Solution Synthesis and Additive Manufacturing of Bismuth Telluride Nanoflakes for Flexible Energy Harvesting

Flexible thermoelectric generators (TEGs) are energy harvesting devices which convert temperature differences into electrical power. These devices require no moving parts and offer silent and autonomous operation. The variety of suitable materials covering a broad range of operating temperatures positions TEGs as a promising renewable energy source using waste heat recovery, especially for space and microgravity applications. Conventional manufacturing of flexible electronic and thermoelectric devices requires complicated and relatively expensive processing, which limits the capabilities of in-space manufacturing. Additive manufacturing (AM) expands the use of flexible electronics to new surfaces, applications, and recently, low gravity conditions. Plasma jet printing (PJP) is a new AM modality in which material is deposited via a gravity- independent plasma. This thesis demonstrates solution processing, ink synthesis, and PJP of bismuth telluride (Bi2Te3) nanoflakes for low temperature energy harvesting. Synthesis conditions were tailored to control nanoflake morphology and ink processing was optimized for direct printing on flexible polyimide substrates. The thermoelectric films demonstrate promising thermoelectric properties, material adhesion, and flexibility, with only a 7.2% variation in performance after 10,000 bending cycles over a 16 mm radius of curvature. This advancement of Bi2Te3 solution processing and demonstration of PJP of thermoelectric films marks a significant contribution to in space manufacturing of flexible thermoelectric devices for wearable technology and low temperature energy harvesting

Prismane C_8: A New Form of Carbon?

Our numerical calculations on small carbon clusters point to the existence of a metastable three-dimensional eight-atom cluster C$_8$ which has a shape of a six-atom triangular prism with two excess atoms above and below its bases. We gave this cluster the name "prismane". The binding energy of the prismane equals to 5.1 eV/atom, i.e., is 0.45 eV/atom lower than the binding energy of the stable one-dimensional eight-atom cluster and 2.3 eV/atom lower than the binding energy of the bulk graphite or diamond. Molecular dynamics simulations give evidence for a rather high stability of the prismane, the activation energy for a prismane decay being about 0.8 eV. The prismane lifetime increases rapidly as the temperature decreases indicating a possibility of experimental observation of this cluster.Comment: 5 pages (revtex), 3 figures (eps

MASTL is enriched in cancerous and pluripotent stem cells and influences OCT1/OCT4 levels

Publisher Copyright: © 2022 The Author(s)MASTL is a mitotic accelerator with an emerging role in breast cancer progression. However, the mechanisms behind its oncogenicity remain largely unknown. Here, we identify a previously unknown role and eminent expression of MASTL in stem cells. MASTL staining from a large breast cancer patient cohort indicated a significant association with β3 integrin, an established mediator of breast cancer stemness. MASTL silencing reduced OCT4 levels in human pluripotent stem cells and OCT1 in breast cancer cells. Analysis of the cell-surface proteome indicated a strong link between MASTL and the regulation of TGF-β receptor II (TGFBR2), a key modulator of TGF-β signaling. Overexpression of wild-type and kinase-dead MASTL in normal mammary epithelial cells elevated TGFBR2 levels. Conversely, MASTL depletion in breast cancer cells attenuated TGFBR2 levels and downstream signaling through SMAD3 and AKT pathways. Taken together, these results indicate that MASTL supports stemness regulators in pluripotent and cancerous stem cells.Peer reviewe

Superconductivity in Fullerides

Experimental studies of superconductivity properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why the A_3 C_60 are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential $\mu^*$, describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described.Comment: 33 pages, latex2e, revtex using rmp style, 15 figures, submitted to Review of Modern Physics, more information at http://radix2.mpi-stuttgart.mpg.de/fullerene/fullerene.htm

Analyzing the Effects of Gold Reflective Coatings on GaAs Quantum Dot Photoluminescence

Molecular Beam Epitaxy (MBE) is a method for making high purity, tensile-strained GaAs quantum dots (QDs) embedded in solid-state semiconductors. QDs, excited by electricity or lasers, emit photons characteristic of the QDs size and composition, which may be used in tunable optoelectronic devices such as LEDs, lasers and solar cells. Understanding the light emission properties of these QDs is essential for these applications, as well as for continued QD research. Photoluminescence (PL) is a laser-excitation technique used to determine these properties. Occasionally, the PL signals from our samples are too low in intensity to be accurately detected. We will investigate whether the addition of gold coatings on the back of QD samples improves PL emission by reflecting additional photons into the detector. To apply these reflective coatings, we first prepare the samples using a chemical wet etch process and then deposit thin gold films via physical vapor deposition. We will analyze the difference in PL intensity between coated and noncoated samples and gauge the influence of gold deposition thickness

Rotational dynamics of nitrous acid (HONO) in Kr matrix

With the help of ultrafast time-resolved infrared spectroscopy, we investigate rotational diffusion of cis- and trans-nitrous acid (HONO) in solid Kr at 30 K, as well as its reorientation upon the IR-driven cis -> trans isomerization. We find different mobilities for the two isomers: cis-HONO is pinned to the matrix with no decay of the anisotropy on the 100 ns time scale, whereas trans-HONO rotates around its long axis, reducing its anisotropy partially on that time scale. The long axis itself, defined by the terminal oxygen and hydrogen atoms of HONO, stays fixed on even a minute time scale. Accompanying molecular dynamics simulations reproduce the anisotropic rotational diffusion of trans-HONO correctly, although on a completely wrong time scale, whereas they would predict complete reorientation of cis-HONO within approximate to 10 ps, in harsh disagreement with the experiment. We attribute the mismatch of orientational time scales to either too soft interaction potentials or to the fact that HONO occupies an interstitial rather than a monosubstitutional matrix site. The experiments furthermore show that the direction of the OH bond hardly changes during the IR-driven cis -> trans isomerization, in contrast to the intuitive picture that it is mostly the light hydrogen which moves. Rather, it is the two central nitrogen and oxygen atoms that are removed during isomerization in a hula hoop fashion, whereas the terminal atoms are still pinned to the matrix cage

Calibration of Silicon- and Tellurium- Doped Gallium Arsenide Using the Hall Effect

Molecular Beam Epitaxy (MBE) provides a method for growing semiconductor crystals whose electrical properties may be fine-tuned through the addition of impurity (dopant) atoms. The addition of impurity atoms, such as tellurium or silicon, to gallium arsenide allows us to increase its electrical conductivity, which is critical for the production of electronic devices. Characterization using the Hall Effect and van der Pauw technique determines the electrical characteristics of these materials, including mobility and carrier (e.g. electron) concentration. It is the goal of this project to optimize both the MBE growth conditions and characterization methods and to produce a data set identifying the relationship between the temperature of the dopant element during deposition and the resulting carrier concentration. These values were found to have a linear Arrhenius relationship for silicon between 1025 – 1250°C, producing a carrier concentration range of 9.37x1015– 6.14x1018cm-3and a mobility range of 1171 – 4951 cm2/Vs, and for tellurium between the temperatures of 500 – 625°C with a carrier concentration range of 5.12x1016– 1.01x1019cm-3and a mobility range of 1284 – 4632 cm2/Vs. These silicon and tellurium dopant calibrations are essential for yielding reproducible materials and serves as the foundation for continued research into doped semiconductor materials