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Abstract: Single-pulse femtosecond laser patterning of nitrobiphenylthiol monolayers on Au-coated Si substrates at λ =800nm, τ <30fs and ambient conditions has been investigated. After laser processing wet etching experiments are performed. Laser irradiation reduces the chemical resistance of the coating. In particular, the monolayer acts as a positive-tone resist. Burr-free pattern transfer is feasible at laser pulse fluences between 1 and 2.7J/cm2. Minimum structure sizes at a 1/e laser spot diameter of about 1μm are close to 300nm, i.e. sub-wavelength processing is demonstrated. Noteworthy, however, no indications for negative-tone resist properties of processed monolayers are evident, that is, cross-linking of the biphenyl moieties, if at all, is marginal. Also, complementary labeling experiments provide no evidence for chemical transformation of the nitro end groups into amine functionalities. Perspectives of resonant fs-laser processing in exploiting the particular prospects of nitrobiphenylthiol monolayers as negative-tone resists and chemically patternable platforms are discussed. [Copyright &y& Elsevier]

Femtosecond laser patterning of octadecylsiloxane monolayers on surface-oxidized silicon substrates via single-pulse processing at λ=800 nm, τ<30 fs, and ambient conditions has been investigated. Depending on the laser pulse fluence, local irradiation results in circular spots of distinct size and morphology. At high fluences, a particular rich complexity of distinct surface morphologies is observed including hole, rim, and ripple formation, and a faint boundary area where monolayer decomposition sets in. At low fluences, subwavelength patterning of the organic monolayer is feasible. In particular, at a 1/e laser spot diameter of 1.3 μm, surface spots with a width down to 300 nm are fabricated. Selective processing of the organic monolayer, though, is restricted to a very narrow range of fluences between 1.1 and 1.2 J/cm2. A significantly larger parameter range for selective processing is anticipated in the case of functional monolayers that incorporate aromatic groups. Promising perspectives in femtosecond laser processing of organic monolayers are discussed. [ABSTRACT FROM AUTHOR]

Laser microprocessing of highly oriented pyrolytic graphite (HOPG) in conjunction with chemical functionalization routines is used to fabricate functional microsized domains. Infrared and Auger electron spectroscopy, contact angle measurements, and electron microscopy are used for characterization of laser-fabricated structures. HOPG samples are coated with alkylsiloxane monolayers. Laser-induced bromination of coated HOPG samples in gaseous bromine is carried out using a microfocused laser beam at a wavelength of 514 nm and 1/e² laser spot diameter of about 2 µm. Subsequent azidation and amination results in functional domains with sizes in the range of 1.2 to 40 µm and more. At low laser powers and irradiation times fully functionalized circular-shaped structures are formed. At high laser powers and irradiation times laser processing results in decomposition of the organic monolayer and substrate in the center of the structures yielding donut-shaped structures. After laser processing and chemical transformation Au nanoparticles are selectively adsorbed onto the functional domains. This provides an opportunity to build up functional nanoparticle microarrays on carbon-based materials, e.g., for applications in sensing and electrocatalysis. [ABSTRACT FROM AUTHOR]

Abstract: A nonlinear photothermal laser patterning technique for rapid fabrication of chemical templates is demonstrated. Hexadecanethiol monolayers on Au-coated Si substrates are processed at λ =532nm, a 1/e2 spot diameter of and ambient conditions. Local laser irradiation at high laser powers and short irradiation times in the micro-/millisecond range induces desorption of thiol molecules. The laser-depleted areas are backfilled with mercaptohexadecanoic acid in order to build up chemical templates. Atomic force microscopy, scanning electron microscopy and scanning Auger electron spectroscopy are used for characterization of these templates. In agreement with a selective laser process, the results indicate the formation of flat chemical patterns with well-defined boundaries. Complementary condensation experiments demonstrate the functionality of the patterns as hydrophilic/hydrophobic templates. In particular, upon decreasing the temperature below the dew point, selective formation of water droplets on the backfilled areas is observed. [Copyright &y& Elsevier]

Abstract: A focused laser beam at a wavelength of 514nm has been used to pattern octadecylsiloxane monolayers grown on distinct substrates which expose a silicon oxide surface. Patterning experiments on conventional silicon substrates with a native oxide layer result in a decomposition of the monolayer along well-confined lines. The line widths generally are well below the focal laser spot diameter of 2.5±0.3μm indicating a nonlinear dependence of the overall process on the laser intensity. Very similar results were obtained using thermally oxidized silicon substrates. In contrast, experiments to pattern coated quartz plates failed even if the laser power and hence the local irradiance at the surface was raised to much higher values. Altogether, these experiments strongly support a photothermal excitation mechanism, that is, a decomposition of the monolayer as a result of the laser induced local temperature rise. [Copyright &y& Elsevier]