Method of calibrating electron paramagnetic resonance spectrometre and calibration sample for realising said method

FIELD: physics.

SUBSTANCE: calibration sample is put into a measuring resonator, which gives an anisotropic spectrum (EPR), made from a rutile monocrystal TiO2 which contains Fe3+ ions in amount of 0.01-0.5 wt %. The calibration sample is turned in a magnetic field until appearance of an EPR anisotropic spectrum of Fe3+ ions whose lines are recorded and the EPR spectrometre is set using the said lines to maximum signal-to-noise ratio by moving the matching piston of the resonator and moving the bottom wall of the resonator in order to adjust the frequency of the resonator.

EFFECT: simple process of tuning and calibrating an electron paramagnetic resonance spectrometre.

4 cl, 2 dwg

 

The invention relates to techniques for spectroscopy electron paramagnetic resonance (EPR)can be used in the manufacture and configuration of EPR spectrometers 3 mm range, as well as for test work on the spectrometers 3 mm range during their operation.

Known methods of calibration of EPR spectrometers using reference samples with the EPR signals in the field g-factor of 2.0. So, there is a method of calibration of the sweep of the magnetic field of an EPR spectrometer (see inventor's certificate SU # 1520416, IPC G01N 24/10 published 07.11.1989), including accommodation in the measuring resonator spectrometer calibration sample, giving isotropic and anisotropic EPR spectra, recorded EPR spectra, combine one of the lines anisotropic spectrum with one of the lines isotropic spectrum, once you determine the splitting and g-factors of spectral lines in the conditions of the specified alignment and perform a calibration scan of the magnetic field with pre-defined splitting and g-factors of spectral lines in the conditions of the specified alignment.

The disadvantage of this method is the possibility of only a calibration scan of the magnetic field, in addition to the registration of EPR spectra in the 3 mm range, it is necessary to apply large magnetic field 3-3,5 TL, Tr shall require the use of superconducting solenoids and cryostats with warm pocket.

As the calibration sample is most often diphenyl-picrylhydrazyl (a pair of charmed mesons), which is issued by the industry, and can also be synthesized in the laboratory. In the solid state a pair of charmed mesons serve as a reference when determining the g-factor (gA pair of charmed mesons=2,0036 0,0003). Depending on what solvent crystallized solid pair of charmed mesons, its line width is different, you can get a line width of 0.15 to 0.47 Tesla. Signal a pair of charmed mesons almost not saturated and can be used for calibration and adjustment of EPR spectrometers at room temperature (see CPOL. - Technique of EPR spectroscopy. - World str, 1970).

Known calibration sample for calibration of an EPR spectrometer (see inventor's certificate SU # 1520416, IPC G01N 24/10 published 07.11.1989)containing substances with isotropic and anisotropic EPR spectra. Substance with an anisotropic spectrum consists of misoriented relative to each other and bonded to each other crystals with anisotropic structure of EPR spectra.

A disadvantage of the known calibration sample is the absence of EPR signals at high frequencies exceeding 90 GHz in the range of magnetic fields less than 2 T, generated by the standard electromagnets EPR spectrometers.

Closest to the claimed technical solution in essential attribute of the Cove is a method of calibration of an EPR spectrometer (see inventor's certificate SU # 1578610, IPC G01N 24/10 published 15.07.1990), including accommodation in the measuring resonator calibration sample, giving isotropic and anisotropic EPR spectra, rotation of the sample in a magnetic field H, the registration of EPR spectra and calibration characteristics of the spectrometer according to the provisions of the lines of the EPR spectra of the calibration sample. In the known method rotate the calibration sample made of ruby and Mao with microprint MP2+establish a line of ruby, the corresponding spectral transition (1/2,-1/2), between the third and fourth line MP2+in MLA, the amplitude of the line ruby, corresponding to the transition (3/2,-1/2), set a minimum and the value of the operating frequency of the spectrometer f is determined from the difference between the spectral positions of the lines crossing point (3/2,-1/2)to(1/2,-1/2).

