Staff directory
Marianna Sledzinska
Research Engineer
marianna.sledzinska(ELIMINAR)@icn2.cat
Thermal Properties of Nanoscale Materials
- ORCID: 0000-0001-8592-1121
Publications
2024
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Imperfect phononic crystals work too: The effect of translational and mid-plane symmetry breaking on hypersound propagation
Babacic, Visnja; Sledzinska, Marianna; Vasileiadis, Thomas; Torres, Clivia M Sotomayor; Graczykowski, Bartlomiej Apl Materials; 12 (4): 041108. 2024. 10.1063/5.0189694.
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MoS2 phononic crystals for advanced thermal management
Xiao, Peng; El Sachat, Alexandros; Angel, Emigdio Chavez; Ng, Ryan C; Nikoulis, Giorgos; Kioseoglou, Joseph; Termentzidis, Konstantinos; Sotomayor Torres, Clivia M; Sledzinska, Marianna Science Advances; 10 (13): eadm8825. 2024. 10.1126/sciadv.adm8825.
2023
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Enhanced Thermal Conductivity of Free-Standing Double-Walled Carbon Nanotube Networks
Mehew, JD; Timmermans, MY; Reig, DS; Sergeant, S; Sledzinska, M; Chávez-Angel, E; Gallagher, E; Torres, CMS; Huyghebaert, C; Tielrooij, KJ Acs Applied Materials & Interfaces; 15 (44): 51876 - 51884. 2023. 10.1021/acsami.3c09210. IF: 9.500
2022
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Effect of crystallinity and thickness on thermal transport in layered PtSe2
El Sachat A., Xiao P., Donadio D., Bonell F., Sledzinska M., Marty A., Vergnaud C., Boukari H., Jamet M., Arregui G., Chen Z., Alzina F., Sotomayor Torres C.M., Chavez-Angel E. npj 2D Materials and Applications; 6 (1, 32) 2022. 10.1038/s41699-022-00311-x.
We present a comparative investigation of the influence of crystallinity and film thickness on the acoustic and thermal properties of layered PtSe2 films of varying thickness (1–40 layers) using frequency-domain thermo-reflectance, low-frequency Raman, and pump-probe coherent phonon spectroscopy. We find ballistic cross-plane heat transport up to ~30 layers PtSe2 and a 35% reduction in the cross-plane thermal conductivity of polycrystalline films with thickness larger than 20 layers compared to the crystalline films of the same thickness. First-principles calculations further reveal a high degree of thermal conductivity anisotropy and a remarkable large contribution of the optical phonons to the thermal conductivity in bulk (~20%) and thin PtSe2 films (~30%). Moreover, we show strong interlayer interactions in PtSe2, short acoustic phonon lifetimes in the range of picoseconds, an out-of-plane elastic constant of 31.8 GPa, and a layer-dependent group velocity ranging from 1340 ms−1 in bilayer to 1873 ms−1 in eight layers of PtSe2. The potential of tuning the lattice thermal conductivity of layered materials with the level of crystallinity and the real-time observation of coherent phonon dynamics open a new playground for research in 2D thermoelectric devices and provides guidelines for thermal management in 2D electronics. © 2022, The Author(s).
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Excitation and detection of acoustic phonons in nanoscale systems
Ng R.C., El Sachat A., Cespedes F., Poblet M., Madiot G., Jaramillo-Fernandez J., Florez O., Xiao P., Sledzinska M., Sotomayor-Torres C.M., Chavez-Angel E. Nanoscale; 2022. 10.1039/d2nr04100f.
Phonons play a key role in the physical properties of materials, and have long been a topic of study in physics. While the effects of phonons had historically been considered to be a hindrance, modern research has shown that phonons can be exploited due to their ability to couple to other excitations and consequently affect the thermal, dielectric, and electronic properties of solid state systems, greatly motivating the engineering of phononic structures. Advances in nanofabrication have allowed for structuring and phonon confinement even down to the nanoscale, drastically changing material properties. Despite developments in fabricating such nanoscale devices, the proper manipulation and characterization of phonons continues to be challenging. However, a fundamental understanding of these processes could enable the realization of key applications in diverse fields such as topological phononics, information technologies, sensing, and quantum electrodynamics, especially when integrated with existing electronic and photonic devices. Here, we highlight seven of the available methods for the excitation and detection of acoustic phonons and vibrations in solid materials, as well as advantages, disadvantages, and additional considerations related to their application. We then provide perspectives towards open challenges in nanophononics and how the additional understanding granted by these techniques could serve to enable the next generation of phononic technological applications. © 2022 The Royal Society of Chemistry.
