From metastable to stable modifications-in situ Laue diffraction investigation of diffusion processes during the phase transitions of (GeTe)(n)Sb2Te3 (6 < n < 15) crystals.

Temperature dependent phase transitions of compounds (GeTe)nSb2Te3 (n = 6, 12, 15) have been investigated by in situ microfocus Laue diffraction. Diffusion processes involving cation defect ordering at B300 8C lead to different nanostructures which are correlated to changes of the thermoelectric characteristics

Layered germanium tin antimony tellurides: element distribution, nanostructures and thermoelectric properties

In the system Ge-Sn-Sb-Te, there is a complete solid solution series between GeSb2Te4 and SnSb2Te4. As Sn2Sb2Te5 does not exist, Sn can only partially replace Ge in Ge2Sb2Te5; samples with 75% or more Sn are not homogeneous. The joint refinement of high-resolution synchrotron data measured at the K-absorption edges of Sn, Sb and Te combined with data measured at off-edge wavelengths unambiguously yields the element distribution in 21R-Ge0.6Sn0.4Sb2Te4 and 9P-Ge1.3Sn0.7Sb2Te5. In both cases, Sb predominantly concentrates on the position near the van der Waals gaps between distorted rocksalt-type slabs whereas Ge prefers the position in the middle of the slabs. No significant antisite disorder is present. Comparable trends can be found in related compounds; they are due to the single-side coordination of the Te atoms at the van der Waals gap, which can be compensated more effectively by Sb3+ due to its higher charge in comparison to Ge2+. The structure model of 21R-Ge0.6Sn0.4Sb2Te4 was confirmed by high-resolution electron microscopy and electron diffraction. In contrast, electron diffraction patterns of 9P-Ge1.3Sn0.7Sb2Te5 reveal a significant extent of stacking disorder as evidenced by diffuse streaks along the stacking direction. The Seebeck coefficient is unaffected by the Sn substitution but the thermal conductivity drops by a factor of 2 which results in a thermoelectric figure of merit ZT = similar to 0.25 at 450 degrees C for both Ge0.6Sn0.4Sb2Te4 and Ge1.3Sn0.7Sb2Te5, which is higher than similar to 0.20 for unsubstituted stable layered Ge-Sb-Te compounds

Distinct IL-1α-responsive enhancers promote acute and coordinated changes in chromatin topology in a hierarchical manner

How cytokine-driven changes in chromatin topology are converted into gene regulatory circuits during inflammation still remains unclear. Here, we show that interleukin (IL)-1α induces acute and widespread changes in chromatin accessibility via the TAK1 kinase and NF-κB at regions that are highly enriched for inflammatory disease-relevant SNPs. Two enhancers in the extended chemokine locus on human chromosome 4 regulate the IL-1α-inducible IL8 and CXCL1-3 genes. Both enhancers engage in dynamic spatial interactions with gene promoters in an IL-1α/TAK1-inducible manner. Microdeletions of p65-binding sites in either of the two enhancers impair NF-κB recruitment, suppress activation and biallelic transcription of the IL8/CXCL2 genes, and reshuffle higher-order chromatin interactions as judged by i4C interactome profiles. Notably, these findings support a dominant role of the IL8 “master” enhancer in the regulation of sustained IL-1α signaling, as well as for IL-8 and IL-6 secretion. CRISPR-guided transactivation of the IL8 locus or cross-TAD regulation by TNFα-responsive enhancers in a different model locus supports the existence of complex enhancer hierarchies in response to cytokine stimulation that prime and orchestrate proinflammatory chromatin responses downstream of NF-κB

Nanostructured rocksalt-type solid solution series (Ge1−xSnxTe)nSb2Te3 (n=4, 7, 12; 0≤x≤1): Thermal behavior and thermoelectric properties

