Publications

1.3 μm photoluminescence of Ge/GaAs multi-quantum-well structure

Aleshkin, V. Y., A. A. Dubinov, K. E. Kudryavtsev, V. V. Rumyantsev, A. A. Tonkikh, N. D. Zakharov, B. N. Zvonkov

Journal of Applied Physics 115 (4), pp 043512/1-4 (2014)

Direct optical mapping of anisotropic stresses in nanowires using transverse optical phonon splitting

Balois, M. V., N. Hayazawa, A. Tarun, S. Kawata, M. Reiche, O. Moutanabbir

Nano Letters 14 (7), pp 3793-3798 (2014)

Pseudo shunts interfering lock-in thermography investigations of solar cells: Characterization and prevention

Bauer, J., L. A. Wägele, K. Gase, O. Breitenstein

IEEE Journal of Photovoltaics 4 (6), pp 1429-1432 (2014)

Biomimetic magnetite formation: From biocombinatorial approaches to mineralization effects

Baumgartner, J., M. Carillo, K. M. Eckes, P. Werner, D. Faivre

Langmuir 30, pp 2129-2136 (2014)

Persistent photoconductivity in strained epitaxial BiFeO₃ thin films

Bhatnagar, A., Y. H. Kim, D. Hesse, M. Alexe

Nano Letters 14, pp 5224-5228 (2014)

Sub-band level-assisted photoconduction in epitaxial BiFeO₃ films

Bhatnagar, A., Y. H. Kim, D. Hesse, M. Alexe

Applied Physics Letters 105 (12), pp 122905/1-4 (2014)

abstract

Sub-band level assisted conduction mechanisms are well known in the field of semiconducting materials. In this work, we explicitly show the validity of such a mechanism in the multiferrroic material BiFeO₃ (BFO). Our study is based on two different systems of epitaxial thin films of BFO, relaxed and strained. By analyzing the spectral distribution of the photoresponse from both the systems, the role of the sub-band levels in the photoconductive phenomena becomes evident. Additionally, the influence of epitaxial strain on the trapping activity of these levels is also observed. A model is proposed by taking into account the reversal of the role of a sub-band gap level, i.e., from a trapping to a ground state.

Preparation of nanowire specimens for laser-assisted atom probe tomography

Blumtritt, H., D. Isheim, S. Senz, D. N. Seidman, O. Moutanabbir

Nanotechnology 25 (43), pp 435704/1-7 (2014)

An alternative one-diode model for illuminated solar cells

Breitenstein, O.

IEEE Journal of Photovoltaics 4 (3), pp 899-905 (2014)

An alternative one-diode model for illuminated solar cells

Breitenstein, O.

Energy Procedia 55, pp 30-37 (2014)

Photoluminescence image evaluation of solar cells based on implied voltage distribution

Breitenstein, O., H. Höffler, J. Haunschild

Solar Energy Materials and Solar Cells 128, pp 296-299 (2014)

abstract

All previous methods for quantitatively evaluating photoluminescence (PL) images of solar cells assumed a laterally constant short circuit current density J_sc. Moreover, they had to subtract a J_sc PL image from all other PL images for considering the diffusion-limited carriers. Here a more realistic PL evaluation method is introduced, which is based on a recently published alternative model of the illuminated solar cell. In this model an analytic expression is derived by considering the illuminated current as a diffusion process between bulk and the pn-junction and linking the implied voltage in the bulk with the local pn-junction voltage under illumination. This model does not assume a laterally constant J_sc but a constant light absorption rate, and it leads to a prediction of the J_sc distribution solely based on PL imaging results. Moreover, it regards the shadowing of the cell by the busbars and grid lines. This model is applied to the quantitative evaluation of PL images of an industrial multicrystalline silicon solar cell. The resulting series resistance and saturation current density images are compared with that of an established PL evaluation method, and the resulting distribution of J_sc is compared with LBIC results. The results of the new method appear slightly more realistic than that of the old one, since they consider the inhomogeneity of J_sc.

