arXiv subjects

O. V. Kolosov

Publications and source records attributed to O. V. Kolosov.

4 recordsLinked to original sources

arXiv2023

Tuning thermoelectric properties of Sb$_2$Te$_3$-AgSbTe$_2$ nanocomposite thin film -- synergy of band engineering and heat transport modulation

The present study demonstrates a large enhancement in the Seebeck coefficient and ultralow thermal conductivity (TE) in Sb$_2$Te$_3$-AgSbTe$_2$ nanocomposite thin film. The addition of Ag leads to the in-situ formation of AgSbTe$_2$ secondary phase nanoaggregates in the Sb$_2$Te$_3$ matrix during the growth resulting in a large Seebeck coefficient and reduction of the thermal conductivity. A series of samples with different amounts of minor AgSbTe$_2$ phases are prepared to optimize the TE performance of Sb$_2$Te$_3$ thin films. Based on the experimental and theoretical evidence, it is concluded that a small concentration of Ag promotes the band flattening and induces a sharp resonate-like state deep inside the valence band of Sb$_2$Te$_3$, concurrently modifying the density of states (DOS) of the composite sample. In addition, the electrical potential barrier introduced by the band offset between the host TE matrix and the secondary phases promotes strong energy-dependent carrier scattering in the composite sample, which is also responsible for enhanced TE performance. A contemporary approach based on scanning thermal microscopy is performed to experimentally obtain thermal conductivity values of both the in-plane and cross-plane directions, showing a reduced in-plane thermal conductivity value by ~ 58% upon incorporating the AgSbTe$_2$ phase in the Sb$_2$Te$_3$ matrix. Benefitting from the synergistic manipulation of electrical and thermal transport, a large ZT value of 2.2 is achieved at 375 K. The present study indicates the importance of a combined effect of band structure modification and energy-dependent charge carrier scattering along with reduced thermal conductivity for enhancing TE properties.

cond-mat.mtrl-sci↗

arXiv2017

Shear Forces and Heat Conductance in Nanoscale Junctions

Nanoscale solid-solid contacts define a wealth of material behaviours from the electrical and thermal conductivity in modern electronic devices to friction and losses in micro- and nanoelectromechanical systems. For modern ultra-high integration processor chips, power electronic devices and thermoelectrics one of the most essential, but thus far most challenging, aspects is the assessment of the heat transport at the nanoscale sized interfaces between their components. While this can be effectively addressed by a scanning thermal microscopy, or SThM, which demonstrates the highest spatial resolution to thermal transport to date, SThM quantitative capability is undermined by the poorly defined nature of the nanoscale contact between the probe tip and the sample. Here we show that simultaneous measurements of the shear force and the heat flow in the probe-sample junction shows distinct correlation between thermal conductance and maximal shear force in the junction for multiple probe-material combinations. Quantitative analysis of this correlation confirmed the intrinsic ballistic nature of the heat transport in the tip-surface nanoscale contact suggesting that they are, ultimately, composed of near-atomic sized regions. Furthermore, in analogy to the Wiedemann-Franz law, which links electrical and thermal conductivity in metals, we suggest and experimentally confirm a general relation that links shear strength and thermal conductance in nanoscale contacts via the fundamental material properties of heat capacity and heat carrier group velocity, thus opening new avenues for quantitative exploration of thermal transport on the nanoscale.

cond-mat.mes-hall↗

arXiv2015

Optical properties of two-dimensional gallium chalcogenide films

Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thickness ranging from from 200 nm to a single unit cell. In both materials, PL shows dramatic decrease by 10$^4$-10$^5$ when film thickness is reduced from 200 to 10 nm. Based on evidence from cw and time-resolved PL, we propose a model explaining the PL decrease as a result of non-radiative carrier escape via surface states.

cond-mat.mes-hall↗

arXiv2014

Nanothermal Characterization of Amorphous and Crystalline Phases in Chalcogenide Thin Films with Scanning Thermal Microscopy

The thermal properties of amorphous and crystalline phases in chalcogenide phase change materials (PCM) play a key role in device performance for non-volatile random-access memory. Here, we report the nanothermal morphology of amorphous and crystalline phases in laser pulsed GeTe and Ge2Sb2Te5 thin films by scanning thermal microscopy (SThM). By performing SThM measurements and applying quantitative physical models to two film thicknesses, the PCM thermal conductivities and thermal boundary conductances between the PCM and SThM probe are independently estimated for the amorphous and crystalline phase of each stoichiometry.

cond-mat.mtrl-sci↗