Spotlight on ...
In the section "Spotlight on..." postdocs, PhD students, or other (young) scientists will tell about his/her work. Every month the spotlight will be on a different candidate. Would you like to be in the spotlight, or would you like to nominate someone, then please contact us!
Name: Aafke Bronneberg
Institute: Institute for Solar Fuels (EE-IF)
At HZB since: 07/2013
Work: I am responsible for the atomic layer deposition (ALD) activities within our institute. ALD is a vapor-phase deposition technique in which ultra-thin films are synthesized sub-monolayer by sub-monolayer by repeating two subsequently executed half cycles. The surface reactions are self-limiting, which leads to excellent growth control (atomic layer precision), uniform deposition over large areas, and conformal deposition on high aspect ratio substrates. These ultrathin films can serve as corrosion protection layer, catalyst, and/or photoelectrode material.
At EE-IF we have two ALD systems. One is a large area plasma-enhanced ALD system which we use to develop novel ternary metal oxides. These materials will be used as photoelectrode material in nanostructured photoelectrodes. The other ALD system is connected to a UHV chamber equipped with XPS and UPS. Here we develop protection layers and catalysts and study the interfacial charge transport and energetics.
Instruments involved: Thermal ALD system, plasma-enhanced ALD system, XPS, UPS, spectroscopic ellipsometry
Favorite article: Probing the interfacial chemistry of ultra-thin ALD-grown TiO2 films: An in-line XPS study, A.C. Bronneberg, C. Höhn, and R. van de Krol, to be published
Figure 2:Evolution of O 1s emission spectra during atomic layer deposition of TiO2 on a silicon substrate with a native oxide layer. The peak around 533 eV originates from O in SiO2, the peak around 530.5 eV from O in TiO2. The intensity of the O 1s peak of SiO2 attenuates with increasing number of ALD cycles due to TiO2 film growth.
Name: Cham Thi Trinh
Institute: Institute Silicon photovoltaics (EE-IS)
At HZB since: 07/2016
Work: My work is to develop advanced technologies for liquid phase -crystallized silicon (LPC-Si) interdigitated back-contact, back junction (IBC) solar cells. LPC-Si film on glass are formed by crystallization of thick amorphous Si film using a line shape continuous wave laser. The process enables to crystalline a-Si with thickness as high as 30 µm with large grain size. LPC-Si has demonstrated as innovative absorber for solar cell with an open voltage above 650 mV and a high efficiency of 13.2% for LPC-Si IBC cells can be achieved. With a target cell efficiency of more than 18 %, my research is mainly focusing on developing IBC cell technologies such as cell design, texturing back-surface, improvement front surface passivation… The efforts for reduction in optical and electrical losses will enhance significantly cell performance.
Instruments involved: Plasma Enhanced Chemical Vapor Deposition (PECVD), Electron beam evaporation, Laser crystallization system, Photolithography, equipment for characterization of cell performances such as QSSPC, solar simulator, External Quantum Efficiency, UV-Vis spectroscopy, etc.
Favorite article: Interdigitated back-contact heterojunction solar cell concept for liquid phase crystallized thin-film silicon on glass, Paul Sonntag et al., Prog. Photovolt: Res. Appl. 2016; 24.716-724
Institute: Institute Competence Centre Photovoltaics Berlin (PVcomB) (EE-IP)
At HZB since: 11/2015
Work: My research focuses on developing new structures for Silicon Heterojunction solar cells. I work in wet chemistry processes to enhance the light absorption of the solar cells by means of different silicon surface texturing processes. I also use a Plasma Enhanced Chemical Vapor Deposition tool in order to optimize different amorphous and nano-crystalline thin silicon layers (as passivating, emitter or back/front surface field layers). The main interest of this work is to improve the transparency of the layers without compromising its electrical properties or the contact between interfaces, aiming at continuously enhancing the solar cell performance.
Instruments involved: Clean Room processes, Plasma Enhanced Chemical Vapor Deposition (PECVD), electrical and optical characterization of thin films and solar cells (QSSPC, solar simulator, External Quantum Efficiency, UV-Vis spectroscopy, etc.).)
