RU2617293C1 - Method of measuring temperature - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: method includes the preliminary construction of the experimental calibration curve depending on the temperature values of the magnetic field at the point of anticrossing of the levels (ACL) of the energy of spin centers with quadruplets excited spin state S = 3/2 contained in the crystal of Silicon Carbide. Then, on the surface of the crystal is placed the sample and measure the luminescence intensity of the spin centers with quadruplets excited spin state S = 3/2 at different values of the constant magnetic field. In the luminescence intensity change read in the curve of dependence of the change of luminescence intensity of the constant magnetic field and determine by the point of ACL of the energy the spin centers the magnetic field. On the found value of magnetic field using a calibration curve determine the temperature at the point of the surface of the sample corresponding to the point of focus of the laser radiation.

EFFECT: ways to simplify and improve the accuracy of measurements.

5 cl, 7 dwg

Description

The invention relates to nanotechnology and can be used in the field of measuring local weak temperature fields with micro- and nanoscale resolution in microelectronics, biotechnology, cytology, biomedicine.

The detection of weak temperature fields with high spatial resolution at the level of micro- and nanometers is the most important problem in various fields, from fundamental physics and materials science to data storage and biomedical science. Of particular interest are the possibilities of a biocompatible approach to thermometry, which provides high temperature sensitivity and reproducibility and can be used to study heat-generating intracellular processes.

After the discovery of the emitting properties of nitrogen-vacancy centers (NV centers) in diamond, which allow optical detection of magnetic resonance in the ground state of these centers at room temperature until the detection of magnetic resonance at single centers (see A. Gruber, A. Drabenstedt, C. Tietz , L. Fleury, J. Wrachtrup, C. Von Borczyskowski. - Scanning Confocal Optical Microscopy and Magnetic Resonance on Single Defect Centers. -Science, V. 276, pp. 2012-2014, 1997; J. Wrachtrup, F. Jelezko. - Processing quantum information in diamond. - Journ. Phys .: Condens. Matter, V. 18, S807, 2006), it became possible to create quantum sensors for measuring magnetic fields and tempo Teratures with nanoscale resolution. A separate NV center is a carbon (V) vacancy, in the nearest coordination sphere, in which one of the four carbon atoms is replaced by a nitrogen (N) atom. NV centers are characterized by the ground triplet spin state (S = 1), in which nonequilibrium filling of spin levels is optically created. In this case, a change in the filling of spin levels under the influence of resonant microwave radiation with which the spin system of NV centers interacts is recorded optically from a change in the luminescence of NV centers. The method of magnetometry and thermometry with spin NV centers is based on the optical detection of magnetic resonance (ODMR).

The possibilities of recording the temperature from the ODMR spectra of NV centers are based on the dependence of the fine structure D splitting temperature, which leads to a shift in the ODMR frequency (see V.M. Acosta, E. Bauch, M.P. Ledbetter, et al., Phys. Rev. . Lett., V. 104, 070801, 2010).

A known method of measuring local temperature (see P. Neumann, I. Jakobi, F. Dolde, C. Burk, R. Reuter, G. Waldherr, J. Honert, T. Wolf, A. Brunner, JH Shim, D. Suter , H. Sumiya, J. Isoya, and J. Wrachtrup, High-Precision Nanoscale Temperature Sensing Using Single Defects in Diamond, Nano Lett., V. 13, 2738-2742, 2013), with spatial resolution in the micro- and nanometer range based on optically detectable magnetic resonance (ODMR) using NV centers in diamonds and nanodiamonds. The method includes the following sequence of operations: the laser radiation is focused on the active material — a diamond or nanodiamond crystal with NV centers at the point of measurement of local temperature; supplying microwave radiation with an energy close to the fine structure splitting for NV centers (2.8 GHz), which interacts with the spin system of NV centers; register the photoluminescence of NV centers; change the frequency of microwave radiation and measure the frequencies at which there is a change in the luminescence intensity of the NV centers, due to magnetic resonance at the spin levels of the NV centers; measure the frequency of magnetic resonance and determine the temperature value from the frequency of magnetic resonance in accordance with the known value of the splitting for a given temperature.

