The authors reported on investigation of the thermal conductivity graphene suspended across trenches in Si∕SiO2 wafer. measurements were performed using a noncontact technique based micro-Raman spectroscopy. amount power dissipated and corresponding temperature rise determined from spectral position integrated intensity graphene’s G mode. extremely high range ∼3080–5150W∕mK phonon mean free path ∼775nm near room extracted for set flakes. obtained results suggest applications as management...

We investigated theoretically the phonon thermal conductivity of single-layer graphene. The dispersion for all polarizations and crystallographic directions in graphene lattice was obtained using valence-force field method. three-phonon Umklapp processes were treated exactly an accurate Brillouin zone, accounting relaxation channels allowed by momentum energy conservation laws. uniqueness reflected two-dimensional density states restrictions on scattering phase-space. defects edges has also...

Thermal conductivity of free‐standing reduced graphene oxide films subjected to a high‐temperature treatment up 1000 °C is investigated. It found that the annealing dramatically increases in‐plane thermal conductivity, K , from ≈3 ≈61 W m −1 at room temperature. The cross‐plane ⊥ reveals an interesting opposite trend decreasing very small value ≈0.09 in annealed °C. obtained demonstrate exceptionally strong anisotropy K/K ≈ 675, which substantially larger even than high‐quality graphite....

The authors proposed a simple model for the lattice thermal conductivity of graphene in framework Klemens approximation. Gruneisen parameters were introduced separately longitudinal and transverse phonon branches through averaging over modes obtained from first-principles. calculations show that Umklapp-limited grows with increasing linear dimensions flakes can exceed basal planes bulk graphite when flake size is on order few micrometers. results are agreement experimental data reflect...

Properties of phonons—quanta the crystal lattice vibrations—in graphene have recently attracted significant attention from physics and engineering communities. Acoustic phonons are main heat carriers in near room temperature, while optical used for counting number atomic planes Raman experiments with few-layer graphene. It was shown both theoretically experimentally that transport properties phonons, i.e. energy dispersion scattering rates, substantially different a quasi-two-dimensional...

We review the thermal properties of graphene, few-layer graphene and nanoribbons, discuss practical applications in management energy storage. The first part describes state-of-the-art field focusing on recently reported experimental theoretical data for heat conduction nanoribbons. effects sample size, shape, quality, strain distribution, isotope composition, point-defect concentration are included summary. second outlines graphene-enhanced phase change materials used It is shown that use...

A discovery of the unusual thermal properties graphene stimulated experimental, theoretical and computational research directed at understanding phonon transport conduction in two-dimensional material systems. We provide a critical review recent results field focusing on dispersion, specific heat, conductivity, comparison different models approaches. The correlation between spectrum graphene-based materials heat is analyzed details. effects atomic plane rotations bilayer graphene, isotope...

We have investigated thermal conductivity of graphene laminate films deposited on polyethylene terephthalate substrates. Two types were studied, as and compressed, in order to determine the physical parameters affecting heat conduction most. The measurements performed using optothermal Raman technique a set suspended samples with thickness from 9 44 μm. was found be range 40 90 W/mK at room temperature. It unexpectedly that average size alignment flakes are more important defining than mass...

Phonons – quanta of crystal lattice vibrations reveal themselves in all electrical, thermal, and optical phenomena materials. Nanostructures open exciting opportunities for tuning the phonon energy spectrum related material properties specific applications. The possibilities controlled modification interactions transport referred to as engineering or phononics increased even further with advent graphene two-dimensional van der Waals We describe methods thermal low-dimensional materials via...

We investigate the thermal conductivity of suspended graphene as a function density defects, ND, introduced in controllable way. High-quality layers are synthesized using chemical vapor deposition, transferred onto transmission electron microscopy grid, and over ∼7.5 μm size square holes. Defects induced by irradiation with low-energy beam (20 keV) quantified Raman D-to-G peak intensity ratio. As defect changes from 2.0 × 1010 cm−2 to 1.8 1011 decreases ∼(1.8 ± 0.2) 103 W mK−1 ∼(4.0 102 near...

We investigated the thermal conductivity K of graphene ribbons and graphite slabs as function their lateral dimensions. Our theoretical model considered anharmonic three-phonon processes to second-order included angle-dependent phonon scattering from ribbon edges. It was found that long mean free path long-wavelength acoustic phonons in can lead an unusual non-monotonic dependence on length L a ribbon. The effect is pronounced for with smooth edges (specularity parameter p>0.5). results also...