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Exciton tuning and strain imaging in WS2 supported on PDMS micropillars
Sledzinska, M; Xiao, P; Vilardell, EP; Angel, EC; Esplandiu, MJ; Torres, CMS Applied Physics Letters; 121 (25) 2022. 10.1063/5.0130927. IF: 3.971
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Heat dissipation in few-layer MoS2and MoS2/hBN heterostructure
Arrighi A., Del Corro E., Urrios D.N., Costache M.V., Sierra J.F., Watanabe K., Taniguchi T., Garrido J.A., Valenzuela S.O., Sotomayor Torres C.M., Sledzinska M. 2D Materials; 9 (1, 015005) 2022. 10.1088/2053-1583/ac2e51. IF: 7.103
State-of-the-art fabrication and characterisation techniques have been employed to measure the thermal conductivity of suspended, single-crystalline MoS2 and MoS2/hBN heterostructures. Two-laser Raman scattering thermometry was used combined with real time measurements of the absorbed laser power. Measurements on MoS2 layers with thicknesses of 5 and 14 nm exhibit thermal conductivity in the range between 12 Wm-1 K-1 and 24 Wm-1 K-1. Additionally, after determining the thermal conductivity of the latter MoS2 sample, an hBN flake was transferred onto it and the effective thermal conductivity of the heterostructure was subsequently measured. Remarkably, despite that the thickness of the hBN layer was less than a hal of the thickness of the MoS2 layer, the heterostructure showed an almost eight-fold increase in the thermal conductivity, being able to dissipate more than ten times the laser power without any visible sign of damage. These results are consistent with a high thermal interface conductance G between MoS2 and hBN and an efficient in-plane heat spreading driven by hBN. Indeed, we estimate G ∼ 70 MW m-2 K-1 for hBN layer thermal conductivity of 450 Wm-1 K-1 which is significantly higher than previously reported values. Our work therefore demonstrates that the insertion of hBN layers in potential MoS2-based devices holds the promise for efficient thermal management. © 2021 IOP Publishing Ltd.
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Unraveling Heat Transport and Dissipation in Suspended MoSe2 from Bulk to Monolayer
Saleta Reig D., Varghese S., Farris R., Block A., Mehew J.D., Hellman O., Woźniak P., Sledzinska M., El Sachat A., Chávez-Ángel E., Valenzuela S.O., van Hulst N.F., Ordejón P., Zanolli Z., Sotomayor Torres C.M., Verstraete M.J., Tielrooij K.-J. Advanced Materials; 34 (10, 2108352) 2022. 10.1002/adma.202108352. IF: 30.849
Understanding heat flow in layered transition metal dichalcogenide (TMD) crystals is crucial for applications exploiting these materials. Despite significant efforts, several basic thermal transport properties of TMDs are currently not well understood, in particular how transport is affected by material thickness and the material's environment. This combined experimental–theoretical study establishes a unifying physical picture of the intrinsic lattice thermal conductivity of the representative TMD MoSe2. Thermal conductivity measurements using Raman thermometry on a large set of clean, crystalline, suspended crystals with systematically varied thickness are combined with ab initio simulations with phonons at finite temperature. The results show that phonon dispersions and lifetimes change strongly with thickness, yet the thinnest TMD films exhibit an in-plane thermal conductivity that is only marginally smaller than that of bulk crystals. This is the result of compensating phonon contributions, in particular heat-carrying modes around ≈0.1 THz in (sub)nanometer thin films, with a surprisingly long mean free path of several micrometers. This behavior arises directly from the layered nature of the material. Furthermore, out-of-plane heat dissipation to air molecules is remarkably efficient, in particular for the thinnest crystals, increasing the apparent thermal conductivity of monolayer MoSe2 by an order of magnitude. These results are crucial for the design of (flexible) TMD-based (opto-)electronic applications. © 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH
2021
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Anisotropic Thermal Conductivity of Crystalline Layered SnSe2
Xiao P., Chavez-Angel E., Chaitoglou S., Sledzinska M., Dimoulas A., Sotomayor Torres C.M., El Sachat A. Nano Letters; 21 (21): 9172 - 9179. 2021. 10.1021/acs.nanolett.1c03018. IF: 11.189
The degree of thermal anisotropy affects critically key device-relevant properties of layered two-dimensional materials. Here, we systematically study the in-plane and cross-plane thermal conductivity of crystalline SnSe2 films of varying thickness (16-190 nm) and uncover a thickness-independent thermal conductivity anisotropy ratio of about ∼8.4. Experimental data obtained using Raman thermometry and frequency domain thermoreflectance showed that the in-plane and cross-plane thermal conductivities monotonically decrease by a factor of 2.5 with decreasing film thickness compared to the bulk values. Moreover, we find that the temperature-dependence of the in-plane component gradually decreases as the film becomes thinner, and in the range from 300 to 473 K it drops by more than a factor of 2. Using the mean free path reconstruction method, we found that phonons with MFP ranging from ∼1 to 53 and from 1 to 30 nm contribute to 50% of the total in-plane and cross-plane thermal conductivity, respectively. © 2021 The Authors. Published by American Chemical Society.
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Electron beam lithography for direct patterning of MoS2on PDMS substrates
Jumbert G., Placidi M., Alzina F., Sotomayor Torres C.M., Sledzinska M. RSC Advances; 11 (32): 19908 - 19913. 2021. 10.1039/d1ra00885d. IF: 3.361
Precise patterning of 2D materials into micro- and nanostructures presents a considerable challenge and many efforts are dedicated to the development of processes alternative to the standard lithography. In this work we show a fabrication technique based on direct electron beam lithography (EBL) on MoS2on polydimethylsiloxane (PDMS) substrates. This easy and fast method takes advantage of the interaction of the electron beam with the PDMS, which at high enough doses leads to cross-linking and shrinking of the polymer. At the same time, the adhesion of MoS2to PDMS is enhanced in the exposed regions. The EBL acceleration voltages and doses are optimized in order to fabricate well-defined microstructures, which can be subsequently transferred to either a flexible or a rigid substrate, to obtain the negative of the exposed image. The reported procedure greatly simplifies the fabrication process and reduces the number of steps compared to standard lithography and etching. As no additional polymer, such as polymethyl methacrylate (PMMA) or photoresists, are used during the whole process the resulting samples are free of residues. © The Royal Society of Chemistry 2021.
