Film properties elastic modulus

Indentation has been used for over 100 years to determine hardness of materials [8J. For a given indenter geometry (e.g. spherical or pyramidal), hardness is determined by the ratio of the applied load to the projected area of contact, which was determined optically after indentation. For low loads and contacts with small dimensionality (e.g. when indenting thin films or composites), a new way to determine the contact size was needed. Depth-sensing nanoindentation [2] was developed to eliminate the need to visualize the indents, and resulted in the added capability of measuring properties like elastic modulus and creep. 

Polyurethanes based on the HDI cyclic trimer show a rubberlike mechanical behavior. In fact, the Z1030/1072 and Z1031-H films show a low elastic modulus E, no yielding, and an ultimate, widely reversible, deformation beyond 100-150%, likely underestimated owing to the difficulty in assessing the ultimate properties of self-supported thin films. 

The stabilising action of the adsorption layers from high molecular substances (protective colloids) is related to the decrease in the forces of molecular attraction. Hence, films from aqueous solution of polyvinyl alcohol obtained between drops of cyclohexane have thickness of 80 nm and respectively, a very low attraction force, in contrast to black films [513]. Along with that the adsorption layers from such compounds possess visco-elasticity properties with modulus of elasticity 104 N m"2, impeding the film thinning and drop coalescence [503]. 

This section examines the dynamic behavior and the electrical response of a TSM resonator coated with a viscoelastic film. The elastic properties of viscoelastic materials must be described by a complex modulus. For example, the shear modulus is represented by G = G + yG", where G is the storage modulus and G" the loss modulus. Polymers are viscoelastic materials that are important for sensor applications. As described in Chapter S, polymer films are commmily aj lied as sorbent layers in gas- and liquid-sensing applications. Thus, it is important to understand how polymer-coated TSM resonators respond. 

The detection of chemical analytes can be based on changes in one or more of the physical characteristics of a thin film or layer in contact with the device surface. Some of the intrinsic film properties that can be utilized for detection include mass/area, elastic stiffness (modulus), viscoelasticity, viscosity, electrical conductivity, and permittivity. In addition, changes in extrinsic variables such as... 

To measure the hardness and elastic modulus of thin films while avoiding the influence of the substrate, peak indentation depth cannot exceed about 30% of the film thickness.Because commercial nanoindenters can make a minimum penetration depth of 10-15 nm, hardness and elastic modulus of films thinner than 30 nm cannot be measured. Clearly, new techniques for fabricating sharper indenters and new nanoindentation theories are needed to extend this technique. For film thicknesses less than 30 nm, nanoscratch tests are widely accepted to evaluate the mechanical properties (discussed later). Alternatively, assuming the hardness and elastic modulus of a film do not change with thickness, thicker films can be used. 

Nanomechanical properties show a distinct dependence on the deposition temperature. Films deposited at 20-200°C possess the highest hardness up to 14 GPa. The lowest friction coefficient was measured for films deposited at 400-600°C. Generally, the CNX-Ni films have higher hardness and elastic modulus but lower coefficient of friction than their C-Ni counterpart films probably due to nitrogen cross-links between graphitic layers. 

The technological importance of thin films in such areas as semiconductor devices and sensors has led to a demand for mechanical property information for these systems. Measuring the elastic modulus for thin films is much harder than the corresponding measurement for bulk samples, since the results obtained by traditional indentation methods are strongly perturbed by the properties of the substrate material. Additionally, the behaviour of the film under conditions of low load, which is necessary for the measurement of thin-film properties, is strongly influenced by surface forces [75]. Since the force microscope is both sensitive to surface forces and has extremely high depth resolution, it shows considerable promise as a technique for the mechanical characterization of thin films. 

For DR values between 10 and 50, a decrease in elastic modulus with DR is observed. In the case of a polymer blend, such as PA6/LDPE, there is an almost independent behavior of the tensile properties in the MD of noncompatibilized blends as a function of the dispersed phase concentration. However, in the TD, a clear dependence of the elastic modulus is observed. It is also observed that compatibilized films have higher modulus compared to noncompatibilized films. For the films presented in Table 24.4, PA6 particulate fibers... 

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