Institute of Solid State Physics

Graz, Austria

Institute of Solid State Physics

Graz, Austria
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A light wave sent through empty space always oscillates in the same direction. However, certain materials can be used to rotate the direction in which the light is oscillating when placed in a magnetic field. This is known as a 'magneto-optical' effect. After much speculation spanning a long period of time, one variant of this type of effect has now been demonstrated at TU Wien for the first time. Rather than switching the direction of the light wave continually, special materials called 'topological insulators' do so in quantum steps in clearly defined portions. The extent of these quantum steps depends solely on fundamental physical parameters, such as the fine-structure constant. It may soon be possible to measure this constant even more accurately using optical techniques than is currently possible via other methods. The latest findings have now been revealed in the open-access journal 'Nature Communications'. "We have been working on materials that can change the direction of oscillation of light for some time now," explains Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. As a general rule, the effect depends on how thick the material is: the larger the distance to be travelled by the light in the material, the larger the angle of rotation. However, this is not the case for the materials that Pimenov's team has now investigated more closely with the assistance of a research group from Würzburg. Their focus has been on 'topological insulators', for which the crucial parameter is the surface rather than the thickness. Insulators on the inside, electricity can usually be conducted very effectively along the surface of a topological insulator. "Even when sending radiation through a topological insulator, the surface is what makes all the difference," says Pimenov. When light propagates in this material, the oscillation direction of the beam is turned by the surface of the material twice - once when it enters and again when it exits. What is most remarkable here is that this rotation takes place in particular portions, in quantum steps, rather than being continuous. The interval between these points is not determined by the geometry or by properties of the material and is instead defined only by fundamental natural constants. For example, they can be specified on the basis of the fine-structure constant, which is used to describe the strength of the electromagnetic interaction. This could open up the possibility of measuring natural constants with more precision than has previously been the case and may even lead to new measuring techniques being identified. The situation is similar for the quantum Hall effect, which is another quantum phenomenon observed in certain materials, in which case a particular variable (here electrical resistance) can rise only by certain amounts. The quantum Hall effect is currently used for high-precision measurements, with the official standard definition of electrical resistance being based on it. Back in 1985, the Nobel Prize in Physics was awarded for the discovery of the quantum Hall effect. Topological materials have also already been the subject of a Nobel Prize victory - this time in 2016. It is expected that these latest results will also make it possible for materials with special topological characteristics (in this case topological insulators) to be used for specific technical applications.


News Article | May 24, 2017
Site: www.eurekalert.org

The 'quantized magneto-electric effect' has been demonstrated for the first time in topological insulators at TU Wien, which is set to open up new and highly accurate methods of measurement A light wave sent through empty space always oscillates in the same direction. However, certain materials can be used to rotate the direction in which the light is oscillating when placed in a magnetic field. This is known as a 'magneto-optical' effect. After much speculation spanning a long period of time, one variant of this type of effect has now been demonstrated at TU Wien for the first time. Rather than switching the direction of the light wave continually, special materials called 'topological insulators' do so in quantum steps in clearly defined portions. The extent of these quantum steps depends solely on fundamental physical parameters, such as the fine-structure constant. It may soon be possible to measure this constant even more accurately using optical techniques than is currently possible via other methods. The latest findings have now been revealed in the open-access journal 'Nature Communications'. "We have been working on materials that can change the direction of oscillation of light for some time now," explains Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. As a general rule, the effect depends on how thick the material is: the larger the distance to be travelled by the light in the material, the larger the angle of rotation. However, this is not the case for the materials that Pimenov's team has now investigated more closely with the assistance of a research group from Würzburg. Their focus has been on 'topological insulators', for which the crucial parameter is the surface rather than the thickness. Insulators on the inside, electricity can usually be conducted very effectively along the surface of a topological insulator. "Even when sending radiation through a topological insulator, the surface is what makes all the difference," says Pimenov. When light propagates in this material, the oscillation direction of the beam is turned by the surface of the material twice - once when it enters and again when it exits. What is most remarkable here is that this rotation takes place in particular portions, in quantum steps, rather than being continuous. The interval between these points is not determined by the geometry or by properties of the material and is instead defined only by fundamental natural constants. For example, they can be specified on the basis of the fine-structure constant, which is used to describe the strength of the electromagnetic interaction. This could open up the possibility of measuring natural constants with more precision than has previously been the case and may even lead to new measuring techniques being identified. The situation is similar for the quantum Hall effect, which is another quantum phenomenon observed in certain materials, in which case a particular variable (here electrical resistance) can rise only by certain amounts. The quantum Hall effect is currently used for high-precision measurements, with the official standard definition of electrical resistance being based on it. Back in 1985, the Nobel Prize in Physics was awarded for the discovery of the quantum Hall effect. Topological materials have also already been the subject of a Nobel Prize victory - this time in 2016. It is expected that these latest results will also make it possible for materials with special topological characteristics (in this case topological insulators) to be used for specific technical applications.