Comment on "Evaluation of the spatial distribution of series and shunt resistance of a solar cell using dark lock-in thermography", J. Appl. Phys. 115, 034901 (2014)

Breitenstein, O., S. Rißland

Journal of Applied Physics 116, pp 046101/1-2 (2014)

Localization and characterization of annealing-induced shunts in Ni-plated monocrystalline silicon solar cells

Büchler, A., S. Kluska, M. Kasemann, M. Breitwieser, W. Kwapil, A. Hähnel, H. Blumtritt, S. Hopman, M. Glatthaar

Physica Status Solidi RRL 8 (5), pp 385-389 (2014)

Tuning, inhibiting and restoring the enzyme mimetic activities of Pt-apoferritin

Carmona, U., L. Zhang, W. Münchgesang, E. Pippel, M. Knez

Chemical Communications 50, pp 701-703 (2014)

abstract

A selective and specific inhibition of the catalase mimetic activity but not SOD-like activity of Pt-apoferritin can be achieved through the choice of the inhibitor. The recovery of activity using a reducing agent was explored and proven to successfully restore the surface-chemistry of NPs.

Thickness-dependent cation order and disorder in PbSc_0.5Ta_0.5O₃ thin films grown by pulsed laser deposition

Chopra, A., B. I. Birajdar, A. Berger, M. Alexe, D. Hesse

New Journal of Physics 16, pp 013059/1-14 (2014)

abstract

We report on thickness-dependent cation ordering and ferroelectric properties of (001)-oriented epitaxial PbSc_0.5Ta_0.5O₃ (PST) thin films grown by pulsed laser deposition on SrTiO₃ (001) and Si (001) substrates. The PST film thickness was varied from 30 to 200 nm. Only films thicker than 40 nm reveal (partial) cation ordering, which increases with thickness as confirmed by the appearance and intensity of superstructure reflections in x-ray diffraction and transmission electron microscopy. In accordance with the two-state thermodynamic model, temperature-dependent dielectric constant investigations showed the presence of two kinds of phase transitions belonging to the normal ferroelectric and the relaxor state, respectively, both being present in the PST films. The influence of cation ordering on the phase transition and ferroelectric properties is discussed in detail.

Piezoelectric non-linearity in PbSc_0.5Ta_0.5O₃ thin films

Chopra, A., Y. S. Kim, M. Alexe, D. Hesse

Journal of Physics and Chemistry of Solids 75, pp 1229-1233 (2014)

abstract

Epitaxial (001)-oriented PbSc_0.5Ta_0.5O₃ (PST) thin films were deposited by pulsed laser deposition. Local piezoelectric investigations performed by piezoelectric force microscopy show a dual slope for the piezoelectric coefficient. A piezoelectric coefficient of 3 pm/V was observed at voltages up to 0.8 V. However, at voltages above 0.8 V, there is a steep increase in piezoelectric coefficient mounting to 23.2 pm/V. This nonlinear piezoelectric response was observed to be irreversible in nature. In order to better understand this nonlinear behavior, voltage dependent dielectric constant measurements were performed. These confirmed that the piezoelectric non-linearity is indeed a manifestation of a dielectric non-linearity. In contrast to classical ferroelectric systems, the observed dielectric non-linearity in this relaxor material cannot be explained by the Rayleigh model. Thus the dielectric non-linearity in the PST films is tentatively explained as a manifestation of a percolation of the polar nano regions.

