Theorie inhomogener kondensierter Materie
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Enzymatically active biomimetic micropropellers for the penetration of mucin gels
Walker (Schamel), D., Käsdorf, B. T., Jeong, H. H., Lieleg, O., Fischer, P.
Science Advances, 1(11):e1500501, December 2015 (article)
In the body, mucus provides an important defense mechanism by limiting the penetration of pathogens. It is therefore also a major obstacle for the efficient delivery of particle-based drug carriers. The acidic stomach lining in particular is difficult to overcome because mucin glycoproteins form viscoelastic gels under acidic conditions. The bacterium Helicobacter pylori has developed a strategy to overcome the mucus barrier by producing the enzyme urease, which locally raises the pH and consequently liquefies the mucus. This allows the bacteria to swim through mucus and to reach the epithelial surface. We present an artificial system of reactive magnetic micropropellers that mimic this strategy to move through gastric mucin gels by making use of surface-immobilized urease. The results demonstrate the validity of this biomimetic approach to penetrate biological gels, and show that externally propelled microstructures can actively and reversibly manipulate the physical state of their surroundings, suggesting that such particles could potentially penetrate native mucus.
pf Walker (Schamel), D., Käsdorf, B. T., Jeong, H. H., Lieleg, O., Fischer, P. Enzymatically active biomimetic micropropellers for the penetration of mucin gels Science Advances, 1(11):e1500501, December 2015 (article)
The EChemPen: A Guiding Hand To Learn Electrochemical Surface Modifications
Valetaud, M., Loget, G., Roche, J., Hueken, N., Fattah, Z., Badets, V., Fontaine, O., Zigah, D.
J. of Chem. Ed., 92(10):1700-1704, September 2015 (article)
The Electrochemical Pen (EChemPen) was developed as an attractive tool for learning electrochemistry. The fabrication, principle, and operation of the EChemPen are simple and can be easily performed by students in practical classes. It is based on a regular fountain pen principle, where the electrolytic solution is dispensed at a tip to locally modify a conductive surface by triggering a localized electrochemical reaction. Three simple model reactions were chosen to demonstrate the versatility of the EChemPen for teaching various electrochemical processes. We describe first the reversible writing/erasing of metal letters, then the electrodeposition of a black conducting polymer "ink", and finally the colorful writings that can be generated by titanium anodization and that can be controlled by the applied potential. These entertaining and didactic experiments are adapted for teaching undergraduate students that start to study electrochemistry by means of surface modification reactions.
pf Valetaud, M., Loget, G., Roche, J., Hueken, N., Fattah, Z., Badets, V., Fontaine, O., Zigah, D. The EChemPen: A Guiding Hand To Learn Electrochemical Surface Modifications J. of Chem. Ed., 92(10):1700-1704, September 2015 (article)
Optimal Length of Low Reynolds Number Nanopropellers
Walker (Schamel), D., Kuebler, M., Morozov, K. I., Fischer, P., Leshansky, A. M.
Nano Letters, 15(7):4412-4416, June 2015 (article)
Locomotion in fluids at the nanoscale is dominated by viscous drag. One efficient propulsion scheme is to use a weak rotating magnetic field that drives a chiral object. Froth bacterial flagella to artificial drills, the corkscrew is a universally useful chiral shape for propulsion in viscous environments. Externally powered magnetic micro- and nanomotors have been recently developed that allow for precise fuel-free propulsion in complex media. Here, we combine analytical and numerical theory with experiments on nanostructured screw-propellers to show that the optimal length is surprisingly short only about one helical turn, which is shorter than most of the structures in use to date. The results have important implications for the design of artificial actuated nano- and micropropellers and can dramatically reduce fabrication times, while ensuring optimal performance.
pf Walker (Schamel), D., Kuebler, M., Morozov, K. I., Fischer, P., Leshansky, A. M. Optimal Length of Low Reynolds Number Nanopropellers Nano Letters, 15(7):4412-4416, June 2015 (article)
A theoretical study of potentially observable chirality-sensitive NMR effects in molecules
Garbacz, P., Cukras, J., Jaszunski, M.
