Subsequent Atomic Force Microscopy Research Articles

Dewetting upside-down: two-sided solid state dewetting of thin gold film on soft KBr substrate

Abstract We deposited a 30 nm-thick Au film on single crystalline KBr substrate and studied the solid state dewetting behavior of the film at a temperature of 350 °C. At this temperature, the ions of the KBr compound exhibit significant mobility along the Au–KBr interface, which affects the morphology and kinetics of the solid state dewetting. We performed statistical morphology analysis of the Au–KBr interface by selectively dissolving the KBr substrate after the dewetting heat treatments and subsequent atomic force microscopy imaging of the “upside-down” oriented Au film. We demonstrated that atomic mobility at the interface leads to embedding of the partially dewetted Au film into the KBr substrate. We proposed a quantitative model of the shape evolution of a disc-shaped Au particle on the KBr substrate under the condition of finite interface mobility of the substrate species. The model predictions were consistent with the experimentally observed sinking rates of Au nanostructures.

Characterization of transient and progressive pulmonary fibrosis by spatially correlated phase contrast microCT, classical histopathology and atomic force microscopy

Pulmonary fibrosis (PF) is a severe and progressive condition in which the lung becomes scarred over time resulting in pulmonary function impairment. Classical histopathology remains an important tool for micro-structural tissue assessment in the diagnosis of PF. A novel workflow based on spatial correlated propagation-based phase-contrast micro computed tomography (PBI-microCT), atomic force microscopy (AFM) and histopathology was developed and applied to two different preclinical mouse models of PF - the commonly used and well characterized Bleomycin-induced PF and a novel mouse model for progressive PF caused by conditional Nedd4-2 KO. The aim was to integrate structural and mechanical features from hallmarks of fibrotic lung tissue remodeling. PBI-microCT was used to assess structural alteration in whole fixed and paraffin embedded lungs, allowing for identification of fibrotic foci within the 3D context of the entire organ and facilitating targeted microtome sectioning of planes of interest for subsequent histopathology. Subsequently, these sections of interest were subjected to AFM to assess changes in the local tissue stiffness of previously identified structures of interest. 3D whole organ analysis showed clear morphological differences in 3D tissue porosity between transient and progressive PF and control lungs. By integrating the results obtained from targeted AFM analysis, it was possible to discriminate between the Bleomycin model and the novel conditional Nedd4-2 KO model using agglomerative cluster analysis. As our workflow for 3D spatial correlation of PBI, targeted histopathology and subsequent AFM is tailored around the standard procedure of formalin-fixed paraffin-embedded (FFPE) tissue specimens, it may be a powerful tool for the comprehensive tissue assessment beyond the scope of PF and preclinical research.

Exploring the Surface Oxidation and Environmental Instability of 2H-/1T'-MoTe2 Using Field Emission-Based Scanning Probe Lithography.

An unconventional approach for the resistless nanopatterning 2H- and 1T'-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide is characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3 /MoOx as well as TeO2 /TeOx . With the presented technology in combination with subsequent AFM imaging it is possible to demonstrate a strong anisotropic sensitivity of 1T'-/(Td )-MoTe2 to aqueous environments. Finally the discussed approach is used to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet.

Towards ballistic transport CVD graphene by controlled removal of polymer residues

Polymer-assisted wet transfer of chemical vapor deposited (CVD) graphene has achieved great success towards the true potential for large-scale electronic applications, while the lack of an efficient polymer removal method has been regarded as a crucial factor for realizing high carrier mobility in graphene devices. Hereby, we report an efficient and facile method to clean polymer residues on graphene surface by merely employing solvent mixture of isopropanol (IPA) and water (H2O). Raman spectroscopy shows an intact crystal structure of graphene after treatment, and the x-ray photoelectron spectroscopy indicates a significant decrease in the C–O and C=O bond signals, which is mainly attributed to the removal of polymer residues and further confirmed by subsequent atomic force microscopy analysis. More importantly, our gated measurements demonstrate that the proposed approach has resulted in a 3-fold increase of the carrier mobility in CVD graphene with the electron mobility close to 10 000 cm2 V−1 S−1, corresponding to an electron mean free path beyond 100 nm. This intrigues the promising application for this novel method in achieving ballistic transport for CVD graphene devices.

