Propagation of priors for more accurate and efficient spectroscopic functional fits and their application to ferroelectric hysteresis

Multi-dimensional spectral-imaging is a mainstay of the scanning probe and electron microscopies, micro-Raman, and various forms of chemical imaging. In many cases, individual spectra can be fit to a specific functional form, with the model parameter maps, providing direct insight into material properties. Since spectra are often acquired across a spatial grid of points, spatially adjacent spectra are likely to be similar to one another; yet, this fact is almost never used when considering parameter estimation for functional fits. On datasets tried here, we show that by utilizing proximal information, whether it be in the spatial or spectral domains, it is possible to improve the reliability and increase the speed of such functional fits by ∼2–3×, as compared to random priors. We explore and compare three distinct new methods: (a) spatially averaging neighborhood spectra, and propagating priors based on functional fits to the averaged case, (b) hierarchical clustering-based methods where spectra are grouped hierarchically based on response, with the priors propagated progressively down the hierarchy, and (c) regular clustering without hierarchical methods with priors propagated from fits to cluster means. Our results highlight that utilizing spatial and spectral neighborhood information is often critical for accurate parameter estimation in noisy environments, which we show for ferroelectric hysteresis loops acquired on a prototypical PbTiO3 thin film with piezoresponse spectroscopy. This method is general and applicable to any spatially measured spectra where functional forms are available. Examples include exploring the superconducting gap with tunneling spectroscopy, using the Dynes formula, or current–voltage curve fits in conductive atomic force microscopy mapping. Here we explore the problem for ferroelectric hysteresis, which, given its large parameter space, constitutes a more difficult task than, for example, fitting current–voltage curves with a Schottky emission formula (Chiu 2014 Adv. Mater. Sci. Eng. 2014 578168).

Deep data analysis via physically constrained linear unmixing: universal framework, domain examples, and a community-wide platform

Many spectral responses in materials science, physics, and chemistry experiments can be characterized as resulting from the superposition of a number of more basic individual spectra. In this context, unmixing is defined as the problem of determining the individual spectra, given measurements of multiple spectra that are spatially resolved across samples, as well as the determination of the corresponding abundance maps indicating the local weighting of each individual spectrum. Matrix factorization is a popular linear unmixing technique that considers that the mixture model between the individual spectra and the spatial maps is linear. Here, we present a tutorial paper targeted at domain scientists to introduce linear unmixing techniques, to facilitate greater understanding of spectroscopic imaging data. We detail a matrix factorization framework that can incorporate different domain information through various parameters of the matrix factorization method. We demonstrate many domain-specific examples to explain the expressivity of the matrix factorization framework and show how the appropriate use of domain-specific constraints such as non-negativity and sum-to-one abundance result in physically meaningful spectral decompositions that are more readily interpretable. Our aim is not only to explain the off-the-shelf available tools, but to add additional constraints when ready-made algorithms are unavailable for the task. All examples use the scalable open source implementation from https://github.com/ramkikannan/nmflibrary that can run from small laptops to supercomputers, creating a user-wide platform for rapid dissemination and adoption across scientific disciplines.

Ultrafast current imaging by Bayesian inversion

Spectroscopic measurements of current–voltage curves in scanning probe microscopy is the earliest and one of the most common methods for characterizing local energy-dependent electronic properties, providing insight into superconductive, semiconductor, and memristive behaviors. However, the quasistatic nature of these measurements renders them extremely slow. Here, we demonstrate a fundamentally new approach for dynamic spectroscopic current imaging via full information capture and Bayesian inference. This general-mode I–V method allows three orders of magnitude faster measurement rates than presently possible. The technique is demonstrated by acquiring I–V curves in ferroelectric nanocapacitors, yielding >100,000 I–V curves in <20 min. This allows detection of switching currents in the nanoscale capacitors, as well as determination of the dielectric constant. These experiments show the potential for the use of full information capture and Bayesian inference toward extracting physics from rapid I–V measurements, and can be used for transport measurements in both atomic force and scanning tunneling microscopy.