The disadvantage of this method is the need to apply a large magnetic field 3-3,5 TL, requiring the use of superconducting solenoids and cryostats with a warm pocket for registration of EPR spectra in the 3 mm range.

Known calibration sample for calibration of an EPR spectrometer, coinciding with the proposed technical solution for essential features and adopted for the prototype (see inventor's certificate SU # 1578610, IPC G01N 24/10 published 15.07.1990). The calibration sample is a prototype, giving isot Opry and anisotropic EPR spectra, made of ruby and Mao with microprint MP2+.

The known method is the prototype and used the calibration sample provide calibration and adjustment of EPR spectrometers traditional ranges up to 35 GHz range, using magnetic fields produced by conventional electromagnets with magnetic fields that do not exceed 2 T, the Situation is completely changed by the use of high frequency EPR spectrometers. So, in the spectrometer 3 mm range with a frequency of 94 GHz for registration of EPR signal ruby, having the fine structure constant, equal 5,745 GHz, the range of possible magnetic fields for EPR-signal lies in the area of 2.9 to 3.7 T. The values of these magnetic fields are beyond the capabilities of the electromagnets, so these signals may not be registered in the available magnetic fields generated by electromagnets To obtain such magnetic fields, you must use a special superconducting solenoids with the camera ("warm pocket") for the premises of the cavity of an EPR spectrometer. Currently there is a single firm producing a commercial EPR spectrometers 3 mm range, which uses a superconducting magnet, and you can use the listed reference samples. The operation of the superconducting solenoid requires liquid gelei the necessary infrastructure, in addition, special devices you need to place the resonator and microwave systems inside the solenoid, transportation of the microwave power on the way, reaching lengths of 1.5 m, which dramatically increases the losses of the microwave power.

The task of the invention is to develop a method of calibration of the spectrometer electron paramagnetic resonance and calibration sample, which would allow to simplify the configuration and calibration of the spectrometer electron paramagnetic resonance.

The problem is solved by a group of inventions combined to form a single inventive concept.

In part of the way the problem is solved in that a method of calibrating the spectrometer electron paramagnetic resonance (EPR) includes accommodation in the measuring resonator calibration sample, giving the anisotropic spectrum (EPR), is made of single crystal rutile TiO2containing ions of Fe3+in an amount of 0.01-0.5 wt %, the rotation of the calibration sample in the magnetic field until the anisotropic EPR spectrum of the ions Fe3+registration of EPR lines of ions of Fe3+and the setting of an EPR spectrometer along the lines of the EPR on the maximum signal-to-noise ratio by moving the piston approval of the cavity and move the bottom wall of the resonator for frequency tuning of the resonator is ora.

Under certain operating frequency EPR spectrometer it is possible to calculate the magnitude of the magnetic field lines EPR ions Fe3+corresponding to transitions between the selected spin sublevels, on known parameters of the spin Hamiltonian for ions of Fe3+in rutile. Then, when the detected orientation of the calibration sample in a magnetic field to calibrate the sweep of the magnetic field on the mapping mentioned calculated values of the magnetic fields with the registered lines EPR ions Fe3+serving the labels of the calibrated magnetic field.

As in the sweep of the magnetic field of an EPR spectrometer can measure the magnetic field corresponding to the EPR signals of the ions Fe3+in the rutile when the detected orientation of the calibration sample in a magnetic field and to determine the operating frequency on known parameters of the spin Hamiltonian for ions of Fe3+in rutile.

In part of the calibration sample task is solved in that the calibration sample made of a material giving the anisotropic EPR spectrum, in the form of a single crystal of rutile Tio2containing ions of Fe3+in an amount of 0.01-0.5 wt %.

The invention is illustrated by drawings, where:

figure 1 shows the diagram of a device for carrying out the setup and calibration of an EPR spectrometer 3 mm range using an electromagnet magnitno modulation EPR spectrometer traditional 3 cm range;

figure 2 shows EPR spectra recorded in the calibration sample in the form of a single crystal of rutile Tio2containing ions of Fe3+two orientations of the calibration sample in a magnetic field at the operating frequency of 94 GHz and a temperature of 300 K (Θ=50° and Θ=55°) In the insets shows the schematic of the energy levels and transitions between levels for the two orientations of the calibration sample in a magnetic field corresponding to the observed EPR spectra.

