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Ca3Co4O9, a p-type thermoelectric material based on transition-metal oxides, has garnered significant interest due to its potential in thermoelectric applications. Its unique misfit-layered crystal structure contributes to low thermal conductivity and a high Seebeck coefficient, leading to a thermoelectric figure of merit (zT) of ≥1 at 1000 K. Conventionally, it has been believed that thermopower reaches its upper limit above 200 K. However, our thermopower measurements on polycrystalline Ca3Co4O9 samples have revealed an unexpected increase in thermopower above 380 K. In this study, we investigate the effects of high oxygen pressure annealing on Ca3Co4O9 and provide an explanation based on the mixed oxide states of cobalt and carrier hopping. Our results demonstrate that annealing induces modifications in the defect chemistry of Ca3Co4O9, leading to a decrease in electron hopping probability and the emergence of a thermal activation-like behavior in thermopower. These findings carry significant implications for the design and optimization of thermoelectric materials based on misfit cobaltates, opening new avenues for enhanced thermoelectric performance.

Glass microspheres are of great interest for numerous industrial, biomedical, or standalone applications, but it remains challenging to evaluate their elastic and optical properties in a non-destructive way. In this work, we address this issue by using two complementary contactless techniques to obtain elastic and optical constants of glass microspheres with diameters ranging from 10 to 60 µm. The first technique we employ is Brillouin Light Scattering, which yields scattering with longitudinal acoustic phonons, the frequency of which is found to be 5% lower than that measured in the bulk material. The second technique involves exciting the optical whispering gallery modes of the microspheres, which allows us to transduce some of their vibrational modes. The combined data allow for extracting the refractive index and the elastic constants of the material. Our findings indicate that the values of those properties are reduced with respect to their bulk material counterpart due to an effective decrease of the density, resulting from the fabrication process. We propose the use of this combined method to extract elastic and optical parameters of glass materials in microsphere geometries and compare them with the values of the pristine material from which they are formed.

Nanophononics has the potential for information transfer, in an analogous manner to its photonic and electronic counterparts. The adoption of phononic systems has been limited, due to difficulties associated with the generation, manipulation, and detection of phonons, especially at GHz frequencies. Existing techniques often require piezoelectric materials with an external radiofrequency excitation that are not readily integrated into existing CMOS infrastructures, while non-piezoelectric demonstrations have been inefficient. In this work, we explore the optomechanical generation of coherent phonons in a suspended 2D silicon phononic crystal cavity with a guided mode around 6.8 GHz. By incorporating an air-slot into this cavity, we turn the phononic waveguide into an optomechanical platform that exploits localized photonic modes resulting from inherent fabrication imperfections for the transduction of mechanics. Such a platform exhibits very fine control of phonons using light, and is capable of coherent self-sustained phonon generation via mechanical lasing around 6.8 GHz. The ability to generate high frequency coherent mechanical vibrations within such a simple 2D CMOS-compatible system could be a first step towards the development of sources in phononic circuitry and the coherent manipulation of other solid-state properties., 13 pages, 4 main text figures, 6 appendix figures

Layered Bi-misfit cobaltates, such as Bi2Sr2Co2Oy, are the natural superlattice of an electrically insulating rocksalt (RS) type Bi2Sr2O4 layer and electrically conducting CoO2 layer, stacked along the crystallographic c-axis. RS and CoO2 layers are related through charge compensation reactions (or charge transfer). Therefore, thermoelectric transport properties are affected when doping or substitution is carried out in the RS layer. In this work, we have shown improved thermoelectric properties of spark plasma sintered Bi2Sr2-xCaxCo2Oy alloys (x = 0, 0.3 and 0.5). The substitution of Ca atoms affects the thermal properties by introducing point-defect phonon scattering, while the electronic conductivity and thermopower remain unaltered.

