Thermal Relaxation Technique Research Articles

Heat capacity of type-I superconductivity in the Dirac semimetalPdTe2

Type I superconductivity has recently been reported for the Dirac semimetal PdTe$_2$ (Tc approximately 1.6K) with, remarkably, multiple critical fields and a complex phase diagram. Here, measurements of the specific heat utilizing a thermal relaxation technique are presented. Conventional weak-coupling BCS superconductivity is confirmed by examining the temperature dependence of the specific heat in zero field. By probing the latent heat accompanying the superconducting transition, thermodynamic evidence for type I superconductivity is attained. The presence of the intermediate state is observed as a significant broadening of the superconducting transition onto lower temperatures at high fields as well as irreversibility in the specific heat in zero field cooled data at 8.5 mT.

New Development of Membrane Base Optoelectronic Devices.

It is known that one factor that affects the operation of optoelectronic devices is the effective protection of the semiconductor materials against environmental conditions. The permeation of atmospheric oxygen and water molecules into the device structure induces degradation of the electrodes and the semiconductor. As a result, in this communication we report the fabrication of semiconductor membranes consisting of Magnesium Phthalocyanine-allene (MgPc-allene) particles dispersed in Nylon 11 films. These membranes combine polymer properties with organic semiconductors properties and also provide a barrier effect for the atmospheric gas molecules. They were prepared by high vacuum evaporation and followed by thermal relaxation technique. For the characterization of the obtained membranes, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to determine the chemical and microstructural properties. UV-ViS, null ellipsometry, and visible photoluminescence (PL) at room temperature were used to characterize the optoelectronic properties. These results were compared with those obtained for the organic semiconductors: MgPc-allene thin films. Additionally, semiconductor membranes devices have been prepared, and a study of the device electronic transport properties was conducted by measuring electrical current density-voltage (J-V) characteristics by four point probes with different wavelengths. The resistance properties against different environmental molecules are enhanced, maintaining their semiconductor functionality that makes them candidates for optoelectronic applications.

Physical properties of antiferromagnetic single crystal GdIn3

A sample of GdIn3 was obtained via the metallic flux technique and its structural, magnetic, and thermodynamic properties were studied. X-ray diffraction (XRD) measurements realized at room temperature were performed in order to verify whether the desired crystalline phase had been obtained. The experimental results show that single crystals were grown successfully by the employed growth technique. The magnetic characterization was carried out through magnetic susceptibility data as a function of temperature (2≤x≤300K) and magnetic field (−7≤H≤7T). The specific heat was measured using a commercial small mass calorimeter that employed the thermal relaxation technique in the temperature range of 2–200K.

Preparation of Hybrid Materials Containing M(II)Pc (M = Fe, Co, Ni)/Nylon films with Optical and Electrical Properties

Hybrid materials consisting of M(II)Pc (M = Fe, Co, Ni) particles dispersed in nylon 11 films have been prepared by using a thermal relaxation technique. The obtained films are characterized by AFM, SEM and TEM, and their structural composition is determined by IR spectroscopy and EDS. The M(II)Pc particles are homogeneously distributed in the nylon 11 matrix after heat treatment. Optical absorption studies of the hybrid films are performed in the 200 - 1150 nm wavelength range. The band-model theory is applied to determine the optical parameters for MPc/nylon 11 hybrid films. The optical band gap of the thin films is determined from the (αhν)1/2 vs. hν plots for indirectly allowing transitions and comparing with the as-deposited M(II)Pc thin films. The values of the optical band gap calculated from the absorption spectra, range between 1.07 and 2.7 eV. The electrical conductivity is measured in order to evaluate the conductivity behavior of these hybrid films.

Antiferromagnetic fluctuations and proton Schottky heat capacity in doped organic conductor κ-(BEDT-TTF)4Hg2.78Cl8

Low temperature heat capacity measurements of hole-doped organic conducting compound of κ-(BEDT-TTF)4Hg2.78Cl8 were performed by the ac calorimetry and the thermal relaxation technique. It was observed that low temperature electronic heat capacity at 0T can be fitted by a kind of spin fluctuations model for two-dimensional (2D) itinerant electrons. The enhancement of electronic heat capacity is originated from these magnetic fluctuations occur at extremely low temperature region. We also observed that the low temperature heat capacity under magnetic fields show large additional contribution explained by the two-level Schottky model of protons located on the edge of BEDT-TTF molecules. The strong spin fluctuations peculiar for 2D electrons in this hole-doped organic compound influence the relaxation process of proton spins to get thermal equilibrium state. This is the first example among organic conducting systems where magnetic fluctuations of itinerant electrons affect on the relaxation of proton spins. Similar tendency was observed in another hole-doped system of κ-(BEDT-TTF)4Hg2.89Br8 of which magnitude is reduced down to 20–25% of that of κ-(BEDT-TTF)4Hg2.78Cl8.

