Tetrathiotetracene thin film morphology and electrical properties

The electrical properties of organic thin films are determined by their chemical constituents and the morphology of the films deposited. In this paper the morphology of vacuum sublimed (7∙10-6 mbar) tetrathiotetracene (TTT) thin films is shown to be strongly affected by the thermal deposition temperature (222-350 K) and rate of deposition. Mostly needle-like morphologies are identified by scanning electron microscopy. Optimal TTT purity (a pre-requisite for device preparation via subsequent oxidation) is evidenced by their initially low electrical conductivity. Altering the TTT morphology, by variation of the evaporation parameters, strongly affects this base electrical conductivity. Four probe conductivity measurements and charge extraction by linear increasing voltage methods are used to characterize film electrical properties. In-plane conductivity of up to 7.03∙10-5 S/cm is achieved for pure TTT thin films. Subsequent aerial oxidation resulted in a 3.4-fold increase in electrical conductivity

Thermoelectric properties of lead chalcogenide core-shell nanostructures

We present the full thermoelectric characterization of nanostructured bulk PbTe and PbTe-PbSe samples fabricated from colloidal core-shell nanoparticles followed by spark plasma sintering. An unusually large thermopower is found in both materials, and the possibility of energy filtering as opposed to grain boundary scattering as an explanation is discussed. A decreased Debye temperature and an increased molar specific heat are in accordance with recent predictions for nanostructured materials. On the basis of these results we propose suitable core-shell material combinations for future thermoelectric materials of large electric conductivities in combination with an increased thermopower by energy filtering.Comment: 12 pages, 8 figure

Thin film organic thermoelectric generator based on tetrathiotetracene

Thin films of p- and n- type organic semiconductors for thermo-electrical (TE) applications are produced by doping of tetrathiotetracene (TTT). To obtain p-type material TTT is doped with iodine during vacuum deposition of thin films or by post-deposition doping using controlled exposure to iodine vapors. Thermal co-deposition in vacuum of TTT and TCNQ is used to prepare n-type thin films. The attained thin films are characterized by measurements of Seebeck coefficient and electrical conductivity. Seebeck coefficient and conductivity could be varied by altering the doping level. P-type TTT:iodide thin films with a power factor of 0.52 μWm-1K-2, electrical conductivity of 130 S m-1 and Seebeck coefficient of 63 μV K-1 and n-type TCNQ:TTT films with power factor of 0.33 μWm-1K-2, electrical conductivity of 57 S m-1 and Seebeck coefficient of -75 μV K-1 are produced. Engineered deposition of both p- and n-type thermoelectric conducting elements on the same substrate is demonstrated. A proof of concept prototype of planar thin film TE generator based on a single p-n couple from the organic materials is built and its power generation characterized

Correlation of film thickness to optical band gap of Sol-gel derived Ba 0.9

Ba0.9Gd0.1TiO3 thin films have been fabricated on SiO2/Si and fused silica by sol-gel method. The films are prepared through a spin coating process and annealed at 900 °C to obtain crystallized films. The effect of film thickness on the microstructure and optical band gap has been investigated using X-ray diffractometer, atomic force microscope and ultraviolet-visible spectroscopy, respectively. XRD patterns confirm that the films crystallized with tetragonal phase perovskite structure. The films surface morphology is analysed through amplitude parameter analysis to find out that the grain size and surface roughness are increased with the increase of films thickness. The transmittance and absorbance spectra reveal that all films exhibit high absorption in UV region. The evaluated optical band gap is obtained in the range of 3.67 - 3.78 eV and is found to be decreased as the thickness increase

Thermoelectric generator (TEG) technologies and applications

2021 The Author(s). Nowadays humans are facing difficult issues, such as increasing power costs, environmental pollution and global warming. In order to reduce their consequences, scientists are concentrating on improving power generators focused on energy harvesting. Thermoelectric generators (TEGs) have demonstrated their capacity to transform thermal energy directly into electric power through the Seebeck effect. Due to the unique advantages they present, thermoelectric systems have emerged during the last decade as a promising alternative among other technologies for green power production. In this regard, thermoelectric device output prediction is important both for determining the future use of this new technology and for specifying the key design parameters of thermoelectric generators and systems. Moreover, TEGs are environmentally safe, work quietly as they do not include mechanical mechanisms or rotating elements and can be manufactured on a broad variety of substrates such as silicon, polymers and ceramics. In addition, TEGs are position-independent, have a long working life and are ideal for bulk and compact applications. Furthermore, Thermoelectric generators have been found as a viable solution for direct generation of electricity from waste heat in industrial processes. This paper presents in-depth analysis of TEGs, beginning with a comprehensive overview of their working principles such as the Seebeck effect, the Peltier effect, the Thomson effect and Joule heating with their applications, materials used, Figure of Merit, improvement techniques including different thermoelectric material arrangements and technologies used and substrate types. Moreover, performance simulation examples such as COMSOL Multiphysics and ANSYS-Computational Fluid Dynamics are investigated

