Gregory Meyers

Tip-Surface Forces During Imaging by Scanning Tunneling Microscopy

The effect of compressive and shear forces between tip and surface during the operation of the scanning tunneling microscope (STM) is illustrated with examples obtained both in air and vacuum environments. We show that at typical gap resistances used in STM (≤20 GΩ) these forces can have significant effects. Compressive or repulsive forces give rise to anomalous topographic corrugations (elastic deformations) as well as to permanent damage (inelastic or plastic deformation). These forces also cause the anomalously low values obtained in measurements of the tunneling barrier height. The effects of shear forces when imaging weakly bound material will also be demonstrated.

Parametrization of atomic force microscopy tip shape models for quantitative nanomechanical measurements

The uncertainty of the shape of the tip is a significant source of error in atomic force microscopy (AFM) based quantitative nanomechanical measurements. Using transmission electron microscopy, scanning electron microscopy, or tip reconstruction images, it is possible to parametrize the models of real AFM tips, which can be used in quantitative nanomechanical measurements. These measurements use algorithms described in this article that extend classical elastic, plastic, and adhesive models of contact mechanics. Algorithms are applicable to the tips of arbitrary axisymmetric shapes. Several models of AFM tip have been utilized. The goal of tip model parameterization is to develop AFM tip-independent quantitative mechanical measurements at the nanometer scale. Experimental results demonstrate independence of the AFM measurements from tips and their closeness to bulk measurements where available. In this article the authors show the correspondence between microtensile, nanoindentation, and AFM based indenta...

Theoretical modelling and implementation of elastic modulus measurement at the nanoscale using atomic force microscope

Quantitative studies of mechanical behaviour and primarily elastic modulus are essential for material science at the nanometer scale. AFM nanoindentation is the most promising approach to address the problem. In our study we perform AFM-based nanoindentation (deflection-versus-distance curves) on a set of polymer materials with microscopic moduli ranging from 1 MPa to 10 GPa. The measurements were done with probes of different tip shapes and force levels from 100 nN to 3 μN. The tip geometry was evaluated from TEM and SEM micrographs and piecewise linearly interpolated for the use of analysis software; probe spring constant was determined from thermal tune data. The comparative analysis of nanoindentation data was carried out using models of Sneddon and Oliver-Pharr. We derived Sneddons integrals in closed form for any practical tip shape using a piecewise linear interpolation. Oliver-Pharrs method to account for plasticity for the unloading curve was adapted for Sneddons integrals. An interactive software implementation with both models was developed and applied.

Underfill adhesion to BCB (Cyclotene/sup TM/) bumping and redistribution dielectrics

The adhesion of several commercial underfills (Dexter Hysol FP4511, FP4527, and CNB775-34) to BCB (CYCLOTENE 4022, 4024) has been studied through die shear testing and subsequent failure analysis. Die shear values range between 69-30 MPa. Failure analysis by optical microscopy, profilometry and XPS spectroscopy indicates mixed mode failure at various interfaces. From the die shear data collected before and after 24 h water boil for Cyclotene 4022 and 4024 (with AP3000 adhesion promoter) and underfillers FP 4511 and 4527 we find the die shear strength decreases an average of 11% for the four comparisons. Adhesion promoters based on vinyltriacetoxysilane or 3-amino-propyltriethoxysilane show equivalent die shear performance. Substrate surface cleaning based on UV ozone treatment reveals oxidation of the BCB surface which by SIMS analysis remains <0.1 /spl mu/m deep after 10 min of treatment.

Feature Article: Tapping Mode Atomic Force Microscopy of Surface Morphology of Polymer Blends

Application of tapping mode atomic force microscopy (TMAFM) phase imaging techniques to characterize the morphology of polymeric blends is reviewed. The basic principle of TMAFM phase imaging capability is introduced. A summary of phase contrast applications for various polymeric blend systems such as rubber-rubber, plastic-rubber, and plastic-plastic blends is extensively discussed. The review shows that AFM is a very useful technique in probing micro-phase dispersion, compatibility between blend components, and local mechanical properties in polymeric blend systems.

Simultaneous Preparation of Multiple Polymer Brushes under Ambient Conditions using Microliter Volumes

The fabrication of well-defined, multifunctional polymer brushes under ambient conditions is described. This facile method uses light-mediated, metal-free atom-transfer radical polymerization (ATRP) to grow polymer brushes with only microliter volumes required. Key to the success of this strategy is the dual action of N-phenylphenothiazine (PTH) as both an oxygen scavenger and polymerization catalyst. Use of simple glass cover slips results in a high degree of spatial and temporal control and allows for multiple polymer brushes to be grown simultaneously. The preparation of arbitrary 3D patterns and functional/emissive polymer brushes demonstrates the practicality and versatility of this novel strategy.