Development of heat capacity measurement system for single crystals of molecule-based compounds

We report on construction of a new low temperature heat capacity measurement system. This system was designed for performing thermodynamic investigation by thermal relaxation technique for small amount of samples at extremely low temperature region between 70 mK and 10 K. Two different calorimetry cells for this system were designed. One is a usual-type calorimetry cell consisting of tiny chip-type thermometer and strain gauge heater. The size of the sample stage has been reduced for measuring small samples. The other is designed for performing heat capacity measurements under magnetic fields of which magnitude and direction are accurately controlled. The calorimetry cells with heat capacity measurement unit can be mounted on a handy top-loading type dilution refrigerator of which outer diameter including the adiabatic space is 27 mm. We discuss basic performance and specification of the constructed cells and low temperature heat capacity data of an organic charge transfer salt obtained by this system.

Anisotropic heat transfer prediction of multiscale wires using pulse laser thermal relaxation technique

A theoretical model is developed that predicts the thermal characterization of multiscale wires using the pulse laser thermal relaxation technique. This into account anisotropic heat transfer and radiation heat lost to the surroundings. The simulation results have better agreement with the experimental results than previous models. Using the validated model, the heat transfer characteristics of multiscale wires with various morphologies (radius of 15–25μm, length of 500–1000μm, radial thermal conductivities of 0.05–5.00W/mK, axial thermal conductivities of 10–2000W/mK) and experimental conditions (laser power outputs of 20–50kW and laser pulse width of 5–9ns) are studied.

Electron–phonon interaction in Gd1−xCaxBaSrCu3O7−δ superconductors

Polycrystalline Gd1−xCaxBaSrCu3O7−δ samples (0≤x≤0.1) were prepared via solid-state reaction. The superconducting critical temperature Tc and lattice parameter decrease with doping content. Temperature dependence of the specific heat of all samples was measured with the thermal relaxation technique using a Physical Property Measurement System from about 2K to 150K. The calculated Debye temperature ΘD at 10K is found to be inversely proportional to Tc. Subsequently, the electron–phonon coupling constant was estimated based on standard BCS theory (λBCS) in the weak coupling limit and two-dimensional Van Hove scenario (λVH). The calculated values of λVH in this study (around 0.04) are close to the experimental data as reported by other researchers on Bi-based and YBCO samples. Hence, the two-dimensional Van Hove scenario seems to be a viable candidate for the mechanism of superconductivity if electron–phonon coupling plays a role in superconductivity of these materials.

Analysis of structural and magnetic phase transition behaviors of La 1− xSr xCrO 3 by measurement of heat capacity with thermal relaxation technique

The heat capacity, C p , of the La 1− x Sr x CrO 3 system and its temperature dependence have been measured by a thermal relaxation technique. Both structural and magnetic phase transitions were detected at temperatures that can be surmised from the phase diagram proposed in previous studies. The observed variation in enthalpy after the first-order structural phase transition, Δ H, showed agreement with those measured by differential scanning calorimetry (DSC). A decrease in the variation in C p in the second-order magnetic phase transition, Δ C p , with an increase in Sr content was detected, which can be attributed to a decrease in electronic spin configuration entropy with an increase in Sr content. In the dependence of Δ C p on Sr content, a bending point was also observed at x ∼ 0.12, at which the crystal system varies from an orthorhombic-distorted perovskite structure to a rhombohedral-distorted perovskite structure.

Development of pulsed laser-assisted thermal relaxation technique for thermal characterization of microscale wires

A transient technique is developed to measure the thermal diffusivity of one-dimensional microscale wires. In this technique, the thin wire is suspended over two copper electrodes. Upon fast (nanosecond) pulsed laser irradiation, the wire’s temperature will quickly increase to a high level and then decrease gradually. Such temperature decay can be used to determine the sample’s thermal diffusivity. To probe this temperature evolution, a dc is fed through the wire to sensor its voltage variation, from which the thermal diffusivity can be extracted. A 25.4 μm thin Pt wire is characterized to verify this technique. Sound agreement is obtained between the measured data and reference value. Applying this pulsed laser-assisted thermal relaxation technique, the thermal diffusivity of multiwall carbon nanotube bundles and microscale carbon fibers is measured. Detailed analysis is conducted to study the effect of the wire embedded in the paste/base on the final measurement result.

