic microstructure embedded in its surface, the elements of which are regions subjected to ion irradiation - implanted cells 4 separated by non-irradiated partitions 5 , and a control screen 6 for observing the diffraction pattern. The deflection angle φ of the laser diffraction probe beam and the redistribution of diffraction maxima by the angular value Δφ on the control screen 6 is determined by the temperature T of the polymer substrate 3 of the optical thermometric device 2 and the resulting change in the geometric dimensions of the diffraction grating during its heating or cooling.

In figure 2. shows the calculated depth distribution of implanted silver in PMMA at an irradiation energy of 30 keV.

In figure 3. The optical transmission spectra of unirradiated (a) and (b) PMMA with ion-synthesized silver nanoparticles are shown.

In figure 4. The TEM image obtained on a transmission electron microscope shows the surface of PMMA with silver nanoparticles synthesized by ion implantation.

5. shows an AFM image obtained using an atomic force microscope, PMMA (a fragment of a periodic diffraction microstructure) implanted with silver ions through a surface mask.

Figure 6 shows a block diagram of an experimental setup for observing the operation of a polymer-based optical thermometric device with a periodic transmission diffraction microstructure.

7. the diffraction patterns of the locations of the maxima of the 0th, 1st, and 32nd orders are shown on the control screen, recorded by an optical thermometric device when heating PMMA. Diffraction patterns are shown from top to bottom with increasing temperature of PMMA: 20, 45, 70 and 95 ° C. Below is a centimeter scale.

On Fig. The optical transmission spectrum of (a) polyimide and polyimide with ion-synthesized copper nanoparticles (b) is shown.

In Fig.9. The image shown on an optical microscope implanted with copper ions through a surface mask of a polyimide (a fragment of a periodic diffraction microstructure) is shown. The cell size is 25 microns.

10. The image of the diffraction scattering pattern shown on the control screen when light is reflected from periodically microstructured polyimide (sample) with ion-synthesized copper nanoparticles probed by a laser at a wavelength of 632.8 nm is shown.

Consider a method of manufacturing an optical thermometric device that provides temperature measurement by changing the diffraction pattern of light, using specific examples. The condition for the manufacture of an optical thermometric device includes the formation on the surface of the initial substrate of the elements of a given periodic diffraction microstructure by ion implantation through a surface mask, while ion implantation is carried out by metal ions with an energy of 2-1300 keV, an irradiation dose that provides a concentration of introduced metal atoms in the irradiated substrate of 2.0 10 ²⁰ -8.0 · 10 ²² atoms / cm ³ , ion current density of 1.2 · 10 ¹² -1.5 · 10 ¹³ ion / cm ² s in an optically transparent polymer substrate.

Figure 1 shows a General diagram (drawing) of the use of an optical thermometric device (product). The elements of the circuit are a light source, for example, a laser 1 and an optical thermometric device 2, which provides temperature measurement by changing the diffraction pattern of light, containing a substrate 3 with a diffraction periodic microstructure embedded in its surface, the elements of which are regions subjected to ion irradiation - implanted cells 4 and characterized by a different dielectric constant relative to the material of the substrate 3, where the substrate 3 is made of an optically transparent polymer, and diffraction The ionic structure contains ion-synthesized metal nanoparticles dispersed in the near-surface region of the substrate at a layer thickness of 20 to 600 nm at a metal concentration of 2.0 · 10 ²⁰ -8.0 · 10 ²² atoms / cm ³ . Non-irradiated partitions 5 located between the implanted cells 4 have the same dielectric constant as the optically transparent substrate 3 (for reference). An element of the circuit is also a control screen 6 for observing the diffraction pattern. The deflection angle φ of the laser diffraction probe beam and the redistribution of diffraction maxima by the angular value Δφ on the control screen 6 is determined by the temperature T of the polymer substrate 3 of the optical thermometric device 2 and the resulting change in the geometric dimensions of the diffraction grating during its heating or cooling.

Example 1. An optical thermometric device that provides temperature measurement by changing the diffraction pattern of light is made by a method that includes forming on the surface of the initial substrate the elements of a given periodic diffraction microstructure by ion implantation on an ILU-3 accelerator through a surface mask — a metal mesh with a mesh size of 25 μm, while ion implantation is performed noble metal ions - Ag ⁺ with an energy E = 30 keV and the irradiation dose of D = 5.0 · October ¹⁶ ion / cm ^2, provides concentration metal atoms introduced in the irradiated substrate (2.0 · October ²² atoms / cm ^3), the ion beam current density J = 3 10 ¹³ ions / cm ² into an optically transparent resin substrate of polymethyl methacrylate (PMMA) at room temperature.

