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- ItemImpact of the precursor chemistry and process conditions on the cell-to-cell variability in 1T-1R based HfO2 RRAM devices(London : Nature Publishing Group, 2018) Grossi, A.; Perez, E.; Zambelli, C.; Olivo, P.; Miranda, E.; Roelofs, R.; Woodruff, J.; Raisanen, P.; Li, W.; Givens, M.; Costina, I.; Schubert, M.A.; Wenger, C.The Resistive RAM (RRAM) technology is currently in a level of maturity that calls for its integration into CMOS compatible memory arrays. This CMOS integration requires a perfect understanding of the cells performance and reliability in relation to the deposition processes used for their manufacturing. In this paper, the impact of the precursor chemistries and process conditions on the performance of HfO2 based memristive cells is studied. An extensive characterization of HfO2 based 1T1R cells, a comparison of the cell-to-cell variability, and reliability study is performed. The cells’ behaviors during forming, set, and reset operations are monitored in order to relate their features to conductive filament properties and process-induced variability of the switching parameters. The modeling of the high resistance state (HRS) is performed by applying the Quantum-Point Contact model to assess the link between the deposition condition and the precursor chemistry with the resulting physical cells characteristics.
- ItemDoppler-free spectroscopy with a terahertz quantum-cascade laser(Washington, DC : Optical Society of America, 2018) Wienold, M.; Alam, T.; Schrottke, L.; Grahn, H.T.; Hübers, H.-W.We report on the Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum-cascade laser and an absorption cell in a collinear pump-probe configuration. A Lamb dip with a sub-Doppler linewidth of 170 kHz is observed for a rotational transition of HDO. We found that a certain level of external optical feedback is tolerable as long as the free spectral range of the external cavity is large compared to the width of the absorption line.
- ItemMicrofluidic Cultivation and Laser Tweezers Raman Spectroscopy of E. coli under Antibiotic Stress(Basel : MDPI, 2018) Pilát, Zdeněk; Bernatová, Silvie; Ježek, Jan; Kirchhoff, Johanna; Tannert, Astrid; Neugebauer, Ute; Samek, Ota; Zemánek, PavelAnalyzing the cells in various body fluids can greatly deepen the understanding of the mechanisms governing the cellular physiology. Due to the variability of physiological and metabolic states, it is important to be able to perform such studies on individual cells. Therefore, we developed an optofluidic system in which we precisely manipulated and monitored individual cells of Escherichia coli. We tested optical micromanipulation in a microfluidic chamber chip by transferring individual bacteria into the chambers. We then subjected the cells in the chambers to antibiotic cefotaxime and we observed the changes by using time-lapse microscopy. Separately, we used laser tweezers Raman spectroscopy (LTRS) in a different micro-chamber chip to manipulate and analyze individual cefotaxime-treated E. coli cells. Additionally, we performed conventional Raman micro-spectroscopic measurements of E. coli cells in a micro-chamber. We found observable changes in the cellular morphology (cell elongation) and in Raman spectra, which were consistent with other recently published observations. The principal component analysis (PCA) of Raman data distinguished between the cefotaxime treated cells and control. We tested the capabilities of the optofluidic system and found it to be a reliable and versatile solution for this class of microbiological experiments.
- ItemElectrical and optical properties of epitaxial binary and ternary GeTe-Sb2Te3 alloys(London : Nature Publishing, 2018) Boschker, Jos E.; Lü, Xiang; Bragaglia, Valeria; Wang,Ruining; Grahn, Holger T.; Calarco, RaffaellaPhase change materials such as pseudobinary GeTe-Sb2Te3 (GST) alloys are an essential part of existing and emerging technologies. Here, we investigate the electrical and optical properties of epitaxial phase change materials: α-GeTe, Ge2Sb2Te5 (GST225), and Sb2Te3. Temperature-dependent Hall measurements reveal a reduction of the hole concentration with increasing temperature in Sb2Te3 that is attributed to lattice expansion, resulting in a non-linear increase of the resistivity that is also observed in GST225. Fourier transform infrared spectroscopy at room temperature demonstrates the presence of electronic states within the energy gap for α-GeTe and GST225. We conclude that these electronic states are due to vacancy clusters inside these two materials. The obtained results shed new light on the fundamental properties of phase change materials such as the high dielectric constant and persistent photoconductivity and have the potential to be included in device simulations.