This broad review summarizes recent advances and "hot"research topics in nanophononics and elastic, acoustic, and mechanical metamaterials based on results presented by the authors at the EUROMECH 610 Colloquium held on April 25-27, 2022 in Benicássim, Spain. The key goal of the colloquium was to highlight important developments in these areas, particularly new results that emerged during the last two years. This work thus presents a "snapshot"of the state-of-the-art of different nanophononics- and metamaterial-related topics rather than a historical view on these subjects, in contrast to a conventional review article. The introduction of basic definitions for each topic is followed by an outline of design strategies for the media under consideration, recently developed analysis and implementation techniques, and discussions of current challenges and promising applications. This review, while not comprehensive, will be helpful especially for early-career researchers, among others, as it offers a broad view of the current state-of-the-art and highlights some unique and flourishing research in the mentioned fields, providing insight into multiple exciting research directions., Nanophotonics, 12 (4), ISSN:2192-8614

Classical thermal rectification arises from the contact between two dissimilar bulk materials, each with a thermal conductivity (k) with a different temperature dependence. Here, we study thermal rectification in a SiGe alloy with a spatial dependence on the atomic composition. Rectification factors (R = k/k) of up to 3.41 were found. We also demonstrate the suitability of such an alloy for logic gates using a thermal AND gate as an example by controlling the thermal conductivity profile via the alloy composition. This system is readily extendable to other alloys, since it only depends on the effective thermal conductivity. These thermal devices are inherently advantageous alternatives to their electric counterparts, as they may be able to take advantage of otherwise undesired waste heat in the surroundings. Furthermore, the demonstration of logic operations is a step towards thermal computation., We acknowledge the support from Spanish MICINN project SIP (PCG2018-101743-B-100). R.C.N. acknowledges funding from the EU-H2020 Research and Innovation Programme under the Marie Sklodowska Curie Individual Fellowship (Grant No. 897148). A.C.-A. acknowledges the support from the Fondecyt Iniciación 11200620.

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., The Catalan Institute of Nanoscience and Nanotechnology (ICN2) is funded by the CERCA program/Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). We acknowledge support from the EU Project Nanosmart (H2020 ICT-07-2018) and ICN2 members acknowledge the Spanish MINECO project SIP (PGC2018-101743-B-I00). P.X. acknowledges support by a PhD fellowship from the EU Marie Skłodowska-Curie COFUND PREBIST project (Grant Agreement No. 754558).

Heat exchangers are essential to optimize the efficiency of Thermoelectric Generators (TEGs), and heat pipes without fans have proven to be an advantageous design as it maintains the characteristic robustness of thermoelectricity, low maintenance and lack of moving parts. However, the efficiency of these heat exchangers decreases under natural convection conditions, reducing their heat transfer capacity and thus thermoelectric power production. This work reports on a novel heat exchanger that combines for the first time, phase change and radiative cooling in a thermoelectric generator to improve its efficiency and increase the production of electrical energy, specially under natural convection. For this, two thermoelectric generators with heat-pipes on their cold sides have been tested: one with the radiative coating and the other without it. Their thermal resistances have been determined and the electric power output was compared under different working conditions, namely, natural convection and forced convection indoors and outdoors. The experimental tests show a clear reduction of the heat exchanger thermal resistance thanks to the radiative coating and consequently, an increase of electric production 8.3 % with outdoor wind velocities of 1 m/s, and up to 54.8 % under free convection conditions. The application of the radiative surface treatment is shown to result in a more stable electrical energy production, suppressing the drastic decrease in the generated electric power that occurs in thermoelectric generators when they work under free convection. The authors acknowledge the support of the Spanish Ministry of Science, Innovation and Universities, and the European Regional Development Fund , under grants PID2021-124014OB-I00 (VIVOTEG), TED2021-129359B-I00 (GEOTEG), PGC2018-101743-B-I00 (SIP) and RTI2018-093921-A-C44 (SMOOTH). Open access funding provided by Universidad Pública de Navarra.

