Force Calibration in Lateral Force Microscopy

An analysis of the contact mechanics and the forces of interaction in lateral force microscopy measurements is presented. This analysis allows for a new method of interpretation of the frictional forces, the lateral contact stiffness, and the contact shear strength. The technique was developed for the interpretation of frictional data obtained with colloidal probes, although results are presented which illustrate its ability to interpret measurements recorded with both colloidal probes and standard atomic force microscopy tips. The technique is found to compensate for the variations in the contact geometry, giving repeatable results for probes of different sizes. A critical review of other techniques which have been employed to interpret the frictional force in lateral force microscopy is also presented. Copyright 2000 Academic Press.     

Force constants

A general semitheoretical method for the evaluation of quadratic, cubic and quartic force constants described previously is extended, and applied to the ground and excited states of heteronuclear diatomic molecules. The agreement of the results with the experimental values is good considering the very wide range of bond types, (neutral, ionic, covalent, excited) for which calculations have been performed.

---

Zusammenfassung Eine allgemeine halbempirische Methode für die Berechnung der Kraftkonstanten k ₂, k ₃, k ₄ wird auf Grund- und angeregte Zustände von Molekülen aus zwei verschiedenen Atomen angewendet. Die Übereinstimmung mit den experimentellen Werten ist bei Berücksichtigung der recht verschiedenen Bindungsarten gut.

---

Résumé Une méthode semithéorique générale pour l'évaluation des constantes de force d'ordre deux, trois et quatre, décrite précédemment est généralisée et appliquée aux états fondamentaux et excités de molécules diatomiques hétéronucléaires. L'accord des résultats avec les valeurs expérimentales est bon si l'on tient compte du large éventail de types de liaisons étudiés (neutre, ionique, covalente, excitée).

---

---

Fellow of the 1851 Exhibition and Fellow of Peterhouse, Cambridge.     

Peak Force Infrared–Kelvin Probe Force Microscopy

Correlative scanning probe microscopy of chemical identity, surface potential, and mechanical properties provide insight into the structure–function relationships of nanomaterials. However, simultaneous measurement with comparable and high resolution is a challenge. We seamlessly integrated nanoscale photothermal infrared imaging with Coulomb force detection to form peak force infrared–Kelvin probe force microscopy (PFIR‐KPFM), which enables simultaneous nanomapping of infrared absorption, surface potential, and mechanical properties with approximately 10 nm spatial resolution in a single‐pass scan. MAPbBr₃ perovskite crystals of different degradation pathways were studied in situ. Nanoscale charge accumulations were observed in MAPbBr₃ near the boundary to PbBr₂. PFIR‐KPFM also revealed correlations between residual charges and secondary conformation in amyloid fibrils. PFIR‐KPFM is applicable to other heterogeneous materials at the nanoscale for correlative multimodal characterizations.     

化学力显微镜对自组装单分子膜的力滴定研究

The concept of force titration was firstly proposed based on the technique of Chemical Force Microscopy (CFM). Self-Assembled Monolayer (SAM) on substrate surface can be titrated with buffer solutions at a nanometer scale by measuring the adhesion force between the SAM-modified substrate and probe tip. The plot of adhesion force vs pH value was termed as force titration curve. As an example, the titration behavior of w-mercaptoundecanoic acid monolayer on gold has been studied. It was found that there is a big hump around pH 5~6 in its force titration curve. Taking the contact angle titration result together, an interaction model for the monolayer was suggested from the chemical hysteresis point of view.     

原子力显微镜中化学成键对力的贡献

迄今非接触原子力显微镜已经成为一个非常强大的工具. 它不仅能够得到表面的原子周期结构,还能给出分子内部的化学键信息. 针尖和样品之间的相互作用是原子力显微镜的有效信号,主要包括三种,即范德瓦尔斯相互作用、静电相互作用和化学键相互作用. 本文在生长于Si(111)-7×7 的铅薄膜上测量了针尖和样品之间的化学键相互作用. 通过获取该相互作用随偏压的变化,并且利用抛物线拟合有效局域接触势的位置,我们发现它是随着针尖和样品之间距离的增大而减小的. 这种趋势来自于针尖和样品之间波函数的交叠. 从而可以得到电子的衰减长度. 我们还测量到了该衰减长度随着铅薄膜厚度的变化会发生振荡,这种振荡归因于平顶楔形铅岛内电子的量子尺寸效应.     

