Doped PMMA films

For EPy-doped PMMA film, a 308 nm excimer laser (Lumonics TE 430T-2, 6ns) was used as as exposure source. We used a tine-correlated single photon counting systen (18) for measuring fluorescence spectra and rise as well as decay curves of a snail ablated area. The excitation was a frequency-doubled laser pulse (295 nm, lOps) generated from a synchronously punped cavity-dumped dye laser (Spectra Physics 375B) and a CW mode-locked YAG laser (Spectra Physics 3000). Decay curves under a fluorescence microscope were measured by the same systen as used before (19). 

Figure 3. Birefringence of /raw -stilbene doped PMMA films, drawn at...

Fig. 14 Black lines. absorption and emission (2exc = 360 nm) spectra measured for Ru-anthryl (X = CH2O) for dispersed in a 45 5 nm thick PMMA film. Absorption peaks associated with the dianthryl unit are indicated by asterisk. Red lines, analogous spectra measured following the formation of the cycloadduct by 400 nm irradiation (10 mW, 5 min) of a 18 mm diameter circular area of the doped PMMA film. (Reprinted with permission from [124])...

Gu, Z. Wang, G. Liang, P. Hou, L. Measurement of optical parameters of azo-dye-doped PMMA films by p-polarized reflectance. Zhongguo Jiguang 1999, A26, 902-906 Chem. Abstr. 2000, 132, 187052. 

Single molecules also have promise as probes for local stmcture when doped into materials tliat are tliemselves nonfluorescent. Rlrodamine dyes in botli silicate and polymer tliin films exliibit a distribution of fluorescence maxima indicative of considerable heterogeneity in local environments, particularly for the silicate material [159]. A bimodal distribution of fluorescence intensities observed for single molecules of crystal violet in a PMMA film has been suggested to result from high and low viscosity local sites witliin tire polymer tliat give rise to slow and fast internal conversion, respectively [160]. 

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

Fluorescence Spectra. Fluorescence spectra of PMMA films doped with a high concentration of EPy are composed of a structured monomer and... 

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

Figure 1. Effect of temperature on the temporal stability of X film (related to and the angle between the applied field and dopant optical axis) for corona poled PS and PMMA films doped with 4 wt.% DANS. X Vilm(0/x film(t=0) versus time after the field is removed, where t=0 denotes the time that the applied field is removed. The initial temperature is 110°C, and the final temperatures after the field is removed are 11 (PC [PS (0),PMMA ( )], 95°C [PS CD,PMMA ( )] or 60°C [PS (A), PMMA (A)].

Figure 2. Surface voltage decay as a function of time for corona poled PS (O) and PMMA ( ) films doped with 4 wt.% DANS. Films poled at -3000V (0.6 cm air gap) for 15 min at 25°C.

Photoablation (diode-pumped Nd YV04 laser, X = 532 nm) was used to create a master on the PMMA layer coated on a Si wafer (see Figure 2.20a). The PMMA layer was doped with rhodamine B to facilitate the absorption of the laser radiation. The width of the ablated features depends on the diameter and the position of the laser focal point. The best aspect ratios were obtained with the laser beam focused 3 1 pm into the PMMA film. The ablated PMMA-Si master was used to cast a PDMS layer (see Figure 2.19b). The cast PDMS layer appeared to have smoother surfaces than the PMMA master [367]. 

FIGURE 3.3 Variation of the absorbance. O.D., of a film of DR I -doped PMMA (2.5% w/w) with (A) low, 0.28 mW/cm and (B) high, 28 mW/cm irradiation (488 nm Ar" laser) intensity. The analysis light was the 514 nm from the same Ar laser, and both A// and are measured. A represents the isotropic absorbance (A//+2AjJ/3. (C) Variation of the absorbance—parallel, perpendicular, and isotropic—with the irradiation light intensity.The data were taken 3 minutes after the irradiation was turned on. At low irradiation intensity, the cis population is small and Aj increases as a consequence of the orientational distribution. At high irradiation intensity, saturation of the orientational hole-burning process tends to equalize A// and A. (After reference 20, by permission.)... 

FIG. 10.6 RAP of Aberchrome 540 doped in PMMA film (10% vy/w) probed by SHG (lj ) at 1064 nm, pumping at 355nm lOmW. cm Experiment II (simultaneous poking and pumping) yields almost the same SHG signal as Experiment I (poling after pumping) (Reprinted from ref. 73 by permission of Taylor Francis Ltd. http //www.tandf.co.uk/journals). 

Charra et al. [137] and Kajzar et al. [159] observed formation of a polar orientation of chromophores in nondegenerate (pump beams at 1064 nm, probe beam at 532 nm) phase conjugate experiments performed on a copolymer of PMMA with DR 1 chromophore. The observed signal at 532 nm rose slowly with time, up to a saturation value. A spontaneous SHG was observed after switching off the probe beam, with a fast relaxation component at the beginning [159]. The maximum second-order nonlinear optical susceptibility value obtained in these experiments was 3 pm [137]. This experiment showed that by using purely optical fields one could obtain a polar orientation of chromophores in a functionalized or a doped polymer film. 

A similar experiment was performed for the PMMA film doped with 1-ethyIpyrene. As shown in Fig. 7, fluorescence spectra were composed of a structured monomer and red-shifted broad excimer bands. As molecular diffusion during fluorescence lifetime is negligible in film, the latter band is due to the ground state dimer of pyrene which is easily formed under its high concentration. It should be notified that the fluorescence intensity ratio of the monomer to excimer emissions under the TIR condition is larger than that under the normal one. This may indicate that the pyrenyl concentration in the interface layer is also lower than that in the bulk. 

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