Modeling the concentration profiles of the distribution of implanted silver with an energy of 30 keV in PMMA in depth using the computer algorithm SRIM-2013 [5] (Fig. 2) showed that silver atoms accumulate in the surface of the implanted polymer layer, leading to the nucleation and growth of metal nanoparticles . The total thickness of the implanted layer with silver nanoparticles, and, consequently, the thickness of the active layer of the formed periodic diffraction microstructure in PMMA, for these implantation conditions, does not exceed 100 nm.

In figure 3. Experimental linear optical transmission spectra are shown for the initial PMMA and also implanted with silver ions (Ag: PMMA), measured on an Avantes-2048 spectrometer. In contrast to the initial PMMA matrix of FIG. 3 (a), the implanted Ag: PMMA sample of FIG. 3 (b) is characterized by the presence in the visible region of the spectrum of a selective absorption band with a maximum of ~ 500 nm. This band indicates the formation of silver nanoparticles in PMMA, and it is due to the manifestation of the surface plasmon resonance effect in metal nanoparticles [6].

The image obtained on a transmission electron microscope - TESLA BS-500, (TEM image) of the surface of PMMA in the region of the polymer, not covered with a mesh mask, after implantation with silver ions is shown in Fig.4. Unlike unirradiated polymer, spherical nanoparticles are visible in the micrograph. From the analysis of microdiffraction (the figure is not shown) it follows that the spherical formations have a face-centered cubic lattice with a constant corresponding to metallic silver. The image of the observed microdiffraction is characterized by a set of thin polycrystalline rings from silver nanoparticles, recorded against the background of wide diffuse, diffuse, low-intensity rings corresponding to an amorphous polymer matrix. Comparison of experimental microdiffraction images with standard international tabular x-ray ASTM data allows us to conclude that the formation of any chemical compounds with silver ions does not occur during polymer ion implantation.

The periodic microstructured surface of PMMA implanted with silver ions through a mask, observed with a FastScan Brucker atomic force microscope (ACM), is shown in FIG. 5. The AFM image shows that the irradiated surface of the sample is an ordered lattice with 25 μm cells, faceted by walls of an unimplanted polymer. In this case, the square region of the cells is ion-irradiated PMMA, i.e. the structure of the polymer with silver nanoparticles, observed in figure 4, characterized by selective plasmon absorption (figure 3).

Since it is known that implantation of metal ions into a dielectric leads to an increase in its refractive index up to ~ 1.7–1.9 for the visible spectral region (especially at the plasmon resonance frequencies of metal nanoparticles) [7], it is obvious that a microstructure is formed as a result of PMMA implantation through a mask (the lattice is an element of an optical thermometric device) with a periodically variable distribution of the optical constants of the material, i.e. between the lattice cells and its walls (n _PMMA = 1.5 [8]).

The operation of the optical thermometric device (Fig. 1) is ensured by determining the temperature of the sample by changing the Fraunhofer diffraction pattern from the periodic diffraction microstructure formed on it (Fig. 5). Due to the increase or decrease in the period (size) of the grating caused by its thermal expansion or contraction with a change in temperature, redistribution of the maxima in the diffraction pattern on the control screen occurs. The value of the current temperature (T) of the sample is determined by the magnitude of the deflection angle of the laser diffraction probe beam (φ) and the redistribution of diffraction maxima by the angular value Δφ on screen 3 (Fig. 1).

The dependence of the change in the diffraction angle Δφ on the temperature change ΔT is expressed by the formula [1, 2]:

where k is the order of the diffraction maximum, λ is the wavelength, α is the coefficient of thermal expansion, and d is the lattice period.

As can be seen from formula 1, the coefficient α is proportional to Δφ. Obviously, ceteris paribus (k, λ, and d), an optical thermometric device formed on the basis of a material with a large value of α has a higher sensitivity. In this example, the PMMA substrate is characterized by the coefficient α _PMMA = 5 · 10 ^-5 K ^-1 [4], which, in comparison with the silicon described in the prototype [2] (α _Si = 4 · 10 ^-6 K ^-1 ), is greater than an order of magnitude. This fact also means that an optical thermometric device made on the basis of PMMA provides greater sensitivity (in the range of operating temperatures of the polymer) than in the case of a silicon sample. Note that in the case of PMMA, the operating temperature cannot exceed 120 ° С, which corresponds to the temperature of destruction and destruction of this polymer [9].