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Fabrication and characterization of large-area suspended MoSe2 crystals down to the monolayer
Varghese S., Reig D.S., Mehew J.D., Block A., El Sachat A., Chávez-Ángel E., Sledzinska M., Ballesteros B., Sotomayor Torres C.M., Tielrooij K.-J. JPhys Materials; 4 (4, 046001) 2021. 10.1088/2515-7639/ac2060. IF: 0.000
Many layered materials, such as graphene and transition metal dichalcogenides, can be exfoliated down to atomic or molecular monolayers. These materials exhibit exciting material properties that can be exploited for several promising device concepts. Thinner materials lead to an increased surface-to-volume ratio, with mono- and bi-layers being basically pure surfaces. Thin crystals containing more than two layers also often behave as an all-surface material, depending on the physical property of interest. As a result, flakes of layered materials are typically highly sensitive to their environment, which is undesirable for a broad range of studies and potential devices. Material systems based on suspended flakes overcome this issue, yet often require complex fabrication procedures. Here, we demonstrate the relatively straightforward fabrication of exfoliated MoSe2 flakes down to the monolayer, suspended over unprecedentedly large holes with a diameter of 15 µm. We describe our fabrication methods in detail, present characterization measurements of the fabricated structures, and, finally, exploit these suspended flakes for accurate optical absorption measurements. © 2021 The Author(s).
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Optomechanical crystals for spatial sensing of submicron sized particles
Navarro-Urrios D., Kang E., Xiao P., Colombano M.F., Arregui G., Graczykowski B., Capuj N.E., Sledzinska M., Sotomayor-Torres C.M., Fytas G. Scientific Reports; 11 (1, 7829) 2021. 10.1038/s41598-021-87558-4. IF: 4.380
Optomechanical crystal cavities (OMC) have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of OMCs operating under ambient conditions as a sensor of submicrometer particles by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region. OMCs have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, viruses and bacteria. © 2021, The Author(s).
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Reversing the Humidity Response of MoS2- And WS2-Based Sensors Using Transition-Metal Salts
Xiao P., Mencarelli D., Chavez-Angel E., Joseph C.H., Cataldo A., Pierantoni L., Sotomayor Torres C.M., Sledzinska M. ACS Applied Materials and Interfaces; 13 (19): 23201 - 23209. 2021. 10.1021/acsami.1c03691. IF: 9.229
Two-dimensional materials, such as transition-metal dichalcogenides (TMDs), are attractive candidates for sensing applications due to their high surface-to-volume ratio, chemically active edges, and good electrical properties. However, their electrical response to humidity is still under debate and experimental reports remain inconclusive. For instance, in different studies, the impedance of MoS2-based sensors has been found to either decrease or increase with increasing humidity, compromising the use of MoS2 for humidity sensing. In this work, we focus on understanding the interaction between water and TMDs. We fabricated and studied humidity sensors based on MoS2 and WS2 coated with copper chloride and silver nitrate. The devices exhibited high chemical stability and excellent humidity sensing performance in relative humidity between 4 and 80%, with response and recovery times of 2 and 40 s, respectively. We have systematically investigated the humidity response of the materials as a function of the type and amount of induced metal salt and observed the reverse action of sensing mechanisms. This phenomenon is explained based on a detailed structural analysis of the samples considering the Grotthuss mechanism in the presence of charge trapping, which was represented by an appropriate lumped-element model. Our findings open up a possibility to tune the electrical response in a facile manner and without compromising the high performance of the sensor. They offer an insight into the time-dependent performance and aging of the TMD-based sensing devices. © 2021 American Chemical Society.
2020
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2D Phononic Crystals: Progress and Prospects in Hypersound and Thermal Transport Engineering
Sledzinska M., Graczykowski B., Maire J., Chavez-Angel E., Sotomayor-Torres C.M., Alzina F. Advanced Functional Materials; 30 (8, 1904434) 2020. 10.1002/adfm.201904434. IF: 16.836
The central concept in phononics is the tuning of the phonon dispersion relation, or phonon engineering, which provides a means of controlling related properties such as group velocity or phonon interactions and, therefore, phonon propagation, in a wide range of frequencies depending on the geometries and sizes of the materials. Phononics exploits the present state of the art in nanofabrication to tailor dispersion relations in the range of GHz for the control of elastic waves/phonons propagation with applications toward new information technology concepts with phonons as state variable. Moreover, phonons provide an adaptable approach for supporting a coherent coupling between different state variables, and the development of nanoscale optomechanical systems during the last decade attests this prospect. The most extended approach to manipulate the phonon dispersion relation is introducing an artificial periodic modulation of the elastic properties, which is referred to as phononic crystal (PnC). Herein, the focus is on the recent experimental achievements in the fabrication and application of 2D PnCs enabling the modification of the dispersion relation of surface and membrane modes, and presenting phononic bandgaps, waveguiding, and confinement in the hypersonic regime. Furthermore, these artificial materials offer the potential of modifying and controlling the heat flow to enable new schemes in thermal management. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Fracturing of Polycrystalline MoS2 Nanofilms
Marianna Sledzinska, Gil Jumbert, Marcel Placidi, Alois Arrighi, Peng Xiao, Francesc Alzina, Clivia M. Sotomayor Torres Acs Applied Electronic Materials. 2 (4): 1169-1175; 2 (4): 1169 - 1175. 2020. 10.1021/acsaelm.0c00189. IF: 0.000
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Graphene related materials for thermal management
Fu Y., Hansson J., Liu Y., Chen S., Zehri A., Samani M.K., Wang N., Ni Y., Zhang Y., Zhang Z.-B., Wang Q., Li M., Lu H., Sledzinska M., Torres C.M.S., Volz S., Balandin A.A., Xu X., Liu J. 2D Materials; 7 (1, 012001) 2020. 10.1088/2053-1583/ab48d9. IF: 7.140
Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field. © 2019 IOP Publishing Ltd.
