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An evaluation of a combined scanning probe and optical microscope for lunar regolith studies
NASA Astrophysics Data System (ADS)
Yang, S.; Pike, W. T.; Staufer, U.; Claus, D.; Rodenburg, J. M.
2011-12-01
The microscopic properties of the lunar regolith such as the shape, the surface texture and the size distribution are required for an understanding of both past surface processes and potential hazards for future human exploration [1]. To reveal the particle morphology at the sub micrometer scale, scanning-probe microscopy (SPM), first used on the 2008 Phoenix mission [1], is a proven approach; however, there are two main challenges for the measurement of lunar particles. Firstly, the SPM tip is liable to move particles during scanning, even when using the lower contact forces of the dynamic-mode imaging. Hence the particles need to be stabilised during imaging. Secondly, typically the AFM tip extends about 10 μm from its cantilever, so larger particles protruding more than this height above their substrates cannot be scanned completely. To immobilize particles and eliminate large particles during SPM scanning, micromachined Si substrates, which have been successfully applied in the Phoenix project for Mars investigation in 2008 [2], have been investigated for lunar analogue material. On these substrates micrometer pits are patterned and serve as traps to enhance the stability of the AFM scanning by grasping the particles. In addition, the diameter of pits can determine the size of dusts to be captured and reduce the adhesion for the larger dust and so eliminate the oversized particles. To extend the imaging range and assist in selecting scan areas for the SPM, we use a type of lensless optical imaging (LOM) which uses ptychographic diffractive imaging [3] to eliminate the restrictions and performance limitations of conventional focusing devices. As a reference, scanning electron microscopy (SEM) which minimizes particle-probe interactions and has the advantage of an extended depth of field, is employed to image the same particle fields at resolutions covering both the SPM and LOM. By comparing the differences and the similarities between SEM and LOM images, the ability of LOM for illuminating the details about the lunar particles sample, is demonstrated. The analysis of SEM and SPM images of the same particles of JSC-LunarA analogue soil reveals the potential of the SPM to obtain reliable microscopic images of lunar dusts including detailed morphology with the help of the micromachined Si substrates. [1] J. D. Carpenter, O. Angerer, M. Durante, D. Linnarson, W. T. Pike, "Life Sciences Investigations for ESA's First Lunar Lander," Earth, Moon, and Planets, Vol.107, pp. 11-23, 2010. [2] S. Vijendran, H.Sykulska, and W. T. Pike, "AFM investigation of Martian soil simulant on micromachined Si substrates," Journal of Microscopy, Vol.227, pp.236-245, Sep. 2007. [3] J.M. Rodenburg, "Ptychography and related diffractive imaging techniques," Advances in Imaging and Electron Physics, Vol.150, pp. 87-184, 2008
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AFM probing in aqueous environment of Staphylococcus epidermidis cells naturally immobilised on glass: physico-chemistry behind the successful immobilisation.
PubMed
Méndez-Vilas, A; Gallardo-Moreno, A M; Calzado-Montero, R; González-Martín, M L
2008-05-01
AFM probing of microbial cells in liquid environments usually requires them to be physically or chemically attached to a solid surface. The fixation mechanisms may influence the nanomechanical characterization done by force curve mapping using an AFM. To study the response of a microbial cell surface to this kind of local measurement this study attempts to overcome the problem associated to the uncertainties introduced by the different fixation treatments by analysing the surface of Staphylococcus epidermidis cells naturally (non-artificially mediated) immobilised on a glass support surface. The particularities of this natural bacterial fixation process for AFM surface analysis are discussed in terms of theoretical predictions of the XDLVO model applied to the systems bacteria/support substratum and bacteria/AFM tip immersed in water. In this sense, in the first part of this study the conditions for adequate natural fixation of three S. epidermidis strains have been analyzed by taking into account the geometries of the bacterium, substrate and tip. In the second part, bacteria are probed without the risk of any possible artefacts due to the mechanical or chemical fixation procedures. Forces measured over the successfully adhered cells have (directly) shown that the untreated bacterial surface suffers from a combination of both reversible and non-reversible deformations during acquisition of force curves all taken under the same operational conditions. This is revealed directly through high-resolution tapping-mode imaging of the bacterial surface immediately following force curve mapping. The results agree with the two different types of force curves that were repeatedly obtained. Interestingly, one type of these force curves suggests that the AFM tip is breaking (rather than pushing) the cell surface during acquisition of the force curve. In this case, adhesive peaks were always observed, suggesting a mechanical origin of the measured pull-off forces. The other type of force curves shows no adhesive peaks and exhibits juxtaposing of approaching and retraction curves, reflecting elastic deformations.
