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The increasing interests in analog computing nowadays call for multi-purpose analog computing platforms with reconfigurability. The advancement of analog computing, enabled by novel electronic elements like memristors, has shown its potential to sustain the exponential growth of computing demand in the new era of analog data deluge. Here, we experimentally demonstrate a platform of a memristive field-programmable analog array (memFPAA) with memristive devices serving as a variety of core analog elements and CMOS components as peripheral circuits. We reconfigure the memFPAA and implement a first-order band pass filter, an audio equalizer, and an acoustic mixed frequency classifier, as application examples. The memFPAA, featured with programmable analog memristors, memristive routing networks, and memristive vector-matrix multipliers, opens opportunities for fast prototyping analog designs as well as efficient analog applications in signal processing and neuromorphic computing. This article is protected by copyright. All rights reserved.

In this work, the effect of rapid thermal annealing (RTA) temperature on the ferroelectric polarization in zirconium-doped hafnium oxide (HZO) was studied. To maximize remnant polarization (2Pr), in-plane tensile stress was induced by tungsten electrodes under optimal RTA temperatures. We observed an increase in 2Pr with RTA temperature, likely due to an increased proportion of the polar ferroelectric phase in HZO. The HZO capacitors annealed at 400°C did not exhibit any ferroelectric behavior, whereas the HZO capacitors annealed at 800°C became highly leaky and shorted for voltages above 1 V. On the other hand, annealing at 700 °C produced HZO capacitors with a record-high 2Pr of ∼ 64 μC cm−2 at a relatively high frequency of 111 kHz. These ferroelectric capacitors have also demonstrated impressive endurance and retention characteristics, which will greatly benefit neuromorphic computing applications.

Memristor devices fabricated using the chalcogenide Ge2Te3 phase change thin films in a metal-insulator-metal structure are characterized using thermal and electrical stimuli in this study. Once the thermal and electrical stimuli are applied, cross-sectional transmission electron microscopy (TEM) and X-ray energy-dispersive spectroscopy (XEDS) analyses are performed to determine structural and compositional changes in the devices. Electrical measurements on these devices showed a need for increasing compliance current between cycles to initiate switching from low resistance state (LRS) to high resistance state (HRS). The measured resistance in HRS also exhibited a steady decrease with increase in the compliance current. High resolution TEM studies on devices in HRS showed the presence of residual crystalline phase at the top-electrode/dielectric interface, which may explain the observed dependence on compliance current. XEDS study revealed diffusion related processes at dielectric-electrode interface characterized, by the separation of Ge2Te3 into Ge- and Te- enriched interfacial layers. This was also accompanied by spikes in O level at these regions. Furthermore, in-situ heating experiments on as-grown thin films revealed a deleterious effect of Ti adhesive layer, wherein the in-diffusion of Ti leads to further degradation of the dielectric layer. This experimental physics-based study shows that the large HRS/LRS ratio below the current compliance limit of 1 mA and the ability to control the HRS and LRS by varying the compliance current are attractive for memristor and neuromorphic computing applications.

Composite interfaces between heterogeneous materials exist in many applications which includes electronics packaging. The interface will affect properties such as mechanical integrity during thermal cycling, heat transport and electrical transport due to the inherent disparate properties such as coefficient of thermal expansion (CTE), atomic structure, interface bonding and fabrication processes. Novel interface engineering will be vital for electronics packaging utilized in extreme environment temperatures beyond the standard ranges such as -55 °C to 150 °C. The failure of standard electronics packaging materials with heterogeneous interfaces under thermal cycle fatigue is investigated. Based on the failure analysis, several multifunctional interfaces are developed to bridge the heterogeneous interface and to provide the desired properties and functionality. Approaches to achieve these heterogeneous structures, the materials choices to preserve the multifunctional properties and the modeling predictions are considered. Test structures are prepared of the candidate interfaces, the morphologies are investigated and testing of the thermal cycle fatigue properties over the range -55 °C to 300 °C is performed and will be discussed.

To measure the thermal conductivity of microscale specimens, the methodology and capability of a novel thermal conductivity measurement technique, applicable to micro- and nanoscale scale measurement, is discussed. The methodology integrates a device consisting of two identical microheaters with thin-filmed platinum heating elements and integrated resistance temperature devices (RTDs) on trenched, thermally isolated silicon substrates. The platinum RTDs used for temperature measurement were calibrated by monitoring the melting points of three metallic microspheres placed on the device as its power was increased. We validated our measurement technique by measuring thermal conductivities of several micrometer-sized metallic wire standards with known values. A multiphysical analysis based on a 3D finite element method (FEM) has been conducted to simulate both the electric and thermal behaviors of the microheaters. These FEM simulations describing the heating and heat flow in the device facilitated optimizing the device geometrical configuration to minimize heat loss and thus to realize high measurement fidelity. The temperature profiles near the microheaters obtained during measurement confirmed the device design objective of localizing heat only to microheaters to achieve the desired high measurement fidelity.