Direct Measurement of the Depletion Force Using an Atomic Force Microscope

The interactions between colloidal particles immersed in solutions of a nonadsorbing polymer are of interest in a variety of applications such as paint and ink formulations and mineral processing. In this Letter we report the use of an atomic force microscope to study the interaction forces between a silica particle (of radius 3.8 μm) and a planar silica surface, both bearing a terminally grafted n-octadecyl alcohol sheath (SiO₂-C₁₈), mediated by cyclohexane solutions of poly(dimethyl siloxane) (PDMS). The experimental results are consistent with theories of the depletion interaction between hard, chemically inert surfaces in the presence of free (nonadsorbing) polymer in solution. The length of the measured (attractive) interaction was commensurate with the radius of gyration of the PDMS sample used, and the magnitude of the force increased with increasing polymer concentration. As the surfaces closely approached each other, a short-range steric interaction was observed as the opposing octadecyl chains came into contact, and this interaction was independent of the free polymer concentration.     

Force Constant Transportability Problem

For XY₃ complexes with light and heavy terminal atoms, the force constant transportability problem is solved by the extrapolation method using semiempirical relations. A potential function is constructed using the transport relations, and the fundamental frequencies are calculated for the hydroxonium ion.     

Force in scf theories

A new force approach is reported in which we improve the wavefunction so that the Hellmann-Feynman theorem is satisfied. A sufficient condition for the Hellmann-Feynman theorem to be satisfied is that the basis set includes AO derivatives ?x_r/?x_rfor any basis x_r. Here we test a procedure in which only the first derivative AOs are added to the “parent” AOs. The results are very encouraging.     

基于原子力显微镜的单分子力谱在生物研究中的应用

原子力显微镜被广泛应用于生物研究领域,基于原子力显微镜的单分子力谱可以在单分子、单细胞水平上研究生物分子内和分子间的相互作用。 本文介绍了原子力显微镜单分子力谱在生物分子间相互作用、蛋白质去折叠、细胞表面生物分子、细胞力学性质和基于单分子力谱成像等研究中的最新进展。     

Unbinding Molecular Recognition Force Maps of Localized Single Receptor Molecules by Atomic Force Microscopy

Atomic force microscopy is a technique capable to study biological recognition processes at the single‐molecule level. In this work we operate the AFM in a force‐scan based mode, the jumping mode, where simultaneous topographic and tip–sample adhesion maps are acquired. This approach obtains the unbinding force between a well‐defined receptor molecule and a ligand attached to the AFM tip. The method is applied to the avidin–biotin system. In contrast with previous data, we obtain laterally resolved adhesion maps of avidin–biotin unbinding forces highly correlated with single avidin molecules in the corresponding topographic map. The scanning rate 250 pixel s^?1 (2 min for a 128×128 image) is limited by the hydrodynamic drag force. We are able to build a rupture‐force distribution histogram that corresponds to a single defined molecule. Furthermore, we find that due to the motility of the polymer used as spacer to anchor the ligand to the tip, its direction at rupture does not generally coincide with the normal to the tip–sample, this introduces an appreciable error in the measured force.     

Force constants in hydrogen-bonded crystals

Hydrogen bond stretching force constants in crystals of imidazole, urea and cyanuric acid are calculated using both a modified CNDO/2 method and a constrained least squares fitting of interatomic pair potentials to the lattice vibrations. Results show that the modified CNDO/2 method gives closer agreement with the experimentally derived force constants than the normal CNDO/2 parameterization.     

Consistent Force Fields for Saccharides

ABSTRACT

Consistent force fields for carbohydrates were hitherto developed by extensive optimization of potential energy function parameters on experimental data and on ab initio results. A wide range of experimental data is used: internal structures obtained from gas phase electron diffraction and from x-ray and neutron diffraction, vibrational frequencies, dipole moments, unit cell dimensions and lattice energies. The range of model compounds covered so far includes alkanes, ethers, alcohols, ketones and mono- and disaccharides. Electrostatic interactions are handled by fractional charges assigned to individual atoms. Charges are modeled such that Mulliken population analyses are reproduced. Morse functions are used for all bonded interactions; experimentally derived dissociation energies are used as parameters. Van der Waals interactions are modeled with Lennard-Jones 12-6 functions. The anomeric and exo-anomeric effects are accounted for without addition of specific terms. The work is done in the framework of the Consistent Force Field which originated in Israel and was further developed in Denmark. The actual methods and strategies employed have been described previously. Extensive testing of the force field is reported, and ways and means of improvement are indicated. Principles of mapping of conformational space are discussed, and a discussion on which properties to preferentially reproduce in modeling is invited.     

