Showing papers by "Anvar A. Zakhidov published in 2010"

Harvesting Waste Thermal Energy Using a Carbon-Nanotube-Based Thermo-Electrochemical Cell

Abstract: Low efficiencies and costly electrode materials have limited harvesting of thermal energy as electrical energy using thermo- electrochemical cells (or "thermocells"). We demonstrate thermocells, in practical configurations (from coin cells to cells that can be wrapped around exhaust pipes), that harvest low-grade thermal energy using relatively inexpensive carbon multiwalled nanotube (MWNT) electrodes. These electrodes provide high electrochemically accessible surface areas and fast redox-mediated electron transfer, which significantly enhances thermocell current generation capacity and overall efficiency. Thermocell efficiency is further improved by directly synthesizing MWNTs as vertical forests that reduce electrical and thermal resistance at electrode/substrate junctions. The efficiency of thermocells with MWNT electrodes is shown to be as high as 1.4% of Carnot efficiency, which is 3-fold higher than for previously demonstrated thermocells. With the cost of MWNTs decreasing, MWNT-based thermocells may become commercially viable for harvesting low-grade thermal energy.

Aerosol-synthesized SWCNT networks with tunable conductivity and transparency by a dry transfer technique.

Abstract: We demonstrate an aerosol CVD process to dry deposit large-area SWCNT networks with tunable conductivity and optical transmittance on a wide range of substrates including flexible polymers. These SWCNT networks can be chemically doped to reach a sheet resistance of as low as 110 Ω/◻ at 90% optical transmittance. A wide application potential of these networks is demonstrated by fabricating SWCNT network-based devices such as a transparent capacitive touch sensors, thin-film transistors (TFTs), and bright organic light-emitting diodes (OLEDs).

Structure and process-dependent properties of solid-state spun carbon nanotube yarns.

Abstract: The effects of processing conditions and apparent nanotube length on properties are investigated for carbon nanotube yarns obtained by solid-state drawing of an aerogel from a forest of multi-walled carbon nanotubes. Investigation of twist, false twist, liquid densification and combination methods for converting the drawn aerogel into dense yarn show that permanent twist is not needed for obtaining useful mechanical properties when nanotube lengths are long compared with nanotube diameters. Average mechanical strengths of 800 MPa were obtained for polymer-free twist-spun multi-walled carbon nanotube (MWNT) yarns and average mechanical strengths of 1040 MPa were obtained for MWNT yarns infiltrated with 10 wt% polystyrene solution. Strategies for increasing the mechanical properties are suggested based on analysis of intra-wall, intra-bundle and inter-bundle stress transfer.

Hole mobility enhancement by chain alignment in nanoimprinted poly(3-hexylthiophene) nanogratings for organic electronics

Abstract: The authors report that the poly(3-hexylthiophene-2,5-diyl) (P3HT) nanogratings shaped by nanoimprint lithography show enhanced hole mobility and strong anisotropy of conductance due to nanoimprint-induced three-dimensional polymer chain alignment Field effect transistors were fabricated using these nanogratings and device measurements show a hole mobility of 003 cm2/V s along the grating direction, which is about 60 times higher than that of nonoptimized thin film transistors Organic photovoltaic devices (OPV) were made using the P3HT nanograting with infiltration of [6,6]-phenyl-C61-butyric acid methyl ester Compared to similar bilayer and bulk heterojunction devices, the nanoimprinted OPV shows improved device performance

Nanoimprinted P3HT/C60 solar cells optimized by oblique deposition of C60

Abstract: Poly(3-hexylthiophene) (P3HT)-C60 organic photovoltaic devices with interpenetrating donor-acceptor interfaces were fabricated by oblique thermal deposition of C60 into the P3HT nanogratings. The uniformity and step coverage of C60 infiltration into the P3HT nanostructures, which can determine the device performance, were dependent on the C60 evaporation angle. It was also observed that the C60 deposition rate and thickness determine the efficiency. A 50% improvement in power conversion efficiency is observed due to the increased exciton dissociation rate at the larger area P3HT-C60 interface at optimal C60 deposition filling. With the proposed technique, a highly efficient organic solar cell using an insoluble acceptor has been fabricated.

Negative refraction in the visible spectrum in photonic crystals: search for focusing by fluorescent quantum dots inside synthetic opals

Abstract: The negative refraction inside two dimensional (2D) photonic crystals (PC) and homogeneous structures was studied numerically by inserting a point source inside the negative index part of these materials. The three-dimensional (3D) counterparts of these structures, the synthetic opal, were examined experimentally by infiltrating them with CdS quantum dots (QDs). Confocal microscopy measurements in which we tracked the infiltration of the QDs inside the opal indicate the focusing of light emitted by QDs, which can be due to negative refraction occurring at the opal/glass interface. The formation of a focus can be an indication of the negative refraction happening in these synthetic opals in the [111] direction in its higher photonic band, above the photonic band gap (PBG). This result is very promising because, until now, negative refraction has not been seen in 3D photonic crystals in the visible region of light. This result was made possible due to the use of infiltrated QDs as internal light sources inside the porous photonic crystal, which appears to be a very useful technique for the study of other negative-index materials (NIM) effects. Finally, the possibility of self-focusing of second harmonic by QD in nonlinear opal was developed.

Search for Negative Refraction in the Visible Region of Light by Fluorescent Microscopy of Quantum Dots Infiltrated into Regular and Inverse Synthetic Opals

Abstract: In this chapter, regular and inverse synthetic opals are examined experimentally by infiltrating them with CdSe quantum dots (QDs). Confocal microscopy measurements in which we track the infiltration of QDs inside the regular and inverse opals show indications of focusing of light emitted by QDs, which can be due to negative refraction occurring at the opal–glass interface. The formation of a focus can be an indication of the left-handed behavior of these synthetic opals in the [111] direction in its higher photonic band, above the photonic band gap (PBG). This result can be very promising because, until now, left-handed behavior has not been demonstrated in 3D photonic crystals in the visible region of light. This result was made possible due to the use of infiltrated QDs as internal light sources inside the porous photonic crystal, which appears to be a very useful technique for the study of other negative-index materials (NIM) effects.