Secondary Thermometers Research Articles

Novel and High‐Sensitive Primary and Self‐Referencing Thermometers Based on the Excitation Spectra of Lanthanide Ions

AbstractRemote sensing through ratiometric luminescence thermometry based on trivalent lanthanide ions (Ln(III)) has lately become a promising technique due to its numerous applications. Most available Ln(III)‐based luminescent thermometers require a calibration process with a reference thermal probe (secondary thermometers) and recurrent calibrations are mandatory, particularly when the thermometers are used in different media. This is sometimes impractical and a medium‐independent calibration relation is postulated, which is potentially inaccurate. Thus, the determination of the temperature based on well‐grounded physical principles by primary thermometers is the only way to overcome these challenges. Despite being considered one of the most important developments in luminescence thermometry, primary luminescent thermometers are scarce. Primary thermometers requiring calibration are proposed, implemented, and validated at one known temperature (primary‐T), which are also self‐referencing, employing ratiometric data from the excitation spectrum of Ln(III). By combining with the emission spectrum, thermometers not requiring calibration (primary‐S) are devised. An Eu(III)‐β‐diketonate complex is used as a proof‐of‐concept, but the approach is universal and other Ln(III)‐based materials can be explored. Because many thermometric parameters are employed for temperature prediction an unprecedented very high accuracy of 0.2% in the physiological range is obtained.

Excitation power density dependence of a primary luminescent thermometer based on Er3+, Yb3+: GdVO4 microcrystals operating in the visible

A discussion about the calibration of the Er3+,Yb3+:GdVO4 microcrystals as a luminescent primary thermometer based on the known equation of state of Boltzmann distribution of the electronic population of the two Erbium emitting coupled levels has been given. Its validity has been demonstrated. Besides, when Er3+,Yb3+:GdVO4 microcrystals acting as secondary thermometer, it has been proven the dependence of the thermometric ratio based on the integrated intensities of the green visible emissions arising from the two thermally coupled levels of erbium, 2H11/2 and 4S3/2, on the excitation power density for the Er3+,Yb3+:GdVO4 microcrystals. The effect of the excitation power density on the relative thermal sensitivity and temperature resolution has been also analyzed.

Clinical evaluation of a cutaneous zero-heat-flux thermometer during cardiac surgery.

We evaluated the disposable non-invasive SpotOn™ thermometer relying on the zero-heat-flux technology. We tested the hypothesis that this technology may accurately estimate the core temperature. The primary objective was to compare cutaneous temperature measurements from this device with blood temperatures measured with the pulmonary artery catheter. Secondary objective was to compare measurements from the zero-heat-flux thermometer indirectly with other routinely used thermometers (nasopharyngeal, bladder, rectal). We included 40 patients electively scheduled for either off-pump coronary artery bypass surgery or pulmonary thromboendarterectomy. Temperatures were measured using zero-heat-flux (SpotOn™), pulmonary artery catheter, nasopharyngeal, rectal, and bladder thermometers. Agreement was assessed using the Bland and Altman random effects method for repeated measures data, and Lin's concordance correlation coefficient. Accuracy was estimated (defined as <0.5° difference with the gold standard), with a 95% confidence interval considering the multiple pairs of measurements per patient. 17 850 sets of temperature measurements were analyzed from 40 patients. The mean overall difference between zero-heat-flux and pulmonary artery catheter thermometer was -0.06°C (95% limits of agreement of ± 0.89°C). In addition, 14 968 sets of temperature measurements were analyzed from 34 patients with all thermometers in situ. Results from the zero-heat-flux thermometer showed better agreement with the pulmonary artery catheter than the other secondary core thermometers assessed. In conclusion,the SpotOn™ thermometer reliably assessed core temperature during cardiac surgery. It could be considered an alternative for other secondary thermometers in the assessment of core temperature during general anesthesia.

Trials of Pt-20%Rh versus Pt thermocouples between 157 °C and 962 °C

For over a century the Type S (Pt-10%Rh) and R (Pt-13%Rh) thermocouples have been used as primary or secondary reference thermometers. However, the measurement uncertainties of both types at the silver point (~962 °C) are typically limited to about 0.5 °C, due to drift caused by crystallographic ordering between 200 °C and 500 °C and rhodium oxidation between 500 °C and 900 °C. Although both processes can be reversed using an 1100 °C anneal, regular annealing can be inconvenient or impracticable. This paper follows up a prior study indicating that an alternative noble-metal thermocouple comprised of Pt-20%Rh and Pt is relatively insensitive to both drift mechanisms. Four thermocouples, assembled using wire from four different manufacturers, were evaluated using a gradient-furnace and homogeneity scanner. Measurements were also made using a salt-bath (200 °C to 500 °C) and fixed points between the indium and silver points. The experiments indicate that individual thermocouples are stable at the silver point to within 0.18 °C for periods of up to 100 h and all four thermocouples have emf versus temperature characteristics within 0.3 °C of each other. This intrinsic stability and similarity, coupled with cost, assembly and use conditions identical to a Type R or S thermocouple make the Pt-20%Rh versus Pt thermocouple an attractive alternative. Recommended annealing procedures enabling the greatest stability are also given.

