CN102226775B - Method and apparatus for measuring material thermal conductivity based on optical-modulated thermo-emission spectroscopy - Google Patents

Abstract

The invention discloses a method and an apparatus for measuring material thermal conductivities based on optical-modulated thermo-emission spectroscopy. The apparatus comprises a Fourier transform infrared (FTIR) spectroscopy measuring system, a laser served as a heat source, a lock-in amplifier for connecting a detector and a circuit controlling panel in the FTIR spectrometer, and a chopper positioned on the optical path between a sample/power testing system and the laser. With the apparatus, optical-modulated thermo-emission spectroscopy measuring can be carried out, temperatures of a sample before and after laser radiation can be accurately determined, such that the thermal conductivity of the sample can be obtained. With advantages of fast, non-contacting, and convenient, the apparatus provided by the present invention is suitable for the detection of thermal characteristics of photovoitaic semiconductors.

Description

A kind of method and apparatus of measuring material thermal conductivity based on the optical modulation thermal emission spectrum

Technical field:

The present invention relates to the method and apparatus that a kind of photoelectric semiconductor material thermal conductivity is measured, specifically, the optical modulation thermal emission spectrum that mainly is based on step-scan fourier-transform infrared (FTIR) spectrometer is measured method and the device of material thermal conductivity.

Background technology:

In recent years, microelectronics/photoelectric device develops rapidly towards high speed, high density and low-power consumption direction, directly causes the increase of the heat that produces in the unit volume, and the heat radiation of system becomes distinct issues.For the body material, impurities/defects wherein and dislocation cause it to have lower thermal conductivity; For the low dimensional structures of being used widely in the device, phonon restriction and interfacial effect can cause its thermal conductivity further to reduce.Lower thermal conductivity can cause heat constantly accumulation in material/device, directly affects device reliability and stability.Because the restriction of size, the heat in the system can only be walked by limited channel transfer, if heat dissipation problem is dealt with improperly, device can namely turn to dust and ashes because of overheated in no time.Therefore, the measurement of the thermal characteristic of material/device becomes a major issue that needs to be resolved hurrily.

Heat dissipation in the low dimensional structures is fast, has brought very large difficulty for relevant experiment measuring.Existing thermal conductivity measurements, such as 3 ω methods, little processing suspension device method, transient state reflection measurement method, scanning thermal microscope technology etc., exist sample need pre-treatment, experimental provision complicated, need the problem such as design specialized circuit, be unfavorable for material/low dimensional structures thermal characteristics is carried out the measurement of quick nondestructive.

Photoluminescence (the Photoluminescence based on fourier-transform infrared (FTIR) spectrometer has been realized in our laboratory with having innovated, PL), Photoreflectance (Photoreflectance, PR) spectrum has been realized the measurement of alternating temperature PL and PR spectrum.PRELIMINARY RESULTS shows: compare with traditional spectrographic technique based on monochromator, said method has the sensitivity of significantly improving, establishment interference of stray light, the quick advantage such as easy to operate.With respect to traditional electrical measurement mode, modulated spectrum has fast harmless characteristics, and very large advantage is arranged.Based on the progress of above-mentioned modulated spectrum aspect, the theory that we propose to utilize step-scan FTIR spectrometer to realize the optical modulation thermal emission spectrum is conceived.Obtain by this semiconductor material and low dimensional structures in the temperature difference of Ear Mucosa Treated by He Ne Laser Irradiation front and back and derive its thermal conductivity, realize that effective measurement of the optical modulation thermal emission spectrum of material and low dimensional structures also carries out the thermal characteristics research of respective material system, for the optimal design of relative photo electrical part provides useful reference.

Summary of the invention:

In sum, how to utilize the optical modulation thermal emission spectrum to obtain the temperature of sample under Ear Mucosa Treated by He Ne Laser Irradiation, it is key technical problem to be solved by this invention, therefore, the object of the present invention is to provide a kind of method and device thereof of measuring material thermal conductivity based on the infrared light modulation thermal emission spectrum of step-scan, enable to obtain the temperature difference of Ear Mucosa Treated by He Ne Laser Irradiation front and back sample surfaces, significantly improve thermometric sensitivity and reliability.Utilize by this thermal conductivity of the derivation sample of spectrographic technique quick nondestructive, thereby provide a kind of effective way for the Thermal characteristic analysis of semiconductor material.

