Minimum penetration depth

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. 

Molten sulfur, both pure and chemically modified, was poured onto the sand contained in 400-ml glass beakers. The average minimum penetration depth of the solidified sulfur into the sand was measured directly. 

At (j> the penetration depth approaches a minimum, particularly for reflective surfaces such as chemi-mechanically polished Si. Total reflection disappears on rough surfaces (Fig. 4.3). Below rj> the penetration depth is in the range of a few nanometers (Fig. 4.4). 

The surface sensitivity of most electron probe techniques is due to the fact that the penetration depth of electrons into metals falls to a minimum of 4 to 20 A when their kinetic energy is between 10 and 500 eV. It is also convenient that electrons at these energies have de Broglie wavelengths on the order of angstroms. With a monochromatic beam, it is possible to do LEED. 

DEPTH PROFILE. The secondary electrons produced by ionization processes from an incident beam of high-energy electrons are randomly directed in space. Spatial "equilibrium" is achieved only after a minimum distance from the surface of a polymer in contact with a vacuum or gaseous environment (of much lower density). Consequently, the absorbed radiation dose increases to a maximum at a distance from the surface (2 mm for 1 MeV electrons) which depends on the energy of the electrons. The energy deposition then decreases towards zero at a limiting penetration depth. 

The existence of a maximum thickness beyond which the performance deteriorates is due to the concerted impact of oxygen and proton transport limitations. Considered separately, each of these limitations would only serve to define a minimum thickness below which performance worsens due to an insufficient electroactive surface. The thickness of the effective layer, in which current density is predominantly generated, is given by the reaction penetration depth ... 

Absolute dosimetry with the electron accelerator is less accurate than with the cobalt-60 source since penetration of the electron is a variable— directly proportional to the energy of the beam and inversely proportional to the density of the material. The absorbed dose varies with depth (18) and is about 60% of maximum at the surface with a steady increase to a maximum at about one-third of the total penetration depth. At about two-thirds of the total penetration, the dose is equivalent to that absorbed at the surface. Therefore, if all parts of the sample are to receive the same minimum dose, the useful penetration is approximately two-thirds of the total, or about 0.33 gram per square centimeter per m.e.v. 

X-ray Fluorescence. The minimum diameter irradiated was 2 mm for accurate data. Some data were obtained with 0.5 mm diameter, but the accuracy is reduced. (This limitation in areas irradiated by the beam is not necessarily true for the general application of this technique to art objects. However, the method samples a surface and thus raises the question as to how representative the volume sampled is of the bulk.) Assuming for silver an average penetration depth of 50 /xm (4), the volume sampled is — 150 X 106 /xm3 = 1500 /xg. 

To explain the difference between the 248- and 308-nm irradiation some properties of the polymer and laser at the two irradiation wavelengths must be discussed. At 248 nm the penetration depth of the laser is about 150 nm, whereas for 308 nm the penetration depth is only 60 nm. In addition, the photon energy at 248 nm is 5 eV as compared to the 4 eV at 308 nm. This is one of the reasons why the quantum yield (QY) of photolysis in solution for 248 nm is higher (1.5%) than for 308 nm (0.22%) [120]. A closer inspection of the UV spectra (Fig. 10) reveals that 248 nm is at a minimum of the absorption curve. Assuming a Lorentzian profile for the different absorption bands, it is obvious that an irradiation with 248 nm can lead to a direct excitation of the absorption bands below and above 248 nm. 

Flute Length. Minimum flute length must equal total drilled depth (total laminate thickness + entry thickness + backup penetration depth) plus at least 0.050 in of unused drill flute remaining above the stack at the bottom of the drill stroke to allow debris to be removed by the vacuum system. If debris cannot be removed from the drill flutes during and between drill strokes, the results are extensive hole quaUty defects and drill breakage. 

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