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High-temperature silicon thermal diode and switch
Kasprzak M., Sledzinska M., Zaleski K., Iatsunskyi I., Alzina F., Volz S., Sotomayor Torres C.M., Graczykowski B. Nano Energy; 78 (105261) 2020. 10.1016/j.nanoen.2020.105261. IF: 16.602
A thermal rectifier/diode is a nonreciprocal element or system that enables preferential heat transport in one direction. In this work we demonstrate a single-material thermal diode operating at high temperatures. The diode is made of nanostructured silicon membranes exhibiting spatially and temperature-dependent thermal conductivity and, therefore, falling into the category of spatially asymmetric, nonlinear nonreciprocal systems. We used an all-optical state-of-the-art experimental technique to prove rectification along rigorous criteria of the phenomenon. Using sub-milliwatt power we achieve rectification of about 14%. In addition, we demonstrate air-triggered thermal switching and passive cooling. Our findings provide a CMOS-compatible platform for heat rectification and applications in energy harvesting, thermal insulation and cooling, as well as sensing and potentially thermal logic. © 2020 The Authors
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Nanoscale Mapping of Thermal and Mechanical Properties of Bare and Metal-Covered Self-Assembled Block Copolymer Thin Films
Alexandros El Sachat, Jean Spièce, Charalambos Evangeli, Alexander James Robson, Martin Kreuzer, Maria R. Rodríguez-Laguna, Emigdio Chavez, Marianna Sledzinska, Clivia M. Sotomayor Torres, Oleg V. Kolosov, Francesc Alzina Acs Applied Polymer Materials; 2 (2): 487 - 496. 2020. 10.1021/acsapm.9b00924. IF: 0.000
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Thermal transport in nanoporous holey silicon membranes investigated with optically induced transient thermal gratings
Ryan A. Duncan, Giuseppe Romano, Marianna Sledzinska, Alexei A. Maznev, Jean-Philippe M. Péraud, Olle Hellman, Clivia M. Sotomayor Torres, and Keith A. Nelson Journal of Applied Physics; 128 (235106) 2020. 10.1063/1.5141804. IF: 2.546
In this study, we use transient thermal gratings—a non-contact, laser-based thermal metrology technique with intrinsically high accuracy—to investigate room-temperature phonon-mediated thermal transport in two nanoporous holey silicon membranes with limiting dimensions of 120 nm and 250 nm, respectively. We compare the experimental results with ab initio calculations of phonon-mediated thermal transport according to the phonon Boltzmann transport equation (BTE) using two different computational techniques. We find that the calculations conducted within the Casimir framework, i.e., based on the BTE with the bulk phonon dispersion and diffuse scattering from surfaces, are in quantitative agreement with the experimental data and thus conclude that this framework is adequate for describing phonon-mediated thermal transport in silicon nanostructures with feature sizes of the order of 100 nm.
2019
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Phonon transport in disordered 2D phononic crystals
Sledzinska M., Graczykowski B., Lacroix D., Alzina F., Termentzidis K., Melia U., Torres C.M.S. 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO; (8873407) 2019. 10.1109/CLEOE-EQEC.2019.8873407.
Phonon transport in 2D phononic crystals has attracted attention due to the possibility to control (a) the heat flow, i.e., achieving directional phonon transport, that is of relevance for diode-like behaviour, and (b) controlling the thermal conductivity over orders of magnitude, which is of interest for thermoelectric applications. In recent years the most important research questions have been: (i) to what degree the thermal transport depends on its nature (ballistic or diffusive)? and consensus is emerging that at room temperature phonon transport is diffusive. (ii) In a patterned suspended membrane what is the role of the porosity and surface roughness? [1]. Published results suggest that it is the roughness and the surface to volume ratio of the holes (pores) making up the phononic crystal. [2] (iii) What is the role of spatial [3] and phase disorder, such as native oxides and amorphous shells [4], in 2D phononic crystals? The latter still being an open question where the roles of filling factors and geometry are being discussed. To understand these issues, it is paramount to be aware of the various length scales, the mean-free path distribution, which is strongly temperature dependent, the suspended membrane thickness and its surface roughness. Furthermore, the boundary conditions, the interplay of diffusive (scattering relevant) and specular (phase relevant) transport, are crucial for the data treatment and comparison to models. Finally, the measurements methods need to be carefully compared, as assumptions on all of the above will make the analysis rather intricate and comparison meaningless. © 2019 IEEE.