According to a kind of method and apparatus based on infrared light modulation thermal emission spectrum measurement material thermal conductivity of the present invention, comprising:

-FFIR measuring system, it has Fourier transformation infrared spectrometer and control desk computing machine, with the detector that interference of light parts in the Fourier transformation infrared spectrometer connect, the circuit control panel that is connected with the control desk computing machine;-optic modulating device, it comprises lock-in amplifier, chopper; The signal input part of lock-in amplifier connects the output terminal of detector, and its output terminal is connected with the input end of circuit control panel;-laser instrument produces continuous laser, and optical maser wavelength is greater than optical wavelength corresponding to the energy gap of testing sample;-sample/power test system, it comprises sample test system, power test system, base; Place testing sample and heat sink alternating temperature Dewar; The controller that is connected with power probe.

Described lock-in amplifier is Stanford SR830 DSP type lock-in amplifier; Described chopper is Stanford SR540 type mechanical chopper; Described laser instrument is Coherent 1064-2500 MN infrared laser, and optical maser wavelength is 1.064 microns; Described fourier-transform infrared spectrometer is Bruker IFS 66v/S type FTIR spectrometer; Described power is counted Newport 2935-C power meter; Described alternating temperature Dewar is JanisST-500 continuous stream cryostat; And described testing sample (optical maser wavelength is greater than optical wavelength corresponding to sample energy gap), for example In _0.54Ga _0.46The As material, optical wavelength corresponding to its energy gap is 1.679 microns.

The core of technical conceive of the present invention is to use to have continuously and the FTIR spectrometer of step-scan function, also comprises the assemblies such as chopper, binary channels lock-in amplifier, laser instrument, power meter, alternating temperature Dewar and base.At first the 4-1 of sample test system is placed on the base 4-3; Alternating temperature Dewar 403 is set in temperature～150K, behind temperature stabilization, the temperature of recording laser pre-irradiation testing sample.Then the exciting power with laser instrument 3 is set in higher numerical value～200 milliwatts, with Ear Mucosa Treated by He Ne Laser Irradiation to the testing sample 401 that places alternating temperature Dewar 403, so that testing sample 401 has enough temperature rises under Ear Mucosa Treated by He Ne Laser Irradiation, guarantee by this accuracy of temperature quantitative measurment; Chopper 2-2 forms modulated laser with incident laser copped wave, and the modulated laser of process chopper 2-2 is incident to sample and produces the optical modulation thermal emission signal, and the chopper signal of modulated laser is as the reference signal input end of reference signal feed-in lock-in amplifier 2-1.The optical modulation thermal emission signal outputs to the detector 102 of Fourier transformation infrared spectrometer 1-1, the input end of the output signal feed-in lock-in amplifier 2-1 of detector, then output to circuit control panel 103, then enter control desk computing machine 1-2, thereby obtain the optical modulation thermal emission spectrum of sample.Then find out the peak of optical modulation thermal emission spectrum, can obtain the temperature of sample when the Ear Mucosa Treated by He Ne Laser Irradiation according to Wien's displacement law again, obtain by this temperature difference of sample before and after the Ear Mucosa Treated by He Ne Laser Irradiation.Utilize Fourier transform infrared spectrometer 1-1 measurement to place the reflectance spectrum of the sample 401 of alternating temperature Dewar 403, obtain the shared ratio of absorption of sample.Remove the 4-1 of sample test system on the base 4-3, power test system 4-2 is placed on the base; The power of measuring incident laser can obtain the corresponding power of absorption of sample energy, can draw the thermal conductivity of sample.

According to inventive concept, a kind of infrared light based on the step-scan Fourier transformation infrared spectrometer of the present invention is modulated the method and apparatus that thermal emission spectrum is measured material thermal conductivity, and its step comprises:

S1, testing sample is placed alternating temperature Dewar, design temperature; The temperature of recording laser pre-irradiation sample;

S2, in the laser beam incident road, move into a chopper, realize incident laser is carried out amplitude modulation(PAM); And between the detector of Fourier transformation infrared spectrometer and circuit control panel, access lock-in amplifier, carry out phase-sensitive detection;

S3, Fourier transformation infrared spectrometer is placed the step-scan state, suitably choose sensitivity and sampling integral time of modulating frequency, the lock-in amplifier of chopper, begin to measure the optical modulation thermal emission signal;

S4, optical modulation thermal emission signal output to the circuit control panel of Fourier transformation infrared spectrometer, then enter the control desk computing machine;

S5, by measuring the optical modulation thermal emission spectrum of sample under the higher exciting power, obtain the peak of spectrum, derive the temperature difference of sample before and after the Ear Mucosa Treated by He Ne Laser Irradiation;

The power that S6, measurement incident excite obtains the corresponding power of absorption of sample energy, obtains the thermal conductivity of sample.