Epitaxial ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ thin films on La_0.7Sr_0.3MnO₃ bottom electrode

Chopra, A., E. Panda, Y. Kim, M. Arredondo, D. Hesse

Journal of Electroceramics 32, pp 404-408 (2014)

Effect of implantation temperature on the H-induced microstructural damage in AlN

Dadwal, U., P. Kumar, O. Moutanabbir, M. Reiche, R. Singh

Journal of Alloys and Compounds 588, pp 300-304 (2014)

abstract

A detailed physical investigation of the H-induced microstructural damage in (0001) AlN epitaxial layers at various implantation temperatures is presented. Cross-sectional transmission electron microscopy revealed that in the case of samples implanted at 300 ^°C, extended defects (nanocracks) were formed only within ∼ 50 nm region situated below the H-concentration peak in the damage band of width ∼ 280 nm compared with lower implantation temperatures. This implantation temperature-dependent behavior of the microstructural damage decides the morphology of the top buckled surface. Various favorable conditions for the buckling of H-implanted surface in the form of large area exfoliation are proposed based on the present study.

Nanoscale Bi₂FeO_6−x precipitates in BiFeO₃ thin films: A metastable Aurivillius phase

Deniz, H., A. Bhatnagar, E. Pippel, R. Hillebrand, A. Hähnel, M. Alexe, D. Hesse

Journal of Materials Science 49, pp 6952-6960 (2014)

abstract

We report the observation of nano-scale precipitates corresponding to a new structure not displayed by the phase diagram of bismuth iron oxide. BiFeO₃ (BFO) thin films grown on terbium scandate and strontium titanate substrates by pulsed laser deposition were investigated using high-resolution transmission and scanning transmission electron microscopy. Precipitate-like structures with a so far unknown metastable phase of bismuth, iron, and oxygen were observed in these films. They consist of well- ordered Bi₂O₂ layers, as they are known from bismuth oxide layered compounds. They have a pseudo-ortho-rhombic structure with a single perovskite-like unit (FeO₆) sandwiched between Bi₂O₂ layers, similar to the Aurivillius phase Bi₂WO₆, with a chemical composition of the precipitates of Bi₂FeO_6−x. The structure of the new phase with its lattice constants was elucidated and the band gap of the precipitates was determined by electron energy loss spectroscopy. The results point to promising future applications for this new phase in the field of electronics, if it might be grown phase pure as an epitaxial thin film.

Anisotropic magnetoresistance in an antiferromagnetic semiconductor

Fina, I., X. Marti, D. Yi, J. Liu, J. H. Chu, C. Rayan-Serrao, S. Suresha, A. B. Shick, J. Zelezný, T. Jungwirth, J. Fontcuberta, R. Ramesh

Nature Communications 4, pp 4671-4677 (2014)

Ultrafast switching of hard X-rays

Gaal, P., D. Schick, M. Herzog, A. Bojahr, R. Shayduk, J. Goldshteyn, W. Leitenberger, I. Vrejoiu, D. Khakhulin, M. Wulff, M. Bargheer

Journal of Synchrotron Radiation 21, pp 380-385 (2014)

Micro-Raman study on the softening and stiffening of phonons in rutile titanium dioxide film: Competing effects of structural defects, crystallite size, and lattice strain

Gautam, S. K., F. Singh, I. Sulania, R. G. Singh, P. K. Kulriya, E. Pippel

Journal of Applied Physics 115 (14), pp 143504/1-5 (2014)

Multiferroic iron oxide thin films at room-temperature

Gich, M., I. Fina, A. Morelli, F. Sanchez, M. Alexe, J. Gazquez, J. Fontcuberta, A. Roig

Advanced Materials 26, pp 4645-4652 (2014)

The influence of a Te-depleted surface on the thermoelectric transport properties of Bi₂Te₃ nanowires

Hamdou, B., A. Beckstedt, J. Kimling, A. Dorn, L. Akinsinde, S. Bäßler, E. Pippel, K. Nielsch

Nanotechnology 25, pp 365401/1-7 (2014)

Interfacial intermixing in SrRuO₃/Pr_0.7Ca_0.3MnO₃ epitaxial superlattices: A HAADF-STEM study

Hillebrand, R., E. Pippel, I. Vrejoiu, D. Hesse

Physica Status Solidi A 211 (3), pp 536-542 (2014)

abstract

We quantitatively interpret HAADF-STEM images of SrRuO₃/ Pr_0.7Ca_0.3MnO₃ (SRO/PCMO) superlattices. The images were taken in a probe-corrected (c_s= 0) FEI microscope at 300 kV. The specimen thickness is estimated by comparing experimental and simulated Z-contrast ratios. The intermixing at the interfaces is different for the growth of SRO on PCMO and that of PCMO on SRO. In addition, the thermal stability of SRO/PCMO superlattices is studied by HAADF-STEM, based on a series of annealing experiments.