Self-Calibrated Double Luminescent Thermometers Through Upconverting Nanoparticles.

Luminescent nanothermometry uses the light emission from nanostructures for temperature measuring. Non-contact temperature readout opens new possibilities of tracking thermal flows at the sub-micrometer spatial scale, that are altering our understanding of heat-transfer phenomena occurring at living cells, micro electromagnetic machines or integrated electronic circuits, bringing also challenges of calibrating the luminescent nanoparticles for covering diverse temperature ranges. In this work, we report self-calibrated double luminescent thermometers, embedding in a poly(methyl methacrylate) film Er3+- and Tm3+-doped upconverting nanoparticles. The Er3+-based primary thermometer uses the ratio between the integrated intensities of the 2I15/2 and 4I15/2 transitions (that follows the Boltzmann equation) to determine the temperature. It is used to calibrate the Tm3+/Er3+ secondary thermometer, which is based on the ratio between the integrated intensities of the 1H6 (Tm3+) and the 4I15/2 (Er3+) transitions, displaying a maximum relative sensitivity of 2.96% K−1 and a minimum temperature uncertainty of 0.07 K. As the Tm3+/Er3+ ratio is calibrated trough the primary thermometer it avoids recurrent calibration procedures whenever the system operates in new experimental conditions.

Upconverting Nanoparticles Working As Primary Thermometers In Different Media

In the past decade, noninvasive luminescent thermometry has become popular due to the limitations of traditional contact thermometers to operate at scales below 100 μm, as required by current demands in disparate areas. Generally, the calibration procedure requires an independent measurement of the temperature to convert the thermometric parameter (usually an intensity ratio) to temperature. A new calibration procedure is necessary whenever the thermometer operates in a different medium. However, recording multiple calibrations is a time-consuming task, and not always possible to perform, e.g., in living cells and in electronic devices. Typically, a unique calibration relation is assumed to be valid, independent of the medium, which is a bottleneck of the secondary luminescent thermometers developed up to now. Here we report a straightforward method to predict the temperature calibration curve of any upconverting thermometer based on two thermally coupled electronic levels independently of the medium, dem...

Thin film cryogenic thermometers defined with optical lithography for thermomagnetic measurements on films.

Resistance thermometers are common secondary thermometers in cryogenic applications. Bulk RuO2 thermometers are used in dilution refrigerators because of their low magnetoresistances in addition to their temperature sensitivity. Thermoelectric and thermomagnetic measurements require multiple thermometers to measure temperature differences. Here, we present a method to fabricate thin film RuO2 thermometers directly onto an experimental substrate. This enhances thermal contact between thermometers and films whose thermoelectric or thermomagnetic properties may be measured. Commercial thermometers have higher temperature sensitivities than the thermometers presented in this study, but commercial thermometers must be carefully heat sunk to the cryostat or sample to be useful. Thin film thermometers can be patterned with ultraviolet (UV) lithography. This allows both the size of the thermometer and its distance from the sample, when also patterned with UV lithography, to be on the order of micrometers. A universal calibration curve for these thin film thermometers has not been produced. The efficacy of these thermometers has been demonstrated through measurements of the Nernst effect in Nb. In this study, the thin film thermometers were calibrated using the cryostat thermometers.

Noise thermometry at low temperatures: MFFT measurements between 1.6 K and 1 mK

Reliable and traceable thermometry is a demanding task at low temperatures. Recently, we have developed a dc SQUID-based noise thermometer, the magnetic field fluctuation thermometer (MFFT), for practical thermometry in the low temperature range [1]. Its operational principle is based on the Nyquist theorem ensuring a linear characteristic over a wide range of temperatures. This makes the MFFT capable to replace a variety of secondary thermometers, which are normally used in the low temperature range.For the first time, we report on MFFT measurements over more than 3 decades in temperature from about 1.6 K down to below 1 mK The deviations from a high-accuracy realization of the PLTS-2000 are found to be ≍ 1%.