The disadvantages of this method is the use of diamonds with NV centers as an active material for measuring temperature, the technology for which is extremely expensive and relatively poorly developed. In addition, the method uses the optical range in the visible region, which is poorly compatible with silicon-based fiber optics, as well as with the transparency band of biological systems. In the known method, it is necessary to use relatively powerful microwave radiation, which complicates the method, creates additional noise and heats the investigated object. The splitting of the fine structure for NV centers in diamond substantially depends on the stresses in the diamond crystal and local magnetic fields, which reduces the accuracy of temperature measurements and requires additional efforts to eliminate these effects.

A known method of measuring temperature (see PCT application WO 2013188732 IPC G01R 19/00, published 06/14/2013), including the effect of optical radiation on a diamond containing NV centers, for alignment of electron spins in a certain spin state; the action of microwave radiation on a diamond containing NV centers, the splitting of the fine structure of which depends on temperature, so as to cause transitions between the electronic spin states of the NV centers for specific microwave frequency frequencies, which depend on temperature, and recording the intensity of the output optical radiation coming out from diamond containing NV centers in such a way as to determine the temperature shift of the fine structure parameters and, consequently, the local temperature.

The disadvantages of this method is the use of diamonds with NV centers as an active material for measuring temperature, the technology for which is extremely expensive and relatively poorly developed. In addition, the method uses the optical range in the visible region, which is poorly compatible with silicon-based fiber optics, as well as with the transparency band of biological systems. In the known method, it is necessary to use relatively powerful microwave radiation, which complicates the method, creates additional noise and heats the investigated object.

A known method of measuring temperature (see PCT application WO 2014165505, IPC G01K 7/32, published 09/10/2014), comprising exposing a diamond containing NV centers to optical radiation to align electronic spins in a specific spin state; exposure to continuous microwave radiation or pulses of microwave radiation in such a way as to cause transitions between the electronic spin states of NV centers for specific values of the frequency of microwave radiation and registration of the intensity of the optical radiation emerging from the diamond to determine the temperature shift of the fine structure parameters and, consequently, the local temperature. In the known method, the temperature value can be recorded on a micro- and nanometer scale with a sensitivity of 10 K to mK using diamond containing 100-10000 NV centers.

The disadvantages of this method is the need to use very expensive diamonds with NV centers as an active material for measuring temperature. The method is difficult to implement, its use is accompanied by additional noise and heating of the investigated object.

A known method of measuring temperature (see PCT application WO 2014210486, IPC C30B 29/04; G02B 3/00; H01S 3/14, published December 31, 2014), including exposure to optical pulses (with a wavelength of 532 nm) and microwave radiation on a single crystal diamond containing NV centers, in such a way as to cause transitions between the electronic spin states of NV centers for specific microwave frequency frequencies, which depend on temperature, and recording the intensity of the output optical radiation emerging from diamond containing NV centers in such a way as to determine Temperature.

The known method has the same disadvantages as for the above methods of measuring temperature.

Recently, vacancy spin centers in silicon carbide (SiC) have been discovered with properties similar to NV centers in diamond; hereinafter, these centers will also be called spin centers with ground and excited quadruplet spin states (see N. Kraus, V.A. Soltamov, F. Fuchs, D. Simin, A. Sperlich, PG Baranov, GV Astakhov, V. Dyakonov; Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide, Scientific Reports, 2014) and a method for measuring temperature that is similar to this decision on the largest number of essential features and taken as a prototype. The prototype method is based on optical magnetic resonance detection (ODMR) at spin centers with a quadruplet spin state in silicon carbide. It is an excited state of a negatively charged silicon vacancy (V _Si ) with spin S = 3/2, interacting with a neutral carbon vacancy (V _c ), located along the hexagonal crystallographic axis (c - axis) relative to the silicon vacancy and not having a molecular bond with silicon vacancy, while there is a family of similar structures that differ in the matrix polytype and the position of silicon and carbon vacancies and their relative positions. For centers with a quadruplet spin state in silicon carbide, the splitting of the fine structure depends on temperature. The prototype method includes the preliminary construction of an experimental calibration curve of the frequency deviations of the ODMR frequency deviations of the signal of spin centers with an excited quadruplet spin state S = 3/2 contained in a silicon carbide hexagonal or rhombic polytype on temperature by acting on said silicon carbide crystal at different temperatures optical radiation in the near infrared range (780-850 nm) and a high-frequency (HF) magnetic field with a magnetic resonance frequency. To measure the temperature of the test sample, it is placed on the surface of the said silicon carbide crystal, it is exposed to the said silicon carbide crystal by optical radiation in the near IR range (780-850 nm) and a high-frequency (HF) magnetic field with a magnetic resonance frequency. Comparing the obtained value of the ODMR deviation of the signal of the silicon carbide crystal with the aforementioned spin centers with the calibration curve of the temperature dependence of the ODMR frequency deviations of the spin centers on temperature, we obtain the temperature value of the test sample.

