Microscopic Probe Research Articles

Modification of magnetic fluctuations by interfacial interactions in artificially engineered heavy-fermion superlattices

Recent progress in the fabrication techniques of superlattices (SLs) has made it possible to sandwich several-layer-thick block layers (BLs) of heavy-fermion superconductor CeCoIn5 between conventional-metal YbCoIn5 BLs or spin-density-wave-metal CeRhIn5 BLs of a similar thickness. However, the magnetic state in each BL, particularly at the interface, is not yet understood, as experimental techniques applicable to the SL system are limited. Here, we report measurements of 59Co nuclear magnetic resonance, which is a microscopic probe of the magnetic properties inside the target BLs. In the CeCoIn5/YbCoIn5 SL, the low-temperature magnetic fluctuations of the CeCoIn5 BL are weakened as expected from the Rashba spin-orbit effect. However, in the CeCoIn5/CeRhIn5 SL, the fluctuations show an anomalous enhancement below 6 K, highlighting the importance of the magnetic proximity effect occurring near a magnetic-ordering temperature TN ~ 3 K of the CeRhIn5 BL. We suggest that the magnetic properties of the BLs can be altered by the interfacial interaction, which is an alternative route to modify the magnetic properties.

Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity.

Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.

Fluorescence Lifetime Imaging of p-tau Protein in Single Neuron with a Highly Selective Fluorescent Probe.

Hyperphosphorylated tau (p-tau) protein is one of the key markers of Alzheimer's disease (AD). However, a lack of analytical methods for p-tau protein with high selectivity and accuracy is the bottleneck to understand the pathological processes of AD. In the present work, a highly selective fluorescence lifetime imaging microscopic (FLIM) probe (τ-p-tau) was rationally designed and developed for determination of p-tauprotein, in which binuclear zinc units were designed as the recognition groups, and an improved cyanine was synthesized as the dye unit. The FLIM measurement is independent of the concentration of fluorescent probes, irradiation light sources, and measurement environments. Meanwhile, the developed τ-p-tau probe demonstrated strong affinity toward p-tau protein, thus enhancing the selectivity of determination of p-tau protein against Aβ, Aβ fibril, tau, protein kinases, ATP, and so on. The fluorescence lifetime of τ-p-tau probe showed a good linearity with the concentration of p-tau protein from 1.0 to 5.0 μM with a low detection limit of 85.15 ± 0.03 nM. The response time of the present probe for p-tau protein was estimated to be less than 6.2 s. Furthermore, taking the advantages of low toxicity and good biocompatibility, the developed probe was successfully applied to monitor the fluctuation of concentration of p-tau protein by FLIM imaging at single neuron level. It was found that the concentration of p-tau protein inside live neurons obviously changed upon oxidative stress.

Two-dimensional triangular-lattice Cu(OH)Cl, belloite, as a magnetodielectric system

Quantum spins on a triangular lattice may bring out intriguing and exotic quantum ground states. Here we report a magnetodielectric system of CuOHCl wherein $S=1/2\mathrm{C}{\mathrm{u}}^{2+}$ spins constitute a two-dimensional triangular lattice with the layers weakly coupled via Cl-H-O bonding. Despite strong magnetic interactions, as expected from the relatively high value of ${\ensuremath{\theta}}_{\mathrm{CW}}=\ensuremath{-}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, antiferromagnetic transition occurred at ${T}_{N}=11\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, followed by an uprising turn of the magnetic susceptibility below \ensuremath{\sim}7 K. Neutron-diffraction experiment revealed a coplanar spin structure on the triangular lattice below the ${T}_{N}$, with each spin pointing toward the center of a triangle. Of the three spins on a triangle, two are antiparallel and the third one is angled ${120}^{\ensuremath{\circ}}$ to the antiparallel spins. A concerted effect of geometric frustration in the triangular lattice and superexchange interactions through a zig-zag path via double Cu-O-Cu and double Cu-Cl-Cu bridges counted for this spin arrangement. Further investigation using dielectric constant and heat capacity measurements, as well as a microscopic probe of muon spin rotation, revealed a magnetodielectric effect and the possibility of multiferroic transition at ${T}^{*}\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is suspected to be in close relation to geometric frustration in this triangular lattice. The present paper presents a magnetodielectric system on a two-dimensional triangular lattice with chemical stoichiometry. It can also serve as a rare reference to the hotly debated quantum spin-orbital liquid compound $\mathrm{LiNi}{\mathrm{O}}_{2}$.