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Stretching of Single Polymer Chains Using the Atomic Force Microscope
NASA Astrophysics Data System (ADS)
Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.
1998-03-01
A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.
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Principles and Applications of the qPlus Sensor
NASA Astrophysics Data System (ADS)
Giessibl, Franz J.
The concept of the atomic force microscope (AFM) is a very simple one: map the surface of a sample by a sharp probe that scans over the surface similar to the finger of a blind person that reads Braille characters. In AFM, the role of that finger is taken by the probe tip that senses the presence of the sample surface by detecting the force between the tip of the probe and a sample. The qPlus sensor is a self sensing cantilever based on a quartz tuning fork that supplements the traditional microfabricated cantilevers made of silicon. Quartz tuning forks are used in the watch industry in quantities of billions annually, with the positive effects on quality and perfection. Three properties of these quartz-based sensors simplify the AFM significantly: (1) the piezoelectricity of quartz allows simple self sensing, (2) the mechanical properties of quartz show very small variations with temperature, and (3) the given stiffness of many quartz tuning forks is close to the ideal stiffness of cantilevers. The key properties of the qPlus sensor are a large stiffness that allows small amplitude operation, the large size that allows to mount single-crystal probe tips, and the self-sensing piezoelectric detection mechanism.
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The structure of [MnIII6 CrIII]3+ single-molecule magnets deposited in submono-layers and monolayers on surfaces studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin Probe Force Microscopy in UHV
NASA Astrophysics Data System (ADS)
Heinzmann, U.; Gryzia, A.; Volkmann, T.; Brechling, A.; Hoeke, V.; Glaser, T.
2014-04-01
Single molecule magnets (SMM) deposited in submonolayers and monolayers have been analyzed with respect to their structures by means of non-contact AFM (topographic as well as damping mode) and Kelvin Probe Force Microscopy with molecular resolution.
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Solidification of a liquid crystal: Morphologies and transitions. Ph.D. thesis, Simon Fraser University (Canada)
NASA Astrophysics Data System (ADS)
Hutter, Jeffrey Lee
When a material freezes, the form it takes depends on the solidification conditions. For instance, as the undercooling is increased, one typically sees solidification into less-ordered forms. The resulting growth modes appear to be generic, with qualitative similarities between systems whose microscopic details are quite dissimilar. I have used both optical and atomic-force microscopy to study the transitions between different growth morphologies during the solidification of a particular liquid crystal, 10 OCB. We have observed six different solidification modes, each with a distinct micro and meso structure. The front-velocity-vs.-undercooling curve has a discontinuity in its slope and, in some cases, in the curve itself at mode transitions, suggesting that these transitions are analogous to phase transitions. Such transitions have been seen in other systems, but no general rule has been found that can predict which morphology will be selected. We show that, contrary to intuition and widespread speculation, the fastest-growing mode is not always the one selected. One of the growth modes exhibited by 10 OCB is known as banded spherulitic growth. Spherulites have been seen in a wide variety of materials including minerals, pure elements, polymers, biomolecules, and metal alloys. However, despite a century of study, there is no generally accepted theory of spherulitic growth. In particular, the cause of the concentric banding seen in many spherulites remains a mystery. Our studies of banded spherulites in 10 OCB using both optical and atomic-force microscopy show that the bands are associated with a density modulation and thus are not merely the result of a birefringent effect, as is commonly believed. As the atomic-force microscope (AFM) is a relatively new tool, some time was spent studying its capabilities. We found that because the AFM resolution is largely determined by attractive forces between the tip of the probe and the sample, resolution can be improved by imaging in a suitable liquid medium. We also developed a simple method for calibrating AFM cantilevers--a crucial step in using the AFM to obtain quantitative force data. This work is presented in an appendix.