Scanning probe microscopy is widely used to characterize material properties with atomic resolution, yet electronic property mapping is normally constrained by slow data acquisition. Somnath et al. show a current–voltage method, which enables fast electronic spectroscopy mapping over micrometer-sized areas.

Alcohol withdrawal syndrome: mechanisms, manifestations, and management

The alcohol withdrawal syndrome is a well‐known condition occurring after intentional or unintentional abrupt cessation of heavy/constant drinking in patients suffering from alcohol use disorders (AUDs). AUDs are common in neurological departments with patients admitted for coma, epileptic seizures, dementia, polyneuropathy, and gait disturbances. Nonetheless, diagnosis and treatment are often delayed until dramatic symptoms occur. The purpose of this review is to increase the awareness of the early clinical manifestations of AWS and the appropriate identification and management of this important condition in a neurological setting.

Highly mobile ferroelastic domain walls in compositionally graded ferroelectric thin films

Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructures stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.

Nanoscale mapping of heterogeneity of the polarization reversal in lead-free relaxor-ferroelectric ceramic composites

Relaxor/ferroelectric ceramic/ceramic composites have shown to be promising in generating large electromechanical strain at moderate electric fields. Nonetheless, the mechanisms of polarization and strain coupling between grains of different nature in the composites remain unclear. To rationalize the coupling mechanisms we performed advanced piezoresponse force microscopy (PFM) studies of 0.92BNT-0.06BT-0.02KNN/0.93BNT-0.07BT (ergodic/non-ergodic relaxor) composites. PFM is able to distinguish grains of different phases by characteristic domain patterns. Polarization switching has been probed locally, on a sub-grain scale. k-Means clustering analysis applied to arrays of local hysteresis loops reveals variations of polarization switching characteristics between the ergodic and non-ergodic relaxor grains. We report a different set of switching parameters for grains in the composites as opposed to the pure phase samples. Our results confirm ceramic/ceramic composites to be a viable approach to tailor the piezoelectric properties and optimize the macroscopic electromechanical characteristics.

Electrocatalysis-induced elasticity modulation in a superionic proton conductor probed by band-excitation atomic force microscopy

Variable temperature band-excitation atomic force microscopy in conjunction with I-V spectroscopy was used to investigate the crystalline superionic proton conductor CsHSO4 during proton exchange induced by a Pt-coated conductive scanning probe. At a sample temperature of 150 °C and under an applied bias <1 V, reduction currents of up to 1 nA were observed. Simultaneously, we show that the electrochemical reactions are accompanied by a reversible decrease in the elastic modulus of CsHSO4, as seen by a contact resonance shift, and find evidence for superplasticity during scanning. These effects were not observed in the room-temperature phase of CsHSO4 or in the case of catalytically inactive conductive probes, proving the utility of this technique for monitoring electrochemical processes on the nanoscale, as well as the use of local contact stiffness as a sensitive indicator of electrochemical reactions.

Quantitative 3D-KPFM imaging with simultaneous electrostatic force and force gradient detection

Kelvin probe force microscopy (KPFM) is a powerful characterization technique for imaging local electrochemical and electrostatic potential distributions and has been applied across a broad range of materials and devices. Proper interpretation of the local KPFM data can be complicated, however, by convolution of the true surface potential under the tip with additional contributions due to long range capacitive coupling between the probe (e.g. cantilever, cone, tip apex) and the sample under test. In this work, band excitation (BE)-KPFM is used to negate such effects. In contrast to traditional single frequency KPFM, multifrequency BE-KPFM is shown to afford dual sensitivity to both the electrostatic force and the force gradient detection, analogous to simultaneous amplitude modulated and frequency modulated KPFM imaging. BE-KPFM is demonstrated on a Pt/Au/SiO(x) test structure and electrostatic force gradient detection is found to lead to an improved lateral resolution compared to electrostatic force detection. Finally, a 3D-KPFM imaging technique is developed. Force volume (FV) BE-KPFM allows the tip-sample distance dependence of the electrostatic interactions (force and force gradient) to be recorded at each point across the sample surface. As such, FVBE-KPFM provides a much needed pathway towards complete tip-sample capacitive de-convolution in KPFM measurements and will enable quantitative surface potential measurements with nanoscale resolution.

