Heat transfer in symmetric U-shaped microreactors for thin film calorimetry

Lopeandía, A. F.; Rodríguez‐Viejo, J.; Chacón, M.; Clavaguera-Mora, M.T.; Muñoz, Francisco

doi:10.1088/0960-1317/16/5/013

Cited by 38 publications

(19 citation statements)

References 18 publications

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“…45,46 Voltage raw data were converted into heat capacity curves following the procedure explained elsewhere. 47 A 100 nm aluminium plate was evaporated on the sensing area of the device in order to obtain a homogeneous thermal profile across the sample.…”

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confidence: 99%

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

Ràfols‐Ribé

González-Silveira

Rodríguez-Tinoco

et al. 2017

Phys. Chem. Chem. Phys.

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Physical vapour deposition (PVD) has settled in as an alternative method to prepare glasses with significantly enhanced properties, providing new insights into the understanding of glass transition. One of the striking properties of some PVD glasses is their transformation into liquid via a heterogeneous mechanism that initiates at surfaces/interfaces. Here, we use membrane-based fast-scanning nanocalorimetry (10 4 K s À1) to analyse the variables that govern the transformation mechanism of vapourdeposited toluene glasses with different stabilities. Thin films ranging from 20 to 250 nm were prepared at deposition temperatures between 0.70 and 1.15 times the glass transition temperature. We show how a propagating growth front is the initial transformation mechanism in all the vapour deposited samples, revealing a clear tendency to faster front velocities for less stable samples. Contrary to other glassformers such as indomethacin, toluene shows a one-to-one relationship between limiting fictive temperature and front velocity. We associate this behaviour with the much simpler molecular geometry of toluene, which would prevent the presence of strong preferential molecular arrangements in the glass. However, the propagation distance of the growth front before the homogenous transformation mechanism dominates the transition is found to be dependent on the preparation conditions rather than on the thermal stability of the glass. Understanding the link between the growth variables and the properties of PVD glasses is crucial for finding and developing potential applications of this type of glass.

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confidence: 99%

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

Ràfols‐Ribé

González-Silveira

Rodríguez-Tinoco

et al. 2017

Phys. Chem. Chem. Phys.

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“…Finally, different nanostructured contact geometries have been defined by using a nanostencil shadow mask. 11 Structural characterization of the samples has been performed by x-ray diffraction, AFM, and high resolution transmission electron microscope. The samples exhibit high crystalline quality with the STO͑001͒/LCMO͑001͒/STO͑001͒ epitaxial relationship and with sharp interfaces.…”