All-atom Molecular Dynamics simulations were used to study the coefficient of thermal expansion (CTE) in Cu/Zr amorphous alloys with various compositions. We explored the possibility of using these alloys as bonding interface material between ceramics chips and copper leads in power electronics and microelectronic packaging applications with an objective of reducing CTE mismatch at the bonding interface. It was expected that with the appropriate design of reduced CTE mismatch at the interface, the Cu/Zr bonding layer could withstand larger thermal loads and significantly extend device life compared to the devices that currently implement directly bonded copper (DBC) approach. The non-monotonic increase of material CTE with copper content in the alloy was analyzed and explained using new tessellation algorithm that is focused on the configuration of close contacts between the neighboring atoms. The modeling using Turner equation shows that the “leveling” of CTE dependence in the mid-composition range is due to the contribution from non-tetrahedral polyhedra and would be expected for any binary glass system. Contrary to that, the “dip” at Cu-rich compositions is caused by the nature of the metallic bonding in the alloy, and is specific to Cu-Zr glass.

A new parameter set to model monoclinic gallium oxide, β-Ga

Commercial off-the-shelf (COTS) electronics are generally not specifically designed to perform in extremely transient high impact scenarios. This research focused on the development of a silver-decorated carbon black-based polymeric nanocomposite with properties such as high conductivity, flexibility, and shock absorbency. Polymeric rubber materials are generally very flexible and shock absorbing, however, most polymeric materials are electrical insulators. The dispersion of the silver-decorated carbon black into the polymeric matrix could significantly improve the electrical conductivity. The processing and fabrication of Ag-CB (silver-carbon black)/Epoxy (thermosetting epoxy polymer) and Ag-CB/TPU (thermoplastic polyurethane) will be reported. Both Ag-CB/Epoxy and Ag-CB/TPU mixtures with solvents showed the shear-thinning behavior, which was an important characteristic for direct printing of traces and Additive Manufacturing (AM). The mechanical properties of the nanocomposites were measured using Dynamic Mechanical Analysis (DMA) over a wide range of temperatures. These nanocomposite materials were also successfully used to print flexible circuits using a 3D-printing machine. The electrical resistance change for the Ag-CB/Epoxy on polydimethylsiloxane (PDMS) and Ag-CB/TPU on PDMS under strain was studied, and the results will be discussed.

This research presents a multi-channel micro-scale heat exchanger for thermal management of microelectronics hot spots. Electro-osmotic flow (EOF) was implemented to drive the cooling liquid through the micro-channels of the heat exchanger. Various cooling liquids including, deionized water, distilled water, borax buffer, and Al2O3 nano-particle solution, were tested and compared based on their flow rates and increase in cooling liquid temperature. The micro-scale heat exchanger was fabricated using a combination of polydimethylsiloxane (PDMS) and silicon dioxide-coated substrate. A constant heat flux heater was used to simulate the heat generated by microelectronic devices. The flow rate of the cooling liquid and its temperatures at the inlet and the outlet reservoirs were measured. Deionized water produced a flow rate of 30.1 μL/min and 2 °C increase between the inlet and the outlet reservoir temperatures at 1 W heating power and 400 V of EOF. The flow rate and the increase in temperature of distilled water at the same conditions were 22.7 μL/min and 3 °C, respectively. For the borax buffer the flow rate was 33.1 μL/min and the increase in temperature was 2.7 °C. Most notably, there was an increase in temperature of 2.4 °C with a lower flow rate of 20.4 μL/min when the Al2O3 nano-particle solution was used. Among all cooling liquids, the Al2O3 nano-particle solution showed the highest scaled specific heat energy removal with a maximum of ~ 69% increase compared to deionized water. Further, the current micro-scale heat exchanger device was able to produce higher electro-osmotic flow rates due to the use of PDMS on three sides of the micro-channel; thus providing smoother walls and higher zeta-potential while the silicon surface allowed heat transfer to the cooling liquid. The increased flow rate allowed enhanced heat removal from higher heat flux areas (hot spots) of microelectronic devices without the need for high-pressure pumping systems.

This work presents electrical characterization and analysis of the dominant charge transport mechanism suggesting inhomogeneous, filamentary conduction for a lithium niobate switching layer based memristor for use in neuromorphic computing. Memristor conductivity has been investigated both for the high and low resistance states. It is suggested that when the device is in a high resistance state, deep trap energy level within the switching layer initiate the device conduction process. The elastic trap assisted tunneling mechanism with a simple steady state approach agrees with the experimental measurements in the high resistance state. This work considers existence of inhomogeneously distributed positively charged oxygen ions/vacancies (within the oxygen deficient switching layer) as the deep trap energy level, required for electron tunneling from memristor electrode. Alternatively, ohmic conduction was found to be the main mechanism for the memristor on state conductivity at room temperature. Existence of intermediate resistive states in the memristor’s high resistive region was experimentally investigated and the elastic trap assisted tunneling mechanism for such phenomena was validated through simulation.