Effect of low Zn doping on the Verwey transition in magnetite single crystals: Mössbauer spectroscopy and x-ray diffraction

To observe, by microscopic probe, how low Zn doping in $\mathrm{F}{\mathrm{e}}_{3\ensuremath{-}x}\mathrm{Z}{\mathrm{n}}_{x}{\mathrm{O}}_{4}$ ($x$ is below 1%) changes the Verwey transition, we have performed M\"ossbauer spectroscopy measurements on three single crystalline samples with various Zn doping. In spectra analysis we used the recently published model of M\"ossbauer data treatment formulated as a result of ab initio calculations for a low-temperature monoclinic structure (of Cc symmetry) of magnetite. It was suggested there that the hyperfine parameters for all 24 Fe distinct positions in the lattice can be grouped into four major components with very similar hyperfine parameters within each set. Using these parameters as starting values, very good fits were obtained for magnetite with low doping level, while for higher doping, $x=0.03$, where the Verwey transition changes its character, one component is significantly different. In particular, low hyperfine field ${B}_{\mathrm{eff}}=36\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, considered as a characteristic feature of the Cc phase spectrum, is absent here. Also, in this case, the high-temperature spectra are different from those for lower doped magnetite showing more pronounced continuous alteration with temperature. This might be due to crystal structure of lower than Fd-3m symmetry, a fact suggested by our x-ray synchrotron studies. All this triggered a discussion about an experimental fingerprint for the difference between these two classes of magnetite, frequently referred to as magnetite of first- and second-order Verwey transition, and about the electronic structure of both kinds of systems.

Effects of Moisture-Based Grain Boundary Passivation on Cell Performance and Ionic Migration in Organic-Inorganic Halide Perovskite Solar Cells.

Because of the polycrystalline nature, grain boundaries (GBs) in hybrid perovskite thin films play critical roles in determining the charge collection efficiency of perovskite solar cells (PSCs), material stability, and in particular the ion migration, considering their relatively soft ionic bonds with low formation energy. Different GB passivation methods are being studied, and introducing PbI2-rich phase at GBs in methylammonium lead iodide (MAPbI3) has been found to be useful. In this study, combining macroscale measurements with tip-based microscopic probing that includes scanning Kelvin probe microscopy for surface potential mapping and conductive atomic force microscopy for charge transport mapping, we revealed the effects of PbI2-rich phase at GBs, which was introduced in moisture-assisted synthesis of MAPbI3 thin films. It was found that PbI2 passivation of GBs could change the surface potential and charge carrier screening and significantly retard current conduction at the GB while enhancing conduction through the grain interior. Inhibition of ion migration at GBs, as well as enhanced PSC device performance, is reported.

Raman, AFM and SNOM high resolution imaging of carotene crystals in a model carrot cell system

Three non-destructive and complementary techniques, Raman imaging, Atomic Force Microscopy and Scanning Near-field Optical Microscopy were used simultaneously to show for the first time chemical and structural differences of carotenoid crystals. Spectroscopic and microscopic scanning probe measurements were applied to the released crystals or to crystals accumulated in a unique, carotenoids rich callus tissue growing in vitro that is considered as a new model system for plant carotenoid research. Three distinct morphological crystal types of various carotenoid composition were identified, a needle-like, rhomboidal and helical. Raman imaging using 532 and 488 nm excitation lines provided evidence that the needle-like and rhomboidal crystals had similar carotenoid composition and that they were composed mainly of β-carotene accompanied by α-carotene. However, the presence of α-carotene was not identified in the helical crystals, which had the characteristic spatial structure. AFM measurements of crystals identified by Raman imaging revealed the crystal topography and showed the needle-like and rhomboidal crystals were planar but they differed in all three dimensions. Combining SNOM and Raman imaging enabled indication of carotenoid rich structures and visualised their distribution in the cell. The morphology of identified subcellular structures was characteristic for crystalline, membraneous and tubular chromoplasts that are plant organelles responsible for carotenoid accumulation in cells.