Topographical changes in high-protein, milk powders as a function of moisture sorption using amplitude-modulation atomic force microscopy

This study aimed to examine how microscopic morphological developments, such as lactose crystallisation, swelling of particles and changes in surface roughness, occur as a function of moisture sorption in skimmed-milk (SMP), milk protein concentrate (MPC) and whey protein isolate (WPI) powders. Atomic force microscopy (AFM) has the potential to identify high-resolution, microstructural changes in high-protein, milk powder particles. A sample preparation technique was developed, which allowed a single-layer of uniformly distributed powder particles to be applied to a mica surface for subsequent AFM analysis. An amplitude modulation (AM)-AFM technique was used, and analysis showed that equilibration of powders under conditions of increasing relative humidity (RH) causes changes in topography and increased surface roughness. In SMP, significant surface changes were observed due to the development of lactose crystallisation and eventual stacking of crystal layers with increased moisture sorption. MPC, however, showed characteristic ‘dimples and folds', which may have been due to shrinkage and compaction of surfaces. With higher moisture content, the number of surface-folds and height-ranges increased, with MPC powders, held at 85% RH appearing highly jagged. The surfaces of WPI powders were smooth but were characterised by the presence of broken powder fragments. Such fragments were absent in SMP and MPC powders, suggesting that WPI powders were the most friable. WPI powders appeared not to change as a function of moisture sorption. AM-AFM was used to provide high-resolution, three-dimensional images of HPMP particles at nano- and micrometre length scales.

Facile fabrication of 2D material multilayers and vdW heterostructures with multimodal microscopy and AFM characterization

Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. With both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics.

Ultra-microstructures and mechanics of plant mucilage functional interfaces investigated via atomic force microscopy in liquid

<p indent="0mm">Mucus plays an important role in regulating biological activities. Accordingly, investigating the structures and properties of mucus can be beneficial for providing a better understanding of physiological and pathological changes. Due to a lack of adequate observation tools, the ultra-microstructures of native mucus functional interfaces are not yet fully understood. Atomic force microscopy (AFM) provides a novel and powerful tool for investigating the structures and properties of biomaterials in their native states. Nevertheless, to date, studies of biomaterials using AFM are commonly performed in air, which cannot faithfully reflect the structures of biomaterials in liquids. In this paper, by adopting the mucilage secreted by the carnivorous sundew plant as an example, high-resolution AFM imaging and analysis of mucous nanostructures in aqueous conditions were achieved. Sundew mucilage was coated onto the surface of a glass slide or mica, and the subsequent AFM imaging of the mucilage-coated substrates in pure water revealed that a large number of nanoparticles were contained in the sundew mucilage. In contrast, AFM imaging of sundew mucilage-coated substrates in air showed that dried mucilage contained a large number of nanofibers. This underscored the structural differences in sundew mucilage in the air and in a solution. Furthermore, AFM multiparametric imaging was employed to visually characterize the mechanical properties of sundew mucilage nanostructures in pure water and showed significant differences in the mechanics between nanoparticles and nanofibers. This study provides a novel approach for investigating the ultra-microstructures and mechanics of mucus’ functional interfaces in their native states <italic>in situ</italic>, which has fundamental impacts on research focused on biomaterials.

In Situ Atomic Force Microscopy Depth-Corrected Three-Dimensional Focused Ion Beam Based Time-of-Flight Secondary Ion Mass Spectroscopy: Spatial Resolution, Surface Roughness, Oxidation.

Atomic force microscopy (AFM) is a well-known tool for studying surface roughness and to collect depth information about features on the top atomic layers of samples. By combining secondary ion mass spectroscopy (SIMS) with focused ion beam (FIB) milling in a scanning electron microscope (SEM), chemical information of sputtered structures can be visualized and located with high lateral and depth resolution. In this paper, a high vacuum (HV) compatible AFM was installed in a TESCAN FIB-SEM instrument that was equipped with a time-of-flight SIMS (ToF-SIMS) detector. To calibrate the sputtering rate and measure the induced roughness caused by the ToF-SIMS analysis, subsequent AFM measurements were performed on an inorganic multilayer vertical cavity surface-emitting laser sample. Normalized sputtering rates were used to aid the accurate three-dimensional reconstruction of the sputtered volume's chemical composition. Achievable resolution, surface roughness during sputtering, and surface oxidation issues were analyzed. The integration of complementary detectors opens up the ability to determine the sample properties as well as to understand the influence of the Ga+ ion sputtering method on the sample surface during the analysis.