A light wave sent through empty space always oscillates in the same direction. However, certain materials can be used to rotate the direction in which the light is oscillating when placed in a magnetic field. This is known as a 'magneto-optical' effect. After much speculation spanning a long period of time, one variant of this type of effect has now been demonstrated at TU Wien for the first time. Rather than switching the direction of the light wave continually, special materials called 'topological insulators' do so in quantum steps in clearly defined portions. The extent of these quantum steps depends solely on fundamental physical parameters, such as the fine-structure constant. It may soon be possible to measure this constant even more accurately using optical techniques than is currently possible via other methods. The latest findings have now been revealed in the open-access journal Nature Communications. "We have been working on materials that can change the direction of oscillation of light for some time now," explains Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. As a general rule, the effect depends on how thick the material is: the larger the distance to be travelled by the light in the material, the larger the angle of rotation. However, this is not the case for the materials that Pimenov's team has now investigated more closely with the assistance of a research group from Würzburg. Their focus has been on 'topological insulators', for which the crucial parameter is the surface rather than the thickness. Insulators on the inside, electricity can usually be conducted very effectively along the surface of a topological insulator. "Even when sending radiation through a topological insulator, the surface is what makes all the difference," says Pimenov. When light propagates in this material, the oscillation direction of the beam is turned by the surface of the material twice – once when it enters and again when it exits. What is most remarkable here is that this rotation takes place in particular portions, in quantum steps, rather than being continuous. The interval between these points is not determined by the geometry or by properties of the material and is instead defined only by fundamental natural constants. For example, they can be specified on the basis of the fine-structure constant, which is used to describe the strength of the electromagnetic interaction. This could open up the possibility of measuring natural constants with more precision than has previously been the case and may even lead to new measuring techniques being identified. The situation is similar for the quantum Hall effect, which is another quantum phenomenon observed in certain materials, in which case a particular variable (here electrical resistance) can rise only by certain amounts. The quantum Hall effect is currently used for high-precision measurements, with the official standard definition of electrical resistance being based on it. Back in 1985, the Nobel Prize in Physics was awarded for the discovery of the quantum Hall effect. Topological materials have also already been the subject of a Nobel Prize victory – this time in 2016. It is expected that these latest results will also make it possible for materials with special topological characteristics (in this case topological insulators) to be used for specific technical applications. More information: V. Dziom et al. Observation of the universal magnetoelectric effect in a 3D topological insulator, Nature Communications (2017). DOI: 10.1038/ncomms15197