Managing thermal transport in nanostructures became a major challenge in the development of active microelectronic, optoelectronic and thermoelectric devices, stalling the famous Moore's law of clock speed increase of microprocessors for more than a decade. To find the solution to this and linked problems, one needs to quantify the ability of these nanostructures to conduct heat with adequate precision, nanoscale resolution, and, essentially, for the internal layers buried in the 3D structure of modern semiconductor devices. Existing thermoreflectance measurements and “hot wire” 3ω methods cannot be effectively used at lateral dimensions of a layer below a micrometre; moreover, they are sensitive mainly to the surface layers of a relatively high thickness of above 100 nm. Scanning thermal microscopy (SThM), while providing the required lateral resolution, provides mainly qualitative data of the layer conductance due to undefined tip–surface and interlayer contact resistances. In this study, we used cross-sectional SThM (xSThM), a new method combining scanning probe microscopy compatible Ar-ion beam exit nano-cross-sectioning (BEXP) and SThM, to quantify thermal conductance in complex multilayer nanostructures and to measure local thermal conductivity of oxide and semiconductor materials, such as SiO2, SiGex and GeSny. By using the new method that provides 10 nm thickness and few tens of nm lateral resolution, we pinpoint crystalline defects in SiGe/GeSn optoelectronic materials by measuring nanoscale thermal transport and quantifying thermal conductivity and interfacial thermal resistance in thin spin-on materials used in extreme ultraviolet lithography (eUV) fabrication processing. The new capability of xSThM demonstrated here for the first time is poised to provide vital insights into thermal transport in advanced nanoscale materials and devices., The authors acknowledge the EU QUANTIHEAT FP7 project no. 604668 and the Horizon 2020 Graphene Flagship Core 3 project no. 881603, EPSRC EP/G015570/1 EP/K023373/1, EP/G06556X/1. EP/V00767X/1 and EP/P006973/1 and Faraday Institution NEXGENNA project for the overall support, and Paul Instrument Fund, c/o The Royal Society grant on “Infrared non-contact atomic force microscopy (ncAFM-IR)” for the equipment support. We are also grateful to our industrial collaborators Leica Microsystems, Lancaster Materials Analysis Ltd and Bruker for the financial and instrumentation support. LTD to ICN2 is supported by the Spanish MINECO (Severo Ochoa Centers of Excellence Program under Grant SEV-2017-0706 and CEX2019-000917-S) and by the Generalitat de Catalunya (Grants 2017SGR806, 2017SGR488, and the CERCA Program). We thank Severine Gomès from CNRS and Harry Hoster from Lancaster Energy for the helpful discussions on the measurements, and Andy Cockburn and Mike Kocsic from IMEC for the interesting materials and discussion of applications.

New composites formed by layered hybrid TiO2(stearic acid) (LHTiO2) and, Cu2O nanoparticles were studied as photocatalysts that extend the response range to light visible for the evolution of hydrogen and the degradation of 4-chlorophenol. The results revealed that LHTiO2/Cu2O exhibited a clearly improved photocatalytic degradation, about 5.6 times faster than pristine TiO2, and hydrogen evolution of about 2.7 times higher than the TiO2 anatase. The enhanced photocatalytic activity can be assigned to the properties of the two-dimensional morphology, in sheets-like arrangement of LHTiO2, benefitting from the high exposure of surface, with more active sites available to improve matching with the surfaces of the Cu2O nanocrystals and significant reduction of migration distances of photogenerated carriers. In the photocatalytic degradation, a mechanism Z-scheme is supported, and in the photocatalytic evolution of hydrogen a mechanism type II band alignment is indicated. Photocatalytic reuse tests showed that stability and catalytic activity of LHTiO2/Cu2O were maintained for three cycles. Photoelectrochemical evaluation were performed through measurements of the photocurrent response and electrochemical impedance., This work was supported by Project funded by the Research Continuity Project Fund, year 2019, code LPC19-01, Universidad Tecnologica Metropolitana, Universidad de Chile, FONDECYT 1171803, CMST Spanish MINECO projects PHENTOM (FIS2015-70862-P) and Severo Ochoa (SEV-2013-0295) and the CERCA Programme/Generalitat de Catalunya, Programa Fondequip XPS EQM 140044 and SEM EQM 150101.

