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Atomic force microscopy data reveal self-affine scaling of plasma polymer films. The rms surface roughness o. increases with film thickness 7. as o( f ( ( )rp, and with measurement length L as o(f ) . L ' ) g ') -L, where g is the surface roughness correlation length. At the deposition rate R = 2 p, m/h, the scaling exponents n and P are 0.9 and 0.7, both increasing to 1 at R = I pm/h. A competition between surface relaxation and deposition rate determine o. and (', which increase rapidly with R or inverse temperature. PACS numbers: 68.55.8d, 05.70.Ln, 68.55.Jk Comparison between self-affine surface structure data, computer simulations, and theoretical models is often made using scaling exponents for the rms surface roughness o(L, t) . [1 -3]: t~cL". a(Lr) = (h, (r, i) 2-1/2 h(r, t)(1) where t is the time, r is the position in the plane perpendicular to the growing direction, h(r, t) is the height of the surface at time t and position r, (h(r, t))" is the spatial average of h(r, t), L is the length of the surface measured, and c is a constant. Thus, cr initially scales with time as tP but shows a saturated scaling as I for thick layers [4]. Knowing the functional form of a and P in terms of process conditions allows the prediction of the surface roughness for any sample size.For simple random deposition with no spatial or temporal correlations between the deposited particles (the extreme kinetic limit), P = 0.5, since o. grows as a "random walk, " and n = 0, since there is no saturated scaling with L, For a real surface, relaxation processes such as in the Langevin type models couple the 2 degrees of freedom in the surface roughness, L and t, so as to change the scaling exponents. For example, Edwards and Wilkinson (EW) [5] use a Langevin equation [Eq. (2) with A = 0] to model the evolution of a surface, and find in d = 1 + 1 1 1 dimensions n = 2 and P = 4. In d = 2 + 1 the power law behavior in Eq. (1) changes to a logarithmic dependence. Kardar, Parisi, and Zhang (KPZ) [6] allowed for a component of interface growth parallel to the plane. They used the equation dh(r, t) 2 dt 2 = vV h(r, t) + -[Vh(r, t)] + rl(r, t), (2)where v is related to surface relaxation, g is the random fluctuation in the incoming flux, which is assumed to be Gaussian with delta function correlation (71(r, t) g(r', t')) = 2DB(rr', tt'), and A is the growth velocity perpendicular to the surface. In d = 1 + 1 dimensions they 1 1 obtained the exponents u = 2 and P = 3. In d = 2 + 1, Amar and Family [7] find that when 10~A2D/2v 25, P -0.25 and n -0.4, while for A2D/2v~-1, the effective value of P decreases. This connects the scaling exponent P to the surface relaxation process (v), and the deposition rate (-D). For the growth of plasma polymer films presented here we find 1 & a & 0.9 and 1 & P~0 .6. Of the experimental studies of the deposition of thin films, only a few have been analyzed in terms of both scaling laws of Eq. (1) [8]. For these studies 1~ct~0.2 and 0.56~P~0.22 [9]. The values of a overlap our own" but our values of P are si...

ABSTRACT:Resorcinol-formaldehyde (RF) aerogel chemistry has been used with encapsulation techniques to fabricate low-density, transparent, foam shells. To accomplish this, the gelation time was reduced from several hours to several minutes by the addition of acid following base-catalyzed RF particle growth. However, additional ''annealing'' of the gel for at least 20 h was needed to maximize crosslinking and minimize swelling in exchange solvents. Increasing the molar ratio of formaldehyde to resorcinol from 2 to 3 also helped to increase crosslinking. Densification of the foam shells due to dehydration during curing was greatly reduced by judicious choice of immiscible oil phases and by saturating the exterior oil phase during the annealing stage. Shells have been produced with diameters of about 2 mm, wall thicknesses ranging from 100 to 200 mm and foam densities approaching 50 mg/cc.

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Coatings for laser fusion targets were deposited up to 135 μm thick by plasma polymerization onto 140 μm diam DT filled glass microspheres. Ultrasmooth surfaces (no defect higher than 0.1 μm) were achieved by eliminating particulate contamination. Process generated particles were eliminated by determining the optimum operating conditions of power, gas flow, and pressure, and maintaining these conditions through feedback control. From a study of coating defects grown over known surface irregularities, a quantitative relationship between irregularity size, film thickness, and defect size was determined. This relationship was used to set standards for the maximum microshell surface irregularity tolerable in the production of hydrocarbon or fluorocarbon coated laser fusion targets.