Aluminum and gallium nuclei as microscopic probes for pulsed electron-nuclear double resonance diagnostics of electric-field gradient and spin density in garnet ceramics doped with paramagnetic ions

The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest environment of impurity ions Mn2+ and Ce3+ in garnets made it possible to use hyperfine and quadrupole interactions with these ions to determine the spatial distribution of the unpaired electron and the gradient of the electric field at the sites of aluminum and gallium in the garnet lattice. High-frequency (94 GHz) electron spin echo detected electron paramagnetic resonance and electron-nuclear double resonance measurements have been performed. Large difference in the electric field gradient and quadrupole splitting at octahedral and tetrahedral sites allowed identifying the positions of aluminum and gallium ions in the garnet lattice and proving that gallium first fills tetrahedral positions in mixed aluminum-gallium garnets. This should be taken into account in the development of garnet-based scintillators and lasers. It is shown that the electric field gradient at aluminum nuclei near Mn2+ possessing an excess negative charge in the garnet lattice is ca. 2.5 times larger than on aluminum nuclei near Ce3+.

Sb121,123nuclear quadrupole resonance as a microscopic probe in the Te-doped correlated semimetalFeSb2: Emergence of electronic Griffith phase, magnetism, and metallic behavior

$^{121,123}Sb$ nuclear quadrupole resonance (NQR) was applied to $Fe(Sb_{1-x}Te_x)_2$ in the low doping regime (\emph{x = 0, 0.01} and \emph{0.05}) as a microscopic zero field probe to study the evolution of \emph{3d} magnetism and the emergence of metallic behavior. Whereas the NQR spectra itself reflects the degree of local disorder via the width of the individual NQR lines, the spin lattice relaxation rate (SLRR) $1/T_1(T)$ probes the fluctuations at the $Sb$ - site. The fluctuations originate either from conduction electrons or from magnetic moments. In contrast to the semi metal $FeSb_2$ with a clear signature of the charge and spin gap formation in $1/T_1(T)T ( \sim exp/ (\Delta k_BT) ) $, the 1\% $Te$ doped system exhibits almost metallic conductivity and a almost filled gap. A weak divergence of the SLRR coefficient $1/T_1(T)T \sim T^{-n} \sim T^{-0.2}$ points towards the presence of electronic correlations towards low temperatures wheras the \textit{5\%} $Te$ doped sample exhibits a much larger divergence in the SLRR coefficient showing $1/T_1(T)T \sim T^{-0.72} $. According to the specific heat divergence a power law with $n\ =\ 2\ m\ =\ 0.56$ is expected for the SLRR. Furthermore $Te$-doped $FeSb_2$ as a disordered paramagnetic metal might be a platform for the electronic Griffith phase scenario. NQR evidences a substantial asymmetric broadening of the $^{121,123}Sb$ NQR spectrum for the \emph{5\%} sample. This has purely electronic origin in agreement with the electronic Griffith phase and stems probably from an enhanced $Sb$-$Te$ bond polarization and electronic density shift towards the $Te$ atom inside $Sb$-$Te$ dumbbell.