In the prototype method, during optical excitation, spin centers are aligned, which affects the nonequilibrium filling of spin levels in the ground and excited states, and when the crystal is irradiated, we rearrange by high-frequency (HF) radiation at the time of magnetic resonance, the luminescence intensity of spin centers with the main and excited quadruplet spin states. From the magnitude of the RF radiation at which magnetic resonance occurs, one can judge the magnitude of the splitting of the fine structure D, which enters the spin Hamiltonian H, which describes the spin levels of the spin center with an excited quadruplet spin state in magnetic field B:

where: B is a constant magnetic field, T;

S _z is the dimensionless operator of projection of the electron spin onto the direction of the external magnetic field;

S = 3/2 — dimensionless quantity equal to the spin of the spin center;

g _e = 2,002 is a dimensionless quantity called the g factor and characterizing the gyromagnetic ratio for the electronic magnetic moment of the used spin center with an excited quadruplet spin state in silicon carbide;

β _e = 9.2740.10-24 - Bohr magneton, J / T;

2D (T) is the fine structure splitting for a spin center with a temperature-dependent quadruplet spin state in silicon carbide, J (MHz), 1 J = 1.509 × 10 ²⁷ MHz.

A disadvantage of the known method of measuring the magnetic field is the need to use RF radiation, which complicates the implementation of the method, and also creates additional RF noise and heats the test object, which is placed close to the silicon carbide crystal with spin centers with a quadruplet spin state and in which the local temperature in the volume is measured excited optically. It is also necessary to use additional equipment to create RF radiation and it is necessary to supply RF radiation to the point of measurement of the magnetic field using a loop or coil.

The present invention was the development of such a method of measuring temperature, which would be easier to use and which would exclude the use of RF radiation and, therefore, would exclude the heating of the RF field of the object whose temperature is measured.

The problem is solved in that the method of measuring the magnetic field includes the preliminary construction of an experimental calibration curve of the magnetic field at the point of intersection of the levels of energy of the spin centers with the excited quadruplet spin state S = 3/2 contained in a silicon carbide crystal of a hexagonal or rhombic polytype , from temperature. The construction of this curve is carried out by exposing the said silicon carbide crystal at different temperatures to focused laser radiation, an alternating low-frequency magnetic field and a constant magnetic field of different magnitude. At each temperature, the luminescence intensity of spin centers with an excited quadruplet spin state S = 3/2 is measured, in the region of variation in the luminescence intensity, a curve of the dependence of the change in luminescence intensity on the constant magnetic field is measured and the magnetic field is found from the inflection point of the signal in the form of the derivative corresponding to AAP energies of the mentioned spin centers in a magnetic field, then the studied sample is placed on the surface of the said silicon carbide crystal, measuring the luminescence intensity of spin centers with an excited quadruplet spin state S = 3/2 is determined for different values of the constant magnetic field; in the region of variation in the luminescence intensity, the curve of the dependence of the change in the luminescence intensity on the constant magnetic field is taken and the magnitude of the magnetic field is determined from the APA point of the energy of the spin centers, according to which using the experimental calibration curve determine the temperature at a point on the surface of the test sample corresponding to the point focus of laser radiation.

New in the present method is the exposure of a silicon carbide crystal to a hexagonal or rhombic polytype containing spin centers with a quadruplet spin state S = 3/2, a variable low-frequency magnetic field and a constant magnetic field, as well as the fact that the calibration curve of the magnetic field the APU point on temperature, when measuring the temperature of the sample, the dependence of the change in the luminescence intensity on the constant magnetic field is removed and the magnetic field for A PU corresponding to the measured temperature.