Heat capacity of GdBaSr(Cu3−x M x)O7−δ superconductor (M=Zn and Ni)

In this study, GdBaSr(Cu3−xMx)O7−δ bulk samples (M=Zn and Ni; 0≤x≤0.1) were prepared via solid-state reaction. Specific heat measurement (measured with thermal relaxation technique using PPMS) shows an obvious specific heat jump around the Tc for GdBaSrCu3O7−δ sample as observed in most of the high temperature superconductors. It shifts towards lower temperature with increasing of both Zn and Ni doping contents, whose tendency is similar to the decreasing of Tc. Debye temperature, ΘD (derived from specific heat measurements) calculated at around 10 K is found to be directly proportional to the Tc.

Thermal Characterization of Micro/Nanoscale Wires/Tubes Using Pulsed Laser-assisted Thermal Relaxation

ABSTRACTA novel transient technique is developed to measure the thermal diffusivity of one-dimensional microscale wires. In this technique, the thin wire is suspended over two copper electrodes. Upon fast (nanosecond) pulsed laser irradiation, the wire's temperature will quickly increase to a high level and then decrease gradually. Such temperature decay can be used to determine sample's thermal diffusivity. To probe this temperature evolution, a dc current is fed through the wire to sensor its voltage variation, from which the thermal diffusivity can be extracted. A 25.4-μ;m thin Pt wire is characterized to verify this technique. Sound agreement is obtained between the measured data and reference value. Applying this pulsed laser-assisted thermal relaxation technique, the thermal diffusivity of multi-wall carbon nanotube bundles and microscale carbon fibers is measured. Detailed analysis is conducted to study the effect of the wire embedded in the paste/base on the final measurement result.

Metrological aspects of thermal relaxation technique by radiation loss for volumetric heat capacity measurements

One of the best-known methods to measure the heat capacity of solids consists in the illumination of the sample and the analysis of the thermal relaxation when the illumination is stopped. In this work, the energy balance equation with heat losses due to radiation is solved exactly. This is used to establish the limits of the usual approximations used to obtain the heat capacity from the experimental data. It is shown that large temperature changes, induced by the heat source during the experiment can generate errors in the calculation of heat capacity when the traditional approach is used.

Heat capacity of glassy and crystalline Zr 0.55Al 0.10Ni 0.05Cu 0.30

The heat capacity ( C p) of Zr 0.55Al 0.10Ni 0.05Cu 0.30 (ZANC) alloy was measured for glassy rod, glassy ribbon, and the crystallized samples by a thermal relaxation technique between 1.8 and 310 K and by the step scanning method of differential scanning calorimetry (DSC) between 300 and 873 K. The low-temperature C p becomes larger as the sample turns from the crystal into the glassy rod and further into the glassy ribbon. The crystallized sample showed no anomaly in C p up to 873 K, while the glassy rod and glassy ribbon samples showed a glass transition around 680 K, and then crystallization at about 726 K. An exothermic phenomenon was observed in the glassy ribbon sample below the glass transition temperature, which was probably caused by another structural relaxation. These results suggest that the degree of vitrification becomes higher with increasing cooling rate in the vitrification process.

Evidence of d-wave pairing in MTG-YBa2Cu2.99Li0.01Ox crystals determined from the low-temperature specific heat

The specific heat of a melted-textured-growth (MTG)YBa2Cu2.99Li0.01Ox crystal has been measured from 1.8 to 30 K in different fields up to 9 T parallel to thec-axis by the thermal relaxation technique. The defects induced by Li-doping and the paramagneticcentres have a strong effect on the low-temperature specific heat. The electronic specific heatCe(T,H)/T at lowertemperatures (T<5 K) follows αT at 0 T and AH1/2 in the magnetic field, and can be scaled on a line,Ce(T,H)/TH1/2 = F(T/H1/2). These results are consistent with that of the d-wave superconductorpredicted theoretically by Volovik, indicating that a Li-dopedMTG-YBa2Cu2.99Li0.01Ox crystal should be a d-wave superconductor.

Single-Electron Tunneling Effects in Nylon 11 Thin Films Containing Nanoparticles

Very thin Nylon 11 films (≤20 nm in thickness) containing Au or Ge nanoparticles (Au/Nylon 11 or Ge/Nylon 11) were prepared by a thermal relaxation technique, and current–voltage (I–V) characteristics in the vertical direction of the films were studied. In the case of Au/Nylon 11, the plan and cross-sectional transmission electron microscopic (TEM) images revealed that Au nanocrystals are spontaneously aligned in the middle of the upper and lower electrodes and Nylon 11 tunneling barriers are formed between Au nanocrystals and electrodes. In the case of Ge/Nylon 11, lattice fringes corresponding to Ge crystals with the diamond structure were not observed in TEM images, suggesting that amorphous Ge particles are dispersed in Nylon 11 films. Clear Coulomb staircases were observed in the I–V characteristics in both cases.

