List of Abstracts 2018: SESSION E - ADVANCED METHODS OF PREPARATION AND CHARACTERIZATION OF NANOMATERIALS
Date: October 18, 2018
Pushing the limits in IC-technology towards the nanometer scale, led to the development of complex systems and 3D-devices (like Finfets, TFET, nanowires) whereby novel materials and in particular interfacial interactions and ultrathin layers play a crucial role. In many cases blanket experiments no longer reflect the fundamental processes operative in small volumes among others due to the influence of the dramatic changes in surface/bulk ratio’s. This has emphasized the importance of metrology apt to deal with small 3D-volumes and atomic scale observations. Novel metrology concepts such as Atomprobe tomography, Scalpel SPM are emerging as a solution to these technological needs. Concurrently a parading shift is observed shifting metrology from high spatial resolution measurements on individual devices towards ensemble measurements on many devices simultaneously, in order to provide statistically relevant information. By exploiting some of their basic physics (cluster emission, photonic effects, detailed data algorithms) large area metrology concepts (SIMS, Raman, Four point probe) can be applied for ensemble measurements on small devices, despite their apparent lack of spatial resolution.
Nanoindentation is a popular method for the measurement of hardness and elastic modulus of nanoscale materials, such as nanocomposites, thin films and other nanostructured materials. The correct evaluation depends crucially on the correct evaluation of the so-called area function, which describes the shape of the indenter tip. For thin films, e.g nanolaminates, it is usually desirable to measure at very low contact depths. This demands a very accurate area function even at very shallow depths. The direct measurement of the area function by atomic force microscopy (AFM) is a less frequent approach. It has however its advantages such as full information about the shape, the possibility to distinguish contamination, and last but not least traceability. In this contribution we present approaches to the evaluation of the measured tip shape. Experimental settings, corrections of experimental data and data processing will be addressed. A detailed procedure for the separation of artifacts due to the AFM tip and those due to the indenter tip will be discussed, especially for contaminated tips. Software tools for the evaluation of tip parameters, such as tip radius, side angle and roughness of sides as well as for the determination of the area function will be presented. Sources of uncertainties will be analyzed and evaluated, the uncertainty budget will be modelled using Monte Carlo simulations. The final results will be compared with the standard calibration procedure for area calibration using reference samples.
Magnetic Force Microscopy (MFM) has become during last decade standard technique used for visualization of the stray field distribution of magnetic samples. Phase measurements of the stray field orientation are routinely presented as colorful images showing the contrast corresponding to the stray field orientation relative to the probe magnetization. Unfortunately no quantitative analysis of the strength of the measured field is usually provided. This information is crucial for many
applications and especially for metrology and industrial production (e.g. magnetic sensors, magnetic storage media etc.) The reason for the lack of such information is the nonexistence of a proper calibration standard for MFM measurements.
Calibration standards based on lithographically patterned planar current loops and parallel wires carrying electric current which produces well controllable source of magnetic field are one of the options.Such standards which are inherently versatile and portable. Such magnetic standards are being developed in cooperation with the Czech Metrology Institute (CMI) which is recognized as a legal institution for calibration. Hand in hand with hardware development we focus on developmet and implementation of a standard calibration routine which enables an easy MFM
Magnetic Force Microscopy (MFM) has become during last decade standard technique used for visualization of the stray field distribution of magnetic samples. Phase measurements of the stray field orientation are routinely presented as colorful images showing the contrast corresponding to the stray field orientation relative to the probe magnetization. Unfortunately no quantitative analysis of the strength of the measured field is usually provided. This information is crucial for many
applications and especially for metrology and industrial production (e.g. magnetic sensors, magnetic storage media etc.) The reason for the lack of such information is the nonexistence of a proper calibration standard for MFM measurements.
Calibration standards based on lithographically patterned planar current loops and parallel wires carrying electric current which produces well controllable source of magnetic field are one of the options. Such standards are inherently versatile and portable. Such magnetic standards are being developed in cooperation with the Czech Metrology Institute (CMI) which is recognized as a legal institution for calibration. Hand in hand with hardware development we focus on developmet and implementation of standard calibration routine which enables an easy MFM calibration. Easy and user friendly calibration routine will be implemented into an open source Scanning Probe Microscopy (SPM) software Gwyddion which was co-developed by researchers from CMI and CEITEC. Long-term maintenance of the software together with further development is expected due to popularity of Gwyddion software within the SPM community. It can help to fill the gap in quantitative MFM measurements which are critical both for research and industry applications.
Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) is a scanning probe approach to optical microscopy and spectroscopy bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 10 nanometer. s-SNOM employs the strong confinement of light at the apex of a sharp metallic AFM tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties (absorption, reflectivity) of the sample directly below the tip and yields nanoscale images simultaneous to topography. In addition to near-field microscopy the technology has been advanced to enable hyperspectral, nanoscale Fourier-transform spectroscopy (nano-FTIR) using broadband radiation from the far-infrared to the visible spectral range.
Identification of individual contaminants has been demonstrated [1]. Other applications show characterization of embedded structural phases in biominerals [2] or organic semiconductors. The patented modular system design allows for tailored system configurations where the ultimate spectral coverage is achieved by using synchrotron-based broadband IR light sources [3].
Equipping s-SNOM systems with cw light sources near-field imaging can be performed at time scales of 30-300s per image. Use of material-selective frequencies in the mid-IR spectral range can be exploited to fully characterize polymer blends or phase change polymers with nanometer-scale domains [4]. Quantification of free-carrier concentration and carrier mobility in doped semiconductor nanowires [5], analysis of 2D (graphene) nanostructures [6], or study phase propagation mechanisms in energy storage materials is achieved by amplitude- and phase-resolved infrared near-field imaging.
REFERENCES: [1] I. Amenabar et al. Nature Comm. 4 2890 (2013); [2] S. Amarie, et al., Beilstein J. of Nanotech. 3, 312 (2012); [3] P. Herrmann, et al., Optics Expr. 22 (2014); [4] C. Westermeier, et al., Nature Comm. 5, 4101 (2014); [5] Li, et al., ACS Nano (2017); [6] M. B. Lundeberg et al., Science (2017) AOP.
Precise analysis via multiple techniques is desired for a successful development of various materials and applications in many scientific fields. The combination of two widely used techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) is not only very useful but necessary in many applications.
LiteScope™ AFM produced by NenoVision is carefully designed for direct integration into many different SEM microscopes. It extends the instrument's capabilities and offers several benefits like 3D surface characterization, height/depth profiling, surface roughness calculation, precise tip navigation, local electric conductivity estimation, spectroscopic regimes, other electric and magnetic measurements, etc. all at the same ambient conditions during simultaneous measurement.
LiteScope™ is not only easy to install but also easy to use. Moreover, it has unique and patented technology for true correlative imaging, so-called Correlative Probe and Electron Microscopy™ (CPEM). The secret behind this method is that neither the electron beam nor the AFM probe tip is scanning. The movement is done by the piezo scanner with the sample while the AFM tip and the electron beam have a constant shift of known value. CPEM can accommodate several signals from different detectors (SE, BSE) or related techniques like FIB, EBIC or CL. LiteScope™ offers also a new approach to conductive measurements, so-called conductive CPEM (c-CPEM). This regime can provide contrast on conductive particles in a nonconductive matrix.
Capabilities of this device including new applications will be presented on various samples and materials.
Date: October 19, 2018
The advantage of ferromagnetic materials is the nonvolatility of the information encoded in the internal magnetic configuration, which can be used for memory storage, logic and sensing devices. Antiferromagnets are another class of magnetic materials that features nonvolatile magnetic ordering, yet its applications have been largely overlooked until recently [1]. In materials featuring a first-order metamagnetic phase transition between the antiferromagnetic (AF) and ferromagnetic (FM) states, the nature of the phase transition can be tuned by strain, pressure, chemical doping, temperature, as well as magnetic and electric fields, potentially offering very high recording densities and huge changes in the order parameters controlled with very low power.
Moreover, metamagnetic materials are outstanding candidates for finding and exploiting new functionalities and emergent phenomena on the mesoscale [2,3]. For instance, the transition from the AF order to FM order in sub-micron-wide FeRh wires becomes greatly asymmetric when comparing the heating and cooling cycles [3,4]. This recovery of the abrupt transition in nanostructures could lead to low-energy, efficient routes to control magnetic properties, leading to potential applications, for instance, in spintronics.
Furthermore, we show the dynamic response of the electronic and magnetic order to ultrafast laser excitation can be followed by time-resolved photoemission electron spectroscopy [5], which unlike techniques probing the total magnetization in the sample provides a direct comparison to the dynamic response of the structural order.
REFERENCES: [1] T. Jungwirth, X. Marti, P. Wadley, and J. Wunderlich, Nature Mater. 11, 231 (2016).; [2] F. Pressacco et al., Sci. Rep. 6, 22383 (2016).; [3] V. Uhlíř, J. A. Arregi, and E. E. Fullerton, Nat. Commun. 7, 13113 (2016).; [4] J. A. Arregi et al., J. Phys. D: Appl. Phys. 51, 105001 (2018).; [5] F. Pressacco et al., Struct. Dyn. 5, 034501 (2018).