The development of neuromorphic computing architectures based on two terminal filamentary resistance switching devices is limited in part by the high degree of variability in resistance states and switching voltages. Because of the large role filament shape plays in directing thermal and electric fields around the filament (and thus switching parameters), unambiguous knowledge of filament morphology resulting from direct characterization of filament shape is essential to solve critical ongoing challenges of device switching variability. Here, we have utilized a conductive atomic force microscopy scalpel technique to simultaneously scribe through a polycrystalline dielectric layer in formed Cu/HfO2/p+Si electrochemical metallization cell devices. Filament tomograms reveal that when conductive filaments are formed at typical bias conditions (4 V, 100 μA), a variety of filament shapes result, which deviate from the inverse conical shape predicted by the phenomenological electrochemical model. Furthermore, the observation of an increasing spectrum of damage which scales with forming voltage (associated with compliance current overshoot), and which is uncorrelated with electric field or oxide microstructure, supports the role of thermal pulses in expanding filaments, leading to irreversible dielectric breakdown structures at the extreme. Overall, these findings suggest that the original conductive filament shape can be highly varied as a result of thermally driven expansion from joule heating during the forming step, which is not explicitly accounted for in the widely accepted electrochemical model.

In emerging flexible electronics survivable to high strain-rate deformation (high impact environment), interconnects materials are to exhibit high strain to failure characteristics while maintaining the desired electrical, and in high power applications thermal properties as well. In this work we present a novel nano materials possessing high strain to failure properties with desired electrical and thermal characteristics. A junctioned interconnected network of nano materials (carbon nanofibers, in our case) is embedded in highly flexible polymers. Atomistic scale simulation reveals that design of network junctions critically influence the electrical and thermal properties, whereas the flexibility in the network provides the strain resiliency. The network contact electrical conductance is influenced by the overlapping electronic orbitals of the adjacent (joining nano elements) at the junction, whereas, the junction thermal conductance depends on the matching of the atomic mass and atomic interaction potentials of the junction materials composition. To facilitate welding of the junctions of the nano elements, junctions with metallic nano particles (Ti, Cr, Au, Ag) have also been studied. On processing of such junctioned hybrid network of carbon nanofibers in flexible polymers, bio-inspired Peptide assisted Au nanoparticle dispersion on carbon nanofibers is being pursued to create metallic nano junctions. In addition, characteristics for direct printing (additive manufacturing) of the material is demonstrated. Both the computational and supporting experimental work will be presented to discuss the potential of this novel hybrid nano material concept for high flexibility and strain resiliency as a viable interconnect materials for flexible electronics.

et al., Tin Selenide (SnSe), a thermoelectric material of the chalcogenide family, has attracted tremendous interest in the past few years due to its unprecedented thermoelectric figure-of-merit, ZT, of 2.6. In this work we have carried out an experimental study of the impact of annealing on the thermoelectric properties of polycrystalline SnSe formed by cold-pressing un-doped SnSe powders with a Hall carrier concentration of 5.37 × 10 cm. The crystalline structure and morphology of the samples are characterized and properties, including electrical conductivity, Seebeck coefficient and thermal conductivity, are measured. It is found that thermal annealing has a large impact on both the microstructure and the thermoelectric properties. Notably, annealing leads to re-alignment of crystalline domains, increase in Seebeck coefficient by a factor of as much as 3, and increase in the electrical conductivity. A peak ZT of 0.11 was achieved at 772 K which is smaller than un-doped polycrystalline SnSe., We wish to thank: Universidad Diego Portales, through the support of the Semilla project, JSR and CMST through the support of the Spanish MINECO project nanoTHERM (Grant No. CSD 2010-0044), the ICN2 – Institut Catala de Nanociencia i Nanotecnologia, the Aerospace and Mechanical Engineering Department at University of Notre Dame, the Physics Institute and Engineering School of Pontificia Universidad Católica de Chile, and finally to the Research Center on Nanotechnology and Advanced Materials, CIEN-UC.

Conventional adhesives show a decrease in the adhesion force with increasing temperature due to thermally induced viscoelastic thinning and/or structural decomposition. Here, we report the counter-intuitive behaviour of carbon nanotube (CNT) dry adhesives that show a temperature-enhanced adhesion strength by over six-fold up to 143 N cm−2 (4 mm × 4 mm), among the strongest pure CNT dry adhesives, over a temperature range from −196 to 1,000 °C. This unusual adhesion behaviour leads to temperature-enhanced electrical and thermal transports, enabling the CNT dry adhesive for efficient electrical and thermal management when being used as a conductive double-sided sticky tape. With its intrinsic thermal stability, our CNT adhesive sustains many temperature transition cycles over a wide operation temperature range. We discover that a ‘nano-interlock' adhesion mechanism is responsible for the adhesion behaviour, which could be applied to the development of various dry CNT adhesives with novel features., Adhesives typically lose adhesion strength at high temperatures. Here, the authors design a carbon nanotube dry adhesive that becomes stronger with rising temperature, and ascribe this counterintuitive behavior to a thermally-induced nanoscale interlocking mechanism.

A new parameter set to model monoclinic gallium oxide, β-Ga2O3, with the density functional tight binding (DFTB) method is developed. Using this new parameter set, DFTB calculations of bulk electronic band structure, surface energy of low-index surfaces, and formation energy of native point vacancy defects are performed and compared with the state-of-the-art density functional theory (DFT) calculations using the advanced hybrid exchange correlation functional. DFTB calculates the bandgap energy of 4.87 eV around the Fermi energy with the conduction band approximately following the DFT study by Peelaers and Van de Walle [Phys. Status Solidi B 252, 828 (2015)]. The surface energies calculated feature the correct order of stability among low index surfaces with surface energies in semiquantitative agreement with Bermudez' report [Chem. Phys. 323, 193 (2006)]. Oxygen and gallium vacancy defect formation energies and respective transition levels calculated using DFTB with a new parameter set are in semiquantitative agreement with the previous DFT reports by Varley et al. and Zacherle et al. [Appl. Phys. Lett. 97, 142106 (2010); Phys. Rev. B 87, 235206 (2013)]. This new semiempirical parameter set for β-Ga2O3, validated in bulk, surface, and point properties, would be useful for large spatiotemporal quantum chemical calculations regarding β-Ga2O3.

