Temperature Modulation Measurements of the Thermal Properties of Nanosystems at Low Temperatures

We report on the dynamic measurements of thermal properties of nanosystems at very low temperatures. These techniques are based on the modulation of the temperature and hence leads to highly sensitive measurements. We will discuss the intrinsic limitations of these methods when the thermal properties of nano-objects are studied at very low temperatures, much below 1 K. Firstly, we will present thermal conductance measurements using the 3ω method. This technique is limited at low temperatures due to the significant increase of the mean free path. Secondly, heat capacity measurements using ac calorimetry are outlined, and again restrictions occur due to the continuous temperature gradient inherent to that technique. Propositions are made in order to overcome these limitations.     

Predicting the thermal conductivity of aluminium alloys in the cryogenic to room temperature range

Aluminium alloys are being used increasingly in cryogenic systems. However, cryogenic thermal conductivity measurements have been made on only a few of the many types in general use. This paper describes a method of predicting the thermal conductivity of any aluminium alloy between the superconducting transition temperature (approximately 1 K) and room temperature, based on a measurement of the thermal conductivity or electrical resistivity at a single temperature. Where predictions are based on low temperature measurements (approximately 4 K and below), the accuracy is generally better than 10%. Useful predictions can also be made from room temperature measurements for most alloys, but with reduced accuracy. This method permits aluminium alloys to be used in situations where the thermal conductivity is important without having to make (or find) direct measurements over the entire temperature range of interest. There is therefore greater scope to choose alloys based on mechanical properties and availability, rather than on whether cryogenic thermal conductivity measurements have been made. Recommended thermal conductivity values are presented for aluminium 6082 (based on a new measurement), and for 1000 series, and types 2014, 2024, 2219, 3003, 5052, 5083, 5086, 5154, 6061, 6063, 6082, 7039 and 7075 (based on low temperature measurements in the literature).     

Low temperature noncollinear behavior in FePt nanogranular thin film system

We report the low temperature noncollinear magnetic behavior of direct current (DC) sputtered FePt thin films investigated by performing DC magnetization, thermoremanence, magnetic relaxation, and electrical transport measurements down to 1.8 K. The obtained results, interestingly, indicate a transition from ferromagnetic state to a low temperature disordered state where a collective frozen magnetic state with grain moments oriented randomly occurs. The magnetic relaxation and electrical resistivity measurements at low temperature support the spin-glass like phase, which diminishes and finally disappears with an applied field of moderate strength. We interpret the observed low temperature noncollinear magnetic behavior to be due to random freezing of grain moments.     

Roton second sound and the roton-roton interaction potential

We report measurements of the roton second sound velocity and absorption at high pressure and low temperature. The velocity measurements show the existence of a dip over a very small range of temperature. Comparing this to the absorption measurements, we show that this dip corresponds to a pure roton second sound regime, which is at a constant number of rotons, in agreement with Maris' predictions. The departure toward the constantchemical-potential regime gives us an estimate of the characteristic frequency of the non-roton-conserving process. The absorption measurements give a roton-roton collision frequency in good agreement with previous measurements at higher temperature. In order to explain its value, we have proposed a new interaction potential between rotons, taking into account the exchange of virtual rotons between them. We then obtain very good agreement with experiment, without any adjustable parameter.Laboratoire associé au Centre National de la Recherche Scientifique.     

Low temperature specific heat of two stainless steels

Stainless steel is often used as a structural material in ctrygenic systems. For many large-scale, low temperature applications, knowledge of specific heat values for such alloys is essential for proper design. Collings et al¹ have recentky made calorimetric measurements on AISI 310S stainless steel. These measurements indicate the occurence of superparamagnetism, presumably associated with magnetic clusters, by a temperature-independent contribution to the specific heat. Corsan and Mitchen² have recently reported specific heat measurement form 4 K to room temperature on a series of laboratory-produced FeCrNi alloys with chromium contents ranging from 12–24 wt.% and nickel contents int he range 12–20 wt.% Differences of up to 30% were observed in the specific heats as measured at 4 K. However, to the best of our knowledge, no data previously existed on the most common low temperature structural stainless steel—AISI 304. This note describes the results of low temperature specific heat measurements on AISI 304 abd AISI 304L stainless. L designated low carbon content.     