Nanoelectro-opto-mechanical systems enable the synergistic coexistence of electrical, mechanical, and optical signals on a chip to realize new functions. Most of the technology platforms proposed for the fabrication of these systems so far are not fully compatible with the mainstream CMOS technology, thus, hindering the mass-scale utilization. We have developed a CMOS technology platform for nanoelectro-opto-mechanical systems that includes piezoelectric interdigitated transducers for electronic driving of mechanical signals and nanocrystalline silicon nanobeams for an enhanced optomechanical interaction. Room-Temperature operation of devices at 2 GHz and with peak sensitivity down to 2.6 cavity phonons is demonstrated. Our proof-of-principle technology platform can be integrated and interfaced with silicon photonics, electronics, and MEMS devices and may enable multiple functions for coherent signal processing in the classical and quantum domains., This research has received funding from the European Union H2020 FET Open Project PHENOMEN (No. 713450). The ICN2 authors acknowledge support by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2019-0706), the MCIN project SIP (PGC2018-101743-B-100), and by the CERCA Programme Generalitat de Catalunya. G.A. was supported by a BIST and MFC by a S. Ochoa Project Ph.D. studentships. G. M. acknowledges support from the EU ERC project LEIT (GA Nr. 885689). A.M. acknowledges support from MCIN/AEI/10.13039/501100011033/ (Projects PGC2018-094490-BC21 and ICTS-2017-28-UPV-9), from Generalitat Valenciana (BEST/2020/178, PROMETEO/2019/123, and IDIFEDER/2021/061) and from “Unión Europea NextGenerationEU/PRTR”.

Controlling thermal energy transfer at the nanoscale and thermal properties has become critically important in many applications since it often limits device performance. In this study, the effects on thermal conductivity arising from the nanoscale structure of free-standing nanocrystalline silicon films and the increasing surface-to-volume ratio when fabricated into suspended optomechanical nanobeams are studied. Thermal transport and elucidate the relative impact of different grain size distributions and geometrical dimensions on thermal conductivity are characterized. A micro time-domain thermoreflectance method to study free-standing nanocrystalline silicon films and find a drastic reduction in the thermal conductivity, down to values below 10 W m–1 K–1 is used, with a stronger decrease for smaller grains. In optomechanical nanostructures, this effect is smaller than in membranes due to the competition of surface scattering in decreasing thermal conductivity. Finally, a novel versatile contactless characterization technique that can be adapted to any structure supporting a thermally shifted optical resonance is introduced. The thermal conductivity data agrees quantitatively with the thermoreflectance measurements. This study opens the way to a more generalized thermal characterization of optomechanical cavities and to create hot-spots with engineered shapes at the desired position in the structures as a means to study thermal transport in coupled photon-phonon structures., This work was supported by the European Commission FET Open project PHENOMEN (G.A. Nr. 713450). ICN2 was supported by the S. Ochoa program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and by the CERCA Programme / Generalitat de Catalunya. ICN2 authors acknowledge the support from the Spanish MICINN project SIP (PGC2018-101743-B-I00). D.N.U. and M.F.C. acknowledge the support of a Ramón y Cajal postdoctoral fellowship (RYC-2014-15392) and a Severo Ochoa studentship, respectively. E.C.A. acknowledges financial support from the EU FET Open Project NANOPOLY. (GA 829061). A.M. acknowledges support from Ministerio de Ciencia, Innovación y Universidades (grant PGC2018-094490-B, PRX18/00126) and Generalitat Valenciana (grants PROMETEO/2019/123, and IDIFEDER/2018/033).

This article is part of the themed collection: Recent Review Articles., 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., We acknowledge the support from the project LEIT funded by the European Research Council, H2020 Grant Agreement No. 885689. ICN2 authors thank the Severo Ochoa (Spanish Research Agency AEI, grant no. SEV-2017-0706) and the CERCA Programme / Generalitat de Catalunya. R. C. N. acknowledges funding from the EU-H2020 Research and Innovation Programme under the Marie Sklodowska Curie Individual Fellowship (Grant No. 897148). A. E. S. acknowledges support by the H2020-MSCA-IF project THERMIC-GA No. 101029727. F. C. acknowledges funding from the scholarship BES-2016-077203 funded by MCIN/AEI/10.13038/501100011033 and by “ESF Investing in your future”. O. F. is supported by BIST PhD fellowship Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 754558. P. X. additionally acknowledges support by a Ph.D. fellowship from the EU Marie Skłodowska-Curie COFUND PREBIST project (Grant No. 754558).