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Experimentally validated 3D MD model for AFM-based tip-based nanomanufacturing
NASA Astrophysics Data System (ADS)
Promyoo, Rapeepan
In order to control AFM-based TBN to produce precise nano-geometry efficiently, there is a need to conduct a more focused study of the effects of different parameters, such as feed, speed, and depth of cut on the process performance and outcome. This is achieved by experimentally validating a MD simulation model of nanomachining, and using it to conduct parametric studies to guide AFM-based TBN. A 3D MD model with a larger domain size was developed and used to gain a unique insight into the nanoindentation and nanoscratching processes such as the effect of tip speed (e.g. effect of tip speed on indentation force above 10 nm of indentation depth). The model also supported a more comprehensive parametric study (than other published work) in terms of number of parameters and ranges of values investigated, as well as a more cost effective design of experiments. The model was also used to predict material properties at the nanoscale (e.g. hardness of gold predicted within 6% error). On the other hand, a comprehensive experimental parametric study was conducted to produce a database that is used to select proper machining conditions for guiding the fabrication of nanochannels (e.g. scratch rate = 0.996 Hz, trigger threshold = 1 V, for achieving a nanochannel depth = 50 nm for the case of gold device). Similar trends for the variation of indentation force with depth of cut, pattern of the material pile-up around the indentation mark or scratched groove were found. The parametric studies conducted using both MD model simulations and AFM experiments showed the following: Normal forces for both nanoindentation and nanoscratching increase as the depth of cut increases. The indentation depth increases with tip speed, but the depth of scratch decrease with increasing tip speed. The width and depth of scratched groove also depend on the scratch angle. The recommended scratch angle is at 90°. The surface roughness increases with step over, especially when the step over is larger than the tip radius. The depth of cut also increases as the step over decreases. Additional study is conducted using the MD model to understand the effect of crystal structure and defects in material when subjected to a stress. Several types of defects, including vacancies and Shockley partial dislocation loops, can be observed during the MD simulation for the case of gold, copper and aluminum. Finally, AFM-based TBN is used with photolithography to fabricate a nano-fluidic device for medical application. In fact, the photolithography process is used to create microchannels on top of a silicon wafer, and AFM-based TBN is applied to fabricate nanochannels between the microchannels that connect to the reservoirs. Fluid flow test was conducted on the devices to ensure that the nanochannel was open and the bonding sealed.
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Interfacial assembly structures and nanotribological properties of saccharic acids.
PubMed
Shi, Hongyu; Liu, Yuhong; Zeng, Qingdao; Yang, Yanlian; Wang, Chen; Lu, Xinchun
2017-01-04
Saccharides have been recognized as potential bio-lubricants because of their good hydration ability. However, the interfacial structures of saccharides and their derivatives are rarely studied and the molecular details of interaction mechanisms have not been well understood. In this paper, the supramolecular assembly structures of saccharic acids (including galactaric acid and lactobionic acid), mediated by hydrogen bonds O-HN and O-HO, were successfully constructed on a highly oriented pyrolytic graphite (HOPG) surface by introducing pyridine modulators and were explicitly revealed by using scanning tunneling microscopy (STM). Furthermore, friction forces were measured in the saccharic acid/pyridine co-assembled system by atomic force microscopy (AFM), revealing a larger value than a pristine saccharic acid system, which could be attributed to the stronger tip-assembled molecule interactions that lead to the higher potential energy barrier needed to overcome. The effort on saccharide-related supramolecular self-assembly and nanotribological behavior could provide a novel and promising pathway to explore the interaction mechanisms underlying friction and reveal the structure-property relationship at the molecular level.