Breaking the limits of structural and mechanical imaging of the heterogeneous structure of coal macerals

The correlation between local mechanical (elasto-plastic) and structural (composition) properties of coal presents significant fundamental and practical interest for coal processing and for the development of rheological models of coal to coke transformations. Here, we explore the relationship between the local structural, chemical composition, and mechanical properties of coal using a combination of confocal micro-Raman imaging and band excitation atomic force acoustic microscopy for a bituminous coal. This allows high resolution imaging (10s of nm) of mechanical properties of the heterogeneous (banded) architecture of coal and correlating them to the optical gap, average crystallite size, the bond-bending disorder of sp(2) aromatic double bonds, and the defect density. This methodology allows the structural and mechanical properties of coal components (lithotypes, microlithotypes, and macerals) to be understood, and related to local chemical structure, potentially allowing for knowledge-based modeling and optimization of coal utilization processes.

Higher order harmonic detection for exploring nonlinear interactions with nanoscale resolution

Nonlinear dynamics underpin a vast array of physical phenomena ranging from interfacial motion to jamming transitions. In many cases, insight into the nonlinear behavior can be gleaned through exploration of higher order harmonics. Here, a method using band excitation scanning probe microscopy (SPM) to investigate higher order harmonics of the electromechanical response, with nanometer scale spatial resolution is presented. The technique is demonstrated by probing the first three harmonics of strain for a Pb(Zr(1-x)Ti(x))O₃ (PZT) ferroelectric capacitor. It is shown that the second order harmonic response is correlated with the first harmonic response, whereas the third harmonic is not. Additionally, measurements of the second harmonic reveal significant deviations from Rayleigh-type models in the form of a much more complicated field dependence than is observed in the spatially averaged data. These results illustrate the versatility of n(th) order harmonic SPM detection methods in exploring nonlinear phenomena in nanoscale materials.

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

Conventional Kelvin probe force microscopy (KPFM) relies on closed loop (CL) bias feedback for the determination of surface potential (SP). However, SP measured by CL-KPFM has been shown to be strongly influenced by the choice of measurement parameters due to non-electrostatic contributions to the input signal of the bias feedback loop. This often leads to systematic errors of several hundred mV and can also result in topographical crosstalk. Here, open loop (OL)-KPFM modes are investigated as a means of obtaining a quantitative, crosstalk free measurement of the SP of graphene grown on Cu foil, and are directly contrasted with CL-KPFM. OL-KPFM operation is demonstrated in both single and multi-frequency excitation regimes, yielding quantitative SP measurements. The SP difference between single and multilayer graphene structures using OL-KPFM was found to be 63 ± 11 mV, consistent with values previously reported by CL-KPFM. Furthermore, the same relative potential difference between Al2O3-coated graphene and Al2O3-coated Cu was observed using both CL and OL techniques. We observed an offset of 55 mV between absolute SP values obtained by OL and CL techniques, which is attributed to the influence of non-electrostatic contributions to the input of the bias feedback used in CL-KPFM.

[Current cerebrospinal fluid diagnostics for pathogen-related diseases]

Cerebrospinal fluid (CSF) analysis is of utmost importance to establish an early diagnosis of central nervous system (CNS) infections and to start appropriate therapy. The CSF white cell count, lactate concentration and total protein levels are usually available very quickly even from non-specialized laboratories and the combination of these parameters often provides sufficient information for decision-making in emergency cases. It is, however, not always possible to identify the underlying infective agent despite further CSF analyses, such as bacterial and fungal staining, evaluation of the blood-CSF barrier function, intrathecal immunoglobulin synthesis and oligoclonal IgG bands. Therefore, close communication between the laboratory and the clinician is an important prerequisite to specify additional pathogen-related diagnostic measures for successful confirmation of the diagnosis.