The breakthrough of on surface confined polymerization strategies has opened up new routes to fabricate self-assembled two dimensional (2D) and one dimensional (1D) organometallic nanostructures, especially those difficult to synthesize in traditional solution polymerization [1,2]. Polyferrocenylenes (PFc), specially homopolymers with direct covalent bonding between the ferrocene units have been a great challenge in wet chemistry due to insolubility and presence of impurities, thus formidable to synthesize high molecular weight PFc and study their properties evidently [3-5].
We present a novel way of generation of long flexible 1D polyferrocenylene chains on metal surface with lengths up to 50 nm, representing the longest homo-coupled polyferrocenylene up to our knowledge. We employ on surface Ullman coupling polymerization of 1,1’-diiodobiferrocene molecules, deposited at room temperature under ultra-high vacuum conditions. The product are analysed using the low temperature scanning tunnelling microscope/atomic force microscopy (LT-STM/AFM). We observe two distinct 2D well-ordered polymer islands after annealing, with different electronic structure, due to the different packing of 1D molecular nanowires within the islands. We identified the internal molecular arrangement of island with help of high-resolution STM/AFM imaging with functionalized tips. We also succeeded in pulling out the 1D PFc chains from the islands to form free-standing 1D chains. We have identified a transition in the electronic behaviour, from semiconducting polymer 2D islands to metallic 1D chains using scanning tunnelling spectroscopy. These observations are rationalised using density functional calculations.
REFERENCES: [1] Di Giovannantonio et.al, J Phys Condens Matter. 2018;30(9).; [2] Fan Q, Dai J, Wang T, et al. , ACS Nano. 2016;10(3):3747-3754.; [3] Neuse EW, Crossland RK. , J Organomet Chem. 1967;7(2):344-347.; [4] Manners I., Adv Organomet Chem. 1995;37(C):131-168.; [5] Park P, Lough AJ, Foucher DA., Macromolecules. 2002;35(10):3810-3818.
This study investigated the stabilization of cadmium sulfide (CdS) nanoparticles in aqueous solutions of the copolymer Pluronic P123. Because of the favorable band gaps of CdS depending on the particle size, they are interesting candidates for optical or opto-electrical applications.
The nanoparticles were stabilized using aqueous solutions of P123 with a concentration of 30 weight percent (wtp) to reach lytropic liquid crystal (LLC) phases. The concentration of the added cadmium sulfide varies between 0.002 and 0.02M. For the synthesis sodium sulfide and cadmium chloride were both dissolved in an aqueous solution with 30 wtp P123. Both solutions were cooled to low temperatures and mixed in a heated container to quickly reach the LLC phase. The stabilized nanoparticle-polymer gels were investigated using ultraviolet-visible spectroscopy (UV-Vis) and small-angle-Xray-scattering (SAXS).
Mostly independent of the chosen temperature procedure, the stabilization of CdS nanoparticles was successful. In the absorption spectra measured by UV-Vis-spectroscopy no shift of the absorption edge depending of the CdS concentration in solution is visible. With SAXS, a shift in the distance between the Pluronic micelles was discovered. This shift towards lower Q-values indicates an increase in the micellar size and can be interpreted as a proof of the stabilization of the CdS nanoparticles in the micelles. It is also possible to stabilize CdS with 23wtp P123, which also indicates that the nanoparticles are located in the core of the micelle. This sample system consisting of polymeric micelles and nanoparticles can be seen as a model for studying the formation of nanoparticles.
The effect of severe plastic deformation on grain size refinement and mechanical properties of coarse-grained steel was investigated. The experimental material used in the present investigation was an advanced tungsten modified 9%Cr P92 steel. The coarse-grained state was deformed at room temperature by high-pressure sliding or high-pressure torsion. The microstructure was investigated using scanning electron microscope Tescan Lyra 3 equipped with electron-back scatter unit and transmission electron microscope Jeol 2100F. It was observed that severe plastic deformation at room temperature led to the subsequent reduction of grain size down to the submicroscopic level. It was found that the grain size and hardness exhibited the significant changes up to equivalent deformation of about 10 and slight changes in mean grain size between equivalent deformations of about 10 - 20. Equivalent plastic deformations higher than 20 led to only insignificant changes in the mean grain size and hardness. The creep behaviour of the ultrafine-grained state exhibited a minimum creep rate about two orders of magnitude faster, and a larger creep ductility, in comparison with the coarse-grained P92 steel.