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Atomic force microscopy as a tool to study Xenopus laevis embryo
NASA Astrophysics Data System (ADS)
Pukhlyakova, E. A.; Efremov, Yu M.; Bagrov, D. V.; Luchinskaya, N. N.; Kiryukhin, D. O.; Belousov, L. V.; Shaitan, K. V.
2012-02-01
Atomic force microscopy (AFM) has become a powerful tool for imaging biological structures (from single molecules to living cells) and carrying out measurements of their mechanical properties. AFM provides three-dimensional high-resolution images of the studied biological objects in physiological environment. However there are only few AFM investigations of fresh tissue explants and virtually no such research on a whole organism, since most researchers work with cell cultures. In the current work AFM was used to observe the surface of living and fixed embryos and to measure mechanical properties of naive embryos and embryos with overexpression of guanine nucleotide-binding protein G-alpha-13.
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Development of Thin Films as Potential Structural Cathodes to Enable Multifunctional Energy-Storage Structural Composite Batteries for the U.S. Army’s Future Force
DTIC Science & Technology
2011-09-01
glancing angle X - ray diffraction (GAXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrochemical...Emission SEM FWHM full width at half maximum GAXRD glancing angle X - ray diffraction H3COCH2CH2OH 2-methoxyethanol LiMn2O4 lithium manganese oxide...were characterized by scanning electron microscopy (SEM), X - ray diffraction (XRD), and atomic force microscopy (AFM). In addition,
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Nanoscale surface characterization using laser interference microscopy
NASA Astrophysics Data System (ADS)
Ignatyev, Pavel S.; Skrynnik, Andrey A.; Melnik, Yury A.
2018-03-01
Nanoscale surface characterization is one of the most significant parts of modern materials development and application. The modern microscopes are expensive and complicated tools, and its use for industrial tasks is limited due to laborious sample preparation, measurement procedures, and low operation speed. The laser modulation interference microscopy method (MIM) for real-time quantitative and qualitative analysis of glass, metals, ceramics, and various coatings has a spatial resolution of 0.1 nm for vertical and up to 100 nm for lateral. It is proposed as an alternative to traditional scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods. It is demonstrated that in the cases of roughness metrology for super smooth (Ra >1 nm) surfaces the application of a laser interference microscopy techniques is more optimal than conventional SEM and AFM. The comparison of semiconductor test structure for lateral dimensions measurements obtained with SEM and AFM and white light interferometer also demonstrates the advantages of MIM technique.
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Influence of alkyl chain length and anion species on ionic liquid structure at the graphite interface as a function of applied potential
NASA Astrophysics Data System (ADS)
Li, Hua; Wood, Ross J.; Endres, Frank; Atkin, Rob
2014-07-01
Atomic force microscopy (AFM) force measurements elucidate the effect of cation alkyl chain length and the anion species on ionic liquid (IL) interfacial structure at highly ordered pyrolytic graphite (HOPG) surfaces as a function of potential. Three ILs are examined: 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP), 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] TFSA). The step-wise force-distance profiles indicate the ILs adopt a multilayered morphology near the surface. When the surface is biased positively or negatively versus Pt quasireference electrode, both the number of steps, and the force required to rupture each step increase, indicating stronger interfacial structure. At all potentials, push-through forces for [HMIM] FAP are the highest, because the long alkyl chain results in strong cohesive interactions between cations, leading to well-formed layers that resist the AFM tip. The most layers are observed for [EMIM] FAP, because the C2 chains are relatively rigid and the dimensions of the cation and anion are similar, facilitating neat packing. [EMIM] TFSA has the smallest push-through forces and fewest layers, and thus the weakest interfacial structure. Surface-tip attractive forces are measured for all ILs. At the same potential, the attractions are the strongest for [EMIM] TFSA and the weakest for [HMIM] FAP because the interfacial layers are better formed for the longer alkyl chain cation. This means interfacial forces are stronger, which masks the weak attractive forces.