In the present method of calibration of an EPR spectrometer as a calibration sample taken a single crystal of rutile Tio2containing ions of Fe3+in an amount of 0.01-0.5 wt.%. Rutile is a chemically stable substance. Ions of Fe3+have the electronic configuration poluzabroshennoy 3d environment (3d5), the state of6S5/2electronic spin S=5/2. This system is close to axial and characterized by large values of the fine structure of the standard spin Hamiltonian D=20,36 GHz and F=2,14 GHz, where D characterizes the axial component of the local crystal field at the location of the ion Fe3+and E gives the characteristic deviation of the crystal field from axial symmetry (see Vlasov M.B. and others - Radiospectroscopic properties of inorganic materials - Kiev, Naukova Dumka, 1987, str). The EPR signal of the ions Fe3+in Tio2much is avisit on the crystal orientation relative to the magnetic field. It is important, also, that due to the absence of the orbital moment and as a consequence, a sufficiently large time spin-lattice relaxation (S) EPR spectra observed at room temperature. Due to the large splitting of the fine structure in the Fe3+in Tio2possible EPR transitions for frequencies corresponding to 3 mm range in magnetic fields of the order of 1 T or less, easily available in standard magnet spectrometer EPR 3 cm range. Based on the above for measurements of EPR spectra of the reference sample can be used nodes of an EPR spectrometer low-frequency range, which allows modulation of the magnetic field, magnetic control system and the system of registration of EPR spectra. In the simplified processes setup and calibration of an EPR spectrometer for use in high frequency.

To implement the proposed method of calibration of an EPR spectrometer can be used in the device shown in figure 1. The device contains calibration sample 1 mounted on the holder 2 and placed in the resonator 3 3 mm range. The holder 2 can be rotated around the vertical axis. The device also contains a microwave unit (EBM) 4, the waveguide 5 3 mm range, the waveguide 6 to 8 mm range, the electromagnet 7, the drive coil 8, the generator (G) 9, the power amplifier (PA) 10, block the Board (BU) 11, contains the processor, analog-to-digital Converter (ADC) and digital-to-analogue Converter (DAC), and PC (K) 12, the scanner magnetic field (BR) 13, the piston 14 of the agreement and the piston 15 of the frequency tuning of the resonator 3.

The inventive method is as follows. Preliminary calculations were performed, which is a direct diagonalization spin Hamiltonian system and found the orientational dependence of the EPR signal of the ions Fe3+in a magnetic field. Using these dependencies can also be used for calibration of the magnetic field EPR spectrometer. The calibration sample 1 (see figure 1) mounted on the holder 2, which can rotate around a vertical axis, and with the help of the holder is placed in the cavity 3. The resonator 3 and the calibration sample 1 is placed in a constant magnetic field created by the electromagnet 7 EPR spectrometer standard 3 cm range, and an alternating magnetic field generated by the modulation coils 8 by 9. In the resonator 3 serves of microwave power from the generator, which is included in EBM 4, which is transported through the system 6 waveguides 3 mm, 5 mm and 8 mm range to reduce losses of the microwave power. Reflected from the resonator 3 microwave power is transported by the same system 6 waveguides in reverse napravleniya detector, in EBM 4. The signal from the detector 4 EBM served on the synchronous detector and the US 10 simultaneously with the signal G 9 and further BU 11, containing a processor, ADC and DAC, and on To 12. BU 11 manages BR 13, the interface 12 displays the EPR signal of the calibration sample 1. Using piston 14 coordination and piston 15 frequency tuning of the resonator 3 make adjustment of the EPR signal in the calibration sample 1 to the maximum value of the ratio signal/noise. By rotation of the holder 2 around the vertical axis set a specific orientation of the calibration sample 1 in a constant magnetic field. Because simultaneously register multiple EPR signals with well-defined design values of magnetic fields, produced if necessary, calibration of the magnetic field. Based on the available data on the concentration of spins in the calibration sample 1 if necessary, make calibration of the sensitivity of the EPR spectrometer. Later in the development process of an EPR spectrometer 3 mm range is selected a different design of the resonator 3 system and 6 for the microwave power, and the setup and calibration is repeated. In the choose the optimal design of the EPR spectrometer using a small magnetic fields, as in the claimed method and does not require the use of superconducting magnetic systems is.

