Nano indentation

Another largely unexplored area is the change of dynamics due to the influence of the surface. The dynamic behavior of a latex suspension as a model system for Brownian particles is determined by photon correlation spectroscopy in evanescent wave geometry [130] and reported to differ strongly from the bulk. Little information is available on surface motion and relaxation phenomena of polymers [10, 131]. The softening at the surface of polymer thin films is measured by a mechanical nano-indentation technique [132], where the applied force and the path during the penetration of a thin needle into the surface is carefully determined. Thus the structure, conformation and dynamics of polymer molecules at the free surface is still very much unexplored and only few specific examples have been reported in the literature. 

A most recent commercial Nano Indenter (Nano Indenter XP (MTS, 2001)) consists of three major components [66] the indenter head, an optical/atomic force microscope, and x-y-z motorized precision table for positioning and transporting the sample between the optical microscopy and indenter (Fig. 28). The load on the indenter is generated using a voice coil in permanent magnet assembly, attached to the top of the indenter column. The displacement of the indenter is measured using a three plate capacitive displacement sensor. At the bottom of the indenter rod, a three-sided... 

Fig. 32—The hardness of the DLC films as a function of indentation depth measured with a Nano Indenter XP system using CSM Technique.

The nano indentation technique can also be used to measure fracture toughness at small scales, by using the radial crack, which occurs when brittle materials are indented by a sharp indenter [72,73]. Lawn et al. [74] have shown that a simple relationship exists between the fracture toughness, Ag, and the lengths of the radial cracks, c, in the form of ... 

This model is not precise, but does identify some of the factors that are important to indentation. Like the model, the hardness measurement process is not precise. At the micro-hardness level, the projected areas of indentations are measured, but this can only be done with about 10% accuracy. At the nano-indentation level, relative values can determined accurately, but absolute values are probably only about 10% accurate. 

Besides compression testing, AFM has been used to derive intrinsic material properties of yeast cell walls by nano-indentation. This technique was employed by Touhami et al. (2003) to determine the... 

Instrumented nano-indentation (Nano Indenter II) under low applied loads (10 to 100 mN) for all the samples. The announced values are the average of the results of 6 indentations, each resulting from two consecutive load/unload cycles. Young s modulus is calculated by the software supplied with the indenter using data from the second unloading with the Berkovich pyramid indenter of known shape function. 

The results indicate that the Young s modulus (E) determined perpendicularly to the surface by instrumented nano-indentation on solid steel and Ta specimens were in good agreement (within 10%) with the values obtained by dynamic bending and by tensile testing. Such a result was corroborated hy measurements obtained from other materials presenting different elastic responses. 

Schall et al. indented colloidal crystals using a needle with an almost hemispherical tip of diameter 40 dm, inducing a strain field in which tine maximum shear strain lies well below the contact surface. The tip diameter, particle radius and crystal thickness in their experiments were chosen to be similar to parameters in typical metallic nano-indentation experiments. The authors discussed their observations using a model that addresses the role played by thermal fluctuations in the nucleation and growth of dislocations. 

The mechanical behavior of coatings under point loading conditions was studied by nanoindentation using Berkovich indenter on Nano Indenter-II (MTS Systems Corporation, Oak Ridge, TN, USA). The nanohardness of chromium and molybdenum coatings was determined by the Oliver and Pharr analysis. 

Its topography reveals the unique structure consisting of aligned prisms or rods with 5pm diameter that extent approximately perpendicular from the dentin-enamel junction towards the tooth surface. Each rod consists of tightly packed carbonated hydroxyapatite crystals with very high aspect ratio. Nano-indentation studies revealed a pronounced anisotropy as the stiffness differs parallel and perpendicular to the rod extension. Even so, different fibre orientation on a micro level as shown in Figure 3.4b account for a quasi-isotropic behaviour. 

Gindl, W. and Gupta, H. S., Cell-Wall Hardness and Young s Modulus of Melamine-Modified Spruce Wood by Nano-Indentation, " Composites Part A Applied Science and Manufacturing, Vol. 33, 2002, pp. 1141-1145. 

Table 2 Elastic modulus and hardness of chitosan coatings determined from nano-indentation...

Considering that for our substrates the maximum indentation depth is 89 nm (Table 3.3), we have decided to perform constant nano-indentation depth experiments up to 80 nm. Moreover, considering the longitudinal stiffness of the can-... 

As the tip of the AFM makes direct contact with the sample, the physical properties as well as topography of the surface can be examined. For example, the AFM can be used as a mechanical nano-indent or. Young s moduli of a living cell were measured with high spatial resolution (Cl, HI, Ml, S2). 

Atomic force microscopy has been combined with nano-indentation and nano-scratching studies [95]. The hardness (and, to a similar extent, the friction coefficient) of passivated titanium was three to four times higher under in situ conditions, this was assigned to a much faster repassivation process in the presence of the passivating electrolyte solution. Nanotribology, particularly surface friction forces mea-... 

The development of thin-film engineering and the increasing use of nanomaterials have led to the development of nano-indenters. These are described in more detail in Section 10.3.3. 

In a nano-indentation test, the load applied to the indenter and the resultant displacement are measured as a function of time. In this sense, the test... 

Figure 10.35 Methods of measuring the mechanical properties of thin films (a) Nano-indentation, (b) beam deflection and (c) disc deflection. (Adapted from G.M. Pharr and W.C. Oliver, 1992, Measurement of Thin Film Mechanical Properties Using Nanoindentation , Materials Research Society Bulletin XVII (July) 28...

---