Phys. Chem. Chem. Phys., 17(35):22642-22651, May 2015 (article)
Two recently predicted nuclear magnetic resonance effects, the chirality-induced rotating electric polarization and the oscillating magnetization, are examined for several experimentally available chiral molecules. We discuss in detail the requirements for experimental detection of chirality-sensitive NMR effects of the studied molecules. These requirements are related to two parameters: the shielding polarizability and the antisymmetric part of the nuclear magnetic shielding tensor. The dominant second contribution has been computed for small molecules at the coupled cluster and density functional theory levels. It was found that DFT calculations using the KT2 functional and the aug-cc-pCVTZ basis set adequately reproduce the CCSD(T) values obtained with the same basis set. The largest values of parameters, thus most promising from the experimental point of view, were obtained for the fluorine nuclei in 1,3-difluorocyclopropene and 1,3-diphenyl-2-fluoro-3-trifluoromethylcyclopropene.
pf Garbacz, P., Cukras, J., Jaszunski, M. A theoretical study of potentially observable chirality-sensitive NMR effects in molecules Phys. Chem. Chem. Phys., 17(35):22642-22651, May 2015 (article)
Dynamic Inclusion Complexes of Metal Nanoparticles Inside Nanocups
Alarcon-Correa, M., Lee, T. C., Fischer, P.
Angew. Chem. Int. Ed., 54(23):6730-6734, May 2015, Featured cover article. (article)
Host-guest inclusion complexes are abundant in molecular systems and of fundamental importance in living organisms. Realizing a colloidal analogue of a molecular dynamic inclusion complex is challenging because inorganic nanoparticles (NPs) with a well-defined cavity and portal are difficult to synthesize in high yield and with good structural fidelity. Herein, a generic strategy towards the fabrication of dynamic 1: 1 inclusion complexes of metal nanoparticles inside oxide nanocups with high yield (> 70%) and regiospecificity (> 90%) by means of a reactive double Janus nanoparticle intermediate is reported. Experimental evidence confirms that the inclusion complexes are formed by a kinetically controlled mechanism involving a delicate interplay between bipolar galvanic corrosion and alloying-dealloying oxidation. Release of the NP guest from the nanocups can be efficiently triggered by an external stimulus. Featured cover article.
pf Alarcon-Correa, M., Lee, T. C., Fischer, P. Dynamic Inclusion Complexes of Metal Nanoparticles Inside Nanocups Angew. Chem. Int. Ed., 54(23):6730-6734, May 2015, Featured cover article. (article)
Surface roughness-induced speed increase for active Janus micromotors
Choudhury, U., Soler, L., Gibbs, J. G., Sanchez, S., Fischer, P.
Chem. Comm., 51(41):8660-8663, April 2015 (article)
We demonstrate a simple physical fabrication method to control surface roughness of Janus micromotors and fabricate self-propelled active Janus microparticles with rough catalytic platinum surfaces that show a four-fold increase in their propulsion speed compared to conventional Janus particles coated with a smooth Pt layer.
pf Choudhury, U., Soler, L., Gibbs, J. G., Sanchez, S., Fischer, P. Surface roughness-induced speed increase for active Janus micromotors Chem. Comm., 51(41):8660-8663, April 2015 (article)
Active colloidal microdrills
Gibbs, J. G., Fischer, P.
Chem. Comm., 51(20):4192-4195, Febuary 2015 (article)
We demonstrate a chemically driven, autonomous catalytic microdrill. An asymmetric distribution of catalyst causes the helical swimmer to twist while it undergoes directed propulsion. A driving torque and hydrodynamic coupling between translation and rotation at low Reynolds number leads to drill-like swimming behaviour.
pf Gibbs, J. G., Fischer, P. Active colloidal microdrills Chem. Comm., 51(20):4192-4195, Febuary 2015 (article)
Selectable Nanopattern Arrays for Nanolithographic Imprint and Etch-Mask Applications
Jeong, H. H., Mark, A. G., Lee, T., Son, K., Chen, W., Alarcon-Correa, M., Kim, I., Schütz, G., Fischer, P.