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Thermal conductivity in disordered porous nanomembranes
Sledzinska M., Graczykowski B., Alzina F., Melia U., Termentzidis K., Lacroix D., Sotomayor Torres C.M. Nanotechnology; 30 (26, 265401) 2019. 10.1088/1361-6528/ab0ecd. IF: 3.399
In this work we study the effects of disorder on the thermal conductivity of porous 100 nm thick silicon membranes, in which the size, shape and position of the pores were varied randomly. Measurements using two-laser Raman thermometry on both non-patterned and porous membranes revealed more than a 10-fold reduction of the thermal conductivity compared to that of bulk silicon and a six-fold reduction compared to non-patterned membranes for the sample with random pore shapes. Using Monte Carlo methods we solved the Boltzmann transport equation for phonons and compared different possibilities of pore organization and its influence on the thermal conductivity of the samples. The simulations confirmed that the strongest reduction of thermal conductivity is achieved for a distribution of pores with arbitrary shapes that partially overlap. Up to a 15% reduction of the thermal conductivity with respect to the purely circular pores was predicted for a porous membrane with 37% filling fraction. The effect of the pore shape and distribution was further studied. Maps of temperature and heat flux distributions clearly showed that for particular pore placement heat transport can be efficiently blocked and hot spots can be found in narrow channels between pores. These findings have an impact on the fabrication of membrane-based thermoelectric devices, where low thermal conductivity is required. This work shows that for porous membranes with a given filling fraction the thermal conductivity can be further modified by introducing disorder in the shape and placement of the pores. © 2019 IOP Publishing Ltd.
2018
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Mechanisms behind the enhancement of thermal properties of graphene nanofluids
Rodríguez-Laguna M.R., Castro-Alvarez A., Sledzinska M., Maire J., Costanzo F., Ensing B., Pruneda M., Ordejón P., Sotomayor Torres C.M., Gómez-Romero P., Chávez-Ángel E. Nanoscale; 10 (32): 15402 - 15409. 2018. 10.1039/c8nr02762e. IF: 7.233
While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties. © The Royal Society of Chemistry.
2017
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Elastic Properties of Few Nanometers Thick Polycrystalline MoS2 Membranes: A Nondestructive Study
Graczykowski B., Sledzinska M., Placidi M., Saleta Reig D., Kasprzak M., Alzina F., Sotomayor Torres C.M. Nano Letters; 17 (12): 7647 - 7651. 2017. 10.1021/acs.nanolett.7b03669. IF: 12.712
The performance gain-oriented nanostructurization has opened a new pathway for tuning mechanical features of solid matter vital for application and maintained performance. Simultaneously, the mechanical evaluation has been pushed down to dimensions way below 1 μm. To date, the most standard technique to study the mechanical properties of suspended 2D materials is based on nanoindentation experiments. In this work, by means of micro-Brillouin light scattering we determine the mechanical properties, that is, Young modulus and residual stress, of polycrystalline few nanometers thick MoS2 membranes in a simple, contact-less, nondestructive manner. The results show huge elastic softening compared to bulk MoS2, which is correlated with the sample morphology and the residual stress. © 2017 American Chemical Society.
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Mechanical oscillations in lasing microspheres
Toncelli A., Capuj N.E., Garrido B., Sledzinska M., Sotomayor-Torres C.M., Tredicucci A., Navarro-Urrios D. Journal of Applied Physics; 122 (5, 053101) 2017. 10.1063/1.4997182. IF: 2.068
We investigate the feasibility of activating coherent mechanical oscillations in lasing microspheres by modulating the laser emission at a mechanical eigenfrequency. To this aim, 1.5%Nd3+:Barium- Titanium-Silicate microspheres with diameters around 50 lm were used as high quality factor (Q>106) whispering gallery mode lasing cavities. We have implemented a pump-and-probe technique in which the pump laser used to excite the Nd3+ ions is focused on a single microsphere with a microscope objective and a probe laser excites a specific optical mode with the evanescent field of a tapered fibre. The studied microspheres show monomode and multi-mode lasing action, which can be modulated in the best case up to 10 MHz. We have optically transduced thermally activated mechanical eigenmodes appearing in the 50-70MHz range, the frequency of which decreases with increasing the size of the microspheres. In a pump-and-probe configuration, we observed modulation of the probe signal up to the maximum pump modulation frequency of our experimental setup, i.e., 20 MHz. This modulation decreases with frequency and is unrelated to lasing emission, pump scattering, or thermal effects. We associate this effect to free-carrier-dispersion induced by multiphoton pump light absorption. On the other hand, we conclude that, in our current experimental conditions, it was not possible to resonantly excite the mechanical modes. Finally, we discuss on how to overcome these limitations by increasing the modulation frequency of the lasing emission and decreasing the frequency of the mechanical eigenmodes displaying a strong degree of optomechanical coupling.