The low frequency internal friction and electric magnetic properties in La0.7Pb0.3MnO3 bulk materials

The polycrystalline samples of La_0.7Pb_0.3MnO₃ synthesized by the sol–gel method were studied by the low frequency internal friction measurements and the resistance and ac susceptibility measurements. There are two internal friction peaks at 258 and 198 K, respectively, the peak positions of which do not shift with frequency but the peak heights of which decrease with increasing frequencies. The modulus softening is evident at the corresponding temperatures. Corresponding to the two internal friction peaks, there are two resistance peaks, and a sharp rise and a following continuous decrease of ac susceptibility. It is suggested that the high temperature peaks correspond to the paramagnetic (PM) to ferromagnetic (FM) transition, while the low temperature peaks originate from the process of an anti-ferromagnetic phase (AFM) separating from the ferromagnetic matrix (phase separation) in polycrystalline materials. The peak positions of internal friction and resistance will move towards higher temperature when the sample was annealed in flowing oxygen, and the low temperature peaks become smaller.     

Bulk magnetic properties of Co-Zn ferrites prepared by the co-precipitation method

The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Zn _x Co_1-x Fe₂ O₄ prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law [1]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.     

Spin Fluctuations and Itinerant Magnetism in PrCo2B2C Compound

Resistivity as a function of the temperature and applied magnetic field was studied in PrCo₂B₂C intermetallic compound. The resistivity as a function of temperature at different magnetic fields shows a parabolic behavior at low temperatures which persists for magnetic fields up to 7.8 T. Magnetoresistance measurements show negative values at temperatures below 15 K and low fields, and becomes positive at high fields. Specific heat measurements reveal a high value of the Sommerfeld coefficient of about 300 mJ(mol?K²)^?1. These results at low temperatures are interpreted from the point of view of the spin fluctuations theory.     

Ergebnisse von Untersuchungen zur Bauteilzähigkeit

Results of tests on structural member toughness . A final evaluation is made of measurements on model vessels of boiler plate and of low temperature steel. These measurements had been the subject of former publications, and are correlated with the properties of the respective materials. It results thereof that, with respect to the bursting behaviour of the vessels (toughness of structural member), certain regions can be defined where materials property data (crack arrest temperature according to Robertson and impact transition temperature) represent characteristic values. The user is thus able to assess the types of fracture to be expected.     

Proof-of-Principle Measurements of the Superfluid Joule-Thomson Refrigerator Concept

The performance of the first Superfluid Joule-Thomson Refrigerator (SJTR) is described. The SJTR has achieved a low temperature of 0.68 K when exhausting its waste heat to a thermal reservoir at a temperature of 1.2 K. Cooling power versus temperature measurements were conducted with two different throttles and with different compressor speeds     

Distributed fiber temperature and strain sensor using coherent radio-frequency detection of spontaneous Brillouin scattering

A novel technique that enables coherent detection of spontaneous Brillouin scattering in the radio-frequency (<500 MHz) region with excellent long-term stability has been demonstrated for distributed measurements of temperature and strain in long fiber. An actively stabilized single-frequency Brillouin fiber laser with extremely low phase noise and intensity noise is used as a well-defined, frequency-shifted local oscillator for the heterodyne detection, yielding measurements of spontaneous Brillouin scattering with high frequency stability. Based on this approach, a highly stable real-time fiber sensor for distributed measurements of both temperature and strain over long fiber has been developed utilizing advanced digital signal processing techniques.     