Effect of Low Temperature Annealing on Microstructural and Optical Properties of (BaTiO3)0.84(CeO2)0.16(BaTiO_3)_{0.84}(CeO_2)_{0.16} Thin Films

$(BaTiO_3)_{0.84}(CeO_2)_{0.16}$ thin films were prepared by electron beam evaporation method. X-ray diffraction and scanning electron microscopy revealed the amorphous structure for the as-prepared films. The thin films were annealed at temperatures: 200, 300, 400 and 500C for 1 h in air. Small and low intensity crystalline peaks were observed at annealing temperature of 200C for 1 h. The intensity and the number of the crystalline peaks were increased with increasing annealing temperature. Nanocrystals, of dimensions in the range 60-76 nm, were obtained when the annealing was performed at 500°C. The indexed diffraction pattern of the annealed thin film revealed a monoclinic structure. A two-layer model was used to describe the experimental ellipsometric data. The Bruggeman effective medium approximation was used to describe the surface roughness layer and the Cauchy dispersion relation was used to describe the main $(BaTiO_3)_{0.84}(CeO_2)_{0.16}$ layer. The optical constants of the thin films over 300-1100 nm spectral range were measured. The optical band gap showed gradual decrease with the annealing temperature. The accurate determination of the optical constants of the thin films is very useful and should be taken into consideration in the design of devices using optical thin films technology

Properties of ptfe impregnated ni-b-sic electroless composite coatings

Akımsız nikel bor kaplamalar (EN-B) Yüksek sertlik ve aşınma direnci gibi iyileştirilmiş kaplama özelliklerine sahiplerdir. Bu çalışmada, iyi aşınma direnci ve düşük sürtünme katsayısı (COF) yanı sıra yüksek sertlikte kompozit kaplamalar elde etmek için çeşitli EN-B kaplamalar üretilmiştir. Çalışma, EN-B kaplamanın matrisi içindeki bir kompozit malzeme olarak SiC ve politetrafloroetilenin (PTFE) etkisine ve EN-B-SiC kaplama üzerinde biriken bir tabaka halinde PTFE'nin etkisine odaklanmaktadır. Ni-B matrisine SiC ve PTFE partiküllerinin ilavesiyle meydan gelen değişimlerin anlaşılması için kaplamalar karakterize edildidi. Bunun için X-ışını difraksiyon (XRD) analizi ve taramalı elektron mikroskopisi (SEM) kullanıldı. İlavelerin, kaplamaların tribolojik özelliklerini nasıl etkilediğini incelendi. Aşınma direncini ve kaplamaların COF'sini ölçmek için sert çelik bilya ile karşılıklı aşınma testleri gerçekleştirilmiştir. Vickers mikro sertlik testleri, kaplamaların sertliğindeki değişimleri tespit etmek için yapılmıştır. Potansiyodinamik polarizasyon tekniği kullanılarak kaplamaların korozyon testleri yapıldı. Elde edilen sonuçlara göre EN-B-SiC-PTFE kaplamaların, EN-B-SiC kaplamaların yüksek sertlik ve aşınma ve korozyon direncindeki avantajlarını ve düşük COF'deki PTFE kaplamalarının bir kombinasyonunu sergilediğini göstermektedir. PTFE-spin kaplı EN-B-SiC kaplamalar, çok düşük COF değerlerinin istendiği uygulamalar için uygundur.--------------------The electroless nickel boron coatings (EN-B) have better coating features like high hardness and wear resistance. In the current work, Various EN-B coatings were produced to achieve composite coatings with good wear resistance and lower coefficient of friction (COF) as well as higher hardness. The work focuses on the effect of SiC and polytetrafluoroethylene (PTFE) as a composite material inside the matrix of the EN-B coating and the effect of PTFE as a layer deposited on the EN-B-SiC coating. The characterization of the structures was performed using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) to have in-depth understanding relating to the inclusion of SiC and PTFE particles into the Ni-B coating and how they influence the tribological properties of these coatings. Reciprocating wear tests were conducted to measure the wear resistance and the COF of the coatings. Vickers microhardness tests were conducted to notice about any possible enhancements in the hardness of the coatings. Corrosion tests were performed using the potentiodynamic polarization technique. The results demonstrate that the EN-B-SiC-PTFE coatings exhibit a combination of the advantages of the EN-B-SiC coatings for high hardness, better wear and improved corrosion resistance, and of the PTFE coatings in low COF. The PTFE-spin coated EN-B-SiC coatings are suitable for the applications where very low COF values are desired