News Article | May 25, 2017
Site: www.sciencedaily.com

A light wave sent through empty space always oscillates in the same direction. However, certain materials can be used to rotate the direction in which the light is oscillating when placed in a magnetic field. This is known as a 'magneto-optical' effect. After much speculation spanning a long period of time, one variant of this type of effect has now been demonstrated at TU Wien for the first time. Rather than switching the direction of the light wave continually, special materials called 'topological insulators' do so in quantum steps in clearly defined portions. The extent of these quantum steps depends solely on fundamental physical parameters, such as the fine-structure constant. It may soon be possible to measure this constant even more accurately using optical techniques than is currently possible via other methods. The latest findings have now been revealed in the open-access journal 'Nature Communications'. "We have been working on materials that can change the direction of oscillation of light for some time now," explains Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. As a general rule, the effect depends on how thick the material is: the larger the distance to be travelled by the light in the material, the larger the angle of rotation. However, this is not the case for the materials that Pimenov's team has now investigated more closely with the assistance of a research group from Würzburg. Their focus has been on 'topological insulators', for which the crucial parameter is the surface rather than the thickness. Insulators on the inside, electricity can usually be conducted very effectively along the surface of a topological insulator. "Even when sending radiation through a topological insulator, the surface is what makes all the difference," says Pimenov. When light propagates in this material, the oscillation direction of the beam is turned by the surface of the material twice -- once when it enters and again when it exits. What is most remarkable here is that this rotation takes place in particular portions, in quantum steps, rather than being continuous. The interval between these points is not determined by the geometry or by properties of the material and is instead defined only by fundamental natural constants. For example, they can be specified on the basis of the fine-structure constant, which is used to describe the strength of the electromagnetic interaction. This could open up the possibility of measuring natural constants with more precision than has previously been the case and may even lead to new measuring techniques being identified. The situation is similar for the quantum Hall effect, which is another quantum phenomenon observed in certain materials, in which case a particular variable (here electrical resistance) can rise only by certain amounts. The quantum Hall effect is currently used for high-precision measurements, with the official standard definition of electrical resistance being based on it. Back in 1985, the Nobel Prize in Physics was awarded for the discovery of the quantum Hall effect. Topological materials have also already been the subject of a Nobel Prize victory -- this time in 2016. It is expected that these latest results will also make it possible for materials with special topological characteristics (in this case topological insulators) to be used for specific technical applications.


Computational materials design is traditionally used to improve and further develop already existing materials. Simulations grant a deep insight into the quantum mechanical effects which determine material properties. Egbert Zojer and his team at the Institute of Solid State Physics of TU Graz go a decisive step beyond that: they use computer simulations to propose an entirely new concept for controlling the electronic properties of materials. Potentially disturbing influences arising from the regular arrangement of polar elements, so-called collective electrostatic effects, are used by the research group to intentionally manipulate material properties. That this radically new approach also works for three-dimensional materials has been demonstrated by the Graz team in Advanced Materials, which according to Google Scholar is internationally the most important journal in the field of materials research. "The basic approach of the electrostatic design concept is to modify the electronic states of semiconductors via the periodic arrangement of dipolar groups. In this way we are able to locally manipulate energy levels in a controlled way. In doing so, we do not try to find ways to bypass such effects which are inevitable especially at interfaces. Rather, we make deliberate use of them for our own purposes," explains Egbert Zojer. This topic has been in the focus of the research of the Zojer group already for some time. The first step was the electrostatic design of molecular monolayers, for example on gold electrodes. Experiments have shown that the predicted energy shifts within the layers actually take place and that charge transport through monolayers can be deliberately modulated. Also, the electronic states of two-dimensional materials, such as graphene, can be controlled by means of collective electrostatic effects. In the publication in Advanced Materials, doctoral student Veronika Obersteiner, Egbert Zojer and other colleagues from the team demonstrate the full potential of the concept by extending it to three-dimensional materials. "For the example of three-dimensional covalent organic networks, we show how - by means of collective electrostatic effects - the energy landscape within three-dimensional bulk material can be manipulated such that spatially confined pathways for electrons and holes can be realised. In this way charge carriers can, for instance, be separated and the electronic properties of the material can be designed as desired," says Zojer. The concept is especially interesting for solar cells. In classical organic solar cells, chemically different building blocks, so-called donors and acceptors, are used to separate the photogenerated electron-hole pairs. In the approach proposed here, the necessary local shift of energy levels occurs due to the periodic arrangement of polar groups. The semiconducting areas onto which the electrons and holes are shifted are chemically identical. "In this way, we can quasi-continuously and efficiently fine tune the energy levels by varying the dipole density. This work is the climax to our intensive research on the electrostatic design of materials," says Zojer. Electrostatic design in 3D systems can also enable the realization of complex quantum structures, such as quantum-cascades and quantum-checkerboards. "Only the imagination of the materials designer can set limits to our concept," Zojer and Obersteiner enthuse in unison. Computational operations for this paper had been executed at the Vienna Scientific Cluster (VSC), Austria's highest performing supercomputer and a joint operation of the partner universities TU Wien, TU Graz, University of Vienna, Boku Vienna and University of Innsbruck. This work is anchored in the Field of Expertise "Advanced Materials Science", one of five research foci of TU Graz.