Temperature correction of radiometric and geometric models for an uncooled CCD camera in the near infrared

This paper presents radiometric and geometric models for both temperature and displacement noncontact measurements using an uncooled charge-coupled device (CCD) video camera. Such techniques ("one sensor-two measures") represent an interest in many industrial low cost applications and scientific domains. To benefit from both measurements, we have to use the camera's spectral response in the near infrared spectral band from 0.75 to 1.1 /spl mu/m. In this spectral band, the temperature variations of an uncooled CCD camera are taken into account in the radiometric and geometric models. By using physical models for CCD camera, we quantify detector's quantum efficiency, sensor noise and spatial resolution as a function of the wavelength and of the detector temperature. These models are confirmed by experimental results of calibration with a low cost uncooled camera based on a Sony detector and operating over the detector temperature range of -30 to -50/spl deg/.     

Fiber-optic Bragg gratings as magnetic field-insensitive strain sensors for the surveillance of cryogenic devices

While conventional electrical resistance strain gages show increasing cross-sensitivities to temperature and magnetic field with decreasing temperature down to liquid helium, it has been found that fiber-optic Bragg grating strain sensors show negligible thermo-optic and magneto-optic effects in cryogenic environments; therefore, they allow reliable strain measurements. These specific application advantages of optical fiber Bragg grating sensors at low temperatures, together with the electrical isolation and low electro-magnetic interference, low thermal conductivity and their multiplexing capability, make them attractive for structural health monitoring in cryogenic devices such as superconductive magnets. In this paper we present low temperature characteristics of fiber Bragg grating-based sensors and address application-based side effects such as induced birefringence.     

The electrical and magnetic properties of the transition in nickel sulfide

The Hall effect and resistivity have been measured on single crystals of hexagonal NiS above and below the transition temperature, and magnetic susceptibility measurements have been made on powders and ground-up single crystals in the same temperature region. It is found that the material behaves as an extrinsic semiconductor in the low temperature region, with the charge carriers arising from the nickel vacancies.     

Influence of dibutyl phthalate on the mechanical,thermal, and relaxation behaviour of poly (methyl methacrylate) for denture-base soft liners

Methyl methacrylate and six solutions of methyl methacrylate/dibutyl phthalate (nominally 5 to 30% v/v) were polymerized into thin sheets using gamma radiation. Dynamic mechanical spectra of the storage modulus, loss modulus and loss tangent, as well as changes in length, were investigated as a function of temperature. From these measurements, the depression of the storage modulus and glass-transition temperature were obtained. Subsequently, differential scanning calorimetry (DSC) and cross-polarization-magic-angle-spinning NMR were used to obtain additional glass-transition and relaxation-time measurements. Based upon these experiments, a specific form of the rule of mixtures described the depression of the glass-transition temperature. From storage-modulus measurements, antiplasticization was evidenced at very low temperatures and at compositions greater than 25% v/v. Solid-state NMR confirmed that plasticization causes an increase in polymer main-chain motion via the physical loosening of secondary bonds between polymer chains.     

On the Way to Determination of the Vapor-Pressure Curve of Pure Water

The determination of the physical properties of pure water, especially the vapor-pressure curve of water, is one of the major issues identified by the Consultative Committee for Thermometry of the International Committee for Weights and Measures (CIPM) to improve the accuracy of the national references in humidity. At the present time the saturation-pressure data, corresponding to ice or liquid?Cvapor equilibrium, at low temperature are scarce and unreliable. This study presents new measurements of vapor and sublimation pressures of, respectively, water and ice, using a static apparatus. Prior to saturation-pressure measurements, the temperature and pressure sensors of the static apparatus were calibrated against reference gauges in use at the LNE- CETIAT laboratories. The effect of thermal transpiration has been studied. The explored temperature range lies between 250 K and 374 K, and the pressure range between 70?Pa and 10⁵ Pa. An automatic data acquisition program was developed to monitor the pressure and temperature. The obtained results have been compared with available literature data. The preliminary uncertainty budget took into account several components: pressure measurements, temperature measurements, and environmental error sources such as thermal transpiration and hydrostatic correction.     