- ItemCarbon chloride-core fibers for soliton mediated supercontinuum generation(Washington D.C. : Optical Society of America, 2018) Chemnitz, Mario; Gaida, Christian; Gebhardt, Martin; Stutzki, Fabian; Kobelke, Jens; Tünnermann, Andreas; Limpert, Jens; Schmidt, Markus A.We report on soliton-fission mediated infrared supercontinuum generation in liquid-core step-index fibers using highly transparent carbon chlorides (CCl4, C2Cl4). By developing models for the refractive index dispersions and nonlinear response functions, dispersion engineering and pumping with an ultrafast thulium fiber laser (300 fs) at 1.92 μm, distinct soliton fission and dispersive wave generation was observed, particularly in the case of tetrachloroethylene (C2Cl4). The measured results match simulations of both the generalized and a hybrid nonlinear Schrödinger equation, with the latter resembling the characteristics of non-instantaneous medium via a static potential term and representing a simulation tool with substantially reduced complexity. We show that C2Cl4 has the potential for observing non-instantaneous soliton dynamics along meters of liquid-core fiber opening a feasible route for directly observing hybrid soliton dynamics.
- ItemUsing machine-learning to optimize phase contrast in a low-cost cellphone microscope(San Francisco, CA : Public Library of Science, 2018) Diederich, Benedict; Wartmann, Rolf; Schadwinkel, Harald; Heintzmann, RainerCellphones equipped with high-quality cameras and powerful CPUs as well as GPUs are widespread. This opens new prospects to use such existing computational and imaging resources to perform medical diagnosis in developing countries at a very low cost. Many relevant samples, like biological cells or waterborn parasites, are almost fully transparent. As they do not exhibit absorption, but alter the light’s phase only, they are almost invisible in brightfield microscopy. Expensive equipment and procedures for microscopic contrasting or sample staining often are not available. Dedicated illumination approaches, tailored to the sample under investigation help to boost the contrast. This is achieved by a programmable illumination source, which also allows to measure the phase gradient using the differential phase contrast (DPC) [1, 2] or even the quantitative phase using the derived qDPC approach [3]. By applying machine-learning techniques, such as a convolutional neural network (CNN), it is possible to learn a relationship between samples to be examined and its optimal light source shapes, in order to increase e.g. phase contrast, from a given dataset to enable real-time applications. For the experimental setup, we developed a 3D-printed smartphone microscope for less than 100 $ using off-the-shelf components only such as a low-cost video projector. The fully automated system assures true Koehler illumination with an LCD as the condenser aperture and a reversed smartphone lens as the microscope objective. We show that the effect of a varied light source shape, using the pre-trained CNN, does not only improve the phase contrast, but also the impression of an improvement in optical resolution without adding any special optics, as demonstrated by measurements.
- ItemMicro-fluorescene lifetime and spectral imaging of ytterbium doped laser materials(Washington D.C. : Optical Society of America, 2018) Schreiber, T.; Kuhn, S.; Feldkamp, G.; Schuster, Kay; Hein, S.; Eberhardt, Ramona; Tünnermann, AndreasWe present the application of a confocal fluorescence microscope to the analysis of Yb-doped solid-state laser materials, with examples of Yb-doped crystals, photonic crystal fibers and fiber preforms made with different manufacturing processes. Beside the fluorescence lifetime image itself, a microscopic spectral fluorescence emission analysis is presented and spatially resolved emission cross sections are obtained. Doping concentration and its distributions and other laser optical parameters are measured, which help to analyze manufacturing steps. Further properties like photodarkening and saturation are addressed.
- ItemImplementation of safe-by-design for nanomaterial development and safe innovation: Why we need a comprehensive approach(Basel : MDPI, 2018) Kraegeloh, Annette; Suarez-Merino, Blanca; Sluijter, Teun; Micheletti, ChristianManufactured nanomaterials (MNMs) are regarded as key components of innovations in various fields with high potential impact (e.g., energy generation and storage, electronics, photonics, diagnostics, theranostics, or drug delivery agents). Widespread use of MNMs raises concerns about their safety for humans and the environment, possibly limiting the impact of the nanotechnology-based innovation. The development of safe MNMs and nanoproducts has to result in a safe as well as functional material or product. Its safe use, and disposal at the end of its life cycle must be taken into account too. However, not all MNMs are similarly useful for all applications, some might bear a higher hazard potential than others, and use scenarios could lead to different exposure probabilities. To improve both safety and efficacy of nanotechnology, we think that a new proactive approach is necessary, based on pre-regulatory safety assessment and dialogue between stakeholders. On the basis of the work carried out in different European Union (EU) initiatives, developing and integrating MNMs Safe-by-Design and Trusted Environments (NANoREG, ProSafe, and NanoReg2), we present our point of view here. This concept, when fully developed, will allow for cost effective industrial innovation, and an exchange of key information between regulators and innovators. Regulators are thus informed about incoming innovations in good time, supporting a proactive regulatory action. The final goal is to contribute to the nanotechnology governance, having faster, cheaper, effective, and safer nano-products on the market.
