Hafez Raeisi Fard

Large‐Area Freestanding Graphene Paper for Superior Thermal Management

Large-area freestanding graphene papers (GPs) are fabricated by electrospray deposition integrated with a continuous roll-to-roll process. Upon mechanical compaction and thermal annealing, GPs can achieve a thermal conductivity of as high as 1238.3-1434 W m(-1) K(-1) . The super-thermally conductive GPs display an outstanding heat-spread ability and are more efficient in removing hot spots than Cu and Al foils.

High thermal conductivity epoxy-silver composites based on self-constructed nanostructured metallic networks

We demonstrate epoxy-silver nanoparticle composites with high thermal conductivity κ enabled by self-constructed nanostructured networks (SCNN) forming during the curing process at relatively low temperatures (150 °C). The networks formation mechanism involves agglomeration of the polyvinylpyrrolidone (PVP) coated nanoparticles, PVP removal, and sintering of the nanoparticles at suppressed temperatures induced by their small diameters (20–80 nm). Sintering and the SCNN formation are supported by differential scanning calorimetry and electron microscopy investigations. The formation of SCNN with high aspect ratio structures leads to enhancements in the measured thermal conductivity κ of the composite by more than two orders of magnitude versus the pure epoxy. However, κ enhancements are modest if microparticles (1.8–4.2 μm) are employed instead of PVP coated nanoparticles. The κ trends are qualitatively explained using a percolating threshold thermal conductivity model for the microcomposites. For the nano...

Thermal conductivity of Er+3:Y2O3 films grown by atomic layer deposition

Cross-plane thermal conductivity of 800, 458, and 110 nm erbium-doped crystalline yttria (Er+3:Y2O3) films deposited via atomic layer deposition was measured using the 3ω method at room temperature. Thermal conductivity results show 16-fold increase in thermal conductivity from 0.49 W m−1K−1 to 8 W m−1K−1 upon post deposition annealing, partially due to the suppression of the number of the -OH/H2O bonds in the films after annealing. Thermal conductivity of the annealed film was ∼70% lower than undoped bulk single crystal yttria. The cumulative interface thermal resistivity of substrate-Er+3:Y2O3-metal heater was determined to be ∼2.5 × 10−8 m2 K/W.

Reducing thermal interface impedance using surface engineering

The ever-increasing demand for more functionality of electronic and optoelectronic components led to increased packaging and thermal power densities. Higher processing density can be reached by developing thermal management solutions. The current technology in electronic packaging is to attach the die to heat spreader, using materials known as Thermal Interface Materials (TIM), such as solder or silver sinter pastes. The advantage of these materials is their relatively high thermal conductivity; however, there are major problems such as voiding and degradation of TIMs over time [1]. Furthermore, the thermal resistance of the interface between TIM and surfaces is considered as a serious issue in electronics packaging. In this work, we present a new scheme to reduce thermal impedance using surface patterning. Heat transfer enhancement in this method is based on increasing heat transfer surface area per unit die are and replacing TIM with patterns made of high thermal conductive materials such as Copper. Effect of different parameters such as pattern height, diameter and pitch on heat transfer rate was investigated both experimentally and numerically. Thermal resistance was measured using conventional 1-dimensional heat transfer setup. Finally, our experimental results show that using this scheme will increase effective thermal conductivity by almost 5-fold.

Modeling and Simulation of Controlled Manipulation by AFM Nano Robot

In this article a model to describe relation between AFM cantilever’s deformation and force (as a force transducer) is developed. Furthermore a state space model is used to find suitable feedback control. A model which relates force and deformation is described. To verify a Finite element simulation is applied and a control algorithm for manipulation purpose is found. Moreover based on nature of the process control system is designed. Due to recent developments in AFM nanorobot applications in biotechnology and manufacturing nanostructures, understanding of cantilever’s response and process control have received great importance.

Heat Conduction in High Thermal Conductivity Networked Composite Films for Thermal Interface Materials

Fast and efficient exchange of thermal energy plays a vital role in the thermal management of electronic and optoelectronic devices. A critical component for thermal management is a thermal interface material (TIM) that is used to minimize the contact thermal resistance between surfaces and to provide a low resistance pathway to spread and remove heat. Ideal TIMs must pass several key requirements: 1) high thermal conductivity κ and low thermal contact resistance with the mating surfaces; 2) easy to apply with controlled thickness; 3) low temperature processing; 4) able to accommodate thermally induced mechanical stresses during on-off cycling of the device1 . Particle-based composites have reasonable slurry viscosities, however their thermal conductivity are usually very low (<10 Wm−1 K−1 ), even when high κ nanofillers are employed, due to the thermal interface resistance between nanoparticles and the polymer matrix2 or the absence of high κ pathways.Copyright

Annealing Temperature Effect on the Structure of High Thermal Conductivity Silver/Epoxy Nanocomposites

The thermal conductivity κ of polymer nanoparticle composites is typically <10 Wm−1 K−1 , even when high κ nanofillers are employed, due to the thermal interface resistance between nanoparticles and the polymer matrix1 or the absence of high thermal conductivity pathways. We recently demonstrated high κ in bulk nanocomposites of silver nanoparticles dispersed in epoxy and cured at low temperature (150 °C). A nanocomposite with 30 vol. % 20nm particles exhibited κ ∼30 Wm−1 K−1 .2 The mechanism responsible for enhancing κ was found to be the self-construction, through in-situ sintering, of high aspect ratio metallic networks inside the nanocomposite.2 In order to control and optimize the network structure and subsequently increase κ even further, this work focuses on studying the effects of curing temperature and nanoparticle surface coating on the structure of the nanocomposite.Copyright

Modeling and Simulation of Nano Structures Based on Molecular Dynamics

As our knowledge about Nano grows we can apply Nano Technology in all fields of Science and Engineering. Molecular simulation can be used to simulate the manufacturing process in nano scale. In this paper, simulations in nano scale were investigated in two main reasons: 1- Morphology in Nano-Micro, 2-Simulation based on molecular dynamics. The basic and main aspects of both methods were explored and also a Matlab algorithm will be suggested to modeling the structure and dynamic in nano scale. First, some pieces in cylindrical and cubic forms were simulated and the effects of thermal treatment in different temperatures were investigated in light of this simulation. Second, a model based on molecular dynamics in 2D was developed to find out the effects of force exerted to AFM..