Mohammad H. Maneshian

Measurement of the thermal conductivity of a water-based single-wall carbon nanotube colloidal suspension with a modified 3- ω method

A modified 3-omega method applied to a suspended platinum microwire was employed to measure the thermal conductivity and convective heat transfer coefficient of a water-based single-walled carbon nanotube (CNT) solution (metallic single-wall nanotubes with 1.33 nm diameter and 1.14 wt% concentration), and an expression for calculating the convective heat transfer coefficient in such a free convective fluid was introduced. The measurement technique was validated for three model systems including vacuum, air and deionized water. It is found that there is excellent agreement between these three model systems with theoretical predictions. In addition, the frequency dependence on the third harmonic response measured in deionized water reveals the existence of a very low working frequency below 60 mHz. The thermal conductivity and convective heat transfer coefficient of the nanofluid (water-based single-wall CNT solution) were determined to be 0.73 +/- 0.013 W m(-1) K(-1) and 14 900 +/- 260 W m(-2) K(-1), respectively, which correspond to an enhancement of 19.4% in thermal conductivity and 18.9% in convective heat transfer as compared to water.

Bulk Nanostructured Metals and Alloys: Processing, Structure, and Thermal Stability

1Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, USA 2Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907, USA 3Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA 4Department of Metals and Materials Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z4

The influence of high dielectric constant aluminum oxide sputter deposition on the structure and properties of multilayer epitaxial graphene

High dielectric constant aluminum oxide (Al(2)O(3)) is frequently used as the gate oxide in high electron mobility transistors and the impact of its deposition by radio frequency (RF) magnetron sputtering on the structural and electrical properties of multilayer epitaxial graphene (MLG) grown by graphitization of silicon carbide (SiC) is reported. Micro-Raman spectroscopy and temperature dependent Hall mobility measurements reveal that the processing induced changes to the structural and electrical properties of the MLG can be minimal when the oxide deposition conditions are optimal. High-resolution transmission electron microscopy (HRTEM) analysis confirms that the Al(2)O(3)/MLG interface is relatively sharp and that our thickness approximation of the MLG using angle resolved x-ray photoelectron spectroscopy (ARXPS) is accurate. An interface trap density of 5.1 × 10(10) eV(-1) cm(-2) was determined using capacitance-voltage techniques. The totality of our results indicates that ARXPS can be used as a nondestructive tool to measure the thickness of MLG, and that RF sputtered Al(2)O(3) can be used as a high dielectric (high-k) constant gate oxide in multilayer graphene based transistor applications.

Nano/Microstructured Materials: Rapid, Low-Cost, and Eco-Friendly Synthesis Methods

1 Department of Materials Science and Engineering, North Carolina State University, 911 Partners Way, Engineering Building I, Raleigh, NC 27695-7907, USA 2Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA 3Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, USA 4Leibniz Institute for Solid State and Materials Research Dresden, P.O. Box 27 01 16, 01171 Dresden, Germany

Structural and electrical characterization of ohmic contacts to graphitized silicon carbide

Titanium was deposited onto silicon carbide (6H-SiC) using the 248 nm line of an excimer laser in a vacuum of 10(-6) Torr, and ohmic contacts were formed by annealing the structure at approximately 1000 degrees C. Further anneals between 1350 and 1430 degrees C did not degrade the formed contacts, and Raman analysis confirmed that sublimation of silicon from the near surface layers of the silicon carbide between the contact pads resulted in graphene formation after 5 min, 1428 degrees C anneals. The graphene formation was accompanied by a significant enhancement of ohmic behavior, and, it was found to be sensitive to the temperature ramp-up rate and annealing time. High-resolution transmission electron microscopy showed that the interface between the metal and silicon carbide remained sharp and free of macroscopic defects even after 30 min, 1430 degrees C anneals. The interface was determined to be carbon rich by elemental analysis, which indicates metal carbide formation. The potential of this approach for achieving ohmic contacts and graphene formation on silicon carbide substrates is discussed. A mechanism for the sequential formation of ohmic contacts then graphene is proposed.

Atomic scale characterization of titanium Ohmic contacts to SiC using three dimensional atom probe tomography and high resolution transmission electron microscopy

Three dimensional atom probe tomography coupled with high resolution transmission electron microscopy were used to analyze the structural and compositional transitions across interfaces of Ti Ohmic contacts on SiC. The results conclusively show that during the interfacial reaction carbon diffuses into the Ti layer, with the reaction zone extending beyond the immediate interface. The resultant TiC/TiCx interfacial layer provides a graded work function profile between the Ti and SiC, and facilitates low contact resistance which was measured by the transmission line, current-voltage method.

Measurement of the Thermal Conductivity of a Water-Based Single-Wall Carbon Nanotube Colloidal Suspension With a Modified 3-ω Method

A modified 3-ω method applied to a suspended platinum microwire was employed to measure the thermal conductivity and convective heat transfer coefficient of a water-based single-walled carbon nanotube (CNT) solution (metallic single-wall nanotubes with 1.33 nm diameter and 1.14 wt% concentration), and an expression for calculating the convective heat transfer coefficient in such a free convective fluid was introduced. The measurement technique was validated for three model systems including vacuum, air and deionized water. It is found that there is excellent agreement between these three model systems with theoretical predictions. In addition, the frequency dependence on the third harmonic response measured in deionized water reveals the existence of a very low working frequency below 60 mHz. The thermal conductivity and convective heat transfer coefficient of the nanofluid (water-based single-wall CNT solution) were determined to be 0.73 ± 0.013 W m −1 K −1 and 14 900 ± 260 W m −2 K −1 , respectively, which correspond to an enhancement of 19.4% in thermal conductivity and 18.9% in convective heat transfer as compared to water. (Some figures in this article are in colour only in the electronic version)