Vertically aligned arrays of multiwall carbon nanotubes (MWCNT) were decorated with gold (Au) nanoparticles of different diameter and areal densities and spun into yarns. The melting point of Au nanoparticles determined by differential scanning calorimetry was approximately 260 °C, well below the oxidation temperature of carbon. A continuous yarn was formed while pulling out a bundle of CNTs from the metalized CNT array. Relatively low temperature (300 °C) thermal processing of the metalized yarn resulted in a 30% improvement in thermal conductivity, 40% increase in electrical conductivity and a 4× increase in elastic modulus. Cross-sections of the yarn were examined with transmission electron microscopy to characterize the physical nature of the metal–nanotube interface. The deposition procedure described to decorate the nanotube yarns is easily scalable to larger CNT arrays or other configurations for commercial applications, such as medical implants, lightweight conductors, smart uniforms for the soldiers, and conformal electronics in aerospace industry.

The creation of three-dimensionally engineered nanoporous architectures via covalently interconnected nanoscale building blocks remains one of the fundamental challenges in nanotechnology. Here we report the synthesis of ordered, stacked macroscopic three-dimensional (3D) solid scaffolds of graphene oxide (GO) fabricated via chemical cross-linking of two-dimensional GO building blocks. The resulting 3D GO network solids form highly porous interconnected structures, and the controlled reduction of these structures leads to formation of 3D conductive graphene scaffolds. These 3D architectures show promise for potential applications such as gas storage; CO2 gas adsorption measurements carried out under ambient conditions show high sorption capacity, demonstrating the possibility of creating new functional carbon solids starting with two-dimensional carbon layers.

Vapor phase growth of gold, nickel and titanium metal nanoparticles on multiwall carbon nanotube (MWCNT) buckypaper by sputtering was investigated. The size and distribution of nanoparticles was dependent on the intrinsic binding energy of the metal elements, but could be altered to mimic that of metals with different binding energies by in situ modification of the MWCNT surfaces by energetic metal ions or annealing of the buckypaper. A range of average gold particle diameters from approximately 5–30 nm could be produced depending on the intrinsic sputter process parameters (especially metal ion flux and kinetic energy) and defect density of the MWCNT surfaces, which could also be controlled by annealing prior to sputtering. The diameter of the MWCNTs had a significant influence on the geometry of the nanoparticles. Particles were elongated along the nanotube axis for tube diameters

In this paper, we utilized a bottom-up method to predict the transverse thermal conductivity of pitched-based carbon fibers. We used molecular dynamics simulations with Green-Kubo formalism to calculate the in-plane thermal conductivity and out-of-plane thermal conductivity of the graphite sheets. The effects of waviness on the thermal conductivity of the graphite sheets were studied by MD simulations. The calculated in-plane thermal conductivity and out-of-plane thermal conductivity of graphite sheets from MD simulations were then used for the prediction of transverse thermal conductivity of the pitch fibers by finite element method. In the finite element simulations, the waviness in the graphite sheets was found to decrease the transverse thermal conductivity of pitch fibers, though not significantly. The defects observed in the pitch fibers were simulated by the damage elements in the finite element analysis. The simulation results showed that the proposed model, in which 12.5% of damage was included, predicted the effective transverse thermal conductivity well compared to the value measured from experiments.

A surface chemical treatment of highly porous carbon foams was adopted to synthesize boron–carbon–nitrogen (B–C–N) foams for thermal energy storage and release using an adsorption/desorption cycle with lightweight hydrocarbons. Microwave treatment in boric acid and urea was used to modify carbon foams with a B–C–N surface. Depending on the initial carbon foam state, B–C–N surface layers were produced with both amorphous and crystalline structures. The resultant B–C–N foams were characterized by TEM, XPS, XRD, FESEM and Raman measurements to quantify their stoichiometry, structure, and morphology. Adsorption enthalpy with methanol and thermal stability of foams was analyzed with DSC and TGA respectively. Thermal conductivity was measured by a transient laser flash technique. Results indicate that the crystalline graphitic carbon foam produces superior B–C–N surfaces compared to amorphous carbon foam. The crystalline B–C–N foams are found to provide the highest adsorption capacity, better thermal and oxidation stability.

In an attempt to study the thermal transport at the interface between nanotubes and graphene, vertically aligned multiwalled carbon nanotubes (CNTs) were grown on graphite thin film substrates. A systematic cross-sectional probing of the materials’ morphology of the interface by scanning electron microscopy and high-resolution transmission electron microscopy revealed that an excellent bond existed between the nanotubes and the substrate along some fraction of interface. Imaging and electron diffraction analyses performed at the boundary reveal a polycrystalline interfacial structure. Compositional probing along the interface by energy dispersive x-ray spectroscopy revealed that there were no catalyst particles or other impurities present. The estimated interfacial thermal resistance of lower than 5–7.5 (mm2K)/W suggests that this type of CNT/graphite interface could open up multiple routes toward the designing and development of advanced thermal interface materials for aerospace and nano-/microelectronics applications.