Electromechanical and elastic probing of bacteria in a cell culture medium

Rapid phenotype characterization and identification of cultured cells, which is needed for progress in tissue engineering and drug testing, requires an experimental technique that measures physical properties of cells with sub-micron resolution. Recently, band excitation piezoresponse force microscopy (BEPFM) has been proven useful for recognition and imaging of bacteria of different types in pure water. Here, the BEPFM method is performed for the first time on physiologically relevant electrolyte media, such as Dulbecco's phosphate-buffered saline (DPBS) and Dulbecco's modified Eagle's medium (DMEM). Distinct electromechanical responses for Micrococcus lysodeikticus (Gram-positive) and Pseudomonas fluorescens (Gram-negative) bacteria in DPBS are demonstrated. The results suggest that mechanical properties of the outer surface coating each bacterium, as well as the electrical double layer around them, are responsible for the BEPFM image formation mechanism in electrolyte media.

Controlling magnetoelectric coupling by nanoscale phase transformation in strain engineered bismuth ferrite

The magnetoelectric coupling in multiferroic materials is promising for a wide range of applications, yet manipulating magnetic ordering by electric field proves elusive to obtain and difficult to control. In this paper, we explore the prospect of controlling magnetic ordering in misfit strained bismuth ferrite (BiFeO(3), BFO) films, combining theoretical analysis, numerical simulations, and experimental characterizations. Electric field induced transformation from a tetragonal phase to a distorted rhombohedral one in strain engineered BFO films has been identified by thermodynamic analysis, and realized by scanning probe microscopy (SPM) experiment. By breaking the rotational symmetry of a tip-induced electric field as suggested by phase field simulation, the morphology of distorted rhombohedral variants has been delicately controlled and regulated. Such capabilities enable nanoscale control of magnetoelectric coupling in strain engineered BFO films that is difficult to achieve otherwise, as demonstrated by phase field simulations.

Substrate clamping effects on irreversible domain wall dynamics in lead zirconate titanate thin films

The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots.

Resolution theory, and static and frequency-dependent cross-talk in piezoresponse force microscopy

Probing the functionality of materials locally by means of scanning probe microscopy (SPM) requires a reliable framework for identifying the target signal and separating it from the effects of surface morphology and instrument non-idealities, e.g. instrumental and topographical cross-talk. Here we develop a linear resolution theory framework in order to describe the cross-talk effects, and apply it for elucidation of frequency-dependent cross-talk mechanisms in piezoresponse force microscopy. The use of a band excitation method allows electromechanical/electrical and mechanical/topographic signals to be unambiguously separated. The applicability of a functional fit approach and multivariate statistical analysis methods for identification of data in band excitation SPM is explored.

Nanoscale mapping of ion diffusion in a lithium-ion battery cathode

The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO(2) at a resolution of ∼100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

Double-layer mediated electromechanical response of amyloid fibrils in liquid environment

Harnessing electrical bias-induced mechanical motion on the nanometer and molecular scale is a critical step toward understanding the fundamental mechanisms of redox processes and implementation of molecular electromechanical machines. Probing these phenomena in biomolecular systems requires electromechanical measurements be performed in liquid environments. Here we demonstrate the use of band excitation piezoresponse force microscopy for probing electromechanical coupling in amyloid fibrils. The approaches for separating the elastic and electromechanical contributions based on functional fits and multivariate statistical analysis are presented. We demonstrate that in the bulk of the fibril the electromechanical response is dominated by double-layer effects (consistent with shear piezoelectricity of biomolecules), while a number of electromechanically active hot spots possibly related to structural defects are observed.