Non-equilibrium pair interactions in colloidal dispersions

We study non-equilibrium pair interactions between microscopic particles moving through a model shear-thinning fluid. Prior efforts to model pair interactions in non-Newtonian fluids have largely focused on constitutive models derived from polymer-chain kinetic theories focusing on conformational degrees of freedom, but neglecting the details of microstructural evolution beyond a single polymer length scale. To elucidate the role of strong structural distortion in mediating pair interactions in Brownian suspensions, we formulate and solve a Smoluchowski equation describing the detailed evolution of the particle configuration between and around a pair of microscopic probes driven at fixed velocity by an external force through a colloidal dispersion. To facilitate analysis, we choose a model system of Brownian hard spheres that do not interact hydrodynamically; while simple, this ‘freely draining’ model permits insight into connections between microstructure and rheology. The flow induces a non-equilibrium particle density gradient that gives rise to both viscous drag and an interactive force between the probes. The drag force acts to slow the centre-of-mass velocity of the pair, while the interactive force arising from osmotic pressure gradients can lead to attraction or repulsion, as well as deterministic reorientation of the probes relative to the external force. The degree to which the microstructure is distorted, and the shape of that distortion, depend on the arrangement of the probes relative to one another and their orientation to the driving force. It also depends on the magnitude of probe velocity relative to the Brownian velocity of the suspension. When only thermal fluctuations set probe velocity, the equilibrium depletion attraction is recovered. For weak forcing, long-ranged interactions mediated via the bath-particle flux give rise to entropic forces on the probes. The linear response is a viscous drag that slows forward motion; only the weakly nonlinear response can produce relative motion–attraction, repulsion or reorientation of the probes. We derive entropic coupling tensors, similar in ethos to pair hydrodynamic tensors, to describe this behaviour. The structural symmetry that permits this analogy is lost when forcing becomes strong, revealing instabilities in system behaviour. Far from equilibrium, the interactive force depends explicitly on the initial probe separation, orientation and strength of forcing; widely spaced probes interact through the distorted microstructure, whereas the behaviour of closely spaced probes is largely set by excluded-volume effects. In this regime, a pair of closely spaced probes sedimenting side-by-side tend to attract and reorient to permit alignment of their line-of-centres with the flow, while widely spaced probes fall without reorienting. Our results show qualitative agreement with experimental observations and provide a potential connection to the observed column instability in shear-thinning fluids.

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li1.17–xNi0.21Co0.08Mn0.54O2, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

Microscopic Dynamics of Li+ in Rutile TiO2 Revealed by 8Li β-Detected Nuclear Magnetic Resonance

We report measurements of the dynamics of isolated $^{8}$Li$^{+}$ in single crystal rutile TiO$_{2}$ using $\beta$-detected NMR. From spin-lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K; and one at higher temperatures. At low temperature, the activation barrier is $26.8(6)$ meV with prefactor $1.23(5) \times 10^{10}$ s$^{-1}$. We suggest this is unrelated to Li$^{+}$ motion, and rather is a consequence of electron polarons in the vicinity of the implanted $^{8}$Li$^{+}$ that are known to become mobile in this temperature range. Above 100 K, Li$^{+}$ undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of $0.32(2)$ eV and $1.0(5) \times 10^{16}$ s$^{-1}$, in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li$^{+}$ concentration does not limit the diffusivity even up to high concentrations, but that some key ingredient is missing in the calculations of the migration barrier. The anomalous prefactors provide further insight into both Li$^{+}$ and polaron motion.

Phase Transitions of the Ionic Liquid [C2C1im][NTf2] under High Pressure: A Synchrotron X-ray Diffraction and Raman Microscopy Study

The interplay between crystallization and glass transition in the archetypal ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2C1im][NTf2], has been studied as a function of pressure up to ca. 12 GPa. Besides heterogeneous crystal nucleation, homogeneous nucleation in the sample inside the diamond anvil cell was also observed depending on compression/decompression rate. Amorphization of the crystal and glass formation under pressure has been followed by synchrotron X-ray diffraction. The characteristic Raman bands of the [NTf2]− anion provide a microscopic probe of the different phases. The crystalline phase is composed of the [NTf2]− cisoid conformer, but moisture implies formation of crystal with the transoid conformer. Raman spectra show that crystalline phases might become microscopically heterogeneous because of [NTf2]− conformational disorder. Raman mapping reveals the order–disorder evolution from crystal to glass. Crystals of [C2C1im][NTf2] formed under high pressure and room temperature are similar to previously reported low temperature and atmospheric pressure crystals. Thus, it is concluded that density is the main factor controlling crystallization and glass formation under high pressure of [NTf2]− based ionic liquids due to hindrance of efficient ion packing. The results highlight that ionic liquids are good models to understand fundamental questions related to the mechanism of crystallization and glass transition.

