Search results for "atomic force"

Where Is the Most Hydrophobic Region? Benzopurpurine Self-Assembly at the Calcite–Water Interface

2017

Control of molecular self-assembly at solid–liquid interfaces is challenging due to the complex interplay between molecule–molecule, molecule–surface, molecule–solvent, surface–solvent, and solvent–solvent interactions. Here, we use in-situ dynamic atomic force microscopy to study the self-assembly of Benzopurpurine 4B into oblong islands with a highly ordered inner structure yet incommensurate with the underlying calcite (10.4) surface. Molecular dynamics and free energy calculations provide insights by showing that Benzopurpurine 4B molecules do not anchor to the surface directly but instead assemble on top of the second hydration layer. This seemingly peculiar behavior was then rationali…

Stabilization of Polar Step Edges on Calcite (10.4) by the Adsorption of Congo Red

2015

In this work, we present the stabilization of polar step edges along the [010] direction of calcite (10.4) by the presence of a water-soluble organic molecule, namely Congo Red. While characteristic etch pits are observed on the surface in the absence of the additive, no etch pits can be found in the presence of the additive. Using atomic force microscopy, we can directly follow the restructuring of the surface. Upon addition of Congo Red, the charge-neutral step edges confining the characteristic etch pits vanish, while polar step edges along the [010] direction appear on the surface, which are entirely decorated by well-ordered molecular islands of the additive. After the restructuring ha…

Structure-Dependent Dissolution and Restructuring of Calcite Surfaces by Organophosphonates

2017

Organophosphonates are well-known to strongly interact with the surfaces of various minerals, such as brucite, gypsum, and barite. In this work, we study the influence of six systematically varied organophosphonate molecules (tetraphosphonates and diphosphonates) on the dissolution process of the (10.4) surface of calcite. In order to pursue a systematic study, we have selected organophosphonates that exhibit similar structural features, but also systematic architectural differences. The effect of this class of additives on the dissolution process of the calcite (10.4) surface is evaluated using in situ dynamic atomic force microscopy. For all of the six organophosphonate derivatives, we ob…

Deposition order controls the first stages of a metal-organic coordination network on an insulator surface

2016

| openaire: EC/FP7/610446/EU//PAMS We report on first stages toward the formation of a surface-confined metal-organic coordination network (MOCN) by sequential deposition of biphenyl-4,4′-dicarboxylic acid and iron atoms on the surface of a bulk insulator, calcite (10.4). The influence of the deposition order on the structure formation is studied by noncontact atomic force microscopy operated in ultrahigh vacuum at room temperature. It is found that sequential deposition facilitates MOCN formation when the organic linker molecules are first adsorbed on the surface, followed by iron deposition. This observation is explained by first-principles computations, indicating that the metal-molecule…

Clear signature of the (2 x 1) reconstruction of calcite (1014).

2010

Calcite is a mineral of fundamental importance that plays a crucial role in many fields of research such as biomineralization, biomolecule adsorption, and reactivity as well as industrial and daily life applications. Consequently, the most stable cleavage plane of calcite has been studied extensively using both direct imaging techniques such as atomic force microscopy as well as spectroscopic and diffraction techniques. Several surface structures have been reported for the (10 (1) over bar4) cleavage plane of calcite differing from the simple bulk-truncated structure and an ongoing controversy exists in literature whether the cleavage plane exhibits a (2 x 1) reconstruction or not. We study…

Morphological characterization of baculovirus Autographa californica multiple nucleopolyhedrovirus

2009

The budded form of baculovirus Autographa californica multiple nucleopolyhedrovirus is used widely in biotechnological applications. In this study, we observed the morphology of baculovirus in nanometer scale by atomic force microscopy. Additionally, the correlation between transduction efficiency and virus stock storage time was evaluated. By atomic force microscopy, asymmetrical baculovirus particles with enlarged head regions were detected. Observed virus stocks contained variable-length particles, 256 ± 40 nm, along with disintegrated particles and/or cellular components. Long-term storage of stocks led to virus aggregation and decreased cellular entry and transgene expression in mammal…

Determining cantilever stiffness from thermal noise

2013

We critically discuss the extraction of intrinsic cantilever properties, namely eigenfrequency fn, quality factor Qn and specifically the stiffness kn of the nth cantilever oscillation mode from thermal noise by an analysis of the power spectral density of displacement fluctuations of the cantilever in contact with a thermal bath. The practical applicability of this approach is demonstrated for several cantilevers with eigenfrequencies ranging from 50 kHz to 2 MHz. As such an analysis requires a sophisticated spectral analysis, we introduce a new method to determine kn from a spectral analysis of the demodulated oscillation signal of the excited cantilever that can be performed in the frequ…

Scanning force microscopy based rapid force curve acquisition on supported lipid bilayers: experiments and simulations using pulsed force mode.

2004

In situ pulsed force mode scanning force microscopy (PFM-SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM-SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiff. ness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator mo…

Cellular basis of abnormal tissue hardening in lung fibrosis examined with atomic force microscopy

2010

Correlation between surface forces and surface reactivity in the setting of plaster by atomic force microscopy

2000

Abstract The setting of mineral binders (cement, plaster, etc.) arises as a direct consequence of surface reactivity by a process of dissociation and rehydration. This transformation induces a complete change of surface forces, of which the nature remains still unknown. The general process of the setting has been studied by means of plaster (CaSO 4 ·0.5H 2 O) crystals, chosen for an experimental convenience. The surface alteration (growth, dissolution, atomic resolution) of the plaster crystal with respect to the introduction of the calcium sulfate solution has been followed by using atomic force microscopy (AFM. Alternatively, this apparatus has been adapted by gluing a plaster microcrysta…