Use of a quartz resonator of the tuning fork type as a thermometer in a dilution refrigerator

The temperature dependences of the resonance frequency and resonance width of a tuning-fork-type quartz resonator, which is placed directly in the dilution chamber of a refrigerator, were measured in order to test the possibility of using it as a secondary thermometer under such conditions. Measurements were performed both in the upper and lower phases of a stratified solution of 3He in 4He in the temperature range 15–350 mK. The dependences obtained indicate that the parameters of resonators depend on not only the temperature, thus making it problematic to use them for thermometry in a cryostat’s dilution chamber.

A Simple Wide-Range Noise Thermometer With DC SQUID Readout for Operation Down to 10 mK

The design and performance of a compact and easy-to-build thermometer for the temperature range of 10 mK-4.2 K, which is wide enough to cover the entire temperature range of a typical dilution refrigerator, are described here. A commercial low-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> dc superconducting quantum interference device (SQUID) is used to measure the thermal current noise of a resistor, i.e., an insulated copper wire, that scales linearly with the temperature, as expected from the Nyquist formula. Although, in principle, this thermometer is a primary thermometer, its performance was evaluated as a secondary thermometer. The relative precision of the temperature, which is independent of the temperature, was estimated at 0.4% in a measuring time of 130 s, in good agreement with the expectations. The accuracy evaluated from the comparison with other calibrated thermometers (i.e., superconducting reference point (SRP), cerium magnesium nitrate, and germanium) on different temperature ranges is better than 2% between 10 mK and 4.2 K. If only the SRP thermometer is considered for the comparison in the temperature range of 20-207 mK, the accuracy improves to 1%. The calibrations performed with a single fixed point have a typical accuracy value of about 1%.

Thermometry by micro and nanodevices

In this paper we briefly discuss the current provisional temperature scale of 2000 (PLTS-2000) for low temperatures. Electronic thermometry is presented and discussed, focusing on its potential in verifying and realizing a future temperature scale. The discussion covers secondary thermometers such as NIS and SIS thermometers and noise, shot noise and Coulomb blockade primary thermometers. The last one is discussed in more detail.

First measurement using three-in-one cell: a new design of the fixed-point cell for the calibration of thermometers

A new design of the fixed-point cell that contains multiple metal elements in a single crucible has been introduced for fixed-point calibration of secondary thermometers such as thermocouples. A multicell with aluminium, silver and copper was fabricated and used for the calibration of a Pt/Pd thermocouple. The expanded uncertainties (k = 2) of the realization of the multicell were 0.07 °C, 0.12 °C and 0.24 °C, plus an additional term from the inhomogeneity of the thermocouple, for aluminium, silver and copper, respectively. These uncertainties are considerably smaller than those obtained from the method of calibration by comparison in similar temperature ranges. This proves the suitability of the metal multicells for the calibration of secondary thermometers.

Propagation of Uncertainty Due to Non-linearity in Radiation Thermometers

The measurement of the non-linearity of radiation thermometers is important in the realization of ITS-90 above the silver point and in the calibration of primary or secondary radiation thermometers using multiple fixed points both above and below the silver point. A non-linearity function is usually derived, enabling correction of the measured signals. Uncertainties in this non-linearity function propagate to the uncertainty in the determination of an unknown temperature. Since the same non-linearity function is used both during calibration and in subsequent use of the thermometer, there is a high degree of correlation between the uncertainties in the corrected calibration signals and the corrected in-use signals. While these correlations obviously lead to zero uncertainty at the calibration points, it is difficult to determine the correlation coefficients for temperatures away from these points. This article sets out a mathematical framework, based on interpolation theory, for propagating the uncertainty due to non-linearity in which correlation is easily included. The method is illustrated for a thermometer realizing ITS-90 up to 3,000°C based on one fixed point (silver, gold, or copper), and also for alternative realization schemes based on two or more fixed points. The total non-linearity uncertainty for the multipoint schemes is considerably lower than for the ITS-90 method. The mathematical framework can also be applied to secondary calibrations below the silver point, where non-linearity is typically more problematic for the detectors used in this temperature range.

