In this paper, lead chalcogenide based thermoelectric nanolaminate structures were fabricated by alternately depositing PbTe and PbSe ALD layers on regular planar silicon wafers and on microporous silicon templates. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb (C 11 H 19 O 2 ) 2 ), plus (trimethylsilyl) telluride ((Me 3 Si) 2 Te) and (trimethylsilyl) selenide ((Me 3 Si) 2 Se) were used as the chemical ALD precursors for lead, tellurium and selenium, respectively. The Seebeck coefficient in horizontal direction (parallel direction to the surface) to the multiple layered PbTe/PbSe nanolaminate structures was measured by an MMR Seebeck system, and benchmarked against the Seebeck coefficient in the vertical direction to the sample surface. The results of the Seebeck measurements clearly indicate that the multiple layered PbTe/PbSe nanolaminate structures synthesized by ALD on microporous silicon templates exhibit significantly increased Seebeck coefficients in both horizontal and vertical directions, in stark contrast to the case when the same ALD thermoelectric nanolaminates are grown on regular planar bulk Si substrates. As a green renewable technology, thermoelectrics (TE) can play an important role in recovering energy from waste heat due to its potential in converting heat into electricity, and consequently this effect could be applied in TE power generators or TE refrigerators. The challenge for current state-of-the-art TE devices is the low conversion efficiency. The efficiency of a thermoelectric device is expressed as:where T C and T H indicates the temperature of the cold and hot side. The conversion efficiency η is determined by the dimensionless thermoelectric figure of merit ZT,where S is the Seebeck coefficient, σ is the electrical conductivity, T is the temperature in Kelvin, κ e is the thermal conductivity due to electrons, and κ L is lattice thermal conductivity due to phonons. 1 Figure 1 shows the simulation result for the dependence of the conversion efficiency η on ZT and temperature difference. This graph demonstrates a clear trend: the higher the figure of merit ZT, the higher the conversion efficiency η would be. For current state-of-the-art TE devices, the figure of merit ZT value is usually around one, which translates into a conversion efficiency that is usually no higher than 5%. For large-scale practical applications, it is critical to synthesize better TE materials with a figure of merit ZT higher than 2 in order to promote attractive conversion efficiencies for TE devices. Much of the previous work demonstrated that alloying can be used to decrease the lattice thermal conductivity and thus to increase ZT due to mass difference enhanced phonon scattering.2 In order to further progress in the development and commercialization of the next generation of thermoelectric devices it is necessary to enhance significantly the figure of merit ZT value. Most recently novel innovative research approaches focused on low dimensional nanostructures, 3 including quantum wells, 4 quantum dots, 5...

In this work highly oriented Surface Anchored Metal-Organic Framework (SURMOF) films were fabricated quasi-epitaxial and were electrically characterized by Seebeck analysis and benchmarked against random polycrystalline MOF films loaded with tetracyano-quinodimethane (TCNQ) infiltration. The horizontal Seebeck coefficient of the oriented SURMOF films and the random polycrystalline MOF films parallel to the sample surface was measured and has been discussed. The isotropic random polycrystalline MOF films exhibit a high positive Seebeck coefficient of 422.32 μV/K at 350 K. However, the horizontal Seebeck coefficient of highly oriented SURMOF films fluctuates around 0 μV/K instead. Because the quasi-epitaxial oriented SURMOF films are highly anisotropic, there is no measurable horizontal carrier transport parallel to the SURMOF surface. However, in contrast to highly oriented (002) SURMOF films, the in-plane thermoelectric properties of random polycrystalline MOF films with sputtered Au contact pads could be measured due to the isotropic nature of these films. The high Seebeck coefficient of these random polycrystalline MOF films demonstrates promising application potential of MOF films in future thermoelectric and electronic devices.

This paper reports an enhancement on the sensing performance of ZnO nanorod ethanol sensors with a new approach by utilizing nested coatings of Aluminum doped ZnO (AZO) thin films by Atomic Layer Deposition (ALD) technology. ZnO nanorods were grown by the hydrothermal method with the ZnO seed layer synthesized on Silicon wafers by ALD. To enhance the sensing performance of ZnO nanorod ethanol sensors, multiple coated AZO thin film 3-D coatings were deposited on the surface of the intrinsic ZnO nanorods by ALD. To investigate the sensing performance of the ZnO nanorods sensor for the detection of ethanol vapor, a gas sensor testing system was designed and built with a sealed reaction chamber and a temperature controller. The demonstrated sensing performance results include the sensing response comparison between ZnO nanorods before and after ALD coatings with AZO films at different temperatures and with various concentrations of input ethanol vapor. The response times and recovery times of ZnO nanorods before and after ALD coatings with AZO thin films were analyzed to investigate the sensing enhancement. The sensing response improvement peaks at 25 • C room temperature with approximately 200% enhancement. However, the sensing response improvement decreases as a function of increasing operating temperature.