Distinct electronic structure of the electrolyte gate-induced conducting phase in vanadium dioxide revealed by high-energy photoelectron spectroscopy

Karel, J., C. E. Viol Barbosa, J. Kiss, J. Jeong, N. Aetukuri, M. G. Samant, X. Kozina, E. Ikenaga, G. H. Fecher, C. Felser, S. S. P. Parkin

ACS Nano 8 (6), pp 5784-5789 (2014)

Origins of domain wall pinning in ferroelectric nanocapacitors

Kim, Y., H. Han, I. Vrejoiu, W. Lee, D. Hesse, M. Alexe

Nano Convergence 1, pp 24/1-6 (2014)

abstract

We have investigated domain wall pinning and its origins in ferroelectric nanocapacitors using piezoresponse force microscopy. Domain wall pinning of two different types was observed in the nanocapacitors. The first type of pinning originates from local point defects similar to previous reports. The second one originates from immobile local defects in the place of pristine domains. In both cases, pinning and de-pinning processes were observed without significant domain wall bowing. The results can be helpful to understand domain wall motion and improve the reliability of nanoscale ferroelectric memory devices.

Microstructure of highly strained BiFeO₃ thin films: Transmission electron microscopy and electron-energy loss spectroscopy studies

Kim, Y. H., A. Bhatnagar, E. Pippel, M. Alexe, D. Hesse

Journal of Applied Physics 115 (4), pp 043526/1-8 (2014)

abstract

Microstructure and electronic structure of highly strained bismuth ferrite (BiFeO₃) thin films grown on lanthanum aluminate substrates are studied using high-resolution transmission and scanning transmission electron microscopies and electron energy loss spectroscopy (EELS). Monoclinic and tetragonal phases were observed in films grown at different temperatures, and a mix of both phases was detected in a film grown at intermediate temperature. In this film, a smooth transition of the microstructure was found between the monoclinic and the tetragonal phases. A considerable increase in the c-axis parameters was observed in both phases compared with the rhombohedral bulk phase. The off-center displacement of iron (Fe) ions was increased in the monoclinic phase as compared with the tetragonal phase. EEL spectra show different electronic structures in the monoclinic and the tetragonal phases. These experimental observations are well consistent with the results of theoretical first-principle calculations performed.

Charge carrier transport along grain boundaries in silicon

Kittler, M., M. Reiche, H.-M. Krause

Solid State Phenomena 205-206, pp 293-298 (2014)

abstract

The influence of GBs contained in the channel of MOS-FETs - fabricated in thin SOI layers - is demonstrated. The drain current measured at room temperature increases about 50 times for nFETs and about 10 times for pFETs, respectively, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

Crystallite-growth, phase transition, magnetic properties, and sintering behaviour of nano-CuFe₂O₄ powders prepared by a combustion-like process

Köferstein, R., T. Walther, D. Hesse, S. G. Ebbinghaus

Journal of Solid State Chemistry 213, pp 57-64 (2014)