A nanobiosensing method based on force measurement of antibody-antigen interaction for direct detection of enterovirus 71 by the chemically modified atomic force microscopic probe

Hand, Foot and mouth disease (HFMD) is a common disease with high infectivity for children, and enterovirus 71 (EV71) is one of the main pathogens to cause the type of illness. Therefore, the aim of this study was to propose a rapid and effective technique for detecting EV71 directly based on the mechanism of biological intermolecular force by using atomic force microscopy (AFM). At first, we coated EV71 particles on the mica surface and made the EV71 antibodies (anti-EV71) fixed on the AFM tip by means of several chemical procedures. Then, AFM chemically modified tip was applied to measure the unbinding forces between EV71 and anti-EV71 by contact mode. Finally, by using AFM imaging calculating software, the EV71 particle size (mean±SD) was 31.36±3.87 nm (n = 200) and this result was concordance with previous literature. Besides, the force (mean±SD) between EV71 antigen and antibody complex was 336.9±64.7 pN. The force (mean±SD) between anti-EV71 and non-specific specimens was 47.1±15.1 pN and was significantly smaller (P < 0.05). Apparently, the results show that we can precisely identify EV71 infection among the samples by measuring the force magnitude and observing the occurrence of EV71/anti-EV71 unbinding events. Therefore, the combination of AFM system and the chemically modified tip has the potential to be a rapid and effective method for detecting EV71 directly.

Shallow Heavily Doped n++ Germanium by Organo-Antimony Monolayer Doping.

Functionalization of Ge surfaces with the aim of incorporating specific dopant atoms to form high-quality junctions is of particular importance for the development of solid-state devices. In this study, we report the shallow doping of Ge wafers with a monolayer doping strategy that is based on the controlled grafting of Sb precursors and the subsequent diffusion of Sb into the wafer upon annealing. We also highlight the key role of citric acid in passivating the surface before its reaction with the Sb precursors and the benefit of a protective SiO2 overlayer that enables an efficient incorporation of Sb dopants with a concentration higher than 1020 cm-3. Microscopic four-point probe measurements and photoconductivity experiments show the full electrical activation of the Sb dopants, giving rise to the formation of an n++ Sb-doped layer and an enhanced local field-effect passivation at the surface of the Ge wafer.

Experimental and analytical investigations of vibrational behavior of U-shaped atomic force microscope probe considering thermal loading and the modified couple stress theory

In this study, experimental and analytical models of a U-shaped atomic force microscopic (AFM) probe are studied based on the modified couple stress theory (MCST). The experimental setup is a commercially fabricated U-shaped probe AN2-300 mounted in the atomic force microscope afm+ system. In the analytical model, the U-shaped probe of the AFM is simulated as a three-beam model (TBM). The governing equations of motion and boundary conditions are obtained by combination of basic equations of the modified couple stress theory and Hamilton’s principle. It is found that the natural frequencies of the AFM predicted by the MCST are size-dependent. The difference between the natural frequencies predicted by the MCST and the classical beam model is very significant when the ratio of characteristic size to internal material length scale parameter is approximately equal to one, but it is diminishing with increase in the ratio. In order to validate the results, the mathematical and experimental models have been compared with each other. It is seen that the analytical model based on MCST has excellent agreement with experimental results. Also, the natural frequencies of the probe have been obtained for different temperature values, aspect ratios, and small scale factor amounts. The results show, natural frequency decrease with increase in temperature value.

Torque measurements during the spontaneous unbraiding of DNA molecules in the absence of pulling forces

We present an improved version of the magnetic tweezers/viscous drag (MTVD) hybrid assay that allows dynamic torque measurements during the spontaneous relaxation of DNA braids. The method relies on the ability of pairs of DNA molecules to rotate a microscopic probe attached to their upper ends using the elastic energy stored when braided. Digital tracking of the rotation of the dumbbell against the viscous drag allowed estimation of the torque exerted by the molecules. The unwinding dynamics of DNA braids against different amounts of viscous drag was characterized employing probes of two different sizes. We identified and characterized different perturbations that may affect the unbraiding dynamics. Estimates of the torques associated to the process of DNA unbraiding are reported.