As a thermal management system, a sandwich construction was developed to have both superior thermal conductivity and structural integrity. The sandwich construction consists of a carbon foam core and unidirectional graphite/epoxy composite facesheets. An emphasis was put on enhancing the thermal conductivity of each phase of sandwich construction as well as interface between the phases. A commercially-available carbon foam was characterized mechanically and thermally. Property variation and anisotropy were observed with the highly conductive graphitic carbon foam. Co-curing of the composite facesheets with the carbon foam core was demonstrated to minimize the thickness of the adhesive layer between the facesheets and the core to produce the best construction of those tested. Comparison made with an adhesively bonded specimen shows that the co-curing is a more efficient method to enhance the through-thickness conductivity. Parametric studies with an analytic model indicate that degree of enhancement in the overall through-thickness conductivity of the sandwich construction from the enhancement of each component including the foam core, facesheet and the bonding methods.

Thermal management in polymeric composite materials has become increasingly critical in the air-vehicle industry because of the increasing thermal load in small-scale composite devices extensively used in electronics and aerospace systems. The thermal transport phenomenon in these small-scale heterogeneous systems is essentially controlled by the interface thermal resistance because of the large surface-to-volume ratio. In this review article, several modeling strategies are discussed for different length scales, complemented by our experimental efforts to tailor the thermal transport properties of polymeric composite materials. Progress in the molecular modeling of thermal transport in thermosets is reviewed along with a discussion on the interface thermal resistance between functionalized carbon nanotube and epoxy resin systems. For the thermal transport in fiber-reinforced composites, various micromechanics-based analytical and numerical modeling schemes are reviewed in predicting the transverse thermal conductivity. Numerical schemes used to realize and scale the interface thermal resistance and the finite mean free path of the energy carrier in the mesoscale are discussed in the frame of the lattice Boltzmann-Peierls-Callaway equation. Finally, guided by modeling, complementary experimental efforts are discussed for exfoliated graphite and vertically aligned nanotubes based composites toward improving their effective thermal conductivity by tailoring interface thermal resistance.

We have developed a rational strategy for creating the 3D pillared vertically aligned carbon nanotube (VACNT)-graphene architectures by intercalated growth of VACNTs into thermally expanded highly ordered pyrolytic graphite (HOPG). By controlling the fabrication process, the length of the VACNT pillars can be tuned. In conjunction with the electrodeposition of nickel hydroxide to introduce the pseudocapacitance, these 3D pillared VACNT–graphene architectures with a controllable nanotube length were demonstrated to show a high specific capacitance and remarkable rate capability, and they significantly outperformed many electrode materials currently used in the state-of-the-art supercapacitors.

Non-uniform heat flux generated by microchips causes ‘‘hot spots’’ in very small areas on the microchip surface. These hot spots are generated by the logic blocks in the microchip bay; however, memory blocks generate lower heat flux on contrast. The goal of this research is to design, fabricate, and test an active cooling micro-channel heat sink device that can operate under atmospheric pressure while achieving high-heat dissipation rate with a reduced chip-backside volume, particularly for spot cooling applications. An experimental setup was assembled and electro-osmotic flow (EOF) was used thus eliminating high pressure pumping system. A flow rate of 82 lL/min was achieved at 400 V of applied EOF voltage. An increase in the cooling fluid (buffer) temperature of 9.6 C, 29.9 C, 54.3 C, and 80.1 C was achieved for 0.4 W, 1.2 W, 2.1 W, and 4 W of heating powers, respectively. The substrate temperature at the middle of the microchannel was below 80.5 C for all input power values. The maximum increase in the cooling fluid temperature due to the joule heating was 4.5 C for 400 V of applied EOF voltage. Numerical calculations of temperatures and flow were conducted and the results were compared to experimental data. Nusselt number (Nu) for the 4 W case reached a maximum of 5.48 at the channel entrance and decreased to reach 4.56 for the rest of the channel. Nu number for EOF was about 10% higher when compared to the pressure driven flow. It was found that using a shorter channel length and an EOF voltage in the range of

The thermal transport in heterogeneous materials systems, such as in composites, is essentially controlled by the phonon scattering phenomena at the materials interface due to the interface materials property mismatch. Such phenomena are also prevalent in joints or component interfaces. The thermal property mismatch at the materials interface, in the molecular scale, is primarily dictated by the phonon density of state across the interface. In this paper, the interface materials configuration for tailoring the thermal properties of composite materials with nano constituents is presented. The materials modeling using both the finite element analysis (FEM) and molecular dynamics (MD) simulations is performed to identify the effect of materials constituent scale as well as the nano constituent surface functionalization on the interface thermal transport phenomena. It is observed that the effect of surface functionalization towards establishing covalent bonding between the nano constituent surface the matrix (such as polymers) is extremely important in enhancing the interface thermal conductance.