We review the results of our experimental investigation heat conduction in suspended graphene and offer a theoretical interpretation its extremely high thermal conductivity. The direct measurements conductivity were performed using non-contact optical technique special calibration procedure with bulk graphite. measured values range ∼3000–5300 W mK−1 near room temperature depended on lateral dimensions flakes. explain enhanced as compared to that graphite basal planes by two-dimensional...

We theoretically investigate phonon dispersion in AA-stacked, AB-stacked, and twisted bilayer graphene with various rotation angles. The calculations are performed using the Born--von Karman model for intralayer atomic interactions Lennard-Jones potential interlayer interactions. It is found that stacking order affects out-of-plane acoustic modes most. difference densities of states AA- or AB-stacked appears frequency range 90--110 cm${}^{\ensuremath{-}1}$. Twisting leads to emergence...

The heat carriers – phonons in twisted bilayer graphene do not behave the same manner as that observed individual layers.

The authors review thermal properties of graphene and few-layer (FLG), discuss applications these materials in management advanced electronics. intrinsic conductivity – among the highest known is dominated by phonons near room temperature. examples include FLG heat spreaders integrated generating areas high-power density transistors. It has been demonstrated that can lower hot-spot temperature during device operation, resulting improved performance reliability devices.

We report on the current-carrying capacity of nanowires made from quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by and mechanical exfoliation were used to fabricate mm-long TaSe3 wires lateral dimensions in 20 70 nm range. Electrical measurements establish that TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm−2—an order-of-magnitude higher than for copper. Some devices...

Phonons, i.e., quanta of lattice vibrations, manifest themselves practically in all electrical, thermal, optical, and noise phenomena semiconductors other material systems. Reduction the size electronic devices below acoustic phonon mean free path creates a new situation for phonons propagation interaction. From one side, it may complicate heat removal from downscaled devices. opens up an opportunity engineering spectrum nanostructured materials, achieving enhanced operation nanoscale This...

Similar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. However, despite strong scientific and practical importance, conclusive experimental evidence of confined acoustic polarization branches individual free-standing nanostructures is lacking. Here we report results Brillouin-Mandelstam light scattering spectroscopy, which reveal multiple (up ten) GaAs nanowires with a diameter as large 128 nm, at length scale that exceeds grey...

We have theoretically demonstrated that phonon heat flux can be significantly suppressed in Si and Si/SiO${}_{2}$ nanowires with the periodically modulated cross-section area---referred to as cross-section-modulated nanowires---in comparison generic uniform nanowires. The energy spectra were obtained using five-parameter Born--von Karman-type model face-centered-cubic cell for description of lattice dynamics. thermal conductivity calculated from Boltzmann transport equation within relaxation...

Abstract We discuss theoretical approaches for description of the phonon thermal transport in graphene and identify open questions problems. Specifically, we show that due to a fundamental ambiguity definition intrinsic conductivity two‐dimensional (2‐D) systems calculations use an arbitrary low‐bound cut‐off frequency integral lead erroneous results. The problem relative contributions longitudinal acoustic (LA), transverse (TA), out‐of‐plane polarization branches is also discussed....

We have studied the phonon specific heat in single-layer, bilayer and twisted graphene. The calculations were performed using Born-von Karman model of lattice dynamics for intralayer atomic interactions spherically symmetric interatomic potential interlayer interactions. found that at temperature T<15 K, varies with as T^n, where n = 1 graphene, 1.6 graphene 1.3 reveals an intriguing dependence on twist angle which is particularly pronounced low temperature. results suggest a possibility...

We have theoretically studied acoustic phonon spectra and propagation in rectangular nanowires embedded within elastically dissimilar materials. As example systems, we considered GaN with AlN plastic barrier layers. It has been established that the acoustically mismatched barriers dramatically influence quantized spectrum of nanowires. The lower sound velocity compress energy reduce group velocities nanowire. higher an opposite effect. physical origin this effect is related to redistribution...

One dimensional quantum-dot superlattices (1D-QDSLs) consisting of acoustically mismatched materials are demonstrated theoretically to possess sub-1 W m${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}1}$ thermal conductivity in the 50--400 K range temperatures. We consider coherent Si/Ge 1D-QDSLs, as well model Si/plastic, Si/SiO${}_{2}$ and Si/SiC 1D-QDSLs. The phonon energy spectra group velocities obtained framework face-centered cubic cell lattice dynamics. On this basis, is calculated. A...