Deterministic control of ferroelastic switching in multiferroic materials

Multiferroic materials showing coupled electric, magnetic and elastic orderings provide a platform to explore complexity and new paradigms for memory and logic devices. Until now, the deterministic control of non-ferroelectric order parameters in multiferroics has been elusive. Here, we demonstrate deterministic ferroelastic switching in rhombohedral BiFeO(3) by domain nucleation with a scanning probe. We are able to select among final states that have the same electrostatic energy, but differ dramatically in elastic or magnetic order, by applying voltage to the probe while it is in lateral motion. We also demonstrate the controlled creation of a ferrotoroidal order parameter. The ability to control local elastic, magnetic and torroidal order parameters with an electric field will make it possible to probe local strain and magnetic ordering, and engineer various magnetoelectric, domain-wall-based and strain-coupled devices.

Disorder identification in hysteresis data: recognition analysis of the random-bond-random-field Ising model

An approach for the direct identification of disorder type and strength in physical systems based on recognition analysis of hysteresis loop shape is developed. A large number of theoretical examples uniformly distributed in the parameter space of the system is generated and is decorrelated using principal component analysis (PCA). The PCA components are used to train a feed-forward neural network using the model parameters as targets. The trained network is used to analyze hysteresis loops for the investigated system. The approach is demonstrated using a 2D random-bond-random-field Ising model, and polarization switching in polycrystalline ferroelectric capacitors.

Functional recognition imaging using artificial neural networks: applications to rapid cellular identification via broadband electromechanical response

Functional recognition imaging in scanning probe microscopy (SPM) using artificial neural network identification is demonstrated. This approach utilizes statistical analysis of complex SPM responses at a single spatial location to identify the target behavior, which is reminiscent of associative thinking in the human brain, obviating the need for analytical models. We demonstrate, as an example of recognition imaging, rapid identification of cellular organisms using the difference in electromechanical activity over a broad frequency range. Single-pixel identification of model Micrococcus lysodeikticus and Pseudomonas fluorescens bacteria is achieved, demonstrating the viability of the method.

Probing the temperature dependence of the mechanical properties of polymers at the nanoscale with band excitation thermal scanning probe microscopy

Understanding local mechanisms for temperature-induced phase transitions in polymers requires quantitative measurements of the thermomechanical behavior, including glass transition and melting temperatures as well as temperature dependent elastic and loss modulus and thermal expansion coefficients in nanoscale volumes. Here, we demonstrate an approach for probing local thermal phase transitions based on the combination of thermal field confinement by a heated SPM probe and multi-frequency thermomechanical detection. The local measurement of the glass transition temperature is demonstrated and the detection limits are established.

Spatially resolved spectroscopic mapping of polarization reversal in polycrystalline ferroelectric films: crossing the resolution barrier

The mesoscopic reversible and irreversible polarization dynamics in polycrystalline PZT thin film capacitors are studied using local spectroscopic mapping and macroscopic first-order reversal curve measurements. The transition from a regime of short range domain wall motion to the formation of mesoscopic clusters to complete switching is observed. The fractal dimension of the clusters is consistent with the random-bond disorder model. The combination of macroscopic and local measurements allows the characteristics length scales corresponding to the transition from Rayleigh to Preisach behaviors and onset of macroscopic averaging to be determined.

Adaptive probe trajectory scanning probe microscopy for multiresolution measurements of interface geometry

An adaptive scanning method in scanning probe microscopy (SPM) is developed for studies of surfaces with a highly-non-uniform information density such as nanowires or interfaces in disordered media. In path-engineered SPM, the surface is pre-scanned to locate features, and a secondary scan is acquired with the pixel density concentrated in the vicinity of the objects of interest. Here, we demonstrate this approach for piezoresponse force microscopy, and develop approaches for fractal and self-affine characterization of domain interfaces. The relationship between the variational roughness, structure factor, and correlation functions is established and resolution effects on these parameters are determined.

Time-resolved electronic phase transitions in manganites

The dynamics of first-order electronic phase transitions in complex transition metal oxides are not well understood but are crucial in understanding the emergent phenomena of electronic phase separation. We show that a manganite system reduced to the scale of its inherent electronic charge-ordered insulating and ferromagnetic metal phase domains allows for the direct observation of single electronic phase domain fluctuations within a critical regime of temperature and magnetic field at the metal-insulator transition.