Chemically functionalized exfoliated graphite-filled epoxy composites were prepared with load levels from 2% to 20% by weight. The viscosities of the composites having load levels >4% by weight were over the processing window for the vacuum-assisted resin transfer molding process. Wide-angle X-ray diffraction revealed a rhombohedral carbon structure in the filler. Enhanced interaction between the epoxy and the graphite filler was evidenced by an improvement in the rubber modulus for the chemically functionalized graphite/epoxy composites. The thermal and electrical properties of the nanoparticle-filled epoxy composites were measured. The electrical property of the chemically functionalized graphite/epoxy composite deteriorated. Thermal conductivity of the chemically functionalized graphite/epoxy composite, however, increased by 28-fold over the pure epoxy resin at the 20% by-weight load level, increasing from 0.2 to 5.8 W/m K.

A concept of incorporating aligned multi-walled carbon nanotubes (MWCNTs) in the adhesive layer has been demonstrated to enhance the through-thickness thermal conductivity in the adhesively bonded joints. Both numerical and experimental studies were performed to determine key components in improving the through-thickness thermal conductivity and to realize the improvement in an adhesively-jointed system. The numerical analysis indicated that the key components to improve the through-thickness thermal conductivity in the adhesive joints are using highly conductive vertically aligned nanotubes as well as the thermal conductivity and the size of a transition zone between the nanotube ends and surrounding matrix materials in the form of either the adhesive or adherends. Therefore, the thermal contact of the conductive phase (the MWNT in this case) with the adherent surfaces is essential to achieve the desirable through-thickness thermal conductivity in joints. This theoretical observation was demonstrated experimentally by using conductive graphite facesheets as adherends and the polymer adhesive layer with the aligned MWCNTs. To ensure the ends of the MWCNTs make thermal contact with the adherent surfaces, the surface of the adhesive with the MWCNTs were plasma-etched and coated with thin Au layer, along with the surface of the graphite facesheet coated with thin Au–Pd layer. The measured value of the through-thickness thermal conductivity of the modified adhesive joint with the MWNCT was over 250 W/m K, which superseded the thermal conductivity of neat adhesive joint by several order of magnitudes. Thus the study demonstrates a new approach as well as opportunities of much needed thermal property tailoring in structural joints.

A new design for an electro-osmotic flow (EOF) driven micropump was fabricated. Considering thermal management applications, three different types of micropumps were tested using multiple liquids. The micropumps were fabricated from a combination of materials, which included: silicon-polydimethylsiloxane (Si-PDMS), Glass-PDMS, or PDMS-PDMS. The flow rates of the micropumps were experimentally and numerically assessed. Different combinations of materials and liquids resulted in variable values of zeta-potential. The ranges of zeta-potential for Si-PDMS, Glass-PDMS, and PDMS-PDMS were −42.5–−50.7 mV, −76.0–−88.2 mV, and −76.0–−103.0 mV, respectively. The flow rates of the micropumps were proportional to their zeta-potential values. In particular, flow rate values were found to be linearly proportional to the applied voltages below 500 V. A maximum flow rate of 75.9 μL/min was achieved for the Glass-PDMS micropump at 1 kV. At higher voltages nonlinearity and reduction in flow rate occurred due to Joule heating and the axial electro-osmotic current leakage through the silicon substrate. The fabricated micropumps could deliver flow rates, which were orders of magnitude higher compared to the previously reported values for similar size micropumps. It is expected that such an increase in flow rate, particularly in the case of the Si-PDMS micropump, would lead to enhanced heat transfer for microchip cooling applications as well as for applications involving micrototal analysis systems (μTAS).

Nanoadhesives of epoxy resin are synthesized and evaluated. They are organically modified by multiwalled carbon nanotubes (MWCNT) (1% by weight) as reinforcement. Tensile tests are conducted on multiple identical unnotched and notched specimens to evaluate the overloading and fracture behavior of the nanoadhesives and are compared with the neat epoxy resin. In comparison with the neat epoxy, it is found that the 1% MWCNT reinforcement increased the ultimate and residual strength by about 29% and 56%, respectively. In comparison with the neat resin, there is a 265% increase in the fracture toughness of the MWCNT adhesive. Fracture surface analysis revealed the various mechanisms by which the MWCNT adhesives acquire their superior strength and toughness in comparison with the neat resin.

The environmental durability of PMR-15 nanocomposites prepared from an unmodified Na+-montmorillonite (PGV) and two organically modified PGV (PGVC10COOH, PGVC12) have been investigated using an accelerated hydrolytic aging test and a long-term thermo-oxidative aging study. PGV was modified with an amino acid (11-amino-undecanoic acid) and a primary amine (dodecylamine). The PGV/PMR-15 nanocomposite exhibited higher moisture gain than the neat resin, while PGVC10COOH, PGVC12/PMR-15 nanocomposites exhibited lower moisture gains. XRD data of the nanocomposites correlated well with the moisture gain data for the nanocomposites. PGVC10COOH and PGVC12/PMR-15 nanocomposites exhibited more than a 50% reduction in the flexural modulus drop off. These results suggest that nanocomposites provide a viable approach in decreasing the susceptibility of PMR-15 to hydrolytic degradation. No improvement in the thermal oxidative stability of the nanocomposites was achieved. This may be attributable to the relatively low thermal stability of the organic modifiers and/or the presence of impurities, which catalyzed the PMR-15 degradation.