News Article | May 12, 2017
Site: phys.org

Computational materials design is traditionally used to improve and further develop already existing materials. Simulations grant a deep insight into the quantum mechanical effects which determine material properties. Egbert Zojer and his team at the Institute of Solid State Physics of TU Graz go a decisive step beyond that: they use computer simulations to propose an entirely new concept for controlling the electronic properties of materials. Potentially disturbing influences arising from the regular arrangement of polar elements, so-called collective electrostatic effects, are used by the research group to intentionally manipulate material properties. That this radically new approach also works for three-dimensional materials has been demonstrated by the Graz team in Advanced Materials, which according to Google Scholar is internationally the most important journal in the field of materials research. "The basic approach of the electrostatic design concept is to modify the electronic states of semiconductors via the periodic arrangement of dipolar groups. In this way we are able to locally manipulate energy levels in a controlled way. In doing so, we do not try to find ways to bypass such effects which are inevitable especially at interfaces. Rather, we make deliberate use of them for our own purposes," explains Egbert Zojer. This topic has been in the focus of the research of the Zojer group already for some time. The first step was the electrostatic design of molecular monolayers, for example on gold electrodes. Experiments have shown that the predicted energy shifts within the layers actually take place and that charge transport through monolayers can be deliberately modulated. Also, the electronic states of two-dimensional materials, such as graphene, can be controlled by means of collective electrostatic effects. In the publication in Advanced Materials, doctoral student Veronika Obersteiner, Egbert Zojer and other colleagues from the team demonstrate the full potential of the concept by extending it to three-dimensional materials. "For the example of three-dimensional covalent organic networks, we show how – by means of collective electrostatic effects – the energy landscape within three-dimensional bulk material can be manipulated such that spatially confined pathways for electrons and holes can be realised. In this way charge carriers can, for instance, be separated and the electronic properties of the material can be designed as desired," says Zojer. The concept is especially interesting for solar cells. In classical organic solar cells, chemically different building blocks, so-called donors and acceptors, are used to separate the photogenerated electron-hole pairs. In the approach proposed here, the necessary local shift of energy levels occurs due to the periodic arrangement of polar groups. The semiconducting areas onto which the electrons and holes are shifted are chemically identical. "In this way, we can quasi-continuously and efficiently fine tune the energy levels by varying the dipole density. This work is the climax to our intensive research on the electrostatic design of materials," says Zojer. Electrostatic design in 3-D systems can also enable the realization of complex quantum structures, such as quantum-cascades and quantum-checkerboards. "Only the imagination of the materials designer can set limits to our concept," says Zojer. Explore further: New data mining resource for organic materials available More information: Veronika Obersteiner et al. Electrostatic Design of 3D Covalent Organic Networks, Advanced Materials (2017). DOI: 10.1002/adma.201700888


Brinkmann M.,Charles Sadron Institute | Contal C.,Charles Sadron Institute | Kayunkid N.,Charles Sadron Institute | Djuric T.,Institute of Solid State Physics | Resel R.,Institute of Solid State Physics
Macromolecules | Year: 2010

A simple method for the nanotexturing and orientation of regioregular poly(3-hexylthiophene) (P3HT) thin films has been developed. Epitaxial growth of P3HT on the surface of an aromatic salt (potassium 4-bromobenzoate) (K-BrBz) leads to highly oriented and nanotextured P3HT films which consist of a regular network of interconnected semicrystalline domains oriented along two preferential in-plane directions. The overall crystallinity and the level of in-plane orientation of the P3HT films are controlled by the temperature of isothermal crystallization (Tiso).Well-defined electron diffraction patternswith sharp reflections obtained for Tiso=180 °C indicate that the crystalline domains grow with a unique (1 0 0) P3HT contact plane on theK-BrBz substratewith the P3HT chains oriented along the [0±2 1]K-BrBz directions of the substrate. During the annealing of the polymer film, the surface of the aromatic salt undergoes a topographic reconstruction resulting in a regular nanostructured "hill and valley" topography that templates and orients the growth of P3HT. Preferred orientation of P3HT crystalline domains occurs at step edges of the substrate and is favored by the matching between the layer period of P3HT and the terrace height of the K-BrBz substrate. © 2010 American Chemical Society.