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[Atomic force microscopy fishing of gp120 on immobilized aptamer and its mass spectrometry identification].
PubMed
Bukharina, N S; Ivanov, Yu D; Pleshakova, T O; Frantsuzov, P A; Andreeva, E Yu; Kaysheva, A L; Izotov, A A; Pavlova, T I; Ziborov, V S; Radko, S P; Archakov, A I
2015-01-01
A method of atomic force microscopy-based fishing (AFM fishing) has been developed for protein detection in the analyte solution using a chip with an immobilized aptamer. This method is based on the biospecific fishing of a target protein from a bulk solution onto the small AFM chip area with the immobilized aptamer to this protein used as the molecular probe. Such aptamer-based approach allows to increase an AFM image contrast compared to the antibody-based approach. Mass spectrometry analysis used after the biospecific fishing to identify the target protein on the AFM chip has proved complex formation. Use of the AFM chip with the immobilized aptamer avoids interference of the antibody and target protein peaks in a mass spectrum.
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Infrared nanoscopy down to liquid helium temperatures
NASA Astrophysics Data System (ADS)
Lang, Denny; Döring, Jonathan; Nörenberg, Tobias; Butykai, Ádám; Kézsmárki, István; Schneider, Harald; Winnerl, Stephan; Helm, Manfred; Kehr, Susanne C.; Eng, Lukas M.
2018-03-01
We introduce a scattering-type scanning near-field infrared microscope (s-SNIM) for the local scale near-field sample analysis and spectroscopy from room temperature down to liquid helium (LHe) temperature. The extension of s-SNIM down to T = 5 K is in particular crucial for low-temperature phase transitions, e.g., for the examination of superconductors, as well as low energy excitations. The low temperature (LT) s-SNIM performance is tested with CO2-IR excitation at T = 7 K using a bare Au reference and a structured Si/SiO2-sample. Furthermore, we quantify the impact of local laser heating under the s-SNIM tip apex by monitoring the light-induced ferroelectric-to-paraelectric phase transition of the skyrmion-hosting multiferroic material GaV4S8 at Tc = 42 K. We apply LT s-SNIM to study the spectral response of GaV4S8 and its lateral domain structure in the ferroelectric phase by the mid-IR to THz free-electron laser-light source FELBE at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Notably, our s-SNIM is based on a non-contact atomic force microscope (AFM) and thus can be complemented in situ by various other AFM techniques, such as topography profiling, piezo-response force microscopy (PFM), and/or Kelvin-probe force microscopy (KPFM). The combination of these methods supports the comprehensive study of the mutual interplay in the topographic, electronic, and optical properties of surfaces from room temperature down to 5 K.
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Electrical characterization of grain boundaries of CZTS thin films using conductive atomic force microscopy techniques
DOE Office of Scientific and Technical Information (OSTI.GOV)
Muhunthan, N.; Singh, Om Pal; Toutam, Vijaykumar, E-mail: toutamvk@nplindia.org
2015-10-15
Graphical abstract: Experimental setup for conducting AFM (C-AFM). - Highlights: • Cu{sub 2}ZnSnS{sub 4} (CZTS) thin film was grown by reactive co-sputtering. • The electronic properties were probed using conducting atomic force microscope, scanning Kelvin probe microscopy and scanning capacitance microscopy. • C-AFM current flow mainly through grain boundaries rather than grain interiors. • SKPM indicated higher potential along the GBs compared to grain interiors. • The SCM explains that charge separation takes place at the interface of grain and grain boundary. - Abstract: Electrical characterization of grain boundaries (GB) of Cu-deficient CZTS (Copper Zinc Tin Sulfide) thin films wasmore » done using atomic force microscopic (AFM) techniques like Conductive atomic force microscopy (CAFM), Kelvin probe force microscopy (KPFM) and scanning capacitance microscopy (SCM). Absorbance spectroscopy was done for optical band gap calculations and Raman, XRD and EDS for structural and compositional characterization. Hall measurements were done for estimation of carrier mobility. CAFM and KPFM measurements showed that the currents flow mainly through grain boundaries (GB) rather than grain interiors. SCM results showed that charge separation mainly occurs at the interface of grain and grain boundaries and not all along the grain boundaries.« less
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Structural studies of a crystalline insulin analog complex with protamine by atomic force microscopy.
