We found that an optimized mixture of graphene and multilayer graphene -produced by the high-yield inexpensive liquid-phase-exfoliation technique -can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was determined that a relatively high concentration of single-layer and bilayer graphene flakes (~10-15%) present simultaneously with thicker multilayers of large lateral size (~ 1 m) were essential for the observed unusual K enhancement. The thermal conductivity of a commercial thermal grease was increased from an initial value of ~5.8 W/mK to K=14 W/mK at the small loading f=2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene -multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene -matrix interface.

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The authors report results of micro-Raman spectroscopy investigation of mechanically exfoliated single-crystal bismuth telluride films with thickness ranging from a few-nm-range to bulk limit.It is found that the optical phonon mode A 1u , which is not-Raman active in bulk Bi 2 Te 3 crystals, appears in the atomically-thin films due to crystal-symmetry breaking. The intensity ratios of the out-of-plane A 1u and A 1g modes to the in-plane E g mode grow with decreasing film thickness.The evolution of Raman signatures with the film thickness can be used for identification of Bi 2 Te 3 crystals with the thickness of few-quintuple layers important for topological insulator and thermoelectric applications.

Bismuth telluride (Bi 2 Te 3 ) and related compounds have recently attracted strong interest owing to the discovery of the topological insulator properties in many members of this family of materials. The few-quintuple films of these materials are particularly interesting from the physics point of view. We report results of the micro-Raman spectroscopy study of the "graphene-like" exfoliated few-quintuple layers of Bi 2 Te 3 , Bi 2 Se 3 and Sb 2 Te 3 . It is found that crystal symmetry breaking in few-quintuple films results in appearance of A 1usymmetry Raman peaks, which are not active in the bulk crystals. The scattering spectra measured under the 633-nm wavelength excitation reveals a number of resonant features, which could be used for analysis of the electronic and phonon processes in these materials. In order to elucidate the influence of substrates on the few-quintuple-thick topological insulators we examined the Raman spectra of these films placed on mica, sapphire and hafnium-oxide substrates. The obtained results help to understand the physical mechanisms of Raman scattering in the few-quintuple-thick films and can be used for nanometrology of topological insulator films on various substrates.

We report on the low-frequency current fluctuations and electronic noise in thin-films made of Bi(2)Se(3) topological insulators. The films were prepared via the "graphene-like" mechanical exfoliation and used as the current conducting channels in the four- and two-contact devices. The thickness of the films ranged from ∼50 to 170 nm to avoid hybridization of the top and bottom electron surface states. Analysis of the resistance dependence on the film thickness indicates that the surface contribution to conductance is dominant in our samples. It was established that the current fluctuations have the noise spectrum close to the pure 1/f in the frequency range from 1 Hz to 10 kHz (f is the frequency). The relative noise amplitude S(I)/I(2) for the examined Bi(2)Se(3) films was increasing from ∼5 × 10(-8) to 5 × 10(-6) (1/Hz) as the resistance of the channels varied from ∼10(3) to 10(5) Ω. The obtained noise data is important for understanding electron transport through the surface and volume of topological insulators, and proposed applications of this class of materials. The results may help to develop a new method of noise reduction in electronic devices via the "scattering immune" transport through the surface states.

We report results of investigation of the low-frequency excess noise in device channels made from topological insulators -a new class of materials with a bulk insulating gap and conducting surface states. The thin-film Bi 2 Se 3 samples were prepared by the 'graphene-like' mechanical exfoliation from bulk crystals. The fabricated four-contact devices had linear current-voltage characteristics in the low-bias regime jV SD j < 0.1 V. The current fluctuations had the noise spectral density S I $1/f for the frequency f < 10 kHz. The noise density S I followed the

We review results of the thermal conductivity studies of graphene, which revealed its excellent heat conduction properties. Using the liquid solutions of graphene and few-layer graphene flakes, we produced composites with graphene as the filler material. The measurements of thermal properties of the resulting graphene composites have been measured with the "laser flash" and transient planar-source "hot disk" techniques. We have demonstrated that graphene flakes can substantially increase the effective thermal conductivity of the composite materials even at small volume loading fractions. The thermal conductivity enhancement exceeded a factor of five at 5% of the volume loading fraction and reached a factor of ten for some specific composites. We argue that graphene and few-layer graphene flakes can become efficient fillers for the thermal interface materials.

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