Solid solutions (Ge1−xSnxTe)nSb2Te3 (n=4, 7, 12; 0≤x≤1) represent stable high-temperature phases and can be obtained as metastable compounds by quenching. High-resolution transmission electron microscopy reveals that the quenched (pseudo-)cubic materials exhibit parquet-like nanostructures comparable to, but especially for n=4 more pronounced than in (GeTe)nSb2Te3 (GST materials). The temperature-dependent phase transitions are comparable; however, substitution with Sn significantly lowers the transition temperatures between cubic high-temperature phase and the long range ordered layered phases that are stable at ambient conditions. In addition, the metrics of the quenched Sn-containing materials remains closer to cubic, especially for samples with n=7 or 12. For samples with high defect concentrations (n=4, 7), Sn-substituted samples exhibit electrical conductivities up to 3 times higher than those of corresponding GST materials. Since the difference in thermal conductivity is much less pronounced, this results in a doubling of the thermoelectric figure of merit (ZT) at high temperatures for (Ge0.5Sn0.5Te)4Sb2Te3 as compared to (GeTe)4Sb2Te3. Sn doping in (GeTe)7Sb2Te3 increases the ZT value by a factor of up to 4 which is also due to an increased Seebeck coefficient

Disorder and Transport Properties of In3SbTe2 – an X-ray, Neutron and Electron Diffraction Study

Quenched metastable In3SbTe2 was investigated by X-ray and neutron powder diffraction as well as by single-crystal X-ray diffraction. The average structure corresponds to the rocksalt type, the anion position being occupied by antimony and tellurium. Neutron data indicate no antisite disorder of indium and antimony. The compound is a high-temperature phase that can be quenched to yield a metastable compound at ambient temperature which, upon heating, decomposes at ca. 320 °C into InSb and InTe. Diffuse scattering in reconstructed X-ray and selected area electron diffraction patterns indicates local distortions of the crystal structure due to static atom displacement along from the average positions, caused by the different size of the anions, but no superstructure. The electrical conductivity of In3SbTe2 is 3.2 × 104 S·cm–1 at 25 °C, the temperature characteristics correspond to metallic behavior. Consequently, the thermal conductivity is also rather high. The decomposition into InSb and InTe reduces the electrical conductivity by a factor of 3 in heterogeneous microstructures

The Solid Solution Series (GeTe)x(LiSbTe2)2 (1 ≤ x ≤ 11) and the Thermoelectric Properties of (GeTe)11(LiSbTe2)2

Exchanging one Ge2+ with two Li+ per formula unit in (GeTe)n(Sb2Te3) (n = 1, 2, 3, ...) eliminates cation vacancies, because it leads to an equal number of cations and anions. This substitution results in the solid solution (GeTe)x(LiSbTe2)2 (with x = n – 1, but n not necessarily an integer). For x 6, (GeTe)x(LiSbTe2)2 forms a GeTe-type structure that shows a phase transition to a cubic high-temperature phase at ca. 280 °C. The thermoelectric properties of (GeTe)11(LiSbTe2)2 have been investigated and show that this compound is a promising thermoelectric material with a ZT value of 1.0 at 450 °C. The high ZT value of the thermodynamically stable compound is caused by a low phononic contribution to the thermal conductivity; probably, Li acts as a “pseudo-vacancy”

Influencing the thermoelectric properties of germanium antimony tellurides (GST) by substitutions with In, Sn and Se