The luminescence of spin centers with a quadruplet spin state S = 3/2 excited by laser radiation can be excited using confocal optics or using microscopy based on suppression of spontaneous emission.

Focused laser radiation, a low-frequency alternating magnetic field and a constant magnetic field can act on a silicon carbide nanocrystal containing at least one spin center with an excited quadruplet spin state S = 3/2. In this case, the silicon carbide nanocrystal can be placed on a probe of an atomic force microscope.

The calibration curve can be built into the software, which will automatically recalculate from the position of the APU to the temperature. If we measure the change in luminescence at different points of silicon carbide (or move silicon carbide in space), then we can obtain the temperature distribution (temperature map) over the studied object.

The present method of measuring temperature with micron and submicron resolution is based on the use of physical processes leading to a change in the photoluminescence (PL) intensity of spin centers with an excited quadruplet spin state S = 3/2, which manifests itself in the existence of an inflection point on the curve of the change in the luminescence intensity of spin centers with an excited quadruplet spin state S = 3/2 of the constant magnetic field. This inflection point corresponds to the moment of antirecrossing of the energy levels in the magnetic field of these spin centers in the silicon carbide crystal.

The present technical solution is illustrated by drawings, presented for the purpose of illustration, but not for limitation, where:

in FIG. Figure 1 shows the structural formulas of spin centers (SCs) with the ground and excited quadruplet spin states S = 3/2 (V _{s is the} vacancy of silicon; V _C is the carbon vacancy) for two polytypes of silicon carbide 6H-SiC and 4H-SiC; 6H-SiC presents two structures of spin centers — SP1 and SP2;

in FIG. Figure 2 shows a diagram of the energy spin levels in a magnetic field for the excited quadruplet state of the SP1 spin center in 6H-SiC with S = 3/2; the point of intersection of levels (AAP) is shown by a circle for spin levels with projections of spins (M _s ) M _s = -3 / 2; M _s = 1/2; and the square for the APU with M _s = -3 / 2; M _s = -1 / 2;

in FIG. Figure 3 shows the curves of changes in the photoluminescence intensity (PL) of the spin centers as a function of the applied magnetic field in the region of antirecrossing levels for excited quadruplet states SC1 and SC2 in a 6H-SiC crystal, recorded at two temperatures of 290 K and 80 K; inflection points for APU1 and APU2 are indicated by a circle and a square, respectively; for SC2 only curves in the area of APU1 are shown;

in FIG. Figure 4 shows a graded curve in the form of the dependence of the position of APU1 for SC1 on temperature in a 6H-SiC crystal;

in FIG. 5 shows a calibration curve as a function of the position of APU1 for SC2 as a function of temperature in a 6H-SiC crystal; ΔВ is the change in the magnetic field of the APA at two points of the active material located at different temperatures (the temperature difference was created by a heater located at different distances from the given points); ΔТ is the temperature difference at predetermined points determined using the calibration curve;

in FIG. Figure 6 shows the curves of changes in the photoluminescence intensity of spin centers as a function of the applied magnetic field in the region of antirecrossing levels of APA1 (indicated by a circle) for the excited quadruplet spin state of SCs in a 4H-SiC crystal recorded at two temperatures of 240 K and 80 K;

7 shows a calibration curve in the form of the dependence of the position of APU1 for SCs on temperature in a 4H-SiC crystal.