Hydrogen, generated from water splitting, is postulated as one of the most promising alternatives to fossil fuels. In this context, direct hydrogen generation by electrolysis and fixation to graphene oxide in an aqueous suspension could overcome storage and distribution problems of gaseous hydrogen. This study presents time-resolved determination of the electrochemical hydrogenation of GO by in-situ Raman spectroscopy, simultaneous to original functional groups elimination. Hydrogenation is found favoured by dynamic modulation of the electrochemical environment compared to fixed applied potentials, with a 160% increase of C–H bond formation. Epoxide groups suppression and generated hydroxide groups point at these epoxide groups being one of the key sites where hydrogenation was possible. FTIR revealed characteristic symmetric and asymmetric stretching vibrations of C–H bonds in CH2 and CH3 groups. This shows that hydrogenation is significantly also occurring in defective sites and edges of the graphene basal plane, rather than H-Csp3 groups as graphane. We also determined a −0.05 VRHE reduction starting potential in alkaline electrolytes and a 150 mV cathodic delay in acid electrolytes. The identified key parameters role, together with observed diverse C-Hx groups formation, points at future research directions for large-scale hydrogen storage in graphene., ICFO and IREC acknowledge financial support from LESGO project (Code: 952068. H2020-EU.1.2.2. funded), BIST Master Program and Severo Ochoa Program. This work was partially funded by CEX2019-000910-S (MCIN/AEI/10.13039/501100011033), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya through CERCA. ICN2 acknowledge support from Severo Ochoa program, the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and the CERCA Programme/Generalitat de Catalunya. E.C.-A., P.X. and C.M.S.T acknowledge support from Spanish MICINN project SIP (PGC2018-101743-B-I00). P.X. acknowledges support by Ph.D. fellowship from the EU Marie Sklodowska-Curie COFUND PREBIST (Grant Agreement 754558). C.R. acknowledges support from the MCIN/AEI (FJC2020-043223-I) and the Severo Ochoa Excellence Post-doctoral Fellowship (CEX2019-000910-S).

The thermal imaging of surfaces with microscale spatial resolution over micro-sized areas remains a challenging and time-consuming task. Surface thermal imaging is a very important characterization tool in mechanical engineering, microelectronics, chemical process engineering, optics, microfluidics, and biochemistry processing, among others. Within the realm of electronic circuits, this technique has significant potential for investigating hot spots, power densities, and monitoring heat distributions in complementary metal–oxide–semiconductor (CMOS) platforms. We present a new technique for remote non-invasive, contactless thermal field mapping using synchrotron radiation-based Fourier-transform infrared microspectroscopy. We demonstrate a spatial resolution better than 10 um over areas on the order of 12 000 um2 measured in a polymeric thin film on top of CaF2 substrates. Thermal images were obtained from infrared spectra of poly(methyl methacrylate) thin films heated with a wire. The temperature dependence of the collected infrared spectra was analyzed via linear regression and machine learning algorithms, namely random forest and k-nearest neighbor algorithms. This approach speeds up signal analysis and allows for the generation of hyperspectral temperature maps. The results here highlight the potential of infrared absorbance to serve as a remote method for the quantitative determination of heat distribution, thermal properties, and the existence of hot spots, with implications in CMOS technologies and other electronic devices. Application of Synchrotron Radiation-Based Fourier-Transform Infrared Microspectroscopy for Thermal Imaging of Polymer Thin Films

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 MoSe

Layered hybrid ZnO (2D) intercalated by myristic acid (MA) with (0D) CdTe quantum dots (QDs) was designed to increase the conversion efficiency of photochemical energy. The results showed that the introduction of CdTe QDs in ZnO(MA) layered with more active sites available enhanced the photocatalytic efficiency. The optimal composite sample ZnO(MA)/CdTe (1:0.02) showed excellent dye removal efficiency under simulated solar light irradiation, above 96% after three cyclic experiments. The correlation coefficients possessed the highest reaction rate. This study offers an efficient research approach and vision to support the development of other photocatalytic systems featuring a direct Z scheme., This work was supported by Project funded by the Research Continuity Project Fund, year 2019, code LPC19-01, Project Scientific Technological Equipment, L318-03 Universidad Tecnologica Metropolitana, Universidad de Chile, FONDECYT 1171803, CONICYT PAI N°77190086 and FONDEQUP SEM EQM 150101.