Raman spectroscopy of biomedical polyethylenes.

With the development of three-dimensional Raman algorithms for local mapping of oxidation and plastic strain, and the ability to resolve molecular orientation patterns with microscopic spatial resolution, there is an opportunity to re-examine many of the foundations on which our understanding of biomedical grade ultra-high molecular weight polyethylenes (UHMWPEs) are based. By implementing polarized Raman spectroscopy into an automatized tool with an improved precision in non-destructively resolving Euler angles, oxidation levels, and microscopic strain, we become capable to make accurate and traceable measurements of the in vitro and in vivo tribological responses of a variety of commercially available UHMWPE bearings for artificial hip and knee joints. In this paper, we first review the foundations and the main algorithms for Raman analyses of oxidation and strain of biomedical polyethylene. Then, we critically re-examine a large body of Raman data previously collected on different polyethylene joint components after in vitro testing or in vivo service, in order to shed new light on an area of particular importance to joint orthopedics: the microscopic nature of UHMWPE surface degradation in the human body. A complex scenario of physical chemistry appears from the Raman analyses, which highlights the importance of molecular-scale phenomena besides mere microstructural changes. The availability of the Raman microscopic probe for visualizing oxidation patterns unveiled striking findings related to the chemical contribution to wear degradation: chain-breaking and subsequent formation of carboxylic acid sites preferentially occur in correspondence of third-phase regions, and they are triggered by emission of dehydroxylated oxygen from ceramic oxide counterparts. These findings profoundly differ from more popular (and simplistic) notions of mechanistic tribology adopted in analyzing joint simulator data. Statement of Significance This review was dedicated to the theoretical and experimental evaluation of the commercially available biomedical polyethylene samples by Raman spectroscopy with regard to their molecular textures, oxidative patterns, and plastic strain at the microscopic level in the three dimensions of the Euclidean space. The main achievements could be listed, as follow: (i) visualization of molecular patterns at the surface of UHMWPE bearings operating against metallic components; (ii) differentiation between wear and creep deformation in retrievals; (iii) non-destructive mapping of oxidative patterns; and, (iv) the clarification of chemical interactions between oxide/non-oxide ceramic heads and advanced UHMWPE liners.

Scanning probes investigate nanoscale phenomena

More than 30 years after achieving atomic resolution with scanning probe microscopes, scientists remain endlessly fascinated with the ability to “see” and study individual atoms and molecules. For years, that fascination drove researchers to devise clever ways to use these tools to do more than just record high-resolution images. They came up with numerous methods to manipulate molecules one at a time and measure chemical spectra and other properties of individual molecules. That innovation shows no sign of slowing down. In the past few months, scientists have demonstrated new ways to couple scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) with powerful tools for spectroscopy and electrochemical analysis. They’ve also come up with novel ways of improving AFMs’ and STMs’ key sensor element—a microscopic probe tip, which may be made from various metals, silicon, and other materials, depending on the application. Researchers have also developed theoretical tools that underpin

Jam Tail Warnings Based on Vehicle Probe Data

Abstract Recent research shows every so often upcoming cases of dangerous accidents happening at jam tails so that the introduction of a proper warning system is helpful to alleviate the problem. Since traffic is a highly dynamic and complex system of spatiotemporal patterns one has to have an outright understanding of the underlying phases of the real traffic to make a qualified assertion when a dangerous jam tail in a traffic pattern occurs. Kerner showed with the three-phase traffic theory an alternate approach of traffic modeling to the classical theories based on the fundamental diagram. With the help of splitting traffic into three distinct phases: free flow, synchronized flow and wide moving jams, potentially dangerous situations can be detected and identified. A method of identifying critical jam tails based on microscopic vehicle probe data and the three-phase traffic theory is proposed. With the sheer amount of vehicle probe data available today a method to identify jam fronts and detect critical jam tails has been developed and evaluated with vehicle probe data. The stable propagation of dangerous jam tails and their detection based on vehicle probe data is presented for a freeway example in the UK. It is further discussion if and how automated and autonomous vehicles can use this information to adapt the behavior to a more safe and comfortable assisted braking and increased safety at jam tails.