- ItemPatterned illumination single molecule localization microscopy (piSMLM): user defined blinking regions of interest cellSTORM - Cost-effective Super-Resolution on a Cellphone using dSTORM(Washington D.C. : Optical Society of America, 2018) Chen, S.-Y.; Bestvater, F.; Heintzmann, Rainer; Cremer, ChristophSingle molecule localization microscopy (SMLM) has been established as an important super-resolution technique for studying subcellular structures with a resolution down to a lateral scale of 10 nm. Usually samples are illuminated with a Gaussian shaped beam and consequently insufficient irradiance on the periphery of the illuminated region leads to artifacts in the reconstructed image which degrades image quality. We present a newly developed patterned illumination SMLM (piSMLM) to overcome the problem of uneven illumination by computer-generated holography. By utilizing a phase-only spatial light modulator (SLM) in combination with a modified Gerchberg-Saxton algorithm, a user-defined pattern with homogeneous and nearly speckle-free illumination is obtained. Our experimental results show that irradiance 1 to 5 kW/cm2 was achieved by using a laser with an output power of 200 mW in a region of 2000 µm2 to 500 µm2, respectively. Higher irradiance of up to 20 kW/cm2 can be reached by simply reducing the size of the region of interest (ROI). To demonstrate the application of the piSMLM, nuclear structures were imaged based on fluctuation binding-activated localization microscopy (fBALM). The super-resolution fBALM images revealed nuclear structures at a nanometer scale.Single molecule localization microscopy (SMLM) has been established as an important super-resolution technique for studying subcellular structures with a resolution down to a lateral scale of 10 nm. Usually samples are illuminated with a Gaussian shaped beam and consequently insufficient irradiance on the periphery of the illuminated region leads to artifacts in the reconstructed image which degrades image quality. We present a newly developed patterned illumination SMLM (piSMLM) to overcome the problem of uneven illumination by computer-generated holography. By utilizing a phase-only spatial light modulator (SLM) in combination with a modified Gerchberg-Saxton algorithm, a user-defined pattern with homogeneous and nearly speckle-free illumination is obtained. Our experimental results show that irradiance 1 to 5 kW/cm2 was achieved by using a laser with an output power of 200 mW in a region of 2000 µm2 to 500 µm2, respectively. Higher irradiance of up to 20 kW/cm2 can be reached by simply reducing the size of the region of interest (ROI). To demonstrate the application of the piSMLM, nuclear structures were imaged based on fluctuation binding-activated localization microscopy (fBALM). The super-resolution fBALM images revealed nuclear structures at a nanometer scale.
- ItemOrdered states in the Kitaev-Heisenberg model: From 1D chains to 2D honeycomb(London : Nature Publishing Group, 2018) Agrapidis, Cliò Efthimia; van den Brink, Jeroen; Nishimoto, SatoshiWe study the ground state of the 1D Kitaev-Heisenberg (KH) model using the density-matrix renormalization group and Lanczos exact diagonalization methods. We obtain a rich ground-state phase diagram as a function of the ratio between Heisenberg (J = cosϕ) and Kitaev (K = sinϕ) interactions. Depending on the ratio, the system exhibits four long-range ordered states: ferromagnetic-z, ferromagnetic-xy, staggered-xy, Néel-z, and two liquid states: Tomonaga-Luttinger liquid and spiral-xy. The two Kitaev points ϕ=π2 and φ=3π2 are singular. The ϕ-dependent phase diagram is similar to that for the 2D honeycomb-lattice KH model. Remarkably, all the ordered states of the honeycomb-lattice KH model can be interpreted in terms of the coupled KH chains. We also discuss the magnetic structure of the K-intercalated RuCl3, a potential Kitaev material, in the framework of the 1D KH model. Furthermore, we demonstrate that the low-lying excitations of the 1D KH Hamiltonian can be explained within the combination of the known six-vertex model and spin-wave theory.