SPM techniques

As a solid scanning probe is used, the specimen can be affected by the imaging process, but the damage is now mechanical instead of radiation damage. It is comparatively easy to make pits and holes in polymer samples with the SPM, so that care still has to be taken in imaging. 

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SPM encompasses a group of surface-detection techniques that include AFM and scanning tunneling microscopy (STM) that allow the topographic profiling of surfaces. SPM techniques investigate only the outermost few atomic layers of the surface with nanometer resolutions and at times atomic-level resolution. 

This book is specifically addressed to the properties of polar oxides as well as to their chac-terization and imaging techniques. The dielectric, optic, piezoelectric, pyroelectric behavior of this class of materials is discussed. Emphasis is placed on novel methods in the field of electrical and optical investigations, scanning probe microcoscopy (spm) techniques and advanced X-ray analysis. The book starts with tutorial reviews, and arrives at up-to-date results about polar oxides. Therefore, it not only stimulates and further motivates young scientists but is of considerable interest for the members of our community. 

The SPM technique allows measurements of the local sample surface potential. The NanoScope recorded two passes. In the first pass, the sample surface topography was obtained by the standard tapping mode. The surface potential was measured during the second pass carried out in the lift mode (lift height was 100 nm). Here the cantilever s vibration is turned off and an oscillating voltage U c cos cot is applied directly to the cantilever tip. This creates an oscillating electrostatic force F at the frequency co on the cantilever ... 

Fig. 1 Distribution of the surface potential (i/>surf) on polymer surfaces visualized by means of the SPM technique for PS (a) and line scan (b) along the white line in the SPM image...

The tribo-electric charging of polymers is a collective phenomenon of numerous electron transfer processes in the contact zone of two colliding particles. The SPM technique allows to visualize the charge distribution on polymer surfaces. It was shown that oppositely charge domains can stably exist side by side although considerable filed strengths are present. 

Nano Manipulation As the name suggests, this is quite literally a technique for physically manipulating matter at the nanoscale. Scanning probe microscopy (SPM) techniques have been most widely used to achieve this using the scanning probe tip as an implement for assembling atoms, molecules, or nanoparticles according to the desired spatial conformation [166-169],... 

It should be noted that near-field scanning optical microscopy (NSOM) (discussed at the beginning of this chapter) is often grouped alongside other SPM techniques. However, for our discussion, we will focus on AFM and STM since these use physical probes to interrogate a surface, rather than focused light. 

In this context, the SPM techniques (and especially STM and AFM) appear, a priori, ideally suited for the direct visualization of the porous structure of materials at scales which are not so readily accessible by other means (e.g., scaiming and transmission electron microscopies). However, the performance of such a task is confronted with two major limitations. The first one arises from the fact that detection with SPM is exclusively restricted to the outermost surface of the sample. Accordingly, this implies that only the most external porosity of the material can be probed, whereas no information on the bulk (inner) porosity, which might not be identical to the former, is revealed. The second drawback is related to the finite dimensions of the probing tip, which limits the size of the voids (pores) physically accessible (and thus detectable) by the tip on the sample surface. Obviously, pores significantly smaller than the tip diameter will pass uimoticed to the instrument when the surface is scanned. As a specific example, the tips normally employed in AFM are not sharp enough to provide access to the whole mesopore range (between 2 and 50 nm). 

The main differences between the different SPM techniques lie in the type of interaction that is used to control the tip-sample distance. Although the SPM offspring are remarkably numerous [3,4], here we will focus only on STM and AFM, as they remain the most widely used and the best suited for high resolution imaging of surface structures. 

New SPM techniques and instruments in which SPM is combined with other techniques continue to be developed. Papers reviewing the state-of-the-art are published regularly. A number of these are included in the reference list in sec. 3.10e. 

The importance of SPM for the study of monolayers is that it allows the visualization of the structure and defects of transferred and self-assembled monolayers on solid substrates at length scales from <0.1 nm to > 10 pm. It is not fyet ) possible to image monolayers at liquid/fluid Interfaces with SPM techniques. However, it has already been shown that it is feasible to measure interaction forces between a colloidal particle and such interfaces in the presence and absence of monolayers ). 

Although both the PCA and the SPM techniques reduce the number of variables, the resulting matrices of PC loadings and variables and the spectral map are still multidimensional. The plot of PC loadings in the first vs. the second principal component has been frequently used for the evaluation of the similarities and differences among the observations. This method takes into consideration only the variance explained in the first two principal components and entirely ignores the impact of variances explained by the other principal com-... 

How can the tunneling barrier width and the lateral position of the tip be controlled so accurately Tire tip is mounted on an actuator consisting of piezoelectric ceramics for reliable and exact positioning in all three dimensions (particular for the scanning). Only the nanometer positioning ability of piezo ceramics (see Tutorial 2 on Piezoelectric Tube Scanners and Translational Stages) made SPM techniques initially possible. 

Despite the experimental problems experienced daily, such as tip/cantilever preparation, scarmed surface preparation, noise dumping, data interpretation, the SPM field is still developing rapidly and new SPM techniques are proposed. 

The other landmarks which happened in the middle of the 8O s were a demonstration of the possibility of appheation of the STM apparatus for lithography (Fig. b), and for controlled atom handling. The invention of AFM microscope opened the route for the construction of several different force microscopies (SPM techniques). This way the use of STM/SPM techniques as a Feynman Machine finally had been realized, the STM apprenticeship time came to an end and the time of travel begau... 

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