Interfacial interaction in Ag/polymer nanocomposite films

Metallic nanoparticles possess a wide range of novel physical properties, such as electrical, optical, magnetic properties, etc. due to their intermediate structures between atomic state and the bulk [1–3]. For example, strong third-order nonlinear optical susceptibility and ultrafast time response of noble metal (i.e. gold, silver, copper, etc.) nanoparticles have been observed around the surface plasma resonance peaks in the visible region as a result of local-field enhancement [4, 5]. From the practical point of view, these particles have to be dispersed in a solid-state matrix, made of polymers or glasses, to form nanocomposites for the purposes of gaining the necessary stability and processability for making devices [6, 7]. Noble metal nanoparticle/organic polymer composite films are of particular interest because of their potential applications for photonics and electro-optics. Polymer matrices can prevent oxidation and coalescence of the particles and provide them with a long-time stability. As a result, the specific optical and electrical properties of the nanoparticles can be brought into full play, while the typical advantages of organic polymers (e.g., elasticity, transparency, relatively simple ways of synthesis, etc.) are retained in the composite films [8– 10]. Up to now, several methods have been developed for the fabrication of nanocomposite films containing noble metal nanoparticles dispersed in polymer matrix, including in-situ formation of nanoparticles in the matrix of a polymer film, simultaneous plasma polymerization associated with metal evaporation, thermal relaxation technique, etc. [11–16]. However, performance tailoring and optimization of the nanocomposite films are limited, because the factors that affect their performance, including size, shape, microstructure, aggregated structure and concentration of nanoparticles, structure and properties of polymer matrices, and interfacial structure of composites [3, 17, 18], are difficult to be controlled simultaneously by the above approaches. In an earlier report of the authors, a simple fabrication process was developed to obtain 0–3 polymer-based silver nanocomposite films through direct mixing of polymer solution with microemlusionsynthesized silver nanoparticles [19]. It was found that nanoparticles with different geometries (e.g. sphere

Preparation and characterization of polymer thin films containing silver and silver sulfide nanoparticles

Composite thin films consisting of nano-sized Ag particles dispersed in nylon 11 thin films have been prepared by using a thermal relaxation technique. The films obtained were characterized by transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray (EDX) microanalysis, and optical absorption spectroscopy. The Ag nanoparticles with 4.5–9.1 nm in diameter were found to be isolated individually and dispersed uniformly in the nylon 11 matrix. The volume fraction and the mean size of Ag nanoparticles in the film could be controlled by varying the initial amount of Ag deposition. Optical absorption peak due to the surface plasmon resonance of the Ag particles were observed around 430 nm and shifted to a longer wavelength with increasing the mean size of Ag nanoparticles, and absorbance increased simultaneously. We have also prepared Ag 2S nanoparticles with 4.7–11.2 nm in diameter in nylon 11 films from exposing the Ag/nylon 11 films to H 2S/O 2 mixed gas. ED patterns of the particles formed after the reaction with H 2S were completely indexed as those of β-Ag 2S with a monoclinic structure. The onset of the optical absorption spectra is similar to that of bulk β-Ag 2S, suggesting that Ag 2S nanoparticles with diameter of ca. 5nm preserve the band structure of bulk Ag 2S.

A novel method of preparing nano-sized gold and palladium particles dispersed in composites that uses the thermal relaxation technique

Stable nana-sized gold and palladium particles dispersed in composites were prepared by way of the thermal relaxation technique. Continuous formation and dispersion of metal particles into a nylon-11 oligomer film were achieved by the heating of the oligomer film to 46 °C during a vapor deposition of the metal. The mean particle size in the composite was 4.4 nm (S.D. = 1.7 nm) for the gold particles prepared by the deposition of about 3.6 × 1018 atoms cm−2. For the palladium particles the particle size was 2.3 nm (S.D. = 0.67 nm) and the deposition 4.2 × 1018 atoms cm−2. The obtained composite of gold or palladium particles was readily dissolved in CH2Cl2, producing stable colloidal solutions. The procedure reported here is very effective for preparing a great deal of metal particles dispersed in composites.

Synthesis and characterization of nano-sized gold-palladium bimetallic particles dispersed in polymer thin film matrix

We have prepared nano-sized Au/Pd bimetallic particles with various compositions dispersed in nylon 11 thin films by thermal relaxation technique. The films obtained were characterized by TEM, EDX, XPS and visible absorption spectroscopy. The Au/Pd molar ratio in the bimetallic particles could be varied over the entire composition range by controlling the initial deposition amount of constituent metals. It was found that the mean size of the dispersed particles decreased from 5.3 to 3.2 nm in diameter with increasing the Pd content in the bimetallic particles. Optical absorption due to surface plasmon resonance absorption of the Au particles decreased with decreasing the Au/Pd ratio, which can be caused by the changes in the band structure of the Au particles due to alloying with Pd.