abstract

The synthesis of nano-crystalline CuFe₂O₄ powders by a combustion-like process is described herein. Phase formation and evolution of the crystallite size during the decomposition process of a (CuFe2) precursor gel were monitored up to 1000 ^°C. Phase-pure nano-sized CuFe₂O₄ powders were obtained after reaction at 750 ^°C for 2 h resulting in a crystallite size of 36 nm, which increases to 96 nm after calcining at 1000 ^°C. The activation energy of the crystallite growth process was calculated as 389 kJ mol⁻¹. The tetragonal cubic phase transition occurs between 402 and 419 ^°C and the enthalpy change (∆H) was found to range between 1020 and 1229 J mol⁻¹ depending on the calcination temperature. The optical band gap depends on the calcination temperature and was found between 2.03 and 1.89 eV. The shrinkage and sintering behaviour of compacted powders were examined. Dense ceramic bodies can be obtained either after conventional sintering at 950 ^°C or after a two-step sintering process at 800 ^°C. Magnetic measurements of both powders and corresponding ceramic bodies show that the saturation magnetization rises with increasing calcination-/sintering temperature up to 49.1 emu g⁻¹1 (2.1 mB fu⁻¹1), whereas the coercivity and remanence values decrease.

Epitaxial growth of ultra-thin NbN films on Al_xGa_1−xN buffer-layers

Krause, S., D. Meledin, V. Desmaris, A. Pavolotsky, V. Belitsky, M. Rudzinski, E. Pippel

Superconductor Science and Technology 27 (6), pp 065009/1-7 (2014)

Molecular dynamics of poly(cis-1,4-isoprene) in 1- and 2-dimensional confinement

F. Kremer

In: Dynamics in Geometrical Confinement, pp 95-127 (Ed.) Kremer, F.,Springer, 2014

Dynamics of modification of Ni/n-GaN Schottky barrier diodes irradiated at low temperature by 200 MeV Ag¹⁴⁺ ions

Kumar, A., T. Kumar, A. Hähnel, D. Kanjilal, R. Singh

Applied Physics Letters 104 (3), pp 033507/1-4 (2014)

Potential-induced degradation (PID): Introduction of a novel test approach and explanation of increased depletion region recombination

Lausch, D., V. Naumann, O. Breitenstein, J. Bauer, A. Graff, J. Bagdahn, C. Hagendorf

IEEE Journal of Photovoltaics 4 (3), pp 834-840 (2014)

Sodium outdiffusion from stacking faults as root cause for the recovery process of potential-induced degradation (PID)

Lausch, D., V. Naumann, A. Graff, A. Hähnel, O. Breitenstein, C. Hagendorf, J. Bagdahn

Energy Procedia 55, pp 486-493 (2014)

Spintronic functionality of BiFeO₃ domain walls

Lee, J. H., I. Fina, X. Marti, Y. H. Kim, D. Hesse, M. Alexe

Advanced Materials 26, pp 7078-7082 (2014)

In situ raman spectroscopic study of Al-infiltrated spider dragline silk under tensile deformation

Lee, S.-M., E. Pippel, O. Moutanabbir, J.-H. Kim, H.-J. Lee, M. Knez

ACS Applied Materials and Interfaces 6, pp 16827-16834 (2014)

Crossover of conduction mechanism in Sr₂IrO₄ epitaxial thin films

Lu, C., A. Quindeau, H. Deniz, D. Preziosi, D. Hesse, M. Alexe

Applied Physics Letters 105 (8), pp 082407/1-5 (2014)

abstract

High quality epitaxial Sr₂IrO₄ thin films with various thicknesses (9-300 nm) have been grown on SrTiO₃ (001) substrates and their electric transport properties have been investigated. All samples showed the expected insulating behavior with a strong resistivity dependence on film thickness, which can be as large as three orders of magnitude at low temperature. A close examination of the transport data revealed interesting crossover behaviors for the conduction mechanism upon variation of thickness and temperature. While Mott variable range hopping (VRH) dominated the transport for films thinner than 85 nm, high temperature (>200 K) thermal activation behavior was observed for films with large thickness ( ≥ 85 nm), which was followed by a crossover from Mott to Efros-Shklovskii (ES) VRH in the low temperature range. This low temperature crossover from Mott to ES VRH indicates the presence of a Coulomb gap ( ∼ 3 meV). Our results demonstrate the competing and tunable conduction in Sr₂IrO₄ thin films, which in turn would be helpful for understanding the insulating nature related to strong spin-orbital-coupling of the 5d iridates.