Favorite article:Study of the Surface Recombination Velocity for Ultraviolet and Visible Laser-Fired Contacts Applied to Silicon Heterojunction Solar Cells. A. Morales-Vilches et al., IEEE J. Photovoltaics Vol. 5, Issue: 4, page(s): 1006 – 1013
Name: Kaan Atak
Institute: Institute Methods for Material Development (EM-IMM) and Freie Universität Berlin, Department of Physics
At HZB since: 07/2011
Work: I perform soft X-ray spectroscopic techniques (X-ray absorption, emission and resonant inelastic X-ray scattering, resonant/non-resonant photoelectron spectroscopy) using synchrotron radiation applied to functional materials in solution (such as transition metal complexes with varying degrees of sophistication having potential catalytic or biochemical functions). On the theoretical side, I apply quantum chemical computational methods such as configuration interaction crucial for interpretation of the spectroscopic results.
Instruments involved: LiXErom (near-edge X-ray absorption fine structure (NEXAFS), resonant inelastic X-ray scattering (RIXS), non-resonant X-ray emission spectroscopy (XES) measurements in liquid phase using micro-jet and flow-cell methods), LiquidPES (photoelectron spectroscopy (PES) and resonant photoelectron spectroscopy (RPES) measurements in liquid phase using micro-jet)
Favorite article: Electronic Structure of Hemin in Solution Studied by Resonant X-ray Emission Spectroscopy and Electronic Structure Calculations. K. Atak et al., J. Phys. Chem. B, 2014
Name: Sean Berglund
Institute: Institute for Solar Fuels (EE-IF)
At HZB since: 04/2014
Work: I mainly characterize and develop complex metal oxide absorber layers and substrate materials for solar fuels production i.e. splitting water into oxygen and hydrogen (chemical fuel) using sunlight. The absorber layer is synthesized on top of a substrate to create a photoelectrode, which is placed in contact with water (aqueous electrolyte) inside a photoelectrochemical cell. The splitting reaction occurs on the photoelectrode surface. The ultimate goal is to develop a photoelectrode that is cost effective, efficient, and stable to enable practical solar fuels production on an industrial scale.
Instruments involved: electrochemical/photoelectrochemical measurement, solar simulation, UV-Vis spectroscopy, x-ray diffraction, time-resolved microwave conductivity, electron paramagnetic resonance spectroscopy, scanning electron microscopy (SEM), x-ray photoelectron emission spectroscopy, thermogravimetric analysis, etc.
Instruments responsible: advanced laser spectroscopy system in B-309 (responsible for lab), PerkinElmer Lambda 950 UV-Vis spectrometer in B-206 (backup)
Favorite article: p-Si/W2C and p-Si/W2C/Pt photocathodes for the hydrogen evolution reaction, S. P. Berglund et al. J. Am. Chem. Soc. 136, 1535-1544 (2014)
Name: Meng Liu
Institute: EM-IAM (Institute of Applied Materials) & TU Berlin
At HZB since: 10/2010
Work: 6000 series Al-Mg-Si alloys are extensively used in the automotive industry due to their excellent mechanical properties. However, due to the practically unavoidable storage for a certain time after quenching, these alloys with various Mg and Si contents exhibit either a “positive” or “negative” strength response during the subsequent paint baking process, which is known to be caused by solute clusters formed during the storage at room temperature. In order to improve the understanding of the underlying microscopic processes, I investigate the early stages of clustering in Al-Mg-Si alloys by Positron Annihilation Spectroscopy utilizing its unique sensitivity to electron density differences in various atomic defects. The spectroscopic signals, which depend on defects and phase compositions, give useful information about the microstructure of solids.
Instruments involved: Positron annihilation lifetime spectroscopy, Doppler broadening spectroscopy
Instruments responsible: Positron lab LR329 & LR015
Favorite article: Early stages of solute clustering in an Al-Mg-Si alloy, M. Liu et al. Acta Materialia, 91 (2015) 355-364.
Name: Galina Gurieva
At HZB since: 09/2011
Work: My work focusses on new, environmentally friendly, cost effective materials, which can be used as absorber layers in high efficient thin films solar cells. My main interest are quaternary AI2BIICIVXVI4 chalcogenides with A-Cu; B-Zn; C-Si, Ge,Sn and X-S,Se which we synthesize in our lab. We use neutron and synchrotron X-ray diffraction to study the crystal structure, especially intrinsic point defects, focusing on the degree of cation order/disorder and its relation to functionality of these materials.
Furthermore, I will start teaching activities in Summer Semester 2016 (Potsdam University) offering the course “Growth and characterization of semiconductor materials” for MSc. and PhD students.
