Synthesis of organic inorganic hybrids based on the conjugated polymer P3HT and mesoporous silicon

Organic inorganic hybrids are a class of functional materials that combine favorable properties of their constituents to achieve an overall improved performance for a wide range of applications. This article presents the synthesis route for P3HT porous silicon hybrids for thermoelectric applications. The conjugated polymer P3HT is incorporated into the porous silicon matrix by means of melt infiltration. Gravimetry, sorption isotherms and energy dispersive X ray spectroscopy EDX mapping indicate that the organic molecules occupy more than 50 of the void space in the inorganic host. We demonstrate that subsequent diffusion based doping of the confined polymer in a FeCl3 solution increases the electrical conductivity of the hybrid by five orders of magnitude compared to the empty porous silicon hos

New synthesis route of highly porous InxCo4Sb12 with strongly reduced thermal conductivity

Highly porous, In filled CoSb3 skutterudite materials with an attractive thermoelectric figure of merit ZT 1 and corresponding dense samples were fabricated through the cost effective method of reduction in oxides in dry hydrogen and the pulsed electric current sintering PECS method, respectively. The reduction process was described in detail using in situ thermogravimetric analysis of Co2O3, Sb2O3 and In NO3 3.5H2O separately and in a mixture. Two methods to synthesise the same material were examined a free sintering of an initially reduced powder and b PECS. The free sintered materials with higher porosities up to 40 exhibited lower values of electrical conductivity than the dense PECS samples porosity up to 5 , but the benefit of an even sixfold reduction in thermal conductivity resulted in higher ZT values. The theoretical values of thermal conductivity for various effective media models considering randomly oriented spheroid pores are in good agreement with the experimental thermal conductivity data. The assumed distribution and shape of the pores correlated well with the scanning electron microscope analysis of the microstructure. The lowest value of thermal conductivity, equal to 0.5 W m K, was measured at 523 K for In0.1Co4Sb12 with 41 porosity. The highest value of ZTmax 1.0 at 673 K was found for the In0.2Co4Sb12 sample in which the porosity was 3

Characterization and modeling of the temperature dependent thermal conductivity in sintered porous silicon aluminum nanomaterials

Nanostructured silicon and silicon aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering SPS of silicon nanopowder, mesoporous silicon pSi , and aluminum nanopowder. The interplay of metal assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity. Morphology and temperature dependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport. Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions. We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples. In contrast, strong grain growth is observed for sintered nanopowders under similar sintering conditions. We observe that aluminum agglomerations induce local grain growth, while aluminum diffusion is observed in porous silicon and dispersed nanoparticles. A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains. With a modified Landauer Lundstrom approach the relative thermal conductivity and the scattering length are extracted. The relative thermal conductivity confirms the applicability of Kirkpatrick s effective medium theory. The extracted scattering lengths are in excellent agreement with the harmonic mean of log normal distributed domain sizes and the interpore distances combined by Matthiessen s rul

A novel electrochemical anodization cell for the synthesis of mesoporous silicon

A novel design of an electrochemical anodization cell dedicated to the synthesis of mesoporous, single crystalline silicon is presented. First and foremost, the design principle follows user safety since electrochemical etching of silicon requires highly hazardous electrolytes based on hydrofluoric HF acid. The novel cell design allows for safe electrolyte handling prior, during, and post etching. A peristaltic pump with HF resistant fluoroelastomer tubing transfers electrolytes between dedicated reservoirs and the anodization cell. Due to the flexibility of the cell operation, different processing conditions can be realized providing a large parameter range for the attainable sample thickness, its porosity, and the mean pore size. Rapid etching on the order of several minutes to synthesize micrometer thick porous silicon epilayers on bulk silicon is possible as well as long time etching with continuous, controlled electrolyte flow for several days to prepare up to 1000 amp; 956;m thick self supporting porous silicon membranes. A highly adaptable, LabVIEW based control software allows for user defined etching profile