Influence of higher order electron-phonon interaction terms on the thermal properties of 2D Dirac crystals

To understand the essential properties of Dirac crystals, such as their thermal conductivity, we require models that consider the interaction between Dirac electrons and dispersive acoustic phonons. The exceptionally high thermal conductivity in 2D Dirac crystals is attributed to near-ideal phonon quantum gases, while undesired limitations arise from electron-phonon (e-ph) interactions which have been shown to limit the thermal conductivity up to several microns away. The e-ph thermal conductivity is directly linked to the phonon scattering rate. Conventional calculations overlook phonons with short-dispersive wavelengths, rendering them inadequate for analyzing 2D Dirac crystals. The phonon scattering rate is typically calculated up to the first-order magnitude, considering 3-particle interactions involving the decay of an electron and phonon (EP-E*) to create a new electron. However, processes involving the decay of an electron and the creation of a new electron and phonon (E-E*P*) are neglected. In this study, we present an accurate expression for the phonon scattering rate and e-ph thermal conductivity in 2D Dirac crystals, accounting for short-dispersive wavelength phonons. We demonstrate the significance of the E-E*P* process even at room temperature in calculating the phonon scattering rate and e-ph thermal conductivity, particularly for first-order e-ph interactions. Furthermore, we emphasize the importance of incorporating second-order e-ph interactions, specifically the EP-E*P* interaction involving the decay of an electron and phonon and the creation of a new electron-phonon pair, to accurately determine the phonon scattering rate and e-ph thermal conductivity at high temperatures and low Fermi energies. This 4-particle interaction process plays a crucial role in characterizing these properties effectively

Dynamic dielectric function and phonon self-energy from electrons strongly correlated with acoustic phonons in 2D Dirac crystals

The unique structure of two-dimensional (2D) Dirac crystals, with electronic bands linear in the proximity of the Brillouin-zone boundary and the Fermi energy, creates anomalous situations where small Fermi-energy perturbations are known to critically affect the electron-related lattice properties of the system. The Fermi-surface nesting (FSN) conditions determining such effects via electron-phonon interaction, require accurate estimates of the crystal's response function $(\chi)$ as a function of the phonon wavevector q for any values of temperature. Numerous analytical estimates of $\chi(q)$ for 2D Dirac crystals beyond the Thomas-Fermi approximation have been so far carried out only in terms of dielectric response function $\chi(q,\omega)$, for photon and optical-phonon perturbations, due to relative ease of incorporating a q-independent oscillation frequency in their calculation. However, models accounting for Dirac-electron interaction with ever-existing acoustic phonons, for which $\omega$ does depend on q and is therefore dispersive, are essential to understand many critical crystal properties. The lack of such models has often led to assume that the dielectric response function $\chi(q)$ in these systems can be understood from free-electron behavior. Here, we show that, different from free-electron systems, $\chi(q)$ calculated from acoustic phonons in 2D Dirac crystals using the Lindhard model, exhibits a cuspidal point at the FSN condition. Strong variability of $\frac{\partial\chi}{\partial q}$ persists also at finite temperatures, while $\chi(q)$ may tend to infinity in the dynamic case even where the speed of sound is small, albeit nonnegligible, over the Dirac-electron Fermi velocity. The implications of our findings for electron-acoustic phonon interaction and transport properties such as the phonon line width derived from the phonon self energy will also be discussed

A contactless scanning near-field optical dilatometer imaging the thermal expansivity of inhomogeneous 2D materials and thin films at the nanoscale

To date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring, with nanoscale lateral resolution, quantitative maps of the thermal expansivity of 2D materials and thin films, despite huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable, because probes in contact with the sample significantly perturb any thermal measurements. Here, we introduce {\omega}-2{\omega} near-field thermoreflectance imaging, as an all-optical and contactless approach to map the TEC at the nanoscale with precision. Testing of our technique is performed on nanogranular films of gold and multilayer graphene (ML-G) platelets. Our method demonstrates that the TEC of Au is higher at the metal-insulator interface, with an average of (17.12 +/- 2.30)x10-6 K-1 in agreement with macroscopic techniques. For ML-G, the average TEC was (-5.77 +/- 3.79)x10-6 K-1 and is assigned to in-plane vibrational bending modes. A vibrational-thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. Our nanoscale method demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces

Electric field dependence of Raman-active modes in single-wall carbon nanotube thin films

We report on electrical Raman measurements in transparent and conducting single-wall carbon nanotube (SWNT) thin films. Application of external electric field results in downshifts of the D and G modes and in reduction of their intensity. The intensities of the radial breathing modes increase with electric field in metallic SWNTs, while decreasing in semiconducting SWNTs. A model explaining the phenomenon in terms of both direct and indirect (Joule heating) effects of the field is proposed. Our work rules out the elimination of large amounts of metallic SWNTs in thin film transistors using high field pulses. Our results support the existence of Kohn anomalies in the Raman-active optical branches of metallic graphitic materials [Phys. Rev. Lett. 93 (2004) 185503].Comment: 17 pages, 4 figure

