Ablation patterns

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

Figure 9.13 shows examples of ablation patterns taken in a single shot and observed by (a) an optical microscope and (b) an atomic force microscope (AFM). The diameter of the circular hole is approximately 2 pm, which agrees well with the Ce YAG scintillator experiment. 

Oxide film laser lithography (OFLL) replaces the UV patterned photoresist of TMEMM by laser ablated patterned oxide mask, which is grown anodically on the titanium surface. OFLL can be appUed precisely to nonplanar complex surface and it also allows multilevel patterning. Fig. 12.11 shows that titanium cylinder surface consists of hemispherical cavities which are electrochemically micro-structured using OFLL. However, the process is serial and slower compared to TMEMM. 

Fig. 6. Luminescence intensities between electrodes in DC-plasma, Ablation (CuF chemiluminescence), PLASLA, and the difference in the luminescence intensity between the PLASLA and laser-ablation patterns.

Li R Bakowsky U, Yu F, Loehbach C, Muecklich F, Lehr CD. (2003) Laser ablation patterning by interference induces directional cell growth. IEEE Trans Nanobioscience 2 ... 

LIBS/RELMA was tested on a series of industrial NBR compounds with various deliberate recipe errors of all components (rubber, fillers, carbon-black, plasticisers, FRs, AOs, accelerators, ZnO, sulfur, mineral oil). UV excimer laser wavelengths must be employed on polymeric surfaces since only then sharp and regular ablation patterns are produced without any thermal side-effects (at variance with IR NdiYAG). LIBS/RELMA can be used for off-line analysis of vulcanisates, homogeneity testing and particle analysis in mixtures and element analysis of raw materials (in particular for fillers). RELMA... 

Quantitative evaluation of global and locahzed creep deformation behavior of solder joints has been developed by mapping the distortion of a straight-hne ablation pattern imprinted by an excimer laser on the surface of shear lap solder joints [45]. Fig. 11 is an illustration of distortion due to creep deformation of a laser ablation pattern placed on a solder joint [46]. 

FIG. 11 Shape of laser ablation patterns placed on a solder joint, (a) Before creep and (b) after creep. (From Ref. 46.)... 

The ablated vapors constitute an aerosol that can be examined using a secondary ionization source. Thus, passing the aerosol into a plasma torch provides an excellent means of ionization, and by such methods isotope patterns or ratios are readily measurable from otherwise intractable materials such as bone or ceramics. If the sample examined is dissolved as a solid solution in a matrix, the rapid expansion of the matrix, often an organic acid, covolatilizes the entrained sample. Proton transfer from the matrix occurs to give protonated molecular ions of the sample. Normally thermally unstable, polar biomolecules such as proteins give good yields of protonated ions. This is the basis of matrix-assisted laser desorption ionization (MALDI). 

Subliming ablators are being used in a variety of manufacturing appHcations. The exposure of some organic polymers to pulsed uv-laser radiation results in spontaneous ablation by the sublimation of a controUed thickness of the material. This photoetching technique is utilized in the patterning of polymer films (40,41) (see PHOTOCHEMICAL TECHNOLOGY). 

During this process, material is selectively removed from the wafer surface as defined by the patterned photoresist in order to define the structure of the previously deposited layer. The etching process is accomplished by exposing the wafer to a plasma, which both chemically reacts with the material to be removed and ph3rslcally ablates it. At the completion of etching, the remaining photoresist is cleared from the wafer. 

Wilson, M.A., and Molliver, M.E. Serotonin innervation patterns in primate cerebral cortex specific local ablations. Abstr Soc Neurosci 12 427, 1986. 

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... 

Figure 39. Secondary-ion maps of 0— (oxygen tracer) and Mn 0— (positional reference) of the patterned thin-film electrode shown in Figure 38 following polarization at —0.34 V at 700 °C. (a) Tracer map at the top surface of LSM/YSZ, showing selective incorporation into LSM. (b) Tracer map near the LSMA"SZ interface (acquired after ablation of LSM off the surface with Cs+), showing deep penetration of tracer into LSM. (Reprinted with permission from ref 230. Copyright 2000 Elsevier.)...

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... 

The dorsal and ventral hippocampus is involved in the formation of social memory (van Wimersma Greidanus and Maigret, 1996). Neonatal ablations of hippocampal regions can lead to decreased and abnormal social behavior in rhesus monkeys that is reminiscent of severe neuropsychiatric disorders in humans such as autism and schizophrenia (Bachevalier et ah, 1999). These monkeys are often withdrawn socially and will develop locomotoric stereotypies a pattern similar to that found in autistic children. 

An analytical procedure has been proposed for precise uranium isotope ratio measurements in a thin uranium layer on a biological surface by LA-ICP-MS using a cooled laser ablation chamber.125 One drop of uranium isotope standard reference materials NIST, 350, NIST 930, of our isotopic laboratory standard CCLU 500 (20p.l, U concentration 200 ng 1) and of uranium with natural isotopic pattern were deposited on the leaf surface and analyzed by LA-ICP-MS at well defined laser crater diameters of 10, 15, 25 and 50 p.m. A precision for measurements of isotope ratios in the range of 2.1-1.0% for 235U/238U in selected isotope standards was observed whereby the precision and the accuracy of isotope ratios compared to the non-cooled laser ablation chamber was improved.125... 

A final alternative for metal patterning is the use of lasers to selectively and accurately etch small metal areas. Lasers are routinely used to trim thin-film resistors (126) they may also be used to repair defects or etch conductor lines by direct ablation in an inert atmosphere (127,129) or by laser-initiated etching in a reactive gas or liquid (128). 

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