**7.2 Dental enamel**

162 Atomic Force Microscopy – Imaging, Measuring and Manipulating Surfaces at the Atomic Scale

Fig. 19. Three individual spaces in a surface profile. The mean spacing is the average of the

Similar to the Rq and Ra, RMS Average Wavelength (λq) takes as reference the root mean square of the spacing between peaks and valleys weighted by their individual frequencies

q

q R

<sup>Δ</sup> (12)

three individual spaces on the evaluation length (Zygo Corporation, 2011).

and amplitudes (Park, 2011). RMS Average Wavelength can be calculated by:

Where Rq is the RMS roughness and Δq the RMS slope of profile (Park, 2011).

spectroscopy). This process is known as electrochemical intercalation.

q

λ 2π

The roughness is a very significant parameter for various applications. The characterization of materials through its roughness allows one to obtain information on the efficiency of

Some materials, usually transition metals oxides, are classified as intercalation materials. These materials are able to receive short radius ions (H+, Li+...) in its network structure via electrochemical techniques (such as cyclic voltammetry and electrochemical impedance

The electrochemical intercalation is a reversible process, making these materials very interesting in applications where the control over the ability of insertion/extraction of an ion

Intercalation materials are commonly used in micro-batteries, smart windows, smart mirrors, displays, gas sensors and other applications. These materials have potential applications due to the possibility of control of their electronic and optical properties.

The electro-physical-chemical properties of intercalation materials are strongly dependent

**6.2.6 RMS average wavelength** 

**7. Applications (materials)** 

materials in various application areas.

**7.1 Electrochemical intercalation** 

in a structure is essential.

on surface roughness.

Where Ra is the roughness average and Δa the mean slope of profile (Park, 2011).

The bleaching process can cause variation in the surface roughness of human tooth enamel. These changes are responsible for color changes, glare reduction, opacity.

The surface roughness is responsible for diffuse scattering of light incident on tooth enamel. Thus the surface roughness is an important variable in the bleaching process and must necessarily be considered.

The search for materials that do not significantly increase the roughness of the tooth surface is a challenge in dentistry. Bleaching agents based on nanoparticles of hidroxiapatatia have been shown to be effective by reducing the surface roughness and increasing the brightness of the tooth enamel (Takikawa et al., 2006).

The brightness and surface roughness are closely associated by an inverse correlation. As shown in the figure 20, the gloss increases with decreasing roughness of tooth enamel (Heintze et al., 2006).

#### **7.3 X-ray anode**

The anode is the positive electrode in an X-ray tube. It receives the impact of electrons accelerated by the potential difference due to the high voltage applied. The anode is generally made of materials that have high thermal dissipation, such as copper, molybdenum or rhenium. Depending on the x-ray application (i.e. energy of x-ray) a metal coating such as tungsten (W) or molybdenum (Mo) is placed over these thermally dissipative metals at the impact area of the accelerated electrons.

A change in the spectral distribution of X-rays in a cathode ray tube with increasing roughness of the anode has been observed. The increased surface roughness implies an increase of characteristic peaks and a decrease corresponds to the lower energies of the bremsstrahlung spectrum, and an increase in the average energy of beams of X-rays (Nagel, 1988; Stears et al., 1986). The increased surface roughness implies an increase of characteristic peaks and a decreasing in the part corresponding to the lower energies of the bremsstrahlung spectrum. Unlike the filtration process for tungsten (W) where a dip occurs at lower energies (Yoriyaz et al., 2009).

#### **7.4 Polymeric membranes**

In the area of environmental protection, a very significant technology is the process of separation by polymeric membranes. Polymeric membranes, such as Polysulfone / Blend Membrane PLURONIC F127, are used to separate the undesired solute in solution. Thus, the active area of the polymer membrane to carry out the process is the surface. The properties related to the surface are important for performing the separation process. Properties such as the pores size distribution, long-range electrostatic interactions and surface roughness are factors that determine the efficiency of polymer membrane for this application.

Measurement of the Nanoscale Roughness by

**8. Effect of RMS roughness on adhesion** 

binding of atoms and molecules.

contact, thus reducing adhesion.

of the tip used in AFM.

the effects that surface roughness plays on adherence.

Atomic Force Microscopy: Basic Principles and Applications 165

The surface roughness of the polymer membrane is a factor proportional to the bond strength of the membrane. The higher roughness leads to greater adhesive strength of the

In the study of surfaces, related applications to adherence are extremely important. The surface morphology plays a significant effect on adherence. In this section we will discuss

Adherence is a chemical-physical phenomenon responsible for the union of two surfaces when they come into contact. This union has force of high magnitude in conditions where there is a chemical bond with sharing of electrons, or Coulomb attraction. In some cases the bond strength has relatively low magnitude to occurring by attractive forces of VdW type. The origin of the adhesion force is the same fundamental force of nature responsible for the

This phenomenon of interest is multidisciplinary, for example, the effect of adherence on civil engineering projects, cell adhesion in different microorganisms, adhesion of bacteria on the surface of dental enamel, adhesion of polymeric membranes in separation processes for

When contact occurs between two solid bodies, adhesion is not observed. This is due to the fact that much of the surface has a roughness at the microscale. This roughness decreases the area of active interaction between two solid bodies, as only regions with peaks come into

Liu, D. -L. et al (2007) conducted a study concerning the effect of RMS roughness on the adhesion using AFM. This study provided a better understanding of the effect of roughness on the adhesion when working in the nanoscale. On this scale the effects of adhesion are

The total adhesion force in this case, the contribution of all molecules involved in the

<sup>R</sup> <sup>h</sup> <sup>2</sup>πω<sup>R</sup>

q c q cq

RR h R

Where: R = tip radius; Rq= RMS of roughness; hc = distance separating the tip/sample, and 2πωR represents the strength of the AFM system. The total force is normalized by the

The adhesion force falls with increasing surface roughness and also with increasing radius

**9. Complementary analysis: Fractal dimension and power spectral density**  Two powerful techniques for further analysis in the study of surfaces are the fractal dimension and Power Spectral Density. These analysis are based on surface roughness. This

2

(13)

solutes, adhesion of nanoparticles, among others (Bowen et al., 1998).

significant in applications of microelectromechanical systems.

process can be described by the equation (Bowen et al., 1998).

*F*

surface energy so that ω is the work of adhesion force.

membrane and greater efficiency in the separation process (Bowen et al., 1998).

Fig. 20. Relationship between surface roughness and brightness of the teeth treated with five different materials (Heintze & Russon, 2006)*.*

Fig. 20. Relationship between surface roughness and brightness of the teeth treated with five

different materials (Heintze & Russon, 2006)*.*

The surface roughness of the polymer membrane is a factor proportional to the bond strength of the membrane. The higher roughness leads to greater adhesive strength of the membrane and greater efficiency in the separation process (Bowen et al., 1998).
