arXiv subjects

Theo Siegrist

Publications and source records attributed to Theo Siegrist.

23 records · Page 2Linked to original sources

arXiv2015

Transport Properties of Cubic Crystalline Ge$_{2}$Sb$_{2}$Te$_{5}$: A Potential Low-temperature Thermoelectric Material

Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200 - 300 $μ$V/K in its cubic crystalline phase ($\it{c}$-GST) at remarkably high $\it{p}$-type doping levels of $\sim$ 1$\times$10$^{19}$ - 6$\times$10$^{19}$ cm$^{-3}$ at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 $μ$V/K for a doping range 1$\times$10$^{19}$ - 3.5$\times$10$^{19}$ cm$^{-3}$. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ($\sim$ 0.7 W/m-K at 300 K),\citep{r51} our results suggest the possibility of using $\it{c}$-GST as a low-temperature thermoelectric material.

cond-mat.mtrl-sci↗

arXiv2015

Ba_{2}TeO as an optoelectronic material: First-principles study

The band structure, optical and defects properties of Ba_{2}TeO are systematically investigated using density functional theory with a view to understanding its potential as an optoelectronic or trans- parent conducting material. Ba_{2}TeO crystallizes with tetragonal structure (space group P4/nmm) and with a 2.93 eV optical band gap 1 . We find relatively modest band masses for both electrons and holes suggesting applications. Optical properties show a infrared-red absorption when doped. This could potentially be useful for combining wavelength filtering and transparent conducting functions. Furthermore, our defect calculations show that Ba_{2}TeO is intrinsically p-type conducting under Ba-poor condition. However, the spontaneous formation of the donor defects may constrain the p-type transport properties and would need to be addressed to enable applications.

cond-mat.mtrl-sci↗

arXiv2011

Synthesis, crystal structure and magnetism of beta-Fe1.00(2)Se1.00(3) single crystals

Understanding iron based superconductors requires high quality impurity free single crystals. So far they have been elusive for beta-FeSe and extraction of intrinsic materials properties has been compromised by several magnetic impurity phases. Herein we report synchrotron - clean beta-FeSe superconducting single crystals grown via LiCl/CsCl flux method. Phase purity yields evidence for a defect induced weak ferromagnetism that coexists with superconductivity below Tc. In contrast to Fe1+yTe - based superconductors, our results reveal that the interstitial Fe(2) site is not occupied and that all contribution to density of states at the Fermi level must come from in-plane Fe(1).

cond-mat.supr-con↗

arXiv2004

Single-crystal field-effect transistors based on copper phthalocyanine

Copper phthalocyanine (Cu-Pc) single crystals were grown by physical vapor transport and field effect transistors (FETs) on the surface of these crystals were prepared. These FETs function as p-channel accumulation-mode devices. Charge carrier mobilities of up to 1 cm2/Vs combined with a low field-effect threshold were obtained. These remarkable FET-characteristics, along with the highly stable chemical nature of Cu-Pc make it an attractive candidate for device applications.

cond-mat.mtrl-sci↗

arXiv2002

6,13-dihydropentacene and pentacene single co-crystals

6,13-dihydropentacene and pentacene co-crystallise in a ratio of 2:1 during vapour transport of commercial pentacene in a gas flow. The crystal structure is monoclinic P2_1/n and contains one dihydropentacene molecule, and half a pentacene molecule in the asymmetric unit.

cond-mat↗