The present method of temperature measurement involves preliminary construction of an experimental calibration curve of the magnetic field at the point of intersection of the levels of energy of the spin centers (SC) with the excited quadruplet spin state S = 3/2 contained in a silicon carbide crystal of a hexagonal or rhombic polytype on temperature ( Fig. 4 shows a calibration curve for the 6H-SiC polytype, and Fig. 7 for 4H-SiC). The calibration curve of the APA of the SC energy is recorded by exposing the aforementioned silicon carbide crystal at different temperatures to focused laser radiation (for example, a wavelength of 785 nm or 808 nm), an alternating low-frequency magnetic field (in the frequency range from tens of Hz to units of kHz) with an amplitude for example, (0.001-0.01) mT and a constant magnetic field (0-500 G), while measuring for each temperature the luminescence intensity (range for recording luminescence 850-950 nm) from the value of the constant magnetic field, and find the magnetic field at the inflection point of the signal in the form of a derivative of the APU energy SC. The structural formulas of spin centers with the ground and excited quadruplet spin states (V _Si is the silicon vacancy; V _C is the carbon vacancy) in the 6H-SiC silicon carbide polytype (two structures of the spin centers — SP1 and SP2 are presented) or 4H-SiC are shown in FIG. 1. By way of example in FIG. Figure 2 shows a diagram of the energy spin levels in a magnetic field for the excited quadruplet state of the SP1 spin center in 6H-SiC with S = 3/2; the point of intersection of levels (AAP) is shown by a circle for spin levels with projections of spins (M _s ) M _s = -3 / 2; M _s = l / 2; and the square for the APU with M _s = -3 / 2; M _s = -1 / 2. In FIG. Figure 3 shows the signals of the change in the photoluminescence (PL) intensity of the spin centers depending on the applied magnetic field in the region of the APA for the excited quadruplet states SC1 and SC2 in a 6H-SiC crystal, recorded at two temperatures 290 K and 80 K; inflection points for APU1 and APU2 are indicated by a circle and a square, respectively; for SC2 only curves in the APU1 region are shown. Similar dependences are recorded at different temperatures, and the magnitude of the magnetic fields at the inflection points indicated in FIG. 3 circles for APU between the levels M _s = -3 / 2; M _s = l / 2, which will be used to measure temperature. Then build a calibration curve of the magnitude of the magnetic field, the corresponding AAP between the levels M _s = -3 / 2; M _s = l / 2 for the excited quadruplet spin state of the spin center (SC) as a function of temperature. The value of the magnitude B of the magnetic field at the inflection point of the curve at which the antisection of the spin sublevels M _s = -3 / 2 and M _s = l / 2 takes place for a spin center with an excited quadruplet spin state:

B = D / g _e β _e ,

where: B is the value of the constant magnetic field at the inflection point of the first curve, mT;

g _e = 2,0028 - a dimensionless quantity called the g-factor and characterizing the gyromagnetic ratio for the electronic magnetic moment of the spin center in silicon carbide;

β _e = 9.2740.10-24 - Bohr magneton, JD;

2D (T) - temperature-dependent fine structure splitting for the spin center in the excited quadruplet spin state in silicon carbide, MHz (GHz).

In FIG. 4 and FIG. Figure 5 shows calibration curves in the form of the dependences of the position of APU1 for SC1 and SC2 on temperature in a 6H-SiC crystal, constructed experimentally. In the calibration curve shown in FIG. 7 shows the change in the magnetic field APU1 (ΔВ) at two points of the active material at different temperatures (the temperature difference was created by a heater located at different distances from the given points); this change corresponds to the temperature difference (ΔТ) at given points determined using the calibration curve.

Then they are placed on the surface of a silicon carbide crystal containing spin centers with an excited quadruplet spin state S = 3/2, the test sample, in which the local temperature must be measured. Again, the measurements of the dependence of the PL intensity of spin centers with the excited quadruplet spin state S = 3/2 on the constant magnetic field are repeated and the magnetic field is found at the inflection point (APU1), then the temperature corresponding to this magnetic field is found from the calibration curve. Then all measurements are repeated at another point in the sample and, as a result, the temperature field of the sample is built.

Example 1. By the method described above, the temperature of a sample placed on a silicon carbide crystal of the 6H-SiC polytype containing SC2 spin centers was determined; a variant of such a measurement is shown in FIG. 3 and FIG. 5. The temperature was changed by pumping cold air at the location of the sample. Laser light with a wavelength of 808 nm was focused on working material in the form of silicon carbide, with a spot size in diameter of about 300 nm, and luminescence of SC2 spin centers at wavelengths of 850–950 nm was recorded from this region. The magnetic field corresponding to APU1 for SC2 was found from the change in luminescence. Then, using a calibration curve, the temperature was determined.