Nanocomposites of a bifunctional epoxy resin are synthesized and evaluated. Organically modified layered silicate (OLS) particles (4% by weight) and multiwalled carbon nanotubes (MWNT) (1% by weight) are used as reinforcements. Thermal and viscoelastic characterization of the two composites are performed and compared with the neat resin. Tensile tests are conducted on multiple identical unnotched and notched specimens to evaluate the overloading and fracture behavior of the nanocomposites. In comparison with the neat bifunctional epoxy, it is found that the 1% MWNT reinforcement increased the ultimate strength and strain to failure by about 139 and 158%, respectively. In comparison, the OLS has increased the ultimate strength and strain by about 30 and 20%, respectively. In comparison with the neat resin, there is a 170% increase in the fracture toughness of the MWNT composites and only 17% in the case of the OLS composites. Fracture surface analysis revealed the various mechanisms by which the MWNT composites acquire their superior strength and toughness in comparison with the neat resin.

Cyanate ester resins are among the most important engineering thermosetting polymers and have received attention because of their outstanding physical properties such as low water absorptivity and low outgassing. However, like most thermosets their main drawback is brittleness. Nanocomposites of cyanate esters were prepared by dispersing organically modified layered silicates (OLS) into the resin. Inclusion of only 2.5% by weight of OLS led to a marked improvement in physical and thermal properties (Coefficient of thermal expansion, Tg and effective thermal stability). Most impressively, a 30% increase in both the modulus and toughness was obtained.

Cyanate esters (CE) have emerged as attractive materials for aerospace applications, due to their ease of processing and excellent high-temperature properties. Using a thermal protection system can increase the service temperature even further. The objective of this research is to develop a co-cure cycle for a cyanate ester/silicon polymer (SM8000) hybrid composite system. The chemorheology and cure kinetics of the CE along with the thermochemical behavior of the SM8000 resin are used to develop a co-cure cycle. Samples prepared by this cure cycle exhibit a 270 'C increase in the onset of thermal decomposition. Interfacial fracture toughness tests reveal a very robust interface, validating the cure cycle.

Non-uniform heat flux generated by microchips can create “hot spots” in localized areas on the microchip surface. This research presents an improved design of an active cooling electro-osmotic flow (EOF) based micro-pump for hot spots thermal management. The design of the micro-pump was simpler and more practical for the application compared to designs presented in literature. Most micro-channel heat sink devices presented in literature were silicon based. Though silicon has better thermal conductivity when compared to polymers used in micro-devices fabrication, processes of silicon fabrication are complicated and time consuming. Also, most micro-channel fabrication processes use silicon etching which leads to rough walls within the micro-channel. An improved design, which uses a combination of silicon and Polydimethylsiloxane (PDMS), is being developed and tested. The main idea of this design is to utilize the favorable thermal properties of silicon while achieving both smoother charged surfaces and ease of fabrication of PDMS material. The EOF micro-pump was tested for four cooling fluid namely, DI water, distilled water, borax buffer, and Al2O3 nano-particles suspended in water solution. A maximum flow rate of 31.2 μL/min was achieved using distilled water at 500 V of EOF voltage. Such micro-pump with this flow rate range can be implemented in a closed loop heat rejection system for hot spot thermal management. Moreover, it can be used in Lap-on-chip and uTAS application for sample transport.

Hashim, Daniel P. et al., The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapour deposition, which influences the formation of atomic-scale “elbow” junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the “elbow” junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this material’s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use., This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 0940902 awarded to D. P. Hashim. P.M. Ajayan, M. Terrones, and N. T. Narayanan acknowledge funding sponsorship from the DOD: Air Force Office of Scientific Research for the Project MURI: Synthesis and Characterization of 3D Carbon Nanotube Solid Networks Award No.: FA9550-12-1-0035. M.G. Hahm, and R.Vajtai acknowledge financial support from ARL/ARO (No.W911NF). M. Terrones thanks JST-Japan for funding the Research Center for Exotic NanoCarbons, under the Japanese regional Innovation Strategy Program by the Excellence. B. G. Sumpter was supported by the Center for Nanophase Materials Sciences, which is sponsored by the Office of Basic Energy Sciences at Oak Ridge National Laboratory, U.S. Department of Energy. V.M. was supported in part by the New York State under NYSTAR contract C080117.

The through-thickness thermal conductivity in conventional adhesive joints (of approximately 0.3 W/m-K) fails to meet the thermal load transfer requirement in numerous applications to enable lean manufacturing and improve system reliability to thermal load. Carbon nanotubes are known to possess extremely high thermal conductivity along the longitudinal axis. According to molecular dynamics simulations, the value can be as high as 3500 W/m-K at room temperature for multi-walled carbon nanotubes (MWCNT). Meanwhile, the transverse thermal conductivity perpendicular to the longitudinal axis of the MWCNTs is known to be relatively low, approximately 10-15 W/m-K. Existing studies of mixing the MWCNTs in polymers for adhesive joints only achieved minimal enhancement in the thermal conductivity and failed to satisfy the thermal property requirement for the adhesive joints. In order to properly utilize the superior axial thermal conductivity of the MWCNTs, vertically aligned MWCNTs have been used in this study and incorporated in the adhesive joint configuration. Analytical parametric study was conducted to identify critical parameters that affect the overall thermal conductivity of the joint and to provide guidelines for the process development. The process development involved growing the vertically aligned MWCNTs on silicon wafers. The aligned nanotube array was partially infused with epoxy adhesive. Selective reactive ion etching of the epoxy revealed the nanotube tips. In order to reduce the impedance mismatch and phonon scattering at the interface between the nanotube tips and the adherends, gold was thermally evaporated on the nanotube tips. The measured thermal conductivity of the adhesive joint device incorporating the MWCNTs was 262 W/m-K, which is significantly larger compared to that of less than 1 W/m-K without the MWCNTs.