Adv. Science, 2(7):1500016, 2015, Featured cover article. (article)
A parallel nanolithographic patterning method is presented that can be used to obtain arrays of multifunctional nanoparticles. These patterns can simply be converted into a variety of secondary nanopatterns that are useful for nanolithographic imprint, plasmonic, and etch-mask applications.
pf Jeong, H. H., Mark, A. G., Lee, T., Son, K., Chen, W., Alarcon-Correa, M., Kim, I., Schütz, G., Fischer, P. Selectable Nanopattern Arrays for Nanolithographic Imprint and Etch-Mask Applications Adv. Science, 2(7):1500016, 2015, Featured cover article. (article)
Circular polarization interferometry: circularly polarized modes of cholesteric liquid crystals
Sanchez-Castillo, A., Eslami, S., Giesselmann, F., Fischer, P.
OPTICS EXPRESS, 22(25):31227-31236, 2014 (article)
We describe a novel polarization interferometer which permits the determination of the refractive indices for circularly-polarized light. It is based on a Jamin-Lebedeff interferometer, modified with waveplates, and permits us to experimentally determine the refractive indices n(L) and n(R) of the respectively left- and right-circularly polarized modes in a cholesteric liquid crystal. Whereas optical rotation measurements only determine the circular birefringence, i.e. the difference (n(L) - n(R)), the interferometer also permits the determination of their absolute values. We report refractive indices of a cholesteric liquid crystal in the region of selective (Bragg) reflection as a function of temperature. (C) 2014 Optical Society of America
pf Sanchez-Castillo, A., Eslami, S., Giesselmann, F., Fischer, P. Circular polarization interferometry: circularly polarized modes of cholesteric liquid crystals OPTICS EXPRESS, 22(25):31227-31236, 2014 (article)
Self-Propelling Nanomotors in the Presence of Strong Brownian Forces
Lee, T., Alarcon-Correa, M., Miksch, C., Hahn, K., Gibbs, J. G., Fischer, P.
NANO LETTERS, 14(5):2407-2412, 2014 (article)
Motility in living systems is due to an array of complex molecular nanomotors that are essential for the function and survival of cells. These protein nanomotors operate not only despite of but also because of stochastic forces. Artificial means of realizing motility rely on local concentration or temperature gradients that are established across a particle, resulting in slip velocities at the particle surface and thus motion of the particle relative to the fluid. However, it remains unclear if these artificial motors can function at the smallest of scales, where Brownian motion dominates and no actively propelled living organisms can be found. Recently, the first reports have appeared suggesting that the swimming mechanisms of artificial structures may also apply to enzymes that are catalytically active. Here we report a scheme to realize artificial Janus nanoparticles (JNPs) with an overall size that is comparable to that of some enzymes similar to 30 nm. Our JNPs can catalyze the decomposition of hydrogen peroxide to water and oxygen and thus actively move by self-electrophoresis. Geometric anisotropy of the Pt-Au Janus nanoparticles permits the simultaneous observation of their translational and rotational motion by dynamic light scattering. While their dynamics is strongly influenced by Brownian rotation, the artificial Janus nanomotors show bursts of linear ballistic motion resulting in enhanced diffusion.
pf Lee, T., Alarcon-Correa, M., Miksch, C., Hahn, K., Gibbs, J. G., Fischer, P. Self-Propelling Nanomotors in the Presence of Strong Brownian Forces NANO LETTERS, 14(5):2407-2412, 2014 (article)
Shape control in wafer-based aperiodic 3D nanostructures
Hyeon-Ho, J., Mark, A. G., Gibbs, J. G., Reindl, T., Waizmann, U., Weis, J., Fischer, P.
NANOTECHNOLOGY, 25(23), 2014, Cover article. (article)
Controlled local fabrication of three-dimensional (3D) nanostructures is important to explore and enhance the function of single nanodevices, but is experimentally challenging. We present a scheme based on e-beam lithography (EBL) written seeds, and glancing angle deposition (GLAD) grown structures to create nanoscale objects with defined shapes but in aperiodic arrangements. By using a continuous sacrificial corral surrounding the features of interest we grow isolated 3D nanostructures that have complex cross-sections and sidewall morphology that are surrounded by zones of clean substrate.