In addition, described testing sample is that optical wavelength corresponding to energy gap is less than the semiconductor material of laser wavelength of incidence, for example In _0.54Ga _0.46The As material.

Great advantage of the present invention is:

1, sample does not need to carry out pre-treatment, and experimental provision does not need to transform, and measures fast can't harm, and belongs to non-destroyed measurement;

2, detection sensitivity thermal characteristic high, that be very beneficial for semiconductor material and low dimensional structures is measured, especially for the measurement of sample temperature under the Ear Mucosa Treated by He Ne Laser Irradiation;

3, have benefited from the well-separated of Fourier transform frequency and Laser Modulation frequency, lock-in amplifier sampling time constant to choose the upper limit no longer limited, be particularly advantageous in the detection of weak thermal emission signal in the semiconductor material.

Description of drawings:

Fig. 1 has provided the synoptic diagram of measuring the experimental provision of material thermal conductivity based on the optical modulation heat emission.1 is the FFIR measuring system among the figure, and 1-1 is Fourier transformation infrared spectrometer, the 101st, and interference of light parts, the 102nd, detector, the 103rd, circuit control panel, 1-2 are the control desk computing machines; 2 is optic modulating devices among the figure, and 2-1 is lock-in amplifier, and 2-2 is chopper; 3 is laser instruments among the figure; 4-3 is base, and 4-1 is the sample test system, the 401st, and testing sample, the 402nd, heat sink, the 403rd, alternating temperature Dewar, 4-2 are power test systems, the 404th, power probe, the 405th, controller.

Fig. 2 has provided the outline flowchart of measuring.

Embodiment:

The below provides better embodiment of the present invention according to Fig. 1 and Fig. 2, and is described in detail, and technical characterictic of the present invention and functional characteristics can be described better, rather than is used for limiting scope of the present invention.

Specific embodiments as shown in Figure 1, the device of measuring material thermal conductivity based on the optical modulation thermal emission spectrum comprises-accesses the lock-in amplifier 2-1 in the optic modulating device 2 between this spectrometer 1-1, computing machine 1-2 and base 4-3, and at the path that laser instrument 3 is incident in base 4-3 chopper 2-2 is set, make it to form the modulation incident laser.More particularly, step-scan optical modulation thermal emission spectrum of the present invention is measured the device of material thermal conductivity, comprise-FFIR system 1, it has Fourier transformation infrared spectrometer 1-1 and control desk computing machine 1-2, with the detector 102 that interference of light parts among the Fourier transformation infrared spectrometer 1-1 101 connect, the circuit control panel 103 that is connected with control desk computing machine 1-2;-laser instrument 3 produces continuous laser, and optical maser wavelength is greater than optical wavelength corresponding to the energy gap of testing sample;-optic modulating device 2, it comprises lock-in amplifier 2-1, chopper 2-2, chopper 2-2 is between laser instrument 3 and base 4-3, continuous laser is modulated into modulated laser incides the 4-1 of sample test system that places on the base 4-3, the optical modulation thermal emission signal intensity of testing sample is changed, the modulating frequency of modulated laser is as the reference signal input end of reference signal feed-in lock-in amplifier 2-1, the signal input part of lock-in amplifier 2-1 connects the output terminal of detector 102, and the output terminal of lock-in amplifier 2-1 is connected with the input end of circuit control panel 103;-sample/power test system 4, it comprises the 4-1 of sample test system, power test system 4-2, base 4-3, the alternating temperature Dewar 403 of placing testing sample 401 and heat sink 402 is placed on the base 4-3, measure by this material optical modulation thermal emission spectrum, utilize simultaneously power probe 404 and controller 405 to measure the power of incident laser.

