Opaque irradiated materials

Effect of Beam Shape on Temperatures in Stationary, Opaque Irradiated Materials. Analytical solutions are available [18-23]. A primary quantity of interest for materials processing purposes is the maximum temperature rise, 0max = Tmm - T , and, at steady state, it is (in dimensionless terms) ... 

Effect of Material Motion on Temperatures in Opaque Irradiated Materials. As the beam velocity is increased from zero, the surface temperatures are modified as shown in Fig. 18.2 [18], At large Pe (= Urxla), surface temperatures are reduced with maximum values (for a particular velocity) remaining at y = 0 (due to symmetry) but migrating downstream from the center of beam irradiation as in Fig. 18.26 for the P = 1 case. Similar results are evident for... 

While "conventional positive photoresists" are sensitive, high-resolution materials, they are essentially opaque to radiation below 300 nm. This has led researchers to examine alternate chemistry for deep-UV applications. Examples of deep-UV sensitive dissolution inhibitors include aliphatic diazoketones (61-64) and nitrobenzyl esters (65). Certain onium salts have also recently been shown to be effective inhibitors for phenolic resins (66). A novel e-beam sensitive dissolution inhibition resist was designed by Bowden, et al a (67) based on the use of a novolac resin with a poly(olefin sulfone) dissolution inhibitor. The aqueous, base-soluble novolac is rendered less soluble via addition of -10 wt % poly(2-methyl pentene-1 sulfone)(PMPS). Irradiation causes main chain scission of PMPS followed by depolymerization to volatile monomers (68). The dissolution inhibitor is thus effectively "vaporized", restoring solubility in aqueous base to the irradiated portions of the resist. Alternate resist systems based on this chemistry have also been reported (69,70). 

The coalescence of atoms into clusters may also be restricted by generating the atoms inside confined volumes of microorganized systems [87] or in porous materials [88]. The ionic precursors are included prior to irradiation. The penetration in depth of ionizing radiation permits the ion reduction in situ, even for opaque materials. The surface of solid supports, adsorbing metal ions, is a strong limit to the diffusion of the nascent atoms formed by irradiation at room temperature, so that quite small clusters can survive. 

Some substances, such as alkaline-earth sulphides, emit visible light when irradiated by X-rays for these substances it is essential to have a sheet of optically opaque material (such as black paper) between the specimen and the film. 

FIGURE 18.2 Steady-state temperature distributions in the x and y directions for an elliptical, CW, Gaussian irradiation of a moving, opaque material [18]. 

Irradiation of Opaque and Volumetrically Absorbing Material with a Pulsed Beam. 

Radiation falUng on an opaque surface is either reflected or absoibed. The proportions reflected and ab-soibed are measured by the surface quahties reflectance p and absorptance a. The sum of the two must be unity pa =. For a surface exposed to radiation, the rate of eneigy input is Ga. As the surface is heated and becomes warmer than its surroundings, it will lose heat at a rate depending on the surface conductance ho) and the temperature difference between the surface Ts) and the air To). ho Ts-Ta). The surface will reach an equilibriiun temperature when the heat input rate equals the heat loss rate, that is, when Ga = ho Ts-Ta), from which the surface temperature can be expressed as Ts = Ta + Gajh. This is the maximum temperature the surface could reach in the absence of any heat flow into the body of material behind that surface, and it is often referred to as the sol-air temperature. (More precise definitions would include a radiant emission term, so that the numerator would become the net irradiance absorbed by the surface.)... 

One useful property of cationic polymerization is that it is not air inhibited. In the absence of nucleophilic impurities, there are no inherent modes of termination. Thus, the polymerization may continue for long periods (hours to days) after the light is turned off, in contrast to photoinitiated free radical polymerization (24). This post-cure should be useful for laminating two opaque materials, in that irradiation of the adhesive followed by lamination should result in a well cured adhesive, although it may take 1-2 days to form maximum bond strength. 

Photolysis at visible wavelengths may be necessary with sensitive materials or with preparations that are opaque to ultraviolet light. The use of Mazda 125 watt MB/V pearl glass lamps or a movie-projector lamp filtered through O.l-l.O M aqueous NaN02 will allow irradiation at >400... 

During this initial phase, it was found for static analysis that the high irradiance required for the FT-Raman analysis, to produce a satisfactory signal-to-noise ratio from the spectrum, led to the buildup of opaque impurities on the sampling window. Thus, it was necessary to construct a sample loop where material was pumped continuously pass the analysis point. Despite this precaution, the sample cell required periodic cleaning to remove impurity buildup [21]. 

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