PubMed Central
Yip, C M; Brader, M L; Frank, B H; DeFelippis, M R; Ward, M D
2000-01-01
Crystallographic studies of insulin-protamine complexes, such as neutral protamine Hagedorn (NPH) insulin, have been hampered by high crystal solvent content, small crystal dimensions, and extensive disorder in the protamine molecules. We report herein in situ tapping mode atomic force microscopy (TMAFM) studies of crystalline neutral protamine Lys(B28)Pro(B29) (NPL), a complex of Lys(B28)Pro(B29) insulin, in which the C-terminal prolyl and lysyl residues of human insulin are inverted, and protamine that is used as an intermediate time-action therapy for treating insulin-dependent diabetes. Tapping mode AFM performed at 6 degrees C on bipyramidally tipped tetragonal rod-shaped NPL crystals revealed large micron-sized islands separated by 44-A tall steps. Lattice images obtained by in situ TMAFM phase and height imaging on these islands were consistent with the arrangement of individual insulin-protamine complexes on the P4(1)2(1)2 (110) crystal plane of NPH, based on a low-resolution x-ray diffraction structure of NPH, arguing that the NPH and NPL insulins are isostructural. Superposition of the height and phase images indicated that tip-sample adhesion was larger in the interstices between NPL complexes in the (110) crystal plane than over the individual complexes. These results demonstrate the utility of low-temperature TMAFM height and phase imaging for the structural characterization of biomolecular complexes. PMID:10620310
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Correlative atomic force microscopy quantitative imaging-laser scanning confocal microscopy quantifies the impact of stressors on live cells in real-time.
PubMed
Bhat, Supriya V; Sultana, Taranum; Körnig, André; McGrath, Seamus; Shahina, Zinnat; Dahms, Tanya E S
2018-05-29
There is an urgent need to assess the effect of anthropogenic chemicals on model cells prior to their release, helping to predict their potential impact on the environment and human health. Laser scanning confocal microscopy (LSCM) and atomic force microscopy (AFM) have each provided an abundance of information on cell physiology. In addition to determining surface architecture, AFM in quantitative imaging (QI) mode probes surface biochemistry and cellular mechanics using minimal applied force, while LSCM offers a window into the cell for imaging fluorescently tagged macromolecules. Correlative AFM-LSCM produces complimentary information on different cellular characteristics for a comprehensive picture of cellular behaviour. We present a correlative AFM-QI-LSCM assay for the simultaneous real-time imaging of living cells in situ, producing multiplexed data on cell morphology and mechanics, surface adhesion and ultrastructure, and real-time localization of multiple fluorescently tagged macromolecules. To demonstrate the broad applicability of this method for disparate cell types, we show altered surface properties, internal molecular arrangement and oxidative stress in model bacterial, fungal and human cells exposed to 2,4-dichlorophenoxyacetic acid. AFM-QI-LSCM is broadly applicable to a variety of cell types and can be used to assess the impact of any multitude of contaminants, alone or in combination.
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Near-Field Spectroscopy with Nanoparticles Deposited by AFM
NASA Technical Reports Server (NTRS)
Anderson, Mark S.
2008-01-01
An alternative approach to apertureless near-field optical spectroscopy involving an atomic-force microscope (AFM) entails less complexity of equipment than does a prior approach. The alternative approach has been demonstrated to be applicable to apertureless near-field optical spectroscopy of the type using an AFM and surface enhanced Raman scattering (SERS), and is expected to be equally applicable in cases in which infrared or fluorescence spectroscopy is used. Apertureless near-field optical spectroscopy is a means of performing spatially resolved analyses of chemical compositions of surface regions of nanostructured materials. In apertureless near-field spectroscopy, it is common practice to utilize nanostructured probe tips or nanoparticles (usually of gold) having shapes and dimensions chosen to exploit plasmon resonances so as to increase spectroscopic-signal strengths. To implement the particular prior approach to which the present approach is an alternative, it is necessary to integrate a Raman spectrometer with an AFM and to utilize a special SERS-active probe tip. The resulting instrumentation system is complex, and the tasks of designing and constructing the system and using the system to acquire spectro-chemical information from nanometer-scale regions on a surface are correspondingly demanding.
