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Leakage current and dielectric breakdown effects are conventionally studied under electrical fields alone, with little regard for mechanical stresses. In this letter, we demonstrate that mechanical stress can influence the reliability of dielectrics even at lower field strengths. We applied tensile stress (up to 8 MPa) to a 33% porous, 504 nm thick carbon doped oxide thin film and measured the leakage current at constant electrical fields (up to 2.5 MV/cm). The observed increase in leakage current at relatively low electric fields suggests that mechanical stress assists in trap/defect mediated conduction by reducing the energy barrier potential to de-trap charges in the dielectric.

Recent computational studies predict mechanical strain–induced changes in thermal transport, which is yet to be validated by experimental data. In this article, we present experimental evidence of an increase in thermal conductivity of nominally 200-nm-thick freestanding amorphous silicon thin films under externally applied tensile loading. Using a combination of nanomechanical testing and infrared microscopy, we show that 2.5% tensile strain can increase thermal conductivity from 1 to 2.4 W/m-K. We propose that such an increase in thermal conductivity might be due to strain-induced changes in microstructure and/or carrier density. Microstructural and optical reflectivity characterization through Raman and infrared spectroscopy are presented to investigate this hypothesis.

Recent studies on free convective heat transfer from micro and nanoscale structures show that the heat transfer coefficient is size dependent. The heat transfer coefficient is found to increase at smaller scales, which is ascribed to the higher surface area to volume ratio. Also, the mode is changed from advection to conduction due to the decaying influence of the gravitational field. Interestingly, it is tacitly assumed that the size effect is due to the specimen, since not a single study on the effect of the size of heat source on the convective heat transfer exists in the literature. In this study, we provide unambiguous experimental evidence of the predominance of heater size on the heat transfer coefficient. For micro-heaters, the heat transfer coefficient is measured to about 3200 W/m2 K. This value drops to about 110 W/m2 K for a millimeter scale heater and to 10 W/m2 K for a macroscopic heater; all for a nanoscale thin film specimen. This finding is particularly significant in microelectronic applications where localized heating (hot spots) in small areas is very common.

The influence of temperature and stress on grain growth was investigated in nanocrystalline nickel thin films in situ inside a transmission electron microscope. Independently, temperature and stress did not show any appreciable effect. However, concurrent loading at only 20% of melting temperature and 20% of yield stress resulted in significant grain boundary mobility and grain growth. We propose that grain growth in nanocrystals is a stress-heterogeneity-relieving mechanism that may not necessarily be associated with plasticity as proposed in the literature.

The thermal conductivity of low-dielectric-constant (low-k) SiOC:H and SiC:H thin films has been measured as a function of porosity using a heat transfer model based on a microfin geometry and infrared thermometry. Microscale specimens were patterned from blanket films, released from the substrate, and subsequently integrated with the experimental setup. Results show that the thermal conductivity of a dense specimen, 0.7 W/mK, can be reduced to as low as 0.1 W/mK by introducing 30% porosity into it. The measured thermal conductivity shows a nonlinear decrease with increasing porosity that approximately follows the porosity-weighted simple medium model for porous materials. Neither the differential effective medium nor the coherent potential model could predict the density dependence of the thermal conductivity. These results suggest that more careful consideration is required for application of generic porous materials modeling to low-k dielectrics.

Accurate prediction of heat transfer from micro and nanoscale devices is very important for their operation and reliability. While the general consensus is that the heat transfer coefficient increases at the smaller scales, the literature also indicates contradiction in the scaling across length scales. In this paper, we present an experimental technique to accurately characterize heat transfer from micro to nano scales using infrared microscopy on nanofabricated specimens that are integrated with micro heaters. The heat transfer coefficient for quiescent air is found to be about two orders of magnitude higher than its bulk counterpart. It also showed pronounced inversely proportional relationship with temperature and suggested that solid to air conduction is the dominant mode of heat transfer. It was found that pressure only indirectly influences heat transfer. Based on the experimental data, we present an empirical relationship for the heat transfer coefficient that depends on the ratio of the surface area to cross-sectional area, temperature of the heated solid and its proximity to other solid bodies.