Instruments involved: E9, KMC 2 diffraction
Instruments responsible: lab responsible for Crystallography Lab (Laboratory for crystallographic materials research for solar energy conversion)
Favorite article: The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study. Schorr et al. Solar Energy Materials and Solar Cells 95 (2011), p. 1482-1488
Name: Franziska Huschmann
Institute: EM-ISFM (Soft Matter and Functional Materials) & Philipps-Universität Marburg
At HZB since: 04/2014
Work: In X-ray crystallography we study three dimensional atomic resolution structures of macromolecules. These can be proteins that are for example essential in the bacterial or viral life cycle. By analyzing the binding of small organic molecules (fragments) to the proteins we would like to understand their function and develop molecules that inhibit reactions that are necessary for the microorganism to survive. Finding suitable fragments is one of the first steps in drug discovery. Therefore we aim at establishing a fragment-screening environment at BESSY II where academic and industrial users can screen target proteins against hundreds of fragments at our beam lines in a high throughput manner.
Instruments involved: Crystallization robot Gryphon (Art Robbins Instruments); Macromolecular crystallography beam lines BL 14.1, BL 14.2 and BL 14.3.
Favorite article: “One Question, Multiple Answers: Biochemical and Biophysical Screening Methods Retrieve Deviating Fragment Hit Lists” Schiebel et al. 2015, ChemMedChem, 10 (9), 1511-1521
Name: Alex Redinger
Institute: Complex Compound Semiconductor Materials for Photovoltaics (EE-AKV)
At HZB since: 01/2015
Work: The work focusses on the development of thin film kesterite (Cu2ZnSnSe4) absorbers and solar cells in conjunction with a detailed optoelectronic characterization. It is the aim of the project to identify the current limitations of this material and to develop new improved processes which lead to higher power conversion efficiencies. We perform hyperspectral photoluminescence imaging in order to measure the quasi fermi level splitting of the absorbers and devices, perform and in depth elemental characterization with scanning electron beam methods such as energy dispersive X-Ray analysis and electron beam induced current. Moreover, the properties of the absorber on the nanometer scale are analyzed with atomic force microscopy techniques such as Kelvin Probe force microscopy.
Instruments involved: Cluster tool (sputtering and evaporation); selenization (tube furnace), IV (current-voltage), QE (quantum efficiency measurements), CV (capacity-voltage), EDX/EBIC/CL (Energy dispersive X-ray spectroscopy/Electron beam-induced current/cathodoluminescence), AFM (atomic force microscope), KPFM (Kelvin probe force microscope), PL (pholtoluminescence) imaging
Instrument responsible?: PL imaging, AFM
Name: Karine Sparta
At HZB since: 09/2014
Work: I develop software solutions for the analysis of single-crystal X-ray diffraction data of protein crystals at our beamlines. In this technique, a series of diffraction images is collected from each sample. My first project, XDSAPP, is an expert system for automated data processing that generates a list of integrated reflection intensities from such diffraction images. Using these intensities, the atomic structure of the crystals can be determined. My second project is an automated refinement and ligand-fitting pipeline for fragment screening experiments, which are widely used in the pharmaceutical industry for drug design. Furthermore, I am involved in the Röntgen-Ångström-Cluster project 2013-597 in collaboration with the Karolinska Institutet in Stockholm to study dynamics in protein crystals.
Instruments involved: Beamlines BL14.1, BL14.2 & BL14.3
Instrument responsible?: Yes, on BL14.1-3.
Favourite article: "The macromolecular crystallography beamlines at BESSY II of the Helmholtz-Zentrum Berlin: Current status and perspectives" Mueller, U. et al. (2015) Eur. Phys. J. Plus 130: 141
Name: Mirko Boin
At HZB since: 09/2002
Work: With the help of neutrons I investigate applied and residual stresses, preferred crystallographic orientations, and phase distributions in the bulk of materials. On the E3 neutron strain scanner I assist scientists from all over the world to study their samples. In parallel, I develop realistic neutron experiment simulations for diffraction and imaging applications to improve instrument performance and data analysis. Setting up a new X-ray lab in Wannsee for material investigations, running the first liquid-metal jet source in HZB, is my latest project.
Instruments involved: Beamline E3 neutron strain scanner at the reactor in Wannsee (E-hall) & new metal jet X-ray lab (LS012)
Instrument responsible?: Yes, on E3.
Favourite article: "Validation of Bragg edge experiments by Monte Carlo simulations for quantitative texture analysis" Boin, M. et al. (2011). J. Appl. Cryst. 44, 1040-1046