Its test philosophy-as shown in Figure 1, the 4-1 of sample test system is placed on the base 4-3, the Temperature Setting of alternating temperature Dewar 403 is T _SetBehind temperature stabilization, T _SetBe the temperature of the front testing sample of Ear Mucosa Treated by He Ne Laser Irradiation.Incident laser power is set higher-wattage (～200 milliwatt), so that testing sample 401 has enough temperature rises under Ear Mucosa Treated by He Ne Laser Irradiation, guarantee by this accuracy of temperature quantitative measurment.The signal I that detector 102 receives ^dComprise two parts

I ^d(δ)=I _MTE(δ)+I _Background(δ) (1)

I wherein _MTE(δ) be the experiment in record from the thermal emission signal of testing sample 401 under Ear Mucosa Treated by He Ne Laser Irradiation, I _BackgroundBe background thermal radiation signal under the room temperature (δ), at room temperature show as a broad peak about 10 microns.

If the method with continuous sweep is measured signal

Directly enter circuit control panel 103.Final signal and be by the spectrum that Fourier transform obtains

Comprising all information of receiving of detector 102.According to formula (2), final signal comprises thermal emission signal and the room temperature background radiation signal of sample.With respect to room temperature background radiation signal, the thermal emission signal of sample is very faint, is buried in the room temperature background radiation signal.

For the measurement of the optical modulation thermal emission spectrum under the step-scan, used chopper 2-2 and lock-in amplifier 2-1, enter lock-in amplifier 2-2 signal and be

Then signal multiply by the reference signal u of phase-sensitive detection device again _RefSin (ω t+ θ _Ref), the signal that enters at last circuit control panel 103 is

$I^{\mathrm{LIA}}\left(\mathrm{\δ}\right)=\frac{u_{\mathrm{ref}}{K}^{\mathrm{LIA}}}{2}{I}_{\mathrm{MTE}}\left(\mathrm{\δ}\right)\cos ({\mathrm{\θ}}_{\mathrm{MTE}}-{\mathrm{\θ}}_{\mathrm{ref}})---\left(4\right)$

K ^LIABe the transport function of lock-in amplifier 2-1, in the frequency range of considering, it can be used as a constant.The spectrum that obtains by Fourier transform is

$B_{\mathrm{SS}}^x\left(\mathrm{\σ}\right)=\frac{u_{\mathrm{ref}}{K}^{\mathrm{LIA}}}{2}{B}_{\mathrm{MTE}}\left(\mathrm{\σ}\right)\cos ({\mathrm{\θ}}_{\mathrm{MTE}}-{\mathrm{\θ}}_{\mathrm{ref}})---\left(5\right)$

Will

Multiply each other with 90 ° of reference signal displacements and to obtain

Obtain final signal B _SS(σ).

$B_{\mathrm{SS}}\left(\mathrm{\σ}\right)=\frac{u_{\mathrm{ref}}{K}^{\mathrm{LIA}}}{2}{B}_{\mathrm{MTE}}\left(\mathrm{\σ}\right)---\left(6\right)$

By comparison expression (2) and (6), measure with respect to continuous sweep, only comprised in the step-scan optical modulation thermal emission spectrum because the thermal emission signal that the incident laser heated sample causes.

Optical modulation thermal emission spectrum is per sample determined the wavelength X that peak is corresponding _MaxAccording to Wien's displacement law, can derive the corresponding temperature T of sample _MTE

λ in the formula _MaxUnit is micron, T _MTEUnit is K.By measuring the optical modulation thermal emission spectrum of sample, derive the temperature T of sample _MTE, obtain by this temperature difference Δ T before and after the Ear Mucosa Treated by He Ne Laser Irradiation _MTE=T _MTE-T _Set, T wherein _SetIt is the temperature of sample before the Ear Mucosa Treated by He Ne Laser Irradiation.

Utilize Fourier transform infrared spectrometer 1-1 measurement to place the reflectance spectrum of the sample 401 of alternating temperature Dewar 403, obtain the reflectivity R of sample, thereby obtain the absorptivity α of sample=1-R, obtain to absorb proportion.