The operability test of an optical thermometric device based on implanted PMMA containing a periodic diffraction microstructure was carried out by probing the polymer into the light with a He-Ne laser beam at a wavelength of 632.8 nm. Figure 6 shows a block diagram of an experimental setup for observing the operation of an optical thermometric device in clearance by the deviation of diffraction maxima on the control screen when the PMMA temperature changes in the stationary heating and cooling mode.

The probe beam of the He-Ne laser is directed to the surface of the PMMA containing a periodic diffraction microstructure (Fig.6). The position of the diffraction maxima was observed on the control screen. In order to increase the visualization of the functioning of the optical thermometric device on the control screen, the position of the 32-order diffraction maximum relative to the central 0-order maximum was estimated. For the convenience of observing these maxima near each other, a 32-order diffraction beam was redirected by a mirror to the control screen in the region near the 0th-order diffraction maximum. The pattern of the shift of the diffraction maxima on the control screen during heating or cooling of the sample was recorded on a Casio Exilim Ex-F1 digital camera. The sample mounted on a copper substrate was heated by a spiral fed through an LATR to a temperature of 95 ° C. The temperature of the sample was also controlled by a thermocouple.

The combined diffraction patterns of the locations of the maxima of the 0th, 1st, and 32nd orders, recorded by an optical thermometric device when heating PMMA from 20 to 95 ° C, are shown in Fig.7. As follows from Fig. 7, with an increase in the PMMA temperature, a shift of the 32nd-order diffraction maximum towards the 1st-order maximum is clearly observed. The recorded beam shift of 1 mm for a given optical configuration of the experiment (Fig.6) is due to a temperature change of ~ 25 degrees. These results demonstrate the operation of an optical thermometric device based on implanted PMMA with a periodic diffraction microstructure when it is probed to the light.

Example 2. As a substrate for an optical thermometric device, a polymer, a polyimide, is used, which is characterized by high transparency (about 90%) in a wide spectral range from 200 to 1000 nm.

The implantation is performed by singly charged Cu ⁺ ions with an energy of E = 40 keV, a dose of D = 5.0 · 10 ¹⁶ ion / cm ² (concentration - 2.0 · 10 ²² atoms / cm ³ ) and a current density in the ion beam of J = 3.5 · 10 ¹³ ion / cm ² s. Other technological operations and modes of ion implantation associated with irradiation through a surface mask, such as in example 1.

The optical absorption spectrum of the synthesized sample, measured on an Avantes-2048 spectrometer, is shown in Fig. 8. As a result of ion implantation of a polymer, a selective plasmon absorption band with a maximum near 630 nm appears in the spectrum of the composite material, which corresponds to ion-synthesized copper nanoparticles [6].

Surface microstructures implanted with copper ions through a polyimide mask were observed on a Micromed POLAR 1 optical microscope (Fig. 9). It can be seen in the above image that the surface of the sample is an ordered lattice with cells 25 microns in size, which are formed upon implantation of polyimide in a given mode. In this case, the square cell is a polymer structure with copper nanoparticles, the spectrum of which is shown in Fig. 8. The walls between the square lattice cells are composed of unirradiated polyimide.

In the considered example, the polyimide substrate is characterized by the coefficient of thermal expansion α _polyimide = 1.1 · 10 ^-4 [10], which, in comparison with the silicon described in the prototype [2] (α _Si = 4 · 10 ^-6 K ^-1 ), is greater than two orders of magnitude. This means that an optical thermometric device made on the basis of polyimide provides greater sensitivity (in the range of operating temperatures of the polymer) than in the case of a silicon sample.

Thus, the microstructure formed by implantation with a periodically variable refractive index (permittivity) is a periodic diffraction microstructure that can be used as an optical polymer thermometric device. Figure 10 shows the diffraction image recorded for reflection when probing the formed grating with a laser at a wavelength of 632.8 nm.

The choice of ion implantation modes, E = 2-1300 keV, D - providing a concentration of introduced metal atoms in the irradiated substrate 2.0 · 10 ²⁰ -8.0 · 10 ²² atoms / cm ³ , J = 1.2 · 10 ¹² -1.5 · 10 ¹³ ion / cm ² s, is caused by the fact that beyond the boundaries of these modes the necessary technical result is not achieved, and the quality of the fabricated periodic diffraction microstructures will not meet the necessary requirements.

The radiation dose is determined by the required number of atoms of the metal substance in order, firstly, to provide high contrast in the reflection coefficients of the formed elements of the diffraction grating, i.e. sufficiently large metal nanoparticles exhibiting plasmon reflection and absorption should be synthesized. This condition, according to our studies of the dependence of the appearance of the plasmon absorption signal in metal nanoparticles on the implantation dose, is fulfilled at metal atom concentrations in the irradiated polymer of the order of 2.0-10 ²⁰ atoms / cm ³ . Secondly, the amount of embedded impurity should not exceed the dose at which the adhesion of growing metal nanoparticles begins, leading to the formation of a continuous metal film, and according to our estimates, is no more than 8.0 · 10 ²² atoms / cm ³ .

