TY - JOUR A1 - Pech May, Nelson Wilbur A1 - Lauster, T. A1 - Retsch, M. T1 - Design of Multimodal Absorption in the Mid-IR: A Metal Dielectric Metal Approach JF - ACS Appl. Mater. Interfaces N2 - Specific control on the mid-infrared (mid-IR) Emission properties is attracting increasing attention for thermal camouflage and passive cooling applications. Metal−dielectric−metal (MDM) structures are well known to support strong magnetic polariton resonances in the optical and near-infrared range. We extend the current understanding of such an MDM structure by specifically designing Au disc arrays on top of ZnS−Au−Si substrates and pushing their resonances to the mid-IR regime. Therefore, we combine fabrication via lift-off photolithography with the finite element method and an inductance−capacitance model. With this combination of techniques, we demonstrate that the magnetic polariton resonance of the first order strongly depends on the individual disc diameter. Furthermore, the fabrication of multiple discs within one unit cell allows a linear combination of the fundamental resonances to conceive broadband absorptance. Quite importantly, even in mixed resonator cases, the absorptance spectra can be fully described by a superposition of the individual disc properties. Our contribution provides rational guidance to deterministically design mid-IR emitting materials with specific narrow- or broadband properties. KW - Mid-IR absorption KW - Thermal emission PY - 2021 DO - https://doi.org/10.1021/acsami.0c18160 VL - 13 IS - 1 SP - 1921 EP - 1929 PB - ACS Publications AN - OPUS4-52070 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Forero-Sandoval, I. A1 - Cervantes-Alvarez, F. A1 - Ramirez-Rincon, J. A1 - Macias, J. A1 - Pech May, Nelson Wilbur A1 - Ordonez-Miranda, J. A1 - Alvarado-Gil, J. T1 - Percolation Threshold of the Thermal, Electrical and Optical Properties of Carbonyl-Iron Microcomposites JF - Applied Composite Materials N2 - Composites made up of microparticles embedded in a polymeric matrix have attracted increasing attention due to the possibility of tailoring their physical properties by adding the adequate quantity of fillers. As the concentration of these fillers increases, their connectivity changes drastically at a given threshold and therefore the electrical, thermal and optical properties of these composites are expected to exhibit a percolation effect. In this work, the thermal and electrical conductivities along with the emissivity of Composites composed of carbonyl-iron microparticles randomly distributed in a polyester resin matrix are measured, for volume fractions ranging from 0 to 0.55. It is shown that both the thermal and electrical conductivities increase with the particles’ concentration, such that their percolation threshold appears at volume fractions of 0.46 and 0.38, respectively. The emissivity, on the other hand, decreases as the fillers’ concentration increases, such that it exhibits a substantial decay at a volume fraction of 0.41. The percolation threshold of the emissivity is thus higher than that of the thermal conductivity, but lower than the electrical conductivity one. This dispersion on the percolation concentration is justified by the different physical mechanisms required to activate the electrical, thermal, and optical responses of the considered composites. The obtained results thus show that the percolation phenomenon can efficiently be used to enhance or reduce the physical properties of particulate composites. KW - Thermal conductivity KW - Emissivity KW - Thermal percolation threshold PY - 2021 DO - https://doi.org/10.1007/s10443-021-09869-z VL - 28 IS - 2 SP - 447 EP - 463 PB - Springer AN - OPUS4-52355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tran, T. A1 - Kodisch, C. A1 - Schöttle, M. A1 - Pech May, Nelson Wilbur A1 - Retsch, M. T1 - Characterizing the thermal diffusivity of single, micrometer-sized fibers via high-resolution lock-in thermography JF - The journal of physical chemistry C N2 - Many advanced materials consist of fibers. They are used as nonwovens, fabrics, or in composite materials. Characterization of individual fibers allows us to predict resulting material properties. We present a measurement setup and analysis software to characterize individual, micrometer-sized fibers fast and reliably. The setup is based on the lock-in thermography principle. Thermal diffusivity values of seven reference samples agree very well with previously reported values. We use our setup to investigate critical measurement parameters like excitation frequency, excitation power, pixel size, and fiber orientation. Our results show that fibers with subpixel diameters can be measured even if they are not aligned. However, special care has to be taken to choose an adequate excitation power. Measurements at high intensities can underestimate thermal diffusivity even though the raw data looks reasonable. By automatically measuring at different excitation powers, our setup solves this issue. KW - Surfaces, coatings and films KW - Physical and theoretical chemistry KW - General energy KW - Electronic, optical and magnetic materials PY - 2022 DO - https://doi.org/10.1021/acs.jpcc.2c04254 SN - 1932-7455 VL - 126 IS - 32 SP - 14003 EP - 14010 PB - American Chemical Society (ACS) CY - Washington, DC AN - OPUS4-58128 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pech May, Nelson Wilbur A1 - Tabasco-Novelo, Carolina A1 - Quintana, Patricia A1 - Rodriguez-Gattorno, Geonel A1 - Alvarado-Gil, Juan J. T1 - Evidence of a Thermal Diffusivity Gap in Sintered Li–Co–Sb–O Solid Solutions JF - ACS Omega N2 - In this work, the thermal properties of ternary Li₃ₓCo₇₋₄ₓSb₂₊ₓO₁₂ solid solutions are studied for different concentrations in the range 0 ≤ x ≤ 0.7. Samples are elaborated at four different sintering temperatures: 1100, 1150, 1200 and 1250 °C. The effect of increasing the content of Li⁺ and Sb⁵⁺, accompanied by the reduction of Co²⁺, on the thermal properties is studied. It is shown that a thermal diffusivity gap, which is more pronounced for low values of x, can be triggered at a certain threshold sintering temperature (around 1150 °C in this study). This effect is explained by the increase of contact area between adjacent grains. Nevertheless, this effect is found to be less pronounced in the thermal conductivity. Moreover, a new framework for heat diffusion in solids is presented that establishes that both the heat flux and the thermal energy (or heat) satisfy a diffusion equation and therefore highlights the importance of thermal diffusivity in transient heat conduction phenomena. KW - General Chemical Engineering KW - General Chemistry PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-593248 DO - https://doi.org/10.1021/acsomega.2c07557 SN - 2470-1343 VL - 8 IS - 8 SP - 7808 EP - 7815 PB - American Chemical Society (ACS) CY - Washington, DC AN - OPUS4-59324 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -