Experimental

    The Laboratory of Multifunctional Materials was established in 2017 as a result of the merger between the Laboratory of Physical Problems in Ion Technology and the Laboratory of Superconductivity and Cryoelectronics. The Laboratory of Superconductivity and Cryoelectronics has been active since 1989. Its activities include synthesis and research of high temperature superconductive (HTS), ferromagnetic (FM), ferroelectric (FE) or multiferroic (MF) films, coatings for biomedical applications, as well as layered HTS/FM structures. The Laboratory of Physical Problems in Ion Technology was founded in 1963 alongside the establishment of the Institute for Electronics at the Bulgarian Academy of Sciences (IE-BAN) with the aim of synthesizing and modifying metal, semiconductor, dielectric, and superconducting materials (primarily as thin layers).

The experimental research in the Laboratory of Multifunctional Materials is focused on the synthesis, functionalization, and characterization of:

- Carbon allotropes: such as thin layers of amorphous a-C, ta-C, a-C:H, ta-C:H, microcrystalline and nanocrystalline taC/DLC, pyrolytic carbon, graphene/defective graphene, nano- to micro- sized graphene-like phases (defective graphene, reduced graphene oxide (rGO) and graphene oxide (GO), graphites and carbon black

- Thin layers of SiC deposited on single crystalline Si substrates

- Different structures of complex HTS/FM oxides (e.g. Y1Ba2Cu3O7-x (YBCO)/La0.7Ca0.3MnO3 (LCMO), YBCO/La0.7Sr0.3MnO3 (LSMO), YBCO/Fe(2-x)O(4-y))

- Biomimetic optimization of various thin layers of tantalum (Ta), tantalum nitride (TaN), tantalum oxide (Ta2O5), aC:H and taC:H, as well as thin composite coatings based on nanocrystalline calcium phosphate hydroxyapatite (Ca10(PO4)6(OH)2)

- Materials from the so-called topological insulators class – mainly monoclinic β-Ag2Te, both as bulk crystals as well as thin films

- Production of ultra-high vacuum (UHV) without residual hydrocarbons by an ion getter pump with hot filament and magnetic field, where the speed of pumping is independent of pressure (as in the case of cold discharge pumps)

The Laboratory of Multifunctional Materials has equipment for:

- Direct current Magnetron Sputtering (dcMS)

- Radiofrequency Magnetron Sputtering (rfMS)

- Decomposition of a-C:H and ta-C:H layers through plasma-assisted chemical vapor deposition (PACVD)

- Decomposition of layers of nanocrystalline DLC and pyrolytic carbon, graphene and graphine-like allotropes, as well as nanodispersed graphene and graphene-like allotropes (including graphene oxide) through thermally assisted chemical vapor deposition (TACVD)

- Modification of the surface of thin layers with ion bombardment (with Ar, N2, O2, H2), DC or AC (mid frequency) plasma

- High-temperature furnaces (1300-1800)°C with corresponding gas systems for synthesis/modification in an inert gas/es media or low vacuum

Theoretical

    Our interests consist of discovery and total characterization of theoretical molecular systems and the corresponding research over existing ones, with emphasis on reaction mechanisms. We often employ multi-configurational methods, DFT and quantum metadynamics. Our research ranges from investigating the excited-state reactivity manifold of candidates for logical elements in chemical computers to simulations of metal cation - RNA interaction and modeling high-temperature synthesis of refractory semiconductors:

- A model of the relations between chemical structure and photo-reactivity of hydroxylated chalcones, including characterization of conical intersections and inter-system crossings (CASPT2//CASSCF)

- Investigation of metal cation location at the backbone and nucleobases of RNA (Quantum Dynamics)

- A model of the formation and reactivity of primordial carbon clusters in space, and their assembly into closed-cage nanoparticles (DFTB2 Dynamics and Metadynamics)

- Discovery of the reaction mechanisms in a novel CVD carbonization of {111} and {001} silicon, while accounting for the presence and reduction of native oxide (Quantum Metadynamics)

- H-atom transfer reactions in reduced graphene oxide (Quantum Dynamics)

- Discovery of multiple novel classes of singlet fission molecules (Hybrid-mGGA)

- The mechanisms of thin layer sp2- and sp3-carbon phase CVD, due to high-temperature decomposition of acetone over {001} silicon (DFTB2 Metadynamics)

The following is an expansion of the modeling capabilities we utilize.
Ab initio discovery and characterization of reaction mechanisms in ground state:

- Quantum Metadynamics

- Free Energy Surface

- Quantum Dynamics

- QM/MM

- Transition States

- Minimum Energy Path

Preferred methods include: DFT (GGA, mGGA and Hybrid-mGGA), DFTB2, GFNX-xTB, MP2 and CC

Ab initio discovery and characterization of reaction mechanisms in excited state:

- Conical Intersections

- Inter-System Crossings

- Avoided Crossings

- Transition States

- Minimum Energy Path

- Adsorption and Emission spectra

- Precise determination and analysis of the Active Space

Preferred are MCSCF methods, such as CASPT2//CASSCF

Our methodology includes the use of:

- Reassessment of the Active Space for competitive reactions

- Visualization of the topology in zones of quasi-degeneracy

- Trajectory analysis

- Band Structure

- Projected Density of States

- Intrinsic Reaction Coordinate

- 1D and 2D Radial Distribution Functions

- Condensed Fukui Functions

- Predicting UV/Vis, IR, Raman and NMR spectra

- Conformational Analysis

- Electron Localization Function and Localized Orbital Locator

- Spatial plot of electronic density difference

- Periodic Boundary Conditions

- Explicit solvent models

- Polarizable Continuum Model

- Natural Bond Orbitals and Restricted ElectroStatic Potential charges

- Atomic radical character

- ElectroStatic Potential-colored vdW surface

The computational packages we use include: CP2K, MOLCAS, Gaussian, Firefly, NWChem, ORCA, xtb and MPQC