Two-State Exchange Dynamics in Membrane-Embedded Oligosaccharyltransferase Observed in Real-Time by High-Speed AFM

Oligosaccharyltransferase (OST) is a membrane-bound enzyme that catalyzes the transfer of oligosaccharide chains from lipid-linked oligosaccharides (LLO) to asparagine residues in polypeptide chains. Using high-speed atomic force microscopy (AFM), we investigated the dynamic properties of OST molecules embedded in biomembranes. An archaeal single-subunit OST protein was immobilized on a mica support via biotin–avidin interactions and reconstituted in a lipid bilayer. The distance between the top of the protein molecule and the upper surface of the lipid bilayer was monitored in real-time. The height of the extramembranous part exhibited a two-step variation with a difference of 1.8 nm. The high and low states are designated as state 1 and state 2, respectively. The transition processes between the two states fit well to single exponential functions, suggesting that the observed dynamic exchange is an intrinsic property of the archaeal OST protein. The two sets of cross peaks in the NMR spectra of the protein supported the conformational changes between the two states in detergent-solubilized conditions. Considering the height values measured in the AFM measurements, state 1 is closer to the crystal structure, and state 2 has a more compact form. Subsequent AFM experiments indicated that the binding of the sugar donor LLO decreased the structural fluctuation and shifted the equilibrium almost completely to state 1. This dynamic behavior is likely necessary for efficient catalytic turnover. Presumably, state 2 facilitates the immediate release of the bulky glycosylated polypeptide product, thus allowing OST to quickly prepare for the next catalytic cycle.

COFs Meet Graphene Nanoribbons

2D covalent organic frameworks (COFs) have received considerable attention because of their crystallinity, permanent porosity, and tunability, yet they exhibit low in-plane conductivity. In this issue of Chem, Fischer and co-workers report an approach for growing 2D COF thin films featuring high in-plane conductivity for potential use in organic electronics.

&amp;lt;italic&amp;gt;In situ&amp;lt;/italic&amp;gt; imaging and analysis of the nanostructures in natural hydrogels from carnivorous plants by atomic force microscopy

Natural hydrogels have been widely applied in the field of biomedicine for their biocompatible and biodegradable characteristics. However, due to the lack of adequate observation tools, so far the detailed organizations and structures of native natural hydrogels at the nanoscale are still not fully understood. The advent of atomic force microscopy (AFM) provides a novel powerful tool for characterizing biomaterials, but studies about utilizing AFM to investigate the nanostructures of native natural hydrogels are still scarce. In this paper, AFM in situ high-resolution imaging was used to reveal the nanoscopic fine structures of the natural hydrogels secreted by four types of carnivorous plants ( Drosera capensis , Pinguicula cyclosecta , Sarracenia rubra , and Dionaea muscipula ). Mucilage secreted by Drosera capensis or Pinguicula cyclosecta was coated on the surface of mica, and the subsequent AFM imaging of the mucilage-coated mica in air clearly revealed that both the mucilage secreted by Drosera capensis and Pinguicula cyclosecta contained a large number of nanofibers which had diverse self-assembly behaviors. Nectar secreted by Sarracenia rubra or Dionaea muscipula was coated on the surface of glass slides, and AFM images of the nectar-coated glass slide recorded in deionized water showed that both the nectar secreted by Sarracenia rubra and Dionaea muscipula considerably contained nanoparticles. Statistical results showed that the size of nanoparticles in the nectar of Dionaea muscipula was significantly larger than that of nanoparticles in the nectar of Sarracenia rubra . The study improves our understanding of the natural hydrogels secreted by carnivorous plants and provides a novel approach for characterizing the nanostructures of natural biomaterials in their native states, offering new possibilities for the studies of supramolecular biomaterials.

Surface Termination-Dependent Nanotribological Properties of Single-Crystal MAPbBr3 Surfaces

Atomistic characterization of surface termination and the corresponding mechanical properties of single-crystal methylammonium lead tribromide (MAPbBr3) are performed using combined atomic force microscopy (AFM) measurements and density functional theory (DFT) calculations. A clean MAPbBr3 surface is obtained by in situ cleavage in ultrahigh vacuum at room temperature, and the subsequent AFM measurements of the as-cleaved MAPbBr3 exhibit the coexistence of two different surface terrace types with step height differences corresponding to about half the thickness of a PbI6 octahedron layer. Concurrent friction force microscopy measurements show that the two surfaces result in two distinct friction values. Based on DFT calculations, we attribute the higher-friction and lower-friction surfaces to MABr-terminated flat and PbBr2-terminated vacant surface terminations, respectively. The calculated electronic band structures of the various MABr- and PbBr2-terminated surfaces show that the midgap states are absent, revealing the defect-tolerant nature of the ideal single-crystal MAPbBr3 surfaces.