Cover article.
pf Hyeon-Ho, J., Mark, A. G., Gibbs, J. G., Reindl, T., Waizmann, U., Weis, J., Fischer, P. Shape control in wafer-based aperiodic 3D nanostructures NANOTECHNOLOGY, 25(23), 2014, Cover article. (article)
Swimming by reciprocal motion at low Reynolds number
Qiu, T., Lee, T., Mark, A. G., Morozov, K. I., Muenster, R., Mierka, O., Turek, S., Leshansky, A. M., Fischer, P.
NATURE COMMUNICATIONS, 5, 2014, Max Planck Press Release. (article)
Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell's scallop theorem, which complicates the actuation scheme needed by microswimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a microswimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here we report a symmetric `micro-scallop', a single-hinge microswimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids.
Max Planck Press Release.
Video - A Swimming Micro-Scallop Video - Winner of the Micro-robotic Design Challenge in Hamlyn Symposium on Medical Robotics DOI [BibTex]
pf Qiu, T., Lee, T., Mark, A. G., Morozov, K. I., Muenster, R., Mierka, O., Turek, S., Leshansky, A. M., Fischer, P. Swimming by reciprocal motion at low Reynolds number NATURE COMMUNICATIONS, 5, 2014, Max Planck Press Release. (article)
Nanohelices by shadow growth
Gibbs, J. G., Mark, A. G., Lee, T., Eslami, S., Schamel, D., Fischer, P.
NANOSCALE, 6(16):9457-9466, 2014 (article)
The helix has remarkable qualities and is prevalent in many fields including mathematics, physics, chemistry, and biology. This shape, which is chiral by nature, is ubiquitous in biology with perhaps the most famous example being DNA. Other naturally occurring helices are common at the nanoscale in the form of protein secondary structures and in various macromolecules. Nanoscale helices exhibit a wide range of interesting mechanical, optical, and electrical properties which can be intentionally engineered into the structure by choosing the correct morphology and material. As technology advances, these fabrication parameters can be fine-tuned and matched to the application of interest. Herein, we focus on the fabrication and properties of nanohelices grown by a dynamic shadowing growth method combined with fast wafer-scale substrate patterning which has a number of distinct advantages. We review the fabrication methodology and provide several examples that illustrate the generality and utility of nanohelices shadow-grown on nanopatterns.
Video - Fabrication of Designer Nanostructures DOI [BibTex]
pf Gibbs, J. G., Mark, A. G., Lee, T., Eslami, S., Schamel, D., Fischer, P. Nanohelices by shadow growth NANOSCALE, 6(16):9457-9466, 2014 (article)
Chiral Nanomagnets
Eslami, S., Gibbs, J. G., Rechkemmer, Y., van Slageren, J., Alarcon-Correa, M., Lee, T., Mark, A. G., Rikken, G. L. J. A., Fischer, P.
ACS PHOTONICS, 1(11):1231-1236, 2014 (article)
We report on the enhanced optical properties of chiral magnetic nanohelices with critical dimensions comparable to the ferromagnetic domain size. They are shown to be ferromagnetic at room temperature, have defined chirality, and exhibit large optical activity in the visible as verified by electron microscopy, superconducting quantum interference device (SQUID) magnetometry, natural circular dichroism (NCD), and magnetic circular dichroism (MCD) measurements. The structures exhibit magneto-chiral dichroism (MChD), which directly demonstrates coupling between their structural chirality and magnetism. A chiral nickel (Ni) film consisting of an array of nanohelices similar to 100 nm in length exhibits an MChD anisotropy factor g(MChD) approximate to 10(-4) T-1 at room temperature in a saturation field of similar to 0.2 T, permitting polarization-independent control of the film's absorption properties through magnetic field modulation. This is also the first report of MChD in a material with structural chirality on the order of the wavelength of light, and therefore the Ni nanohelix array is a metamaterial with magnetochiral properties that can be tailored through a dynamic deposition process.
pf Eslami, S., Gibbs, J. G., Rechkemmer, Y., van Slageren, J., Alarcon-Correa, M., Lee, T., Mark, A. G., Rikken, G. L. J. A., Fischer, P. Chiral Nanomagnets ACS PHOTONICS, 1(11):1231-1236, 2014 (article)
Wireless powering of e-swimmers
Roche, J., Carrara, S., Sanchez, J., Lannelongue, J., Loget, G., Bouffier, L., Fischer, P., Kuhn, A.
