Depth micrometers

Hydrogen to uranium all isotopes Yes, on a scale of few micrometers depth Yes, depending on the laser irradiance... 

Laser ablation is a technique frequently applied in many industrial applications. However, for generating micro structures of several hundred micrometers depth the method appears not to be cost competitive. However, for smaller channel dimensions in the range well below 100 pm, laser ablation might well be a cost competitive option especially for small-scale applications. 

Spatially offset Raman spectroscopy (SORS) Conventional Raman Spectroscopy is limited to the near-surface of diffusely scattering objects and to the first few hundred micrometers depth of surface material. Spatially Offset Raman Spectroscopy (SORS) is a variant of Raman Spectroscopy that allows highly accurate chemical analysis of objects beneath obscuring surfaces. This is done by making at least two Raman measurements one at the surface and one at an offset position of t3q>ically a few millimeters away. To do this without using an offset measurement would be severely restricted by photon shot noise generated... 

Laser ablation is a frequently apphed fabrication technique of proven industrial suitabihty [41, 42]. However, fabrication of microchaimels of several hundred micrometers depth, as typically required for many apphcations using microstructured reactors, will take too long and therefore the method is not cost competitive. For smaller chaimel dimensions, laser ablation is a viable option, especially for apphcations on the smaUer scale. 

A multilayer-type structure probably due to cords in the molten zone between single arc sprayed (0.25 MPa) Ni droplets and steel substrate were found in AES point depth profiles [2.158]. That particular arc spraying condition turned out to yield the best adhesion. Plasma-sprayed AI2O3 layers separated from pre-oxidized Ni Substrate had a micrometer-thick NiO layer on the substrate-sided face and micrometer-deep oxide interdiffusion [2.159]. In this work also, AES point depth profiling substantiated technological assumptions about adhesion mechanisms. 

FTIR also has several disadvantages. For example, depth profiling is not possible in RAIR. In ATR, surfaee sensitivity is limited to approximately the wavelength of infrared radiation or about one micrometer (see below). The spatial resolution of eonventional infrared teehniques is limited by diffraetion effeets and is only approximately a few tens of micrometers. 

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

SIMS has superb surface sensitivity since most of the secondary ions originate within a few nanometers of the surface and since high detection efficiency enables as little as 10 " of a monolayer to be detected for most elements. Because of its very high surface sensitivity, SIMS can be used to obtain depth profiles with exceptionally high depth resolution (<5 nm). Since the beam of primary ions can be focused to a small spot, SIMS can be used to characterize the surface of a sample with lateral resolution that is on the order of micrometers. Elements with low atomic numbers, such as H and He, can be detected, isotope analysis can be conducted, and images showing the distribution of chemical species across... 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

In non-highly focussed laser desorption ionisation, employing spot sizes in the range of 50-200 pm in diameter, the surface is deformed by an ablation volume of about 1 pm3 per pixel per laser pulse. But this ablated volume is spread over a large desorption area leading to ablation depths of the order of a few nanometres. In laser microprobing, the same ablation volume leads to ablation crater depths in the micrometer range. 

As already indicated above, what one may consider a surface depends on the property under consideration. Adhesion is very much an outer atomic layer issue, unless one is dealing with materials like fibreboard in which the polymer resin may also be involved in mechanical anchoring onto the wood particles. Gloss and other optical properties are related to the penetration depth of optical radiation. The latter depends on the optical properties of the material, but in general involves more than a few micrometer thickness and therewith much more than the outer atomic layers only. It is thus the penetration depth of the probing technique that needs to be suitably selected with respect to the surface problem under investigation. Examples selected for various depths (< 10 nm, 10 s of nm, 100 nm, micrometer scale) have been presented in Chapter 10 of the book by Garton on Infrared Spectroscopy of Polymer Blends, Composites and Surfaces... 

In recent years, the measurement of thick adlayers has received an increasing interest in the field of so-called polyelectrolyte multilayer films. These films sometimes have a thickness of several micrometers. Such large thicknesses are obviously not easily monitored using conventional waveguide sensors because of the limited penetration depth into the adlayer. Simply, waveguide sensors loses their sensitivity when the adsorbed layer thickness exceeds 2 3 times the penetration depth of the evanescent field and cannot be used to monitor films thicker than 350 nm12. 

Figure 3. Depth in micrometers of charge injection in a 25-fitn fluoroethylene polymer film as a function of energy of injected electrons.

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