Jan. 23, 2012

Principal Component Analysis in Dynamic Force Spectroscopy

A simple method to direct identify nanometer sized textures in composite materials by means of AFM Spectroscopy, aiming at recognizing nanometer structures embedded in a sample. It consists in acquiring a set of dynamic data organized in spectroscopy maps and subsequently extracting most valuable information by means of the Principal Component Analysis (PCA) method [1]. In this work we explain the main features of the method and show its application on a nanocomposite sample. Force Spectroscopy by AFM moreJan. 16, 2012

Triple-Frequency Atomic Force Microscopy

It has previously been shown that bimodal tapping-mode AFM can provide increased compositional contrast. Here we discuss the addition of a third eigenmode to this scheme in order to acquire simultaneous topography, phase and frequency shift. The results suggest that, in general, the phase and frequency shift contrast exhibit anti-parallel behavior, although deviations from this trend are often observed in the experiments, such that all sources of contrast can provide complementary information. Multi-Frequency AFM moreDec. 19, 2011

Multifrequency Atomic Force Microscopy

Multifrequency Atomic Force Microscopy (AFM) involves several force microscopy methods that aim to improve spatial resolution, data acquisition times and quantitative mapping of surface properties with respect to the level that has been achieved by conventional AFM. About twenty years ago, amplitude modulation AFM (tapping-mode) was introduced to avoid the sample modifications introduced by lateral forces that existed during contact AFM operation. moreDec. 05, 2011

Tip Mass Effects on Image Contrast

When an oscillating AFM cantilever approaches a sample, the tip-sample interaction force influences the cantilever dynamics. The magnitude of the contact interaction force depends on the stiffness of the materials. Stiffness of the material affects sensitivity of different modes differently. This sensitivity controls the image contrast. Here, the effect of tip mass on the modal flexural sensitivity of AFM cantilever to the variations of surface stiffness and image contrast is investigated.
moreNov. 25, 2011

High Resolution Optical Tweezers for Single-Molecule Studies of Eukaryotic Transcription

Investigating mechanical aspects of single RNA polymerases will further our understanding of the molecular mechanism of transcription elongation.
moreNov. 24, 2011

Drag Reduction by DNA-grafting for Single Microspheres in a Dilute λ-DNA Solution

The fluid resistance of single micrometre-sized blank and DNA-grafted polystyrene microspheres under shear flow is compared in purified water and dilute λ-DNA solutions by means of optical tweezers experiments with a high spatial (±4 nm) and temporal (±0.2 ms) resolution.
moreAug. 04, 2011

Consistent Isolation and Fluorescence Imaging of Individual Atoms

We describe new methods to consistently isolate and image individual atoms. We isolate one atom by inducing inelastic light assisted collisions in a group of atoms held in optical tweezers. Each atom pair that undergoes a collision gains enough energy for only one of the atoms to leave the optical tweezers, leading to a single atom remaining. This atom is imaged using fluorescence microscopy. moreAug. 01, 2011

Laser-Guided Atomic Force Microscopy

Application of Atomic Force Microscopy (AFM) to a broad range of research, and biological systems in particular, is hampered by two longstanding technical problems: mechanical drift and finding sparsely distributed samples. By adapting ideas from the optical-trapping community, we have made significant progress in addressing both of these issues, including a 100-fold improvement in the stability of AFM at ambient conditions. more