Lydia Nemec

Technische Universität München | TUM · Chair for Theoretical Chemistry

The Density-Functional Tight Binding (DFTB) method is a popular semiempirical approximation to Density Functional Theory (DFT). In many cases, DFTB can provide comparable accuracy to DFT at a fraction of the cost, enabling simulations on length- and time-scales that are unfeasible with first principles DFT. At the same time (and in contrast to empi...

Silicon carbide (SiC) is an excellent substrate for growth and manipulation of large scale, high quality epitaxial graphene. On the carbon face (the ($\bar{1}\bar{1}\bar{1}$) or $(000\bar{1}$) face, depending on the polytype), the onset of graphene growth is intertwined with the formation of several competing surface phases, among them a (3$\times$...

The Density-Functional Tight Binding (DFTB) method is a popular semiempirical approximation to Density Functional Theory (DFT). In many cases, DFTB can provide comparable accuracy to DFT at a fraction of the cost, enabling simulations on length- and time-scales that are unfeasible with first principles DFT. At the same time (and in contrast to empi...

The structure of the SiC(0001¯) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperat...

The structure of the SiC(000-1) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si2H6). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperat...

We first briefly report on the status and recent achievements of the ELPA-AEO (Eigen value Solvers for Petaflop Applications—Algorithmic Extensions and Optimizations) and ESSEX II (Equipping Sparse Solvers for Exascale) projects. In both collaboratory efforts, scientists from the application areas, mathematicians, and computer scientists work toget...

We first briefly report on the status and recent achievements of the ELPA-AEO (Eigenvalue Solvers for Petaflop Applications - Algorithmic Extensions and Optimizations) and ESSEX II (Equipping Sparse Solvers for Exascale) projects. In both collaboratory efforts, scientists from the application areas, mathematicians, and computer scientists work toge...

Multi-photon absorption (MPA) is among the most prominent nonlinear optical (NLO) effects and has applications, for example in telecommunications, defense, photonics and bio-medicines. Established MPA materials include dyes, quantum dots, organometallics and conjugated polymers, most often dispersed in solution. We demonstrate how metal-organic fra...

Multiphotonenabsorption (MPA) ist eine der wichtigsten nichtlinear-optischen (NLO) Effekte und hat verschiedene Anwendungen, z. B. in Telekommunikation, Verteidigung, Photonik und Biomedizin. Bekannte MPA-Materialien sind Farbstoffe, Quantenpunkte, metallorganische Verbindungen und konjugierte Polymere, die oft als Dispersion in Lösung verwendet we...

Stimulated emission as the new intrinsic property of metal–organic frameworks is demonstrated in article number 1605637 by Roland A. Fischer and co-workers, by the observation of stimulated emission peak, and time-resolved photoluminescence, along with the support of density of state calculations. The results identify that immobilization of strong...

Blue-color stimulated emission with low threshold power is observed from In- and Zn-MOFs, which feature a highly fluorescent chromophore densely packed and rigidly linked to the metal-ion centers in the solid state. The density-of-states and transition dipole moments are calculated and the stimulated emission phenomenon is correlated with these pro...

Die besonderen Eigenschaften von Graphen ermöglichen das Design von elektronischen Bauteilen im Nanometerbereich. Graphen kann auf der Oberfläche von Siliziumkarbonat (SiC) durch das Ausdampfen von Si epitaktisch gewachsen werden. Ein detailliertes Verständnis der atomaren und elektronischen Struktur der Grenzschicht zwischen Graphen und SiC ist ei...

We address the stability of the surface phases that occur on the C-side of 3C-SiC($\bar{1} \bar{1} \bar{1}$) at the onset of graphene formation. In this growth range, experimental reports reveal a coexistence of several surface phases. This coexistence can be explained by a Si-rich model for the unknown (3$\times$3) reconstruction, the known (2$\ti...

We measure the adsorption height of hydrogen-intercalated quasi-free-standing monolayer graphene on the (0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full ($6 \sqrt{3} \times 6 \sqrt{3}$)-R30$^\circ$ unit cell, based on a van der Waals corrected exchange correlation...

Growth of nanocrystalline graphene films on (6 √ 3 × 6 √ 3)R30 -reconstructed SiC surfaces was achieved by molecular beam epitaxy, enabling the investigation of quasi-homoepitaxial growth. The structural quality of the graphene films, which is investigated by Raman spectroscopy, increases with growth time. X-ray photoelectron spectroscopy proves th...

First-principles surface phase diagrams reveal that epitaxial monolayer graphene films on the Si side of 3C-SiC(111) can exist as thermodynamically stable phases in a narrow range of experimentally controllable conditions, defining a path to the highest quality graphene films. Our calculations are based on a van der Waals corrected density function...

SiC is a favorite growth substrate for mono- and few-layer graphene by Si sublimation. On the Si side, large ordered graphene areas can be obtained as commensurate (6√3x6√3)-R30^o (``6√3'') periodic films [1]. From a thermodynamic perspective, graphene formation competes with several other phases, including graphite on one side, and several Si-rich...