Room-temperature antiferromagnetic memory resistor

Marti, X., I. Fina, C. Frontera, J. Liu, P. Wadley, Q. He, R. J. Paull, J. D. Clarkson, J. Kudrnovsky, I. Turek, J. Kunes, D. Yi, J.-H. Chu, C. T. Nelson, L. You, E. Arenholz, S. Salahuddin, J. Fontcuberta, T. Jungwirth, R. Ramesh

Nature Materials 13, pp 367-374 (2014)

abstract

The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.

Localization and characterisation of ferritin in Demospongiae: A possible role on spiculogenesis

Natalio, F., S. Wiese, N. Friedrich, P. Werner, M. N. Tahir

Marine Drugs 12 (8), pp 4659-4676 (2014)

abstract

Iron, as inorganic ion or as oxide, is widely used by biological systems in a myriad of biological functions (e.g., enzymatic, gene activation and/or regulation). In particular, marine organisms containing silica structures-diatoms and sponges-grow preferentially in the presence of iron. Using primary sponge cell culture from S. domuncula-primmorphs-as an in vitro model to study the Demospongiae spiculogenesis, we found the presence of agglomerates 50 nm in diameter exclusively inside sponge specialized cells called sclerocytes. A clear phase/material separation is observed between the agglomerates and the initial stages of intracellular spicule formation. STEM-HRTEM-EDX analysis of the agglomerates (30-100 nm) showed that they are composed of pseudohexagonal nanoparticles between 5 and 15 nm in size, displaying lattice parameters corresponding to hematite (Fe₂O₃) and mixed iron oxide phases typically attributed to ferritin. Further analysis, using western blotting, inductively coupled plasma mass spectrometry (ICP-MS), sequence alignment analysis, immunostaining and magnetic resonance imaging (MRI), of mature spicule filaments confirm the presence of ferritin within these organic structures. We suggest that S. domuncula can be classified as a dual biomineralizating organism, i.e., within the same cellular structure two distinct biomineralizing processes can occur as a result of the same cellular/metabolic function, spiculogenesis.

Explanation of potential-induced degradation of the shunting type by Na decoration of stacking faults in Si solar cells

Naumann, V., D. Lausch, A. Hähnel, J. Bauer, O. Breitenstein, A. Graff, M. Werner, S. Swatek, S. Großer, J. Bagdahn, C. Hagendorf

Solar Energy Materials and Solar Cells 120, pp 383-389 (2014)

Yield and leakage currents of large area lattice matched InP/InGaAs heterostructures

Olsson, A., A. Aierken, H. Jussila, J. Bauer, J. Oksanen, O. Breitenstein, H. Lipsanen, J. Tulkki

Journal of Applied Physics 116 (8), pp 083105/1-6 (2014)

Hierarchically structured ZnO/petal hybrid composites with tuned optoelectronic and mechanical properties

Park, C., H.-M. So, H. J. Jeong, M. S. Jeong, E. Pippel, W. S. Chang, S.-M. Lee

ACS Applied Materials and Interfaces 6, pp 16243-16248 (2014)

Tailoring the interfacial magnetic anisotropy in multiferroic field-effect devices

Preziosi, D., I. Fina, E. Pippel, D. Hesse, X. Marti, F. Bern, M. Ziese, M. Alexe

Physical Review B 90 (12), pp 125155/1-6 (2014)