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles

The electronic, thermal, and optical properties of graphene-based materials depend strongly on the fabrication method used and can be further manipulated through the use of metal nanoparticles deposited on the graphene surface. Metals that strongly interact with graphene such as Co and Ni can form strong chemical bonds which may significantly alter the band structure of graphene near the Dirac point. Weakly interacting metals such as Au and Cu can be used to induce shifts in the graphene Fermi energy, resulting in doping without significant alteration to the graphene band structure. The deposition and nucleation conditions such as deposition rate, annealing temperature and time, and annealing atmosphere can be used to control the size and distribution of metal nanoparticles. Under ideal conditions, self-assembled arrays of nanoparticles can be obtained on graphene-based films for use in new types of nano-devices such as evanescent waveguides

identifying the most promising agronomic adaptation strategies for the tomato growing systems in southern italy via simulation modeling

Abstract The main cultivation area of the Italian processing tomato is the Southern Capitanata plain. Here, the hardest agronomic challenge is the optimization of the irrigation water use, which is often inefficiently performed by farmers, who tend to over-irrigate. This could become unsustainable in the next years, given the negative impacts of climatic changes on groundwater availability and heat stress intensification. The aim of the study was to identify the most promising agronomic strategies to optimize tomato yield and water use in Capitanata, through a modeling study relying on an extensive dataset for model calibration and evaluation (22 data sets in 2005–2018). The TOMGRO simulation model was adapted to open-field growing conditions and was coupled with a soil model to reproduce the impact of water stress on yield and fruit quality. The new model, TomGro_field, was applied on the tomato cultivation area in Capitanata at 5 × 5 km spatial resolution using an ensemble of future climatic scenarios, resulting from the combination of four General Circulation Models, two extreme Representative Concentration Pathways and five 10-years time frames (2030–2070). Our results showed an overall negative impact of climate change on tomato yields (average decrease = 5–10%), which could be reversed by i) the implementation of deficit irrigation strategies based on the restitution of 60–70% of the crop evapotranspiration, ii) the adoption of varieties with longer cycle and iii) the anticipation of 1–2 weeks in transplanting dates. The corresponding irrigation amounts applied are around 360 mm, thus reinforcing that a rational water management could be realized. Our study provides agronomic indications to tomato growers and lays the basis for a bio-economic analysis to support policy makers in charge of promoting the sustainability of the tomato growing systems

Redox Polymers Incorporating Pendant 6-Oxoverdazyl and Nitronyl Nitroxide Radicals

Polymers comprised of redox-active organic radicals have emerged as promising materials for use in a variety of organic electronics, including fast-charging batteries. Despite these advances, relatively little attention has been focused on the diversification of the families of radicals that are commonly incorporated into polymer frameworks, with most radical polymers being comprised of nitroxide radicals. Here, we report two new examples prepared via ring-opening methathesis polymerization containing 6-oxoverdazyl and nitronyl nitroxide radicals appended to their backbones. The polymerization reaction and optoelectronic properties were explored in detail, revealing high radical content and redox activity that may be advantageous for their use as semiconducting thin films. Initial studies revealed that current-voltage curves obtained from thin films of the title polymers exhibited memory effects making them excellent candidates for use in resistive memory applications

MARS Bulletin Vol 18 No 1

The annexed document is the template for the bulletin that will be issued on the 9th March. This bulletin covers meteorological analysis and crop yield forecasts for the period 1st November 2009 to 28 February 2010JRC.DG.G.3-Monitoring agricultural resource

A Review of Three-Dimensional Scanning Near-Field Optical Microscopy (3D-SNOM) and Its Applications in Nanoscale Light Management

In this article, we present an overview of aperture and apertureless type scanning near-field optical microscopy (SNOM) techniques that have been developed, with a focus on three-dimensional (3D) SNOM methods. 3D SNOM has been undertaken to image the local distribution (within ~100 nm of the surface) of the electromagnetic radiation scattered by random and deterministic arrays of metal nanostructures or photonic crystal waveguides. Individual metal nanoparticles and metal nanoparticle arrays exhibit unique effects under light illumination, including plasmon resonance and waveguiding properties, which can be directly investigated using 3D-SNOM. In the second part of this article, we will review a few applications in which 3D-SNOM has proven to be useful for designing and understanding specific nano-optoelectronic structures. Examples include the analysis of the nano-optical response phonetic crystal waveguides, aperture antennae and metal nanoparticle arrays, as well as the design of plasmonic solar cells incorporating random arrays of copper nanoparticles as an optical absorption enhancement layer, and the use of 3D-SNOM to probe multiple components of the electric and magnetic near-fields without requiring specially designed probe tips. A common denominator of these examples is the added value provided by 3D-SNOM in predicting the properties-performance relationship of nanostructured systems