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Modification of thermal conductivity and phonon dispersion relation by means of phononic crystals
Sledzinska M., Sachat A.E., Reparaz J.S., Wagner M.R., Alzina F., Torres C.M.S. THERMINIC 2017 - 23rd International Workshop on Thermal Investigations of ICs and Systems; 2017-January: 1 - 4. 2017. 10.1109/THERMINIC.2017.8233817.
Heat conduction in silicon can be effectively reduced by means of periodic patterning of free-standing membranes. In this work we show a straightforward method for fabrication of free-standing phononic crystals based on thin silicon membranes. We use the contactless two-laser Raman thermometry method to measure thermal conductivity of the hexagonal phononic crystals. The aim of the study is to understand and control the behaviour of phonons in phononic crystals, with the target of minimizing the thermal conductivity. In particular, we are interested in the influence of the surface-to-volume ratio on the thermal conductivity. © 2017 IEEE.
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Nonlinear dynamics and chaos in an optomechanical beam
Navarro-Urrios D., Capuj N.E., Colombano M.F., Garciá P.D., Sledzinska M., Alzina F., Griol A., Martínez A., Sotomayor-Torres C.M. Nature Communications; 8 ( 14965) 2017. 10.1038/ncomms14965. IF: 12.124
Optical nonlinearities, such as thermo-optic mechanisms and free-carrier dispersion, are often considered unwelcome effects in silicon-based resonators and, more specifically, optomechanical cavities, since they affect, for instance, the relative detuning between an optical resonance and the excitation laser. Here, we exploit these nonlinearities and their intercoupling with the mechanical degrees of freedom of a silicon optomechanical nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser we demonstrate accurate control to activate two- A nd four-dimensional limit cycles, a period-doubling route and a six-dimensional chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between two- A nd four-dimensional limit cycles, between different coherent mechanical states and between four-dimensional limit cycles and chaos. Our findings open new routes towards exploiting silicon-based optomechanical photonic crystals as a versatile building block to be used in neurocomputational networks and for chaos-based applications. © 2017 The Author(s).
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Record Low Thermal Conductivity of Polycrystalline MoS2 Films: Tuning the Thermal Conductivity by Grain Orientation
Sledzinska M., Quey R., Mortazavi B., Graczykowski B., Placidi M., Saleta Reig D., Navarro-Urrios D., Alzina F., Colombo L., Roche S., Sotomayor Torres C.M. ACS Applied Materials and Interfaces; 9 (43): 37905 - 37911. 2017. 10.1021/acsami.7b08811. IF: 7.504
We report a record low thermal conductivity in polycrystalline MoS2 obtained for ultrathin films with varying grain sizes and orientations. By optimizing the sulfurization parameters of nanometer-thick Mo layers, five MoS2 films containing a combination of horizontally and vertically oriented grains, with respect to the bulk (001) monocrystal, were grown. From transmission electron microscopy, the average grain size, typically below 10 nm, and proportion of differently oriented grains were extracted. The thermal conductivity of the suspended samples was extracted from a Raman laser-power-dependent study, and the lowest value of thermal conductivity of 0.27 W m-1 K-1, which reaches a similar value as that of Teflon, is obtained in a polycrystalline sample formed by a combination of horizontally and vertically oriented grains in similar proportion. Analysis by means of molecular dynamics and finite element method simulations confirm that such a grain arrangement leads to lower grain boundary conductance. We discuss the possible use of these thermal insulating films in the context of electronics and thermoelectricity. © 2017 American Chemical Society.
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Thermal conductivity and air-mediated losses in periodic porous silicon membranes at high temperatures
Graczykowski B., El Sachat A., Reparaz J.S., Sledzinska M., Wagner M.R., Chavez-Angel E., Wu Y., Volz S., Wu Y., Alzina F., Sotomayor Torres C.M. Nature Communications; 8 (1, 415) 2017. 10.1038/s41467-017-00115-4. IF: 12.124
Heat conduction in silicon can be effectively engineered by means of sub-micrometre porous thin free-standing membranes. Tunable thermal properties make these structures good candidates for integrated heat management units such as waste heat recovery, rectification or efficient heat dissipation. However, possible applications require detailed thermal characterisation at high temperatures which, up to now, has been an experimental challenge. In this work we use the contactless two-laser Raman thermometry to study heat dissipation in periodic porous membranes at high temperatures via lattice conduction and air-mediated losses. We find the reduction of the thermal conductivity and its temperature dependence closely correlated with the structure feature size. On the basis of two-phonon Raman spectra, we attribute this behaviour to diffuse (incoherent) phonon-boundary scattering. Furthermore, we investigate and quantify the heat dissipation via natural air-mediated cooling, which can be tuned by engineering the porosity. © 2017 The Author(s).