Example 2. By the method described above, the temperature of a sample placed on a 4H-SiC carbide crystal was determined in two measurements, the carbide crystal contains SC spin centers, a variant of such a measurement is shown in FIG. 6 and FIG. 7. The temperature was changed by pumping cold air at the location of the sample. Laser light with a wavelength of 808 nm was focused on working material in the form of silicon carbide, with a spot size of about 300 nm in diameter, and luminescence of the SC spin centers at wavelengths of 850–950 nm was recorded from this region. The magnetic field corresponding to APU1 for SC was found from the change in luminescence. Then, using a calibration curve, the temperature was determined.

The present method can be used to obtain a temperature field gradient with the spatial movement of a spot excited by light in a plane perpendicular to the laser beam. In this case, high accuracy of relative measurements can be achieved using the APU signal in the form of a derivative, which is recorded using synchronous detection with a small low-frequency modulation of the magnetic field. In this case, the APU line width in the magnetic field is determined, and then, when the temperature is shifted, the APU line is shifted in the magnetic field, the magnitude and sign of the shift are recorded by the PL change within the line width. A sensitivity of 50 mK can be achieved over a recording time of 1 s with a resolution of ~ 200 nm, corresponding to the spot size of the focused laser.

An embodiment of the present method of measuring the temperature field consists in using a surface layer of a silicon carbide crystal containing a high concentration of spin centers with an excited quadruplet spin state to measure the distribution of local temperatures at the nanoscale, with the possibility of using molecular organic or biological temperature fields and their gradients to obtain images structure deposited on the surface of silicon carbide.

An embodiment of the present method for measuring a temperature field is to use an atomic force microscope or a near field microscope. A crystal or nanocrystal of silicon carbide containing spin centers with an excited quadruplet state S = 3/2 is placed on the tip of the probe of an atomic force microscope, then the probe is touched to the test sample in the form, for example, of a living cell or other condensed system, at certain points. In view of the high thermal conductivity of silicon carbide and the strong dependence of the fine structure splitting on temperature in almost the entire measured temperature range of 10-350 K, the temperature at the point of contact between the probe and the sample can be measured.

Claims (5)

1. A method of measuring temperature, including preliminary construction of an experimental calibration curve of the dependence of the magnetic field at the point of intersection of the levels of energy of the spin centers with the excited quadruplet spin state S = 3/2 contained in a silicon carbide crystal of a hexagonal or rhombic polytype, on temperature by exposure to the said silicon carbide crystal at different temperatures by focused laser radiation, a low-frequency alternating magnetic field, and various with a constant magnetic field of magnitude; in this case, the luminescence intensity of spin centers with an excited quadruplet spin state S = 3/2 is measured at each temperature; in the region of variation in the luminescence intensity, the curve of the dependence of the change in luminescence intensity on the constant magnetic field is measured and the magnetic field is found from the inflection point of the signal in the form of a derivative corresponding to the APA of the energy of the mentioned spin centers in a magnetic field, then placed on the surface of the aforementioned of a silicon carbide crystal, the test sample, the luminescence intensity of spin centers with an excited quadruplet spin state S = 3/2 is measured at different values of the constant magnetic field; in the region of change in the luminescence intensity, a curve of the dependence of the change in luminescence intensity on the constant magnetic field is measured and determined by the energy spin centers the magnitude of the magnetic field, according to which using the experimental calibration curve determine the temperature at a point the surface of the investigated sample corresponding to the focal point of laser radiation. 2. The method according to p. 1, characterized in that the excitation of luminescence of spin centers with a quadruplet spin state S = 3/2 by focused laser radiation is carried out using confocal optics. 3. The method according to p. 1, characterized in that the luminescence of spin centers with a quadruplet spin state S = 3/2 by focused laser radiation is excited using microscopy based on the suppression of spontaneous emission. 4. The method according to p. 1, characterized in that the alternating low-frequency magnetic field, constant magnetic field and focused laser radiation act on a silicon carbide nanocrystal containing at least one spin center with an excited quadruplet spin state S = 3/2. 5. The method according to p. 4, characterized in that the said silicon carbide nanocrystal is placed on a probe of an atomic force microscope.

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