The nanostructure of bulk germanium antimony tellurides (GST materials) can be tuned by utilizing phase transitions between a cubic disordered rocksalt-type high-temperature phase and a layered trigonal phase, which is stable at ambient temperature. In the cubic phases, Te occupies the anion position and Ge, Sb and vacancies are randomly disordered at the cation position, whereas the layered trigonal phases consist of 2D extended rocksalt-type slabs interconnected by van der Waals gaps. Quenching the cubic high-temperature phases of (GeTe)nSb2Te3 (4 n 19) yields pseudocubic thermoelectric materials with finite intersecting defect layers and figures of merit (ZT) up to 1.3 at 720 K [Rosenthal et al., Chem. Mater. 2011, 23, 4349.]. Their thermoelectric properties depend on the GeTe content (n) and the synthesis conditions (temperature, annealing time, cooling rate). The substitution with In, Sn or Se is possible over a wide compositional range. Quenching results in pseudocubic solid solution series with promising thermoelectric properties. Doping bulk GST material with Se and In reduces the transition temperature between the thermodynamically stable trigonal phase and the cubic high-temperature phase. This affects the formation of nanostructures as diffusion rates determine the lateral extension of the defect layers that are formed upon quenching the high-temperature phase. In addition to their influence on the electronic band structure, real-structure phenomena and mixed occupancies enhance the phonon scattering and thus provide a way to tune the thermoelectric properties. Substituting Ge with Sn results in a more pronounced parquet-like nanostructure at low GeTe contents (e. g. n = 4) and an increased electrical conductivity. For these samples, the Seebeck coefficient is unaffected and the higher electrical conductivity is compensated by the thermal conductivity so that the ZT value is nearly unchanged compared to unsubstituted GST. Due to a pronounced increase of the Seebeck coefficient, the ZT value of In-substituted samples like Ge12SbInTe15 is higher than that of unsubstituted samples with comparable GeTe content up to 570 K. As a rule, the Seebeck coefficient increases and the thermal conductivity is reduced when Te is substituted by Se. Therefore the ZT value of Ge7Sb2Te8Se2, for instance, increases up to 1.2 at 720 K, 6 times higher compared to the unsubstituted sample

Enhancing the Thermoelectric Properties of Germanium Antimony Tellurides by Substitution with Selenium in Compounds GenSb2(Te1-xSex)n+3 (0 ≤ x ≤ 0.5; n ≥ 7)

Quenched pseudocubic germanium antimony tellurides (GST compounds) exhibit promising thermoelectric properties. These are related to the nanostructures which can be influenced by varying the composition and the thermal treatment. The substitution of Te by Se in bulk samples of GenSb2Ten+3 with high thermoelectric figures of merit (ZT) is possible over a wide compositional range. This results in solid solution series GenSb2(Te1–xSex)n+3 with 0 < x < 0.75 for n ≥ 7. Se substitution reduces the average lateral extension of the defect layers in quenched samples. This is a consequence of the reduced mobility during the quenching process due to the lower cubic to trigonal phase transition temperatures of Se-substituted samples. Most pronounced for n = 7, Se doping increases the transition temperatures between the nanostructured (pseudo)cubic modification of quenched samples and their layered trigonal phase. This increases the temperature ranges in which the materials can be employed without altering their nanostructures and properties. When Se is introduced, the Seebeck coefficient increases and the thermal conductivity decreases. The ZT value of Ge7Sb2Te8Se2, for instance, increases up to 1.2 at 425 °C, which is 6 times higher than that of Ge7Sb2Te10. Similarly, the ZT value of Ge12Sb2(Te1–xSex)15 increases up to a factor of 2 for x = 0.2 at temperatures below 400 °C. The most promising thermoelectric properties (ZT = 1.2 at 425 °C for n = 7 and ZT = 1.1 at 350 °C for n = 12) are observed for x = 0.2 whereas higher Se substitution rates result in a less pronounced effect. The average structures were determined by powder as well as single crystal X-ray diffraction (SCXRD). The real structure of quenched GenSb2(Te1–xSex)n+3 (0 ≤ x ≤ 0.5; n ≥ 7) bulk material was investigated by high-resolution electron microscopy (HRTEM) with respect to the degree of substitution (x) and correlated with the resulting changes of the thermoelectric properties. The decrease of the lateral extension of the defect layers with increasing Se content as found by HRTEM and electron diffraction is confirmed by SCXRD data for Ge∼5Sb2(Te0.13Se0.87)∼8

L'énergie solaire pour la production d'électricité au Maghreb : transition énergétique et jeux d'échelles