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Aqueous solutions of triblock copolymers like Pluronic P123 show temperature and concentration dependent self-assembly The agglomerates vary in size and shape ranging from spherical micelles to highly entangled networks of wormlike aggregates Thus scientific and industrial applications of P123 range form the fabrication of novel materials like SBA-15 to promising candidates as carrier systems in drug delivery Latter application especially needs investigations of the aggregation number (number of polymers per micelle).
In this study small-angle-X-ray-scattering (SAXS), densometric, static and dynamic light scattering (SLS/DLS) measurements were performed on aqueous P123 solutions. SAXS experiments with absolute calibrated intensities allow simultaneous evaluation of the sample shape, size and scattering length density (SLD) of the sample. Through additional densometric measurements of the polymer solution, precise calculations of its volume fraction and density are possible. The results of both methods can be combined to a model-based calculation method for the aggregation number of micelles using particle number conservation.
The standard procedure by Kell Mortensen for deriving micellar aggregation numbers from small-angle-scattering data considers only the chemical composition and size of the core of a micelle. Comparing the results for the aggregation number of P123 micelles gained by Mortensen’s approach, the combined SAXS and densometric method and the SLS/DLS data, shows a discrepancy. It indicates that each method provides a special case or limit for the number of polymers forming one micelle based on the methods assumptions. The range of the discrepancy can
provide a confidence band for the aggregation number.
Surface-enhanced Raman scattering (SERS) has been widely applied as an ultra-sensitive and efficient method of characterization of different analytes, including biological objects bacteria and viruses adsorbed onto substrate surface. SERS substrates are usually based on noble metals nanoparticles with wide range of shapes and sizes. Nowadays, many methods are employed for the substrate preparation; however, there is still an open challenge to develop a simple and robust technique of preparation of SERS-active nanostructures with large number of hot spots. Controlled aggregation of metal nanoparticles is well known method for active SERS substrates preparation [1,2].
It is possible to predict and control nanoparticles aggregation applying colloid science principles based on extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory. In this work, we studied influence of various parameters related to the attractive and repulsive forces described by xDLVO theory, such as pH, zeta potential and various capping agents, on nanoparticles aggregation process and structure of the aggregates. We also found the optimal conditions for highly active SERS substrate preparation with large number of hotspots and good signal reproducibility.
This work is supported by the Ministry of Education and Science of the Russian Federation (Grant 14.Z50.31.0035).
REFERENCES: [1] Shiohara, A., Wang, Y., & Liz-Marzán, L. M. (2014). Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 21, 2-25. [2] M.V. Gorbachevskii, D.S. Kopitsyn, M.S. Kotelev, E.V. Ivanov, V.A. Vinokurov, A.A. Novikov (2018) RSC Advances, 8, 19051-19057.
Many challenges in material science and life science require the combination of complementary techniques for understanding of complex systems. As an example multiscale and multimodal investigation of Li ion batteries is presented here. While a wide-field light microscope provides only 2D overview images of anode-separator-cathode interfaces, a confocal microscope can be used for characterization of separator foil roughness. By correlation of these data with the information of an electron microscope high resolution information of surface and chemical element and distribution can be achieved. By means of integrated Raman systems the multi-phase nature of the separator can be revealed. On the other hand the samples can also be investigated in an X-ray microscope which provides 3D data to localize interesting features inside the sample. By applying parameters like e.g. temperature or pressure, the development of the sample over time provides 4D data. The regions of interest can then be exposed with highest 3D resolution by using a FIB-SEM system. By combining a He ion beam system with SIMS even Li distribution maps can be achieved.
A numerical analysis aiming to describe the plasticity effects in free-standing square thin films subjected to a bulge test is presented. The principle of the bulge test consists in applying gas pressure on a free standing membrane and measuring the shape of the membrane. According to the load-deflection analysis, linear relations are established in elastic case, however when the plasticity of the films occurs, these relations become nonlinear. The onset of the plasticity, the yield stress, can be identified in the deformed membrane using this assumption. A numerical database of load-deflection curves was created with a bilinear material model with the aim to determine the yield stress from the relation of the maximum principal stress and pressure. For this purpose, stress models based on the displacement field and elastic properties are presented and compared with finite element solutions. It is possible to reconstruct biaxial stress-strain curve of the thin film by applying the proposed models for stress and strain. Further, it was verified that the equation used in the literature to determine the yield stress from load-deflection analysis overestimate its value since constant curvature of the film is assumed. This calculation is corrected in our study.