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 SnSe

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 MoSe 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., The authors would like to thank Emerson Coy (CNBM-AMU) for sharing the HR-TEM images. S V and D S R acknowledge the support of the Spanish Ministry of Economy through FPI-SO 2018 and FPI-SO 2019, respectively. ICN2 was supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). K J T acknowledges funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 804349 (ERC StG CUHL), RyC Fellowship No. RYC-2017-22330, and IAE Project PID2019-111673GB-I00. A E S, E C A, M S and C M S T acknowledge support of the Spanish MICINN Project SIP (PGC2018-101743-B-I00).

The development of antimicrobial surfaces has become a high priority in recent times. There are two ongoing worldwide health crises: the COVID-19 pandemic provoked by the SARS-CoV-2 virus and the antibiotic-resistant diseases provoked by bacteria resistant to antibiotic-based treatments. The need for antimicrobial surfaces against bacteria and virus is a common factor to both crises. Most extended strategies to prevent bacterial associated infections rely on chemical based-approaches based on surface coatings or biocide encapsulated agents that release chemical agents. A critical limitation of these chemistry-based strategies is their limited effectiveness in time while grows the concerns about the long-term toxicity on human beings and environment pollution. An alternative strategy to prevent bacterial attachment consists in the introduction of physical modification to the surface. Pursuing this chemistry-independent strategy, we present a fabrication process of surface topographies [one-level (micro, nano) and hierarchical (micro+nano) structures] in polypropylene (PP) substrates and discuss how wettability, topography and patterns size influence on its antibacterial properties. Using nanoimprint lithography as patterning technique, we report as best results 82 and 86% reduction in the bacterial attachment of E. coli and S. aureus for hierarchically patterned samples compared to unpatterned reference surfaces. Furthermore, we benchmark the mechanical properties of the patterned PP surfaces against commercially available antimicrobial films and provide evidence for the patterned PP films to be suitable candidates for use as antibacterial functional surfaces in a hospital environment., This work is funded by the European Commission, under the project FLEXPOL (H2020-NMBPPILOT-2016-721062). The present study was carried out as part of a European project called “Antimicrobial FLEXible POLymers for its use in hospital environments” (FLEXPOL grant agreement No. 721062) funded by Horizon 2020 Framework Programme for Research and Innovation (2014-2020).

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 MoS

In this work, polymer nanocomposite films based on poly(L-lactic acid) (PLLA) were reinforced with mesoporous silica nanoparticles, mesoporous cellular foam (MCF) and Santa Barbara amorphous-15 (SBA). PLLA is a biobased aliphatic polyester, that possesses excellent thermomechanical properties, and has already been commercialized for packaging applications. The aim was to utilize nanoparticles that have already been established as nanocarriers to enhance the mechanical and thermal properties of PLLA. Since the introduction of antibacterial properties has become an emerging trend in packaging applications, to achieve an effective antimicrobial activity, micro/nano 3D micropillars decorated with cone- and needle-shaped nanostructures were implemented on the surface of the films by means of thermal nanoimprint lithography (t-NIL), a novel and feasible fabrication technique with multiple industrial applications. The materials were characterized regarding their composition and crystallinity using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), respectively, and their thermal properties using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Their mechanical properties were examined by the nanoindentation technique, while the films’ antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus strains was tested in vitro. The results demonstrated the successful production of nanocomposite PLLA films, which exhibited improved mechanical and thermal properties compared to the pristine material, as well as notable antibacterial activity, setting new groundwork for the potential development of biobased smart packaging materials., This work was funded from the European Union’s Horizon 2020 Research and Innovation Program under Grant Agreement No. 952941 (BIOMAC Project). Also, ICN2 is supported by the Severo Ochoa Program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and by the CERCA Program/Generalitat de Catalunya.

Heat dissipation and thermal management are central challenges in various areas of science and technology and are critical issues for the majority of nanoelectronic devices. In this review, we focus on experimental advances in thermal characterization and phonon engineering that have drastically increased the understanding of heat transport and demonstrated efficient ways to control heat propagation in nanomaterials. We summarize the latest device-relevant methodologies of phonon engineering in semiconductor nanostructures and 2D materials, including graphene and transition metal dichalcogenides. Then, we review recent advances in thermal characterization techniques, and discuss their main challenges and limitations., ICN2 is supported by the Severo Ochoa program, the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and the CERCA Programme/Generalitat de Catalunya. Authors acknowledge support from Spanish MICINN project SIP (PGC2018-101743-B-I00), and the EU project NANOPOLY (GA 289061).