The current density in the ion beam J determines, on the one hand, the time it takes for the implantation dose to be set, and on the other hand, the degree of heating of the irradiated material. It was experimentally established that at J = 1.5 · 10 ¹³ ion / cm ² s the temperature of the irradiated surface of the sample increases and leads to its destruction (change). Irradiation with a low ion current density does not expediently increase the implantation time. Therefore, the minimum ion current density is limited to J = 1.2 · 10 ¹² ion / cm ² s.

The energy of the ion E determines the value of its average projection range, which determines the depth of the implanted ion, and, consequently, the thickness of the modified layer and diffraction grating. From above, the ion acceleration energy is limited to E = 1300 keV, since with an increase in this implantation energy and a reasonable duration of irradiation, the required concentration of metal atom impurity is not reached, which is necessary for nucleation of metal nanoparticles at a great depth. The limitation from below to E = 2 keV, according to our experiments, is due to the fact that with a further decrease in E, it is not possible to obtain such large elements of the lattice structure on which light diffraction is observed. When E = 2-1300 nm, the diffraction periodic microstructure contains ion-synthesized metal nanoparticles dispersed in the surface region of the polymer substrate at a layer thickness of 10 to 600 nm.

The technical result is the possibility of obtaining an optical thermometric device with increased sensitivity due to a higher coefficient of thermal expansion of the polymer substrate. Additionally, the optical transparency of the product makes it possible to use it, both for reflected and transmitted light.

List of references

1. Magunov A.N. Laser thermometry of solids. M .: Fizmatlit, 2001.224 s.

2. Farrakhov B.F., Galyautdinov M.F., Fattakhov Y. V., Zakharov M.V. Investigation of heating and recrystallization in implanted silicon under pulsed light irradiation. Scientist notes. Kazan, state un-that. ser. physical and mathematical sciences. 2010 T. 152. Book 3. S.164-170.

3. Fattakhov Y. V., Galyautdinov M. F., Lvova T. N., Khaibullin I. B. The formation of periodic diffraction structures on the surface of semiconductors to study the dynamics of photoinduced phase transitions. Optics and spectrum. 2000.V. 89. No. 1. S.150-156.

4. Arakcheeva E.M., Tanklevskaya E.M., Nesterov S.I., Maksimov M.V., Gurevich S.A., Seekamp J., Sotomayor Torres S.M. Obtaining photonic crystals in structures based on semiconductors and polymers using the nanoimprint method. ZHTF. 2005.V. 75. No. 8. S. 80-84.

5. Ziegel J.F., Biersak J.P., Littmark U. The stopping and range of ions in solids. N.Y .: Pergamon, 1996.

6. Kreibig U., Vollmer M. Optical properties of metal clusters. Berlin: Springer. 1995.

7. Faik A., Allen L., Eicher C, Gagola A., Townsend P.D. Dispersion and luminescence measurements of optical waveguides. J. Appl. Phys. 1983. V. 54. P. 2597-2601.

8. Ananyev CC, Bernal ID, Demidov BA, Kalinin Yu.G., Petrov VA, Experimental measurements of the refractive index of polymethyl methacrylate behind the front of a shock wave excited by a high-current electron beam, ZhTF 2010, T. 80 , issue 5, pp. 111-116.

9. Salimgareeva V.N., Kolesov S.V. Thermal degradation and stabilization of polymethyl methacrylate, Izvestiya Vysshikh Uchebnykh Zavedenii. Chemistry and chemical technology. 2007, T. 50, No. 7, S. 3-11.

10. Kryzhanovsky V.K., Burlov V.V., Panimatchenko A.D., Kryzhanovskaya Yu.V. Technical properties of polymeric materials. Art. Petersburg: Profession, 2005, 248 p.

Claims (1)

An optical thermometric device that provides temperature measurement by changing the diffraction pattern of light, containing a substrate with a diffraction periodic microstructure embedded in its surface, the elements of which are regions subjected to ion irradiation and characterized by a different dielectric constant relative to the substrate material, characterized in that the substrate is made of optically transparent polymer, and the diffraction structure contains ion-synthesized metal nanoparticles, dispersed in the near-surface region of the substrate at a layer thickness of 10 to 600 nm at a metal concentration of 2.0 · 10 ²⁰ - 8.0 · 10 ²² atoms / cm ³ .

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