Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.

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Nanoscale thermal transport

A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, thermal management of nanoscale electronics, and nanoparticles for thermal medical therapies are motivating studies of the applied physics of thermal transport at the nanoscale. This review emphasizes developments in experiment, theory, and computation in the past ten years and summarizes the present status of the field. Interfaces become increasingly important on small length scales. Research during the past decade has extended studies of interfaces between simple metals and inorganic crystals to interfaces with molecular materials and liquids with systematic control of interface chemistry and physics. At separations on the order of ∼1 nm, the science of radiative transport through nanoscale gaps overlaps with thermal conduction by the coupling of electronic and vibrational excitations across weakly bonded or rough interface...

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Nanoscale thermal transport. II. 2003–2012

Over the past 20 years, organic transistors have developed from a laboratory curiosity to a commercially viable technology. This critical review provides a short summary of several important aspects of organic transistors, including materials, microstructure, carrier transport, manufacturing, electrical properties, and performance limitations (200 references).

Organic thin-film transistors.

Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3ω method. SiO2 and SiNx films are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films >100 nm thick, the thermal conductivity shows little dependence on film thickness: the thermal conductivity of PECVD SiO2 films is only ∼10% smaller than the conductivity of SiO2 grown by thermal oxidation. The thermal conductivity of PECVD SiNx films is approximately a factor of 2 smaller than SiNx deposited by atmospheric pressure CVD at 900 °C. For films <50 nm thick, the apparent thermal conductivity of both SiO2 and SiNx films decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistance RI. At room temperature, RI∼2×10−8 K m2 W−1 and is equivalent to the thermal resistance of a ∼20 nm thick layer of SiO2 .

Heat transport in thin dielectric films

The thermal conductivity of Si–Ge superlattices with superlattice periods 30  2 × 109 W m−2 K−1 at 200 K. Superlattices with relatively longer periods, L>130 A, have smaller thermal conductivities than the short-period samples. This unexpected result is attributed to a strong disruption of the lattice vibrations by extended defects produced during lattice-mismatched growth.

Thermal conductivity of Si–Ge superlattices

The thermal conductivity of sputtered a-Si:H thin films for a hydrogen content of 1--20 % and a film thickness of 0.2--1.5 \ensuremath{\mu}m is determined in the temperature range 80--400 K using an extension of the 3\ensuremath{\omega} measurement technique. The reliability of the method is demonstrated on 1-\ensuremath{\mu}m-thick a-${\mathrm{SiO}}_{2}$ thermally grown on Si. Scattering of phonons at the interface between the a-Si:H film and the substrate places a simple upper limit on the heat transport by long-wavelength phonons and facilitates the comparison of the experimental data to recent numerical solutions of a Kubo formula using harmonic vibrations.

Thermal conductivity of a -Si:H thin films

An analysis of the difference in behavior of top and bottom contact organic thin film transistors using device simulation

Various approaches to white organic light emitting diodes and their recent advancements

Optoelectronic devices and methods for their fabrication having enhanced and controllable rates of the radiative relaxation of triplet light emitters are provided exemplified by organic light emitting devices based on phosphorescent materials with enhanced emission properties. Acceleration of the radiative processes is achieved by the interaction of the light emitting species with surface plasmon resonances in the vicinity of metal surfaces. Non-radiative Forster-type processes are efficiently suppressed by introducing a transparent dielectric or molecular layer between the metal surface and the chromophore. For materials with low emission oscillator strengths (such as triplet emitters), the optimal separation distance from the metal surface is determined, thus suppressing energy transfer and achieving a significant acceleration of the emission rate.

Plasmon assisted enhancement of organic optoelectronic devices

This article experimentally identifies the hydrogen incorporation and release processes which control the final hydrogen content of hydrogenated amorphous silicon films (a‐Si:H). We deposit films using reactive magnetron sputtering of a silicon target in an Ar and H2 atmosphere. Hydrogen incorporation or loss is measured using real time infrared reflectance spectroscopy. An optical cavity substrate increases the sensitivity, allowing us to observe Si–H bonding in layers ≥5 A thick via the stretching mode absorption (1800–2300 cm−1). We observe a narrow component at ∼2100 cm−1 corresponding to all SiHx bonds on the physical surface; the line width allows us to distinguish this contribution from the broader bulk modes. Various combinations of growth flux (isotope labeling, hydrogen partial pressure between 0.1 and 2.0 mTorr) and substrate material (on SiO2, a‐Si, or a‐Si:D) at substrate temperatures between 120 and 350 °C are used to distinguish various mechanisms. From the deposition of a‐Si:H films on SiO...

Hydrogen‐surface reactions during the growth of hydrogenated amorphous silicon by reactive magnetron sputtering: A real time kinetic study by in situ infrared absorption

Monica Katiyar

Papers

Thermal conductivity of a -Si:H thin films

An analysis of the difference in behavior of top and bottom contact organic thin film transistors using device simulation

Various approaches to white organic light emitting diodes and their recent advancements

Plasmon assisted enhancement of organic optoelectronic devices

Hydrogen‐surface reactions during the growth of hydrogenated amorphous silicon by reactive magnetron sputtering: A real time kinetic study by in situ infrared absorption