News Article | August 22, 2016
Site: www.spie.org

Novel devices feature improved carrier transport and operate under higher-order modulation schemes to enable increased data transmission rates. Ethernet protocols (i.e., the IEEE 802.3ba 100Gb/s and the forthcoming IEEE P802.3bs 400Gb/s standards) provide the definitions for data transmission systems that are used in long-range (10km) and extended-range (40km) fiber links. These transmission systems include multichannel 25GBd on-off keying (OOK)—the simplest form of intensity modulation in which digital information is represented by low (0) and high (1) amplitude levels—and four-level pulse-amplitude modulation (PAM4). Directly modulated lasers (DMLs) are an attractive option for a light source in such applications because of their low cost, small footprint, and low power consumption. In addition, they allow simple direct detection, while being operated in an intensity-modulation mode. DMLs, however, are strongly limited by their bandwidth. Indeed, much higher data rates are possible with coherent systems in which more advanced modulation schemes and complex transmitters are used. As an alternative to conventional quantum-well-based DMLs, quantum-dot lasers (QDLs) have been studied extensively. QDLs feature several unique properties, e.g., they have temperature-insensitive and ultralow threshold current, and low linewidth enhancement factors.1 Gallium-arsenide-based (GaAs-based) QDLs exhibit at least three confined electronic energy levels, i.e., a ground state (GS) and two very close excited states (ESs). The GS is twofold degenerate, whereas the ES is fourfold degenerate. The larger degeneracy translates to a larger differential gain and smaller nonlinear gain compression.2 Direct modulation of QDLs on the GS, at over 20Gb/s, has been demonstrated for both indium arsenide (InAs)/GaAs lasers at 1.31μm (O-band)3 and for InAs/indium phosphide (InP) devices at 1.55μm (C-band).4 The bandwidth of these structures, however, is limited by several factors, including inhomogeneous broadening (low modal gain),5 the hot-carrier effect, and the slow capture time into the quantum dots (large gain compression).6 To ensure sufficient gain, several quantum dot (QD) layers with wide spacers (limiting carrier transport across the active region) are usually incorporated into QDLs. The holes tend to accumulate on the p-side of the active region because of their short diffusion length. This inhomogeneous distribution of carriers limits the modulation response of the devices.7 In our work,8 we have designed a novel GaAs-based QDL in which we incorporate graded p-doping of spacers to compensate for the hole distribution. We have designed this grading so that there is a small amount of p-doping on the topside of the active region and a large amount of doping on the bottom (i.e., substrate) side. Our lasers feature a larger maximum modulation bandwidth (9.2GHz) compared with standard p-doped samples (7.2GHz). Furthermore, by modifying the reflectivity of one laser facet, our lasers (operating exclusively at the ES) exhibit an increased maximum modulation bandwidth of 11.7GHz. We can also realize InAs/indium gallium arsenide/InP QD structures at 1.55μm, which exhibit a –3dB bandwidth of 12.1GHz, by shortening the distance between the electrical contacts and the active region, and by incorporating seven QD layers. We can thus provide sufficient gain, but do not limit the carrier transport. Our O-band and C-band QDLs exhibit data transmission at a rate of 25Gb/s for direct modulation in the non-return-to-zero OOK scheme. To further increase the digital bandwidth of our devices, we also explored higher-order modulation formats, e.g., PAM4 and eight-level PAM (PAM8). PAM4 results for the O-band and C-band lasers—see Figure 1(a)—show that 17.5GBd (35Gb/s) data transmission was realized with both structures. We thus achieved a 40% increase in the maximum bit rate. Doubling the bit rate, however, was not possible. This is because in PAM schemes (particularly PAM8), the noise level of the lasers becomes the major limiting factor. The 7.5GBd (22.5Gb/s) PAM8 response of a standard p-doped laser structure across 10km of single-mode fiber (SMF) is shown in Figure 1(b). We successfully demonstrated PAM8 for this particular laser structure because it features a strongly damped (but linear) small signal response, an ability to operate at low currents (threshold of 3mA), and a relatively large modulation-current-efficiency factor.8 Figure 1. Eye diagrams and corresponding bit-error ratio (BER) curves of (a) the O-band (1.31μm) and C-band (1.55μm) lasers under 17.5GBd four-level pulse-amplitude modulation (PAM4) in back-to-back configuration and (b) of a standard p-doped laser under 7.5GBd eight-level PAM (PAM8) across 10km of single-mode fiber (SMF). In (a) the aggregated BERs were determined by direct detection with an error analyzer. In (b) the BERs were retrieved using digital signal processing of single-shot traces that were acquired with a real-time oscilloscope. The improved BERs at lower received powers were achieved by means of equalization. In another part of our work, we have packaged a 39.813GHz monolithic two-section mode-locked laser (MLL) that is based on the 1.31μm graded p-doped laser structure into a module. MLLs (which generate optical and electrical pulse trains) are ideal candidates for various applications, e.g., microwave photonics and radio-over-fiber