2016
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Fabrication of phononic crystals on free-standing silicon membranes
Sledzinska M., Graczykowski B., Alzina F., Santiso Lopez J., Sotomayor Torres C.M. Microelectronic Engineering; 149: 41 - 45. 2016. 10.1016/j.mee.2015.09.004. IF: 1.277
Free-standing Si films have been and remain an excellent example to study experimentally the effect of the reduction of the characteristic size on the phonon dispersion relation. A step further in geometrical complexity and, therefore, in increasing the control and manipulation of phonons is achieved by introducing periodicity in the medium to form phononic crystals. Here we report on the development of the fabrication process of large-area, solid-air and solid-solid two-dimensional phononic crystals, directly on free-standing, single crystalline silicon membranes. The patterning of the membranes involved electron-beam lithography and reactive ion etching for holes or metal evaporation and lift-off for pillars. The fabrication was possible due to the external strain induced on the membrane in order to reduce the buckling, which is typically found in large area free-standing structures. As a result, we obtained 250 nm thick structured membranes with patterned areas up to 100 × 100 μm, feature size between 100 and 300 nm and periodicity between 300 and 500 nm. The changes in dispersion relations of hypersonic acoustic phonons due to nanopatterning in free-standing silicon membranes were measured by Brillouin light scattering and the results were compared with numerical calculations by finite elements method. Information on phonon dispersion relation combined with a reliable fabrication process for large-scale structures opens a way for phonon engineering in more complex devices. © 2015 Elsevier B.V. All rights reserved.
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Measurement and modeling of the effective thermal conductivity of sintered silver pastes
Ordonez-Miranda J., Hermens M., Nikitin I., Kouznetsova V.G., Van Der Sluis O., Ras M.A., Reparaz J.S., Wagner M.R., Sledzinska M., Gomis-Bresco J., Sotomayor Torres C.M., Wunderle B., Volz S. International Journal of Thermal Sciences; 108: 185 - 194. 2016. 10.1109/THERMINIC.2015.7389630. IF: 2.769
The effective thermal conductivity of sintered porous pastes of silver is modeled through two theoretical methods and measured by means of three experimental techniques. The first model is based on the differential effective medium theory and provides a simple analytical description considering the air pores like ellipsoidal voids of different sizes, while the second one arises from the analysis of the scanning-electron-microscope images of the paste cross-sections through the finite element method. The predictions of both approaches are consistent with each other and show that the reduction of the thermal conductivity of porous pastes can be minimized with spherical pores and maximized with pancake-shaped ones, which are the most efficient to block the thermal conducting pathways. A thermal conductivity of 151.6 W/m K is numerically determined for a sintered silver sample with 22% of porosity. This thermal conductivity agrees quite well with the one measured by the Lateral Thermal Interface Material Analysis for a suspended sample and matches, within an experimental uncertainty smaller than 16%, with the values obtained by means of Raman thermometry and the 3u technique, for two samples buried in a silicon chip. The consistence between our theoretical and experimental results demonstrates the good predictive performance of our theoretical models to describe the thermal behavior of porous thermal interface materials and to guide their engineering with a desired thermal conductivity. © 2016 Elsevier Masson SAS.
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Self-pulsing and phonon lasing in optomechanical crystals
Navarro-Urrios D., Capuj N.E., Gomis-Bresco J., Colombano M.F., García P.D., Sledzinska M., Alzina F., Griol A., Martinez A., Sotomayor-Torres C.M. International Conference on Transparent Optical Networks; 2016-August (7550436) 2016. 10.1109/ICTON.2016.7550436.
We report on a novel and efficient strategy that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical (OM) cavities. The pumping mechanism is based on a self-pulsing limit-cycle, which is a spontaneous process that modulates the intracavity radiation pressure force in resonance with a mechanical eigenmode of the OM cavity. © 2016 IEEE.
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Thermal conductivity of MoS2 polycrystalline nanomembranes
Sledzinska M., Graczykowski B., Placidi M., Reig D.S., El Sachat A., Reparaz J.S., Alzina F., Mortazavi B., Quey R., Colombo L., Roche S., Torres C.M.S. 2D Materials; 3 (3, 035016) 2016. 10.1088/2053-1583/3/3/035016. IF: 9.611
Heat conduction in 2D materials can be effectively engineered by means of controlling nanoscale grain structure. Afavorable thermal performance makes these structures excellent candidates for integrated heat management units. Here we show combined experimental and theoretical studies for MoS2 nanosheets in a nanoscale grain-size limit.Wereport thermal conductivity measurements on 5 nm thick polycrystalline MoS2 by means of 2-laser Raman thermometry. The free-standing, drum-like MoS2 nanomembranes were fabricated using a novel polymer- and residue-free, wet transfer, in which we took advantage of the difference in the surface energies between MoS2 and the growth substrate to transfer the CVD-grown nanosheets. The measurements revealed a strong reduction in the in-plane thermal conductivity down to about 0.73 ± 0.25 W m-1 K-1. The results are discussed theoretically using finite elements method simulations for a polycrystalline film, and a scaling trend of the thermally conductivity with grain size is proposed. © 2016 IOP Publishing Ltd.