The « low carbon » transition in the Maghreb, analyzed with a focus on the deployment of solar energy for electricity generation, is considered in both a Euro-Mediterranean and national context. This transition is the result of projects that were designed by supranational organizations and agreed on at the highest level. On a Euro-Mediterranean level, initiatives were implemented to support a large scale development of solar energy, whether it be at an intergovernmental level (Mediterranean Solar Plan, 2008), by private industrial consortia (Desertec Industrial Initiative, Medgrid 2009), or by international donors (The World Bank CSP MENA Initiative, 2009). At national level, the three Maghreb countries (Algeria, Morocco, Tunisia), have formulated explicit renewables development policies, (especially since 2009), and established national plans and programs (Moroccan Solar Plan, Tunisian Solar Plan, National Renewable and Efficiency Energy Program in Algeria). In Tunisia, a control policy on Energy Demand has nevertheless been initiated since the mid-1980’s, resulting in particular in the Prosol programs. The purpose of this thesis is to explore the implementation of the « low carbon » transition in the Maghreb and show what spatial and relational implications it had both at European and national level. Thus, we explain how electrical energy contributes to redefine how regional areas connect and to what extent the implementation of solar technologies helps reshape the geography of electrical energy in the Maghreb. The technical aspect (network infrastructure and electricity production unit by solar energy) will be studied following a systemic approach, at the crossroads of spatial, social, political and economical spheres.La transition énergétique « bas carbone » au Maghreb, analysée sous l’angle du déploiement de l’énergie solaire pour la production d’électricité, est appréhendée dans un double contexte euro-méditerranéen et national. Elle est notamment le fruit de projets imaginés par des structures supranationales et décidés au plus haut niveau des États. À l’échelle euro-méditerranéenne, des initiatives ont été mises en place pour appuyer le développement à grande échelle de l’énergie solaire, qu’elles émanent de dispositifs intergouvernementaux (Plan Solaire Méditerranéen en 2008), de consortia industriels privés (Desertec Industrial Initiative, Medgrid en 2009) ou de bailleurs de fonds internationaux (The World Bank CSP MENA Initiative en 2009). À l’échelle nationale, les trois pays du Maghreb (Algérie, Maroc, Tunisie) ont formulé, surtout depuis 2009, des politiques de développement des énergies renouvelables, et élaboré, pour leur mise en œuvre, des plans et programmes nationaux (Plan Solaire Marocain, Plan Solaire Tunisien, Programme National des Énergies Renouvelables et de l’Efficacité Énergétique en Algérie). En Tunisie, une véritable politique de maîtrise énergétique a néanmoins été initiée depuis le milieu des années 1980, donnant lieu notamment aux programmes Prosol. L’objet de cette thèse est d’analyser la mise en œuvre de la transition énergétique « bas carbone » au Maghreb et d’en montrer les implications spatiales et relationnelles aux échelles euro-méditerranéenne et nationale. Ainsi, nous montrons en quoi l’électricité contribue à redéfinir la mise en réseau des espaces régionaux et dans quelles mesures la diffusion des technologies solaires participe à redessiner la géographie de l’électricité au Maghreb. L’objet technique (infrastructure de réseau et unité de production d’électricité à partir de l’énergie solaire) est appréhendé à partir d’une approche systémique, à l’interface des sphères spatiale, sociale, politique et économique

Optoelectronic Heterodyne THz Receiver for 100&#x2013;300 GHz Communication Links

Terahertz wireless communications is an increasingly interesting research topic due to the high demand for un-allocated channels and high data rates. Photonic solutions have shown great potential in this field. However, most photonics assisted THz links so far have employed optoelectronics only on the transmit side. Thus, the full potential of photonic THz communication has not been utilized yet. Here, we introduce optoelectronics also on the receive side by using a photoconductive antenna based heterodyne THz detector. This allows down-conversion of data signals from the W-, D-, and THz-band to the baseband using a laser beat signal as local oscillator. Using electromagnetic modeling, we designed passive radio frequency structures and a receiver package to handle high intermediate frequency output signals. In a homodyne spectroscopic setup, the receiver shows a frequency response superior to state-of-the-art photoconductive antennas due to an improved photoconductive material. In a heterodyne testbed, the receiver exhibits a large intermediate frequency bandwidth of 11 GHz and a conversion gain of &#x2212;47 dB. This enabled us to employ the receiver in a fully photonic wireless link at sub-terahertz and terahertz frequencies together with a PIN photodiode emitter. We achieved error-free transmission of 4-QAM signals with gross data rates up to 12 Gbit/s at carrier frequencies up to 320 GHz. This work shows the huge potential of optoelectronic receivers for THz wireless communications and enables the exploration of full photonic THz links