Remove the 4-1 of sample test system on the base 4-3, power test system 4-2 is placed on the base, measure the real power Δ P of incident laser.According to the definition of thermal conductivity, can obtain

$\mathrm{\κ}=\mathrm{\α}\frac{\mathrm{\ΔE}}{\mathrm{\Δt}}\frac{\mathrm{\Δx}}{\mathrm{\Δ}{T}_{\mathrm{MTE}}}\frac{1}{A}=\mathrm{\α}\frac{\mathrm{\ΔP}}{\mathrm{\Δ}{T}_{\mathrm{MTE}}}\frac{\mathrm{\Δx}}{A}---\left(8\right)$

Δ x is the thickness of sample in the formula, and A is sample area (direction parallel with heat sink surface).Sample area is at 0.5 * 0.5mm ²～5 * 5mm ²In the scope, scioptics guarantee that useful area and the sample area of laser facula is roughly suitable.Final through type (8) is determined the thermal conductivity of sample.

In view of above-mentioned thinking, in the present embodiment, lock-in amplifier 2-1 adopts Stanford SR830 DSP lock-in amplifier, chopper 2-2 to adopt Stanford SR540 mechanical chopper, laser instrument 3 to adopt Coherent 1064-2500 MN infrared laser, alternating temperature Dewar 403 to adopt Janis ST-500 continuous stream cryostat, power test system 4-2 to adopt Newport 2935-C power meter, FTIR spectrometer 1-1 to adopt Bruker IFS 66v/S type FTIR spectrometer to carry out the enforcement that the present invention proposes new method.Its light path has provided concise and to the point operating process still as shown in Figure 1 among Fig. 2, specific operation process is as follows:

Data acquisition: at first remove chopper 2-2, and the electrical output signal of detector 102 is directly fed into circuit control panel 103.FTIR spectrometer 1-1 is placed the signal monitoring state of continuous sweep, and by adjusting, optimize the relevant light paths of the sample test 4-1 of system, the signal that FTIR spectrometer 1-1 is monitored reaches very big.Then obtain the optical modulation thermal emission spectrum based on step-scan FTIR, the present invention is keeping under the constant prerequisite of the sample test 4-1 of system relevant light paths, move into and open chopper 2-2, and detector 102 output signals are fed to the input end of lock-in amplifier 2-1 by AC coupling, the output of lock-in amplifier 2-1 is received on the input channel of circuit control panel 103 of FTIR spectrometer 1-1.Set after the modulating frequency of chopper 2-2, with the reference signal locking lock-in amplifier 2-1 of chopper 2-2.Then, FTIR spectrometer 1-1 is placed the step-scan state, and trial run spectral scan process, suitably choose sensitivity and the sampling integral time of lock-in amplifier 2-1, be in the lock state all the time in the step-scan process to guarantee it.According to sampling integral time, set the FTIR spectrometer 1-1 stepping stand-by period again.So far, can formally begin the measurement of optical modulation thermal emission spectrum.

Data are processed: the optical modulation thermal emission spectrum based on step-scan FTIR that the present invention proposes can utilize the FTIR system to control software and finish Fourier transform work, therefore is convenient to implement.Can obtain the optical modulation thermal emission spectrum of step-scan according to formula (6).Before incident laser irradiation sample 401, the actual temperature of sample 401 in the record alternating temperature Dewar 403.Then select the laser of higher exciting power (～200 milliwatt) to incide on the sample 401, obtain its optical modulation thermal emission spectrum.Find out the peak of thermal emission spectrum, obtain the temperature of sample 401 according to formula (7).Further by measuring the reflectance spectrum of sample 401, obtain it and absorb shared ratio.Power corresponding to sample 401 absorbed energy can be obtained by the real power of measuring incident laser again, the thermal conductivity of sample 401 can be drawn at last according to formula (8).

The of the present invention crucial inventive point that comprises in aspect above-mentioned two is (1) by incident laser is carried out amplitude modulation(PAM), and in conjunction with techniques of phase-sensitive detecting technique, detection sensitivity is high; (2) can accurately determine the temperature of sample under the specific incident laser power, thereby fast and the convenient thermal conductivity that obtains sample, be very beneficial for the thermal characteristics rapid evaluation of photoelectric semiconductor material; (3) utilize the step-scan function of FTIR spectrometer to eliminate the Fourier frequency, loosen the harshness restriction that external modulating frequency is chosen, make based on the method for optical modulation thermal emission spectrum measurement material thermal conductivity really feasible.