Structural and optical properties of hydrothermally grown zinc oxide nanorods on polyethersulfone substrates as a function of the growth temperature and duration

Zinc oxide (ZnO) nanorods were grown on polyethersulfone substrates with a seed layer by hydrothermal synthesis. The effects of the growth temperature and duration on the structural and optical properties of the ZnO nanorods were investigated by X-ray diffraction, field emission scanning electron microscope and photoluminescence measurements. Improvement of the structural properties was confirmed when the ZnO nanorods were grown at a moderate thermal energy. Thermal energies that were too high or too low resulted in structural degradation: low thermal energies did not provide enough energy for the ZnO growth, and high thermal energies contributed to improper growth by creating an uncommon flake-like structure. Photoluminescence measurements showed that the near-band-edge emission to deep-level emission peak ratio increases with increasing growth temperature at growth duration of 5 h.     

液氮低温环境下电阻应变片测试性能的试验研究

分别采用低温电阻应变片及拉线式位移传感器的电测技术,该文开展了液氮浸泡下的悬臂梁结构在静载条件下的应变测量。对两种实验测试结果和理论分析结果进行了对比和精度分析,给出了相应的实验标定曲线,并探讨了测量过程中应变片粘接、电桥连接方式、液氮冷却和数据采集对实验结果精度的影响因素等。结果表明:在采用温度补偿和应变片的正确粘贴和良好固化情形下,低温应变片能够在液氮低温区给出较高精度的应变测量;拉线式位移传感器几乎不受低温的影响,测量简单易行。相关技术和结果将为中科院近代物理研究所自主研制的兰州潘宁离子阱7T超导磁体的低温下应变测量提供方法和指导。     

Vapour-deposited silicon dioxide for device applications

Silicon dioxide layers deposited from the vapour phase at low temperatures are extensively applied in integrated circuit technology. Applications include doped oxide diffusion sources, protective layers and cross-over insulators in multilevel metallization systems.In this paper we show the feasibility of obtaining a SiO₂Si interface whose electrical characteristics closely approach those of thermally grown SiO₂Si sandwich structures. Interface state densities lying in the low 10¹⁰ cm^?2 eV^?1 range have been determined from quasi-static C(V) measurements. The results of excess noise measurements made on deposited gate oxide and thermally grown gate oxide MOSFETs are in reasonable agreement with the interface state density measurements. C(V) dispersion and C(V) hysteresis measurements prior to and after exposure to 10⁷ rad of ⁶⁰Co γ radiation are also presented. Potential applications of low temperature vapour-deposited oxides include the silicon on insulating substrate (SOS) technology where it is generally desirable to minimize high temperature processing steps. Other applications are in the field of impurity profile determinations using the MOS capacitor method. In these applications one desires to measure the original profile without having to deal with the additional complication of the diffusion and redistribution phenomena that occur unavoidably during high temperature thermal oxide growth.     

Analysis of the low frequency damping observed at medium and high temperatures

Isothermal internal friction measurements performed versus frequency exhibit often a large damping rise at very low frequency (10⁻² to 10⁻⁴ Hz). This increasing is found for experiments at very high temperature above 0.7T_M, (T_M=melting point) similarly to the so-called high temperature background obtained during measurements at fixed frequency and often described in the literature. In some cases, as for instance in cold work metals or metallic alloys, such low frequency background occurs at lower temperature (0.3 T_M<T<0.7T_M) and disappears after high temperature sample annealing. This exponential background depends on the sample microstructure and can be analysed with the Schoeck’ model. On the contrary, experiments performed at temperature close to the melting point or the liquidus temperature for metallic alloys exhibit a peak. The high temperature background measured for instance at 1 Hz, is only the lower part of a peak and does not correspond to an exponential increase. This fact explains why none of the different expressions proposed in the literature is able to describe properly the experimental high temperature background.