Electric field-dependent phonon spectrum and heat conduction in ferroelectrics.

This article shows experimentally that an external electric field affects the velocity of the longitudinal acoustic phonons (), thermal conductivity (κ), and diffusivity () in a bulk lead zirconium titanate-based ferroelectric. Phonon conduction dominates κ, and the observations are due to changes in the phonon dispersion, not in the phonon scattering. This gives insight into the nature of the thermal fluctuations in ferroelectrics, namely, phonons labeled ferrons that carry heat and polarization.

Controlling Thermal Conductivity in Mesoporous Silica Films Using Pore Size and Nanoscale Architecture.

This work investigates the effect of wall thickness on the thermal conductivity of mesoporous silica materials made from different precursors. Sol-gel- and nanoparticle-based mesoporous silica films were synthesized by evaporation-induced self-assembly using either tetraethyl orthosilicate or premade silica nanoparticles. Since wall thickness and pore size are correlated, a variety of polymer templates were used to achieve pore sizes ranging from 3-23 nm for sol-gel-based materials and 10-70 nm for nanoparticle-based materials.

Intrinsic Low Thermal Conductivity and Phonon Renormalization Due to Strong Anharmonicity of Single-Crystal Tin Selenide.

Two-dimensional (2D) van der Waals material tin selenide (SnSe) has recently attracted intensive interest due to its exceptional thermoelectric performance. However, the thermal properties and phonon transport mechanisms in its single-crystal form remain elusive. Here, we measured high-quality SnSe single crystals using nanoscale thermometry based on ultrafast optical spectroscopy and found that its intrinsic thermal conductivity is highly anisotropic in different crystallographic directions.

Anisotropic Thermal Boundary Resistance across 2D Black Phosphorus: Experiment and Atomistic Modeling of Interfacial Energy Transport.

Interfacial thermal boundary resistance (TBR) plays a critical role in near-junction thermal management of modern electronics. In particular, TBR can dominate heat dissipation and has become increasingly important due to the continuous emergence of novel nanomaterials with promising electronic and thermal applications. A highly anisotropic TBR across a prototype 2D material, i.

High-performance field emission based on nanostructured tin selenide for nanoscale vacuum transistors.

Vacuum field effect transistors have been envisioned to hold the promise of replacing solid-state electronics when the ballistic transport of electrons in a nanoscale vacuum can enable significantly high switching speed and stability. However, it remains challenging to obtain high-performance and reliable field-emitter materials. In this work, we report a systematic study on the field emission of novel two-dimensional tin selenide (SnSe) with rational design of its structures and surface morphologies.

Anisotropic thermal conductivity measurement using a new Asymmetric-Beam Time-Domain Thermoreflectance (AB-TDTR) method.

Anisotropic thermal properties are of both fundamental and practical interests, but remain challenging to characterize using conventional methods. In this work, a new metrology based on asymmetric beam time-domain thermoreflectance (AB-TDTR) is developed to measure three-dimensional anisotropic thermal transport by extending the conventional TDTR technique. Using an elliptical laser beam with controlled elliptical ratio and spot size, the experimental signals can be exploited to be dominantly sensitive to measure thermal conductivity along the cross-plane or any specific in-plane directions.

Experimental observation of high thermal conductivity in boron arsenide.

Improving the thermal management of small-scale devices requires developing materials with high thermal conductivities. The semiconductor boron arsenide (BAs) is an attractive target because of ab initio calculation indicating that single crystals have an ultrahigh thermal conductivity. We synthesized BAs single crystals without detectable defects and measured a room-temperature thermal conductivity of 1300 watts per meter-kelvin.

Thermal Properties and Phonon Spectral Characterization of Synthetic Boron Phosphide for High Thermal Conductivity Applications.

Heat dissipation is an increasingly critical technological challenge in modern electronics and photonics as devices continue to shrink to the nanoscale. To address this challenge, high thermal conductivity materials that can efficiently dissipate heat from hot spots and improve device performance are urgently needed. Boron phosphide is a unique high thermal conductivity and refractory material with exceptional chemical inertness, hardness, and high thermal stability, which holds high promises for many practical applications.

A Solution Processable High-Performance Thermoelectric Copper Selenide Thin Film.

A solid-state thermoelectric device is attractive for diverse technological areas such as cooling, power generation and waste heat recovery with unique advantages of quiet operation, zero hazardous emissions, and long lifetime. With the rapid growth of flexible electronics and miniature sensors, the low-cost flexible thermoelectric energy harvester is highly desired as a potential power supply. Herein, a flexible thermoelectric copper selenide (Cu Se) thin film, consisting of earth-abundant elements, is reported.

Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus.

Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode.

Continuous aerosol size separator using inertial microfluidics and its application to airborne bacteria and viruses.

A microchannel-based aerosol size separator that separates submicron aerosols according to particle inertial differences and Dean vortices in the airflow was developed for use in low-cost, portable, real-time aerosol collectors, detectors, concentrators and other such devices. The microfluidic inertial separator was furthermore applied to simultaneously separate airborne microorganisms by size, such as airborne viruses and bacteria from larger aerosols and viral particles from bacterial cells. The entire system was designed by numerical simulation and analysis.

Fast and continuous microorganism detection using aptamer-conjugated fluorescent nanoparticles on an optofluidic platform.

Fast and accurate pathogen detection in aquatic environments is challenging in many biomedical studies and microbial diagnostic applications. In this study, we developed a real-time, continuous, and non-destructive single cell detection method using target specific aptamer-conjugated fluorescent nanoparticles (A-FNPs) and an optofluidic particle-sensor platform. A-FNPs selectively bound to the surfaces of target bacteria (Escherichia coli) and labeled them with high affinity and selectivity so that target bacteria can be countable particles in an optofluidic particle-sensor.

Real-time detection of an airborne microorganism using inertial impaction and mini-fluorescent microscopy.

To achieve successful real-time detection of airborne pathogenic microorganisms, the problem must be considered in terms of their physical size and biological characteristics. We developed an airborne microorganism detection chip to realize the detection of microorganisms, ensuring compactness, sensitivity, cost-efficiency, and portability, using three key components: an inertial impaction system, a cartridge-type impaction plate, and a mini-fluorescent microscope. The inertial impaction system was used to separate microorganisms in terms of their aerodynamic particle size, and was fabricated with three impaction stages.