Atomic Force Microscopy Tools Research Articles

Utilization of AFM for Observing Early-Onset Mechanisms of Lithium-Metal

Lithium metal is seen as a “Holy Grail” material for battery technology, due to its high capacity and low electrochemical potential. However, the intrinsic plating/stripping mechanism of lithium metal, coupled with heterogeneous ionic pathways leads to treacherous dendrite growth and rapid consumption of active materials, diminishing cycle life. Variability in the mechanical and electrochemical properties of lithium’s surface initiates a cascading effect that ultimately ends in the failure mechanisms that plague lithium metal.Simulations and ultra-resolved techniques (e.g., cryo-TEM) can provide fundamental understanding of certain phenomena but need to be closely coupled with realistic conditions to drive commercialization of lithium. Cell-level studies can provide clarity between different parameters, such as temperature, pressure, lithium preparation, electrolyte optimization, and cathode characteristics. However, cell-to-cell variability makes repeatability of results difficult, slowing the advancement in the readiness-level of novel cell designs. In this work, phenomena at the micro- to nanoscale were observed to better understand the behavior of lithium. At this scale, investigation of Li+ flux during deposition and dissolution is a crucial piece to solving the lithium-metal battery puzzle. This was accomplished with the use of different atomic force microscopy (AFM) techniques, coupled with other characterization tools to correlate to cell-level evaluation. The multi-functional capabilities of AFM may provide a bridge between atomistic/fundamental studies and cell-level testing, thanks in part to its non-destructive nature, high reproducibility, and ability to decipher the effect of various parameters on reaction mechanisms at the electrode-electrolyte interface.Scanning Kelvin probe force microscopy (SKPFM), electrochemical AFM (EC-AFM) and quantitative nanomechanical mapping (QNM) were utilized to acquire spatially resolved properties for different use conditions and under different design parameters. SKPFM is a tool used to measure the surface potential, which directly relates to the work function. With this tool, local heterogeneities can be distinguished as a function of surface treatment or operation in a cell-level build. EC-AFM is utilized to observe mechanistic variations in-situ, detecting morphological changes caused by either lithiation/de-lithiation or solid-electrolyte interphase (SEI) breakdown/formation. Coupled with QNM, EC-AFM can also provide simultaneous topography and mechanical properties such as adhesion, modulus, and deformation.These AFM tools can provide high-resolution insight into mechanistic phenomena such as dendrite/pit growth, “dead” Li formation, as well as SEI formation, furthering the understanding of the lithium-metal anode. The investigations accomplished with AFM advances the field of battery technologies, providing insight into the initiation and propagation of failure mechanisms, along with how to solve them.

Light polarization and intensity behaviour in aperture cantilevers with carbon tip created by focused ion beam

Modern atomic force microscopy (AFM) techniques and their combination with other methods give us a possibility to investigate the same samples from the new side at nano-scale. One of very promising combinations is polarization near field microscopy integrated into AFM tool. It allows one to make topography imaging by standard AFM tool and optical magnetic structure imaging by magneto-optical method simultaneously. Moreover, this combination gives synergy effect on both methods by improving their weak sides: elimination of magnetic influence of magnetic force microscopy on the sample, on the one hand, and overcoming the diffraction limit of the magneto-optical microscopy, on another hand. The cantilevers play a very important role in this combination of the methods since they interact with the surface and allow focusing the laser beam to the sample in near field mode. The geometry and other parameters of cantilevers are determined as a result of the combined methods implementation. Authors investigate the new type of carbon-tips aperture cantilevers for AFM and high resolution magneto-optical combination.

Atomic Force Microscopy Identifying Fuel Pyrolysis Products and Directing the Synthesis of Analytical Standards.

Here we present a new method that integrates atomic force microscopy (AFM) with analytical tools such as high-performance liquid chromatography (HPLC) with diode-array ultraviolet-visible (UV) absorbance, and mass spectrometry (MS) along with synthetic chemistry. This allows the detection, identification, and quantification of novel polycyclic aromatic hydrocarbons (PAH) in complex molecular mixtures. This multidisciplinary methodology is employed to characterize the supercritical pyrolysis products of n-decane, a model fuel. The pyrolysis experiments result in a complex mixture of both unsubstituted as well as highly methylated PAH. We demonstrate the AFM-driven discovery of a novel compound, benz[ l]indeno[1,2,3- cd]pyrene, with the chemical structure assignment serving as input for the chemical synthesis of such molecule. The synthesis is verified by AFM, and the synthesized compound is used as a reference standard in analytical measurements, establishing the first-ever unequivocal identification and quantification of this PAH as a fuel product. Moreover, the high-resolution AFM analysis detected several five- to eight-ring PAH, which represents novel fuel pyrolysis and/or combustion products. This work provides a route to develop new analytical standards by symbiotically using AFM, chemical synthesis, and modern analytical tools.

