UV ablation

Knoll and coworkers were the first to synthesize polymer brushes from SAM-coated silicon wafers via a photoinitiation strategy [37-39]. They used an AIBN type initiator that was developed by Riihe. In particular, a chlorosi-lane terminus was used to form a covalent bond to the native oxide surface of the silicon this was followed by irradiation at 350 nm in the presence of styrene to yield a PS brush (Fig. 4). They were able to write patterns by irradiating through a mask to activate the surface-bound initiators. Alternatively, they synthesized a polymer film and then used deep UV ablation through masks to remove some of the polymer in the irradiated regions. By... 

Conducting carbon polymer ink, which filled a UV-ablated microchannel, was used to construct the integrated microelectrode on a plastic chip. Both chronoamperometry and CV were employed to detect a model compound (fer-rocenecarboxylic acid) down to 3 iM, corresponding to 0.4 fmol within a volume 120 pL [758], In another report, a carbon-paste electrode was constructed by filling a laser-ablated (PET or PC) channel with C ink. The whole structure was then cured at 70°C for 2 h [189]. 

Rat skeletal myoblasts, human embryonic kidney cells, colon carcinoma cells pCP of etching solution or UV ablation of PVA 2006 [98]... 

Keywords UV laser irradiation UV ablation Art conservation Polymers Photochemical processes Structural modifications... 

The interaction of intense laser pulses with molecular materials is, in general, quite complex. It is customary to delineate the induced processes in three types, namely thermal, photochemical, and photomechanical. Though this formalistic division provides a convenient basis for the discussion of the mechanisms and effects of UV ablation of polymers, the three phenomena are certainly closely interrelated. The inadequacies of this division will be most clearly illustrated in the examination of the chemical effects. The present review addresses all three types of side effects, but the major emphasis concentrates on the photochemical phenomena. 

Systematic studies on the nature/dynamics of the excitation processes in the UV ablation of polymers have been reported by Masuhara and co-work-ers [61-63]. To this end, they have relied on the use of dopants dispersed within polymers. Given the relevance of their approach to the topic of the present article, their work will be presented in some detail. Time-resolved absorption and luminescence spectroscopies have been used to probe the dynamics of electronic excitation and deexcitation of the dopants. In the irradiation of fluorescing dopants (biphenyl or phenanthrene), the total emis-... 

Interestingly, variations of this cyclic multiphotonic scheme have been independently advanced in the study of the UV ablation of cryogenic films [65] as well as in the matrix-assisted laser desorption/ionization (MALDI) of biomolecules [66]. The reason for giving these results is to illustrate the emergence of common concepts/processes concerning UV ablation of molecular substrates. 

Aside from its importance for material ejection, the description of (pho-to)chemical processes and effects in the UV ablation of organic/polymer substrates has a wider scientific interest. Conventional photochemistry considers bond breaking and formation in a well-defined environment under... 

In all, multipulse irradiation protocols are indicated to be detrimental for the chemical integrity of the substrates. Of course, in the various implementations of UV ablation, the number of required pulses is specified by the... 

Generally, peak pressure amplitudes range from a few MPa at the ablation threshold up to several hundred MPa at high laser fluences [104-108]. During propagation through the substrate, these high-amplitude waves may induce structural modifications at areas away from the ablation spot. Thus, in contrast to the photochemical effects which are confined to the laser-irradiated area, the photomechanical effects of UV ablation can be much more delocalized. 

Fig.18 Interferograms recorded in the UV ablation of PMMA polymeric films on a Su-prasil substrate at 193 nm (FLAser 1 J/cm2) with 200 pulses. The interferogram clearly demonstrates defect formation at distances far away from the irradiation spot. For the purpose of enhancing defect formation, this particular film has not been annealed...

Fig. 19 Top Growth of defects in the irradiation of PMMA and PS films (Mw= 1,900) on a Suprasil substrate at 193 nm as a function of successive laser pulses (Flaser 1 J/cm2). Bottom Spatial distribution of the defects following UV ablation of nonannealed PMMA films at 193 nm (FLASer 1 J/cm2, 200 pulses). The lines serve only as a guide to the eye. The ordinate values represent the average distance of the center of the defects, independently of their size, from the irradiation spot...

Irradiation experiments in the near-IR range at 800 nm with pulses in the pico- and femtosecond range were also performed. For femtosecond pulses, a lower ablation threshold fluence was found than for picosecond pulses, which indicates the presence of a thermal mechanism [ 145]. Also, no complete removal of a thin triazene polymer film from a glass substrate was possible with lOOfs pulses. These short pulses in the near-IR do not yield better results and are therefore no alternative to UV ablation [146],... 

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