Resistivity Characterization of Solid Electrolyte Interphase on Lithium Ion Battery Silicon Anodes

Lithium-ion battery (LIB) technology plays a critical role the clean energy sector, with applications in electronic devices, electric and hybrid vehicles, and stationary energy storage. In order to improve battery efficiency and performance, novel materials must be developed and studied. Battery anode materials are of particular interest, and silicon has been selected for materials research due to its high theoretical storage capacity as well as the extensive existing knowledge regarding silicon material processing and fabrication. The initial cycling of a LIB, regardless of anode material, results in the formation of a solid electrolyte interphase (SEI) layer between the electrolyte and the anode. This passivating layer, consisting of decomposition products from the electrolyte solution, is critical to the reliability and performance of the battery. The SEI must be both electronically insulating and ionically conductive: permeable to lithium ions yet resistant to electron flow. The resistance can be inhomogeneous along the anode plane or perpendicular to it. To our knowledge, no characterization technique has been capable of measuring spatial variation in SEI resistivity. In order to measure SEI resistivity with nanometer-scale resolution, our group has utilized scanning spreading resistance microscopy (SSRM) with a specialized atomic force microscopy (AFM) system installed in an argon glove box to minimize sample exposure to oxygen and water. The setup employs a doped diamond coated silicon probe that exhibits high wear resistance and low electronic resistance. Through application of a sample-probe bias voltage while utilizing variable forces on the probe in AFM contact mode, the technique allows for the measurement of SEI resistivity laterally and vertically. The vertical depth of measurement is controllable by the applied probe force (as well as raster scan line density) and is thus capable of milling away SEI material to measure resistivity at defined depths. Subsequent AFM height measurement allows for measured resistance to be associated with the depth of measurement. The electronic system attached to the system measures current through the probe-sample with a logarithm-scale amplifier, which can be directly converted to resistance or resistivity. Our measurements of resistance vs. depth for SEIs formed on single-crystal silicon wafers [001] after a single cycle of lithiation/delithiation demonstrate strong trends for decrease in resistance as the probe penetrates deeper levels of the SEI. Such plots provide an interesting basis for the study of SEIs formed under different cycling conditions with distinct electrolyte solutions. Figure: (a) Schematic diagram of electronic setup of the described system, (b) resistance map at a depth of 43 nm on a SEI formed on a single-crystal silicon wafer [001], with a single cycle of lithiation (0.01 V for 5 hours) and delithiation (1.0 V for 5 hours) in a battery cell containing ethylene carbonate (EC) and diethyl carbonate(DEC) electrolytes, (c) topography map displaying the SEI depth of resistance mapping. Figure 1

A rapid FIB-notch technique for characterizing the internal morphology of high-performance fibers

This work introduces an innovative technique to characterize the internal morphology of high-performance fibers by using a focused ion beam (FIB) sample preparation method and subsequent atomic force microscopy (AFM). A FIB is used to mill opposing notches that facilitate direct failure along a longitudinal shear plane, and expose the internal surface of the fiber. By exposing this surface via longitudinal shear, distortion of the cleaved surface is minimal, which is an advantage over surface preparation methods such as microtoming. After cleaving the notched fibers, an AFM technique is used to generate modulus maps of the fiber fracture surfaces. These modulus maps provide qualitative and quantitative microstructural information. Initial results obtained from Kevlar KM2 and Dyneema SK76 fibers are presented and a brief analysis of the observed internal features is provided. Extending the technique to image internal features in other materials is also discussed.

Short-pulse laser excitation of quartz: experiments and modelling of transient optical properties and ablation

Time-resolved optical studies using spectral interferometry and reflectance measurements of ultrafast laser excitation of quartz have been performed and combined with subsequent atomic force microscopy imaging of the laser-formed holes. A comprehensive investigation of these transient properties of the dielectric has been analysed in view of a single theoretical model describing the laser–material interaction in a multirate equation model including light propagation. Simulations demonstrate that self-trapped excitons in quartz significantly change the optical properties immediately after excitation.

Fabrication of single titanium oxide nanodot ultraviolet sensors by atomic force microscopy nanolithography

We report on the fabrication of single titanium oxide nanodot (ND) ultraviolet sensors by atomic force microscopy (AFM) nanolithography. A single titanium nanowire is first fabricated by AFM nanomachining and gold contact electrodes are then created by photolithography. By subsequent AFM nano-oxidation, a single titanium oxide ND sensor is produced. Two types of ND sensors, namely ohmic contact and Schottky contact, have been obtained and the sensitivities are around 0.25 and 320, respectively, under ultraviolet illumination. The rise and the reset times of the Schottky contact sensor are also significantly faster.