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 MoS

Passive daytime radiative cooling has recently become an attractive approach to address the global energy demand associated with modern refrigeration technologies. One technique to increase the radiative cooling performance is to engineer the surface of a polar dielectric material to enhance its emittance atwavelengths in the atmospheric infrared transparency window (8-13 ìm) by outcoupling surface-phonon polaritons (SPhPs) into free-space. Here we present a theoretical investigation of new surface morphologies based upon self-assembled silica photonic crystals (PCs) using an in-house built rigorous coupled-wave analysis (RCWA) code. Simulations predict that silica micro-sphere PCs can reach up to 73 K below ambient temperature, when solar absorption and conductive/convective losses can be neglected. Micro-shell structures are studied to explore the direct outcoupling of the SPhP, resulting in near-unity emittance between 8 and 10 ìm. Additionally, the effect of material composition is explored by simulating soda-lime glass micro-shells, which, in turn, exhibit a temperature reduction of 61 K below ambient temperature. The RCWA code was compared to FTIR measurements of silica micro-spheres, self-assembled on microscope slides., Horizon 2020 Framework Programme (721062); H2020 Marie Skłodowska-Curie Actions (665919); Ministerio de Ciencia, Innovación y Universidades (PGC2018-101743-B-I00, RTI2018-093921-B-C41, SEV-2017-0706, RTI2018-093921-B-44, RyC-2015-18124, FPI programme); Centres de Recerca de Catalunya.

In this work, we report the fabrication of the new heterojunction of two 2D hybrid layered semiconductors—ZnO (stearic acid)/V2O5 (hexadecylamine)—and its behavior in the degradation of aqueous methylene blue under visible light irradiation. The optimal photocatalyst efficiency, reached at a ZnO (stearic acid)/V2O5 (hexadecylamine) ratio of 1:0.25, results in being six times higher than that of pristine zinc oxide. Reusability test shows that after three photocatalysis cycles, no significant changes in either the dye degradation efficiency loss, nor the photocatalyst structure, occur. Visible light photocatalytic performance observed indicates there is synergetic effect between both 2D nanocomposites used in the heterojunction. The visible light absorption enhancement promoted by the narrower bandgap V2O5 based components; an increased photo generated charge separation favored by extensive interface area; and abundance of hydrophobic sites for dye adsorption appear as probable causes of the improved photocatalytic efficiency in this hybrid semiconductors heterojunction. Estimated band-edge positions for both conduction and valence band of semiconductors, together with experiments using specific radical scavengers, allow a plausible photodegradation mechanism., Work supported by UTEM, UCh, FONDECYT 1151189, 1171803, Basal Financing Program CONICYT, FB0807 (CEDENNA). CMST acknowledges the support from the Spanish MINECO projects PHENTOM (FIS2015-70862-P), Severo Ochoa (SEV-2013-0295) and from the CERCA Programme/Generalitat de Catalunya. Conicyt-Programa Fondequip XPS EQM 140044.

[EN] Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform., This research was funded by EU FET Open project PHENOMEN (GA: 713450). ICN2 is supported by the Severo Ochoa program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and by the CERCA Programme/Generalitat de Catalunya. G. A. and C. M. S.-T. acknowledge the support from the Spanish MICINN project SIP (PGC2018-101743-B-I00). D. N. U., G. A. and M. F. C. gratefully acknowledge the support of a Ramon y Cajal postdoctoral fellowship (RYC-2014-15392), a BIST studentship, and a Severo Ochoa studentship, respectively. D. N. U. acknowledges the funding through the Ministry of Science, Innovation and Universities (PGC2018-094490-B-C22).