Probing the role of single defects on the thermodynamics of electric-field induced phase transitions

The kinetics and thermodynamics of first order transitions are universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially resolved imaging of a single defect center in multiferroic BiFeO3 thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.

Controlling polarization dynamics in a liquid environment: from localized to macroscopic switching in ferroelectrics

The effect of disorder on polarization switching in ferroelectric materials is studied using piezoresponse force microscopy in a liquid environment. The spatial extent of the electric field created by a biased tip is controlled by the choice of medium, resulting in a transition from localized switching dictated by tip radius, to uniform switching across the film. In the localized regime, the formation of fractal domains has been observed with dimensionality controlled by the length scale of the frozen disorder. In the nonlocal regime, preferential nucleation at defect sites and the presence of long-range correlations has been observed.

Application of spectromicroscopy tools to explore local origins of sensor activity in quasi-1D oxide nanostructures

We have tested a range of imaging and spectroscopic techniques to address their ability to locally explore the interplay between surface reactivity and transport properties of the metal oxide nanostructure wired as a chemiresistor and chemi-FET. In particular, we used scanning surface potential microscopy (SSPM) to monitor the spatial and temporal particularities of the dc potential distributions in an operating device. We also successfully implemented synchrotron radiation-based photoelectron emission microscopy (PEEM) to explore submicron lateral compositional and electronic (work function) inhomogeneity on the surface of an individual nanowire sensor. These results open new avenues to visualize and spectroscopically address the chemical phenomena on an individual quasi-1D nanostructure both in real time and at nano- and mesoscopic level.

Spatial resolution, information limit, and contrast transfer in piezoresponse force microscopy

Scanning probe-based ferroelectric domain imaging and patterning has attracted broad attention for use in the characterization of ferroelectric materials, ultrahigh density data storage, and nanofabrication. The viability of these applications is limited by the minimal domain size that can be fabricated and reliably detected by scanning probe microscopy. Here, the contrast transfer mechanism in piezoresponse force microscopy (PFM) of ferroelectric materials is analysed in detail. A consistent definition of resolution is developed both for the writing and the imaging processes, and the concept of an information limit in PFM is established. Experimental determination of the object transfer function and the subsequent reconstruction of an 'ideal image' is demonstrated. This contrast transfer theory provides a quantitative basis for image interpretation and allows for the comparison of different instruments in PFM. It is shown that experimentally observed domain sizes can be limited by the resolution of the scanning probe microscope to the order of tens of nanometres even though smaller domains, of the order of several nanometres, can be created.

Bioelectromechanical imaging by scanning probe microscopy: Galvani's experiment at the nanoscale

Since the discovery in the late 18th century of electrically induced mechanical response in muscle tissue, coupling between electrical and mechanical phenomena has been shown to be a near-universal feature of biological systems. Here, we employ scanning probe microscopy (SPM) to measure the sub-Angstrom mechanical response of a biological system induced by an electric bias applied to a conductive SPM tip. Visualization of the spiral shape and orientation of protein fibrils with 5 nm spatial resolution in a human tooth and chitin molecular bundle orientation in a butterfly wing is demonstrated. In particular, the applicability of SPM-based techniques for the determination of molecular orientation is discussed.

Electromechanical imaging of biomaterials by scanning probe microscopy

The majority of calcified and connective tissues possess complex hierarchical structure spanning the length scales from nanometers to millimeters. Understanding the biological functionality of these materials requires reliable methods for structural imaging on the nanoscale. Here, we demonstrate an approach for electromechanical imaging of the structure of biological samples on the length scales from tens of microns to nanometers using piezoresponse force microscopy (PFM), which utilizes the intrinsic piezoelectricity of biopolymers such as proteins and polysaccharides as the basis for high-resolution imaging. Nanostructural imaging of a variety of protein-based materials, including tooth, antler, and cartilage, is demonstrated. Visualization of protein fibrils with sub-10nm spatial resolution in a human tooth is achieved. Given the near-ubiquitous presence of piezoelectricity in biological systems, PFM is suggested as a versatile tool for micro- and nanostructural imaging in both connective and calcified tissues.