Characterization of thermal transport in nanoscale thin films with very low thermal conductivity (

We present experimental evidence of anomalously high grain boundary mobility in 3–5 nm grain size platinum films at near room temperature. This mobility can be explained in terms of the localized electromigration stresses of the order of a few GPa that we observed. In the absence of conventional deformation mechanisms, the stress is relaxed through rapid grain growth up to a grain size of 40 nm. For larger grain sizes, grain boundary mobility is reduced as the stresses are relaxed by grain rotation and dislocation-based deformation mechanisms.

We demonstrate a microelectromechanical-system-based setup for fatigue studies on 200-nm-thick freestanding aluminum specimens in situ inside the transmission electron microscope. The specimens did not show any sign of fatigue damage even at 1.2 ×106 cycles under nominal stresses about 80% of the static ultimate strength. We show direct evidence to propose that the conventional theory of fatigue crack nucleation through slip bands does not work for nanoscale freestanding thin films, which gives rise to the anomalous fatigue insensitivity.

While the current trend in nanoscale materials characterization is to investigate single domain (mechanical, electrical, thermal) properties, this study explore if the extremely small size also `couples' these domains. However, even single domain studies are challenging at the nanoscale and the literature suggests the need for new multi-domain characterization techniques. In this paper, we present experimental design for performing nanoscale multi-physics characterizations. Demonstrative results on the role of mechanical strain on the thermal and electrical conductivity of metals, semiconductors and insulators are also presented.

Oxidation of polycrystalline diamond films on (111) Si wafers in air at temperatures up to 1073 K was investigated by thermogravimetry. The diamond films before and after partial oxidation were characterized by optical and scanning electron microscopy, x-ray, infrared, and Raman spectroscopy. The oxidation of synthetic diamond films started at a lower temperature than that for natural diamond. The rates of oxidation of the diamond films synthesized by the hot filament and the microwave plasma methods were intermediate between the rates of oxidation of the 111 and 100 planes of natural diamond crystals. The apparent activation energy for the oxidation of the synthetic diamond films agreed well with that for the oxidation of natural diamond via diamond to graphite transition at low oxygen pressures.

Preparation de graphite polycristallin et irradiation par un laser CO 2 sous vide. Observation des echantillons par diffraction RX et plusieurs methodes de microscopie electronique. Ces deux types d'echantillons correspondent au materiau preleve dans le cratere d'irradiation ou au materiau de depart, dont le cratere est rempli d'une pâte de graphite et d'epoxy. Les grains observes dans le premier cas seraient du lonsdaleite

Thermal conductivity of freestanding 10 nm and 20 nm thick chemical vapor deposited hexagonal boron nitride films was measured using both steady state and transient techniques. The measured value for both thicknesses, about 100 ± 10 W m−1 K−1, is lower than the bulk basal plane value (390 W m−1 K−1) due to the imperfections in the specimen microstructure. Impressively, this value is still 100 times higher than conventional dielectrics. Considering scalability and ease of integration, hexagonal boron nitride grown over large area is an excellent candidate for thermal management in two dimensional materials-based nanoelectronics.

We present a micro-electro-mechanical system-based experimental technique to measure thermal conductivity of freestanding ultra-thin films of amorphous silicon nitride (Si3N4) as a function of mechanical strain. Using a combination of infrared thermal micrography and multi-physics simulation, we measured thermal conductivity of 50 nm thick silicon nitride films to observe it decrease from 2.7 W (m K)?1?at zero strain to 0.34 W (m K)?1?at about 2.4% tensile strain. We propose that such strong strain?thermal conductivity coupling is due to strain effects on fraction?phonon interaction that decreases the dominant hopping mode conduction in the amorphous silicon nitride specimens.

Diamond and other high-pressure phases of carbon were synthesized in air by exposing fine particles of carbon black to carbon dioxide and Nd-YAG laser radiation. The high-pressure phases were separated from the carbon black by selective oxidation and were characterized by electron and x-ray diffraction. Formation of cubic diamond, chaoite and graphite was confirmed.

Exposure of a falling stream of 1 μm average size α‐quartz particles to a continuous wave or pulsed CO2 laser beam in air resulted in the formation of a complete series of high‐pressure phases of silica: coesite, stishovite, and apparently even denser forms with α‐PbO2 and Fe2N structures. Since the laser exposure technique works with the carbon black to diamond transition, the technique is confirmed as a simple and generally applicable means to achieve the same effects as exposure to several hundred kilobars pressure.