Atomic force microscopy study of the biofouling and mechanical properties of virgin and industrially fouled reverse osmosis membranes

The mechanical properties of virgin and industrially fouled reverse osmosis membranes (composite polyamide) used for the purification and desalination of seawater in desalination processes were characterised using novel atomic force microscopy (AFM) methods. Polymeric surface elasticity has previously been demonstrated to strongly affect the adhesion of bacteria; hence the study examined membrane surface elasticity to demonstrate how AFM can be used to assess the bio-fouling potential of membranes. An AFM colloid probe technique was used to determine the mechanical properties of the membrane, the adhesion forces and the work of adhesion at the membrane surfaces. The mean values of Young's modulus for the virgin membrane decreased in magnitude with increasing pH values, where these values were significantly different (p<0.017) between both pH3 (1450kPa), pH7 (1327kPa) and pH9 (788kPa). These differences were attributed to differences in membrane swelling and indicate possible control parameters that could be exploited to improve membrane cleaning regimes. A membrane with a higher modulus will be stronger and potentially more resistant to chemical and physical processes during operation and cleaning. Significant differences (p<0.017) in force measurements were also found between different electrolytic conditions for each of the membranes, where for the virgin membrane the adhesion force values were 6.00nN at pH3, 1.77nN at pH7 and 0.98N at pH9, and also the work of adhesion were 153.6nJ at pH3, 22.8nJ at pH7 and 9.9nJ at pH9 in 0.6M NaCl. These observations further confirm the importance of the electrolytic environment on the nanoscale interactions of the membrane which should be considered to control fouling during operation and cleaning cycles. AFM images and streaming potential measurements of virgin and fouled membranes were also obtained to aid analysis of the industrial membrane system. The novel application of AFM to membranes to measure Young's moduli and work of adhesion is a new addition to the AFM tools that can be used to unravel separation processes at the membrane surface. In addition, this study further demonstrates that AFM force spectroscopy can be used as part of a sophisticated membrane autopsy procedure for the elucidation of the mechanisms involved in membrane fouling.

AFM Characterization of Structural Evolution and Roughness of AISI 304 Austenitic Stainless Steel under Severe Deformation by Wavy Rolling

Stainless steels such as ferrritic, austenitic, martensitic and duplex stainless steels are well known for their corrosion resistance to varying extents. Among these, austenitic stainless steels exhibit superior corrosion resistance and better ductility for formability. Therefore, the ability to give simple to intricate shapes in this grade of steel brings their potential for a wide range of applications. However, the meta-stable austenite in AISI 304 is known to undergo a strain induced martensitic (SIM) transformation during conventional rolling at room temperature. This strain induced martensite causes reduction in ductility and limits formability of stainless steel. Therefore, wavy rolling technique was developed to strengthen the stainless steel through microstructural refinement. In the current study, wavy rolling with 1.5 mm amplitude was conducted on 1 mm thick stainless steel sheet to different cycles ranging from 1-4. These rolled samples were characterized by optical and Atomic Force Microscopy (AFM) with resolutions down to the nanolevel. This AFM tool is in a position to bring out the details of grain refinement and topographical roughness emerging from crystalline and microstructural defects like orientation, precipitation, stacking faults, deformation bands, slip lines and shear bands with progress in rolling as referred by the number of rolling cycles here. The structural development is semi-quantitatively related to the degree of deformation and its effect on tensile properties during wavy rolling cycle. Keywords: Structural properties; Roughness; Deformation; Wavy rolling.

Multiparametric imaging of biological systems by force-distance curve–based AFM

A current challenge in the life sciences is to understand how biological systems change their structural, biophysical and chemical properties to adjust functionality. Addressing this issue has been severely hampered by the lack of methods capable of imaging biosystems at high resolution while simultaneously mapping their multiple properties. Recent developments in force-distance (FD) curve-based atomic force microscopy (AFM) now enable researchers to combine (sub)molecular imaging with quantitative mapping of physical, chemical and biological interactions. Here we discuss the principles and applications of advanced FD-based AFM tools for the quantitative multiparametric characterization of complex cellular and biomolecular systems under physiological conditions.

Development of a new generation of active AFM tools for applications in liquids

Atomic force microscopy (AFM) is a powerful imaging tool with high-resolution imaging capability. AFM probes consist of a very sharp tip at the end of a silicon cantilever that can respond to surface artefacts to produce an image of the topography or surface features. They are intrinsically passive devices. For imaging soft biological samples, and also for samples in liquid, it is essential to control the AFM tip position, both statically and dynamically, and this is not possible using external actuators mounted on the AFM chip. AFM cantilevers have been fabricated using silicon micromachining to incorporate a piezoelectric thin film actuator for precise control. The piezoelectric thin films have been fully characterized to determine their actuation performance and to characterize the operation of the integrated device. Examples of the spatial and vertical response are presented to illustrate their imaging capability. For operation in a liquid environment, the dynamic behaviour has been modelled and verified experimentally. The optimal drive conditions for the cantilever, along with their dynamic response, including frequency and phase in air and water, are presented.

InGaN quantum well epilayers morphological evolution under a wide range of MOCVD growth parameter sets

AbstractThis study exemplifies the use of TappingModeTM atomic force microscopy (AFM) surface morphology imaging to investigate and optimise the metalorganic chemical vapour deposition (MOCVD) growth conditions and post‐growth stability of thin (&lt;40 Å) InGaN layers with direct implications to the structural and optical properties of blue (460 nm) and green (520 nm) LEDs. InGaN epilayers less than 40 Å thick of ∼20% solid phase indium were produced on thick (3‐4 µm) 2″ GaN templates grown on (0001) c ‐plane sapphire substrates. The morphological evolution of the InGaN material was studied utilising a DI3100 AFM tool. Surface morphology and its correlation with photoluminescence and X‐ray diffraction results will be discussed for every set of conditions employed. More specifically, the post‐growth ambient exposure and thermal stability of the uncapped InGaN epilayers were investigated. In addition, the initial stage of subsequent GaN growth, which is an essential step towards the manufacture of LED active regions, was examined. Based on the above findings, a flexible MOCVD growth parameter space and improved LED constituent layer sequencing techniques have been established leading to more efficient and stable LED devices. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)