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Characterization of chemically and enzymatically treated hemp fibres using atomic force microscopy and spectroscopy
NASA Astrophysics Data System (ADS)
George, Michael; Mussone, Paolo G.; Abboud, Zeinab; Bressler, David C.
2014-09-01
The mechanical and moisture resistance properties of natural fibre reinforced composites are dependent on the adhesion between the matrix of choice and the fibre. The main goal of this study was to investigate the effect of NaOH swelling of hemp fibres prior to enzymatic treatment and a novel chemical sulfonic acid method on the physical properties of hemp fibres. The colloidal properties of treated hemp fibres were studied exclusively using an atomic force microscope. AFM imaging in tapping mode revealed that each treatment rendered the surface topography of the hemp fibres clean and exposed the individual fibre bundles. Hemp fibres treated with laccase had no effect on the surface adhesion forces measured. Interestingly, mercerization prior to xylanase + cellulase and laccase treatments resulted in greater enzyme access evident in the increased adhesion force measurements. Hemp fibres treated with sulfonic acid showed an increase in surface de-fibrillation and smoothness. A decrease in adhesion forces for 4-aminotoulene-3-sulfonic acid (AT3S) treated fibres suggested a reduction in surface polarity. This work demonstrated that AFM can be used as a tool to estimate the surface forces and roughness for modified fibres and that enzymatic coupled with chemical methods can be used to improve the surface properties of natural fibres for composite applications. Further, this work is one of the first that offers some insight into the effect of mercerization prior to enzymes and the effect on the surface topography. AFM will be used to selectively screen treated fibres for composite applications based on the adhesion forces associated with the colloidal interface between the AFM tip and the fibre surfaces.
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Real Space Imaging of Nanoparticle Assembly at Liquid-Liquid Interfaces with Nanoscale Resolution.
PubMed
Costa, Luca; Li-Destri, Giovanni; Thomson, Neil H; Konovalov, Oleg; Pontoni, Diego
2016-09-14
Bottom up self-assembly of functional materials at liquid-liquid interfaces has recently emerged as method to design and produce novel two-dimensional (2D) nanostructured membranes and devices with tailored properties. Liquid-liquid interfaces can be seen as a "factory floor" for nanoparticle (NP) self-assembly, because NPs are driven there by a reduction of interfacial energy. Such 2D assembly can be characterized by reciprocal space techniques, namely X-ray and neutron scattering or reflectivity. These techniques have drawbacks, however, as the structural information is averaged over the finite size of the radiation beam and nonperiodic isolated assemblies in 3D or defects may not be easily detected. Real-space in situ imaging methods are more appropriate in this context, but they often suffer from limited resolution and underperform or fail when applied to challenging liquid-liquid interfaces. Here, we study the surfactant-induced assembly of SiO2 nanoparticle monolayers at a water-oil interface using in situ atomic force microscopy (AFM) achieving nanoscale resolved imaging capabilities. Hitherto, AFM imaging has been restricted to solid-liquid interfaces because applications to liquid interfaces have been hindered by their softness and intrinsic dynamics, requiring accurate sample preparation methods and nonconventional AFM operational schemes. Comparing both AFM and grazing incidence X-ray small angle scattering data, we unambiguously demonstrate correlation between real and reciprocal space structure determination showing that the average interfacial NP density is found to vary with surfactant concentration. Additionally, the interaction between the tip and the interface can be exploited to locally determine the acting interfacial interactions. This work opens up the way to studying complex nanostructure formation and phase behavior in a range of liquid-liquid and complex liquid interfaces.