abstract

Ferroelectric field-effect devices based on perovskite oxide materials offer a new possibility to exploit emergent interfacial effects such as the electrostatic modification of the transport and magnetic properties of strongly correlated materials and to prove the magneto-electric coupling at the interface between the two different ferroic materials. Here we report on the reversible modulation of the interfacial magnetic and magnetotransport properties of La_0.825Sr_0.175MnO₃ thin films induced by switching the ferroelectric polarization of a top PbZr_0.2Ti_0.8O₃ layer. Anisotropic magnetoresistance (AMR) measurements were performed applying a magnetic field H in a plane perpendicular to the current density. By rotating H from the out-of-plane towards the in-plane direction, upon the ferroelectric polarization switching, a modulation of the normalized AMR amplitude was achieved. The dynamical electrostatic coupling at the interface of the two oxides is responsible for a reconstruction of the Mn 3deg orbitals which in turn affects the surface magnetic anisotropy of the magneto-electric system. The present work might have a broader impact, including in the field of multiferroic tunnel junctions, due to a better understanding of the coupling at the interface of the two ferroic oxides where the influence of the polarization on the magnetic degree of freedom is accomplished.

Programmable ferroelectric tunnel memristor

Quindeau, A., D. Hesse, M. Alexe

Frontiers in Physics 2 (7), pp 1-5 (2014)

abstract

We report a programmable analog memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr_0.2Ti_0.8)O₃ film sandwiched between La_0.7Sr_0.3MnO₃ and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10-7 s. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

On the electronic properties of a single dislocation

Reiche, M., M. Kittler, W. Erfurth, E. Pippel, K. Sklarek, H. Blumtritt, A. Hähnel, H. Uebensee

Journal of Applied Physics 115 (19), pp 194303/1-6 (2014)

Carrier transport on dislocations in silicon

Reiche, M., M. Kittler, H.-M. Krause, H. Uebensee

AIP Conference Proceedings 1583, pp 33-36 (2014)

Single-electron transitions in one-dimensional native nanostructures

Reiche, M., M. Kittler, M. Schmelz, R. Stolz, E. Pippel, H. Uebensee, M. Kermann, T. Ortlepp

Journal of Physics C 568 (5), pp 052024 (2014)

Trap-assisted tunneling on extended defects in tunnel field-effect transistors

Reiche, M., M. Kittler, H. Uebensee, M. Krause, E. Pippel

Japanese Journal of Applied Physics 53 (4S), pp 04EC03/1-6 (2014)

Single dislocations as nanostructure devices: Physics and applications

Reiche, M., M. Kittler, H. Uebensee, E. Pippel, W. Erfurth

ECS Transactions 64 (11), pp 267-281 (2014)

Dislocations as native nanostructures - electronic properties

Reiche, M., M. Kittler, H. Uebensee, E. Pippel, S. Hopfe

Advanced Nano Research 2, pp 1-14 (2014)

Low rate deep level transient spectroscopy - a powerful tool for defect characterization in wide bandgap semiconductors

Schmidt, F., H. v. Wenckstern, O. Breitenstein, R. Pickenhain, M. Grundmann

Solid State Electronics 92, pp 40-46 (2014)

abstract

We present an overview of implementation and application of low rate Deep-Level Transient Spectroscopy (LR-DLTS). In conventional DLTS the sensitivity of the capacitance meter must be chosen so low that the whole capacitance drift range between lowest and highest temperature can be measured. In LR-DLTS the bridge is automatically balanced (capacitance and conductivity) after each measured transient. Thus, the highest available sensitivity still avoiding an overload can be used. With LR-DLTS it is now possible to extend the rate windows to the mHz range while preserving highest possible sensitivity. This allows the detection of energetically close levels and levels with large thermal activation energy. Also low emission rates in optical DLTS can be detected this way.

Nanocrystalline calcitic lens arrays fabricated by self-assembly followed by amorphous-to-crystalline phase transformation

Schmidt, I., K. Lee, E. Zolotoyabko, P. Werner, T. S. Shim, Y.-K. Oh, P. Fratzl, W. Wagermaier

ACS NANO 8 (9), pp 9233-9238 (2014)

abstract

Natural calcium carbonate-based nanocomposites often have superior physical properties and provide a comprehensive source for bioinspired synthetic materials. Here we present thermodynamically stable, transparent CaCO₃ microlens arrays (MLA) produced by transforming an amorphous CaCO₃ phase into nanocrystalline calcite. We analyze the structure and properties of crystallized MLA by X-ray scattering, transmitted and polarized light microscopy, and electron microscopy and find that MLA are crystallized in spherulite-like patterns without changing the shape of the microlens. The key finding is that nanocrystallinity of the calcite formed diminishes structural anisotropy on the wavelength scale and results in greatly reduced birefringent effects. The remnant preferred orientation of the optical axes of calcite crystals in the plane of the microlens arrays leads to some directionality of optical properties, which may be beneficial for technical applications.

