Photo-ablation

Fig. 4 and Fig. 5 show the surface morphologies aftm photo-ablation of PMMA/pyrene, and CMS, CMS/pyrene respectively. In these figures a copper-mesh mask was used in contact with the polymer films for the gena-atkm of sharp etch patterns. For PMMA/pyrene films, in the low pyrene concentration range, the etched surface is quite rough with dendritic and needle-like structures as well as solidified droplets on the bottom of the irradiated areas present although the edges of the etched features are reasonably sharp (Fig. 4a). When the laser fiuence is increased, the etched surface becomes cleaner and more smooth. At a high pyrene concentration, clean and sharp etch patterns can be obtained at a relatively low fiuence, e.g., at a = 1.04 x 10 cm and F = 0.3 J/cm as shown in Fig. 4b. In most cases, periodic structures are observed near the edges of the wire mask, which most likely result from the optical diffraction effect of the wires.

Polyimides, chlorinated poly(methylstyrene) and novolac resins are all crosslinking polymers under ordinary UV light irradiation, whereas PMMA and PMGI are main-chain scission-type polymers under deep UV irradiation (23). Even for such scission-type polymers, photo-thermal effects cannot be neglected. For crosslinking-type polymers, photo-thermal effects become more important and are the predominant mechanism for photo-ablation. 

H. Masuhara, N. S. Allen (eds.). Photo-ablation of Materials, J. Photochem. 

Uncovered the highly efficient tumor passive targeting ability of PEGylated NGS and used graphene as a powerful photothermal therapy agent for effective photo-ablation of tumors in a mouse model... 

Photo ablation This process breaks molecular bonds. Minimal heat damage is inflicted on the surrounding area. 

As already stated, monolithic and flexible polyimide (PI) film microreactors, which can be easily fabricated by photo-ablating a PI film, are durable under highly addic conditions and also at reasonably high temperatures (up to 100 °C) [11]. 

Lin et al carried out an analysis of photoablation products resulting from polymer materials following supersonic beam/multi-photon ionization/time of flight mass spectrometry. They examined the photo-ablation products obtained in this technique and compared them with those obtained by thermal decomposition. 

Faraggi et al. [785] demonstrated fabrication of a CP-LED pixel microarray having the CP sandwiched between ITO and Al, with pixel size as small as 20 /im X 20 /im and claimed extendable to the nm-range. A photo-ablation method employing a 193 nm excimer laser was used. A schematic representation of the procedure is shown... 

Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles. Cancer Letters, 209, 171-176. 

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

Fluorescence Characterization of Ablated Polymeric Materials. In order to produce sharply etched patterns, the film was ablated with a photo-lithographically prepared mesh mask in the contact mode. The ablation was conducted with two laser shots with the laser fluence of 0.2 J/cm2. The decay curves of the ablated film was measured by a... 

O Neal DP, Hirsch LR, Halas NJ, Payne JD, West J (2004) Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles. Cancer Lett 209 171-176... 

In order to produce surface-relief electro-optic gratings, Munakata et compared two fabrication methods of SRG inscription. In the first, the SRG was produced with an interference pattern of cw laser, with relatively modest intensities. The gratings so recorded were photo- and thermally erasable, and efficient writing was polarization dependent. In the second method, a phase mask was employed to provide the periodic intensity modulation of a pulsed laser, the 3rd-order harmonic (at 355 nm) of a Nd YAG laser. The SRG was produced with a single laser pulse, allowing a very short fabrication time (less than Is). The direshold for ablation was 500 mj/(em pulse), and the amplitude of the SRG increased with pulse energy. A depth of up to 300 rim could be achieved, leading to a smooth but not sinusoidal surface modulation. 

The photo-stimulated ablation of neutrals and ions from various substrates has been studied experimentally and theoretically (12,15,25,26). This technique can be used for study of ion-molecule reactions (27,28). The ions photoablated may have quite a wide range of kinetic energy of up to 1000 eV (29). 

Photochemical surface reactions of polymer systems are an important field not only from the point of view of micro-electronic materials processing, but also from a more general scientific and materials application perspective. We have reviewed our studies in this field, which include investigations of excimer laser ablation, studies of the photo-oxidation of polymer surfaces, and the use of surface cross-linking and surface polymer depositions for microlithographic applications. With the increasing miniaturization of microelectronic devices, the fundamental and the applied aspects of surface photochemistry of polymers becomes increasingly important. 

On exposure, the Ols/Cls ratios in the surface layers of the films, obtained from simulation of the spectra, rapidly increase initially with exposure time and then plateau to essentially constant values, see example for 6FDA/DAB in Figure 7. This observation of a plateau in the ratio is consistent with the ablation of the surface layers of the film during photo-oxidation. 

The majority of a series of shadowgraphs recorded at a laser fluence of 50 mj cm 2 are displayed in Fig. 38 and most of those from a series of experiments with a 250 mj cm 2 fluence laser are shown in Fig. 39. The time zero chosen for these photographs was at the peak of the excimer laser irradiation [209]. In this time zero reference, a photo was also taken at time=-4.8 ns for the 50 mj cm-2 fluence laser and at time=-7.2 ns for the 250 mj cm 2 fluence laser. Although both of these negative time photos were well after the beginning of the laser irradiation, neither showed any indication of shock wave formation or material expansion [94]. A depth profiler was used to measure a final ablation depth of 50 nm in one of the 50 mj cm 2 fluence case experiments and 650 nm in one of the 250 mj cm-2 fluence case experiments. 

In general, most TOF-MS studies have given strong indications for photo-thermal ablation mechanisms. To test whether a photochemical mechanism could be identified with TOF-MS, we chose a polymer considered photola-bile, which also has excellent properties as a resist for high-resolution microlithography [111, 225-228]. Here we show that the principal products (chiefly N2) from this triazene polymer have components that are much... 

Experiments with a reference material, i.e., polyimide, for which a photo-thermal ablation mechanism has been suggested, exhibited pronounced differences, e.g., swelling of the surface prior to ablation, modifications of the surface after irradiation, and higher threshold (at an irradiation wavelength where polyimide has the same absorption coefficient as the designed materials). 

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