Electronic Transport Properties of Speer Carbon Resistors—Experimental Results and Semi-empirical Fits

Speer carbon composition resistors, in particular the 470 Ω and 220 Ω 1/2 W grade 1002 resistors, have been used as secondary thermometers at temperatures below 4 K for many years. Their zero field resistances have been measured between 300 K and 4 K using a “dip” probe. Above 10 K, the resistance behavior can be explained using a simple temperature power law, R(T) ≈ R0/T0.16. The resistance measurements have been extended to 0.02 K using dilution refrigerators. Between 4 K and 0.3 K, the resistances exhibited activated laws having hopping exponents y ≈ 0.5. Below 0.3 K, the 470 Ω resistors exhibit a crossover to a weaker activated law. Crossover resistance expressions suggest that the resistances follow a Mott variable-range hopping (VRH) law below 0.05 K. The low temperature magnetoresistance (MR) data showed changes of less than ±12 % of the zero field resistance values in fields up to 10 T. Fits using the wave function shrinkage and the forward interference models gave only fair agreement with the MR data.

Vibrating Wire Thermometry in Superfluid3He

We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid 3He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T c < T < 50 mK.

EU dissemination of the provisional ultra-low-temperature scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3 He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available.

Sub-Micron Normal-Insulator-Superconductor Tunnel Junctions for Sensitive Thermometry and Micro-Refrigerators

We report on measurements of normal-insulator-superconductor tunnel junctions at temperatures below 1K. The junctions have been fabricated by shadow mask technique and e-beam lithography and have submicron dimensions. The measurements on our junctions show that their characteristics are very sensitive to temperature changes making them suitable to be used as a sensitive secondary thermometer. To demonstrate this we use this tunnel structure for sensing the electron temperature drop in a copper strip of an electronic micro-refrigerator, that was made by arrays of tunnel junctions, as well.

Thermoelectric properties of the Au/Pt thermocouple

An Au/Pt thermocouple having a gold-bridged junction instead of a Pt coil is fabricated and its thermoelectric properties are investigated at the Sn, Zn, Al, and Ag freezing points. Reproducibility is found to be excellent and standard deviation is as small as ±4 mK at the Ag fixed point. Immersion properties, which indicate homogeneity of the thermocouple wire, are also shown to be very good, with standard deviation estimated as about 10 mK. In order to investigate interchangeability, 20 sets of Au/Pt thermocouples are made and their emfs are measured at the same fixed points. Thermocouples from the same spool are reproducible within ±0.02 °C for the whole temperature range. For practical use of the Au/Pt thermocouple, an inverse function and a deviation function for calibration are proposed. The inverse function has two temperature ranges and is accurate within ±1 mK, while the deviation function is a third-order polynomial without a constant term. The Au/Pt thermocouple is stable at high temperatures for long periods. After 1500 h at 1000 °C, the thermal emf at the Ag fixed point is changed by about 0.9 μV (about 40 mK). After the other experiments, calibration uncertainties at the fixed points are evaluated. At the Ag fixed point, the maximum expanded uncertainty is calculated and is about ±30 mK at a confidence interval of 95%. It is shown that the gold-bridged Au/Pt thermocouple is reproducible, accurate, and stable. At present, the Korea Research Institute of Standards and Science (KRISS) uses Au/Pt thermocouples as secondary standard thermometers; they are supplied to industry as certified references.

1000 h stability test of the Au/Pd thermocouple at 1000 °C

A newly developed Au/Pd thermocouple has shown very high reproducibility and good immersion characteristics. A stability test of the Au/Pd thermocouple has been conducted for 1000 h at 1000 °C in air to assess its suitability for practical application. Two thermocouples from two manufacturers were fabricated and their emf values were checked in a silver freezing-point cell before and after the soaking at 1000 °C. It was found that the high-temperature stability of the Au/Pd thermocouple is within ±30 mK (2σ) throughout the test time. This result implies that the Au/Pd thermocouple possesses characteristics which may make it suitable for use as a secondary high-temperature thermometer in industry.

Primary thermometry with nanoscale tunnel junctions

We have found current-voltage (I-V) and conductance (dI/dV) characteristics of arrays of nanoscale tunnel junctions between normal metal electrodes to exhibit suitable features for primary thermometry. The current through a uniform array depends on the ratio of the thermal energy kBT and the electrostatic charging energy E c of the islands between the junctions and is completely blocked by Coulomb repulsion at T = 0 and at small voltages eV/2 ≤ Ec. In the opposite limit, kBT ≫ Ec, the width of the conductance minimum scales linearly and universally with T and N, the number of tunnel junctions, and qualifies as a primary thermometer. The zero bias drop in the conductance is proportional to T−1 and can be used as a secondary thermometer. We will show with Monte Carlo simulations how background charge and nonuniformities of the array will affect the thermometer.