Demersal crustacean assemblages along the Pacific coast of Costa Rica: a quantitative and multivariate assessment based on the Victor Hensen Costa Rica expedition (1993/1994)

During the first cruise leg with the RV Victor Hensen to the Pacific coast of Costa Rica in December 1993 (end of the rainy season) the crustacean fauna found in the demersal collections revealed an unexpected species richness and biomass. The Crustacea collections were analyzed qualitatively and quantitatively during the fourth leg (February 1994, dry season) in the three study areas Golfo Dulce (GD), Bahía Coronado in the Sierpe-Térraba-estuary (ST) and Golfo de Nicoya (GN). Qualitative data were available for comparison from the first leg in december 1993. A total of 24 beamtrawl and ten ottertrawl sample collections were done on an area of 860.000 m2 yielding a total of 119 species with a biomass of 37.8 kg (10275 specimens). Despite the smaller area covered by the beamtrawl, it collected a higher number of species and more biomass than the ottertrawl due to the smaller mesh size (0.8 cm). Judging from the shape of the species -per-area-curves, the crustacean fauna appeared as representatively sampled for the study area. As compared with the GN (biomass 0.36 g +/- 0.26, SR = 97) and the ST (0.41 g +/- 0.27, SR = 59) and according to the results of the log-series-plots constructed from the abundance data, the GD seems to be a depauperated area with significantly lower biomass (0.05 g +/- 0.07) and species richness (45 sp.). No crustaceans were found in the center of the deep basin of the GD put parts of the interior gulf with adjacent mangrove areas seem to be important as nursery area for some commercially important penaeid shrimp species. The ST-estuary revealed the highest mean species number per station in the whole study area, but the GN had the highest total number of species. Biomass seems to be regularly distributed and not depth-depending within the GN, while species abundance varies clearly, confirming previous results. In contrast, abundance and biomass correlated well in the ST. Based on the results of the multivariate analysis, seven station groups of particular species assemblages can be distinguished in the study areas. Despite a high variability between stations in abundance and biomass, the following four areas of characteristic species assemblages can be identified which are also confirmed by an independent study on demersal fishes: (1) the interior part of the GN, characterized by juvenile shrimps (Sicyonia disdorsalis, Trachypenaeus fuscina), several patchily distributed anomurans, brachyurans and other predator species like portunids (especially Portunus asper) and pre-adult stomatopods (Squilla spp.); (2) the exterior part of the GN with high amounts of caridean (Pantomus affins, Plesionika spp.) and penaeid shrimps (Sicyonia picta, Solenocera mutator), the highly abundant Iliacantha hancocki and some specimens of the stomatopod Hemisquilla stylifera and the deep water portunid Portunus iridescens; (3) a transition zone between 60 and 120 m water depth with a heterogeneous faunal composition, located in the ST and east of Isla Tortugas in the GN, and (4) the oxygen-depleted shelf edge area, dominated by the galatheid Pleuroncodes monodon. Mass occurrence of this species takes place off the GD and to a lesser extent off the ST-estuary, associated with high numbers of Solenocera spp. There seems to be a general trend of species groupings along abiotic gradients (depth, temperature, oxygen saturation) interrupted by small-scale variations in habitat type, current regime, food availability and other factors not identified in this study. Neither total abundance and biomass nor biotic summary parameters like diversity, dominance or species richness correlated well with the abiotic factors measured during this survey.

Checklist of crustaceans (Decapoda and Stomatopoda), collected during the Victor Hensen Costa Rica expedition (1993/1994)

A checklist of the marine crustaceans (Decapoda and Stomatopoda) from the Pacific coast of Costa Rica collected by trawling during the RV Victor Hensen Cruise (1993-1994) is presented. A total of 117 species were identified, 10 stomatopods and 107 decapods.