David Doblas

High-resolution thermal imaging with a combination of nano-focus X-ray diffraction and ultra-fast chip calorimetry

A microelectromechanical-systems-based calorimeter designed for use on a synchrotron nano-focused X-ray beamline is described. This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤100000 K s(-1)) and temperature modulation frequencies (≤1 kHz). The calorimeter was used for high-resolution thermal imaging of nanogram-sized samples subjected to X-ray-induced heating. For a 46 ng indium particle, the measured temperature rise reaches ∼0.2 K, and is directly correlated to the X-ray absorption. Thermal imaging can be useful for studies of heterogeneous materials exhibiting physical and/or chemical transformations. Moreover, the technique can be extended to three-dimensional thermal nanotomography.

Contrasting strategies to cope with drought by invasive and endemic species of Lantana in Galapagos

This study compares how Lantana camara, an invasive species, and L. peduncularis, an autochthonous one, cope with drought in Galapagos. Soil surface temperature was the abiotic environmental parameter that best explained variations in photosynthetic stress. Higher soil surface temperatures were recorded in the lowlands and in rain-shadow areas, which were also the driest areas. L. peduncularis, with a shallow root system, behaved as a drought-tolerant species, showing lower relative growth rates, which decreased with leaf water content and higher photosynthetic stress levels in the lowlands and in a northwest rain-shadow area in comparison with higher and wetter locations. Its basal and maximal fluorescences decreased at lower altitudes, reflecting the recorded drops in chlorophyll concentration. In contrast, L. camara with a deep root system behaved as a drought-avoiding species, showing leaf and relative water contents higher than 55% and avoiding permanent damage to its photosynthetic apparatus even in the driest area where it showed very low chlorophyll content. Its relative growth rate decreased more in dry areas in comparison to wetter zones than did that of L. peduncularis, even though it had greater water content. Furthermore, L. camara showed higher water contents, growth rate, and lower photosynthetic stress levels than L. peduncularis in the arid lowlands. Thus, L. peduncularis maintained lower maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) than L. camara even at sunrise, due to higher basal fluorescence values with similar maximal fluorescence, which indicated permanent damage to PSII reaction centres. Our results help to explain the success and limitations of L. camara in the invasion of arid and sub-arid environments.

Thermal Transformations of Self-Assembled Gold Glyconanoparticles Probed by Combined Nanocalorimetry and X-ray Nanobeam Scattering

Noble metal nanoparticles with ligand shells are of interest for applications in catalysis, thermo-plasmonics, and others, involving heating processes. To gain insight into the structure-formation processes in such systems, self-assembly of carbohydrate-functionalized gold nanoparticles during precipitation from solution and during further heating to ca. 340 °C was explored by in situ combination of nanobeam SAXS/WAXS and nanocalorimetry. Upon precipitation from solution, X-ray scattering reveals the appearance of small 2D domains of close-packed nanoparticles. During heating, increasing interpenetration of the nanoparticle soft shells in the domains is observed up to ca. 81 °C, followed by cluster formation at ca. 125 °C, which transform into crystalline gold nuclei at around 160 °C. Above ca. 200 °C, one observes the onset of coalescence and grain growth resulting in gold crystallites of average size of about 100 nm. The observed microstructural changes are in agreement with the in situ heat capacity measurements with nanocalorimetry.

Design of an In Situ Setup Combining Nanocalorimetry and Nano- or Micro-focus X-Ray Scattering to Address Fast Structure Formation Processes

In the present chapter, we describe an original experimental setup combining micro- or nano-focus X-ray scattering and chip calorimetry (nanocalorimetry), which is designed for simultaneous in situ measurements. Some technical aspects of the setup design regarding its adaptation to the sample environment specific to the nano- and micro-focus synchrotron beamlines are discussed in the first part. In the following, we provide examples of applications of the setup for thermal studies of inorganic and nanostructured hybrid systems with nano-focus X-ray diffraction. In the last part, we report for the first time on the in situ nanocalorimetry/fast micro-focus X-ray scattering experiments on a semicrystalline polymer using heating ramps of 2000 °C/s at the X-ray detector acquisition rate of 4 ms/frame. For such real-time combination, one has to employ fast X-ray detectors with a high photon efficiency. In addition, one would absolutely need intense sources of X-rays such as the ones provided at the ID beamlines of the ESRF. We show that the setup capable of simultaneously probing the microstructural and thermodynamic properties can be useful for studies of materials having complex thermal behavior. In particular, the microstructural evolution during fast heating of a typical aromatic polyester, poly(trimethylene terephthalate), can be analyzed in much detail, which sheds light on the long-standing issue of multiple melting behavior in semirigid-chain polymers.

Design of a Combined Setup for Simultaneous Measurements of the Microstructural and Thermo-Analytical Parameters of Nanogram-Size Samples

In the present paper, we describe an experimental setup combining micro- and nano-focus X-ray scattering and chip calorimetry (nanocalorimetry), which is designed for in-situ measurements on nanogram-size samples. Such combination of techniques capable to simultaneously probe the micro-structural and thermodynamic properties of materials can be useful for studies of materials having a complex phase behavior or prone to form metastable states. The setup is made compatible with micro- and nano-focus synchrotron beamlines.

Chip Calorimetry for the Sensitive Identification of Hexogen and Pentrite from Their Decomposition inside Copper Oxide Nanoparticles

Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.