Atomic force microscopy and Langmuir–Blodgett monolayer technique to assess contact lens deposits and human meibum extracts

PurposeThe purpose of this exploratory study was to investigate the differences in meibomian gland secretions, contact lens (CL) lipid extracts, and CL surface topography between participants with and without meibomian gland dysfunction (MGD). MethodsMeibum study: Meibum was collected from all participants and studied via Langmuir–Blodgett (LB) deposition with subsequent Atomic Force Microscopy (AFM) visualization and surface roughness analysis. CL Study: Participants with and without MGD wore both etafilcon A and balafilcon A CLs in two different phases. CL lipid deposits were extracted and analyzed using pressure-area isotherms with the LB trough and CL surface topographies and roughness values were visualized using AFM. ResultsMeibum study: Non-MGD participant meibum samples showed larger, circular aggregates with lower surface roughness, whereas meibum samples from participants with MGD showed more lipid aggregates, greater size variability and higher surface roughness. CL Study: Worn CLs from participants with MGD had a few large tear film deposits with lower surface roughness, whereas non-MGD participant-worn lenses had many small lens deposits with higher surface roughness. Balafilcon A pore depths were shallower in MGD participant worn lenses when compared to non-MGD participant lenses. Isotherms of CL lipid extracts from MGD and non-MGD participants showed a seamless rise in surface pressure as area decreased; however, extracts from the two different lens materials produced different isotherms. ConclusionsMGD and non-MGD participant-worn CL deposition were found to differ in type, amount, and pattern of lens deposits. Lipids from MGD participants deposited irregularly whereas lipids from non-MGD participants showed more uniformity.

A novel approach to investigate vascular wall in 3D: Combined Raman spectroscopy and atomic force microscopy for aorta en face imaging

A novel approach based on the combination of Raman confocal 3D imaging with atomic force microscopy (AFM) for analysis of the murine vessel wall en face is described. The approach is based on subsequent Raman and AFM imaging of the same areas of the sample. This methodology allows for direct correlation of the chemical structure (Raman data) with morphology of the surface (AFM). The sub-cellular structures of the tissue e.g., cell nuclei, heme, or lipid-rich species are visualized and localized by the application of Raman imaging, while AFM complements these data with high-resolution information about the surface topography and size of lipid-rich structures. Overall, the applied approach enables detailed characterization of the inner layer of the vessel wall.

Molecular functionalization of graphite surfaces: basal plane versus step edge electrochemical activity.

The chemical functionalization of carbon surfaces has myriad applications, from tailored sensors to electrocatalysts. Here, the adsorption and electrochemistry of anthraquinone-2,6-disulfonate (AQDS) is studied on highly oriented pyrolytic graphite (HOPG) as a model sp(2) surface. A major focus is to elucidate whether adsorbed electroactive AQDS can be used as a marker of step edges, which have generally been regarded as the main electroactive sites on graphite electrode surfaces. First, the macroscopic electrochemistry of AQDS is studied on a range of surfaces differing in step edge density by more than 2 orders of magnitude, complemented with ex situ tapping mode atomic force microscopy (AFM) data. These measurements show that step edges have little effect on the extent of adsorbed electroactive AQDS. Second, a new fast scan cyclic voltammetry protocol carried out with scanning electrochemical cell microscopy (SECCM) enables the evolution of AQDS adsorption to be followed locally on a rapid time scale. Subsequent AFM imaging of the areas probed by SECCM allows a direct correlation of the electroactive adsorption coverage and the actual step edge density of the entire working area. The amount of adsorbed electroactive AQDS and the electron transfer kinetics are independent of the step edge coverage. Last, SECCM reactive patterning is carried out with complementary AFM measurements to probe the diffusional electroactivity of AQDS. There is essentially uniform and high activity across the basal surface of HOPG. This work provides new methodology to monitor adsorption processes at surfaces and shows unambiguously that there is no correlation between the step edge density of graphite surfaces and the observed coverage of electroactive AQDS. The electroactivity is dominated by the basal surface, and studies that have used AQDS as a marker of steps need to be revised.

Bending manipulation and measurements of fracture strength of silicon and oxidized silicon nanowires by atomic force microscopy

Abstract