We have demonstrated that the infiltration of temperature-responsive polymers (e.g., PNIPAAm) into vertically-aligned carbon nanotube forests created synergetic effects, which provided the basis for the development of smart nanocomposite films with temperature-induced self-cleaning and/or controlled release capabilities.

The quest for improvement of thermal conductivity in aerospace structures is gaining momentum. This is even more important as modern day aerospace structures are embedded with electronics which generate considerable amounts of heat energy. This generated heat if not dissipated might potentially affect the structural integrity of the composite structure. The use of polymer based composites in aerospace applications has also increased due to their obvious superior specific properties. But the thermal conductivity of the polymer matrix is very low and not suited for the design demands in aerospace applications. Several research studies have been conducted to improve the thermal conductivity of the polymeric composites. Different fillers have been used to improve the thermal conductivity of the polymeric matrix. Fillers may be in the form of fibers or in the form of particles uniformly distributed in the polymer matrix. The thermophysical properties of fiber filled composites are anisotropic, except for the very short, randomly distributed fibers, while the thermophysical properties of particle filled polymers are isotropic. Numerous studies have also been conducted in recent years where nanoparticles have been dispersed in the polymeric matrix to improve the thermal conductivity. Putman et al. [1] used the 3ω method to study the thermal conductivity of composites of nanoscale alumina particles in polymethylmethacrylate (PMMA) matrices in the temperature range 40 to 280 K. For 10% of 60 nm of alumina particle filler by weight (3.5% by volume) thermal conductivity of the composite slightly decreased at low temperatures. Whereas, above 100 K, thermal conductivity of the nanocomposite increased by 4% at room temperature. Kruger and Alam [2] studied the thermal conductivity of aligned, vapor grown carbon nanoscale fiber reinforced polypropylene composite. They measured thermal conductivity by laser flash instrument in the longitudinal and transverse directions for 9%, 17% and 23% fiber reinforcements by volume. The values of thermal conductivity as reported by them were 2.09, 2.75, 5.38 W/m.K for the longitudinal directions and 2.42, 2.47, 2.49 W/m-K for the transverse direction respectively, while the thermal conductivity of unfilled PP was 0.24 W/m-K. Exfoliated graphite platelets are another filler material of promise for improving the thermo-mechanical properties of the polymeric matrix. Aylsworth [3, 4] developed and proposed expanded graphite as reinforcement of polymers in 1910s. Lincoln and Claude [5] in 1980s proposed the dispersion of intercalated graphite in polymeric resins by conventional composite processing techniques. Since that time, research has been conducted on exfoliated graphite reinforced polymers using graphite particles of various dimensions and a wide range of polymers. Drzal et al. [6] have demonstrated the use of exfoliated graphite platelets to enhance the thermal and mechanical properties of polymeric resins. They concluded that composites made by in situ processing have better mechanical properties compared to composites made by melt-mixing or other ex situ fabrication methods due to better dispersion, prevention of agglomeration and stronger interactions between the reinforcement and the polymer. In the present study we use silver nano-filaments, nickel nano-filaments, alumina and exfoliated graphite platelets to enhance the thermal conductivity of an epoxy thermoset resin. The objective of this research is to identify the right filler to achieve the thermal conductivity as required by aerospace design engineers which is around 10 W/ m-K. An arbitrary filler loading of 8 wt% was chosen to compare the different fillers used in this study.

This study assesses the impacts of the North America Free Trade Agreement (NAFTA) and the World Trade Organization (WTO) negotiations on the U.S. forest products industries using a computable general equilibrium model. A global trade model consisting of ten sectors and ten regions was developed. Several scenarios were designed to simulate the tariff reductions proposed in the NAFTA and WTO negotiations. The effects of NAFTA and WTO on output, trade balance, welfare, and factor income were examined. The results indicate that NAFTA liberalizations will benefit the U.S. lumber sector, but reduce the output and trade balance of the paper and pulp and forestry sectors. The WTO will improve the trade balance of the U.S. forest products industries. In general, free trade will be beneficial to the U.S. economy as well as the forest products industries.

We have developed a novel thermal conductivity measurement technique that is applicable to micro- and nanoscale structures. The methodology integrates a device consisting of two identical microheaters with thin-filmed platinum heating elements and integrated resistance temperature devices (RTDs) on trenched, thermally isolated silicon substrates. The platinum RTDs used for temperature measurement were calibrated by monitoring the melting points of three metallic microspheres placed on the device as its power was increased. We validated our measurement technique by measuring thermal conductivities of several micrometer-sized metallic wire standards with known values. A multiphysical analysis based on a 3D finite element method has been conducted to simulate both the electric and thermal behaviors of the microheaters. These simulations describing the heating and heat flow in the device yield similar temperature profiles near the microheaters obtained in the experimental system.