systems. When combined with modulators, MLLs act as transmitters for optical time-division multiplexing (OTDM) systems in optical communication networks. MLLs operate at frequencies far beyond the intrinsic bandwidth of DMLs. In contrast to DMLs, they benefit strongly from an inhomogeneously broadened QD gain spectrum. When all the longitudinal modes are locked, sub-picosecond pulses are emitted. QD MLLs also exhibit ultrafast recovery, which enables pulse generation up to 100GHz. We achieve jitter reduction and frequency tuning through hybrid mode-locking. In addition, dual-tone injection gives rise to a narrow optical linewidth (essential for coherent systems). We observe a pulse width of 2ps and integrated jitter of 340fs, which makes our MLL suitable for OTDM.9 We generated return-to-zero (RZ) differential quadrature phase-shift keying (DQPSK) data signals by superimposing bit sequences on the MLL pulse train, via successively sequenced dual-drive Mach–Zehnder and phase modulators. We have also conducted data transmission experiments at 40GBd (80Gb/s) across 45km of SMF (see inset of Figure 2). Through the use of DQPSK and OTDM we were thus able to quadruple the bit rate (compared with standard OOK). The corresponding 80GBd (160Gb/s) RZ DQPSK bit-error ratio curves and eye diagrams are also shown in Figure 2.10 Figure 2. Illustration of 80GBd return-to-zero (RZ) differential quadrature phase-shift keying (DQPSK) in back-to-back configuration. Eye diagrams of tributary 1 (Tr 1) and tributary 2 (Tr 2) at the maximum received optical power were measured by a differential receiver, based on a delay interferometer. The signal-to-noise ratios are 6.7 and 6.5, respectively. BERs were detected by means of an electrical demultiplexer (DEMUX). The BER curves of both DEMUX output signals (0P and 1P) and tributaries show error-free performance (i.e., without error floor to below 10−10. Inset: Constellation diagram of 40GBd RZ DQPSK across 45km of SMF, for the maximum received power obtained with an O-band optical modulation analyzer. The error-vector magnitude is 10.1%. In summary, in our novel GaAs-based QDL we incorporate graded p-doping of spacers to compensate for carrier transport limitations across the active region, and thus bandwidth limitations, in DMLs. The ES emission has larger differential gain than the GS emission. These improvements lead to higher cut-off frequencies of 1.31μm-InAs/GaAs devices. In addition, our 1.55μm InAs/InP QD lasers, which have a narrowed active region and barriers, exhibit large 3dB bandwidths. We have demonstrated data rates of 35Gb/s using PAM4 for both wavelength bands, and PAM8 reveals that further optimization of the lasers (in terms of their noise performance) is required. This will therefore be the focus of our future research. We have also shown that integration of MLLs as sources in coherent OTDM systems enables 160Gb/s RZ DQPSK data transmission. Funding for this research was provided by the German Research Foundation in the SFB 787 framework. The authors would like to thank Finisar (Germany) for packaging the quantum-dot mode-locked laser module and C. Meuer at Sicoya for assistance with the digital signal processing. Department of Solid-State Physics and Center of Nanophotonics Technische Universität Berlin Dejan Arsenijević received his diploma in physics from the Technische Universität Berlin in 2009. His current research interests include higher-order modulation formats, as well as low-jitter optical and electrical pulse sources for future high-speed data communications. Department of Solid-State Physics and Center of NanophotonicsTechnische Universität Berlin Department of Solid-State Physics and Center of Nanophotonics Technische Universität Berlin Berlin, Germany and King Abdulaziz University Dieter Bimberg received his diploma in physics and PhD from Goethe University, Germany, in 1968 and 1971, respectively. Between 1972 and 1979 he was a principal scientist at the Max Planck Institute for Solid State Research in Germany. He was then appointed as a professor of electrical engineering at the Technical University of Aachen (Germany) and, in 1981, as the chair of the Technische Universität Berlin's Applied Solid State Physics department. From 1990 to 2011 he was the executive director of the Institute of Solid State Physics, and in 2004 he founded the Center of Nanophotonics. In addition, he was the chairman of the board of the German Federal Government's Centers of Excellence in Nanotechnologies between 2006 and 2011. His many honors include the Russian State Prize in Science and Technology (2001), the Max Born Award (2006), the William Streifer Scientific Achievement Award (2010), the United Nations Educational, Scientific, and Cultural Organization's Nanoscience Medal (2012), and the Welker Award (2015). Department of Solid-State Physics and Center of NanophotonicsTechnische Universität BerlinBerlin, GermanyandKing Abdulaziz University 2. D. Arsenijević, A. Schliwa, H. Schmeckebier, M. Stubenrauch, M. Spiegelberg, D. Bimberg, V. Mikhelashvili, G. Eisenstein, Comparison of dynamic properties of ground- and excited-state emission in p-doped InAs/GaAs quantum-dot lasers, Appl. Phys. Lett. 104, p. 181101, 2014. doi:10.1063/1.4875238 5. H. Dery, G. Eisenstein, The impact of energy band diagram and inhomogeneous broadening on the optical differential gain in nanostructure lasers, IEEE J. Quantum Electron. 41, p. 26-35, 2005. doi:10.1109/JQE.2004.837953