Nanospectroscopic imaging of twinning superlattices in an individual GaAs-AlGaAs core-shell nanowire

Senichev, A. V., V. G. Talalaev, I. Shtrom, H. Blumtritt, G. Cirlin, J. Schilling, C. Lienau, P. Werner

ACS Photonics 1 (11), pp 1099-1106 (2014)

Improved local efficiency imaging via photoluminescence for silicon solar cells

Shen, C., M. A. Green, O. Breitenstein, T. Trupke, M. Zhang, H. Kampwerth

Solar Energy Materials and Solar Cells 123, pp 41-46 (2014)

abstract

We present an improved method that uses photoluminescence images to calculate the spatially-resolved efficiency in addition to other performance parameters of silicon solar cells. This new method is simpler than our previously-presented two-diode method, using only one diode with a variable ideality factor. Experimental results show that the simplified method is more tolerant of very large variations in local series resistance, a characteristic commonly seen in silicon cells. Using dark lock-in thermography techniques, we quantitatively verify the efficiency images produced by our improved method.

Grain boundary characterization in multicrystalline silicon using joint EBSD, EBIC, and atom probe tomography

Stoffers, A., O. Cojocaru-Mirédin, O. Breitenstein, W. Seifert, S. Zaefferer, D. Raabe

Proceedings 40th IEEE Photovoltaics Specialists Conference (PVSC), pp 42-46 Denver, USA (2014)

Effect of nanobridges on the emission spectra of a quantum dot-quantum well tunneling pair

Talalaev, V. G., G. E. Cirlin, L. I. Goraye, B. V. Novikov, M. E. Labzovskaya, J. W. Tomm, P. Werner, B. Fuhrmann, J. Schilling, P. N. Racec

Semiconductors 48 (9), pp 1178-1184 (2014)

Defects related to Sb-mediated Ge quantum dots

Tonkikh, A. A., V.-T. Rangel-Kuoppa, N. D. Zakharov, P. Werner

Solid State Phenomena 205-206, pp 497-501 (2014)

Aperiodic SiSn/Si multilayers for thermoelectric applications

Tonkikh, A. A., N. D. Zakharov, C. Eisenschmidt, H. S. Leipner, P. Werner

Journal of Crystal Growth 392, pp 49-51 (2014)

Cubic phase Sn-rich GeSn nanocrystals in a Ge matrix

Tonkikh, A. A., N. D. Zakharov, A. Suvorova, C. Eisenschmidt, J. Schilling, P. Werner

Crystal Growth & Design 14, pp 1617-1622 (2014)

Molecular dynamics of condensed (semi-) isolated polymer chains

Tress, M. and E. U. Mapesa, W. Kossack, W. K. Kipnusu, M. Reiche, F. Kremer

In: Dynamics in Geometrical Confinement, pp 61-94 (Eds.) Kremer, F. and Kremer, F.,Springer, 2014

Control of defects in a novel aluminium-induced heteroepitaxial growth of Al_xGa_1−xP nanocrystals on silicon nanowires

Zhou, Q., Z. Zhang, S. Senz, F. Zhao, L. Chen, X. Lu, X. Gao, J. Liu

Scripta Materialia 89, pp 57-60 (2014)

A perfectly periodic three-dimensional protein/silica mesoporous structure produced by an organism

Zlotnikov, I., P. Werner, H. Blumtritt, A. Graff, Y. Dauphin, E. Zolotoyabko, P. Fratzl

Advanced Materials 26, pp 1682-1687 (2014)