Artificial photonic materials, nanofabricated through wavelength-scale engineering, have shown astounding and promising results in harnessing, tuning, and shaping photonic beams. Metamaterials have proven to be often outperforming the natural materials they take inspiration from. In particular, metallic chiral metasurfaces have demonstrated large circular and linear dichroism of light which can be used, for example, for probing different enantiomers of biological molecules. Moreover, the precise control, through designs on demand, of the output polarization state of light impinging on a metasurface, makes this kind of structures particularly relevant for polarization-based telecommunication protocols. The reduced scale of the metasurfaces makes them also appealing for integration with nanomechanical elements, adding new dynamical features to their otherwise static or quasi-static polarization properties. To this end we designed, fabricated and characterized an all-dielectric metasurface on a suspended nanomembrane. Actuating the membrane mechanical motion, we show how the metasurface reflectance response can be modified, according to the spectral region of operation, with a corresponding intensity modulation or polarization conversion. The broad mechanical resonance at atmospheric pressure, centered at about 400 kHz, makes the metasurfaces structure suitable for high-frequency operation, mainly limited by the piezo-actuator controlling the mechanical displacement, which in our experiment reached modulation frequencies exceeding 1.3 MHz.

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., D. N. U. gratefully acknowledges funding from the Ministry of Science, Innovation and Universities (PGC2018-094490-B-C22) and Fundació Bosch i Gimpera (F2I-FVal_2019-012). ICN2 is supported by the Severo Ochoa program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) by the CERCA Programme / Generalitat de Catalunya and by the Ministry of Science, Innovation and Universities (PGC2018-101743-B-I00). G. A and P.X acknowledge the support of a BIST and COFUND PREBIST studentships, respectively. E.K. and G.F. acknowledge the financial support by ERC AdG SmartPhon (Grant No. 694977).

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., This work was partially funded by the European Union under the H2020 FET-OPEN NANOPOLY (GA 289061) and Spanish Ministry of Science projects SIP (PGC2018-101743-B-I00), ADAGIO (PGC2018-094490-B-C22), 2DTecBio (FIS2017-85787-R) and 2DENGINE (PID2019-111773RB- I00/AEI/10.13039/501100011033). E D C acknowledges the Spanish Ministry of Science for the Juan de la Cierva Fellowship (JC-2015-25201) and the Ramon y Cajal fellowship (RYC2019-027879-I). D N U and J F S acknowledge the Ramón y Cajal fellowships RYC2014-15392 and RYC2019-028368-I/AEI/10.13039/501100011033. M V C acknowledges project (Reference No. 103739) funded by the Agencia Estatal de Investigación through the PCI 2019 call. The Catalan Institute of Nanoscience and Nanotechnology (ICN2) is funded by the CERCA program/Generalitat de Catalunya, and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). K W and T T acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (Grant Number JPMXP0112101001) and JSPS KAKENHI (Grant Numbers 19H05790 and JP20H00354).

The precise control over electronic and optical properties of semiconductor (SC) materials is pivotal for a number of important applications like in optoelectronics, photocatalysis or in medicine. It is well known that the incorporation of heteroelements (doping as a classical case) is a powerful method for adjusting and enhancing the functionality of semiconductors. Independent from that, there already has been a tremendous progress regarding the synthesis of differently sized and shaped SC nanoparticles, and quantum-size effects are well documented experimentally and theoretically. Whereas size and shape control of nanoparticles work fairly well for the pure compounds, the presence of a heteroelement is problematic because the impurities interfere strongly with bottom up approaches applied for the synthesis of such particles, and effects are even stronger, when the heteroelement is aimed to be incorporated into the target lattice for chemical doping. Therefore, realizing coincident shape control of nanoparticle colloids and their doping still pose major difficulties. Due to a special mechanism of the emulsion based synthesis method presented here, involving a gelation of emulsion droplets prior to crystallization of shape-anisotropic ZnO nanoparticles, heteroelements can be effectively entrapped inside the lattice. Different nanocrystal shapes such as nanorods, -prisms, -plates, and -spheres can be obtained, determined by the use of certain emulsification agents. The degree of morphologic alterations depends on the type of incorporated heteroelement M(n+), concentration, and it seems that some shapes are more tolerant against doping than others. Focus was then set on the incorporation of Eu(3+) inside the ZnO particles, and it was shown that nanocrystal shape and aspect ratios could be adjusted while maintaining a fixed dopant level. Special PL properties could be observed implying energy transfer from ZnO excited near its band-gap (3.3 eV) to the Eu(3+) states mediated by defect luminescence of the nanoparticles. Indications for an influence of shape on photoluminescence (PL) properties were found. Finally, rod-like Eu@ZnO colloids were used as tracers to investigate their uptake into biological samples like HeLa cells. The PL was sufficient for identifying green and red emission under visible light excitation. published