SCIENTIFIC REPORTS, 4, 2014 (article)
Miniaturized structures that can move in a controlled way in solution and integrate various functionalities are attracting considerable attention due to the potential applications in fields ranging from autonomous micromotors to roving sensors. Here we introduce a concept which allows, depending on their specific design, the controlled directional motion of objects in water, combined with electronic functionalities such as the emission of light, sensing, signal conversion, treatment and transmission. The approach is based on electric field-induced polarization, which triggers different chemical reactions at the surface of the object and thereby its propulsion. This results in a localized electric current that can power in a wireless way electronic devices in water, leading to a new class of electronic swimmers (e-swimmers).
pf Roche, J., Carrara, S., Sanchez, J., Lannelongue, J., Loget, G., Bouffier, L., Fischer, P., Kuhn, A. Wireless powering of e-swimmers SCIENTIFIC REPORTS, 4, 2014 (article)
Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures
Czugala, M., O'Connell, C., Blin, C., Fischer, P., Fraser, K. J., Benito-Lopez, F., Diamond, D.
SENSORS AND ACTUATORS B-CHEMICAL, 194, pages: 105-113, 2014 (article)
Photoresponsive N-isopropylacrylamide ionogel microstructures are presented in this study. These ionogels are synthesised using phosphonium based room temperature ionic liquids, together with the photochromic compound benzospiropyran. The microstructures can be actuated using light irradiation, facilitating non-contact and non-invasive operation. For the first time, the characterisation of the swelling and shrinking behaviour of several photopatterned ionogel microstructures is presented and the influence of surface-area-to-volume ratio on the swelling kinetics is evaluated. It was found that the swelling and shrinking behaviour of the ionogels is strongly dependent on the nature of the ionic liquid. In particular, the {[}P-6,P-6,P-6,P-14]{[}NTf2] ionogel exhibits the greatest degree of swelling, reaching up to 180\% of its initial size, and the fastest shrinkage rate (k(sh) = 29 +/- 4 x 10(-2) s(-1)). (C) 2014 Elsevier B. V. All rights reserved.
pf Czugala, M., O'Connell, C., Blin, C., Fischer, P., Fraser, K. J., Benito-Lopez, F., Diamond, D. Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures SENSORS AND ACTUATORS B-CHEMICAL, 194, pages: 105-113, 2014 (article)
Molecular QED of coherent and incoherent sum-frequency and second-harmonic generation in chiral liquids in the presence of a static electric field
Fischer, P., Salam, A.
MOLECULAR PHYSICS, 108(14):1857-1868, 2010 (article)
Coherent second-order nonlinear optical processes are symmetry forbidden in centrosymmetric environments in the electric-dipole approximation. In liquids that contain chiral molecules, however, and which therefore lack mirror image symmetry, coherent sum-frequency generation is possible, whereas second-harmonic generation remains forbidden. Here we apply the theory of molecular quantum electrodynamics to the calculation of the matrix element, transition rate, and integrated signal intensity for sum-frequency and second-harmonic generation taking place in a chiral liquid in the presence and absence of a static electric field, to examine which coherent and incoherent processes exist in the electric-dipole approximation in liquids. Third- and fourth-order time-dependent perturbation theory is employed in combination with single-sided Feynman diagrams to evaluate two contributions arising from static field-free and field-induced processes. It is found that, in addition to the coherent term, an incoherent process exists for sum-frequency generation in liquids. Surprisingly, in the case of dc-field-induced second-harmonic generation, the incoherent contribution is found to always vanish for isotropic chiral liquids even though hyper-Rayleigh second-harmonic generation and electric-field-induced second-harmonic generation are both independently symmetry allowed in any liquid.
pf Fischer, P., Salam, A. Molecular QED of coherent and incoherent sum-frequency and second-harmonic generation in chiral liquids in the presence of a static electric field MOLECULAR PHYSICS, 108(14):1857-1868, 2010 (article)
Chiral molecules split light: Reflection and refraction in a chiral liquid
Ghosh, A., Fischer, P.