Claims (2)

1. measurement mechanism of measuring material thermal conductivity based on the optical modulation thermal emission spectrum, it comprises: FFIR measuring system (1), optic modulating device (2), laser instrument (3) and sample/power test system (4) is characterized in that:

-described FFIR measuring system (1) has Fourier transformation infrared spectrometer (1-1) and control desk computing machine (1-2), with the detector (102) that interference of light parts (101) in the Fourier transformation infrared spectrometer (1-1) connect, the circuit control panel (103) that is connected with control desk computing machine (1-2);

-described optic modulating device (2) comprises lock-in amplifier (2-1), chopper (2-2); The signal input part of lock-in amplifier (2-1) connects the output terminal of detector (102), and the output terminal of lock-in amplifier (2-1) is connected with the input end of circuit control panel (103);

-described laser instrument (3) produces continuous laser, and optical maser wavelength is greater than optical wavelength corresponding to the energy gap of testing sample;

-described sample/power test system (4) comprises sample test system (4-1), power test system (4-2), base (4-3); In the sample test system (4-1), testing sample (401) and heat sink (402) are placed in the alternating temperature Dewar (403); In the power test system (4-2), power probe (404) is connected with controller (405);

During measurement, at first sample test system (4-1) is placed on the base (4-3); Alternating temperature Dewar (403) is set in temperature 150K, behind temperature stabilization, the temperature of recording laser pre-irradiation testing sample; The exciting power of laser instrument (3) is set in high value 200 milliwatts, with Ear Mucosa Treated by He Ne Laser Irradiation to the testing sample that places alternating temperature Dewar (403) (401), so that testing sample (401) has enough temperature rises under Ear Mucosa Treated by He Ne Laser Irradiation, guarantee by this accuracy of temperature quantitative measurment; Chopper (2-2) forms modulated laser with incident laser copped wave, modulated laser through chopper (2-2) is incident to testing sample and produces the optical modulation thermal emission signal, and the chopper signal of modulated laser is as the reference signal input end of reference signal feed-in lock-in amplifier (2-1); The optical modulation thermal emission signal outputs to the detector (102) of Fourier transformation infrared spectrometer (1-1), the input end of the output signal feed-in lock-in amplifier (2-1) of detector (102), lock-in amplifier (2-1) signal outputs to circuit control panel (103), then enter control desk computing machine (1-2), thereby obtain the optical modulation thermal emission spectrum of sample; Then find out the peak of optical modulation thermal emission spectrum, can derive the temperature of testing sample when the Ear Mucosa Treated by He Ne Laser Irradiation according to Wien's displacement law again; Obtain by this temperature difference of Ear Mucosa Treated by He Ne Laser Irradiation front and back sample;

Utilize Fourier transform infrared spectrometer (1-1) to measure the reflectance spectrum of the sample (401) that places alternating temperature Dewar (403), obtain the shared ratio of absorption of sample;

Remove the sample test system (4-1) on the base (4-3), power test system (4-2) is placed on the base; Utilize power probe (404) to measure the power of incident laser, can obtain the corresponding power of absorption of sample energy, derive by this thermal conductivity of sample.

2. measuring method based on the material thermal conductivity of the described measurement mechanism of claim 1 is characterized in that may further comprise the steps:

S1, testing sample is placed alternating temperature Dewar, design temperature; The temperature of recording laser pre-irradiation sample;

S2, in the laser beam incident road, move into a chopper, realize incident laser is carried out amplitude modulation(PAM); And between the detector of Fourier transformation infrared spectrometer and circuit control panel, access lock-in amplifier, carry out phase-sensitive detection;

S3, Fourier transformation infrared spectrometer is placed the step-scan state, suitably choose sensitivity and sampling integral time of modulating frequency, the lock-in amplifier of chopper, begin to measure the optical modulation thermal emission signal;

S4, optical modulation thermal emission signal output to the circuit control panel of Fourier transformation infrared spectrometer, then enter the control desk computing machine;

S5, be the optical modulation thermal emission spectrum of sample under 200 milliwatts by measuring exciting power, obtain the peak of spectrum, derive the temperature difference of sample before and after the Ear Mucosa Treated by He Ne Laser Irradiation;

The power of S6, measurement incident laser obtains the corresponding power of absorption of sample energy, derives the thermal conductivity of sample.

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