Experiments were carried out and registered EPR spectra of ions of Fe3+in Tio2using an experimental single-mode cylindrical resonator with a working fashion THOSE011and with the possibility of frequency tuning of the Resonator connected to the output of the microwave unit 3 mm range using waveguides. To reduce losses of the microwave power used waveguides with large cross-section (8 mm range) and the transition section of waveguide 3 mm - waveguide 8 mm near the microwave unit and in the vicinity of the resonator. The calibration sample size of 0.5×0,3×0.3 mm3placed inside a thin-walled quartz tube was installed in the center of the cavity, which was placed in the magnetic field of the electromagnet standard EPR spectrometer 3 cm range. Registration of EPR spectra was performed using the modulation system of the magnetic field of an EPR spectrometer 3 cm range.

EPR spectra of ions of Fe3+in the crystal Tio2, which is the calibration sample, registered at a frequency of 94 GHz at room temperature for two orientations of the magnetic field relative to the axis of the crystal (the angle θ, shown in figure 2. There on the insets shows the energy levels and the transitions between these levels, which are presented in the EPR spectra. Then spent tuning the resonator system spectromet is and on the optimal ratio of signal to noise ratio for the EPR-signal of the calibration sample.

These experiments Desk ESR at a frequency of 94 GHz, conducted at room temperature using a standard electromagnet, to allow tuning and calibration and confirm the operability and high frequency stability of the new microwave unit and the effectiveness of the system of detection of the microwave signal. Thus, a methodology was developed configuration of an EPR spectrometer operating in the 3 mm range (frequency range 90-100 GHz) using conventional electromagnet, whereas previously for similar operations used large magnetic fields generated by superconducting magnets, requiring significant consumption of expensive liquid helium. As a result of savings is approximately 0.2-0.3 million rubles, also significantly reduced the time required to design and configure the device, i.e. labour productivity several times.

The staffing of the inventive calibration samples with the corresponding spectra of EPR spectrometers 3 mm range directly at their manufacturing allows you to control the calibration and adjustment of the microwave tract without the use of superconducting magnets.

1. A method of calibrating the spectrometer electron paramagnetic resonance (EPR), including accommodation in a measure the flax resonator calibration sample, giving the anisotropic spectrum (EPR), is made of single crystal rutile TiO2containing ions of Fe3+in an amount of 0.01-0.5 wt.%, rotation of the calibration sample in the magnetic field until the anisotropic EPR spectrum of the ions Fe3+registration of EPR lines of ions of Fe3+and the setting of an EPR spectrometer along the lines of the EPR on the maximum signal-to-noise ratio by moving the piston approval of the cavity and move the bottom wall of the resonator for frequency tuning of the resonator.

2. The method according to claim 1, characterized in that the calculated value of magnetic field lines EPR ions Fe3+corresponding to transitions between the selected spin sublevels, on known parameters of the spin Hamiltonian for ions of Fe3+in rutile, when the detected orientation of the calibration sample in a magnetic field and known operating frequency calibrate the sweep of the magnetic field on the mapping mentioned calculated values of the magnetic fields with the registered lines EPR ions Fe3+employees of the labels of the calibrated magnetic field.

3. The method according to claim 1, characterized in that the measured magnetic field corresponding to the EPR signals of the ions Fe3+in the rutile when the detected orientation of the calibration sample in the magnetic field and determine the operating frequency on known parameters of the spin guilt is the nian ions Fe 3+in rutile.

4. The calibration sample for calibration of the spectrometer electron paramagnetic resonance (EPR), consisting of a material that gives the anisotropic EPR spectrum, in the form of a single crystal of rutile TiO2containing ions of Fe3+in an amount of 0.01-0.5 wt.%.



 

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