PHYSICAL REVIEW LETTERS, 97(17), 2006, Featured highlight 'Fundamental optical physics: Refraction' Nature Photonics, Nov. 2006. (article)
A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes.
Featured highlight 'Fundamental optical physics: Refraction' Nature Photonics, Nov. 2006.
pf Ghosh, A., Fischer, P. Chiral molecules split light: Reflection and refraction in a chiral liquid PHYSICAL REVIEW LETTERS, 97(17), 2006, Featured highlight 'Fundamental optical physics: Refraction' Nature Photonics, Nov. 2006. (article)
Direct chiral discrimination in NMR spectroscopy
Buckingham, A., Fischer, P.
CHEMICAL PHYSICS, 324(1):111-116, 2006 (article)
Conventional nuclear magnetic resonance spectroscopy is unable to distinguish between the two mirror-image forms (enantiomers) of a chiral molecule. This is because the NMR spectrum is determined by the chemical shifts and spin-spin coupling constants which - in the absence of a chiral solvent - are identical for the two enantiomers. We discuss how chirality may nevertheless be directly detected in liquid-state NMR spectroscopy: In a chiral molecule, the rotating nuclear magnetic moment induces an electric dipole moment in the direction perpendicular to itself and to the permanent magnetic field of the spectrometer. We present computations of the precessing electric polarization following a pi/2 pulse. Our estimates indicate that the electric polarization should be detectable in favourable cases. We also predict that application of an electrostatic field induces a chirally sensitive magnetization oscillating in the direction of the permanent magnetic field. We show that the electric-field-perturbed chemical shift tensor, the nuclear magnetic shielding polarizability, underlies these chiral NMR effects. (c) 2005 Elsevier B.V. All rights reserved.
pf Buckingham, A., Fischer, P. Direct chiral discrimination in NMR spectroscopy CHEMICAL PHYSICS, 324(1):111-116, 2006 (article)
Ring-resonator-based frequency-domain optical activity measurements of a chiral liquid
Vollmer, F., Fischer, P.
OPTICS LETTERS, 31(4):453-455, 2006 (article)
Chiral liquids rotate the plane of polarization of linearly polarized light and are therefore optically active. Here we show that optical rotation can be observed in the frequency domain. A chiral liquid introduced in a fiber-loop ring resonator that supports left and right circularly polarized modes gives rise to relative frequency shifts that are a direct measure of the liquid's circular birefringence and hence of its optical activity. The effect is in principle not diminished if the circumference of the ring is reduced. The technique is similarly applicable to refractive index and linear birefringence measurements. (c) 2006 Optical Society of America.
pf Vollmer, F., Fischer, P. Ring-resonator-based frequency-domain optical activity measurements of a chiral liquid OPTICS LETTERS, 31(4):453-455, 2006 (article)
Sign of the refractive index in a gain medium with negative permittivity and permeability
Chen, Y., Fischer, P., Wise, F.
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 23(1):45-50, 2006 (article)
We show how the sign of the refractive index in any medium may be derived using a rigorous analysis based on Einstein causality. In particular, we consider left-handed materials, i.e., media that have negative permittivities and permeabilities at the frequency of interest. We find that the consideration of gain in such media can give rise to a positive refractive index. (c) 2006 Optical Society of America.
pf Chen, Y., Fischer, P., Wise, F. Sign of the refractive index in a gain medium with negative permittivity and permeability JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 23(1):45-50, 2006 (article)
Chemical Nanomotors at the Gram Scale Form a Dense Active Optorheological Medium
(article)
pf Chemical Nanomotors at the Gram Scale Form a Dense Active Optorheological Medium (article)
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