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confidence: 99%

Transport properties across the La2∕3Ca1∕3MnO3∕SrTiO3 heterointerface

Balcells

Abad

Rojas

et al. 2008

Journal of Applied Physics

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The transport properties across La 2/3 Ca 1/3 MnO 3 / SrTiO 3 ͑LCMO/STO͒ heterostructures with different thicknesses of the STO insulating barrier have been studied by using atomic force microscopy measurements in the current sensing ͑CS͒ mode. To avoid intrinsic problems of the CS method we have developed a nanostructured contact geometry of Au dots. The conduction process across the LCMO/STO interface exhibits the typical features of a tunneling process. The analysis of I͑V͒ curves by using the Simmons model allows us to determine the barrier height ͑ 0 Ϸ 0.6 eV͒ of STO barriers. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2833760͔Complex oxides have attracted much interest recently because they show a broad spectrum of intrinsic functionalities that allow envisaging the development of a new generation of oxide-based electronic, magnetic, and magnetoresistive devices. 1,2 Among them manganese perovskites occupy a prominent place due to their very peculiar properties, such as the colossal magnetoresistive response and the half metallic character. Nevertheless, the successful implementation of oxide-based devices requires preserving bulklike magnetic and transport properties at surfaces and interfaces. Thus, the physics and chemistry of surfaces and interfaces become a subject of primary interest since they can drastically modify magnetic and electronic properties reducing the performances of thin films and multilayered structures due to chemical inhomogeneity, strain, charge transfer, or spin exchange interactions. 3,4 Interfacial effects are especially relevant in manganitebased magnetic tunneling junctions where not only electronic but also magnetic properties are important. Due to the strong orbital-lattice coupling lattice strain effects may be very important in manganites 5 thus, playing a relevant role on the degradation of the magnetic properties. 6 However, other causes, such as polar discontinuity across the interface, may also be important. 7 In this sense, recent theoretical studies predict the appearance of electronic phase segregation with the formation of a spin-and orbital-ordered insulator phase at the manganite-insulator interface due to the reduction of carriers at the interface. 8 In this work we have carefully analyzed the transport properties across SrTiO 3 ͑STO͒ insulating barriers on top of La 2/3 Ca 1/3 MnO 3 ͑LCMO͒ films at room temperature by using atomic force microscopy ͑AFM͒ working in the current sensing ͑CS͒ mode. To avoid intrinsic problems of the CS method we have developed a nanostructured contact geometry of Au dots. The conduction process across the LCMO/ STO/Au heterostructure exhibits the typical features of a tunneling process. The analysis of I͑V͒ curves by using the Simmons model allows us to determine the barrier height, 0 Ϸ 0.6 eV, in good agreement with previous reports for STO tunneling barriers.LCMO epitaxial thin films of about 60 nm thick have been grown by rf sputtering on top of ͑001͒ STO substrates ͓T D = 800°C and a pressure of 330 mTorr ͑Ar+ 20% O 2...

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“…Traditional calorimetry has been well developed for bulk materials, but is not sensitive enough to perform measurements on nanoscale samples. Nanocalorimetry is a novel technique that has developed rapidly in recent years [2][3][4][5][6][7][8][9][10]. It enables ultrasensitive calorimetry measurements on very small samples of materials through use of micromachined sensors with vanishingly small thermal mass.…”

Section: Scanning Calorimetry and Nanocalorimetrymentioning

confidence: 99%

Scanning AC Nanocalorimetry and Its Applications

Xiao

Vlassak

2016

Fast Scanning Calorimetry

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This thesis presents an AC nanocalorimetry technique that enables calorimetry measurements on very small quantities of materials over a wide range of scanning rates (from isothermal to 3×10^3 K/s), temperatures (up to 1200 K), and environments. Such working range bridges the gap between traditional scanning calorimetry of bulk materials and nanocalorimetry. The method relies on a micromachined nanocalorimeter with negligible thermal lags between heater, thermometer, and sample. The ability to perform calorimetry measurements over such a broad range of scanning rates makes it an ideal tool to characterize the kinetics of phase transformations, reactions at elevated temperatures or to explore the behavior of materials far from equilibrium. We By combining scanning DC and AC nano-calorimetry techniques, we study the nucleation behavior of undercooled liquid Bi at cooling rates ranging from 10^1 to 10^4 K/s. Upon initial melting, the Bi thin-film sample breaks up into isolated islands. The number of islands in a typical sample is sufficiently large that highly repeatable nucleation behavior is observed, despite the stochastic nature of the nucleation process.We establish a data reduction technique to evaluate the nucleation rate from DC and AC calorimetry results. The results show that the driving force for the nucleation of melted Bi is well described by classical nucleation theory over a wide range of cooling rates. The proposed technique provides a unique and efficient way to examine nucleation kinetics v with cooling rates over several orders of magnitude. The technique is quite general and can be used to evaluate reaction kinetics in other materials.Lastly, we apply the scanning AC nanocalorimetry technique to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59±0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.vi

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Heat transfer in symmetric U-shaped microreactors for thin film calorimetry

Cited by 38 publications

References 18 publications

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

Transport properties across the La2∕3Ca1∕3MnO3∕SrTiO3 heterointerface

Scanning AC Nanocalorimetry and Its Applications

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