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Thermal transport in suspended silicon membranes measured by laser-induced transient gratings
Vega-Flick A., Duncan R.A., Eliason J.K., Cuffe J., Johnson J.A., Peraud J.-P.M., Zeng L., Lu Z., Maznev A.A., Wang E.N., Alvarado-Gil J.J., Sledzinska M., Sotomayor Torres C.M., Chen G., Nelson K.A. AIP Advances; 6 (12, 121903) 2016. 10.1063/1.4968610. IF: 1.444
Studying thermal transport at the nanoscale poses formidable experimental challenges due both to the physics of the measurement process and to the issues of accuracy and reproducibility. The laser-induced transient thermal grating (TTG) technique permits non-contact measurements on nanostructured samples without a need for metal heaters or any other extraneous structures, offering the advantage of inherently high absolute accuracy. We present a review of recent studies of thermal transport in nanoscale silicon membranes using the TTG technique. An overview of the methodology, including an analysis of measurements errors, is followed by a discussion of new findings obtained from measurements on both "solid" and nanopatterned membranes. The most important results have been a direct observation of non-diffusive phonon-mediated transport at room temperature and measurements of thickness-dependent thermal conductivity of suspended membranes across a wide thickness range, showing good agreement with first-principles-based theory assuming diffuse scattering at the boundaries. Measurements on a membrane with a periodic pattern of nanosized holes (135nm) indicated fully diffusive transport and yielded thermal diffusivity values in agreement with Monte Carlo simulations. Based on the results obtained to-date, we conclude that room-temperature thermal transport in membrane-based silicon nanostructures is now reasonably well understood. © 2016 Author(s).
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Two-Dimensional Phononic Crystals: Disorder Matters
Wagner M.R., Graczykowski B., Reparaz J.S., El Sachat A., Sledzinska M., Alzina F., Sotomayor Torres C.M. Nano Letters; 16 (9): 5661 - 5668. 2016. 10.1021/acs.nanolett.6b02305. IF: 13.779
The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder. © 2016 American Chemical Society.
2015
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A diffractometer for quality control in nano fabrication processing based on subwavelength diffraction
Kreuzer M., Gomis Bresco J., Sledzinska M., Sotomayor Torres C.M. Proceedings of SPIE - The International Society for Optical Engineering; 9424 (942426) 2015. 10.1117/12.2085924. IF: 0.000
Mass production of nanostructured surfaces relies on the periodic repetition of micrometre scale patterns. A unit cell with nanometre features in the micrometre size range is repeated thousands of times. The ensemble can used as a diffraction grating for visible light. The relative intensity distribution of the diffraction orders is characteristic for the grating and sensitive to nanometre scale changes. A newly designed subwavelength diffraction setup allows the measurement in real time of the diffraction pattern of an illuminated polymer grating with only one detector image. The setup records diffraction patterns of, for example, polymer gratings with intentionally low scattering contrast and line features ranging from 610 to 80 nm. Thus, sub-100 nm features can be traced. The comparison of the measured diffraction patterns with simulated patterns allows to sense nanometre scale deviations from fabrication goals. © 2015 SPIE.
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In-line metrology setup for periodic nanostructures based on sub-wavelength diffraction
Kreuzer M., Gomis Bresco J., Sledzinska M., Sotomayor Torres C.M. Proceedings of SPIE - The International Society for Optical Engineering; 9628 ( 96281Q) 2015. 10.1117/12.2191346. IF: 0.000
The analysis of diffracted light from periodic structures is shown to be a versatile metrology technique applicable to inline metrology for periodic nanostructures. We show that 10 nm changes in periodic structures can be traced optically by means of sub-wavelength diffraction. Polymer gratings were fabricated by electron beam lithography. The gratings have a common periodicity of 6 μm, but different line width, ranging from 370 to 550 nm in 10 nm steps. A comparison between the resulting diffraction patterns shows marked differences in intensity which are used to sense nanometre scale deviations in periodic structures. © 2015 SPIE.
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Phonon dispersion in hypersonic two-dimensional phononic crystal membranes
Graczykowski B., Sledzinska M., Alzina F., Gomis-Bresco J., Reparaz J.S., Wagner M.R., Sotomayor Torres C.M. Physical Review B - Condensed Matter and Materials Physics; 91 (7, 075414) 2015. 10.1103/PhysRevB.91.075414. IF: 3.736
We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes. © 2015 American Physical Society.
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Tuning Thermal Transport in Ultrathin Silicon Membranes by Surface Nanoscale Engineering
Neogi S., Reparaz J.S., Pereira L.F.C., Graczykowski B., Wagner M.R., Sledzinska M., Shchepetov A., Prunnila M., Ahopelto J., Sotomayor-Torres C.M., Donadio D. ACS Nano; 9 (4): 3820 - 3828. 2015. 10.1021/nn506792d. IF: 12.881
A detailed understanding of the connections of fabrication and processing to structural and thermal properties of low-dimensional nanostructures is essential to design materials and devices for phononics, nanoscale thermal management, and thermoelectric applications. Silicon provides an ideal platform to study the relations between structure and heat transport since its thermal conductivity can be tuned over 2 orders of magnitude by nanostructuring. Combining realistic atomistic modeling and experiments, we unravel the origin of the thermal conductivity reduction in ultrathin suspended silicon membranes, down to a thickness of 4 nm. Heat transport is mostly controlled by surface scattering: rough layers of native oxide at surfaces limit the mean free path of thermal phonons below 100 nm. Removing the oxide layers by chemical processing allows us to tune the thermal conductivity over 1 order of magnitude. Our results guide materials design for future phononic applications, setting the length scale at which nanostructuring affects thermal phonons most effectively. © 2015 American Chemical Society.
2014
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Hypersonic phonon propagation in one-dimensional surface phononic crystal
Graczykowski, B.; Sledzinska, M.; Kehagias, N.; Alzina, F.; Reparaz, J.S.; Sotomayor Torres, C.M. Applied Physics Letters; 2014. 10.1063/1.4870045. IF: 3.515