Stefanovsky S.V.,Moscow Scientific and Industrial Association | Purans J.J.,Institute of Solid State Physics
Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B | Year: 2012

Cesiums ion speciation in sodium cesium borosilicate and sodium aluminophosphate glasses potentially suitable for immobilization of Cs-containing radioactive wastes or ionizing radiation sources was studied using x-ray absorption spectroscopy (XAS). At relatively low Cs2O content (~1-2 mol%) in Na-Cs borosilicate glasses, Cs ions are present in a slightly distorted twelve-fold coordinated oxygen environment where nine oxygens are positioned at a distance of 3·22 Å and three - at a distance of 3·37 Å. The closest Si atoms are positioned at a distance of ~3·31 Å. With the increase of Cs2O concentration in the glass both the coordination number (CN) and the average Cs-O distances reduce, whereas, the Cs-Si distances increase. Both the first and the second coordination shells are split into two subshells pointing to distortion of cesium-oxygen polyhedra.


Gertners U.,Institute of Solid State Physics | Teteris J.,Institute of Solid State Physics
Physics Procedia | Year: 2013

In this report direct photo-induced formation of surface relief gratings (SRG) in thin layers of arsenic sulfide (As2S3) are shown. This anisotropic light-induced mass transfer phenomenon has been discussed with the special attention focused on the polarization and intensity of the corresponding light. The experimental setup for the SRG recording is straight-forward consisting of ∼ 10 m optical slit through which an unfocused beam of light is projected on the surface of sample. The evolution of surface relief in dependence from the recording time and polarization has been investigated in detail. The processes of SRG formation and mass transfer which are based on the photo-induced plasticity have discussed. © 2013 The Authors. Published by Elsevier B.V.

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