Force microscopy and surface interactions

The force microscope provides the most flexible of surface force measurement techniques for probing the richness and complexity of surface interactions. The technique is reviewed over the past 3 years for developments in instrumentation, colloidal force measurement, and nano-mechanical measurements on single molecules.     

Force field parameters for carbohydrates

A new set of force field parameters for carbohydrates is reported. The parameter set is based on the CHARMM22 force field of Karplus and co-workers. The parameterization is based on newly performed high-level ab initio calculations [MP2/6-311 + G (2d, 2p)/ /6-31G**] of fragment molecules. A good agreement of the modified force field and ab initio data is achieved, which is demonstrated with a variety of molecules. © 1996 by John Wiley & Sons, Inc.     

采用超低场生物力谱技术研究核酸适配体与凝血酶蛋白的相互作用

蛋白质和核酸是构成生命体最为重要的两类生物大分子,它们之间的相互作用是分子生物学研究的中心问题之一,也是许多生命活动的重要组成部分。本文基于一种全新的超低场生物力谱技术,以凝血酶蛋白为研究对象,考察了凝血酶与其对应的核酸适配体之间的相互作用。结果表明,凝血酶蛋白与核酸适配体之间的结合力大小约为80 p N。同时,在分子水平上获得了凝血酶蛋白与核酸适配体之间的解离动力学信息。     

Calculation of Second- and Higher-Order Force Constants Including Electron Correlation Effects and Hartree-Fock Force Constant Scaling

A formalism suitable for practical implementation is suggested for computation of quadratic, cubic, and quartic force constants using the configuration interaction (CI) method. Expressions are compared which involve the Hartree-Fock (HF) harmonic and anharmonic force constants calculated by the HF and CI methods. Also, physical assumptions are formulated to perform scaling of the diagonal harmonic and, which is more important, of anharmonic HF force constants with a common scaling factor. This approach is consistent with the data of ab initio quantum-chemical calculations. A table is presented which compares the results of valence force constant calculations for a series of simple organic molecules.     

分子力场发展的新趋势

分子模拟中的力场方法是用来精确计算分子结构和能量的计算方法,它通过原子核的位置来计算体系能量。最初的分子力场都是针对某一特定体系的,它们的许多参数要由观测数据拟合得到。当时要建立新的分子力场是十分困难的,因为实验归属振动谱带需要花费大量的时间。所以此后大多数工作者都致力于发展涵盖尽可能多体系的“求全”型分子力场,这种趋势一直延续至今。但是随着各个学科研究的不断深入,所需要研究的体系越来越复杂,要求的精度也越来越高。在保证相当精度的条件下,“求全”型的分子力场要想涵盖所有需要研究的体系常常是十分困难的事情。2003年问世的Direct Force Field软件包能够便捷的建立针对某一特定分子体系,并且有相当精度的分子力场。它的出现为分子力场从“求全”转为向“求精”发展提供了可能。     

Arene-Perfluoroarene Force Driven Sublimation-Removable Chiral Coassemblies

Multiple constituent coassembly is an emerging strategy to manipulate supramolecular chirality and chiroptical properties such as circularly polarized luminescence (CPL). However, the second or third constituent could not be removed from pristine self-assembly. Here we developed a constitute-removable chiral coassembly using sublimation that could realize coassembly with tunable supramolecular chirality, luminescence and CPL properties. Octafluoronapthalene (OFN) with small sublimation enthalpy formed coassemblies with perylene-conjugated peptoids via arene-perfluoroarene (AP) interaction that induced the emergence of macroscopic chirality and hypsochromic luminescence from yellow to green. Coassembly with OFN accelerated one-dimensional growth and induced the emergence of macroscopic chirality and CPL. Despite the stability at ambient conditions, vacuum-treatment triggered fast sublimation of OFN, which behaved as a sacrificial template. Physical removal of OFN retained the helical nanoarchitectures as well as the basic features of Cotton effects and CPL activities. X-ray diffraction suggested the back-fill consolidation occurred on the molecular voids by OFN removal that slightly varied the templated molecular arrangements. Sublimation of perfluorinated building units is green and efficient and non-destructive, which is potentially applicable in constructing template-directed chiroptical materials and devices.